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1

Reconstructing glacier retreat since the Little Ice Age in SE Tibet by glacier mapping and equilibrium line altitude calculation  

NASA Astrophysics Data System (ADS)

Temperate glaciers in the eastern Nyainqêntanglha Range, southeastern Tibet, are highly sensitive to climate change and therefore of particular high interest for research on late Holocene changes of the monsoonal climate in High Asia. However, because of the remoteness of the area, the scarcity of empirical data, and the challenges to remote sensing work posed by cloud and snow cover, knowledge about the glacier dynamics and changes in this region is still very limited. In this study, we applied a remote sensing approach in which 1964 glaciers were mapped from a Landsat ETM+ scene and subsequently parameterized by DEM-supported measurements. Geomorphological evidence, i.e., trimlines and latero-frontal moraines, were used to obtain quantitative data on the glaciers' morphological characteristics and the changes since the Little Ice Age (LIA) maximum glacier advance. Statistical analysis of glacier length change revealed an average retreat of ~ 27% and a trend toward stronger retreat for smaller glaciers. An evaluation of different methods to calculate equilibrium line altitudes (ELAs) indicates that an optimized toe-to-ridge altitude method (TRAM) is more suitable than other methods in settings with complex topography and a lack of mass balance measurements. A large number of glacier measurements are crucial for high quality of TRAM results, and special attention has to be paid to different glacier characteristics. In order to determine the best-fitting TRAM ratio value and to test the quality of the calculated ELAs, a remote sensing approach was applied: for each investigated glacier, the altitudes of transient snowlines visible in the late summer Landsat scene were measured from the DEM and compared to TRAM results. The interpolated ELA results show a SE–NW gradient ranging from 4400 to 5600 m asl and an average ELA rise of ~ 136 m since the LIA. Because of the high spatial resolution of measurements, the ELA distribution reveals topographic effects down to the catchment scale, specifically orographic rainfall and leeward shielding. The interpretation of these patterns reveals that the eastern Nyainqêntanglha Range is influenced by both, the Indian (ISM) and East Asian summer monsoon (EASM). However, the EASM does not reach the western part of the study area. The results indicate that the monsoonal temperate glaciers' high sensitivity to climate change is driven by two double forcings owing to the coincidence of accumulation and ablation phases.

Loibl, David; Lehmkuhl, Frank; Grießinger, Jussi

2014-06-01

2

A 1600 year history of Alpine glacier equilibrium line altitude inferred from glacier length records, and the relation to summer temperature and radiation  

NASA Astrophysics Data System (ADS)

A new history of glacier equilibrium line altitude (ELA) for the time span 400-2010 is inferred from the combined interpretation of length change records of six glaciers from the Alps with help of a macroscopic model of glacier dynamics. This history is completely independent of proxy data from other sources. Comparison with proxy-based reconstructions of European summer temperature shows a generally good agreement, with the exception of a low-ELA (cold) period between 1300-1350, corresponding to rapid glacier advance, which is absent in the other records. Correlation of the glacier-derived record with total solar irradiance is high between 1800-1950, but deviates significantly from it after 1950.

Lüthi, M. P.

2012-04-01

3

Equilibrium-line altitude during the Antarctic Cold Reversal at Río Tranquilo glacier (47°S), Central Patagonia  

NASA Astrophysics Data System (ADS)

Documenting the magnitude of former glacial fluctuations is critical for understanding the mechanisms and climate signals underlying these glacial events. Here, we estimate the equilibrium line altitudes (ELA) associated with the most prominent glacial advance occurred during the Last Glacial Termination (T1) at Tranquilo glacier (47°S). Geomorphic evidence suggest that, following the Last Glacial Maximum, several small glaciers, which today occupy the headwalls of Río Tranquilo valley, expanded and coalesced, forming the extended version of the Tranquilo glacier at least three different times. 10Be ages suggest that the most prominent of these glacial advances occurred ~13 kyr BP, at the end of the Antarctic Cold Reversal (ACR). Based on glacial geomorphic mapping and the application of a glaciological model (GC2D), we reconstruct the former glacial surface at Tranquilo glacier and estimate the ELA for this major glacial advance. Preliminary data show that the equilibrium line altitude at Tranquilo glacier during the ACR could have been up to 500 m lower than the present. This study represents the first effort to quantify the ELA during the Antarctic Cold Reversal in Patagonia, and provides a baseline to decipher the climatic signals driving this glacial event.

Sagredo, E. A.; Ward, D.; Gonzalez, M. A.; Lowell, T. V.; Kelly, M. A.; Aravena, J. C.

2013-12-01

4

Younger Dryas and Holocene glacier fluctuations and equilibrium-line altitude variations in the Jostedalsbre region, western Norway  

SciTech Connect

Reconstructed Younger Dryas (11000-10000 y BP) valley- and cirque glaciers west of the Jostedalsbre ice cap suggest an equilibrium-line altitude (ELA) depression of (450{+-}200 y BP) deglaciation was characterized by vertical wastage, indicating that the LA was above the summit plateaus. During the Erdalen event (9100{+-}200 y BP) marginal moraines were formed up to 1 km beyond the Little Ice Age (LIA) moraines which lie in front of the present valley outlet glaciers of the Jostedalsbre ice cap. The average ELA lowering during this event is calculated to 325 m below the modern level. Lithostratigraphic and paleobotanical studies show that the Hypsithermal (ca. 8000-6000 y BP) ELA was about 450 m higher than at present. As a result, Jostedalsbreen probably disappeared entirely during that period. The glacier reformed about 5300 y BP. The ELA intersected the modern mean equilibrium line altitude five times from ca. 2600 y BP to the present. The outlet valley glaciers reached their maximum Neoglacial extent during the LIA in the mid-18th century, when the ELA was depressed 100-150 m below the present level. 25 refs., 9 figs.

Nesje, A. [Univ. of Bergen (Norway)

1992-01-01

5

Modern and Little Ice Age equilibrium-line altitudes on Outlet Valley glaciers from Jostedalsbreen, western Norway: An evaluation of different approaches to their calculation  

SciTech Connect

The modern and Little Ice Age (LIA) equilibrium-line altitude (ELA) of 20 outlet valley glacier from Jostedalsbreen, western Norway, has been calculated using different approaches. Using an accumulation area ratio (AAR) of 0.6 [+-] 0.05 gave a mean little Ice Age ELA depression of 70 m. A method developed by M. Kuhle, taking the influence by topography into account gave a mean ELA depression of 35-255 m, the median elevation of glaciers 115 m, and the toe-to-headwall altitude ration 140 m. Differences in the ELA estimates can be attributed to the differences in topography and morphology of the glaciers. The AAR method appears to provide the most reliable results. This will aid in determining mean global temperatures during the LIA. 34 refs., 9 figs., 5 tabs.

Torsnes, I.; Rye, N. (Univ. of Bergen (Norway)); Nesje, A. (Univ. of Bergen, Bergen-Sandviken (Norway))

1993-05-01

6

Reconstruction of glacier equilibrium-line altitudes for the Last Glacial Maximum on the High Plain of Bogotá, Eastern Cordillera, Colombia: climatic and topographic implications  

NASA Astrophysics Data System (ADS)

The High Plain of Bogotá in the Andes of Colombia provides an exceptionally detailed record of glaciation. A two-stage Last Glacial Maximum (LGM) is noted in Bogotá; the older stage (max) presents an opportunity to reconstruct individual valley glaciers and explore spatial patterns. Well-mapped geomorphic features on topographic base maps permit the reconstruction of 23 palaeoglacier surfaces. Glacier extent varies across the region, with lower altitudes reached farther to the east. Equilibrium line altitudes (ELAs) are reconstructed using the area-altitude balance ratio (AABR) method, with BRs in three groups reflecting the W-E gradient in glacier extent and selected by minimising variation from group means. Average LGM ELA for all palaeoglaciers is 3488 m with a standard deviation of 182 m. The average lowering in ELA from LGM to modern of ca. 1300 m is best explained by a considerable drop in temperature. Significant intra-regional variance in LGM ELA can be ascribed to topography and its influence on precipitation and/or glacier form, with lower headwall elevations being correlated to larger accumulation areas.

Mark, Bryan G.; Helmens, Karin F.

2005-10-01

7

Automating the implementation of an equilibrium profile model for glacier reconstruction in a GIS environment  

NASA Astrophysics Data System (ADS)

Reconstruction of glacier equilibrium line altitudes (ELAs) associated with advance stages of former ice masses is widely used as a tool for palaeoclimatic reconstruction. This requires an accurate reconstruction of palaeo-glacier surface hypsometry, based on mapping of available ice-marginal landform evidence. Classically, the approach used to define ice-surface elevations, using such evidence, follows the 'cartographic method', whereby contours are estimated based on an 'understanding' of the typical surface form of contemporary ice masses. This method introduces inherent uncertainties in the palaeoclimatic interpretation of reconstructed ELAs, especially where the upper limits of glaciation are less well constrained and/or the age of such features in relation to terminal moraine sequences is unknown. An alternative approach is to use equilibrium profile models to define ice surface elevations. Such models are tuned, generally using basal shear stress, in order to generate an ice surface that reaches 'target elevations' defined by geomorphology. In areas where there are no geomorphological constraints for the former ice surface, the reconstruction is undertaken using glaciologiaclly representative values for basal shear stress. Numerical reconstructions have been shown to produce glaciologically "realistic" ice surface geometries, allowing for more objective and robust comparative studies at local to regional scales. User-friendly tools for the calculation of equilibrium profiles are presently available in the literature. Despite this, their use is not yet widespread, perhaps owing to the difficult and time consuming nature of acquiring the necessary inputs from contour maps or digital elevation models. Here we describe a tool for automatically reconstructing palaeo-glacier surface geometry using an equilibrium profile equation implemented in ArcGIS. The only necessary inputs for this tool are 1) a suitable digital elevation model and 2) mapped outlines of the former glacier terminus position (usually a frontal moraine system) and any relevant geomorphological constraints on ice surface elevation (e.g. lateral moraines, trimlines etc.). This provides a standardised method for glacier reconstruction that can be applied rapidly and systematically to large geomorphological datasets.

Frew, Craig R.; Pellitero, Ramón; Rea, Brice R.; Spagnolo, Matteo; Bakke, Jostein; Hughes, Philip D.; Ivy-Ochs, Susan; Lukas, Sven; Renssen, Hans; Ribolini, Adriano

2014-05-01

8

A semi-automatic method to create central glacier flow lines: A pilot study with Alaskan glaciers  

NASA Astrophysics Data System (ADS)

Glacier length is an important, but largely missing parameter in digital glacier inventories as it has to be digitized by hand (with the related variability). Length changes of glaciers are key indicators of climate change, but can only be measured in the field for a few hundred selected glaciers globally. Its vector representation (a central flow line) is a most important input for modelling future glacier evolution, but only seldom available from digital databases. Hence, there is an urgent need to generate such flow lines for a large number of glaciers from automated methods. The study describes a new method to automatically create central flowlines of glaciers along with an application to a study site where its suitability to automatically derive changes in glacier length is demonstrated. Our new method will likely strongly facilitate the number of available data on both issues (length values and changes) and thus help to improve the assessment and modelling of climate change impacts on glaciers. This new algorithm is based on Python scripting and additional libraries (GDAL / OGR) and requires only a DEM and glacier outlines as an input. The core of the method is based on a glacier axis concept that is combined with geometry rules such as the k-d Tree, Nearest Neighbour and crossing test theory. We have applied the method to 400 glaciers located in Western Alaska, where a new glacier inventory was recently created. The accuracy of the method was assessed by a quantitative and qualitative (outline overlay) comparison with a manually digitized data set for 20 glaciers. This comparison revealed for 17 out of the 20 glaciers a length value that is within the range of the manual digitizations. Other potential methods to determined glacier length performed less good. Combined with previous glacier outlines from the same region we determined and analysed length changes for 390 glaciers over a c. 50 year period.

Le Bris, R.; Paul, F.

2012-04-01

9

An approach to derive regional snow lines and glacier mass change from MODIS imagery, western North America  

NASA Astrophysics Data System (ADS)

We describe a method to calculate regional snow line elevations and annual equilibrium line altitudes (ELAs) from daily MODIS imagery (MOD02QKM) on large glaciers and icefields in western North America. An automated cluster analysis of the cloud-masked visible and near-infrared bands at 250 m resolution is used to delineate glacier facies (snow and ice) for ten glacierized regions between 2000-2011. For each region and season, the maximum observed value of the 20th percentile of snow-covered pixels (ZS(20)) is used to define a regional ELA proxy (ELAest). Our results indicate significant increases in the regional ELA proxy at two continental sites (Peyto Glacier and Gulkana Glacier) over the period of observation, though no statistically significant trends are identified at other sites. To evaluate the utility of regional ELA proxies derived from MOD02QKM imagery, we compare standard geodetic estimates of glacier mass change with estimates derived from historical mass balance gradients and observations of ZS(20) at three large icefields. Our approach yields estimates of mass change that more negative than traditional geodetic approaches, though MODIS-derived estimates are within the margins of error at all three sites. Both estimates of glacier mass change corroborate the continued mass loss of glaciers in western North America. Between 2000 and 2009, the geodetic change approach yields mean annual rates of surface elevation change for the Columbia, Lillooet, and Sittakanay icefields of -0.29 ± 0.05, -0.26 ± 0.05, and -0.63 ± 0.17 m a-1, respectively. This study provides a new technique for glacier facies detection at daily timescales, and contributes to the development of regional estimates of glacier mass change, both of which are critical for studies of glacier contributions to streamflow and global sea level rise.

Shea, J. M.; Menounos, B.; Moore, R. D.; Tennant, C.

2013-04-01

10

Glaciers  

NSDL National Science Digital Library

This interactive Flash exercise and animation explores glaciers, including their formation, growth, and retreat. This resource provides animations, diagrams, models in which students can see the influence of temperature and precipitation on glacier growth, and supplementary information that may serve as an overview or review of glaciers for introductory level physical geology or Earth science students at the high school or undergraduate level.

Smoothstone; Mifflin, Houghton

11

Equilibrium-Line Altitudes In Cold Hyperarid Settings  

NASA Astrophysics Data System (ADS)

Equilibrium-line altitude (ELA) is a climatically sensitive elevation on the glacier surface where annual accumulation equals annual ablation. Although local effects including debris cover, slope and aspect can influence the mass balance, ELA responds most strongly to snowfall and summer temperature (positive degree days). ELA can be estimated from the distribution and elevations of glacial deposits and is thus a useful parameter in the study of paleoclimate, although it is highly sensitive to extraneous factors, especially for small glaciers confined to cirques. This problem can be overcome by examining numerous nearby glaciated drainages, instead of point studies, for example with remote sensing using images and DEMs provided there is chronologic control from field work. However, the concept of ELA was developed and most studies of ELA have been undertaken in temperate regions with relatively high mean annual snowfall where ablation increases at lower elevations and there actually is a well-defined altitude of equilibrium. In cold arid regions such as Central Asia or parts of the Andes, snowfall can be so low (<150 mm/yr) that solar irradiation alone is sufficient to evaporate the accumulation directly (sublimation), in contrast to regions in which high amounts of snowfall require warm temperatures for melting. In these hyperarid regions, the ELA may be a poorly defined concept since the entire glacier experiences ablation, not just the lower elevations. However, because glaciers in these settings can only exist where there is no melting, the precipitation-limited arid paleoglaciers are easy to distinguish and map from the temperature-controlled glaciers, which occur hundreds of meters lower. Remote mapping can therefore be used to map the ~150 mm/yr isohyet in continental settings.

Jigjidsuren, B.; Gillespie, A. R.

2012-12-01

12

Equilibrium line altitudes and climate during the Late Holocene glacial maximum in the Andes  

NASA Astrophysics Data System (ADS)

Documenting the spatial and temporal pattern of climate change associated with widespread glacial fluctuations during Late Holocene time is critical for understanding the mechanisms underlying these climatic/glacial events. Here, we estimate the change in equilibrium line altitudes (ELAs) associated with the most prominent glacial advance during the last millennium for four alpine glaciers in different climatic regimes in the Andes. We reconstruct scenarios of the climatic conditions (temperature and precipitation anomalies) that accommodate the ELA depressions. The glaciers studied are an unnamed glacier in the Cordillera Vilcanota (13°S), Tapado glacier (30°S), Cipreses glacier (34°S) and Tranquilo glacier (47°S). Results from the combined geomorphic analysis and application of a surface energy and mass balance model suggest that there is not a unique combination of temperature and precipitation conditions that accommodates the ELA change recorded since the Late Holocene maximum at the four sites. Assuming no change in precipitation, the ELA depressions could be explained by a cooling (with respect to present-day values) of at least -0.7°C at Cordillera Vilcanota, -1.0°C at Tapado glacier, -0.5°C at Cipreses glacier and -1.3°C at Tranquilo glacier. In contrast, assuming no change in temperature, the ELA depressions could be explained by an increase in the precipitation of at least 0.51 m (63% of the annual precipitation) at Cordillera Vilcanota, 0.33 m (95%) at Tapado glacier, 0.17 m (21%) at Cipreses glacier and 0.68 m (62%) at Tranquilo glacier. Our results serve as targets to test predictions from models of global climate dynamics for the last millennium and contribute to the understanding of the mechanisms underlying the Late Holocene glacial fluctuations.

Sagredo, E. A.; Lowell, T. V.; Kelly, M. A.; Aravena, J.

2012-12-01

13

Estimates of Regional Equilibrium Line Altitudes and Net Mass Balance from MODIS Imagery  

NASA Astrophysics Data System (ADS)

Glacier mass balance is a key variable used to assess the health of glaciers and ice sheets. Estimates of glacier mass balance are required to model the dynamic response of glaciers and ice sheets to climate change, estimate sea-level contribution from surface melt, and document the response of glaciers to climate forcing. Annually resolved estimates of regional mass balance for mountain ranges is often inferred from a sparse network of ground-based measurements of mass balance for individual glaciers. Given that net mass balance is highly correlated with the annual equilibrium line altitude (ELA), we develop an automated approach to estimate the ELA, and by inference net mass balance, on large glaciers and icefields using MODIS 250 m imagery (MOD02QKM). We discriminate areas of bare ice and snow/firn using the product of MODIS' red (0.620 - 0.670 ? m) and near infrared (0.841 - 0.876 ? m) bands. To assess the skill in estimating glacier ELAs, we compare ELAs derived from (1) manual delineation and (2) unsupervised classification of the band product to ground-based observations of ELA and net mass balance at seven long term mass-balance monitoring sites in western North America (Gulkana, Wolverine, Lemon Creek, Taku, Place, Peyto, and South Cascade). Spatial and temporal variations in MODIS-derived ELAs provide an opportunity to validate regional mass-balance models, estimate surface melt contributions to sea-level rise, and examine the cryospheric response to climate change.

Shea, J. M.; Menounos, B.; Moore, R. D.

2011-12-01

14

Evaluation of conditions along the grounding line of temperate marine glaciers: An example from Muir Inlet, Glacier Bay, Alaska  

USGS Publications Warehouse

In the marine environment, stability of the glacier terminus and the location of subglacial streams are the dominant controls on the distribution of grounding-line deposits within morainal banks. A morainal bank complex in Muir Inlet, Glacier Bay, SE Alaska, is used to develop a model of terminus stability and location of subglacial streams along the grounding line of temperate marine glaciers. This model can be used to interpret former grounding-line conditions in other glacimarine settings from the facies architecture within morainal bank deposits. The Muir Inlet morainal bank complex was deposited between 1860 A.D. and 1899 A.D., and historical observations provide a record of terminus positions, glacial retreat rates and sedimentary sources. These data are used to reconstruct the depositional environment and to develop a correlation between sedimentary facies and conditions along the grounding line. Four seismic facies identified on the high-resolution seismic-reflection profiles are used to interpret sedimentary facies within the morainal bank complex. Terminus stability is interpreted from the distribution of sedimentary facies within three distinct submarine geomorphic features, a grounding-line fan; stratified ridges, and a field of push ridges. The grounding-line fan was deposited along a stable terminus and is represented on seismic-reflection profiles by two distinct seismic facies, a proximal and a distal fan facies. The proximal fan facies was deposited at the efflux of subglacial streams and indicates the location of former glacifluvial discharges into the sea. Stratified ridges formed as a result of the influence of a quasi-stable terminus on the distribution of sedimentary facies along the grounding line. A field of push ridges formed along the grounding line of an unstable terminus that completely reworked the grounding-line deposits through glacitectonic deformation. Between 1860 A.D. and 1899 A.D. (39 years), 8.96 x 108 m3 of sediment were deposited within the Muir Inlet morainal bank complex at an average annual sediment accumulation rate of 2.3 x 107 m3/a. This rate represents the annual sediment production capacity of the glacier when the Muir Inlet drainage basin is filled with glacial ice.

Seramur, K. C.; Powell, R. D.; Carlson, P. R.

1997-01-01

15

The length of the glaciers in the world - a straightforward method for the automated calculation of glacier center lines  

NASA Astrophysics Data System (ADS)

Glacier length is an important measure of glacier geometry but global glacier inventories are mostly lacking length data. Only recently semi-automated approaches to measure glacier length have been developed and applied regionally. Here we present a first global assessment of glacier length using a fully automated method based on glacier surface slope, distance to the glacier margins and a set of trade-off functions. The method is developed for East Greenland, evaluated for the same area as well as for Alaska, and eventually applied to all ∼200 000 glaciers around the globe. The evaluation highlights accurately calculated glacier length where DEM quality is good (East Greenland) and limited precision on low quality DEMs (parts of Alaska). Measured length of very small glaciers is subject to a certain level of ambiguity. The global calculation shows that only about 1.5% of all glaciers are longer than 10 km with Bering Glacier (Alaska/Canada) being the longest glacier in the world at a length of 196 km. Based on model output we derive global and regional area-length scaling laws. Differences among regional scaling parameters appear to be related to characteristics of topography and glacier mass balance. The present study adds glacier length as a central parameter to global glacier inventories. Global and regional scaling laws might proof beneficial in conceptual glacier models.

Machguth, H.; Huss, M.

2014-05-01

16

Widespread, rapid grounding line retreat of Pine Island, Thwaites, Smith, and Kohler glaciers, West Antarctica, from 1992 to 2011  

NASA Astrophysics Data System (ADS)

We measure the grounding line retreat of glaciers draining the Amundsen Sea sector of West Antarctica using Earth Remote Sensing (ERS-1/2) satellite radar interferometry from 1992 to 2011. Pine Island Glacier retreated 31 km at its center, with most retreat in 2005-2009 when the glacier ungrounded from its ice plain. Thwaites Glacier retreated 14 km along its fast flow core and 1 to 9 km along the sides. Haynes Glacier retreated 10 km along its flanks. Smith/Kohler glaciers retreated the most, 35 km along its ice plain, and its ice shelf pinning points are vanishing. These rapid retreats proceed along regions of retrograde bed elevation mapped at a high spatial resolution using a mass conservation technique that removes residual ambiguities from prior mappings. Upstream of the 2011 grounding line positions, we find no major bed obstacle that would prevent the glaciers from further retreat and draw down the entire basin.

Rignot, E.; Mouginot, J.; Morlighem, M.; Seroussi, H.; Scheuchl, B.

2014-05-01

17

SAR Firn Line Detection and Correlation to Glacial Mass Balance; Svartisen Glacier, Northern Norway  

Microsoft Academic Search

The glacial firn line of the Svartisen Glacier has been de- tected using ERS II SAR data from 1995 and up till to- day. The firn line is detected by first correcting the im- age backscatter intensity for topographic and geometric contributions using the Muhleman backscattering model. Then we discriminate between firn and ice facies based on the backscatter intensity

Rune Storvold; K. A. Høgda; E. Malnes; I. Lauknes

2005-01-01

18

Simulation of runoff processes of a continental mountain glacier in the Tian Shan, China  

Microsoft Academic Search

Based on calculations of energy, water and mass balance and on measurements of water routine, a model is developed to simulate glacial runoff processes for Glacier No. 1, a continental mountain glacier at the source of the Urumqi River in the Chinese Tian Shan. The melt at the equilibrium line is related to the mean melt of the glacier. The

KANG ERSI; ATSUMU OHMURA; HERBERT LANG

19

Active water exchange and life near the grounding line of an Antarctic outlet glacier  

NASA Astrophysics Data System (ADS)

The grounding line (GL) of the Antarctic ice sheet forms the boundary between grounded and floating ice along the coast. Near this line, warm oceanic water contacts the ice shelf, producing the ice sheet's highest basal-melt rate. Despite the importance of this region, water properties and circulations near the GL are largely unexplored because in-situ observations are difficult. Here we present direct evidence of warm ocean-water transport to the innermost part of the subshelf cavity (several hundred meters seaward from the GL) of Langhovde Glacier, an outlet glacier in East Antarctica. Our measurements come from boreholes drilled through the glacier's ?400-m-thick grounding zone. Beneath the grounding zone, we find a 10-24-m-deep water layer of uniform temperature and salinity (-1.45 °C; 34.25 PSU), values that roughly equal those measured in the ocean in front of the glacier. Moreover, living organisms are found in the thin subglacial water layer. These findings indicate active transport of water and nutrients from the adjacent ocean, meaning that the subshelf environment interacts directly and rapidly with the ocean.

Sugiyama, Shin; Sawagaki, Takanobu; Fukuda, Takehiro; Aoki, Shigeru

2014-08-01

20

Sensitivities of the equilibrium line altitude to temperature and precipitation changes along the Andes  

NASA Astrophysics Data System (ADS)

Equilibrium line altitudes (ELAs) of alpine glaciers are sensitive indicators of climate change and have been commonly used to reconstruct paleoclimates at different temporal and spatial scales. However, accurate interpretations of ELA fluctuations rely on a quantitative understanding of the sensitivity of ELAs to changes in climate. We applied a full surface energy- and mass-balance model to quantify ELA sensitivity to temperature and precipitation changes across the range of climate conditions found in the Andes. Model results show that ELA response has a strong spatial variability across the glaciated regions of South America. This spatial variability correlates with the distribution of the present-day mean climate conditions observed along the Andes. We find that ELAs respond linearly to changes in temperature, with the magnitude of the response being prescribed by the local lapse rates. ELA sensitivities to precipitation changes are nearly linear and are inversely correlated with the emissivity of the atmosphere. Temperature sensitivities are greatest in the inner tropics; precipitation becomes more important in the subtropics and northernmost mid-latitudes. These results can be considered an important step towards developing a framework for understanding past episodes of glacial fluctuations and ultimately for predicting glacier response to future climate changes.

Sagredo, Esteban A.; Rupper, Summer; Lowell, Thomas V.

2014-03-01

21

Using glacier inventory data to determine the sea-level contribution of glaciers  

NASA Astrophysics Data System (ADS)

Glaciers are widely considered as the best natural climate indicators. While this is certainly the case for glacier changes (length, volume), it also applies to glaciers itself as they can only exist within a certain range of climate conditions. A key parameter for the climatic classification of glaciers is their equilibrium line altitude (ELA) when referring to a balanced mass budget (ELA0). The ELA0 can be approximated by the mean or median elevation that is readily available for individual glaciers from inventories. Using well-established relations between temperature and precipitation at the ELA0, precipitation can be derived from mean elevations. Annual precipitation sums are indicative of the climatic regime and can be used to infer mass balance gradients. Once these are known, mass loss by melt can be approximated for each glacier under balanced conditions. By shifting the ELA0 upwards, the ablation region is increased and in combination with the mass balance gradient the additional glacier melt can be calculated for each glacier. In this contribution we applied the above methods to all glaciers in the Swiss Alps using glacier outlines from the mid 1970s and a digital elevation model (DEM) from the mid 1980s as an input. The mass balance gradients derived from annual precipitation are within the range of known values (measured and modeled). The modelled ablation under balanced conditions is rather similar to the observed precipitation amounts over glaciers (considering measurement uncertainties). For a one degree temperature increase, specific mass loss increases by about 0.65 m / yr (the mass balance sensitivity) which gives a total mass loss of about 1 Gt / year over a glacier area of 1000 sqkm and for a temperature increase of 1.5 degrees. These values are in good agreement with the observed annual mass changes of glaciers in the Alps over the past two decades, thus confirming the observed temperature increase in the mid 1980s.

Paul, Frank

2014-05-01

22

Geochronology and Equilibrium Line Altitudes of LLGM through Holocene Glaciations from the Tropical Cordillera Huayhuash, Peru  

NASA Astrophysics Data System (ADS)

Geomorphologic relationships and cosmogenic 10Be ages from the Central Peruvian Andes reveal a rich record of glaciations from at least the late Holocene, Late Glacial, Last Local Glacial Maximum (LLGM), and older more extensive glaciations - dated between 50ka and 440ka in both the Cordillera Blanca, to the north and the Junin Region to the south. The Cordillera Huayhuash (10.3°S, 76.9°W) is located between these two well-studied regions. The spine of the range trends nearly north-south and contains a substantial east-west spur which together can be used to evaluate the spatial variation in paleo-ELAs. The range is thus a key location to study changes in ice extent and equilibrium line altitudes (ELAs) between the LLGM and modern periods. Modern glaciers are confined to altitudes >4800 m and the present (1997) ELA is 4800- 5100m. In order to determine the paleo-ice positions of glaciers in different valleys we have developed a new chronology from cosmogenic 10Be ages of moraine boulder and 14C basal bog core ages. Through field mapping of glacial features, analysis of satellite imagery, digital elevation models (DEMs), and geochronology, we have delineated the ice limits associated with the LLGM, Late Glacial, and Late Holocene advances. Ages in the three valleys we have studied cluster at ~29ka, ~13ka, and ~9ka and overall we have identified surfaces with ages that range from 39.9±1.4ka to 0.2ka±0.05ka. Based on these data, we have mapped the extent of the correlative paleo-glaciers in these three drainages and extracted the modern hypsometry for each paleo-glacier from the DEMs. From this data set, we have generated paleo- ELAs using a range of methods: Toe-to-Headwall-Altitude Ratio (THAR), the Accumulation Area Ratio (AAR), and Accumulation Area Balance Ratio (AABR). For each of the LLGM, Late Glacial and Holocene stages, we have calculated both: (1) the temperature depression assuming no moisture variations, and (2) the potential relative moisture gradients assuming a constant temperature depression. Our results suggest that variations in glacial extent (and therefore paleo-ELAs) are strongly correlated with differences in valley orientation and morphology as eastern drainages receive more moisture and have shallower topographic gradients than western drainages. Additionally, while there is an extensive record of older (>39.9±1.4ka) advances to the north (Cordillera Blanca) and to the south (Junin region), the confined morphology of the Cordillera Huayhaush valleys may have inhibited the preservation of older glacial geomorphologic features, thereby explaining the apparent lack of old moraines in this range.

Hall, S. R.; Ramage, J. M.; Rodbell, D. T.; Finkel, R. C.; Smith, J. A.; Mark, B. G.; Farber, D. L.

2006-12-01

23

Quasi-equilibrium electron density along a magnetic field line  

NASA Astrophysics Data System (ADS)

A methodology is developed to determine the density of high-energy electrons along a magnetic field line for a low-? plasma. This method avoids the expense and statistical noise of traditional particle tracking techniques commonly used for high-energy electrons in bombardment plasma generators. By preserving the magnetic mirror and assuming a mixing timescale, typically the elastic collision frequency with neutrals, a quasi-equilibrium electron distribution can be calculated. Following the transient decay, the analysis shows that both the normalized density and the reduction fraction due to collision converge to a single quasi-equilibrium solution.

Mao, Hann-Shin; Wirz, Richard

2012-11-01

24

Remote Sensing Applications for the Bering Glacier, Alaska  

NASA Astrophysics Data System (ADS)

Satellite remote sensing is an invaluable tool to monitor and characterize the Bering Glacier System. The Bering Glacier is located in coastal, south-central Alaska and is the largest and longest glacier in continental North America, with an area of approximately 5,175 km2, and a length of 190 km. It is also the largest surging glacier in America, having surged at least five times during the twentieth century. The last great surge occurred in 1993- 1995. Bering Glacier alone covers more than 6 percent of the glacier covered area of Alaska and may contain 15- 20 percent of Alaska's total glacier ice. Applications of glacier remote sensing include but are not limited to: mapping extent and features, ice velocities through sequential observations, glacier terminus locations, snow line location, glacier albedo, changes in glacier volume, iceberg surveys and calving rates, hydrographic and water quality parameters in ice marginal lakes, and land cover classification maps. Historical remote sensing images provide a much needed geospatial time record of the dynamic changes Bering Glacier has undergone, including changes due to its surge behavior and response to climate change. Remote sensing images dating back to the early 1990s have been used to map the glacier terminus retreat of approximately five to seven kilometers which has resulted in Vitus Lake increasing in volume approximately 260 percent since 1995 to the current (2006) volume of 9.4 km3 of water. Using elevation data obtained from remote sensing and GPS surface points, we have determined that the glacier elevation has decreased approximately 150 m in elevation at the terminus and 30 m at a position 300 m below the present (2006) equilibrium line (~1,300 m) since 1972. Satellite observations have recorded the upward migration in altitude of the equilibrium line to its present position (slightly > 1,200 m). The decrease in glacier volume, obtained using remote sensing derived elevation data, from 1957 to 2004 is estimated at approximately 104 km3. Remote sensing data has also mapped the sediment rich (rock flower) water flowing into Vitus Lake providing insight into the hydrologic circulation of the Bering Glacier system, showing major glacier discharge from the Abandoned River, Arrowhead Point, and Lamire Bay in the area of Vitus Lake west of Taggland.

Liversedge, L.; Shuchman, R.; Josberger, E.; Payne, J.; Hatt, C.; Spaete, L.

2007-12-01

25

Remote Sensing Characterization of Glaciers in the N. Himachal Pradesh  

NASA Astrophysics Data System (ADS)

Glaciers in high mountain Asia represent the largest volume of ice outside of the polar regions. They play an important role in the water resources of communities downstream and there has been recent dispute over the total amount of ice present how it is changing. The immense quantity of glaciers and variability of glacier types in the Himalayas coupled with the sparse amount of suitable satellite data limits the capability of conducting detailed and efficient remote sensing observations on a regional scale. This study aims to develop a semi-automated characterization of approximately 5,000 glaciers in the N. Himachal Pradesh region of India using multi-spectral data. We use an August 2002 Landsat 7 Enhanced Thematic Mapper Plus (ETM+) image because of its small percentage of snow and cloud cover, and because it is acquired late in the summer allowing for delineation of ablation and accumulation zones. Glacier outlines from the GLIMS glacier database for this region comprise total glacier area including debris covered ice regions. We outline the accumulation (snow-covered) region for each glacier exploiting the high reflectance value of snow compared to ice and debris. We further outline debris-free, bare-ice using a threshold on a ratio image of ETM+ bands 4 and 5. Subtracting this region from the GLIMS outlines leaves us with the debris-covered ice region. Using our resulting ablation and accumulation areas, we compute the area-accumulation ratio (AAR) for the many glaciers in our region. These data are compared to mean aspect, mean elevation, glacier size, percentage of debris cover, and mean equilibrium line altitude (ELA) for each glacier. This study hopes to contribute to and improve on glacier databases for the Himalayan region and to advance glacier analyses using remote sensing data. A possible future aim is to identify benchmark glaciers which can be used for detailed future study.

Le, D.; Catania, G. A.

2012-12-01

26

Linking glacier annual mass balance and glacier albedo retrieved from MODIS data  

NASA Astrophysics Data System (ADS)

Albedo is one of the variables controlling the mass balance of temperate glaciers. Multispectral imagers, such as MODerate Imaging Spectroradiometer (MODIS) on board the TERRA and AQUA satellites, provide a means to monitor glacier surface albedo. In this study, different methods to retrieve broadband glacier surface albedo from MODIS data are compared. The effect of multiple reflections due to the rugged topography and of the anisotropic reflection of snow and ice are particularly investigated. The methods are tested on the Saint Sorlin Glacier (Grandes Rousses area, French Alps). The accuracy of the retrieved albedo is estimated using both field measurements, at two automatic weather stations located on the glacier, and albedo values derived from terrestrial photographs. For summers 2008 and 2009, the root mean square deviation (RMSD) between field measurements and the broadband albedo retrieved from MODIS data at 250 m spatial resolution was found to be 0.052 or about 10% relative error. The RMSD estimated for the MOD10 daily albedo product is about three times higher. One decade (2000-2009) of MODIS data were then processed to create a time series of albedo maps of Saint Sorlin Glacier during the ablation season. The annual mass balance of Saint Sorlin Glacier was compared with the minimum albedo value (average over the whole glacier surface) observed with MODIS during the ablation season. A strong linear correlation exists between the two variables. Furthermore, the date when the average albedo of the whole glacier reaches a minimum closely corresponds to the period when the snow line is located at its highest elevation, thus when the snow line is a good indicator of the glacier equilibrium line. This indicates that this strong correlation results from the fact that the minimal average albedo values of the glacier contains considerable information regarding the relative share of areal surfaces between the ablation zone (i.e. ice with generally low albedo values) and the accumulation zone (i.e. snow with a relatively high albedo). As a consequence, the monitoring of the glacier surface albedo using MODIS data can provide a useful means to evaluate the interannual variability of the glacier mass balance. Finally, the albedo in the ablation area of Saint Sorlin Glacier does not exhibit any decreasing trend over the study period, contrasting with the results obtained on Morteratsch Glacier in the Swiss Alps.

Dumont, M.; Gardelle, J.; Sirguey, P.; Guillot, A.; Six, D.; Rabatel, A.; Arnaud, Y.

2012-12-01

27

Bistability in a hyperchaotic system with a line equilibrium  

NASA Astrophysics Data System (ADS)

A hyperchaotic system with an infinite line of equilibrium points is described. A criterion is proposed for quantifying the hyperchaos, and the position in the three-dimensional parameter space where the hyperchaos is largest is determined. In the vicinity of this point, different dynamics are observed including periodicity, quasi-periodicity, chaos, and hyperchaos. Under some conditions, the system has a unique bistable behavior, characterized by a symmetric pair of coexisting limit cycles that undergo period doubling, forming a symmetric pair of strange attractors that merge into a single symmetric chaotic attractor that then becomes hyperchaotic. The system was implemented as an electronic circuit whose behavior confirms the numerical predictions.

Li, Chunbiao; Sprott, J. C.; Thio, Wesley

2014-03-01

28

Linking glacier annual mass balance and glacier albedo retrieved from MODIS data  

NASA Astrophysics Data System (ADS)

Albedo is one of the variables controlling the mass balance of temperate glaciers. Multispectral imagers, such as MODerate Imaging Spectroradiometer (MODIS) on board the TERRA and AQUA satellites, provide a means to monitor glacier surface albedo. In this study, different methods to retrieve broadband glacier surface albedo from MODIS data are compared. The effect of multiple reflections due to the rugged topography and of the anisotropic reflection of snow and ice are particularly investigated. The methods are tested on the Saint Sorlin Glacier (Grandes Rousses area, French Alps). The accuracy of the retrieved albedo is estimated using both field measurements, at two automatic weather stations located on the glacier, and albedo values derived from terrestrial photographs. For summers 2008 and 2009, the Root Mean Square Deviation (RMSD) between field measurements and the broadband albedo retrieved from MODIS data at 250 m spatial resolution was found to be 0.052 or about 10% relative error. The RMSD estimated for the MOD10 daily albedo product is about three times higher. One decade (2000-2009) of MODIS data were then processed to create a time series of albedo maps of Saint Sorlin Glacier during the ablation season. The annual mass balance of Saint Sorlin Glacier was compared with the minimum albedo value (average over the whole glacier surface) observed with MODIS during the ablation season. A strong linear correlation exists between the two variables. Furthermore, the date when the average albedo of the whole glacier reaches a minimum closely corresponds to the period when the snowline is located at its highest elevation, thus when the snowline is a good indicator of the glacier equilibrium line. This indicates that this strong correlation results from the fact that the minimal average albedo values of the glacier contains a considerable information regarding the relative share of areal surfaces between the ablation zone (i.e. ice with generally low albedo values) and the accumulation zone (i.e. snow with a relatively high albedo). As a consequence, the monitoring of the glacier surface albedo using MODIS data can provide a useful means to evaluate the inter-annual variability of the glacier mass balance. Finally, the albedo in the ablation area of Saint Sorlin Glacier does not exhibit any decreasing trend over the study period, contrasting with the results obtained on Morteratsch Glacier in the Swiss Alps.

Dumont, M.; Gardelle, J.; Sirguey, P.; Guillot, A.; Six, D.; Rabatel, A.; Arnaud, Y.

2012-07-01

29

Linking glacier annual mass balance and glacier albedo retrieved from MODIS data  

NASA Astrophysics Data System (ADS)

Spectroradiometer (MODIS) on board the TERRA and AQUA satellites, provide a means to monitor glacier surface albedo. In this study, different methods to retrieve broadband glacier surface albedo from MODIS data are compared. The effect of multiple reflections due to the rugged topography and of the anisotropic reflection of snow and ice are particularly investigated. The methods are tested on the Saint Sorlin Glacier (Grandes Rousses area, French Alps). The accuracy of the retrieved albedo is estimated using both field measurements, at two automatic weather stations located on the glacier, and albedo values derived from terrestrial photographs. For summers 2008 and 2009, the Root Mean Square Deviation (RMSD) between field measurements and the broadband albedo retrieved from MODIS data at 250m spatial resolution was found to be 0.052 or about 10% relative error. The RMSD estimated for the MOD10 daily albedo product is about three times higher. One decade (2000-2009) of MODIS data were then processed to create a time series of albedo maps of four glaciers in the French Alps including Saint Sorlin Glacier during the ablation season. The annual mass balance of each glacier was compared with the minimum albedo value (average over the whole glacier surface) observed with MODIS during the ablation season. A strong linear correlation exists between the two variables. Furthermore, the date when the average albedo of the whole glacier reaches a minimum closely corresponds to the period when the snowline is located at its highest elevation, thus when the snowline is a good indicator of the glacier equilibrium line. This indicates that this strong correlation results from the fact that the minimal average albedo values of the glacier contains a considerable information regarding the relative share of areal surfaces between the ablation zone (i.e. ice with generally low albedo values) and the accumulation zone (i.e. snow with a relatively high albedo). As a consequence, the monitoring of the glacier surface albedo using MODIS data can provide a useful means to evaluate the inter-annual variability of the glacier mass balance. Finally, the albedo in the ablation area of Saint Sorlin Glacier does not exhibit any decreasing trend over the study period, contrasting with the results obtained on Morteratsch Glacier in the Swiss Alps.

Dumont, M.; Gardelle, J.; Sirguey, P. J.; Guillot, A.; Décaux, L.; Rabatel, A.; Six, D.; Arnaud, Y.

2012-12-01

30

Variations in Melt-Flow Acceleration Above and Below the Greenland Equilibrium Line  

NASA Astrophysics Data System (ADS)

Initial observations of accelerated ice flow at the equilibrium line in West-central Greenland during summer melt periods (1996 to 1999) indicated that surface melt-water rapidly propagated to the base and enhanced the basal sliding. Since then numerous observational and theoretical results have provided additional information on the melt-acceleration effect, while leading to some differing conclusions about the climatological and hydrological processes involved. Additional velocity measurements since 1999 show further characteristics of the melt-acceleration in the ice flowline though Swiss Camp, which terminates on land, and in a nearby flowline, which terminates in an outlet glacier. Accelerations as large as three times the average winter velocity are observed during stronger melt events. At downstream locations, accelerations begin earlier in the melt season, but accelerations at multiple sites along a flow line occur simultaneously later in the season. At the equilibrium line, a short period of surface uplift of about 50 cm occurs when the flow abruptly changes from acceleration to deceleration, apparently caused by ice compression during the transition. At downstream locations, the surface rises at the beginning of the melt season and drops at the end of melting suggesting an uplift forced by sub-ice water and sediment. Equivalence of the net additional displacement at upstream and downstream sites indicates no net longitudinal ice strain after the acceleration-deceleration periods. Approximate equivalence of the ratio of peak summer velocities to average winter velocities along the flowline indicate that local melt-acceleration is occurring at and above the equilibrium as well as from longitudinal coupling of downstream effects. High-frequency velocity observations show that the ice flow continues to accelerate with increasing water production during melt events, follow by an abrupt deceleration after the event, indicating that saturation of the acceleration effect from production of efficient sub-glacial channelization is not generally occurring. As the EL migrates inland with climatic warming, the melt-acceleration effect has also been migrating. The net additional displacement of several meters during the summer is about 3 to 5% of the total annual displacement, and is increasing as summer temperatures and surface melting increases.

Zwally, H.; Saba, J. L.; Steffen, K.

2013-12-01

31

Variations in ELA of glaciers in the Tibetan Plateau over the past two decades and their implications for future glacier change  

NASA Astrophysics Data System (ADS)

The equilibrium line altitude (ELA) is a theoretical line on a glacier at which annual mass accumulation equals annual mass loss. Glacier behaviors such as advancing or retreating are controlled by the variations in ELA. Relative to its steady state, a glacier advances when its ELA falls, retreats when its ELA rises, or melts entirely when its ELA rises above its summit. In contrast to variations in glacier length or area, variations in ELA respond almost simultaneously to climate change. With global warming, studying ELA variations is of prime importance for understanding the behaviors of glaciers. Based on observations of the ELAs of the Qiyi Glacier in the Qilian Mountains, the Meikuang Glacier in the Kunlun Mountains and the Xiaodongkemadi Glacier in the Tanggula Mountains in the Tibetan Plateau, we found that the ELAs have risen about 160-180m since 1989. After analyzing the correlations between the ELAs and air temperature and precipitation, it was found that the warm season air temperature was the leading climatic factor influencing ELA. The present ELAs of those observed glaciers are much higher than their ELAs under the status of that their mass balances are zero. This suggests that those glaciers will continue to retreat in the near future.

Wang, N.; Pu, J.; Duan, K.; Yao, T.

2013-05-01

32

Rapid Thinning of a Lake Calving Glacier: Yakutat Glacier, Southeast Alaska  

NASA Astrophysics Data System (ADS)

Calving glaciers around the world have recently undergone a rapid retreat and are important contributors to global sea level rise. Due to their greatly increased mass loss, tidewater glaciers in particular have long received much attention, whereas lake calving glaciers have just been identified as significant contributors. In southeast Alaska, numerous glaciers have experienced rapid retreat and significant thinning during the last several decades. To better understand the causes for these rapid changes we have focused on Yakutat Glacier, a lake calving glacier in southeast Alaska. Yakutat Glacier is part of the Yakutat Ice field and drains into Harlequin Lake, which has depths of over 300 m at the calving face. The ice field covers an area of 668 sq km and lies in a maritime area off the coast of the Gulf of Alaska. The average precipitation in the nearby town of Yakutat is over 3800 mm per year. However, the ice field divide is essentially at or below the current equilibrium line altitude (ELA) of 800 - 900 m for this region, thereby ensuring the glacier will continue to thin, provided the current trend of regional warming does not reverse. The ongoing thinning continues to lower the glaciers average elevation, increasing its average ablation, even under constant climate. This forms a positive feedback loop that is known as the Bovardsson effect. In addition, radio echo sounding shows much of the glacier base near or below sea level, indicating that lake calving will remain playing a role in the retreat. We obtained a 40 m-grid digital elevation model (DEM) derived from September 3, 2007 SPOT imagery and obtained under the IPY SPIRIT program. We used August 26, 2007 laser altimetry profiles to check the accuracy of the DEM and found a mean difference of 2 m (DEM greater) with a standard deviation of 2.3 m. We differenced this DEM from a DEM from the February 2000 Shuttle Radar Topography Mission to determine the extent of the volume change and thinning. During this period, the Yakutat Ice field lost about 22.4 ± 7.5 cubic km of ice, with thinning rates increasing down glacier, especially towards the glacier's grounding line. Just up glacier from this grounding line, we found elevation changes of over 10 m per year. The same trend is visible in a comparison between the 2007 Spot DEM and a July 2009 DEM generated from photogrammetry imagery. Little change in surface elevation occurred over the 2-km-long floating tongue during this time period, but recently the entire floating tongue has started to disintegrate.

Truessel, B.; Motyka, R. J.; Larsen, C. F.; Truffer, M.

2010-12-01

33

Reconstructing glaciers: Sedimentary sources, sinks and fingerprints  

NASA Astrophysics Data System (ADS)

Glaciers are natural systems that shape and influence their geological surroundings through erosion and redistribution of sediments and rocks from one place to another. Their presence are determined by the landscape, regional climatic parameters such as wind, precipitation and temperature, and for these reasons they are valuable proxies of present and past climatic change. During the last four decades researchers have attempted to develop and assess methods that reliably and accurately reproduce continuous glacier variability over timescales extending thousands of years back in time. At the core of this multi-disciplinary endeavour is a strong desire to enhance our knowledge about how glaciers respond to a wider spectre of climatic change beyond what has been observed and documented for the last ~100 years. By far the majority of existing continuous glacier reconstructions are based on empirical evidence derived from soft sediment archives - mainly from lakes and fjords - making it quintessential to understand the sedimentary sources and sinks operating in glacierized catchment systems. If paleoclimatic inferences are to be made from such glacier reconstructions it is imperative that relevant sources of noise is considered, identified and, preferentially, eliminated. Here we review some of the problems and prospects of reconstructing temperate mountain or cirque glaciers as well as basic assumptions underlying most continuous glacier reconstructions. We will illustrate this challenge by presenting new data from a glacierized catchment surrounding a small lake called Blåvatnet located in Northern Norway at 68°N. A suit of piston and short gravity cores from the lake have been analysed and the results have been tested and corroborated by catchment samples from different sedimentary sources - an approach that is deemed to be of critical value when it comes to fingerprinting the glacier signal. Methodological emphasis is put on rock magnetism, which we demonstrate to be exceptionally well suited for identifying different sedimentary sources and characteristics typical for glacierized catchments. High sedimentation rates allow for a decadal glacier reconstruction covering the last 4000 years. Specifically, we observe major fluctuations in glacier activity that corresponds to an Equilibrium-Line-Altitude (ELA) variability of +/- 100 m. Peak activity is associated with the 'Little Ice Age' (1400-1800 AD) and a Neoglacial Maximum which occurred around 2500 years ago.

Paasche, O.; Lovlie, R.; Bakke, J.; Hirt, A. M.

2012-12-01

34

The influence of shear bands on the grounding line retreat in Pine Island Glacier  

NASA Astrophysics Data System (ADS)

Pine Island Glacier (PIG), West Antarctica, is known as the weak underbelly of the West Antarctic Ice Sheet. During the last 30 years, it has undergone a dramatic acceleration along with a retreat of its grounding line. The main ice stream draining PIG is laterally bounded by two thin bands of damaged ice. These shear bands may play a key role in the dynamics of the grounding line since they likely decrease the ice-shelf buttressing. The traditional approach is generally to infer the viscosity from surface velocity using data assimilation methods. However, in that case the inverse problem is under-constrained when it is coupled to the inversion of basal drag: different set of basal drag and viscosity pattern solution can lead to a good match between modelled and observed surface velocities, but would lead to different prognostic solutions associated to different grounding line migrations. Here, we follow a simpler approach and perform a sensitivity study on the shear bands effective viscosity, and its consequences for the ice dynamics. The areas of fractured ice at PIG are located using a recent SPOT satellite image. The non-fractured ice viscosity depends on ice temperatures while the fractured ice viscosity is decreased through a sensitivity study to reproduce the damaged ice of the shear bands. Using two different higher-order models (Elmer/Ice and BISICLES), we investigate the influence of the shear bands' damage on the grounding line dynamics. Each experiment in the sensitivity study gathers successively (i) the determination of basal drag through assimilation methods, (ii) a geometry relaxation over 15 years and (iii) transient perturbation experiments driven by different calving sizes. The initial geometry of the ice sheet arises from the ALBMAP data set on a 1 km grid resolution, velocities were acquired during the last International polar Year, and non-fractured ice viscosities are deduced from prescribed temperatures computed with a higher order model. We show that the presence of the shear bands modifies the buttressing state in the ice shelf, i.e. the amount of back stress transmitted to the grounding line. The discharge of grounded ice in response to a calving event is thus influenced by the estimation of the ice shelf rheology. This suggests that future projections of PIG behaviour will have to carefully evaluate the ice-shelf stress pattern and its evolution.

Favier, Lionel; Durand, Gaël; Cornford, Stephen; Gagliardini, Olivier; Zwinger, Thomas

2013-04-01

35

Benchmark Glaciers  

NSDL National Science Digital Library

The United States Geological Survey (USGS) operates a long-term "benchmark" glacier program to intensively monitor climate, glacier motion, glacier mass balance, glacier geometry, and stream runoff at a few select sites. The data collected are used to understand glacier-related hydrologic processes and improve the quantitative prediction of water resources, glacier-related hazards, and the consequences of climate change. This page presents some of the balance, runoff, and temperature data for three glaciers: Gulkana, South Cascade and Wolverine. Reports for each of these glaciers uses the collected data to draw many conclusions. There is also a section with common questions and myths about glaciers.

36

Water, ice, and meteorological measurements at South Cascade glacier, Washington, balance year 2003  

USGS Publications Warehouse

Winter snow accumulation and summer snow and ice ablation were measured at South Cascade Glacier, Washington, to estimate glacier mass-balance quantities for balance year 2003. The 2003 glacier-average maximum winter snow balance was 2.66 meters water equivalent, which was about equal to the average of such balances for the glacier since balance year 1959. The 2003 glacier summer balance (-4.76 meters water equivalent) was the most negative reported for the glacier, and the 2003 net balance (-2.10 meters water equivalent), was the second-most negative reported. The glacier 2003 annual (water year) balance was -1.89 meters water equivalent. The area of the glacier near the end of the balance year was 1.89 square kilometers, a decrease of 0.03 square kilometer from the previous year. The equilibrium-line altitude was higher than any part of the glacier; however, because snow remained along part of one side of the upper glacier, the accumulation-area ratio was 0.07. During September 13, 2002-September 13, 2003, the glacier terminus retreated at a rate of about 15 meters per year. Average speed of surface ice, computed using a series of vertical aerial photographs dating back to 2001, ranged from 2.2 to 21.8 meters per year. Runoff from the subbasin containing the glacier and from an adjacent non-glacierized basin was gaged during part of water year 2003. Air temperature, precipitation, atmospheric water-vapor pressure, wind speed, and incoming solar radiation were measured at selected locations on and near the glacier. Summer 2003 at the glacier was among the warmest for which data are available.

Bidlake, William R.; Josberger, Edward G.; Savoca, Mark E.

2005-01-01

37

MODIS albedo products used to detect ELA on Svalbard glaciers  

NASA Astrophysics Data System (ADS)

MODIS L3 albedo products (MCD43A3) for the period 2000-2011 are used to derive a proxy for the equilibrium line altitude (ELA) using a simple threshold method to determine the location of the annual snow line on the glacier. This albedo-derived ELA proxy is then compared to ELA determined from glacier mass balance measurements made on selected glaciers in Svalbard, which range in size from 5-500 km2. There is a good 1:1 correlation between the proxy and observed ELA on the larger study glaciers, which are covered by many MODIS pixels, with no need for calibration of the relation. Detecting the snow line on the smaller glaciers, which are covered by only a small number of MODIS pixels, does not work as well. There is the expected negative relation between minimum albedo and ELA, but the relation must be calibrated for individual glaciers. Nevertheless, the distribution of icefields and large glaciers in Svalbard allows the threshold method to be used to determine the spatial distribution of ELA around the archipelago.

Kohler, J.; Nuth, C.; König, M.; Hagen, J. O.

2012-12-01

38

Modeling on the Steady State of Thwaites Glacier  

NASA Astrophysics Data System (ADS)

Thwaites Glacier (TWG) is the second largest ice stream in West Antarctica in terms of ice discharge, and the broadest ice stream in Antarctica (120 km wide). Observations and theory suggest that its configuration is inherently unstable in a warming climate. Satellite observations have revealed grounding line retreat, ice thinning, ice stream broadening and in more recent years ice flow acceleration. The most important part of the glacier evolution involves its grounding line dynamics and the impact of ice-ocean interactions. In a region between the grounding line and the limit of the flexure zone, some 10 km downstream, however, the glacier is not in hydrostatic equilibrium. Proper treatment of the grounding line dynamics requires full Stokes solution. Here, we model the grounding line of TWG in 2D, full Stokes, with the goal to examine whether the glacier is in a steady state configuration or not. The model treats ice sheet and ice shelf as two fluids coupled through the ice mass flux (Nowicki, 2008). Water stress is used as a constraint on the ice shelf instead of hydrostatic equilibrium. We use radar interferometry (InSAR) measurements of ice velocity and grounding line position through time, Bedmap2 and IceBridge thickness, and surface mass balance from RACMO to constrain the model. The results are used to conclude on the state of dynamic balance of the glacier. This work is funded by NASA Cryospheric Science Program.

Yu, H.; Rignot, E. J.; Morlighem, M.; Seroussi, H.

2013-12-01

39

Glacier Melt  

NSDL National Science Digital Library

This short video shows an example of melting alpine glaciers in the Austrian Alps (Goldberg Glacier). Disappearing alpine glaciers have social and environmental impacts, including the decline of fresh water supplies and contributing to sea level rise.

Geographic, National

40

Linking glacier annual mass balance and glacier albedo from MODIS data  

NASA Astrophysics Data System (ADS)

The albedo is one of the variables controlling the mass balance of temperate glaciers. Multispectral imagers, such as MODIS on board TERRA and AQUA, provide a means to monitor glacier albedo. In this study, different methods to retrieve broadband glacier albedo from MODIS data are compared. In particular, the effect of the multiple reflections due to the rugged topography and that of the anisotropic reflection of snow and ice are investigated. The methods are tested on the Saint Sorlin glacier (Grandes Rousses area, French Alps). The accuracy of the retrieved albedo is estimated using both field measurements and albedo derived from terrestrial photographs. The root mean square deviation between field measurements and the broadband albedo retrieved from MODIS pixels at 250m spatial resolution was found to be less than 0.06. One decade (2000-2010) of MODIS data were then processed to create a time series of albedo maps of Saint Sorlin glacier during the ablation season. It appears that the albedo in the ablation area of the glacier does not exhibit any marked decreasing trend during the decade under study. This contrasts with the situation observed on other glaciers in the Alps. In addition, the annual mass balance of Saint Sorlin Glacier was compared with the minimum albedo value (spatial averaged over the whole glacier) observed with MODIS during the ablation season. A high linear correlation exists between the two variables. Furthermore, the day on which the albedo reaches a minimum over the glacier closely corresponds to the day on which the snowline is found to be at its highest elevation, thus close to the glacier's equilibrium line. This indicates that the high correlation can be explained by the fact that this minimal albedo contains a high degree of information regarding the relative share of areal surfaces between the ablation zone (i.e., ice with a generally lower albedo) and the accumulation zone (i.e., snow with a relatively high albedo). This implies that monitoring the albedo of glacier with MODIS data can provide a useful means to approach the inter-annual variability of the glacier's mass balance.

Dumont, M.; Gardelle, J.; Arnaud, Y.; Guillot, A.; Sirguey, P.; Six, D.

2012-04-01

41

What do We Know the Snow Darkening Effect Over Himalayan Glaciers?  

NASA Technical Reports Server (NTRS)

The atmospheric absorbing aerosols such as dust, black carbon (BC), organic carbon (OC) are now well known warming factors in the atmosphere. However, when these aerosols deposit onto the snow surface, it causes darkening of snow and thereby absorbing more energy at the snow surface leading to the accelerated melting of snow. If this happens over Himalayan glacier surface, the glacier meltings are expected and may contribute the mass balance changes though the mass balance itself is more complicated issue. Glacier has mainly two parts: ablation and accumulation zones. Those are separated by the Equilibrium Line Altitude (ELA). Above and below ELA, snow accumulation and melting are dominant, respectively. The change of ELA will influence the glacier disappearance in future. In the Himalayan region, many glacier are debris covered glacier at the terminus (i.e., in the ablation zone). Debris is pieces of rock from local land and the debris covered parts are probably not affected by any deposition of the absorbing aerosols because the snow surface is already covered by debris (the debris covered parts have different mechanism of melting). Hence, the contribution of the snow darkening effect is considered to be most important "over non debris covered part" of the Himalayan glacier (i.e., over the snow or ice surface area). To discuss the whole glacier retreat, mass balance of each glacier is most important including the discussion on glacier flow, vertical compaction of glacier, melting amount, etc. The contribution of the snow darkening is mostly associated with "the snow/ice surface melting". Note that the surface melting itself is not always directly related to glacier retreats because sometimes melt water refreezes inside of the glacier. We should discuss glacier retreats in terms of not only the snow darkening but also other contributions to the mass balance.

Yasunari, T. J.; Lau, K.-U.; Koster, R. D.; Suarez, M.; Mahanama, S. P.; Gautam, R.; Kim, K. M.; Dasilva, A. M.; Colarco, P. R.

2011-01-01

42

Equilibrium  

NSDL National Science Digital Library

Using a visual approach, this applet is designed to help students learn to solve equilibrium calculations and also to help them gain a deeper understanding of the topic. It can be used by the instructor in the classroom as equilibrium topics are introduced. Sample exercises for students are included. The text is available in both English and Spanish.

43

36Cl Exposures Ages and Equilibrium Line Altitude (ELA) of the Ampato Volcanic Complex (Southern Peru).  

NASA Astrophysics Data System (ADS)

In this work we present the results obtained from the reconstruction of the ancient glacial Equilibrium Line Altitude (paleoELA) and the dating of various glacial phases on the Ampato volcanic complex (15°24´S-15°51´S, 73° W; 6.288 m asl), in the Central Andes. In order to calculate the paleoELAs we used two methods: the Accumulation Area Ratio (AAR) and the Area X Altitude Balance Ratio (AABR). The dating was obtained by cosmogenic methods (36Cl). We sampled: 1) boulders, in a stable position, larger than 1m and located on the crest of the moraines; and 2) polished and striated bedrock outcrops, which indicate the retreat of ice. In every studied valley we found voluminous moraines related to the Local Last Glacial Maximum of the Pleistocene (LLGMP). The dating obtained from the sampled boulders ranges from 17.9 ± 0.1 to 13.6 ± 0.1 kyr. We estimate that the most significant deglaciation process started at 12 ka on the Ampato volcanic complex and adjacent areas also covered by ice, such as the Patapampa altiplano. In certain valleys we found re-advance moraines such as in Huayuray valley, located on the Northern slope of the volcanic complex, dated at 11.4 ± 0.21 kyr. The last generalised advance is related to the Little Ice Age (LIA). During this event the glaciers formed small moraines which are close to the current glacial fronts. In Huayuray valley we estimated a paleoELA (AAR) of ~5,200 m during the LLGMP asl and ~5.810 m asl during the LIA. Similar data was obtained using the AABR method: ~5.150 m asl during the LLGMP, and ~5.750 m asl during the LIA. In Mollebaya valley (East face of the volcanic complex) the paleoELA (AAR) during the LLGMP was at ~5.350 m asl and during the LIA it reached ~5.740 m asl. Using the AABR method the LLGMP and LIA paleoELAs are ~5.070 and ~5.700 m asl, respectively. In Pujro-Huayjo valley, to the Soutwest, the paleoELA (AAR) during the LLGMP was ~5.390 m asl. LIA moraines are absent in this valley. We calculated the ELA from the glacier in 1955 at ~5.725 m asl. Using the AABBR method, the ELA was lower: ~4.940 m asl during LLGMP and ~5.635 m asl in 1955. Finally, in the Mucurca valley, West face of the volcanic complex, the LLGMP paleoELA was at ~4.930 m asl and at 5.100 m asl during the most recent advance (Lateglacial phase). Using the AABR method we obtained a value of ~4.865 m asl for the LLGMP paleoELA and ~5.015 m asl for the Late glacial phase. On average the the LLGMP ELA was 5220 m asl (AAR) and 5010 m asl (AABR). Based on the modern (1955) ELA from Pujro-Hayjo valley, the LLGMP ELA lowering was ~550 m (AAR) and ~625 m (AABR). Research funded by CGL2009-7343 project, Government of Spain.

Alcalá, J.; Palacios, D.; Vázquez-Selém, L.

2012-04-01

44

Debris-Covered Glaciers in the Sierra Nevada, California, and Their Implications for Snowline Reconstructions  

USGS Publications Warehouse

Ice-walled melt ponds on the surfaces of active valley-floor rock glaciers and Matthes (Little Ice Age) moraines in the southern Sierra Nevada indicate that most of these landforms consist of glacier ice under thin (ca. 1 - 10 m) but continuous covers of rock-fall-generated debris. These debris blankets effectively insulate the underlying ice and greatly reduce rates of ablation relative to that of uncovered ice. Such insulation explains the observations that ice-cored rock glaciers in the Sierra, actually debris-covered glaciers, are apparently less sensitive to climatic warming and commonly advance to lower altitudes than do adjacent bare-ice glaciers. Accumulation-area ratios and toe-to-headwall-altitude ratios used to estimate equilibrium-line altitudes (ELAs) of former glaciers may therefore yield incorrect results for cirque glaciers subject to abundant rockfall. Inadvertent lumping of deposits from former debris-covered and bare-ice glaciers partially explains an apparently anomalous regional ELA gradient reported for the pre-Matthes Recess Peak Neoglacial advance. Distinguishing such deposits may be important to studies that rely on paleo-ELA estimates. Moreover, Matthes and Recess Peak ELA gradients along the crest evidently depend strongly on local orographic effects rather than latitudinal climatic trends, indicating that simple linear projections and regional climatic interpretations of ELA gradients of small glaciers may be unreliable.

Clark, D. H.; Clark, M. M.; Gillespie, A. R.

1994-01-01

45

Glacier Webquest  

NSDL National Science Digital Library

A project to learn about ice cores and Antarctica. Use handout lab (Webquest: Glaciers) and follow instructions given for each procedure. Go to Ice Core Changes Go to Glacial Loss Go to Glacial Cover Animation Go to Snow Cover Go to Gulkana Glacier Home Page Go to Glacial Topography Go to Glacial Picture Archive Go to Additional Glacier Pictures ...

Kio, Mr.

2008-11-06

46

Modeled and measured glacier change and related glaciological, hydrological, and meteorological conditions at South Cascade Glacier, Washington, balance and water years 2006 and 2007  

USGS Publications Warehouse

Winter snow accumulation and summer snow and ice ablation were measured at South Cascade Glacier, Washington, to estimate glacier mass balance quantities for balance years 2006 and 2007. Mass balances were computed with assistance from a new model that was based on the works of other glacier researchers. The model, which was developed for mass balance practitioners, coupled selected meteorological and glaciological data to systematically estimate daily mass balance at selected glacier sites. The North Cascade Range in the vicinity of South Cascade Glacier accumulated approximately average to above average winter snow packs during 2006 and 2007. Correspondingly, the balance years 2006 and 2007 maximum winter snow mass balances of South Cascade Glacier, 2.61 and 3.41 meters water equivalent, respectively, were approximately equal to or more positive (larger) than the average of such balances since 1959. The 2006 glacier summer balance, -4.20 meters water equivalent, was among the four most negative since 1959. The 2007 glacier summer balance, -3.63 meters water equivalent, was among the 14 most negative since 1959. The glacier continued to lose mass during 2006 and 2007, as it commonly has since 1953, but the loss was much smaller during 2007 than during 2006. The 2006 glacier net balance, -1.59 meters water equivalent, was 1.02 meters water equivalent more negative (smaller) than the average during 1953-2005. The 2007 glacier net balance, -0.22 meters water equivalent, was 0.37 meters water equivalent less negative (larger) than the average during 1953-2006. The 2006 accumulation area ratio was less than 0.10, owing to isolated patches of accumulated snow that endured the 2006 summer season. The 2006 equilibrium line altitude was higher than the glacier. The 2007 accumulation area ratio and equilibrium line altitude were 0.60 and 1,880 meters, respectively. Accompanying the glacier mass losses were retreat of the terminus and reduction of total glacier area. The terminus retreated at a rate of about 13 meters per year during balance year 2006 and at a rate of about 8 meters per year during balance year 2007. Glacier area near the end of balance years 2006 and 2007 was 1.74 and 1.73 square kilometers, respectively. Runoff from the basin containing the glacier and from an adjacent nonglacierized basin was gaged during all or parts of water years 2006 and 2007. Air temperature, wind speed, precipitation, and incoming solar radiation were measured at selected locations on and near the glacier. Air-temperature over the glacier at a height of 2 meters generally was less than at the same altitude in the air mass away from the glacier. Cooling of the air by the glacier increased systematically with increasing ambient air temperature. Empirically based equations were developed to estimate 2-meter-height air temperature over the glacier at five sites from site altitude and temperature at a non-glacier reference site.

Bidlake, William R.; Josberger, Edward G.; Savoca, Mark E.

2010-01-01

47

Low beta equilibrium and stability for anisotropic pressure closed field line plasma confinement systems.  

National Technical Information Service (NTIS)

General formalism is developed to analyze the equilibrium and stability of low beta anisotropic pressure plasmas confined in closed field line magnetic systems. The formalism allows one to consider rather general magnetic systems with nonuniform axis curv...

V. P. Pastukhov V. I. Ilgisonis A. A. Subbotin

1994-01-01

48

Equilibrium Line Altitudes and paleotemperature reconstructions from Nevado Hualcán (9°S) and Nevado Coropuna (15°S), Tropical Andes (Peru).  

NASA Astrophysics Data System (ADS)

We have reconstructed the Equilibrium Line Altitude (ELA) in seven valleys on the SW slope of Nevado Hualcán (9°S, 77°W; 6122 m asl) and on the SE slope of Nevado Coropuna (15°S, 72°W; 6377masl) using the Area x Altitude Balance Ratio method (Osmaston 2005). We have also deduced the paleotemperatures using the following equation: ?T=ATLR•?ELA; being ?T (°C) the paleotemperature depression; ATLR (°C/m) the Atmospheric Temperature Lapse Rate; and ?ELA (m) the ELA depression. The ATLR for Coropuna was deduced through the use of data loggers. For Hualcán we used the value ATLR =0.0065°C/m, valid for the tropics (Kaser and Osmaston, 2002). We obtained the following results: 1) Hualcán: a) ELAs: 5124m (2003); 5018m (1962); 4994m during the Little Ice Age (LIA); and 4652m during the last studied maximum advance considered to be the Younger Dryas (YD, ~13-11ka) by correlation with nearby mountains (Glasser et al., 2009). b) ?ELAs: 106m (1962); 130m (LIA); and 199m (YD). c) ?T: -0.69°C (1962); -0.85°C (LIA); -3.07°C (YD). 2) Coropuna: a) ELAs: 5862m (2007); 5853m (1986); 5787m (1955); 5776 (LIA); and 4951m in the 13-1136Cl ka phase (Ubeda, 2011). b) ?ELA: 9m (1986); 66m (1955); 86m (LIA); and 911m in 13-1136Cl ka. C) ?T: -0.20°C (1986); -0.71°C (1955); and -7.65°C (13-1136Cl ka). The values ?T during LIA in Hualcán and Coropuna (0.85 and 0.72°C) are consistent with the global warming considered to be 0,74°C between 1906 and 2005 (IPCC, 2007). During the mid XXth century and the LIA, ?T is higher in Hualcán (0.69°C and 0.85°C) than in Coropuna (0.55°C and 0.72°C), with a regional gradient of -0.02°C per degree of latitude (°C/°). However, during the YD (13-1136Cl ka), ?T was higher in Coropuna (7.65°C) than in Hualcán (3.07°C), with a gradient of 0.76°C/°. Although other evidences exist of a pantropical cooling of >5°C during the last glaciation, in Coropuna this cooling was strengthened by the retro-alimentation of its glacial system which in 13-1136Cl ka had a surface of >400 km2 (Ubeda, 2011). Glasser, N.F., Clemmens, S., Schnabel, C., Fenton, C.R. and McHargue, L., 2009. Tropical glacier fluctuations in the Cordillera Blanca, Peru between 12.5 and 7.6 ka from cosmogenic 10Be dating. Quaternary Science Reviews, 28: 3448-3458. IPCC, 2007: Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, Pachauri, R.K and Reisinger, A. (eds.)]. IPCC, Geneva, Switzerland, 104 pp. Kaser, G. and Osmaston, H., 2002. Tropical Glaciers. International Hydrology Series. Cambridge University Press, Cambridge (U.K.), 207 pp. Osmaston, H., 2005. Estimates of glacier equilibrium line altitudes by the Area x Altitude, the Area x Altitude Balance Ratio and the Area x Altitude Balance Index methods and their validation. Quaternary International, 22-31: 138-139. Úbeda, J., 2011. El impacto del cambio climático en los glaciares del complejo volcánico Nevado Coropuna (cordillera occidental de los Andes, Sur del Perú). PhD Thesis. Universidad Complutense de Madrid, (Spain), 558 pp. Available online: http://eprints.ucm.es/12076/ Research funded by CGL2009-7343 project, Government of Spain.

Úbeda, J.; Giráldez, C.; Palacios, D.

2012-04-01

49

Mass balance sensitivity to climate change: A case study of glacier No. 1 at urumqi riverhead, Tianshan Mountains, China  

Microsoft Academic Search

In this paper the degree-day mass balance model is applied to the sensitivity test of mass-balance\\/ELA (equilibrium line altitude)\\u000a to climate change of Glacier No. 1 at Urumqi Riverhead, the Tianshan Mountains, China. The results demonstrate that the mass\\u000a balance of Glacier No. 1, which is of continental type and accumulates in warm seasons, is less sensitive than that of

Liu ShiyinU; Zichu Xie; Ninglian Wang; Baisheng Ye

1999-01-01

50

Little Ice Age climate reconstruction from ensemble reanalysis of Alpine glacier fluctuations  

NASA Astrophysics Data System (ADS)

Mountain glaciers sample a combination of climate fields - temperature, precipitation and radiation - by accumulation and melting of ice. Flow dynamics acts as a transfer function that maps volume changes to a length response of the glacier terminus. Long histories of terminus positions have been assembled for several glaciers in the Alps. Here I analyze terminus position histories from an ensemble of seven glaciers in the Alps with a macroscopic model of glacier dynamics to derive a history of glacier equilibrium line altitude (ELA) for the time span 400-2010 C.E. The resulting climatic reconstruction depends only on records of glacier variations. The reconstructed ELA history is similar to recent reconstructions of Alpine summer temperature and Atlantic Multidecadal Oscillation (AMO) index, but bears little resemblance to reconstructed precipitation variations. Most reconstructed low-ELA periods coincide with large explosive volcano eruptions, hinting at a direct effect of volcanic radiative cooling on mass balance. The glacier advances during the LIA, and the retreat after 1860, can thus be mainly attributed to temperature and volcanic radiative cooling.

Lüthi, M. P.

2014-04-01

51

Water, ice, and meteorological measurements at South Cascade Glacier, Washington, balance year 2002  

USGS Publications Warehouse

Winter snow accumulation and summer snow and ice ablation were measured at South Cascade Glacier, Washington, to estimate glacier mass balance quantities for balance year 2002. The 2002 glacier-average maximum winter snow balance was 4.02 meters, the second largest since 1959. The 2002 glacier summer, net, and annual (water year) balances were -3.47, 0.55, and 0.54 meters, respectively. The area of the glacier near the end of the balance year was 1.92 square kilometers, and the equilibrium-line altitude and the accumulation area ratio were 1,820 meters and 0.84, respectively. During September 20, 2001 to September 13, 2002, the terminus retreated 4 meters, and computed average ice speeds in the ablation area ranged from 7.8 to 20.7 meters per year. Runoff from the subbasin containing the glacier and from an adjacent non-glacierized basin were measured during part of the 2002 water year. Air temperature, precipitation, atmospheric water-vapor pressure, wind speed and incoming solar radiation were measured at selected locations near the glacier.

Bidlake, William r.; Josberger, Edward G.; Savoca, Mark E.

2004-01-01

52

Little Ice Age climate reconstruction from ensemble reanalysis of Alpine glacier fluctuations  

NASA Astrophysics Data System (ADS)

Mountain glaciers sample a combination of climate parameters - temperature, precipitation and radiation - by their rate of volume accumulation and loss. Flow dynamics acts as transfer function which maps volume changes to a length response of the glacier terminus. Long histories of terminus positions have been assembled for several glaciers in the Alps. Here I analyze terminus position histories from an ensemble of seven glaciers in the Alps with a macroscopic model of glacier dynamics to derive a history of glacier equilibrium line altitude (ELA) for the time span 400-2010 C.E. The resulting climatic reconstruction depends only on records of glacier variations. The reconstructed ELA history is similar to recent reconstructions of Alpine summer temperature and Atlantic Meridional Oscillation (AMO) index. Most reconstructed low-ELA periods coincide with large explosive volcano eruptions, hinting to mass balance reduction by volcanic radiative cooling. The glacier advances during the LIA, and the retreat after 1860 are thus explained by temperature and volcanic cooling alone.

Lüthi, M. P.

2013-10-01

53

Secular trend of the equilibrium-line altitude on the western side of the southern Andes, derived from radiosonde and surface observations  

NASA Astrophysics Data System (ADS)

The altitude of the 0°C isotherm obtained from radiosonde data of the aerological Chilean stations Antofagasta, Quintero/Santo Domingo, Puerto Montt and Punta Arenas are analyzed, along with surface temperature and precipitation records from nearby stations. The strong effect of the 1976/77 climate shift due to a change in the Pacific Decadal Oscillation is evident in the temperature and precipitation data. The data are used as input for an empirical model which reconstructs annually the equilibrium-line altitude (ELA) for the last 49 years on the western side of the southern Andes. The model takes air temperature, precipitation and altitude as the main parameters, and was first developed by Fox (1993) and applied by Condom and others (2007). From the radiosonde data, a significant positive trend of the 0°C isotherm has occurred in the northern, central and southern regions, indicating an ELA rise due to regional warming. General glacier retreat, ice thinning and negative mass balance observed during the past few decades in virtually all the Chilean Andes concur with the observed ELA reconstruction. In the Punta Arenas radiosonde record there is slight evidence for precipitation increase but no evidence for significant warming in the past few decades. This results in a slight lowering of the ELA according to the model reconstruction, which does not agree with the strong and increased glacier retreat observed in recent decades in Patagonia.

Carrasco, Jorge F.; Osorio, Roberto; Casassa, Gino

54

Water, Ice, and Meteorological Measurements at South Cascade Glacier, Washington, Balance Years 2004 and 2005  

USGS Publications Warehouse

Winter snow accumulation and summer snow and ice ablation were measured at South Cascade Glacier, Washington, to estimate glacier mass-balance quantities for balance years 2004 and 2005. The North Cascade Range in the vicinity of South Cascade Glacier accumulated smaller than normal winter snowpacks during water years 2004 and 2005. Correspondingly, the balance years 2004 and 2005 maximum winter snow balances of South Cascade Glacier, 2.08 and 1.97 meters water equivalent, respectively, were smaller than the average of such balances since 1959. The 2004 glacier summer balance (-3.73 meters water equivalent) was the eleventh most negative during 1959 to 2005 and the 2005 glacier summer balance (-4.42 meters water equivalent) was the third most negative. The relatively small winter snow balances and unusually negative summer balances of 2004 and 2005 led to an overall loss of glacier mass. The 2004 and 2005 glacier net balances, -1.65 and -2.45 meters water equivalent, respectively, were the seventh and second most negative during 1953 to 2005. For both balance years, the accumulation area ratio was less than 0.05 and the equilibrium line altitude was higher than the glacier. The unusually negative 2004 and 2005 glacier net balances, combined with a negative balance previously reported for 2003, resulted in a cumulative 3-year net balance of -6.20 meters water equivalent. No equal or greater 3-year mass loss has occurred previously during the more than 4 decades of U.S. Geological Survey mass-balance measurements at South Cascade Glacier. Accompanying the glacier mass losses were retreat of the terminus and reduction of total glacier area. The terminus retreated at a rate of about 17 meters per year during balance year 2004 and 15 meters per year during balance year 2005. Glacier area near the end of balance years 2004 and 2005 was 1.82 and 1.75 square kilometers, respectively. Runoff from the basin containing the glacier and from an adjacent nonglacierized basin was gaged during all or parts of water years 2004 and 2005. Air temperature, wind speed, precipitation, and incoming solar radiation were measured at selected locations on and near the glacier.

Bidlake, William R.; Josberger, Edward G.; Savoca, Mark E.

2007-01-01

55

Surface elevation changes on glaciers in 1974-2010 in the Mt. Naimona'Nyi region in the Himalayas  

NASA Astrophysics Data System (ADS)

Glaciers, especially those in mountain regions, are considered as one of the sensitive indicators of climate change nowadays. Glacier mass changes on the Tibetan Plateau significantly affect water resources and eco-systems in Asia. In this paper, surface elevation changes on glaciers were studied by DEMs and in-situ measurements. A DEM in Naimona'Nyi region was generated by Takeo Tanado at JAXA using stereo pairs from ALOS/PRISM in 2006, which was evaluated and calibrated by in-situ differential GPS points measured in 2012 and ICESat/GLAS points in non-glacier area. The 1:50,000 topographic maps and the base 1:50,000 DEM in 1974 was projected into WGS84 UTM 44N and then co-registered to PRISM DEM. The elevation change on glacier surface was calculated by PRISM DEM and 1974 DEM. The results suggested that the surface elevation was decreased rapidly on most glaciers, with an average downwasting rate of 0.7×0.2m per year. The in-situ measurement of glacier surface elevation indicated a decrease of ~1.4m (~0.7m per year) from 2008 to 2010 by Ground Penetrating Radar (GPR)differential GPS. It also showed that glacier ice on south slope downwasting faster than those on north slope. According to glacier surface elevation changes at different altitudes, the Equilibrium Line Altitude (ELA) might reach about 6300m a.s.l.

Zong, J.; YE, Q.; Tian, L.; Gou, P.

2013-12-01

56

Lagrangian Simulations of Current Sheet Formation During Relaxation of an Unstable Line-Tied Equilibrium  

NASA Astrophysics Data System (ADS)

Our recent theory, based on reduced MHD equations, predicts the formation of current sheets (tangential discontinuities) in an ideal line-tied plasma when an unstable equilibrium relaxes to a state of minimum energy [C. S. Ng and A. Bhattacharjee, Phys. Plasmas 5, 4028 (1998)]. This mechanism has important implications for the heating of the solar corona, first envisioned by E. N. Parker. Testing of this prediction using conventional Eulerian simulations is subjected to the intrinsic numerical difficulty that the magnetic field line mapping is not kept fixed explicitly, as required by the line-tied condition. In fact, field line mapping can change substantially by reconnection due to numerical resistivity. To overcome this obstacle, we have developed a Lagrangian relaxation algorithm to simulate the evolution of an unstable equilibrium by following the movement of magnetic field lines explicitly. Preliminary simulation results will be presented.

Lin, Liwei; Ng, C. S.; Bhattacharjee, A.

2007-11-01

57

Fastest Glacier  

NSDL National Science Digital Library

This video from a 2005 NOVA program features scientists who study how the Jakobshavn Isbrae glacier in western Greenland is shrinking and moving faster due to increased melting over the past ten years. The video includes footage of scientists in the field explaining methods and animation of ice sheet dynamics leading to faster glacier movement.

Sciencenow, Nova

58

Glacier fluctuation using Satellite Data in Beas basin, 1972-2006, Himachal Pradesh, India  

NASA Astrophysics Data System (ADS)

Glaciers are widely recognized as sensitive indicators for regional climate change. Very few studies have been conducted to investigate the long term deglaciation status in the Himalaya. In the present study, glaciers in the Beas basin, Himachal Pradesh, India were mapped by interpretation of various glacio-morphological features using the Landsat and IRS images. The mapping of 224 glaciers during the period 1972-2006 reveals that the glacier cover reduced from 419 to 371 km2, witnessing approximately 11.6% deglaciation in the Beas basin. A higher rate of retreat of the glaciers was observed during 1989-2006 as compared to the retreat during 1972-1989. Also, the loss has been more prominent in the glaciers with an areal extent of 2-5 km2. The number of glaciers increased from 224 to 236 due to fragmentation in this period. The average elevation of the ablation zone basin showed an upward shift from 3898 m (1972) to 4171 m (2006) which may be a consequence of a shift in Equilibrium Line Altitude (ELA) reflecting imbalance.

Dutta, Shruti; Ramanathan, A. L.; Linda, Anurag

2012-10-01

59

Loch Lomond Stadial glaciers in North Harris, Outer Hebrides, North-West Scotland: glacier reconstruction and palaeoclimatic implications  

NASA Astrophysics Data System (ADS)

Geomorphological mapping of North Harris provides evidence for the former existence of 10 glaciers with a total area of ca 35 km 2. A Loch Lomond (Younger Dryas) Stadial age (ca 12.9-11.5 kyr BP) for this glacial episode is inferred from glacier configuration, landsystems dominated by hummocky recessional moraines, and relationships with Lateglacial periglacial phenomena. Equilibrium line altitudes (ELAs) of 150-289 m were calculated for individual glaciers. ELA variability mainly reflects differences in snow-contributing area. The area-weighted mean ELA (204 m) is consistent with a northwards decline in ELAs along the western seaboard of the British Isles of 69.5 m (100 km) -1, equivalent to a northwards ablation-season temperature decrease of 0.42 °C (100 km) -1. This latitudinal temperature gradient implies a mean July sea-level temperature of ca 7.2 °C for the coldest part of the stade, roughly 6 °C lower than at present. Sea-level precipitation at the time of the LLS glacial maximum is inferred to have been between ca 1970±200 and 2350±200 mm yr -1, implying that LLS precipitation was up to 25% greater than now. Patterns of recessional moraines indicate that the glaciers remained close to climatic equilibrium as they retreated to their sources, though moraine belts implying near-stationary or readvancing ice margins on flat valley floors are separated by moraine-free zones indicating uninterrupted retreat. Calculation of ELAs for 'residual' glaciers in former source areas suggests that summer warming of ?1.0 °C would have resulted in shrinkage of the glaciers to their sources.

Ballantyne, Colin K.

2007-12-01

60

Comparison of Late Pleistocene and Modern Glacier Extents in Central Nepal Based on Digital Elevation Data and Satellite Imagery  

Microsoft Academic Search

Late Pleistocene and modern ice extents in central Nepal are compared to estimate equilibrium line altitude (ELA) depressions. New techniques are used for determining the former extent of glaciers based on quantitative, objective geomorphic analyses of a ?90-m resolution digital elevation model (DEM). For every link of the drainage network, valley form is classified as glacial or fluvial based on

Christopher C. Duncan; Andrew J. Klein; Jeffrey G. Masek; Bryan L. Isacks

1998-01-01

61

Shrinkage of selected southcentral Alaskan glaciers AD 1900-2010 - a spatio-temporal analysis using photogrammetric, GIS-based and historical techniques  

NASA Astrophysics Data System (ADS)

The knowledge about the recent glacier change in the Chugach Mountains of southcentral Alaska is still scarce. In an effort to fill this gap we took an interdisciplinary approach and reconstructed the history of ten selected glaciers in the vicinity of Valdez (e.g., Valdez Glacier) and Cordova (e.g., Sheridan, Childs and Allen Glacier): Historical data such as early maps and photographs allowed for refining the glacier outlines of the early 20th century. Based upon photogrammetric methods, we further derived elevation models and orthomosaics from various airborne images. The Alaska High Altitude Program (AHAP) imagery, taken during the late 1970s, were the primary data of interest and provided a valuable source of information, primarily because they had not been quantitatively evaluated before. Together with the first USGS maps from the1950s and most recent data (airborne LiDAR; as well as air- and space-borne optical data), they allowed for determining the volume and area changes that have occurred within the last 60 years. A GIS analysis revealed that the recent decades have been characterized by rising equilibrium lines and thus retreating and thinning glaciers. The glaciers did not show a consistent recession pattern, which might partly be attributed to the varying area-altitude distributions. Simple hypsographic modeling indicated that the glaciers generally are far away from a state of equilibrium. Given the current climate scenarios and the unfavorable hypsography of most glaciers, the hitherto prevailing trend of glacier melt and recession is likely to continue or accelerate in the upcoming years. Reliably predicting the extents and characteristics of these glaciers at the end of the century remains an important yet poorly answered research question.

Kienholz, Christian; Prakash, Anupma; Nussbaumer, Samuel; Zumbühl, Heinz

2010-05-01

62

Melting Glaciers  

NSDL National Science Digital Library

Due to the potential disastrous consequences to the environment and to numerous societies, scientists, governments, and civilians are concerned with the growing trend of glacial melt. This topic-in-depth explores various geographic regions where this phenomenon has recently been observed. Providing background into the study of glaciology, this report begins with a Web site (1) discussing the unique features of glaciers. The US Army Corps of Engineers offers visitors an insight to glacial properties including their locations, movements, and influences; along with a series educational images. The second site (2) explains the exceptionality of the two hundred sixty six glaciers at Glacier National Park. Through a collection of images, animations, and pictures provided by the National Park Service, users can learn about ice dams, climatic impacts, and the erosive powers of ice and water. The rest of the topic-in-depth discusses findings of glacial melting from around the world. NASA (3) addresses the Artic warming's affects on glacier formations. This Web site provides a few animations displaying ice sheet extent and the cracking of icebergs. On a positive note, visitors can learn how the decrease in glaciers has opened up new habitat for some Artic species. The next Web site (4), also by NASA, discusses the findings of a twenty-five year study of Patagonia's glaciers. Educators and students can discover how NASA utilized the Space Shuttle Endeavor to study the entire 17,200 square kilometer region. The site also discusses potential causes of the melting in this region, which has contributed to almost ten percent of the global sea-level change from mountain glaciers. As reported by the BBC (5), Dr. Harrison at the University of Oxford has determined that the glaciers in parts of Kazakhstan have been decreasing annually by almost two cubic kilometers between 1955 and 2000. Visitors can learn how the melting of these four hundred sixteen glaciers will adversely affect the region's rivers and its water supply. The Taipei Times (6) reports that the Swiss Alpine glacial melting has probably intensified due to this summer's record-breaking heat wave. This Web site provides short, intriguing descriptions of consequences of the "rush of melt water streaming from the ice wall." Users can learn about predictions in the 1990s that the glaciers would shrink to ten percent of their 1850 size by the end of the twenty first century. In the next Web site (7), the BBC provides a captivating illustration of the effects the Peruvian glacial melts may have on tourism, the country's water supply, and more. Students and educators can learn about NASA studies showing cracks in the ice, which could lead to the flooding of large cities. Visitors can also find out how the recent glacier recessions have affected some ancient spiritual traditions. The last site, by the USGS, (8) features excerpts from Myrna Hall and Daniel Fagre's 2003 research paper in BioScience. Visitors can discover the melt rate and spatial distributions of glaciers for two possible future climate situations. Providing an amazing animation, users will be amazed by the changes predicted by the model.

Enright, Rachel

63

Energy balance estimates during the summer season of glaciers of the Antarctic Peninsula  

NASA Astrophysics Data System (ADS)

Two small glaciers in Marguerite Bay on the west coast of the Antarctic Peninsula were chosen to monitor the accumulation and ablation pattern of the snow cover and the reaction of the glacial system in respect with global change. Both glaciers are located at 68°08'S and 67°06'W in the vicinity of the Argentine research base 'San Martín'. McClary Glacier is a short valley glacier with an accumulation area not extending higher than 600 m asl. Its short snout joins the snout of Northeast Glacier to form an ice-cliff to the sea. Northeast Glacier is separated from McClary Glacier by a mountain ridge and is fed by a large ice-fall coming down from the plateau of the Antarctic Peninsula at 1500 m asl. As the topography of the glaciers in terms of accumulation area, length and surface elevation differs widely it is assumed that the glaciers react differently to climate variations. However the response time of these systems is believed to be of the same order of magnitude as the anticipated climatic variability. Therefore measures were taken to monitor the seasonal development of the snow cover on the lower parts of the glaciers in order to detect changes at an early stage. During the field campaign in the Austral summer 1994/1995 micro-meteorological measurements were carried out with automatic weather stations (AWS) at three locations on the glaciers. More than 40 snow pits were dug during the summer season to obtain data from the snow cover. Data was sampled on snow temperature variations, water equivalent, liquid water content, stratification of the snow cover, crystal types and crystal sizes. Furthermore the accumulation during the whole year from March 1994 to February 1995 was measured with stakes placed on the glaciers. The data from the AWS was used to compute energy available for ablation. This correlated well ( r=0.9) with the changes observed in the snow pits. Turbulent heat fluxes account for 55% of the summer-time energy budget at the surface of the snow cover. Sensible heat is the dominant energy source for ablation during the summer. The equilibrium line was estimated between sea-level and 110 m asl. It is assumed that further warming will cause the development of an ablation zone on the two glaciers.

Schneider, Christoph

1999-10-01

64

The influence of future glacier extents on hydrological flow regimes in the Ötztal Alps  

NASA Astrophysics Data System (ADS)

The ongoing retreat of glaciers since 1850 and especially within the last 20 years already impacts the natural environment. Rising temperatures as projected by the IPCC Fifth Assessment Report (AR5) will affect future glacier extents with the inherent consequences e.g. on runoff. This contribution presents a relative simple approach to analyze mostly temperature but also precipitation driven potential changes on the extent of glacierized areas and the resulting impact on runoff within the catchment of the Ötztaler Ache (Ötztal, Austria) until 2050. Changes of mean summer temperatures are derived from simulation results realized with three different regional climate models (ALADIN, REMO and REGCM3). The realizations are driven with the SRES A1B emission scenario of the Fourth Assessment Report (AR4). Potential future glacier extents are calculated according to the approach of Paul et al. (2007). Thereby, the steady-state equilibrium line of altitude (ELA) is calculated and then shifted depending on temperature change. Future glacier extents are calculated under consideration of the 2:1 steady state accumulation area ratio (AARo) based on the Austrian Glacier Inventory 2006 and a digital elevation model (DEM). Impacts of potential future glacier extents but also of changes in temperature and precipitation are analyzed with the semi-distributed hydrological model HQsim. According to Paul et al. (2007), the ELA in the Swiss Alps rises with approx. 140 m per degree Celsius warming. The evaluation of the available regional climate change realizations for the study area shows a potential increase of the mean summer temperature of approx. 2.7 °C by 2050. Based on the considered approach ELA will increase by 370 m. The retreat of glacierized areas will be calculated incrementally by a temperature increase with 0.5 °C steps. The glacierized area (Austrian Glacier Inventory 2006) of glaciers > 500,000 m² in 2006 will be reduced by 82 % from 68 km² to 3.8 km² in 2050. Glaciers with an area smaller than 500,000 m² are not considered. Potential future runoffs based on changes in the cryosphere but also in temperature and precipitation indicates a change in future flow regimes. As the study area is of high priority for the further expansion of hydropower generation in the Alps such or more sophisticated studies are of strategic relevance. The introduced approach only considers the shift of the ELA with a constant 2:1 accumulation-ablation ratio. Further factors like volume, lateral melting, glacier-specific response times or a change of the AARo are neglected.

Zimmermann, Moritz; Huttenlau, Matthias; Schneider, Katrin; Stötter, Johann

2014-05-01

65

Seasonal and annual mass balances of Mera and Pokalde glaciers (Nepal Himalaya) since 2007  

NASA Astrophysics Data System (ADS)

In the Everest region, Nepal, ground-based monitoring programmes were started on the debris-free Mera Glacier (27.7° N, 86.9° E; 5.1 km2, 6420 to 4940 m a.s.l.) in 2007 and on the small Pokalde Glacier (27.9° N, 86.8° E; 0.1 km2, 5690 to 5430 m a.s.l., ~ 25 km north of Mera Glacier) in 2009. These glaciers lie on the southern flank of the central Himalaya under the direct influence of the Indian monsoon and receive more than 80% of their annual precipitation in summer (June to September). Despite a large inter-annual variability with glacier-wide mass balances ranging from -0.67 ± 0.28 m w.e. in 2011-2012 (Equilibrium-line altitude (ELA) at ~ 5800 m a.s.l.) to +0.46 ± 0.28 m w.e. in 2010-2011 (ELA at ~ 5340 m a.s.l.), Mera Glacier has been shrinking at a moderate mass balance rate of -0.08 ± 0.28 m w.e. yr-1 since 2007. Ice fluxes measured at two distinct transverse cross sections at ~ 5350 m a.s.l. and ~ 5520 m a.s.l. confirm that the mean state of this glacier over the last one or two decades corresponds to a limited mass loss, in agreement with remotely-sensed region-wide mass balances of the Everest area. Seasonal mass balance measurements show that ablation and accumulation are concomitant in summer which in turn is the key season controlling the annual glacier-wide mass balance. Unexpectedly, ablation occurs at all elevations in winter due to wind erosion and sublimation, with remobilised snow potentially being sublimated in the atmosphere. Between 2009 and 2012, the small Pokalde Glacier lost mass more rapidly than Mera Glacier with respective mean glacier-wide mass balances of -0.72 and -0.23 ± 0.28 m w.e. yr-1. Low-elevation glaciers, such as Pokalde Glacier, have been usually preferred for in-situ observations in Nepal and more generally in the Himalayas, which may explain why compilations of ground-based mass balances are biased toward negative values compared with the regional mean under the present-day climate.

Wagnon, P.; Vincent, C.; Arnaud, Y.; Berthier, E.; Vuillermoz, E.; Gruber, S.; Ménégoz, M.; Gilbert, A.; Dumont, M.; Shea, J. M.; Stumm, D.; Pokhrel, B. K.

2013-11-01

66

Seasonal and annual mass balances of Mera and Pokalde glaciers (Nepal Himalaya) since 2007  

NASA Astrophysics Data System (ADS)

In the Everest region, Nepal, ground-based monitoring programs were started on the debris-free Mera Glacier (27.7° N, 86.9° E; 5.1 km2, 6420 to 4940 m a.s.l.) in 2007 and on the small Pokalde Glacier (27.9° N, 86.8° E; 0.1 km2, 5690 to 5430 m a.s.l., ˜ 25 km North of Mera Glacier) in 2009. These glaciers lie on the southern flank of the central Himalaya under the direct influence of the Indian monsoon and receive more than 80% of their annual precipitation in summer (June to September). Despite a large inter-annual variability with glacier-wide mass balances ranging from -0.77± 0.40 m w.e. in 2011-2012 (Equilibrium-line altitude (ELA) at ˜ 6055 m a.s.l.) to + 0.46 ± 0.40 m w.e. in 2010-2011 (ELA at ˜ 5340 m a.s.l.), Mera Glacier has been shrinking at a moderate mass balance rate of -0.10± 0.40 m w.e. yr-1 since 2007. Ice fluxes measured at two distinct transverse cross sections at ˜ 5350 m a.s.l. and ˜ 5520 m a.s.l. confirm that the mean state of this glacier over the last one or two decades corresponds to a limited mass loss, in agreement with remotely-sensed region-wide mass balances of the Everest area. Seasonal mass balance measurements show that ablation and accumulation are concomitant in summer which in turn is the key season controlling the annual glacier-wide mass balance. Unexpectedly, ablation occurs at all elevations in winter due to wind erosion and sublimation, with remobilized snow likely being sublimated in the atmosphere. Between 2009 and 2012, the small Pokalde Glacier lost mass more rapidly than Mera Glacier with respective mean glacier-wide mass balances of -0.72 and -0.26 ± 0.40 m w.e. yr-1. Low-elevation glaciers, such as Pokalde Glacier, have been usually preferred for in-situ observations in Nepal and more generally in the Himalayas, which may explain why compilations of ground-based mass balances are biased toward negative values compared with the regional mean under the present-day climate.

Wagnon, P.; Vincent, C.; Arnaud, Y.; Berthier, E.; Vuillermoz, E.; Gruber, S.; Ménégoz, M.; Gilbert, A.; Dumont, M.; Shea, J. M.; Stumm, D.; Pokhrel, B. K.

2013-07-01

67

Past and future evolution of Himalayan glaciers: a regional climate model study  

NASA Astrophysics Data System (ADS)

Over 800 million people depend on glacier melt water runoff throughout the Hindu-Kush and Himalaya (HKH) region. The region, also called as "Water tower of Asia", is the location of several major rivers basins, like Ganges, Brahmaputra, and Indus etc. Glaciers in the HKH region are the primary source of water for the perennial rivers. Previous studies have assessed glacier areas and volumes in the HKH region by remote sensing techniques and slope-dependent thickness estimations. We here present a study in which, for the first time a glacier parameterization scheme is dynamically coupled to a regional climate model and applied over the South Asian Himalayan mountain range. The glacier scheme interactively simulates the mass balance as well as changes of the areal extent of glaciers on a sub-grid scale. Various observational data sets, in particular a regional glacier inventory, have been compiled and were used to initialize glacier area and volume in the year 1989. A simulation for the period 1989-2008 using the ECMWF ERA-Interim reanalysis as atmospheric boundary forcing was carried out. Preliminary results show a simulated decrease of glacier area of about 20% between 1989 and 2008. The spatial patterns of glacier area change show a remarkable decrease, but do show some regions of increase especially over the Karakoram (western Himalaya), a region for which available observations-based estimates also indicate a positive mass balance anomaly. The positive relation between altitude and mass balance is qualitatively reproduced by the model. The model is able to approximately represent the equilibrium line altitude (ELA) for selected sub-region when compared to observed values but simulated ELA's seem to have a systematic negative bias which, in turn, suggests an overestimation of the mean regional mass balance. Our results indicate that observed glacier changes can be approximately reproduced within a regional climate model based on simplified concepts of glacier-climate interaction. This, in turn, underlines the general applicability of the model system for scenarios of 21st century climate and glacier change. Presently, two climate change simulations forced with two GCMs are under preparation and the results will be presented.

Kumar, Pankaj; Kotlarski, Sven; Moseley, Christopher; Sieck, Kevin; Frey, Holger; Stoffel, Markus; Jacob, Daniela

2013-04-01

68

Climate change impacts on glaciers and runoff in Tien Shan (Central Asia)  

NASA Astrophysics Data System (ADS)

Climate-driven changes in glacier-fed streamflow regimes have direct implications on freshwater supply, irrigation and hydropower potential. Reliable information about current and future glaciation and runoff is crucial for water allocation and, hence, for social and ecological stability. Although the impacts of climate change on glaciation and runoff have been addressed in previous work undertaken in the Tien Shan (known as the 'water tower of Central Asia'), a coherent, regional perspective of these findings has not been presented until now. In our study, we explore the range of changes in glaciation in different climatic regions of the Tien Shan based on existing data. We show that the majority of Tien Shan glaciers experienced accelerated glacier wasting since the mid-1970s and that glacier shrinkage is most pronounced in peripheral, lower-elevation ranges near the densely populated forelands, where summers are dry and where snow and glacial meltwater is essential for water availability. The annual glacier area shrinkage rates since the middle of the twentieth century are 0.38-0.76% per year in the outer ranges, 0.15-0.40% per year in the inner ranges and 0.05-0.31% per year in the eastern ranges. This regionally non-uniform response to climate change implies that glacier shrinkage is less severe in the continental inner ranges than in the more humid outer ranges. Glaciers in the inner ranges react with larger time lags to climate change, because accumulation and thus mass turnover of the mainly cold glaciers are relatively small. Moreover, shrinkage is especially pronounced on small or fragmented glaciers, which are widely represented in the outer regions. The relative insensitivity of glaciers in the inner ranges is further accentuated by the higher average altitude, as the equilibrium line altitude ranges from 3'500 to 3'600 masl in the outer ranges to 4'400 masl in the inner ranges. For our study, we used glacier change assessments based both on direct data (mass balance measurements) and on indirect data (aerial and satellite imagery, topographic maps). Latter can be plagued with high uncertainties and considerable errors. For instance, glaciated area has been partly overestimated in the Soviet Glacier catalogue (published in 1973, with data from the 1940s and 1950s), probably as a result of misinterpreted seasonal snowcover on aerial photographs. Studies using the Soviet Glacier catalogue as a reference are thus prone to over-emphasize glacier shrinkage. A valuable alternative is the use of continued in situ mass balance and ice thickness measurements, but they are currently conducted for only a few glaciers in the Tien Shan mountains. Efforts should therefore be encouraged to ensure the continuation and re-establishment of mass balance measurements on reference glaciers, as is currently the case at Karabatkak, Abramov and Golubin glaciers. Only on the basis of sound data, past glacier changes can be assessed with high precision and future glacier shrinkage can be estimated according to different climate scenarios. Moreover, the impact of snowcover changes, black carbon and debris cover on glacier degradation needs to be studied in more detail. Only with such model approaches, reflecting transient changes in climate, snowcover, glaciation and runoff, can appropriate adaptation and mitigation strategies be developed within a realistic time horizon.

Sorg, A. F.; Bolch, T.; Stoffel, M.; Solomina, O.; Beniston, M.

2012-12-01

69

The status of glaciers in Sikkim Himalaya  

NASA Astrophysics Data System (ADS)

This study focuses on the influence of lakes and debris cover on the glacier area changes, in the data scarce Sikkim Himalayas, between 1990 and 2010, using Landsat TM and IRS images. A new technique of estimating 'interpretation uncertainty' while mapping glacier terminus on satellite images, is introduced. The overall study showed (i) a glacier area loss of 3 × 0.8 % in 20 years. We also observed the presence of lakes on many debris-covered glaciers, and its expansion accelerated the glacier retreat by 9 ×1.4 %. Though some 'debris-covered glaciers' showed stable fronts, the gradual development and coalescence of supraglacial lakes led to the formation of moraine dam lakes at the terminus. This investigation suggests that 'debris cover' on glaciers can enhance the development of glacial lakes. As a consequence, the retreat of debris-covered glaciers associated with lakes is clearly higher than that of debris-free glaciers. Location of glacier in Sikkim. The map shows the location of glaciers studied in this investigation. : Evolution and coalescence of a supra glacial lake and the formation of a moraine dam. Figs. a and b show no frontal change between 1990 and 1997. Fig. b shows the evolution of a supraglacial lake and fig. c shows the coalescence of supraglacial lake, which occupies glacier area between two lateral moraines. Fig. d shows the formation of a moraine dam lake leading to glacierarea loss.(The yellow line represents the glacier boundary for the year 1990; and red line is the glacier terminus for the year 2009). The four imagesused is a false colour composite with a band combination of red, NIR and SWIR.

basnett, S.; Kulkarni, A. V.; Bolch, T.

2013-12-01

70

Glacier microseismicity  

USGS Publications Warehouse

We present a framework for interpreting small glacier seismic events based on data collected near the center of Bering Glacier, Alaska, in spring 2007. We find extremely high microseismicity rates (as many as tens of events per minute) occurring largely within a few kilometers of the receivers. A high-frequency class of seismicity is distinguished by dominant frequencies of 20–35 Hz and impulsive arrivals. A low-frequency class has dominant frequencies of 6–15 Hz, emergent onsets, and longer, more monotonic codas. A bimodal distribution of 160,000 seismic events over two months demonstrates that the classes represent two distinct populations. This is further supported by the presence of hybrid waveforms that contain elements of both event types. The high-low-hybrid paradigm is well established in volcano seismology and is demonstrated by a comparison to earthquakes from Augustine Volcano. We build on these parallels to suggest that fluid-induced resonance is likely responsible for the low-frequency glacier events and that the hybrid glacier events may be caused by the rush of water into newly opening pathways.

West, Michael E.; Larsen, Christopher F.; Truffer, Martin; O'Neel, Shad; LeBlanc, Laura

2010-01-01

71

Recent changes in freezing level heights in High Asia and their impact on glacier changes  

NASA Astrophysics Data System (ADS)

heights of the atmospheric freezing level have increased over most glacierized areas of High Asia during 1971-2010, especially in the Altai Mountains, the eastern Tianshan Mountains, and the northeastern margins of the Tibetan Plateau. The systematic increase of freezing level heights (FLHs) is evidenced from both radiosonde and National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis data. Eleven glaciers with long-term observations are selected in typical high-elevation mountain ranges to examine the relationship between changes in FLHs and cryospheric response. Long-term trends in glacier mass balance and equilibrium line altitude (ELA) show significant correlations with changes in FLHs. A rise of 10 m in summer FLH causes mass balance of reference glaciers in High Asia to decrease by between 7 and 38 mm (water equivalent) and ELA to increase by between 3.1 and 9.8 m, respectively, depending on location. Both relationships are statistically significant (p < 0.01) for most reference glaciers. Thus, rapid deglaciation in these high mountain ranges during recent decades is related to the increase in FLH. Similar relationships may exist in other high-elevation glaciers of High Asia with changes in FLHs having significant ecological and social consequences, especially in arid and semiarid regions.

Wang, Shengjie; Zhang, Mingjun; Pepin, N. C.; Li, Zhongqin; Sun, Meiping; Huang, Xiaoyan; Wang, Qiong

2014-02-01

72

Photographic Snow-cover Monitoring on St Sorlin Glacier, France.  

NASA Astrophysics Data System (ADS)

Like most other glaciers in the Alps, the St Sorlin glacier (french Alps, 45.16°N, 6.16°E, 2900 m asl mean elevation and 3km2 of surface area) has been retreating fast in the last 20 years. To understand the meteorological factors responsible for this retreat, and to tentatively predict glaciers evolution in a changing (warming) climate, we use a distributed snow/ice mass and energy balance model derived from the CROCUS snow model (Météo-France). There is no direct meteorological observation on or near St Sorlin glacier yet, and hourly meteorology to force the snow/ice model is obtained from disaggregated meteorological analyses. The model is found to reproduce the St Sorlin mass balance of the last 20 years as obtained from field glaciological measurements and stereophotographic reconstructions. The model is also found to reproduce the interannual variations of the equilibrium line as determined from optical satellite imagery. Because of the albedo feedback involved, it is also important to verify that the summer snow/ice transition on the glacier is correctly simulated. Thus, an automated photographic system was set up facing St Sorlin glacier to monitor the evolution of the snow cover. The system was installed on the 13th of July 2004 and is still in operation at time of abstract writing. Digital photographies are taken every 4 hours, permitting so far at least one non-obstructed (rain, fog) picture per day. The first pictures in the series show an almost fully snow-covered glacier while the latest ones show bare ice up to the highest parts of the glacier. Snow is occasionally deposited during precipitation events but hardly last more than 3 days. Snow line position is deduced from pictures using a DEM with georeferenced points visible on pictures. It should then be compared with the modelled one. The automated photographic system provides not only snow cover to check snow/ice model results at seasonal time-scales, but also qualitative meteorological information (precipitation, cloud cover, fog) that may also help verify some aspects of the disaggregated meteorology in input of the model.

Gerbaux, M.; Genthon, C.; Dedieu, J.; Balestrieri, J.

2004-12-01

73

Do Glacier Dams Retard River Incision Into Southeast Tibet?  

NASA Astrophysics Data System (ADS)

The southeastern fringe of the Tibetan plateau around the Namche Barwa syntaxis is characterized by rapid uplift and fluvial incision, having created spectacular relief along the Yarlung Tsangpo river gorge. This region hosts numerous monsoonal temperate glaciers, some of which have been historically dynamic, and many of which have advanced from steep tributaries to repeatedly block or divert trunk rivers during the Quaternary. We propose that repeated glacial damming has resulted in knickpoint formation, as well as valley-floor aggradation and increases in active channel widths that serve to retard fluvial bedrock incision into the flanks of the Tibetan Plateau. The coupled reduction of fluvial incision upstream of glacier dams and enhanced incision downstream of the lowermost dams would act to maintain an edge to the Tibetan Plateau by defeating propagation of knickpoints into the Plateau in a region of high uplift and precipitation. The positions of several large moraine dams in an area where local relief and erosion are highest require depressions of the regional equilibrium line altitude (ELA) of ~ 450 m, which is within the range of ELA depression for Holocene glacial advances. Such an ELA depression would on average impound ~ 40% of the river network of major rivers upstream of glacier dams; estimated, though debated, Last Glacial Maximum ELA depression of 1000 m would result in damming of about 75% of these river networks. Whether driven by increased monsoon precipitation, temperature fluctuations, or changes to supraglacial sediment flux, Quaternary glacier advances indirectly contribute to effectively retarding river incision into southeast Tibet.

Korup, O.; Montgomery, D. R.

2007-12-01

74

Continuous Measurements of Ice Motion and Associated Seismicity at Bering Glacier, Alaska.  

NASA Astrophysics Data System (ADS)

In April 2007, we established an array of GPS and seismic stations on the Bering Glacier, Alaska, to investigate the relationship between glacier motion and glacier-generated seismicity. Bering Glacier is North America's largest mountain glacier and has an area of more than 5000 km2. Dual-frequency GPS data were recorded continuously at 15 second intervals at five stations on the glacier from April to September. Four of the GPS glacier stations were established in a strain diamond located roughly halfway between the equilibrium line and the terminus, at a distance of 40 km from a GPS base station located near the terminus. These four GPS glacier stations were co-located with seismometers, which, together with a fifth seismometer located at center of the strain diamond, form a cross pattern seismic array with a 4-km aperture. The fifth GPS station is located 20 km up glacier from the strain diamond and seismic array, at a point where the upper icefield feeds into a narrow gate to the lower glacier. GPS antennas were fixed to tripods constructed of steel poles drilled 5-7 m deep into the surface of the glacier. This provides a stable reference relative to the glacier surface, which is subject to several meters of annual ablation at the elevation of the strain diamond. The GPS data have been processed using the GAMIT kinematic utility Track. The motion recorded at all sites is rapid (3+ m/day) but smooth and steady down to the temporal resolution of the data. Specifically, we find no evidence for sudden motion events in the timeseries, but rather find only small perturbations superimposed on slowly varying velocities. The seismic records from short period (L-22) and broadband (6TD) instruments reveal frequent icequakes including both emergent low frequency events and impulsive high frequency events. Many of the events recorded show strong time domain correlations across the array. We will construct a timeseries of seismicty using an automatic icequake detector, allowing comparison of the GPS and seismic timeseries. The effect of alternative processing methods for the GPS data, such as GYPSY precise point positioning analysis, will also be explored.

Larsen, C. F.; Truffer, M.; Leblanc, L.; O'Neel, S.; West, M.; None, N.

2007-12-01

75

Alpine Glaciers  

NASA Technical Reports Server (NTRS)

[figure removed for brevity, see original site]

Released 27 August 2003

This image shows part of the western flank of Arsia Mons, the southernmost of the three great Tharsis Montes. The surface shows parallel ridges more reminiscent of a Zen garden than any typical geological feature. These ridges are not typical of lava flow fronts, so a different explanation has been proposed by Mars scientists. These ridges may instead be ancient signs of previously existing glaciers that formed high on the volcano's flank. As glaciers retreat with the seasons and shifting climate, they leave behind a mound of debris along their receding edge. Successive retreats can produce a series of parallel ridges similar to those seen here.

Image information: VIS instrument. Latitude -6.9, Longitude 230.5 East (129.5 West). 19 meter/pixel resolution.

2003-01-01

76

Catchment-scale reconstruction of glacier mass balance using observations and global climate data: Case study of the Hailuogou catchment, south-eastern Tibetan Plateau  

NASA Astrophysics Data System (ADS)

SummaryDebris-covered glaciers are common in the Tibetan Plateau, where ablation zones are mantled in a supraglacial debris cover that influences glacier mass balance, runoff, and response to climate change by affecting the melt rate of the underlying ice. The impact of debris cover has not yet been taken into account in regional- or global-scale assessments of glacier mass balances and freshwater resources by using physically based numerical models. Here, a surface energy-mass balance model that accounts for the significance of debris cover and its effect on the ice melt rate is applied to reconstruct the glacier mass balance of Hailuogou catchment, which is located in the south-eastern Tibetan Plateau and contains three debris-covered and four debris-free monsoonal maritime glaciers. According to our calculations, the glaciers in Hailuogou catchment show a mean annual balance of -0.42 m water equivalent (w.e.) per year, for a total mass loss of 24.3 m w.e. over the period 1952-2009. A comparison of summer temperature- and precipitation-mass balance/equilibrium line altitude (ELA) relations indicates that the glaciers in the catchment are much more sensitive to temperature change than to precipitation change. In the last 20 yrs, increasing summer temperature is the main cause of rapid wasting of the glacier mass in the catchment. Meanwhile, the presence of supraglacial debris markedly accelerates glacier mass loss, resulting in the unstable termini of debris-covered glaciers in Hailuogou catchment. This highlights the importance of debris cover for understanding glacier mass balance and hydrology in the Tibetan Plateau.

Zhang, Yong; Hirabayashi, Yukiko; Liu, Shiyin

2012-06-01

77

Northeast Glaciers  

NSDL National Science Digital Library

This reference guide provides a brief review of glaciers in the Northeastern U.S. It then focuses on the glacial affects in four areas, an inland basin near the Finger Lakes area of New York, the Appalachian/Piedmont through New York and Pennsylvania, the coastal plain and the exotic terrane of New England. Topics covered include glacial scouring, glacial deposits and periglacial features.

2003-01-01

78

The influence of line-tying on coronal perturbations in a gravitationally stratified equilibrium  

NASA Astrophysics Data System (ADS)

We study the influence of gravitational stratification of the solar atmosphere on the stability of coronal magnetic structures. In particular we question whether the (presumably stabilizing) influence of the anchoring of the magnetic field lines in the solar photosphere ('line-tying') can be adequately modeled by either 'rigid wall' or 'flow through' boundary conditions on the coronal perturbations, as is commonly done. Using the ideal magnetohydrodynamic (MHD) model without gravitational effects, inertial line-tying alone cannot lead to a full stabilization, as marginal stability cannot be crossed by including only the rapid density increase at the photospheric interface. We demonstrate, using the (localized) ballooning ordering, that when gravity and the corresponding intrinsically stable stratification of the photosphere is included, the points of marginal stability are no longer independent of the density. The sharp increase in density and associated decrease in pressure scale height at the solar surface leads to a stabilizing effect, which may result in a full transition from unstable to stable modes. Gravitational effects imply that rigid wall conditions represent photospheric field line anchoring better than flow-through conditions for determining the stability or modes of oscillation of a coronal equilibrium. Applying rigid wall conditions gives good approximations for frequencies that are much larger than photospheric time scales when the plasma is stable, and growth rates when the plasma is unstable. At the same time we show however that near marginal stability, even when gravity is included, rigid wall conditions are still violated.

van der Linden, R. A. M.; Hood, A. W.; Goedbloed, J. P.

1994-09-01

79

Glaciers in the Rupal Valley (Nanga Parbat)  

NASA Astrophysics Data System (ADS)

The widely discussed controversy about Himalayan glacier changes instigated a current boom in studies on a regional scale. In contrast to often simplified assumptions of general and mostly rapid glacier retreat, recent studies show a more complex pattern with stable, advancing and retreating glaciers. Furthermore, changes of debris covered glaciers are discussed controversial. Due to the great vertical span and steep relief, large ice streams in the Himalaya and Karakoram are often primarily fed by avalanches. Their impact on glacier mass balances is often unconsidered in present studies. However, Hewitt (2014) highlighted the crucial role of snow and ice re-distribution by avalanches for Karakoram glaciers. He used a concept of glacier typology based on different nourishment processes introduced at the beginning of the 20th century. By using this concept, Hewitt classified large glaciers in order to identify the effect of avalanches on the mass balance, because many Karakoram glaciers show low down-wasting or even thickening processes described as the "Karakoram anomaly" (Hewitt 2005). Also in the Nanga Parbat region, the western corner of the High Himalaya, the topography is characterized by steep rock walls with vertical distances up to 4700 m. The debris covered glaciers reach down to 2920 m a.s.l. and are regularly fed by small and large avalanches. Our field based investigations show that the glaciers are characterized by small retreating rates since 1857, when Adolph Schlagintweit has mapped them for the first time; others such as the Raikot Glacier are fluctuating since 1934. Furthermore, the extent of down-wasting varies between different glaciers. By using multi-temporal satellite data, topographical maps, sketches and terrestrial photographs changes of glacier lengths were measured. In order to calculate the down-wasting rates, a digital elevation model (DEM) with a spatial resolution of 30x30 m² was derived from the digitized contour lines of the topographic map of 1934 and compared to the SRTM-DEM. Furthermore, based on topographical parameters derived from the SRTM-DEM, the glaciers were classified, using Hewitt's concept. The area of steep rock walls and the ratio between accumulation and ablation zones were calculated for each glacier basin. References: Hewitt, K. 2005: The Karakoram anomaly? Glacier expansion and the 'elevation effect', Karakoram Himalaya. Mountain Research and Development 25 (4), S. 332-340 Hewitt, K. 2014: Glaciers of the Karakoram Himalaya: Glacial Environments, Processes, Hazards and Resources. Springer. Dordrecht.

Schmidt, Susanne; Nüsser, Marcus

2014-05-01

80

Recent glacier variations on active ice capped volcanoes in the Southern Volcanic Zone (37°-46°S), Chilean Andes  

NASA Astrophysics Data System (ADS)

Glaciers in the southern province of the Southern Volcanic Zone (SVZ) of Chile (37-46°S) have experienced significant frontal retreats and area losses in recent decades which have been primarily triggered by tropospheric warming and precipitation decrease. The resulting altitudinal increase of the Equilibrium Line Altitude or ELA of glaciers has lead to varied responses to climate, although the predominant volcanic stratocone morphologies prevent drastic changes in their Accumulation Area Ratios or AAR. Superimposed on climate changes however, glacier variations have been influenced by frequent eruptive activity. Explosive eruptions of ice capped volcanoes have the strongest potential to destroy glaciers, with the most intense activity in historical times being recorded at Nevados de Chillán, Villarrica and Hudson. The total glacier area located on top of the 26 active volcanoes in the study area is ca. 500 km2. Glacier areal reductions ranged from a minimum of -0.07 km2 a -1 at Mentolat, a volcano with one of the smallest ice caps, up to a maximum of -1.16 km2 a -1 at Volcán Hudson. Extreme and contrasting glacier-volcano interactions are summarised with the cases ranging from the abnormal ice frontal advances at Michinmahuida, following the Chaitén eruption in 2008, to the rapid melting of the Hudson intracaldera ice following its plinian eruption of 1991. The net effect of climate changes and volcanic activity are negative mass balances, ice thinning and glacier area shrinkage. This paper summarizes the glacier changes on selected volcanoes within the region, and discusses climatic versus volcanic induced changes. This is crucial in a volcanic country like Chile due to the hazards imposed by lahars and other volcanic processes.

Rivera, Andrés; Bown, Francisca

2013-08-01

81

Mechanisms and causes of glacier variations  

Microsoft Academic Search

Glaciers are aperiodical physical systems subject to variations forced by variable external influences on gravitational energy and bonds; moreover, self-exciting of variations is possible since they are nonlinear systems with internal energy sources. As glaciers are completely dissipative systems, the auto-variations are of relaxational character and are connected with non-uniformity of the system in time. The field of stable equilibrium

P. A. Shumsky

82

Debris emergence at Fox Glacier, New Zealand and formation of an ablation-dominant medial moraine  

NASA Astrophysics Data System (ADS)

Medial moraines can form important routeways of sediment transport in valley glaciers, and may consist of sediment from a range of sources. Despite the presence of medial moraines on several glaciers in the New Zealand Southern Alps, medial moraines there have hitherto generally escaped attention. The evolving morphology and debris content of the 12.5 km-long Fox Glacier on the western flank of the Southern Alps is the focus of this study. This tests the hypothesis that medial moraine at Fox Glacier is the product of down-glacier lateral compression of accumulation zone rockfall material within a narrow valley tongue, followed by supraglacial emergence due to down-glacier ablation gradients. Using clast orientation, clast shape, and clast lithological data, combined with ablation rates and topographic surveys, this hypothesis is applicable to such a valley glacier with an accumulation area ratio (AAR) of 0.8. Metamorphic grade increases down-valley toward the Alpine Fault at the range front. Hence, as the debris consists of slabby, very angular to angular argillaceous mudstones that generally cleave, and very angular to subangular blocky sandstones, it is likely sourced from rocks located well above the equilibrium line altitude (ELA) near the Main Divide. The debris takes a medium-level to high-level passive transport pathway through the glacier, emerging at a point-source left of centerline in the lower icefall. As the debris layers progressively melt-out, down-glacier widening of the moraine occurs. This growth in moraine width is accompanied by an increase in local relief of the moraine above adjacent debris-free ice. This width and relief increase is itself accompanied by an increase in maximum cross-glacier slope of the moraine down-glacier, reaching around 30° toward the terminus. Cross-sections of the medial moraine exposed in chevron crevasses display a layer of debris around 5 cm thick, with exceptions at the base of steep slopes. Margins of the medial moraine are marked by a discontinuous cover of debris, grading to scattered clasts forming rock tables. Dirt cones are also prevalent along the margins, forming beneath <2 cm thick coarse/very coarse sand-sized (0.5-2 mm) 'fines'. Fabric of clasts reveals a consistent flow-parallel orientation, consistent with foliation and measured strain-rates and vectors. The proglacial area preserves limited evidence of the medial moraine, in the form of low-relief 'dumped' material at the terminus. However, this has low preservation potential due to continual switching of the proglacial river exit portal across the snout.

Brook, M.

2012-04-01

83

Glacier (?) National Park  

NSDL National Science Digital Library

This activity engages learners in examining data pertaining to the disappearing glaciers in Glacier National Park. After calculating percentage change of the number of glaciers from 1850 (150) to 1968 (50) and 2009 (26), students move on to the main glacier-monitoring content of the module--area vs. time data for the Grinnell Glacier, one of 26 glaciers that remain in the park. Using a second-order polynomial (quadratic function) fitted to the data, they extrapolate to estimate when there will be no Grinnell Glacier remaining (illustrating the relevance of the question mark in the title of the module).

Mcllrath, University O.; Curriculum/serc, Spreadsheets A.

84

The Contributions of the Global Fiducial Program to the Long-Term Satellite Monitoring of the Bering Glacier, Alaska  

NASA Astrophysics Data System (ADS)

The United States Global Fiducial Program is a significant contribution to the time series monitoring and ongoing observations of the Bering Glacier system. The Bering Glacier, in south-central coastal Alaska, is undergoing rapid change largely due to increasing summer air temperatures. These changes to the largest surging glacier in North America (nearly 5000 km2 in area and over 190 km in length), have been documented via satellite remote sensing observations using a suite of electro-optical and microwave systems. The satellite record has documented changes in the terminus location, glacier velocity, snow equilibrium line altitude, snow-versus-ice area, surface elevation and volume change estimates, iceberg production and calving rates, surface albedo, and glacier features, as well as changes in the area of the ice-marginal lakes. Additionally, the satellite remote sensing observations documented the 1994-95 and 2010-11 surges of the Bering Glacier where glacial velocities in excess of 20 m/day were measured. These remote sensing products drive surface-based models of ablation and glacial hydrology where equivalent meltwater and the adiabatic lapse rate are required inputs. The United States Global Fiducials Program is an archive of free publicly available images from U.S. National Imagery Systems (http://gfp.usgs.gov) and represents a long-term periodic record for time series analysis at selected scientifically important sites.

Shuchman, R. A.; Endsley, K.; Jenkins, L. K.; Josberger, E. G.; Molnia, B. F.; Roussi, C.; Bawden, G. W.

2012-12-01

85

Muir Glacier in Glacier Bay National Monument 1941  

USGS Multimedia Gallery

This August 1941 photograph is of Muir Glacier in Glacier Bay National Monument, Alaska. It shows the lower reaches of Muir Glacier, then a large, tidewater calving valley glacier and its tributary, Riggs Glacier. For nearly two centuries before 1941, Muir Glacier had been retreating. In places, a t...

86

Parthenogenetic cell lines: an unstable equilibrium between pluripotency and malignant transformation.  

PubMed

Human parthenogenetic embryos have been recently proposed as an alternative, less controversial source of embryonic stem cells. However many aspects related to the biology of parthenogenetic cell lines are not fully understood and still need to be elucidated. These cells have great potentials; they possess most of the main features of bi-parental stem cells, show the typical morphology and express most of the pluripotency markers distinctive of ESC. They also have high telomerase activity, that disappears upon differentiation, and display great plasticity. When cultured in appropriate conditions, they are able to give rise to high specification tissues and to differentiate into mature cell types of the neural and hematopoietic lineages. However, their injection in immune deficient mice has been reported to result in tumor formations. Aberrant levels of molecules related to spindle formation, cell cycle check points and chromosome segregation have also been detected in these cells, that are characterized by the presence of an abnormal number of centrioles and massive autophagy. All these observations indicate the presence of an intrinsic deregulation of the mechanisms controlling proliferation versus differentiation in parthenogenetic stem cells. In this manuscript we summarize data related to these aberrant controls and describe experimental evidence indicating their uniparental origin as one of the possible cause. Finally we propose their use as an intriguing experimental tool where the pathways controlling potency, self renewal and cell plasticity are deeply interconnected with cell transformation, in an unstable, although highly controlled, equilibrium between pluripotency and malignancy. PMID:21044006

Brevini, Tiziana A L; Pennarossa, Georgia; deEguileor, Magda; Tettamanti, Gianluca; Ragni, Guido; Paffoni, Alessio; Gandolfi, Fulvio

2011-02-01

87

X-ray Line Diagnostics and Non-equilibrium Ionization Applications based on AtomDB v3.0  

NASA Astrophysics Data System (ADS)

Based on newly updated AtomDB v3.0, we will present our theoretical investigations of X-ray line Diagnostics and a couple of applications for some typical non-equilibrium ionization(NEI) plasmas in massive star binaries, stellar cluster winds and supernova remnants.

Ji, Li; Foster, Adam; Smith, Randall K.; Zhang, Shuinai; Zhou, Xin; Cheng, Yu; Ji, Zhiyuan

2014-08-01

88

The plateau glacier in the Sierra de Béjar (Iberian Central System) during its maximum extent. Reconstruction and chronology  

NASA Astrophysics Data System (ADS)

A detailed study of the glacial morphology in the Sierra de Béjar (Iberian Central System) provided a data set of geomorphic indicators to reconstruct the paleoglaciers developed in this mountain area during the last glacial cycle (Late Pleistocene). Applying a physical-based glacier model and using the geomorphic indicators, a three dimensional reconstruction of the ice mass during the maximum extent of the glaciers has been carried out. We used this reconstruction to project hypsometric curves over the former glaciers and to estimate the ELAs (Equilibrium Line Altitudes) of the paleoglaciers for their stage of maximum extent. At this stage the Sierra de Béjar hosted a plateau glacier, considered as a dome-shaped icecap around 57 km2 in area. According to our estimations, the maximum thickness of the ice was 211 m, the minimum elevation of paleoglaciers 1210 m asl, and the regional ELA was at 2010 m asl. During later stages, reduction in ice mass due to deglaciation caused the icecap to evolve into an icefield, and finally the main glacier was fragmented in valley and cirque glaciers. The geochronological data obtained with 10Be provides an age of ~ 27 ka for the maximum extent of the glaciers (GM), whereas the global Last Glacial Maximum (LGM) represents a younger stage of the Sierra de Béjar glacier evolution. Finally, the new data obtained in the Sierra de Béjar allow evaluating the influence of some factors such as the continentality and latitudinal location, in the development of glacial processes in these areas of the Iberian Central System.

Carrasco, R. M.; Pedraza, J.; Domínguez-Villar, D.; Villa, J.; Willenbring, J. K.

2013-08-01

89

Online Glacier Photograph Database  

NSDL National Science Digital Library

This image collection from the National Snow and Ice Data Center features 14 pairs of Alaskan glacier photographs. Each photographic pair consists of a late-19th or early-20th century photograph and a 21st century photograph taken from the same location. The comparative photographs clearly show substantial changes in glacier position and size and document significant landscape evolution and vegetative succession. The site also provides links to pairs of photographs of glaciers in Switzerland, a repeat photography project at Glacier National Park by the USGS, a glacier database which features satellite images and maps, and further information on glaciers.

The National Snow and Ice Data Center (NSIDC)

90

Freezing Level Height in the Western Equatorial Pacific over the Last 200 Years: Glacier Evidence from Mt. Jayawijaya, Papua Province, Indonesia  

NASA Astrophysics Data System (ADS)

The temperature and moisture history of the equatorial lower free troposphere over the last few hundred years is important for evaluating and predicting global warming. New evidence constrains the freezing level height (FLH) in the western equatorial Pacific over the last 200 years using the snow-line altitude (ELA) on glaciers at elevations of 4000 to 5000 m (600 hPa) on Mt. Jayawijaya, Papua Province, Indonesia (4oS, 136oE). The ELA of these wet tropical glaciers is closely coupled to the mean annual 0oC isotherm. The areal recession of the Jayawijaya glaciers continued to May 2011 by which time 95 percent of the ice cover that existed between 1936 and 1942 disappeared; 1 km2 remained. For the periods 2000-2006 and 2006-2011, the ELA was above 4950 m above sea level (asl). Revised reconstructions of the glaciers from 1936 to 1942 based on aerial photographs indicate that the concurrent ELA was at 4610 ± 10 m asl. The glaciers were interpreted to be in mass balance equilibrium between 1936 and 1942 because no appreciable areal change was detected and the glacier fronts had steep profiles. We assumed an accumulation area ratio of 0.8, typical of tropical glaciers. Extensive, fresh moraines downvalley from the 1936 ice margin indicate that the glaciers were more extensive and had lower ELAs in recent centuries. We define the most extensive, fresh moraine system of the Jayawijaya glaciers as representing the local Little Ice Age (LLIA) maximum and, following previous work, assign its age as ~1850. Our reconstruction of the Jayawijaya glaciers at the LLIA maximum based on moraines and current topographic divides indicates that they covered an area of 30 km2, considerably more than previous estimates. A concurrent ELA at ~4450 m asl was calculated assuming an accumulation area ratio of 0.8. The moraines indicate that the glaciers were in equilibrium. Taken together, glacier ELAs on Mt. Jayawijaya, approximating the FLH, have risen 500 m since the LLIA maximum. The average ELA and FLH rose at ~100 m/decade from 1972 to 2005, after which they exceeded 4950 m. For 125 years before 1972, the ELA rose on average at less than 20 m/decade. We seek a link between the rise in FLH, atmospheric warming, and western Pacific sea-surface temperature change.

Prentice, M. L.; Hope, G.; Susanto, R. D.

2012-12-01

91

Pine Island Glacier  

article title:  Pine Island Glacier, Antarctica     View Larger Image ... (MISR) images of the Pine Island Glacier in western Antarctica was acquired on December 12, 2000 during Terra orbit 5246. At left ...

2013-04-16

92

Glaciers: A water resource  

USGS Publications Warehouse

Most Americans have never seen a glacier, and most would say that glaciers are rare features found only in inaccessible, isolated wilderness mountains. Are they really so rare? Or are they really potentially important sources of water supply?

Meier, Mark; Post, Austin

1995-01-01

93

Gas temperature determination from rotational lines in non-equilibrium plasmas: a review  

NASA Astrophysics Data System (ADS)

The gas temperature in non-equilibrium plasmas is often obtained from the plasma-induced emission by measuring the rotational temperature of a diatomic molecule in its excited state. This is motivated by both tradition and the availability of low budget spectrometers. However, non-thermal plasmas do not automatically guarantee that the rotational distribution in the monitored vibrational level of the diatomic molecule is in equilibrium with the translational (gas) temperature. Often non-Boltzmann rotational molecular spectra are found in non-equilibrium plasmas. The deduction of a gas temperature from these non-thermal distributions must be done with care as clearly the equilibrium between translational and rotational degrees of freedom cannot be achieved. In this contribution different methods and approaches to determine the gas temperature are evaluated and discussed. A detailed analysis of the gas temperature determination from rotational spectra is performed. The physical and chemical background of non-equilibrium rotational population distributions in molecular spectra is discussed and a large range of conditions for which non-equilibrium occurs are identified. Fitting procedures which are used to fit (non-equilibrium) rotational distributions are analyzed in detail. Lastly, recommendations concerning the conditions for which the gas temperatures can be obtained from diatomic spectra are formulated.

Bruggeman, P. J.; Sadeghi, N.; Schram, D. C.; Linss, V.

2014-04-01

94

World Glacier Inventory  

NSDL National Science Digital Library

The National Snow and Ice Data Center (NSIDC) provides the World Glacier Inventory data, which was collected by the World Glacier Monitoring Service. This inventory contains geographic location, area, length, orientation, elevation, and classification of morphological type and moraines of more than 67,000 glaciers throughout the world. The data may be downloaded via FTP or through form-based queries.

95

The complex behavior of the Cordilleran Ice Sheet and mountain glaciers to abrupt climate change during the latest Pleistocene  

NASA Astrophysics Data System (ADS)

Surficial mapping and more than 70 radiometric ages 10Be, 14C] constrain the evolution of the Cordilleran Ice Sheet (CIS) and associated mountain glaciers in western Canada during the latest Pleistocene. Our data suggest that: i) there is widespread evidence for the Younger Dryas (YD) throughout the mountains of western Canada; ii) late Pleistocene climate reconstructions based solely on alpine moraines may be misleading in regions with decaying ice sheets; iii) extensive interfluves in some mountain regions were ice-free between 16 ka and 13 ka (kilo calibrated yrs BP). Initial decay of the CIS from its maximum extent around 16 ka was likely due to a combination of climatic (surface melting) and dynamical factors. Climate amelioration during the Bølling-Allerød Warm Period [14.7-12.9 ka], likely the cause for the major phase of CIS decay, resulted in ice sheet equilibrium line altitudes (ELAs) ranging from 2500 m asl in southern BC to around 2000 m asl along the BC-Yukon border. Hence, before the onset of the Younger Dryas (YD) Cold Period [12.9-11.7 ka], the ice sheet shrank and became a labyrinth of individual and coalescing valley glaciers fed by major accumulation zones centered on the Coast Mountains and other high ranges of NW Canada. The response of remnant ice and cirque glaciers to the YD climate deterioration was highly variable. In some cases, small glaciers (0.5-2 km2) built YD moraines that were only hundreds of meters beyond those constructed during the Little Ice Age (LIA) [0.30-0.15 ka]. Our dating also reveals that much larger glaciers persisted in nearby valleys that lie hundreds of meters below the cirques. Hence, we infer that many cirques were completely deglaciated prior the YD, in contrast to low-lying valleys where ice sheet remnants persisted. Glaciers also advanced in north-central British Columbia during the YD, but here glaciers constructed large terminal and lateral moraines. In the Cassiar and northern Coast mountains, for example, 25 10Be [13.10-12.00 ka] and four minimum-limiting 14C ages from lakes impounded by moraines show that glaciers existed up to 10 km beyond LIA glacier limits during the YD. These glaciers thus had ELAs that were 300-500 m lower than contemporary glaciers. We are currently performing high-resolution (

Menounos, Brian; Goehring, Brent; Osborn, Gerald; Clarke, Garry K. C.; Ward, Brent; Margold, Martin; Bond, Jeff; Clague, John J.; Lakeman, Tom; Schaefer, Joerg; Koch, Joe; Gosse, John; Stroeven, Arjen P.; Seguinot, Julien; Heyman, Jakob; Fulton, Robert

2014-05-01

96

Glacier Ecosystems of Himalaya  

NASA Astrophysics Data System (ADS)

Biological activity on glaciers has been believed to be extremely limited. However, we found various biotic communities specialized to the glacier environment in various part of the world, such as Himalaya, Patagonia and Alaska. Some of these glacier hosted biotic communities including various cold-tolerant insects, annelids and copepods that were living in the glacier by feeding on algae and bacteria growing in the snow and ice. Thus, the glaciers are simple and relatively closed ecosystems sustained by the primary production in the snow and ice. In this presentation, we will briefly introduce glacier ecosystems in Himalaya; ecology and behavior of glacier animals, altitudinal zonation of snow algal communities, and the structure of their habitats in the glacier. Since the microorganisms growing on the glacier surface are stored in the glacial strata every year, ice-core samples contain many layers with these microorganisms. We showed that the snow algae in the ice-core are useful for ice core dating and could be new environmental signals for the studies on past environment using ice cores. These microorganisms in the ice core will be important especially in the studies of ice core from the glaciers of warmer regions, in which chemical and isotopic contents are often heavily disturbed by melt water percolation. Blooms of algae and bacteria on the glacier can reduce the surface albedo and significantly affect the glacier melting. For example, the surface albedo of some Himalayan glaciers was significantly reduced by a large amount of dark-colored biogenic material (cryoconite) derived from snow algae and bacteria. It increased the melting rates of the surfaces by as much as three-fold. Thus, it was suggested that the microbial activity on the glacier could affect the mass balance and fluctuation of the glaciers.

Kohshima, S.; Yoshimura, Y.; Takeuchi, N.; Segawa, T.; Uetake, J.

2012-12-01

97

The World Glacier Inventory  

NSDL National Science Digital Library

This web site is part of the National Snow and Ice Data Center's World Glacier Monitoring Service. The World Glacier Inventory contains information for over 67,000 glaciers throughout the world. Parameters within the inventory include: geographic location, area, length, orientation, elevation, and classification of morphological type and moraines. The inventory entries are based upon a single observation in time and can be viewed as a "snapshot" of the glacier at this time. These data are collected and digitized by the World Glacier Monitoring Service, Zurich. A point and click map of the world will also take users to the region of interest with a list of glaciated areas.

Haggerty, C.

98

Bathymetric control of tidewater glacier mass loss in northwest Greenland  

NASA Astrophysics Data System (ADS)

It has been suggested that fjord geometry could be an important contributor to the observed mass loss variability in Greenland by modulating the flow of warm water to marine-terminating glaciers. New gravity-derived bathymetry of Greenlandic fjords confirms the link between the grounding line depth and rates of glacier mass loss, a relationship previously predicted only in ice models. We focus on two neighboring glaciers to minimize differences in external forcing and therefore isolate the role of the fjord bathymetry. Tracy Glacier has a deeper grounding line and has been retreating since 1892 with a contemporary mass budget of -1.63 Gt a-1. Heilprin Glacier has a shallower grounding line depth, a stable ice terminus, and a mass budget of only -0.53 Gt a-1. Because of its deeper grounding line, Tracy has more ice in contact with warm subsurface water, leaving it more vulnerable to changes in ocean forcing and therefore mass loss.

Porter, David F.; Tinto, Kirsty J.; Boghosian, Alexandra; Cochran, James R.; Bell, Robin E.; Manizade, Serdar S.; Sonntag, John G.

2014-09-01

99

Energy balance-based distributed modeling of snow and glacier melt runoff for the Hunza river basin in the Pakistan Karakoram Himalayan region  

NASA Astrophysics Data System (ADS)

A spatially distributed biosphere hydrological model with energy balance-based multilayer snow physics and multilayer glacier model, including debris free and debris covered surface (enhanced WEB-DHM-S) has been developed and applied to the Hunza river basin in the Pakistan Karakoram Himalayan region, where about 34% of the basin area is covered by glaciers. The spatial distribution of seasonal snow and glacier cover, snow and glacier melt runoff along with rainfall-contributed runoff, and glacier mass balances are simulated. The simulations are carried out at hourly time steps and at 1-km spatial resolution for the two hydrological years (2002-2003) with the use of APHRODITE precipitation dataset, observed temperature, and other atmospheric forcing variables from the Global Land Data Assimilation System (GLDAS). The pixel-to-pixel comparisons for the snow-free and snow-covered grids over the region reveal that the simulation agrees well with the Moderate Resolution Imaging Spectroradiometer (MODIS) eight-day maximum snow-cover extent data (MOD10A2) with an accuracy of 83% and a positive bias of 2.8 %. The quantitative evaluation also shows that the model is able to reproduce the river discharge satisfactorily with Nash efficiency of 0.92. It is found that the contribution of rainfall to total streamflow is small (about 10-12%) while the contribution of snow and glacier is considerably large (35-40% for snowmelt and 50-53% for glaciermelt, respectively). The model simulates the state of snow and glaciers at each model grid prognostically and thus can estimate the net annual mass balance. The net mass balance varies from -2 m to +2 m water equivalent. Additionally, the hypsography analysis for the equilibrium line altitude (ELA) suggests that the average ELA in this region is about 5700 m with substantial variation from glacier to glacier and region to region. This study is the first to adopt a distributed biosphere hydrological model with the energy balance- based multilayer snow and glacier module to estimate the spatial distribution of snow/glacier cover and snow and glacier melt runoff for a river basin in the Karakoram Himalayan region.

Shrestha, M.; Wang, L.; Koike, T.; Xue, Y.; Hirabayashi, Y.; Ahmad, S.

2012-12-01

100

The influence of air temperature inversions on snowmelt and glacier mass-balance simulations, Ammassalik island, SE Greenland  

SciTech Connect

In many applications, a realistic description of air temperature inversions is essential for accurate snow and glacier ice melt, and glacier mass-balance simulations. A physically based snow-evolution modeling system (SnowModel) was used to simulate eight years (1998/99 to 2005/06) of snow accumulation and snow and glacier ice ablation from numerous small coastal marginal glaciers on the SW-part of Ammassalik Island in SE Greenland. These glaciers are regularly influenced by inversions and sea breezes associated with the adjacent relatively low temperature and frequently ice-choked fjords and ocean. To account for the influence of these inversions on the spatiotemporal variation of air temperature and snow and glacier melt rates, temperature inversion routines were added to MircoMet, the meteorological distribution sub-model used in SnowModel. The inversions were observed and modeled to occur during 84% of the simulation period. Modeled inversions were defined not to occur during days with strong winds and high precipitation rates due to the potential of inversion break-up. Field observations showed inversions to extend from sea level to approximately 300 m a.s.l., and this inversion level was prescribed in the model simulations. Simulations with and without the inversion routines were compared. The inversion model produced air temperature distributions with warmer lower elevation areas and cooler higher elevation areas than without inversion routines due to the use of cold sea-breeze base temperature data from underneath the inversion. This yielded an up to 2 weeks earlier snowmelt in the lower areas and up to 1 to 3 weeks later snowmelt in the higher elevation areas of the simulation domain. Averaged mean annual modeled surface mass-balance for all glaciers (mainly located above the inversion layer) was -720 {+-} 620 mm w.eq. y{sup -1} for inversion simulations, and -880 {+-} 620 mm w.eq. y{sup -1} without the inversion routines, a difference of 160 mm w.eq. y{sup -1}. The annual glacier loss for the two simulations was 50.7 x 10{sup 6} m{sup 3} y{sup -1} and 64.4 x 10{sup 6} m{sup 3} y{sup -1} for all glaciers - a difference of {approx}21%. The average equilibrium line altitude (ELA) for all glaciers in the simulation domain was located at 875 m a.s.l. and at 900 m a.s.l. for simulations with or without inversion routines, respectively.

Mernild, Sebastian Haugard [Los Alamos National Laboratory; Liston, Glen [COLORADO STATE UNIV.

2009-01-01

101

In Brief: Melting glaciers  

NASA Astrophysics Data System (ADS)

Glaciers in Patagonia and Alaska have been losing their mass, and for longer than glaciers elsewhere in the world, according to a 7 December report compiled by the United Nations Environment Programme (UNEP). “Climate change is causing significant mass loss of glaciers in high mountains worldwide,” notes the report, which calls for accelerated research, monitoring, and modeling of glaciers and snow and their role in water supplies. The report “also highlights the vulnerability and exposure of people dependent upon [glacier-fed] rivers to floods, droughts and eventually shortages as a result of changes in the melting and freezing cycles linked with climate change and other pollution impacts,” according to UNEP executive director Achim Steiner. For more information, visit http://www.grida.no/publications/high­mountain-glaciers/.

Showstack, Randy; Tretkoff, Ernie

2010-12-01

102

Black carbon concentrations from a Tibetan Plateau ice core spanning 1843-1982: recent increases due to emissions and glacier melt  

NASA Astrophysics Data System (ADS)

Black carbon (BC) deposited on snow and glacier surfaces can reduce albedo and lead to accelerated melt. An ice core recovered from Guoqu glacier on Mt. Geladaindong and analyzed using a Single Particle Soot Photometer provides the first long-term (1843-1982) record of BC concentrations from the Central Tibetan Plateau. The highest concentrations are observed from 1975-1982, which corresponds to a 2.0-fold and 2.4-fold increase in average and median values, respectively, relative to 1843-1940. BC concentrations post-1940 are also elevated relative to the earlier portion of the record. Causes for the higher BC concentrations include increased regional BC emissions and subsequent deposition, and melt induced enrichment of BC, with the melt potentially accelerated due to the presence of BC at the glacier surface. A qualitative comparison of the BC and Fe (used as a dust proxy) records suggests that if changes in the concentrations of absorbing impurities at the glacier surface have influenced recent glacial melt, the melt may be due to the presence of BC rather than dust. Guoqu glacier has received no net ice accumulation since the 1980s, and is a potential example of a glacier where an increase in the equilibrium line altitude is exposing buried high impurity layers. That BC concentrations in the uppermost layers of the Geladaindong ice core are not substantially higher relative to deeper in the ice core suggests that some of the BC that must have been deposited on Guoqu glacier via wet or dry deposition between 1983 and 2005 has been removed from the surface of the glacier, potentially via supraglacial or englacial meltwater.

Jenkins, M.; Kaspari, S.; Kang, S.; Grigholm, B.; Mayewski, P. A.

2013-10-01

103

Fast Glacier Flow  

NASA Astrophysics Data System (ADS)

An AGU Chapman Conference on Fast Glacier Flow was held at Whistler Village, Canada, from May 4 to 8, 1986. The timing of the conference seemed particularly propitious because of results of recent observational programs, such as the breakup of the tidewater Columbia Glacier in Alaska, the imbalance of Ice Stream B in Antarctica and the existence of deforming sediment under it, and the surge of Variegated Glacier in Alaska.

Whillans, Ian M.; Harrison, William D.

104

Glacier activity at the Lateglacial / Holocene transition inferred from the Swiss Alps  

NASA Astrophysics Data System (ADS)

High-alpine environments react sensitively to changes in climate. Depending on size, catchment area and valley topography, mountain glaciers response relatively fast with advances and recessions to shifts in temperature and precipitation (e.g. Oerlemans, 2005). About half of the present glaciers in the Swiss Alps are located in the highest mean altitudes areas. Past glacier activity beyond actual glacier extent is sometimes easily identified, such as the moraines related to the Little Ice Age. Records of older glacier activity, however, are usually less abundant. Lateglacial glacier advances are often documented by moraine complexes. By comparing geomorphological characteristics within and between several investigated sites across the Swiss Alps, a relative chronology of glacier oscillations and re-advances was established. A cross-correlation of moraines in the same high-alpine climatic region allows to conclude that moraine ridges in comparable relative positions with similar morphologies and characterized by similar equilibrium line altitude depressions (Gross et al. 1977; Maisch, 1987), may be allocated to the same supra-regional trends in climate change. Surface exposure dating on well defined moraines gives the absolute chronology for the relative framework. More than 50 samples from erratic boulders on the crestline of moraines and glacially abraded bedrock were dated using the radionuclide 10Be. According to the results on boulders of the outer moraines, the oldest ridge coincides in time with the initial phase of the Younger Dryas (e.g. Gerzensee Oscillation). In addition, a number of Lateglacial and early Holocene advances have been identified (Preboreal Oscillation, Younger Dryas and Gerzensee Oscillation). 10Be exposure ages on moraines of the innermost Lateglacial complexes, but distinctly downvalley from Little Ice Age moraines point to cold conditions in the Alps during the early Holocene. REFERENCES Gross, G., Kerschner, H. & Patzelt, G. (1977): Methodische Untersuchungen über die Schneegrenze in alpinen Gletschergebieten. Zeitschrift für Gletscherkunde und Glazialgeologie, 12, 223-251. Maisch, M. (1987): Zur Gletschergeschichte des alpinen Spätglazials: Analyse und Interpretation von Schneegrenzdaten. Geographica Helvetica, 42, 63-71. Oerlemans, J. (2005): Extracting a Climate Signal from 169 Glacier Records. Science, 308, 675-677.

Schindelwig, Inga; Akçar, Naki; Lukas, Sven; Kubik, Peter W.; Schlüchter, Christian

2010-05-01

105

Response of major Greenland outlet glaciers to oceanic and atmospheric forcing: Results from numerical modeling on Petermann, Jakobshavn and Helheim Glacier.  

NASA Astrophysics Data System (ADS)

Oceanic forcing has been suggested as a major trigger for dynamic changes of Greenland outlet glaciers. Significant melting near their calving front or beneath the floating tongue and reduced support from sea ice or ice melange in front of their calving front can result in retreat of the terminus or the grounding line, and an increase in calving activities. Depending on the geometry and basal topography of the glacier, these oceanic forcing can affect the glacier dynamic differently. Here, we carry out a comparison study between three major outlet glaciers in Greenland and investigate the impact of a warmer ocean on glacier dynamics and ice discharge. We present results from a numerical ice-flow model applied to Petermann Glacier in the north, Jakobshavn Glacier in the west, and Helheim Glacier in the southeast of Greenland.

Nick, F. M.; Vieli, A.; Pattyn, F.; Van de Wal, R.

2011-12-01

106

Crustal and Lithospheric Structural Controls on Thwaites Glacier, West Antarctica  

Microsoft Academic Search

Thwaites Glacier in the Amundsen Sea Embayment of West Antarctica is changing rapidly. Satellite observations show that the glacier is accelerating, its grounding line is retreating, and its floating portion is thinning. These changes are dynamic and could be related to the nature of the sub-ice geology, though the geology is not well- understood. We know from the Ross Sea

T. M. Diehl; D. D. Blankenship; T. A. Jordan; D. A. Young

2007-01-01

107

A non-local thermodynamic equilibrium, line-blanketed synthetic spectrum of Iota Herculis - C, Al, and Si lines  

NASA Technical Reports Server (NTRS)

A non-LTE line-blanketed model stellar atmosphere is used to compute a model of I Herculis (B3 IV) with a Teff of 17,500 K and a log g of 3.75, following the conclusions of Peters and Polidan (1985). Detailed profiles of a number of lines of C, Al, and Si in the 1200-2000-A region are computed, including the resonance lines of C II, Al II, and Al III. These profiles are compared to observations obtained from the coaddition of eight IUE SWP images, using a technique developed by Leckrone and Adelman (1989). Comparison of carbon lines with a model that is underabundant in carbon by a factor of 2 relative to the sun indicates that the C abundance of Iota Her is at most one-half solar. Non-LTE effects are examined by comparing an LTE model possessing identical atmospheric parameters with the non-LTE model. Substantial differences in the populations of the model atomic states are found, but differences in the temperature structure of the two models often mask the non-LTE effects in the synthetic spectra.

Grigsby, James A.

1991-01-01

108

Denali Fault: Susitna Glacier  

USGS Multimedia Gallery

Helicopters and satellite phones were integral to the geologic field response. Here, Peter Haeussler is calling a seismologist to pass along the discovery of the Susitna Glacier thrust fault. View is to the north up the Susitna Glacier. The Denali fault trace lies in the background where the two lan...

2008-12-15

109

Glaciers and Rocks  

NSDL National Science Digital Library

This formative assessment item uncovers students' ideas about glacial erosion and how glaciers transport rocks and other sediment. The assessment is aligned with the National Science Education Standards. It contains instructional suggestions as well as links to other helpful resources dealing with glaciers and glacial movement.

Fries-Gaither, Jessica

110

Melting Mountain Glaciers  

NSDL National Science Digital Library

The world's glaciers are shrinking at alarming rates, and many scientists believe it is due to changes in climate. Dr. Lonnie Thompson of Ohio State University and Dr. Douglas Hardy of UMass-Amherst discuss glaciers and how they melt, and pay special attention to Africa's tallest mountain, Mt. Kilimanjaro. "Changing Planet" is produced in partnership with the National Science Foundation.

Learn, Nbc

2010-10-07

111

Columbia Glacier Calving  

USGS Multimedia Gallery

A dramatic iceberg calving from Columbia Glacier in Prince William Sound, Alaska. The iceberg has just broken free from under the water and shot to the surface, spinning towards the ice face. The ice cliff here is about 70 m (229.7 ft) tall. Icebergs are calved as stress fractures in the glacier mer...

2010-07-14

112

Holocene glacier history from alpine speleothems, Milchbach cave, Switzerland  

NASA Astrophysics Data System (ADS)

Mountain glaciers and their sediments are prominent witnesses of climate change, responding sensitively to even small modifications in meteorological parameters. Even in such a classical and thoroughly studied area as the European Alps the record of Holocene glacier mass-balance is only incompletely known. Here we explore a novel and continuous archive of glacier fluctuations in a cave system adjacent to the Upper Grindelwald Glacier in the Swiss Alps. Milchbach cave became partly ice-free only recently and hosts Holocene speleothems. Four coeval stalagmites show consistent petrographic and stable isotopic changes between 9.2 and 2.0 ka which can be tied to abrupt modifications in the cave environment as a result of the closing and opening of multiple cave entrances by the waxing and waning of the nearby glacier. During periods of Holocene glacier advances, columnar calcite fabric is characterized by ? 18O values of about -8.0‰ indicative of speleothem growth under quasi-equilibrium conditions, i.e. little affected by kinetic effect related to forced degassing or biological processes. In contrast, fabrics formed during periods of glacier minima are typical of bacterially mediated calcite precipitation within caves overlain by an alpine soil cover. Moreover, ? 18O values of the bacterially mediated calcite fabrics are consistent with a ventilated cave system fostering kinetic fractionation. These data suggest that glacier retreats occurred repeatedly before 5.8 ka, and that the amplitudes of glacier retreats became substantially smaller afterwards. Our reconstruction of the Upper Grindelwald Glacier fluctuations agrees well with paleoglaciological studies from other sites in the Alps and provides a higher temporal resolution compared to traditional analyses of peat and wood remains found in glacier forefields.

Luetscher, M.; Hoffmann, D. L.; Frisia, S.; Spötl, C.

2011-02-01

113

Analysis of meteorological data and the surface energy balance of Keqicar Glacier, Tien Shan, China  

NASA Astrophysics Data System (ADS)

Northwestern China currently experiences a climate change with fundamental consequences for the hydrological cycle. In the strongly arid region where water resources are essential for agriculture and food production, glaciers represent important water resources, contributing significantly to streamflow. The debris is an important glaciological feature of the region and has major impact on melt rates. It is essential to understand and quantify the interaction of climate and sub-debris melt in order to assess the current situation and to predict future water yield. Note that the surface energy balance determines glacier melt. However, little is known about the variability characteristics of the surface energy fluxes in this region. For this reason, we set up two automatic weather stuation (AWSs) in the ablation area of Keqicar Glacier. Keqicar Glacier is located in the Tarim River basin (largest inland river basin in China), southwestern Tien Shan, China. It is a representative debris-covered glacier with a length of 26.0 km and a total surface area of 83.6 km2. The thickness of the debris layer varies from 0.0 to 2.50 m in general. In some places large rocks are piled up to several meters. In this study, we report on analysis of meteorological data for the period 1 July-13 September 2003, from two automatic weather stations, aimed at studying the relationship between climate and ablation. One station is located on the lower part of the ablation area where the glacier is covered by debris layer, and the other near the equilibrium line altitude (ELA). All sensors were sampled every 10 seconds, and data were stored as hourly averages. The stations were visited regularly for maintenance at two weeks intervals depending on the weather conditions and location of the AWS. A total of 17 ablation stakes were drilled into the glacier at different elevations to monitor glacier melt during the study period. Readings were taken regularly in connection with AWS maintenance. The weather station on the glacier measured an average temperature of 2.6 °C (at 2m height above surface). The lapse rate of air temperature is close to the standard free atmospheric lapse rate (0.6 °C per 100m), which shows the cold effect of glacier is not significant. The local mountain-valley winds is significant, the speed of which is 2.3 m s-1 (at 2m height). Glacier is dominated by the convectional precipitation, 75% of which occurs in day time. The ablation stakes indicate a specific mass balance of -2.5 m w.e. between 1 July and 13 September. The specific mass balance calculated from the surface energy balance, -2.6 m w.e., is in close correspondence to this. The thermal processes on the debris layer are quite different from those on bare ice or snow. The main physical characteristics of the debris layer are the thermal conductivity and albedo that control heat conduction to the ice-debris interface. Net radiation is the main melt energy whether the debris layer is taken into consideration or not, which is lager between July and the middle of August, and then decreases. This is coincides with the glacier ablation. On the debris-covered area, the sensible- and latent-heat fluxes contribute 19.6% of the melt energy, higher than that on the debris-free ice (4.1%). Hence, due to the existing debris layer, the ablation shows a significant spatial distribution.

Zhang, Y.; Liu, S.; Fujita, K.; Han, H.; Li, J.

2009-04-01

114

Temperature index modeling of the Kahiltna Glacier: Comparison to multiple field and geodetic mass balance datasets  

NASA Astrophysics Data System (ADS)

Glaciers of Alaska, USA, and Northwestern Canada are shedding mass at one of the highest rates of any mountain glacier system, with significant impact at the global and local scales. Despite advances in satellite and airborne technologies, fully characterizing the temporal evolution of glacier mass change in individual watersheds remains a challenge. Temperature index modeling is an approach that can be used to expand on sparse ground observations, and that can help bridge the gap between regional and individual watershed estimates of the time series of glacier mass change. Here we present a study on temperature index modeling of glacier-wide mass balance for the large Kahiltna Glacier (502 km2, 270 to 6100 m in elevation) in the Central Alaska Range, using a combination of ground observations and past climate data products. We reproduce mass changes from 1991 to 2011, and assess model performance by comparing our results to several field and remote sensing datasets. First, we compare our results to a 20-year record of mass balance measurements at a National Park Service index site at the glacier's equilibrium line altitude. We find low correlation between index site measurements and modeled glacier-wide balances (R2 = 0.24), indicating that the index site may not be representative of the glacier-wide mass balance regime. We compare next to glacier-wide mass balances derived from airborne laser altimetry, to assess the model's long-term mass change estimates. We find disagreement between the mean annual balances for 1995 to 2010 (-0.95 +/-0.49 m w.e. yr --1 from the model versus -0.69 +0.07/-0.08 m w.e. yr --1 from laser altimetry). To validate the laser altimetry methods, we then compare estimates from 1951 to 2011 from laser altimetry and digital elevation model differencing, finding close agreement (-0.48 +0.08/-0.09 m w.e. yr--1 and -0.41 +/-0.26 m w.e. yr--1 , respectively), and lending strength to the laser altimetry centerline extrapolation techniques. We also examine estimates derived from regionally-downscaled satellite gravimetry. While gravimetry likely underestimates long-term mass loss for this glacier (-0.36 +/-0.13 m w.e. yr--1 for 2003 to 2010), it correlates well to individual modeled annual balances (R2 = 0.72) and to the time series of mass balance at an ablation stake location (R2 = 0.81). Given ongoing refinements to gravimetry downscaling and geodetic techniques, our results point to the potential for integrating multiple methods to obtain the most information on subannual and long-term mass changes at the basin scale for remote sites such as the Kahiltna Glacier.

Young, Joanna C.

115

Topography, relief, climate and glaciers: a global prespective  

NASA Astrophysics Data System (ADS)

The examination of the relationship between Earth's topography and present and past climate (i.e. long-term elevation of glaciers Equilibrium Line Altitude) reveals that the elevation of mountain ranges may be limited or controlled by glaciations. This is of prime importance, because glacial condition would lead to a limit the mountain development, hence the accumulation of gravitational energy and prevent the development of further glacial conditions as well as setting the erosion in (peri)glacial environments. This study examines the relationships between topography and the global Equilibrium Line Altitude of alpine glaciers around the world (long term snowline, i.e. the altitude where the ice mass balance is null). Two main observations can be drawn: 1) The distance between the (averaged and maximum) topography, and the ELA decreases pole ward the poles, and even become reversed (mean elevation above to ELA) at high latitude. Correlatively, the elevation of very large portion of land at mid-latitude cannot be related to glaciations, simply because it was never glaciated (large distance between topography and long-term mean ELA). The maximum distance between the ELA and the topography is greater close to the equator and decreases poleward. In absence of glacial and periglacial erosion, this trend cannot have its origin in glacial and periglacial processes. Moreover, the ELA elevation shows a significant (1000 - 1500m) depression in the intertropical zone. This depression of the ELA is not reflected at all in the topography. 2) The distribution of relief on Earth, if normalized by the mean elevation of mountain ranges (as a proxy for available space to create relief) shows a latitudinal band of greater relief between 40° and 60° (or between ELA of 500m to 2500m a.s.l.). This mid-latitude relatively greater relief challenges the straightforward relationship between glaciations, erosion and topography. Oppositely, it suggests that glacier may be more efficient agent in temperate area, with important amplitude between glacial and interglacial climate. This is consistent with the view of a very variable glacier erodibility that can erode and protect the landscape, as well as with studies documenting a bimodal location of the preferred glacial erosion, at relatively high elevation (around the long-term ELA), and at much lower elevation (close to the glacial maximum lower reaches), thanks to efficient water lubrication of the glacier bases that greatly enhance the sliding velocity. These findings show that the relation between the mountain topography and the long term snowline is not as straightforward as previously proposed. Beside the role of tectonic forcing highlighted by several authors, the importance of the glacial erosion appears to be crucial at mid latitude, but more complex at both high and low latitude. Moreover, the relief at mid latitude appears to be higher, hence suggesting a positive correlation between relief and topographic control of glacier on the landscape.

Champagnac, Jean-Daniel; Valla, Pierre; Herman, fred

2014-05-01

116

Volume Estimation for Glaciers in China Based on Topographical Parameters  

NASA Astrophysics Data System (ADS)

Glaciers outside of Greenland and Antarctic ice sheets have attracted continuous attention due to the large contribution to global sea level rise during the last century and in future. However, this depends on the volume estimation of mountain glaciers except for knowledge of their dynamic response to climate change. Thicknesses of some glaciers in China were measured by pulse RADAR sounding equipment in the 1980s and the measured samples increased in the 2010s. The early data are important base for the volume and water resource storage estimation of glaciers in China and this estimation has not updated by now although new measurements and method are available, for example ice thickness along the flow line of a glacier based on digital elevation model and shallow ice approximation simplification. The method is applied here with the available thickness data acquired in the 1980s and 2010s as well as glacier boundaries and digital elevation models. It is found that there exists good relationship between average basal shear stress and topographic parameters. The method is validated for the estimation of the ice volume of well-studied glaciers inventoried from the photogrammetrical mapping and glaciated trimlines based on field investigation. This provides an update to the estimation of glacier ice volume and a base for modeling of glacier response to climate change.

Wei, J.; Liu, S.; Guo, W.

2012-12-01

117

Glaciological investigations beneath an active polar glacier  

NASA Astrophysics Data System (ADS)

Meserve Glacier, Antarctica, was used as a natural laboratory for research on the effective viscosity of subfreezing polycrystalline ice, and on the interaction of cold-based glaciers with their beds. A tunnel was excavated through basal layers of this glacier, which allowed sampling of ice for subsequent measurements of physical and chemical properties and allowed in-situ measurements of ice deformation and glacier sliding. Analyses of deformation reveal a direct dependence of strain rate on crystal size, which reflects an important role for grain-size-sensitive deformation mechanisms such as grain boundary sliding. The sensitivity of strain rate to chemical impurity content and rock particle content is found to be very low. Variations of crystal size probably are an important control on shear enhancement in the ice sheets. The enhanced shear strain rate inferred from tilt of the Dye 3 borehole can be explained as a result of combined fabric and crystal size variations. I infer that interactions between Meserve glacier and its bed are influenced by the presence of liquid water films at ice-rock interfaces despite the low temperature of -17°C. Such films allow slip at ice-rock interfaces and cause in-situ segregation of ice into clean lenses amidst dirty layers. Using slip rate and bed surface roughness measurements I infer la liquid film thickness of at least tens of nanometers. Such films should generally be present in polar glaciers, and will have a thickness controlled by soluble impurities and temperature. Analyses of gas and isotopic composition of basal ices reveal that entrainment of bed material into this glacier actively occurs without bulk freeze-on and conventional regelation. Cold-based glaciers have the capacity to striate and erode their beds, and to create glacial landforms. I reinterpret the clear and persistent relationship between d18O and dD of polar precipitation, which allows isotopic composition to be an important tool for studying glacier-bed interactions and deuterium excess measurements on ice cores to reveal subtropical paleoclimate. I argue that the isotopic composition of precipitation is determined by water-vapor equilibrium to temperatures as low as -35°C. This implies deuterium excess is not sensitive to cloud supersaturation.

Cuffey, Kurt Marshall

118

Geological Field Trips: Glaciers  

NSDL National Science Digital Library

Students will utilize the Internet to take a virtual field trip to visit a glacier and discover what physical effects glaciers have on the land. They will also have the opportunity to virtually visit Vermont and trace the pictorial history of how a whale's fossils were found there. The site also contains a student worksheet for their visual field trip. The site also provides an explanation of the formation of fossils.

Zvanut, Patti

2000-03-23

119

A strategy for monitoring glaciers  

USGS Publications Warehouse

Glaciers are important features in the hydrologic cycle and affect the volume, variability, and water quality of runoff. Assessing and predicting the effect of glaciers on water resources require a monitoring program to provide basic data for this understanding. The monitoring program of the U.S. Geological Survey employs a nested approach whereby an intensively studied glacier is surrounded by less intensively studied glaciers and those monitored solely by remote sensing. Ideally, each glacierized region of the United States would have such a network of glaciers. The intensively studied glacier provides a detailed understanding of the physical processes and their temporal changes that control the mass exchange of the glaciers in that region. The less intensively studied glaciers are used to assess the variability of such processes within the region.

Fountain, Andrew G.; Krimmel, Robert M.; Trabant, Dennis C.

1997-01-01

120

A new glacier inventory for 2009 reveals spatial and temporal variability in glacier response to atmospheric warming in the Northern Antarctic Peninsula, 1988-2009  

NASA Astrophysics Data System (ADS)

The Northern Antarctic Peninsula has recently exhibited ice-shelf disintegration, glacier recession and acceleration. However, the dynamic response of land-terminating, ice-shelf tributary and tidewater glaciers has not yet been quantified or assessed for variability, and there are sparse published data for glacier classification, morphology, area, length or altitude. This paper firstly uses ASTER images from 2009 and a SPIRIT DEM from 2006 to classify the area, length, altitude, slope, aspect, geomorphology, type and hypsometry of 194 glaciers on Trinity Peninsula, Vega Island and James Ross Island. Secondly, this paper uses LANDSAT-4 and ASTER images from 1988 and 2001 and data from the Antarctic Digital Database (ADD) from 1997 to document glacier change 1988-2009. From 1988-2001, 90 % of glaciers receded, and from 2001-2009, 79 % receded. Glaciers on the western side of Trinity Peninsula retreated relatively little. On the eastern side of Trinity Peninsula, the rate of recession of ice-shelf tributary glaciers has slowed from 12.9 km2 a-1 (1988-2001) to 2.4 km2 a-1 (2001-2009). Tidewater glaciers on the drier, cooler Eastern Trinity Peninsula experienced fastest recession from 1988-2001, with limited frontal retreat after 2001. Land-terminating glaciers on James Ross Island also retreated fastest in the period 1988-2001. Large tidewater glaciers on James Ross Island are now declining in areal extent at rates of up to 0.04 km2 a-1. This east-west difference is largely a result of orographic temperature and precipitation gradients across the Antarctic Peninsula. Strong variability in tidewater glacier recession rates may result from the influence of glacier length, altitude, slope and hypsometry on glacier mass balance. High snowfall means that the glaciers on the Western Peninsula are not currently rapidly receding. Recession rates on the eastern side of Trinity Peninsula are slowing as the floating ice tongues retreat into the fjords and the glaciers reach a new dynamic equilibrium. The rapid glacier recession of tidewater glaciers on James Ross Island is likely to continue because of their low elevations and flat profiles. In contrast, the higher and steeper tidewater glaciers on the Eastern Antarctic Peninsula will attain more stable frontal positions after low-lying ablation areas are removed.

Davies, B. J.; Carrivick, J. L.; Glasser, N. F.; Hambrey, M. J.; Smellie, J. L.

2011-12-01

121

Analysis of the relationship between glacier ELA with climatic and morpho-topographic parameters, for tropical glaciers in the Peruvian Andes  

NASA Astrophysics Data System (ADS)

In recent decades, climate change has produced an important glacier shrinkage in the Peruvian mountain chains, with accelerated melting of ice and snow masses and an increase in the equilibrium-line altitude (ELA). These changes have led to conflicts on water availability for local and regional populations and increasing glacier risks (proglacial lakes formation). In this study we have determined the spatio-temporal variations of ELA obtained through the snowline altitude (SLA) for a total of 17 glaciers of the Cordillera Blanca (Peru, 9°S) during the period 2001-2010. These time series have been analysed in function to climate and morpho-topographic parameters in order to quantify their influences on the spatio-temporal variations of the ELA. The investigation is based on optical remote-sensing images and geographic information systems (GIS). The relationship between the snowline measured on the satellite images recorded during the dry season and the ELA has been validated on four glaciers where mass balance field measurements are conducted since the early 2000s. For the study period, the average ELA at the scale of the Cordillera Blanca is about ~ 4920 m a.s.l. and an increasing trend (~ 11 m / year) is observed. The comparison with climatic and morpho-topographic parameters, shows that the average ELA over the study period is mainly controlled by morpho-topographic parameters, but the interannual variations are mainly driven by climate conditions (the best correlation being found when comparing ELA anomalies with temperature at 500 hPa anomalies).

Loarte, Edwin; Rabatel, Antoine

2013-04-01

122

Fifty years of meteo-glaciological change in Toll Glacier, Bennett Island, De Long Islands, Siberian Arctic  

NASA Astrophysics Data System (ADS)

Rapid environmental change has been observed in the De Long Islands, Siberian Arctic, where warming has extensively occurred over the area. To quantitatively evaluate glaciological changes since the 1980s, the climate, mass balance, and the equilibrium line altitude (ELA) of Toll Glacier on Bennett Island were analyzed. Air temperature has increased and solid precipitation has decreased since the 1960s, especially after 2000. The cumulative mass balance of Toll Glacier has had a negative trend since the 1960s and reached approximately -20 m water equivalent (w.e.) in 2000, which is one of the largest changes in the Arctic. These changes are much larger than those in the west Russian Arctic. The warming trend is also correlated with the sea ice distribution in the Siberian Arctic and may lead to feedback effects that cause further Arctic warming.

Konya, Keiko; Kadota, Tsutomu; Yabuki, Hironori; Ohata, Tetsuo

2014-06-01

123

Melt trends above the equilibrium line of the Greenland Ice Sheet during the period of 2003-2012 (Invited)  

NASA Astrophysics Data System (ADS)

Warming in the Arctic has raised concern about the effects that increased fresh water input from Greenland and other ice caps into the oceans could have on sea level rise and on the thermohaline ocean circulation. Melt over the Greenland Ice Sheet (GIS) has been increasing steadily over the last 20 years, and although mass loss has been limited to the margins, the departure from the 1979-1999 mean melt rate in the last decade has become particularly large in the interior. This has resulted in variable conditions that make ice volume changes derived from remote sensing measurements difficult to interpret, and an equilibrium line that is continuously migrating. We present a combined analysis of field measurements obtained in western Greenland and results from the Regional Atmospheric Climate Model to estimate trends in melt and refreezing rates over the interior of the Greenland ice sheet. The combined dataset show the evolution of melt intensity in regions with little or no meltwater runoff during the last 20 years. We estimated a threefold increase in the total area experiencing significant melt in the last decade, and an amount of refrozen meltwater larger than the total mass balance of the ice sheet. Conditions observed after the extreme melt event of July 2012 at and above the 2000 m elevation line contrast sharply with previous studies, and illustrate the current and future state of the Greenland interior if warming trends continue. We will discuss changes during the last decade in surface mass balance conditions, and the melting and refreezing processes occurring above the equilibrium line of the GIS. Additionally, we will summarize some implications these processes may have in estimating mass balance from altimetry techniques, and how in-situ data and models can help improving altimetry-derived results. The intensity of melt and the huge ice reservoirs found in the field are an indication that percolation facies are no longer just an interesting feature with no real relevance other than their effects in radar altimetry signals, but rather the result of an intense melting process of at least the same scale as the total mass imbalance of the GIS.

de la Peña, S.; Howat, I. M.; van den Broeke, M. R.; Price, S. F.; Nienow, P. W.; Mosley-Thompson, E. S.

2013-12-01

124

Proposed Glacier Bay Wilderness, Glacier Bay National Monument.  

National Technical Information Service (NTIS)

The National Park Service proposes to establish 2,052,700 acres as wilderness in Glacier Bay National Monument. The area contains rugged mountains; enormous complex glaciers; ice-sculptured fjords; and large areas of vegetation, displaying the entire spec...

1973-01-01

125

Temporal and spatial changes in Western Himalayan firn line altitudes from 1998 to 2009  

NASA Astrophysics Data System (ADS)

Understanding changes in glacier mass balance is important because it is indicative of changes in climate and the hydrologic cycle. The latter also has particular influence on people living near glaciers and/or glacier-fed rivers. The Western Himalayas remain one of the regions where recent changes in glacier mass balance are not well-known. The temporal and spatial changes in firn line altitudes are an indicator of equilibrium line altitudes and thus reflect changes in glacier mass balance. Here, we use Himalayan Landsat TM/ETM + data in July and August (the late summer melt season) to quantify changes in firn line altitudes from 1998 to 2009. We produced reflectance maps through radiometric calibration and atmospheric correction and use topographic correction to remove or reduce terrain or shadow effects. The real ‘surface albedo’ is obtained by narrowband-to-broadband (NTB) albedo conversion from the combined solar radiation. The firn line altitude was then extracted by combining the ‘surface albedo’ with pre-registered digital elevation model. The individual firn line altitude varies by region. The Western Himalayas display the largest range of firn line variability, where the firn line altitudes vary from 4840 m a.s.l. to 5770 m a.s.l. The individual glacier mean firn line altitude from 1998 to 2009 rose from 5072 ± 77 m a.s.l. to 5640 ± 74 m a.s.l. in the Western Himalayas. The mean firn line altitude increased from 1998 to 2009. The lowest mean recorded firn line altitude recorded was 5237 ± 166 m a.s.l. in 1998, whereas the highest was 5397 ± 135 m a.s.l. in 2000. We also observed a difference between the changes in fine line altitudes of northern and southern slopes of the western Himalayans, as the northern slope glaciers display a greater increase in firn line altitudes than the southern slope glaciers. In the southern slope, changes in firn line altitudes correlate with NCDC-NOAA temperature and precipitation data. This sustained increase of firn line altitudes and associated loss of glacier mass imply a persistent loss of stored freshwater in the Western Himalaya.

Guo, Zhongming; Wang, Ninglian; Kehrwald, Natalie M.; Mao, Ruijuan; Wu, Hongbo; Wu, Yuwei; Jiang, Xi

2014-07-01

126

Knik Glacier; Alaska, May 1979 monument and glacier survey  

USGS Publications Warehouse

From 1915, or earlier, to 1966, with the exception of 1963, Knik Glacier annually formed and released Lake George, the largest glacier-dammed lake in Alaska. Eleven geodetically controlled survey stations were defined in the basin, and 22 glacier surface altitudes were measured. This is the first effort in a continuing program whose goal is predicting the future behavior of Knik Glacier and Lake George. (Kosco-USGS)

Trabant, Dennis C.; Mayo, L. R.

1979-01-01

127

Jakobshavns Glacier drainage basin - A balance assessment  

NASA Technical Reports Server (NTRS)

Maximum and minimum estimates are made of the drainage basin feeding the Jakobshavns Glacier by using surface elevation maps derived from Seasat altimetry. Benson's (1962) net balance measurements are used to calculate the balance flow within the basin. Comparisons of the balance flux at the terminus with estimates of actual flux suggest the basin is in overall equilibrium or slightly thickening. This agrees with measurements along the nearby EGIG traverse. Balance velocities accelerate rapidly within 100 km of the coast. Farther upstream, balance velocities are consistent with both measured velocities along the EGIG traverse and calculated deformation velocities. It is estimated that Jakobshavns Glacier discharges between 4.8 and 7.6 percent of the annual net balance over Greenland and drains between 3.7 and 5.8 percent of the ice sheet area.

Bindschadler, R. A.

1984-01-01

128

Comparing In Situ Spectra and Multispectral Classifications of Glacier Surfaces  

NASA Astrophysics Data System (ADS)

Glaciers can be divided into distinct surface zones (or facies) such as new snow, firn, slush, and glacier ice, which can then be quantitatively linked to the mass balance state of a glacier. Due to similarities in reflective properties, persistent difficulty is had identifying the snow line and accumulation area rather than the more distinct glacier ice-firn line. Yet, it is the snow line rather than the firn line which provides a sensitive indicator of how a given year's climate influences a glacier. As small icecaps and glaciers contribute significantly to current sea level rise and will continue to do so in the coming decades, it would be highly beneficial to develop a technique which measures a glacier mass balance proxy - the glacier accumulation area ratio - using widespread, high resolution multispectral imagery. In situ glacier surface spectra (350-2300 nm) were measured on Midtre Lovénbreen (Svalbard) in August 2010 and Langjökull (Iceland) in August 2011 using an ASD field spectroradiometer. The full-spectrum reflectance measurements allow simulation of various airborne and spaceborne multispectral sensors including the Airborne Thematic Mapper, Landsat ETM+, MODIS or MERIS, and ESA's forthcoming Sentinel 2. Published studies have applied methods such as spectral band ratios, normalized indices, thresholding, principal component analysis, unsupervised classification, supervised classification, and spectral mixing analysis to classify glacier surfaces. The work presented here uses the collected in situ surface reflectance data to inform interpretation of ISODATA classification schemes of airborne and satellite multispectral imagery, can provide end member points for spectral mixing studies, and gives a starting point from which to further develop useful analysis strategies for remote imagery. Future research directions could integrate elevation and intensity data from airborne LiDAR campaigns. While spectra and classifications of airborne/satellite multispectral imagery match reasonably for Svalbard data, this is not the case between in situ measurements from Svalbard and imagery from Iceland. This paper will investigate not only the potential causes of differing spectral properties of glacier surfaces in Svalbard and Iceland, but also use the in situ spectra to evaluate classification techniques and inform more effective and reliable strategies for remotely measuring a glacier's accumulation area.

Pope, A.; Rees, G.; Willis, I. C.; Arnold, N. S.

2011-12-01

129

Glaciers of Greenland  

USGS Publications Warehouse

Landsat imagery, combined with aerial photography, sketch maps, and diagrams, is used as the basis for a description of the geography, climatology, and glaciology, including mass balance, variation, and hazards, of the Greenland ice sheet and local ice caps and glaciers. The Greenland ice sheet, with an estimated area of 1,736,095+/-100 km2 and volume of 2,600,000 km3, is the second largest glacier on the planet and the largest relict of the Ice Age in the Northern Hemisphere. Greenland also has 48,599+/-100 km2 of local ice caps and other types of glaciers in coastal areas and islands beyond the margin of the ice sheet.

edited by Williams, Richard S., Jr.; Ferrigno, Jane G.

1995-01-01

130

Iceland Glacier Recession 1973 to 2000, Glacier Terminus contrast emphasized  

NSDL National Science Digital Library

This animation shows glacier recesion at the Breidamerkurjokull glacier in Iceland. The data from 1973 is taken from Landsat 1 and the 2000 data is from Landsat 7. The Breidamerkurjokull glacier in Iceland has been measured by Landsat to be receding since 1973. The glacierologists in Iceland and here at Nasas Goddard Space Flight Center have measured the recession throughout the entire glacier and found different rates of recession in different areas. In genral, the glacier seems to be receding at about 2% annually. It is extremely controversial whether this recession is caused by global warming.

Perkins, Lori; Hall, Dorothy

2001-04-09

131

Global Trends in Glacial Cirque Floor Altitudes and Their Relationships with Climate, Equilibrium Line Altitudes, and Mountain Range Heights  

NASA Astrophysics Data System (ADS)

Glacial erosion at the base of cirque headwalls and the creation of threshold slopes above cirque floors may contribute to the 'glacial buzzsaw' effect in limiting the altitude of some mountain ranges. Since glacial extent and therefore glacial erosion rate depends on the equilibrium line altitude (ELA) of a region, the altitude of cirque formation should be a function of the ELA. Several regional studies have shown that cirque floors form at an altitude approximating average Quaternary ELAs in some mountain ranges, but a global correlation has not yet been demonstrated. We examined the correlation between cirque altitudes and global ELA trends by compiling existing and new cirque altitude and morphometry data from > 30 mountain ranges at a wide range of latitudes. Where available, we calculate or present the average cirque altitude, relief, and latitude. We compared these altitudes to both the global East Pacific ELA and local ELAs where available. For the locations analyzed, the majority of average cirque altitudes fall between the Eastern Pacific modern and LGM ELAs, and mountain range height is typically limited to < 600 m above that altitude. This evidence supports the hypothesis that cirque formation is dependent upon the ELA, and that cirques likely form as a result of average, rather than extreme, glacial conditions. Furthermore, the correlation between cirque altitude and ELA, along with the restricted window of relief, implies that cirque formation is a factor in limiting peak altitude in ranges that rise above the ELA.

Mitchell, S. G.; Humphries, E.

2013-12-01

132

Five 'Supercool' Icelandic Glaciers  

NASA Astrophysics Data System (ADS)

Sediment entrainment by glaciohydraulic supercooling has recently been demonstrated as an effective process at Matanuska glacier, Alaska. Although subfreezing meltwater temperatures have been recorded at several Alaskan glaciers, the link between supercooling and sediment accretion remains confined to Matanuska. This study presents evidence of glaciohydraulic supercooling and associated basal ice formation from five Icelandic glaciers: Skeidarárjökull, Skaftafellsjökull, Kvíárjökull, Flaájökull, and Hoffellsjökull. These observations provide the best example to-date of glaciohydraulic supercooling and related sediment accretion outside Alaska. Fieldwork undertaken in March, July and August 2001 confirmed that giant terraces of frazil ice, diagnostic of the presence of supercooled water, are forming around subglacial artesian vents. Frazil flocs retrieved from these vents contained localised sandy nodules at ice crystal boundaries. During periods of high discharge, sediment-laden frazil flocs adhere to the inner walls of vents, and continue to trap suspended sediment. Bands of debris-rich frazil ice, representing former vents, are texturally similar to basal ice exposures at the glacier margins, implying a process-form relationship between glaciohydraulic freeze-on and basal ice formation. It is hypothesised that glaciohydraulic supercooling is generating thick sequences of basal ice. Observations also confirm that in situ melting of basal ice creates thick sedimentary sequences, as sediment structures present in the basal ice can be clearly traced into ice-marginal ridges. Glaciohydraulic supercooling is an effective sediment entrainment mechanism at Icelandic glaciers. Supercooling has the capacity to generate thick sequences of basal ice and the sediments present in basal ice can be preserved. These findings are incompatible with established theories of intraglacial sediment entrainment and basal ice formation; instead, they concur with, and extend, the current model of Matanuska-type glaciohydraulic supercooling. This work adds a new dimension to the understanding of debris entrainment in temperate glaciers.

Knudsen, O.; Roberts, M. J.; Roberts, M. J.; Tweed, F. S.; Russell, A. J.; Lawson, D. E.; Larson, G. J.; Evenson, E. B.; Bjornsson, H.

2001-12-01

133

Glaciers and Icebergs  

NSDL National Science Digital Library

This lesson plan is part of the DiscoverySchool.com lesson plan library for grades 6-8. It focuses on glaciers and icebergs, specifically, glacial scraping and landforms left behind by glaciers, and information about icebergs in the oceans. Students do a lab simulating glacial scouring. It includes objectives, materials, procedures, discussion questions, evaluation ideas, extensions, suggested readings, and vocabulary. There are videos available to order which complement this lesson, an audio-enhanced vocabulary list, and links to teaching tools for making custom quizzes, worksheets, puzzles and lesson plans.

Weisel, Frank

134

Svalbard surging glacier landsystems  

NASA Astrophysics Data System (ADS)

The percentage of Svalbard glaciers thought to be of surge-type is somewhere between 13-90% according to different sources variously based on statistical analysis and observations of diagnostic glaciological and geomorphological features, e.g. looped moraines. Developing a better understanding of which of these figures, if either, is most realistic is important in the context of glacier dynamics and related contributions of small glaciers and ice caps to sea level change in the immediate future. We present detailed geomorphological assessments of the margins of several known surge-type glaciers in Svalbard in order to update and improve the existing framework by which they are identified, and to provide a foundation for future reassessments of the surge-type glacier population based on distinct landform-sediment assemblages. Three landsystems are proposed: (1) Surges of small valley glaciers produce a prominent ice-cored latero-frontal moraine at their surge maximum and are characterised by an inner zone of ice stagnation terrain (hummocky topography, kettle lakes, debris flows) with no or only very few poorly-defined bedforms (crevasse squeeze ridges, eskers and flutes) and no recessional moraines. Many of these glaciers may have surged in the past but show no signs that they have the capability to do so again in the future. (2) Larger land-terminating glaciers, often with several tributaries, typically produce a push moraine complex which contains evidence for multiple advances, as identified from ridge-meltwater channel relationships. The inner zone often contains a large lagoon, partly dammed by the push moraine complex, and widespread ice stagnation terrain. Crevasse squeeze ridges, eskers and flutes are well-defined but small and limited in number and distribution. (3) Surges of large tidewater glaciers produce distinctive, often multi-generational, landform assemblages both in submarine and lateral terrestrial positions. The well-preserved submarine record is characterised by large cross-fjord push moraines of fjord floor sediments with lobe-shaped debris flows on their distal slope, glacial lineations, dense rhombohedral networks of crevasse squeeze ridges, and eskers. Annual push moraines associated with the quiescent phase are also observed and are unique to the submarine record. The terrestrial record consists of large lateral moraine systems alongside the fjord which contain outer push ridges composed of shallow marine sediments and an inner zone of ice stagnation terrain. Eskers, flutes and large, sharp-crested crevasse fill ridges in dense networks are superimposed on this inner zone; the latter are similar in character to their submarine counterparts but typically higher. We suggest that these three landsystems broadly characterise the geomorphology of the vast majority of known Svalbard surge-type glaciers and may allow previously unknown surge-type glaciers to be identified, both in the field and from aerial photographs and sea floor imagery.

Lovell, Harold; Benn, Douglas; Lukas, Sven; Flink, Anne

2014-05-01

135

Glacier Instability, Rapid Glacier Lake Growth and Related Hazards at Belvedere Glacier, Macugnaga, Italy  

NASA Astrophysics Data System (ADS)

Starting in summer 2000, Belvedere Glacier, near Macugnaga, Italian Alps, developed an extraordinary change in flow, geometry and surface appearance. A surge-type flow acceleration started in the lower parts of the Monte-Rosa east face, leading to strong crevassing and deformation of Belvedere Glacier, accompanied by bulging of its orographic right margin. In September 2001, a small supraglacial lake developed on the glacier. High water pressure and accelerated movement lasted into winter 2001/2002. The ice, in places, started to override moraines from the Little Ice Age. In late spring and early summer 2002, the supraglacial lake grew at extraordinary rates reaching a maximum area of more than 150'000 m2 by end of June. The evolution of such a large supraglacial lake, a rather unique feature in the Alps, was probably enabled by changes in the subglacial drainage system in the course of the surge-like developments with high water pressure in the glacier. At the end of June, an enhanced growth of the lake level with a rise of about 1 m per day was observed such that the supraglacial lake became a urgent hazard problem for the community of Macugnaga. Emergency measures had to be taken by the Italian Civil Protection. The authors thereby acted as the official expert advisers. Temporal evacuations were ordered and a permanent monitoring and alarm system was installed. Pumps with a maximum output of 1 m3/s were brought to the lake. Bathymetric studies yielded a maximum lake depth of 55 m and a volume of 3.3 millions of cubic meters of water. Aerial photography of 1995, 1999, September 2001 and October 2001 was used to calculate ice flow velocities and changes in surface altitude. Compared to the period of 1995 to 1999, the flow accelerated by about five times in 2001 (max. speeds up to 200 m/yr). Surface uplift measured was about 10-15 m/yr. The results of the photogrammetric studies were used to evaluate different possible lake-outburst scenarios, in particular overtopping and failure of ice dam with catastrophic subglacial drainage. In consideration of the current bathymetric studies and ice thickness measurements from the 1980ies, it was assumed that the floatation equilibrium was possibly reached by end of June. In case of an ice dam, the maximum discharge of a related subglacial drainage was estimated at 200 m3/s, probably involving a large debris flow. Extension and nature of thermokarst processes of the lake/ice interface are currently studied by repeated bathymetric measurements and adaption of corresponding models. In July/August 2002, geodetic ice flow velocity measurements showed that the enhanced flow velocities have decreased probably indicat ing the end of the surge-like movement. In conclusion, the developments at Macugnaga are an excellent example illustrating the need for inte grated hazard assessments in consideration of complex process chains. The current situation requires studies on different aspects, such as rock instabilities, glacier dynamics and hydrology, geomorphody namics, and mitigation-construction planning.

Huggel, C.; Kaeaeb, A.; Haeberli, W.; Mortara, G.; Chiarle, M.; Epifani, F.

2002-12-01

136

Changing Planet: Melting Glaciers  

NSDL National Science Digital Library

This NBC Learn video features climate scientists doing their research on Mt. Kilimanjaro to study the climate of the past. The scientists put the recently observed changes on the glacier into perspective by comparing past climate fluctuations, stressing that the current observed rate of change is unprecedented.

Planet, Nbc L.; Universe, Windows T.

137

Gifts of the Glaciers  

NSDL National Science Digital Library

This website highlights the glacial formation of the Great Lakes: - Lake Superior, Lake Huron, Lake Michigan, Lake Erie and Lake Ontario. This site provides photos and descriptions of the lakes and how they formed by the glaciers thousands of years ago.

Wittman, Stephen

1998-04-01

138

Melting Glaciers Threaten Peru  

NSDL National Science Digital Library

Thousands of people in the Andes mountains of Peru are having their lives affected in both a practical and cultural way by climate change, which is causing the region's glaciers to melt. This document explores the causes of the glacial melt and its impacts on the local cultures.

2003-10-09

139

Taking a Glacier's Pulse  

NSDL National Science Digital Library

This article profiles Dr. Leigh Stearns, a research scientist with the National Science Foundation's Science and Technology Center for Remote Sensing of Ice Sheets (CReSIS) and Assistant Professor in Geology at the University of Kansas who studies glaciers in Greenland.

Landis, Carol

140

Glacier Goo Erosion Experiments  

NSDL National Science Digital Library

Using a glacier proxy, students design an experiment to connect glacial erosion with glacial flow. Students choose from a variety of materials, determined what question they want their experiment or experiments to answer, design the procedure, test the experiment, and write up a lab report on the experiment.

Headley, Rachel

141

Variable glacier response to atmospheric warming, northern Antarctic Peninsula, 1988-2009  

NASA Astrophysics Data System (ADS)

The northern Antarctic Peninsula has recently exhibited ice-shelf disintegration, glacier recession and acceleration. However, the dynamic response of land-terminating, ice-shelf tributary and tidewater glaciers has not yet been quantified or assessed for variability, and there are sparse data for glacier classification, morphology, area, length or altitude. This paper firstly classifies the area, length, altitude, slope, aspect, geomorphology, type and hypsometry of 194 glaciers on Trinity Peninsula, Vega Island and James Ross Island in 2009 AD. Secondly, this paper documents glacier change 1988-2009. In 2009, the glacierised area was 8140±262 km2. From 1988-2001, 90% of glaciers receded, and from 2001-2009, 79% receded. This equates to an area change of -4.4% for Trinity Peninsula eastern coast glaciers, -0.6% for western coast glaciers, and -35.0% for ice-shelf tributary glaciers from 1988-2001. Tidewater glaciers on the drier, cooler eastern Trinity Peninsula experienced fastest shrinkage from 1988-2001, with limited frontal change after 2001. Glaciers on the western Trinity Peninsula shrank less than those on the east. Land-terminating glaciers on James Ross Island shrank fastest in the period 1988-2001. This east-west difference is largely a result of orographic temperature and precipitation gradients across the Antarctic Peninsula, with warming temperatures affecting the precipitation-starved glaciers on the eastern coast more than on the western coast. Reduced shrinkage on the western Peninsula may be a result of higher snowfall, perhaps in conjunction with the fact that these glaciers are mostly grounded. Rates of area loss on the eastern side of Trinity Peninsula are slowing, which we attribute to the floating ice tongues receding into the fjords and reaching a new dynamic equilibrium. The rapid shrinkage of tidewater glaciers on James Ross Island is likely to continue because of their low elevations and flat profiles. In contrast, the higher and steeper tidewater glaciers on the eastern Antarctic Peninsula will attain more stable frontal positions after low-lying ablation areas are removed, reaching equilibrium more quickly.

Davies, B. J.; Carrivick, J. L.; Glasser, N. F.; Hambrey, M. J.; Smellie, J. L.

2012-09-01

142

Influences of Climate Warming and Facility Management on Continuous Permafrost at Matterhorn Glacier Paradise, Zermatt, Swiss Alps.  

NASA Astrophysics Data System (ADS)

In many parts of the Alps, hazardous bedrock instabilities occur more often during the past 30 years. In many cases, permafrost degradation played a central role for instability (e.g. in 1987 the Val Pola rockslide, Italy). At other events, the role of permafrost degradation is more complex or unpredictable (e.g. in 1991 the Randa rockfall, Wallis, Swiss Alps). However, instabilities in perennially frozen bedrock may also be provoked by human influence. This is exemplarily shown at touristic facilities in the Alps. Human impact on permafrost is often underestimated, or even carelessly taken into account. The tourist resort Zermatt with more than 1.8 million overnight stays per year is located at 1600 m a.s.l. and is surrounded by high mountain ranges that often reach above 4000 m. The dry and sunny climate results in a high glacier equilibrium line thus leaving space for vast non-glaciated permafrost terrain. Numerous tourist facilities provide excellent logistics and easy access to permafrost sites, and the region is thus especially suitable for permafrost research. The infrastructure erected on permafrost consists of hotels, restaurants and mountain huts, station buildings of railways, funiculars, ski lifts and installations for artificial snowing the ski-runs. Some problems at these constructions due to permafrost degradation are shown. At the Matterhorn Glacier Paradise station at an altitude of 3820 meters, todays MAAT ranges between -6 °C and -8°C. During the construction of a tunnel in 1981 bedrock temperatures were at -12°C. Over the past 30 years, these bedrock temperatures have risen to -3 to -2°C, due to the heat brought into the tunnel by facilities and more than 490,000 visitors per year. In an elevator shaft, the temperature temporarily even rose above freezing point. Several new construction sites in continuous permafrost are described and new research data is presented. Another interesting site for permafrost and ice studies at Matterhorn Glacier Paradise is the glacier palace. Since summer 2011 this tourist attraction can be accessed via two elevators leading to an ice tunnel about 12 meters below the glaciers surface. Interesting thermal interactions exist between the permafrost bedrock that is in direct contact to the glacier ice. Great care has to be taken that there is no heat transfer from buildings to the glacier ice. Degradation of permafrost due to climatic change and human interference may become a serious threat to many installations of high mountain tourist centers. These facilities need appropriate management. Permafrost scientists may provide the necessary expertise for a proper hazard management.

King, Lorenz; Duishonakunov, Murataly; Imbery, Stephan

2014-05-01

143

Observed changes in glaciers in China  

NASA Astrophysics Data System (ADS)

Small glaciers are highly sensitive to changes in temperature and precipitation making them important indicators of regional climate change. At present, worldwide evaluation and prediction of glacier change are based on or aided by detailed observations from a small number of glaciers due to the inaccessibility of many glacier areas. Thus, the ground-based detailed glacier monitoring is of strong need and extremely important for glacier variability evaluation in both regional and global scale. China has 46,377 glaciers with a total area of 59,425 km2 and 5600 km3 in volume. Most of the glaciers have experienced rapid and accelerated shrinkage during last few decades. Although some of the glaciers have been investigated or observed through field expeditions and ground-based monitoring, the information of the glacier changes are poorly documented and relatively new to international community. This paper summarizes the observed changes of 9 reference glaciers in China: 1) Urumqi Glacier No. 1, located at the headwaters of Urumqi River in eastern Tianshan which is the best observed glacier in China; 2) Haxilegen Glacier No. 51, at Kuitun River in eastern Tianshan; 3) Qingbingtan Glacier No.72, located at the upper reach of Aksu River in the middle of Tianshan; 4) Miaoergou ice cap, located in the most east part of Tianshan; 5) Laohugou Glacier No. 12, located in Shule River in Qinlian Mountains; 6) Qi Yi glacier (also named as July First Glacier), located in Qinlian Mountains; 7) Dongkemadi Glacier located in Tianggula Mountains in Qinghai-Xizang (Tibetan) Plateau; 8) Rongbu Glacier at the north slop of Mt. Everest in Himalaya Mountains; and 9) Baishui Glacier No. 1, the only temperate glacier in this glacier group, located at Yulong Snow Mountain. Geographically those reference glaciers well represent the glaciers in the major high mountain system in western China. In addition, they have been monitored for 5-53 years and promise the best datasets for glacier changes in their regions.

Li, L.; Li, H.; Wang, F.

2012-04-01

144

Area and volume loss of the glaciers in the Ortles-Cevedale group (Eastern Italian Alps): controls and imbalance of the remaining glaciers  

NASA Astrophysics Data System (ADS)

A widespread loss of glacier area and volume was observed in the European Alps since the 1980s. Besides differences among various regions of the Alps, different responses characterize neighboring glaciers within the same region. In this study we describe the glacier changes in the Ortles-Cevedale group, the largest glacierized area in the Italian Alps. We characterize the drivers, the spatial variability and the main factors controlling the current loss of ice in this region by comparing glacier extents and snow covered areas derived from Landsat images acquired in 1987 and 2009. Glacier outlines were obtained from a band ratio with manual corrections and snow was classified from a near infrared image after topographic correction. The total glacierized area shrank by 23% in this period, with no significant changes in the mean altitude of the glaciers. The snowline is now 240 m higher than in the 1960s and 1970s. From the snow covered area of 2009, which fairly represents the extent of the accumulation areas over the last decade, we estimate that about 50% of the remaining glacier surfaces have to melt away to re-establish equilibrium with present climatic conditions. The average geodetic mass budget rate, calculated for 112 ice bodies by differencing two Digital Terrain Models (DTMs), ranged from -0.15 to -1.50 m w.e. a-1, averaging -0.68 m w.e. a-1. A correlation analysis of mass budgets vs. topographic variables confirmed the important role of the hypsometry in controlling area and volume loss of larger glaciers, while a higher variability characterizes smaller glaciers and glacierets, likely due to the increasing importance of local topo-climatic conditions.

Carturan, L.; Filippi, R.; Seppi, R.; Gabrielli, P.; Notarnicola, C.; Bertoldi, L.; Paul, F.; Rastner, P.; Cazorzi, F.; Dinale, R.; Dalla Fontana, G.

2013-01-01

145

Characteristics of Glacier Ecosystem and Glaciological Importance of Glacier Microorganisms  

NASA Astrophysics Data System (ADS)

Biological activity on glaciers has been believed to be extremely limited. However, we found various biotic communities specialized to the glacier environment in various part of the world, such as Himalaya, Patagonia and Alaska. Some of these glacier hosted biotic communities including various cold-tolerant insects, annelids and copepods that were living in the glacier by feeding on algae and bacteria growing in the snow and ice. Thus, the glaciers are simple and relatively closed ecosystems sustained by the primary production in the snow and ice. Since these microorganisms growing on the glacier surface are stored in the glacial strata every year, ice-core samples contain many layers with these microorganisms. Recently, it was shown that the snow algae in the ice-core are useful for ice core dating and could be new environmental signals for the studies on past_@environment using ice cores. These microorganisms in the ice core will be important especially in the studies of ice core from the glaciers of warmer regions, in which chemical and isotopic contents are often heavily disturbed by melt water percolation. Blooms of algae and bacteria on the glacier can reduce the surface albedo and significantly affect the glacier melting. For example, the surface albedo of some Himalayan glaciers was significantly reduced by a large amount of dark-colored biogenic material (cryoconite) derived from snow algae and bacteria. It increased the melting rates of the surfaces by as much as three-fold. Thus, it was suggested that the microbial activity on the glacier could affect the mass balance and fluctuation of the glaciers.

Kohshima, S.; Yoshimura, Y.; Takeuchi, N.; Segawa, T.; Uetake, J.

2004-12-01

146

Radar Sounding of Fast-Flowing Glaciers  

NASA Astrophysics Data System (ADS)

A major challenge in radio glaciology is sounding of fast-flowing glaciers such as Jakobshavn, Helheim, and Kangardlussuq in Greenland. Weak ice-bed echoes from fast-flowing glaciers are masked by off-vertical surface clutter. We need fine resolution both in the along-track and cross-track directions to reduce surface clutter. Synthetic Aperture Radar (SAR) techniques can be used to improve resolution in the along-track direction. However, SAR technique is not useful to synthesize a long-aperture in the cross-track direction unless data can be collected over a grid with a line spacing of about 1 m at 150 MHz. This is impossible to do with an airborne radar. We developed a high-sensitivity radar with array-processing capability in the cross-track direction to reduce clutter. The radar is designed to measure signals as low as 2 nV with a loop sensitivity of about 215 dB with peak power of about 800 W. We have successfully used this radar to obtain ice thickness and bed topography of three outlet glaciers. The radar soundings over Jakobshavn reveal a complex topography with a thickness of about 800 m at calving front and increasing to 2.7 km at about 40 km from the front. In this paper we will provide a brief review of the system that allowed first successful radar soundings of several fast-flowing glaciers, show sample results, and bed topography of a few glaciers.

Gogineni, S.; Leuschen, C.; Li, J.; Smith, L.; Plummer, J.; Hoch, A.

2008-12-01

147

Controlling mechanisms of Thwaites Glacier, West Antarctica  

NASA Astrophysics Data System (ADS)

Ice shelves play a major role in the stability of fast flowing ice streams in Antarctica, by exerting buttressing on inland ice and controlling the discharge of ice into the ocean. However, the mechanisms at work remain poorly understood and interactions between floating and grounded ice need to be better characterized in order to estimate the impact of climate change on the ice sheets. Thwaites glacier, in West Antarctica, features a small and heavily fractured ice shelf that provides limited back stress pressure on inland ice but is pinned on the eastern part on a prominent ridge. Thwaites glacier has maintained a consistently high velocity and negative mass balance for at least 20 years. Recent observations show a widening of its fast flowing area as well as a sustained acceleration since 2006 and a rapid retreat of its grounding line in the center of the glacier. The objective of this work is to characterize the dynamic response of Thwaites glacier to changes in its floating tongue on decadal to centennial time scales. To achieve this objective, we rely on high resolution ice flow modeling and grounding line dynamics using the Ice Sheet System Model (ISSM). We will focus on the complex interplay between the main floating tongue of Thwaites Glacier and its eastern, slow moving ice shelf, which is pinned down by an ice rumple. The speed of the eastern ice shelf is strongly affected by the coupling with the main floating ice tongue, which results in significant fluctuations in speed of the eastern ice shelf the formation of ice shelf cracks at the grounding line during acceleration phases. Our results show that ice rigidity at the junction between the eastern and western part of the shelf controls the dynamic regime of the ice shelf and suggest that Thwaites Glacier is likely to undergo substantial changes in the coming decades. This work was performed at the California Institute of Technology's Jet Propulsion Laboratory and the University of California Irvine under a contract with the National Aeronautics and Space Administration, Cryospheric Sciences and Modeling, Analysis and Prediction Programs

Seroussi, H. L.; Morlighem, M.; Rignot, E. J.; Larour, E. Y.; Mouginot, J.; Khazendar, A.

2013-12-01

148

The Lateglacial to Holocene transition as recorded by glacier fluctuations  

NASA Astrophysics Data System (ADS)

Examination of glacier associated records may contribute to a better understanding of the ice-continent-ocean-atmosphere interactions, since glacial deposits related to short-term temperature fluctuations, driven by climate change, might be preserved. Surface exposure dating (SED) of such glacial deposits can improve the chronology of climate records. The western Swiss Alps repeatedly hosted mountain glaciers during the Pleistocene, and even during the Last Glacial-Interglacial transition, with abundant stadial and interstadial transitions during the Lateglacial (e.g. Björck et al. 1998). In this study, the adjacent valleys of Belalp and Great Aletsch (catchment area is generally south facing) in the western Swiss Alps are investigated. The slow responding Great Aletsch valley glacier shows only one confirmed moraine ridge related to the Lateglacial (Egesen stadial) (Kelly et al. 2004). However, the rather fast responding Unnerbäch cirque (recent) glacier at the Belalp (a similarly exposed - and tributary - valley to the Great Aletsch valley), features 6 individual lateral-terminal moraine ridges related to Lateglacial and early Holocene times. In the Belalp valley, 22 erratic boulders from four out of six well-preserved moraines were sampled in order to establish a detailed chronological framework. From the Great Aletsch valley four samples (boulder and ice moulded bedrock) of the lateral moraine were collected for SED. Our 10Be exposure dates suggest a stabilization of the Great Aletsch moraine related to the Egesen advance in the beginning of the Younger Dryas, assuming that the ages of the oldest erratic boulders on a single moraine ridge are representative for the time of moraine stabilization (Putkonen & Swanson, 2003). According to our investigations on the right-lateral moraine and the dataset (recalculated from Kelly et al. 2004) for the left-lateral moraine, the Egesen stadial is the first preserved re-advance after the last deglaciation. In contrast, the glacier at the Belalp shows multiple advances during the Lateglacial to early Holocene. 10Be exposure age data suggest that the outer moraine ridge can be an advance older than the Egesen stadial and younger than the LGM. This is in concert with other Younger Dryas related glacial landsystems in Switzerland (reviewing the outer moraine ages e.g. Julier Pass, Ivy-Ochs et al. 1996, 2008). A large number of Lateglacial moraines have been identified and relative correlations on the basis of elevation, equilibrium line altitude (Gross et al. 1977; Maisch, 1987) and morphological characteristics have been established. Nevertheless, it remains important to refine the absolute chronology in order to put further temporal constraints on these relative frameworks. This allows the allocation of such absolutely dated deposits to distinguished cold phases (Preboreal oscillation, Younger Dryas, Aegelsee oscillation) thus underlining their potential significance in the context of regional, as well as global Lateglacial climate conditions. The 10Be exposure ages from an inner moraine ridge are in a good agreement with the recalculated previously published 10Be exposure ages from the Egesen moraines in the Alps. This suggests a synchronicity of the Egesen stadial in the European Alps at the end of the Younger Dryas cold phase. REFERENCES Björck, S., Walker, M. J.C., Cwynar, L.C., Johnson, S., Knudsen, K-L., Lowe, J. J. & Wohlfarth, B. (1998): An event stratigraphy for the Last Termination in the North Atlantic region based on the Greenland ice-core record: a proposal by the INTIMATE group. Journal of Quarternary Science, 13, 283-292. Gross, G., Kerschner, H. & Patzelt, G. (1977): Methodische Untersuchungen über die Schneegrenze in alpinen Gletschergebieten. Zeitschrift für Gletscherkunde und Glazialgeologie, 12, 223-251. Ivy-Ochs, S., Kerschner, H., Reuther, A., Preusser, F., Heine, K., Maisch, M., Kubik, P.W. & Schlüchter, C. (2008): Chronology of the last glacial cycle in the European Alps. Journal of Quaternary Science, 23, 559-573. Ivy-Ochs, S., Schlü

Schindelwig, I.; Akçar, N.; Kubik, P. W.; Schlüchter, C.

2009-04-01

149

Glacier National Park  

NSDL National Science Digital Library

This is the homepage of Glacier National Park. Users can access materials on the park's ecology and environment (plants and animals, biodiversity and air quality, geology, and fires), the culture and history of the park, park activities, and publications on naturalist activities. There are also video clips of park wildlife and scenery, a photo gallery, and live webcams. Links are provided to additional information, such as research activities on bear DNA and global climate change.

150

Comparison of Late Pleistocene and Modern Glacier Extents in Central Nepal Based on Digital Elevation Data and Satellite Imagery  

NASA Astrophysics Data System (ADS)

Late Pleistocene and modern ice extents in central Nepal are compared to estimate equilibrium line altitude (ELA) depressions. New techniques are used for determining the former extent of glaciers based on quantitative, objective geomorphic analyses of a ˜90-m resolution digital elevation model (DEM). For every link of the drainage network, valley form is classified as glacial or fluvial based on cross-valley shape and slope statistics. Down-valley transitions from glacial to fluvial form indicate the former limits of glaciation in each valley. Landsat Multispectral Scanner imagery for the same region is used to map current glacier extents. For both full-glacial and modern cases, ELAs are computed from the glacier limits using the DEM and a toe-to-headwall altitude ratio of 0.5. Computed ELA depressions range from 100-900 m with a modal value of ˜650 m and a mean of ˜500 m, values consistent with previously published estimates for the central Himalaya but markedly smaller than estimates for many other regions. We suggest that this reflects reduced precipitation, rather than a small temperature depression, consistent with other evidence for a weaker monsoon under full-glacial conditions.

Duncan, Christopher C.; Klein, Andrew J.; Masek, Jeffrey G.; Isacks, Bryan L.

1998-05-01

151

New climate change scenarios reveal uncertain future for Central Asian glaciers  

NASA Astrophysics Data System (ADS)

Central Asian water resources largely depend on (glacier) melt water generated in the Pamir and Tien Shan mountain ranges, located in the basins of the Amu and Syr Darya rivers, important life lines in Central Asia and the prominent water source of the Aral Sea. To estimate future water availability in the region, it is thus necessary to project the future glacier extent and volume in the Amu and Syr Darya river basins. The aim of this study is to quantify the impact of uncertainty in climate change projections on the future glacier extent in the Amu and Syr Darya river basins. The latest climate change projections provided by the fifth Coupled Model Intercomparison Project (CMIP5) generated for the upcoming fifth assessment report of the Intergovernmental Panel on Climate Change (IPCC) are used to model future glacier extent in the Central Asian region for the two large river basins. The outcomes are compared to model results obtained with the climate change projections used for the fourth IPCC assessment (CMIP3). We use a regionalized glacier mass balance model to estimate changes in glacier extent as a function of glacier size and projections of temperature and precipitation. The model is developed for implementation in (large scale) hydrological models, when the spatial model resolution does not allow for modelling of individual glaciers and data scarcity is an issue. Both CMIP3 and CMIP5 model simulations point towards a strong decline in glacier extent in Central Asia. However, compared to the CMIP3 projections, the CMIP5 projections of future glacier extent in Central Asia provide a wider range of outcomes, mostly owing to greater variability in precipitation projections among the latest suite of climate models. These findings have great impact on projections of the timing and quantity of water availability in glacier melt dominated rivers in the region. Uncertainty about the size of the decline in glacier extent remains large, making estimates of future Central Asian glacier extent and downstream water availability uncertain.

Lutz, A. F.; Immerzeel, W. W.; Gobiet, A.; Pellicciotti, F.; Bierkens, M. F. P.

2012-11-01

152

Glacier-specific elevation changes in western Alaska  

NASA Astrophysics Data System (ADS)

Deriving glacier-specific elevation changes from DEM differencing and digital glacier outlines is rather straight-forward if the required datasets are available. Calculating such changes over large regions and including glaciers selected for mass balance measurements in the field, provides a possibility to determine the representativeness of the changes observed at these glaciers for the entire region. The related comparison of DEM-derived values for these glaciers with the overall mean avoids the rather error-prone conversion of volume to mass changes (e.g. due to unknown densities) and gives unit-less correction factors for upscaling the field measurements to a larger region. However, several issues have to be carefully considered, such as proper co-registration of the two DEMs, date and accuracy of the datasets compared, as well as source data used for DEM creation and potential artefacts (e.g. voids). In this contribution we present an assessment of the representativeness of the two mass balance glaciers Gulkana and Wolverine for the overall changes of nearly 3200 glaciers in western Alaska over a ca. 50-year time period. We use an elevation change dataset from a study by Berthier et al. (2010) that was derived from the USGS DEM of the 1960s (NED) and a more recent DEM derived from SPOT5 data for the SPIRIT project. Additionally, the ASTER GDEM was used as a more recent DEM. Historic glacier outlines were taken from the USGS digital line graph (DLG) dataset, corrected with the digital raster graph (DRG) maps from USGS. Mean glacier specific elevation changes were derived based on drainage divides from a recently created inventory. Land-terminating, lake-calving and tidewater glaciers were marked in the attribute table to determine their changes separately. We also investigated the impact of handling potential DEM artifacts in three different ways and compared elevation changes with altitude. The mean elevation changes of Gulkana and Wolverine glaciers (about -0.65 m / year) are very similar to the mean of the lake-calving and tidewater glaciers (about -0.6 m / year), but much more negative than for the land-terminating glaciers (about -0.24 m / year). The two mass balance glaciers are thus well representative for the entire region, but not for their own class. The different ways of considering positive elevation changes (e.g. setting them to zero or no data) influence the total values, but has otherwise little impact on the results (e.g. the correction factors are similar). The massive elevation loss of Columbia Glacier (-2.8 m / year) is exceptional and strongly influences the statistics when area-weighting is used to determine the regional mean. For the entire region this method yields more negative values for land-terminating and tidewater glaciers than the arithmetically averaged values, but for the lake-calving glaciers both are about the same.

Paul, Frank; Le Bris, Raymond

2013-04-01

153

Remote sensing and GIS techniques for assessing decadal glacier changes in the Sikkim and Nepal Himalayas  

NASA Astrophysics Data System (ADS)

There is urgency in developing and testing remote sensing tools for developing extensive glacier datasets in high altitude areas of the Himalayas. Detailed information about glacier parameters is missing in many areas of the Himalayas, limiting our understanding of glacier fluctuations in this area. One of the biggest challenges in glacier mapping from spaceborne imagery is the delineation of debris-covered glacial tongues. The high Himalayas provide interesting challenges and unique opportunities for testing glacier mapping algorithms including debris cover. This research exploits the potential of visible, infrared and thermal ASTER data combined with SRTM elevation datasets for mapping glacier parameters (glacier area, elevations and snow lines) in the Himalayas. Multi-spectral classification techniques (ASTER ¾ band ratios and normalized differences NDSI and NDVI), single band thresholds, topographic characteristics (elevation and slope) and thermal information were combined in a decision tree to map clean ice and debris-covered ice. Snow lines were mapped from ASTER imagery acquired at the end of the ablation season, with instrument gains suitable for snow and ice. Ground control points (GCPs) collected in the field were used to assess the accuracy of the remote sensing-derived elevations. Changes in glacier parameters were derived by comparison with glacier datasets from older topographic maps and were linked with changes in climate parameters (precipitation and temperature).

Racoviteanu, A.

2009-04-01

154

Muir Glacier in Glacier Bay National Monument 1950  

USGS Multimedia Gallery

This August 1950 photo documents the significant changes that occurred during the 9 years between photographs A and B. Muir Glacier has retreated more than 2 miles, exposing Muir Inlet, and thinned 340 feet or more. However, it still is connected with tributary Riggs Glacier....

155

Denali Fault: Black Rapids Glacier  

USGS Multimedia Gallery

View eastward along Black Rapids Galcier. The Denali fault follows the trace of the glacier. These very large rockslides went a mile across the glacier on the right side. Investigations of the headwall of the middle landslide indicate a volume at least as large as that which fell, has dropped a mete...

2008-12-15

156

Glaciers and the Changing Earth  

NSDL National Science Digital Library

In this lesson, students will investigate how glaciers affect the landscape in the context of wondering how the rocks used in the stone walls first got into the ground. Following a directed reading and discussion, they will perform an activity in which they use ice cubes and a bucket of sand to simulate the effects of a glacier.

157

Malaspina Glacier, Alaska  

NASA Technical Reports Server (NTRS)

This image from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument on NASA's Terra satellite covers an area of 55 by 40 kilometers (34 by 25 miles) over the southwest part of the Malaspina Glacier and Icy Bay in Alaska. The composite of infrared and visible bands results in the snow and ice appearing light blue, dense vegetation is yellow-orange and green, and less vegetated, gravelly areas are in orange. According to Dr. Dennis Trabant (U.S. Geological Survey, Fairbanks, Alaska), the Malaspina Glacier is thinning. Its terminal moraine protects it from contact with the open ocean; without the moraine, or if sea level rises sufficiently to reconnect the glacier with the ocean, the glacier would start calving and retreat significantly. ASTER data are being used to help monitor the size and movement of some 15,000 tidal and piedmont glaciers in Alaska. Evidence derived from ASTER and many other satellite and ground-based measurements suggests that only a few dozen Alaskan glaciers are advancing. The overwhelming majority of them are retreating.

This ASTER image was acquired on June 8, 2001. With its 14 spectral bands from the visible to the thermal infrared wavelength region, and its high spatial resolution of 15 to 90 meters (about 50 to 300 feet), ASTER will image Earth for the next six years to map and monitor the changing surface of our planet.

ASTER is one of five Earth-observing instruments launched December 18,1999, on NASA's Terra satellite. The instrument was built by Japan's Ministry of Economy, Trade and Industry. A joint U.S./Japan science team is responsible for validation and calibration of the instrument and the data products. Dr. Anne Kahle at NASA's Jet Propulsion Laboratory, Pasadena, Calif., is the U.S. science team leader; Bjorn Eng of JPL is the project manager. ASTER is the only high-resolution imaging sensor on Terra. The Terra mission is part of NASA's Earth Science Enterprise, along-term research and technology program designed to examine Earth's land, oceans, atmosphere, ice and life as a total integrated system.

The broad spectral coverage and high spectral resolution of ASTER will provide scientists in numerous disciplines with critical information for surface mapping, and monitoring dynamic conditions and temporal change. Example applications are: monitoring glacial advances and retreats; monitoring potentially active volcanoes; identifying crop stress; determining cloud morphology and physical properties; wetlands evaluation; thermal pollution monitoring; coral reef degradation; surface temperature mapping of soils and geology; and measuring surface heat balance.

Size: 55 by 40 kilometers (34 by 25 miles) Location: 60.0 degrees North latitude, 140.7 degrees West longitude Orientation: North at top Image Data: ASTER bands 2, 3 and 4 Original Data Resolution: 15 meters (49 feet) Date Acquired: June 8, 2001

2001-01-01

158

Ice Flow and Strain Rate over Campbell Glacier in East Antarctica Observed from COSMO-SkyMed InSAR Images  

NASA Astrophysics Data System (ADS)

Campbell Glacier (74°25?S 164°22?E), originated from the end of Mesa Range in Victoria Land, East Antarctica, is a fast-flowing outlet glacier with length of about 110 km approximately. Campbell Glacier flows into northern Terra Nova Bay in Ross Sea and forms a seaward extension of the glacier named as Campbell Glacier Tongue. Campbell Glacier Tongue experiences gravitational ice flow as well as the vertical tidal deflection responding to tide variations. The ice beyond the hinge zone of Campbell Glacier Tongue is not free-floating but in a partially hydrostatic equilibrium state by 96%. In this study, we extracted surface displacement of Campbell Glacier from the 14 COSMO-SkyMed one-day tandem InSAR pairs obtained from January to November 2011. The topographic phases were removed by using ASTER Global Digital Elevation Model. As the DInSAR signals of Campbell Glacier Tongue contain both gravitational ice flow and the vertical tidal deflection, we removed the signals of tidal deflection by using the map of tide deflection rate of the glacier that was generated by Double-differential InSAR images. We then extracted one-day ice flow velocity and strain rate of Campbell Glacier. Campbell Glacier showed steady ice flow during the DInSAR observations. The maximum ice flow velocity was 0.7 m/day at the seaward edge of Campbell Glacier Tongue, while minimum ice flow velocity of 0.2 m/day was observed over the upper grounded part of the glacier. The crevasses on the grounded part of Campbell Glacier appeared near the tensile zone, while that disappeared at the compression zone. The moraines of the glacier migrated downstream along the shear zone. Campbell Glacier Tongue showed shear strain in general, from which we could investigate the nonlinear rotation of the glacier tongue. As a conclusion, we could accurately analyze the ice flow velocity and strain rate of Campbell Glacier from COSMO-SkyMed one-day tandem InSAR images by removing the signals of tidal deflection of the glacier. The glacier showed different flow velocity and strain rate along the streamline. By this research, we could conclude that the ice flow of outlet glacier from InSAR images should be estimated after removing the signals of tidal deflection of the glacier.

Han, H.; Lee, H.

2013-12-01

159

Seasonal and altitudinal variations in snow algal communities on an Alaskan glacier (Gulkana glacier in the Alaska range)  

NASA Astrophysics Data System (ADS)

Snow and ice algae are cold tolerant algae growing on the surface of snow and ice, and they play an important role in the carbon cycles for glaciers and snowfields in the world. Seasonal and altitudinal variations in seven major taxa of algae (green algae and cyanobacteria) were investigated on the Gulkana glacier in Alaska at six different elevations from May to September in 2001. The snow algal communities and their biomasses changed over time and elevation. Snow algae were rarely observed on the glacier in May although air temperature had been above 0?° C since the middle of the month and surface snow had melted. In June, algae appeared in the lower areas of the glacier, where the ablation ice surface was exposed. In August, the distribution of algae was extended to the upper parts of the glacier as the snow line was elevated. In September, the glacier surface was finally covered with new winter snow, which terminated algal growth in the season. Mean algal biomass of the study sites continuously increased and reached 6.3 × 10 ?l m-2 in cell volume or 13 mg carbon m-2 in September. The algal community was dominated by Chlamydomonas nivalis on the snow surface, and by Ancylonema nordenskiöldii and Mesotaenium berggrenii on the ice surface throughout the melting season. Other algae were less abundant and appeared in only a limited area of the glacier. Results in this study suggest that algae on both snow and ice surfaces significantly contribute to the net production of organic carbon on the glacier and substantially affect surface albedo of the snow and ice during the melting season.

Takeuchi, Nozomu

2013-09-01

160

Pine Island Glacier Calving (WMS)  

NSDL National Science Digital Library

The Pine Island Glacier is the largest discharger of ice in Antarctica and the continents fastest moving glacier. Even so, when a large crack formed across the glacier in mid 2000, it was surprising how fast the crack expanded, 15 meters per day, and how soon the resulting iceberg broke off, mid-November, 2001. This iceberg, called B-21, is 42 kilometers by 17 kilometers and contains seven years of glacier outflow released to the sea in a single event. This series of images from the MISR instrument on the Terra satellite not only shows the crack expanding and the iceberg breakoff, but the seaward moving glacial flow in the parts of the Pine Island Glacier upstream of the crack.

Perkins, Lori; Mitchell, Horace; Bindschadler, Bob; Diner, Dave

2005-03-09

161

Canadian Glacier Hydrology, 2003-2007  

Microsoft Academic Search

Glacier hydrological research in Canada from 2002-2007 continues to advance, driven by new observations of glacier retreat in all regions of the country. New observation networks have been formed to study various aspects of glacier change and linkages with the hydrological system. Small- scale studies of accumulation and melt processes on glacier surfaces continue, and are being used to parameterize

Sarah Boon; Gwenn E. Flowers; D. Scott Munro

2009-01-01

162

Recent behaviour of Slovenian glaciers  

NASA Astrophysics Data System (ADS)

Just two glaciers, below the peaks of Triglav (2864 m) and Skuta (2532 m), are persisting in Slovenian Alps, both on a relatively very low elevation. Their present surfaces do not exceed one hectare, thus we can speak only about two glacierets or very small glaciers. The Anton Melik Geographical Institute of the Scientific Research Centre at the Slovenian Academy of Sciences and Arts has regularly performed measurements since 1946. The size of the Triglav glacier, measured in 1946, was 14.4 hectares, and by the year 2012 the glacier had shrunk to a half of a hectare. The direct vicinity of the meteorological station on Mt. Kredarica makes possible an analysis of the dependency of the glacier's fluctuation on weather changes. Several methods of measuring have been applied. Since 1999 we have regularly performed photogrammetric measurements of the glacier, which render possible exact calculations of changes in the glacier's area and volume by individual years. In addition, we also performed georadar measurements in 2000 and 2013. Besides regular annual measurements performed at the end of melting seasons, the Triglav glacier has also been photographed monthly since 1976, from two fixed positions on Mt. Kredarica. In 2012, we performed aerial laser scanning (LIDAR) of the Triglav glacier. While for the last decade of the 20th century we reported that the Triglav glacier has not only retreated but literally disintegrated, in the first decade of the 21st century we can observe its stagnation. Due to the present concave form of the glacier's surface, snow remains on it late into summer, and since the year 2007, the ice of the lower part of the glacier has not been revealed even at the end of the melting season but has remained covered with the firn and snow of previous winters. Should such weather conditions continue and the amount of winter precipitation further increase, the remainder of the Triglav glacier will, though very small in size, continue to exist for next ten years or even more.

Gabrovec, Matej; Ferk, Mateja; Ortar, Jaka

2014-05-01

163

Polythermal glacier hydrology and ice flow dynamics  

NASA Astrophysics Data System (ADS)

Measurements at polythermal John Evans Glacier, Ellesmere Island, indicate strong links between spatial and temporal variations in subglacial hydrology and changes in surface velocity. Radio-echo sounding was used to determine ice thicknesses and bed topography, which allowed reconstruction of likely subglacial flow routing. Spatial patterns in residual bed reflection power (BRPr) enabled identification of warm and cold areas of the glacier bed. Within warm areas, the detailed pattern of BRPr was similar to the pattern of predicted subglacial water flow. Long-term ice motion measurements along a centre-line of 20 stakes indicate summer velocities slightly higher than overwinter levels in the accumulation area, but up to double overwinter levels in the ablation area. To assess the importance of basal motion in accounting for these patterns, expected ice deformation rates were calculated based on the likely range of ice temperatures and longitudinal coupling lengths at the glacier. In the accumulation and upper ablation areas, predicted motion due to ice deformation closely matched observations in both summer and winter. In the lower ablation area, basal motion was required in addition to ice deformation, with the largest basal velocities centred over the areas of predicted subglacial drainage. In addition, there was a rapid onset to summer basal motion directly below a set of moulins which provide the main route for surface meltwater to reach the glacier bed. Short-term ice motion measurements record three short-term (two- to four-day) high velocity events in summer 1998 and 1999, with velocities >100% above overwinter levels. These events were associated with periods of rapidly increasing meltwater input to the subglacial drainage system. The first events in 1998 and 1999 occurred at the start of the melt season at the transition from a snow covered to an ice covered surface. A second event in 1999 occurred midway through the summer as surface melting resumed following a cold period, and was strongly localised along a predicted subglacial drainage axis.

Copland, Luke

2001-07-01

164

Glacier and Ice Shelves Studies Using Satellite SAR Interferometry  

NASA Technical Reports Server (NTRS)

Satellite radar interferometry is a powerful technique to measure the surface velocity and topography of glacier ice. On ice shelves, a quadruple difference technique separates tidal motion from the steady creep flow deformation of ice. The results provide a wealth of information about glacier grounding lines , mass fluxes, stability, elastic properties of ice, and tidal regime. The grounding line, which is where the glacier detaches from its bed and becomes afloat, is detected with a precision of a few tens of meters. Combining this information with satellite radar altimetry makes it possible to measure glacier discharge into the ocean and state of mass balance with greater precision than ever before, and in turn provide a significant revision of past estimates of mass balance of the Greenland and Antarctic Ice Sheets. Analysis of creep rates on floating ice permits an estimation of basal melting at the ice shelf underside. The results reveal that the action of ocean water in sub-ice-shelf cavities has been largely underestimated by oceanographic models and is the dominant mode of mass release to the ocean from an ice shelf. Precise mapping of grounding line positions also permits the detection of grounding line migration, which is a fine indicator of glacier change, independent of our knowledge of snow accumulation and ice melting. This technique has been successfully used to detect the rapid retreat of Pine Island Glacier, the largest ice stream in West Antarctica. Finally, tidal motion of ice shelves measured interferometrically provides a modern, synoptic view of the physical processes which govern the formation of tabular icebergs in the Antarctic.

Rignot, Eric

1999-01-01

165

Glaciers and why they surge  

NASA Astrophysics Data System (ADS)

Researchers studying southern Alaska's Variegated Glacier believe they have found an explanation for why the 24-km-long ice mass, like other "surging" glaciers, periodically speeds up in its movement down valley. The surges, they propose, have to do with increases in water pressure beneath the glacier— the result of inhibited drainage at the base of the ice—that cause it to become more slippery and to flow faster.The Variegated Glacier, located northwest of Juneau near the village of Yakutat, is small among surging glaciers, but it has been one of the most extensively studied in this century. Every 18-20 years, it begins to accelerate its flow rate. The last time such a surge began was in January 1982. The glacier reached a peak velocity of 9 m per day by summertime, then returned to near normal flow rates of 1-2 m per day by early fall. It started up again in November 1982, however, and by the next spring was speeding along at 54 m per day. Then, in early July 1983, the surge stopped abruptly when large amounts of water drained out of the glacier.

1984-04-01

166

Quarternary History of Northern Cumberland Peninsula, Baffin Island, N. W. T., Canada: Part IV: Maps of the Present Glaciation Limits and Lowest Equilibrium Line Altitude for North and South Baffin Island.  

National Technical Information Service (NTIS)

Maps of the glaciation limit and lowest equilibrium line altitude (ELA) are presented for southern and northern Baffin Island. The glaciation limit was determined by the 'summit method'; the ELAs were determined by assuming a steady state accumulation are...

G. H. Miller J. T. Andrews

1971-01-01

167

Re-establishment of long-term glacier monitoring in Kyrgyzstan and Uzbekistan, Central Asia  

NASA Astrophysics Data System (ADS)

Glacier mass balance is an important indicator of climate change. The internationally recommended multi-level strategy for monitoring mountain glaciers combines in-situ measurements (mass balance, front variations) with remote sensing (inventories) and numerical modelling. This helps to bridge the gap between detailed local process-oriented studies and global coverage. Several glaciers in Central Asia, i.e. Abramov and Golubina Glacier were some of the most important reference glaciers in the world-wide glacier monitoring program representing important mountain ranges, such as the Pamir-Alay and the Tien Shan mountains. For these glaciers long-term series of more than 20 years are available. After the break-down of the former Soviet Union, most of the measurements were abandoned. In a cooperative effort between the countries Kyrgyzstan, Uzbekistan, Germany and Switzerland, the measurement series are currently re-initiated and will be continued within the next years. This study shows the measurement strategy and network, and discusses new installations, which have been set up at Abramov in summer 2011 and Golubina Glacier in summer 2010. The research strategy is composed of three main components. The first component is based on mass balance measurements using the glaciological method, the second relies on snow line observations with installed automatic cameras taking several pictures per day in order to document the snow line evolution on the glaciers during the summer months. The third is the application of a mass balance model driven by a nearby automatic weather station. The advantage of this strategy is that the three different components can be used to test them against each other, or to use them for calibration purposes. A second objective of the re-established glacier monitoring programs is to reconstruct the mass balance for the time period, where no measurements are available. Continuous mass balance series for each glacier will be derived based on a well calibrated mass balance model.

Hoelzle, M.; Azisov, E.; Barandun, M.; Hagg, W.; Huss, M.; Kriegel, D.; Machguth, H.; Mandychev, A.; Merkushkin, A.; Moldobekov, B.; Schöne, T.; Thoss, H.; Vorogushyn, S.; Zemp, M.

2012-04-01

168

Mass balance model parameter transferability on a tropical glacier  

NASA Astrophysics Data System (ADS)

The mass balance and melt water production of glaciers is of particular interest in the Peruvian Andes where glacier melt water has markedly increased water supply during the pronounced dry seasons in recent decades. However, the melt water contribution from glaciers is projected to decrease with appreciable negative impacts on the local society within the coming decades. Understanding mass balance processes on tropical glaciers is a prerequisite for modeling present and future glacier runoff. As a first step towards this aim we applied a process-based surface mass balance model in order to calculate observed ablation at two stakes in the ablation zone of Shallap Glacier (4800 m a.s.l., 9°S) in the Cordillera Blanca, Peru. Under the tropical climate, the snow line migrates very frequently across most of the ablation zone all year round causing large temporal and spatial variations of glacier surface conditions and related ablation. Consequently, pronounced differences between the two chosen stakes and the two years were observed. Hourly records of temperature, humidity, wind speed, short wave incoming radiation, and precipitation are available from an automatic weather station (AWS) on the moraine near the glacier for the hydrological years 2006/07 and 2007/08 while stake readings are available at intervals of between 14 to 64 days. To optimize model parameters, we used 1000 model simulations in which the most sensitive model parameters were varied randomly within their physically meaningful ranges. The modeled surface height change was evaluated against the two stake locations in the lower ablation zone (SH11, 4760m) and in the upper ablation zone (SH22, 4816m), respectively. The optimal parameter set for each point achieved good model skill but if we transfer the best parameter combination from one stake site to the other stake site model errors increases significantly. The same happens if we optimize the model parameters for each year individually and transfer these combinations to the other year. We show that multi-site and multi-year analyses are crucial before extrapolating ablation modeling to larger glacier areas. So far tested surface albedo schemes and respective parameterizations can obviously not satisfyingly reproduce the dynamics of glacier surface conditions at our study site and new solutions to the problem have to be explored.

Gurgiser, Wolfgang; Mölg, Thomas; Nicholson, Lindsey; Kaser, Georg

2013-04-01

169

Evidence for soft-bedded, marine-terminating outlet glaciers in East Antarctica  

NASA Astrophysics Data System (ADS)

Dronning Maud Land (DML), East Antarctica, has been considerd less dynamic than many other areas in Antarctica. Here, we present evidence that questions this view. We report results of a radar survey carried out on the West Ragnhild Glacier (WRG): the longest and widest glacier in DML. It reveals that the glacier bed is smooth and low (~600 m b.s.l.) in its seaward 65 km becoming even lower toward in a deep valley further upstream. The grounding line lies well below sea level, which characterizes WRG as a marine terminating glacier. Moreover, across-flow radar profiles of the basin show little topographic controls on the glacier-outlet position. In the seaward part of the glacier (< 65 km away of the grounding line), very low roughness occurs at the bed-ice interface in both direction (across and along). Our interpretation indicates that this flat basin is continuously covered with sediments. Analysis of the radar power returned from the bed shows that the bed is smoother and water richer within ~40 km of the grounding line, so we conclude that most of the sediment basin is water-saturated and, therefore, acts as a soft bed and enhances the ice flow. We verified this hypothesis using a higher-order ice flow model. We modeled the ice deformation along the flow line and pointed out an increasing discrepancy between modeled and observed (by interferometry) surface velocities toward the grounding line. It shows that basal motion occurs only over the sediment basin, with magnitude increasing further downstream up to 75% of the total surface speed. These geographic settings make the glacier's grounding-line position unstable. As other outlet glaciers in DML have similar geographical settings, the inter-connected system of outlet glaciers and ice shelves in DML may be much more likely subject to a sudden change than previously thought.

Callens, Denis; Matsuoka, Kenichi; Steinhage, Daniel; Smith, Ben; Pattyn, Frank

2013-04-01

170

Physical sediment properties utilized to portray Holocene glacier activity from the distal glacier-fed lake Sørsendalsvatna, Western Norway  

NASA Astrophysics Data System (ADS)

Here we present a Holocene record of glacier activity as documented in physical sediment properties from the distal glacier-fed lake Sørsendalsvatna (918m asl), located 35 km inland from the coast in Western Norway. The up-valley cirque glacier Blåbreen has an altitudinal extent from 1420 to 960m asl, with a present mean equilibrium-line altitude (ELA) close to 1050m asl. Three cores were collected from Sørsendalsvatna in 2005 using a piston corer from a raft. Standard sedimentological and geochemical parameters such as loss-on-ignition (LOI), dry bulk density (DBD), magnetic susceptibility (MS), grain-size distribution (GS) and scanning x-ray fluorescence (XRF) were measured in all three cores. The amount of detrital input was further determined by means of visible reflectance spectroscopy (VIS-RS). Multivariate data sets were compared with each other by calculating the multivariate correlation coefficient (RV-coefficient), and the common signals of multivariate data sets were extracted by means of principle component analysis (PCA). The age-depth model is based on twelve 14C dates and was constructed by smoothing spline interpolation using the 'classical' age-modelling algorithm available in Clam.R. Uncertainties of the age-model are moderate (100 years) back to 8300 cal BP and increase to 400 years before 9500 cal BP. The geochemical elements Si, K, Ca, Ti, Fe and Sr have significant count rates as measured by an ITRAX core scanner. Count rates of different geochemical elements are in accordance with each other, and the only significant PC-axis explains 89% of the variance. Further LOI, DBD, MS and VIS-RS are highly correlated among each other and with the XRF data (RV= 0.95). Applying PCA to the combined data sets, we find one significant axis that explains 92% of the variance. Grain-size data, however, do not show any accordance with other sedimentological parameters (RV=0.28). LOI, DBD, MS, XRF and VIS-RS are interpreted as indicative of increased deposition of sediments derived from glacial abrasion. The common signal of these data sets was extracted by means of PCA and is interpreted to vary in concert with the changing glacier ELA. The ELA increased sharply between 9500 and 9300 cal BP. This increase is marked by a change in the sediments, from gray silty-clay to brown gyttja. Values remained constant between 9300 and 8300 cal BP followed by a pronounced decrease lasting until 7800 cal BP, with minimum values recorded around 8000 cal BP. This ELA lowering is most probably associated with the 8.2k Event recorded in Greenland ice cores, in Norway termed the Finse Event. The highest ELA during the Holocene was recorded between 7800 and 6000 cal BP followed by a decrease between 6000 and 5500 cal BP. The ELA was rather stable between 5500 and 3500 cal BP followed by a steady decrease lasting until 1500 cal BP where the sediment is again composed of gray silty-clay. During the last 1500 years the ELA seems rather stable again, showing the lowest values since the end of the early Holocene deglaciation. In Sørsendalsvatna, no clear signal of the 'Little Ice Age' is detectable, possibly due to a hiatus in the upper part of the cores.

Trachsel, M.; Bakke, J.; Nesje, A.

2011-12-01

171

Formation condition of debris-covered glaciers in the Bhutan Himalaya  

NASA Astrophysics Data System (ADS)

Debris-covered glaciers are widely distributed along the Himalayas. It is well known that insulation effect of debris mantle and heterogeneous topography make the response of the debris-covered glaciers to climate change complex. Furthermore, glacial lakes, which have often caused outburst floods and thus threatened Himalayan countries, are formed at the termini of debris-covered glaciers. It is little understood, however, what kinds of geomorphological and climatic environments determine the glacier termini as debris-covered or debris-free. In this study, we analyze remotely sensed satellite data to describe formation condition of debris-covered glaciers. We first delineated glaciers, debris-covered areas, and surrounding slopes using ALOS AVNIR-2, visible ortho-rectified images. We analyzed inclinations and aspects of the surrounding slopes using ASTER-GDEM by assuming that the debris mantle was supplies from the slope steeper than 40 degrees.We also estimated surface temperature distribution using thermal infrared data of ASTER because freeze-thaw activity on the bedrock should produce debris mantle. More than 1,200 glaciers in the Bhutan Himalaya including north-facing glaciers on the Tibetan side were delineated. Spatial analysis shows that the debris-covered glaciers have ten times larger area of steep slopes than the debris-free glaciers. Spatial distribution of surface temperature obtained from the nighttime ASTER TIR data shows a significant negative correlation with the altitude whereas daytime data shows no dependency on altitude. The surface exceeding 0 degrees Celsius is found on the south-facing steep slopes even in a winter season. It suggests that the more south-facing steep slope should have more active freeze-melt cycles and provide more debris onto glaciers. We also find a significant positive correlation among the areas of south-facing steep slopes and of debris-covered surface. In addition, the ablation areas of the south-facing debris-covered glaciers are fully covered by debris mantle, which seems to be supplied from the widely distributed south-facing steep slopes. On the other hand, the north-facing glaciers have elongated debris-covered areas along the flow lines of the glaciers, on which debris mantle seems to be supplied from very limited south-facing steep slopes within the glacier catchment. Our analysis suggest that the spatial distribution of south-facing steep slopes determines the extent and the shape of a debris-covered area of glaciers in the Bhutan Himalaya.

Nagai, H.; Fujita, K.; Nuimura, T.

2011-12-01

172

Terminus Geometry as Main Control on Outlet Glacier Velocity  

NASA Astrophysics Data System (ADS)

Ice flow velocities close to the terminus of major outlet glaciers of the Greenland Ice Sheet can vary on the time scale of years to hours. Observations at Jakobshavn Isbræ show that slowing in winter and speedup in spring are related to the formation and disintegration of a floating terminus, and that removal of 400 m long parts from the terminus in big calving events leads to immediate increase of glacier flow velocity. Such flow speed variations can be explained as the reaction to changes in terminus geometry with help of a 3D full-Stokes ice flow model on a fjord topography that is typical for Greenland outlet glaciers. Starting from an initial steady state geometry, parts of an initially 7 km long floating terminus are removed. Flow velocity increases everywhere up to 4 km upstream of the grounding line, and complete removal of the floating terminus leads to a doubling of flow speed. The model results conclusively show that the observed velocity variations of outlet glaciers is dominated by the terminus geometry, even in absence of friction or pinning of the floating terminus. Since terminus geometry is mainly controlled by calving processes and melting under the floating portion, changing ocean conditions most probably have triggered the recent geometry and velocity variations of Greenland outlet glaciers.

Lüthi, M. P.

2009-04-01

173

The sensitivity of flowline models of tidewater glaciers to parameter uncertainty  

NASA Astrophysics Data System (ADS)

Depth-integrated (1-D) flowline models have been widely used to simulate fast-flowing tidewater glaciers and predict future change because their computational efficiency allows for continuous grounding line tracking, high horizontal resolution, and a physically-based calving criterion, which are all essential to realistic modeling of tidewater glaciers. As with all models, the values for parameters describing ice rheology and basal friction must be assumed and/or tuned based on observations. For prognostic studies, these parameters are typically tuned so that the glacier matches observed thickness and speeds at an initial state, to which a perturbation is applied. While it is well know that ice flow models are sensitive to these parameters, the sensitivity of tidewater glacier models has not been systematically investigated. Here we investigate the sensitivity of such flowline models of outlet glacier dynamics to uncertainty in three key parameters that influence a glacier's resistive stress components. We find that, within typical observational uncertainty, similar initial (i.e. steady-state) glacier configurations can be produced with substantially different combinations of parameter values, leading to differing transient responses after a perturbation is applied. In cases where the glacier is initially grounded near flotation across a basal overdeepening, as typically observed for rapidly changing glaciers, these differences can be dramatic owing to the threshold of stability imposed by the flotation criterion. The simulated transient response is particularly sensitive to the parameterization of ice rheology: differences in ice temperature of ˜ 2 °C can determine whether the glaciers thin to flotation and retreat unstably or remain grounded on a marine shoal. Due the highly non-linear dependence of tidewater glaciers on model parameters, we recommend that their predictions are accompanied by sensitivity tests that take parameter uncertainty into account.

Enderlin, E. M.; Howat, I. M.; Vieli, A.

2013-06-01

174

The sensitivity of flowline models of tidewater glaciers to parameter uncertainty  

NASA Astrophysics Data System (ADS)

Depth-integrated (1-D) flowline models have been widely used to simulate fast-flowing tidewater glaciers and predict change because the continuous grounding line tracking, high horizontal resolution, and physically based calving criterion that are essential to realistic modeling of tidewater glaciers can easily be incorporated into the models while maintaining high computational efficiency. As with all models, the values for parameters describing ice rheology and basal friction must be assumed and/or tuned based on observations. For prognostic studies, these parameters are typically tuned so that the glacier matches observed thickness and speeds at an initial state, to which a perturbation is applied. While it is well know that ice flow models are sensitive to these parameters, the sensitivity of tidewater glacier models has not been systematically investigated. Here we investigate the sensitivity of such flowline models of outlet glacier dynamics to uncertainty in three key parameters that influence a glacier's resistive stress components. We find that, within typical observational uncertainty, similar initial (i.e., steady-state) glacier configurations can be produced with substantially different combinations of parameter values, leading to differing transient responses after a perturbation is applied. In cases where the glacier is initially grounded near flotation across a basal over-deepening, as typically observed for rapidly changing glaciers, these differences can be dramatic owing to the threshold of stability imposed by the flotation criterion. The simulated transient response is particularly sensitive to the parameterization of ice rheology: differences in ice temperature of ~ 2 °C can determine whether the glaciers thin to flotation and retreat unstably or remain grounded on a marine shoal. Due to the highly non-linear dependence of tidewater glaciers on model parameters, we recommend that their predictions are accompanied by sensitivity tests that take parameter uncertainty into account.

Enderlin, E. M.; Howat, I. M.; Vieli, A.

2013-10-01

175

Debris-covered glaciers during the LGM and Lateglacial at the eastern margin of the Alps  

NASA Astrophysics Data System (ADS)

We present the reconstruction of paleo-glaciers in the easternmost part of the Alps (Schneeberg mountain) with the main focus on sedimentology, chronology and glacial dynamics. The area is dominantly made up of limestone bedrock and hence characterized by steep slopes and cirques. Two juvenile moraine-systems can be deciphered based on geological mapping. The major system is characterized by an up to 60 m high latero-frontal dump moraine with a prominent breach-lobe moraine in a lateral position. It is regarded to represent the Last Glacial Maximum (LGM; Würm Pleniglacial). The other system is much smaller and was formed most probably during the Würm Lateglacial. The angular to subangular shape of the clasts and the abundant boulders on top of the ridges indicate a high portion of passive (Boulton, 1978) i.e. supraglacial and englacial transport of debris before deposition.Thus the model of a debris-covered glacier is favored to explain both landforms and as well the corresponding sediment facies. For the pleniglacial moraine such an assumption is backed by a low accumulation/ablation area ratio (AAR) of around 1:1 based on the reconstruction of the equilibrium line altitude (ELA) using the maximum elevation of lateral moraines (MELM; Lichtenecker, 1938). Furthermore as there is no indication of a former glacier snout glacio-fluvial processes should have played a limited role in sediment transport into the forefield. Such setting pinpoints to very cold-arid conditions, which are as well found in paleo-climate reconstructions of the eastern foreland (Frenzel et al. 1992). Boulton, G.S., 1978: Boulder shapes and grain-size distribution of debris as indicators of transport paths through a glacier and till genesis.- Sedimentology, 25, 773-799. Lichtenecker, N.,1938. Die gegenwärtige und die eiszeitliche Schneegrenze in den Ostalpen. In: Verhandlungen der III. Internationalen Quartär - Konferenz, Vienna, 1936, 141-147. Frenzel, B., Pecsi, M. & Velichko, A. A., 1992. Atlas of Paleoclimate and Paleoenvironments of the Northern Hemisphere: Late Pleistocene - Holocene. Geogr. Res. Institute, G. Fischer Verlag, Budapest-Stuttgart.

Seidl, Sabrina; Reitner, Jürgen M.; Wagreich, Michael

2013-04-01

176

Last glacial maximum climate based on cosmogenic 10Be exposure ages and glacier modeling for the head of Tashkurgan Valley, northwest Tibetan Plateau  

NASA Astrophysics Data System (ADS)

Fully understanding the timing and climate of Last Glacial Maximum (LGM) is still lack in the head of the Tashkurgan Valley, northwest Tibetan Plateau (TP). The recent improvements in cosmogenic 10Be exposure dating and glacier modeling present an opportunity to estimate the LGM climatic conditions. In the paper, we investigated the moraines and used the 10Be exposure dating on the moraine boulders to constrain the timing of the LGM, the Kuzigun glacial stage in the head of the Tashkurgan Valley. Then, we used a coupled mass-balance and ice-flow model to quantify the paleoclimate from past glacier extents constrained by mapped and dated Kuzigun glacial moraines in the area. We showed that the glaciers terminated at an elevation of 4100-4200 m asl during the Kuzigun glacial stage and the glacial stage occurred during or slightly before 15-23 ka, corresponding to the timing of the global LGM. The modeled mass balances indicated that present-day equilibrium line altitude (ELA) ranges from 5150 to 5250 m asl, and LGM ELA is between 4550 and 4600 m asl in the area, suggesting an ELA lowering of ˜600 m during the LGM. Model results suggested that the temperature during the LGM in the head of the Tashkurgan Valley is 5-8 °C colder than today, considering a 30-70% reduction in precipitation compared to today. The paleoclimate estimates are generally consistence with previous studies that showed the LGM climate was colder and drier than today on the TP.

Xu, Xiangke; Hu, Gang; Qiao, Baojin

2013-11-01

177

Transition of flow regime along a marine-terminating outlet glacier in East Antarctica  

NASA Astrophysics Data System (ADS)

We present results of a multi-methodological approach to characterize the flow regime of West Ragnhild Glacier, the widest glacier in Dronning Maud Land, Antarctica. A new airborne radar survey points to substantially thicker ice (>2000 m) than previously thought. With a discharge estimate of 13-14 Gt yr-1, West Ragnhild Glacier thus becomes of the three major outlet glaciers in Dronning Maud Land. Its bed topography is distinct between the upstream and downstream section: in the downstream section (<65 km upstream of the grounding line), the glacier overlies a wide and flat basin well below the sea level, while the upstream region is more mountainous. Spectral analysis of the bed topography also reveals this clear contrast and suggests that the downstream area is sediment covered. Furthermore, bed-returned power varies by 30 dB within 20 km near the bed flatness transition, suggesting that the water content at bed/ice interface increases over a short distance downstream, hence pointing to water-rich sediment. Ice flow speed observed in the downstream part of the glacier (~250 m yr-1) can only be explained through very low basal friction, leading to a substantial amount of basal sliding in the downstream 65 km of the glacier. All the above lines of evidence (sediment bed, wetness and basal motion) and the relatively flat grounding zone give the potential for West Ragnhild Glacier to be more sensitive to external forcing compared to other major outlet glaciers in this region, which are more stable due to their bed geometry (e.g. Shirase Glacier).

Callens, D.; Matsuoka, K.; Steinhage, D.; Smith, B.; Witrant, E.; Pattyn, F.

2014-05-01

178

Transition of flow regime along a marine-terminating outlet glacier in East Antarctica  

NASA Astrophysics Data System (ADS)

We present results of a~multi-methodological approach to characterize the flow regime of West Ragnhild Glacier, the widest glacier in Dronning Maud Land, Antarctica. A new airborne radar survey points to substantially thicker ice (> 2000 m) than previously thought. According to the new data, West Ragnhild Glacier discharges 13-14 Gt yr-1. Therefore, it is one of the three major outlet glaciers in Dronning Maud Land. Glacier-bed topography is distinct between the upstream and downstream section. In the downstream section (< 65 km upstream of the grounding line), the glacier overlies a wide and flat basin well below the sea level while the upstream region is more mountainous. Spectrum analysis of the bed topography reveals a clear contrast between these two regions, suggesting that the downstream area is sediment covered. The bed returned power varies by 30 dB within 20 km near the bed flatness transition, which suggests that water content at bed/ice interface increases over a short distance downstream, hence pointing to water-rich sediment. Ice flow speed observed in the downstream part of the glacier (~ 250 m yr-1) can only be explained if basal motion accounts for ~ 60% of the surface motion. All above lines of evidence (sediment bed, wetness and basal motion) and the relative flat grounding zone give the potential for West Ragnhild Glacier to be more sensitive to external forcing compared to other major outlet glaciers in this region which are more stable due to their bed geometry (e.g. Shirase Glacier).

Callens, D.; Matsuoka, K.; Steinhage, D.; Smith, B.; Pattyn, F.

2013-10-01

179

Mapping of subaqueous glacier topography in Greenland with multibeam sonars to document ice-ocean interactions  

NASA Astrophysics Data System (ADS)

Very few attempts have been made to map the submerged calving face of tidewater glaciers in the past. Here, we present results from the August 2012 and 2013 campaigns in West Greenland where we visited several glaciers in Atasund, Torssukataq, Uummannaq and Upernavik Fjords. We employ a low frequency multibeam sonar tilted to the side to image the side walls of the glacial fjords, including the submerged calving faces. The results reveal the true depth of the grounding line of these glaciers, which is typically unknown - or known with enormous uncertainties - from traditional ship soundings or from the mapping of glacier thickness, the general shape and slope of the submerged calving fronts, and the presence and spatial distribution of channels of subglacial water discharge that fuel high rates of ice face melting. By repeating the mapping over time on a few glaciers and compensating the data for ice motion, we are able to calculate calving rates and ice melt rates over periods of a few days and compare the ice melt production results with estimates derived from hydrographic surveys. In most examples, knowledge of the sea floor topography is the principal information retrieved from these surveys because it determines whether subsurface warm waters can access the glacier face, but the spatial imaging of the submerged calving face reveals spatial details about ice-ocean interactions that are fundamental to the process of ice melt and complex. Such mappings should be extended to other glaciers and eventually to all tidewater glaciers in Greenland.

Rignot, E. J.; Fenty, I. G.; Xu, Y.; Cai, C.; Aykutlug, E.; Dupont, T. K.

2013-12-01

180

Aletsch Glacier, Switzerland  

NASA Technical Reports Server (NTRS)

Aletsch Glacier, the largest glacier of Europe, covers more than 120 square kilometers (more than 45 square miles)in southern Switzerland. At its eastern extremity lies a glacierlake, Mdrjelensee (2,350 meters/7,711 feet above sea level). To the west rises Aletschhorn (4,195 meters/13,763 feet), which was first climbed in 1859. The Rhone River flows along the southern flank of the mountains.

This image was acquired on July 23, 2001 by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA's Terra satellite. With its 14 spectral bands from the visible to the thermal infrared wavelength region, and its high spatial resolution of 15 to 90 meters (about 50 to 300 feet), ASTER will image Earth for the next 6 years to map and monitor the changing surface of our planet. ASTER is one of five Earth-observing instruments launched December 18, 1999, on NASA's Terra satellite. The instrument was built by Japan's Ministry of Economy, Trade and Industry. A joint U.S./Japan science team is responsible for validation and calibration of the instrument and the data products.

The broad spectral coverage and high spectral resolution of ASTER will provide scientists in numerous disciplines with critical information for surface mapping, and monitoring dynamic conditions and temporal change. Example applications are: monitoring glacial advances and retreats; monitoring potentially active volcanoes; identifying crop stress; determining cloud morphology and physical properties; wetlands evaluation; thermal pollution monitoring; coral reef degradation; surface temperature mapping of soils and geology; and measuring surface heat balance.

Dr. Anne Kahle at NASA's Jet Propulsion Laboratory, Pasadena, California, is the U.S. Science team leader; Bjorn Eng of JPL is the project manager. The Terra mission is part of NASA's Earth Science Enterprise, a long-term research and technology program designed to examine Earth's land, oceans, atmosphere, ice and life as a total integrated system.

Size: 60 x 56 km (37.2 x 34.7 miles) Location: 46.5 deg. North lat., 8.0 deg. East long. Orientation: North at top Image Data: ASTER bands 1,2, and 3. Original Data Resolution: 15 m Date Acquired: July 23, 2001

2002-01-01

181

Holocene glacier history of Bjørnbreen and climatic reconstruction in central Jotunheimen, Norway, based on proximal glaciofluvial stream-bank mires  

NASA Astrophysics Data System (ADS)

Holocene variations of Bjørnbreen, Smørstabbtinden massif, west-central Jotunheimen are reconstructed from the lithostratigraphy of two alpine stream-bank mires flooded episodically by meltwater. The approach uses multiple sedimentological indicators (weight loss-on-ignition, mean grain size, grain-size fractions, bulk density, moisture content and magnetic susceptibility), an a priori model of overbank deposition of suspended glaciofluvial sediments, a detailed chronology based on 56 radiocarbon dates, and a Little Ice Age sedimentological analogue. Rapid, late-Preboreal deglaciation was indicated by immigration of Betula pubescens by 9700 cal. BP. An interval of at least 3000 years in the early Holocene when glaciers were absent was interrupted by two abrupt episodes of glacier expansion around the time of the Finse Event, the first at ca 8270-7900 cal. BP (Bjørnbreen I Event) and the second at ca 7770-7540 cal. BP (Bjørnbreen II Event). Neoglaciation began shortly before ca 5730 cal. BP with gradual build-up to the maximum of the Bjørnbreen III Event at ca 4420 cal. BP. Later maxima occurred at ca 2750 cal. BP (Bjørnbreen IV Event) and at 1300, 1260, 1060 and 790 cal. BP (all within the Bjørnbreen V Event). Glaciers were smaller than today and possibly melted away on several occasions in the late Holocene (ca 3950, 1410 and 750 cal. BP). Minor maxima also occurred at ca 660 and 540 cal. BP, within the late Mediaeval Warm Period and the early Little Ice Age, respectively. The Little Ice Age maximum was dated to 213±25 BP (ca 205 cal. BP). The relative magnitudes of the main glacier maxima were determined: Erdalen Event>Little Ice Age Event (Bjørnbreen VI)>Bjørnbreen I (Finse Event) ? Bjørnbreen II>Bjørnbreen V?Bjørnbreen IV>Bjørnbreen III. These episodic events of varying magnitude and abruptness were used in conjunction with an independent summer-temperature proxy to reconstruct variations in equilibrium-line altitude (ELA) and a Holocene record of winter precipitation. Since the Preboreal, ELA varied within a range of about 390 m, and winter precipitation ranged between 40 and 160% of modern values. Winter precipitation variations appear to have been the main cause of these century- to millennial-scale Holocene glacier variations.

Matthews, John A.; Berrisford, Mark S.; Quentin Dresser, P.; Nesje, Atle; Olaf Dahl, Svein; Elisabeth Bjune, Anne; Bakke, Jostein; John, H.; Birks, B.; Lie, Øyvind; Dumayne-Peaty, Lisa; Barnett, Catherine

2005-01-01

182

Modeling glacier beds in the Austrian Alps: How many lakes will form in future?  

NASA Astrophysics Data System (ADS)

Glacial retreat exposes landscapes with relief characteristics greatly differing from the former ice covered surfaces. If glacial retreat exposes natural basins capable of forming proglacial lakes, then the downstream hydrologic and geomorphic systems in such catchments will be significantly altered due to discharge modifications, sediment trapping, decoupling effects and long term sediment storage (e.g. Geilhausen et al. 2013). Further implications are related to hydropower management, tourism and natural hazards. Consequently, sound knowledge of present day glacier beds ("proglacial zones of tomorrow") and in particular the total number, locations and characteristics of overdeepenings are of importance. For Austria, however, this important information about significant future changes of high alpine regions is yet missing. An interdisciplinary research project is currently in preparation to close this gap. This paper presents results of a pilot study. We used a novel GIS-based approach (GlabTop, cf. Linsbauer et al. 2012) to compute approximate glacier beds in the Austrian Alps. GlabTop ('Glacier bed Topography') is based on an empirical relation between average basal shear stress and elevation range of individual glaciers and makes use of digital elevation models (DEM), glacier outlines and branch lines (i.e. a set of lines covering all important glacier branches). DEMs and glacier outlines were derived from the Austrian glacier inventory (1998) and branch lines were manually digitized. The inventory includes 911 glaciers of which 876 (96%) were considered and 35 were excluded due to size restrictions (< 0.01 km²) or insufficient DEM coverage. We found 165 overdeepenings (> 0.01 km²) with the potential of forming proglacial lakes when glacier retreat reveals the bed. The total area and volume of all overdeepenings is approx. 10 km² and 236 Mio m³ respectively and 33 lakes will be larger than 1 km³. A total glacier volume of 16 ± 5 km³ with an average ice thickness of 36 ± 11 m was calculated for 1998. Comparisons with geophysical surveys (13 GPR profiles) revealed that ice thickness is mostly within the ± 30 % model uncertainty range and locations of potential future lakes are robust. Future work will focus on further model validation and optimization. References: Geilhausen, M., Morche, D., Otto, J.-C. & L. Schrott (2013): Sediment discharge from the proglacial zone of a retreating Alpine glacier (Obersulzbachkees, Hohe Tauern, Austria). Zeitschrift für Geomorphologie Vol. 57, Suppl. 2:29-53. Linsbauer, A., Paul, F. & Haeberli, W. (2012): Modeling glacier thickness distribution and bed topography over entire mountain ranges with GlabTop: Application of a fast and robust approach. J. Geophys. Res. 117. F03007, doi:10.1029/2011JF002313.

Koehler, Dominik; Geilhausen, Martin; Linsbauer, Andreas

2014-05-01

183

An AEM investigation of the formation of precipitate-free zones in an AI-16 Wt Pct Ag alloy: Determination of equilibrium and metastable solvus lines  

NASA Astrophysics Data System (ADS)

Precipitation of the equilibrium y-phase at grain boundaries in an aged Al-16 wt pct (˜4.5 at. pct) Ag alloy is responsible for the formation of a solute depleted region, free of metastable Guinier-Preston (GP) zones, in the immediate vicinity of the grain boundary. Solute concentration profiles have been obtained across these grain boundary regions using Analytical Electron Microscopy (AEM) in thin foils of the alloy aged at low temperatures. The Ag concentrations at the grain boundary (between ? precipitates) and at the edge of the precipitate-free zone have been used to determine the solid solubility of Ag in Al (the ?/ (? + ?) solvus) and the metastable GP zone solvus line, respectively.

Merchant, Sailesh M.; Notis, Michael R.; Williams, David B.

1983-09-01

184

Columbia Glacier, Alaska, 1986-2011  

NASA Video Gallery

The Columbia Glacier in Alaska is one of many vanishing around the world. Glacier retreat is one of the most direct and understandable effects of climate change. The consequences of the decline in ...

185

Arctic polynya and glacier interactions  

NASA Astrophysics Data System (ADS)

Major uncertainties surround future estimates of sea level rise attributable to mass loss from the polar ice sheets and ice caps. Understanding changes across the Arctic is vital as major potential contributors to sea level, the Greenland Ice Sheet and the ice caps and glaciers of the Canadian Arctic archipelago, have experienced dramatic changes in recent times. Most ice mass loss is currently focused at a relatively small number of glacier catchments where ice acceleration, thinning and calving occurs at ocean margins. Research suggests that these tidewater glaciers accelerate and iceberg calving rates increase when warming ocean currents increase melt on the underside of floating glacier ice and when adjacent sea ice is removed causing a reduction in 'buttressing' back stress. Thus localised changes in ocean temperatures and in sea ice (extent and thickness) adjacent to major glacial catchments can impact hugely on the dynamics of, and hence mass lost from, terrestrial ice sheets and ice caps. Polynyas are areas of open water within sea ice which remain unfrozen for much of the year. They vary significantly in size (~3 km2 to > ~50,000 km2 in the Arctic), recurrence rates and duration. Despite their relatively small size, polynyas play a vital role in the heat balance of the polar oceans and strongly impact regional oceanography. Where polynyas develop adjacent to tidewater glaciers their influence on ocean circulation and water temperatures may play a major part in controlling subsurface ice melt rates by impacting on the water masses reaching the calving front. Areas of open water also play a significant role in controlling the potential of the atmosphere to carry moisture, as well as allowing heat exchange between the atmosphere and ocean, and so can influence accumulation on (and hence thickness of) glaciers and ice caps. Polynya presence and size also has implications for sea ice extent and therefore potentially the buttressing effect on neighbouring tidewater glaciers. The work presented discusses preliminary satellite observations of concurrent changes in the North Water and Nares Strait polynyas and neighbouring tidewater glaciers in Greenland and the Canadian Arctic where notable thinning and acceleration of glaciers have been observed. Also included is an outline of how these observations will fit into a much wider project on the topic involving ocean, atmosphere and sea ice modelling and short-term and longer-term in-situ measurements.

Edwards, Laura

2013-04-01

186

Glacier Mass Balance measurements in Bhutan  

NASA Astrophysics Data System (ADS)

Long-term glacier measurements are scarce in the Himalayas, partly due to lack of resources as well as inaccessibility of most of the glaciers. There are over 600 glaciers in Bhutan in the Eastern Himalayas, but no long-term measurements. However, such studies are an important component of hydrological modelling, and especially relevant to the proposed expansion of hydropower resources in this area. Glaciological studies are also critical to understanding the risk of jøkulhlaups or GLOFS (glacier lake outburst floods) from glaciers in this region. Glacier mass balance measurements have been initiated on a glacier in the Chamkhar Chu region in central Bhutan by the Department of Hydro-Met Services in co-operation with the Norwegian Water Resources and Energy Directorate. Chamkhar Chu is the site of two proposed hydropower plants that will each generate over 700 MW, although the present and future hydrological regimes in this basin, and especially the contribution from glaciers, are not well-understood at present. There are about 94 glaciers in the Chamkhar Chhu basin and total glacier area is about 75 sq. km. The glaciers are relatively accessible for the Himalayas, most of them can be reached after only 4-5 days walk from the nearest road. One of the largest, Thana glacier, has been chosen as a mass balance glacier and measurements were initiated in 2013. The glacier area is almost 5 sq. km. and the elevation range is 500 m (5071 m a.s.l. to 5725 m a.s.l.) making it suitable as a benchmark glacier. Preliminary measurements on a smaller, nearby glacier that was visited in 2012 and 2013 showed 1 m of firn loss (about 0.6 m w.eq.) over 12 months.

Jackson, Miriam; Tenzin, Sangay; Tashi, Tshering

2014-05-01

187

Analysis of time series of glacier speed: Columbia Glacier, Alaska  

USGS Publications Warehouse

During the summer of 1984 and 1985, laser measurements were made of the distance from a reference location to markers on the surface of the lower reach of Columbia Glacier, Alaska. The speed varies from 7 to 15 m/d and has three noteworthy components: 1) a low-frequency perturbation in speed with a time scale of days related to increased precipitation, 2) semidiurnal and diurnal variations related to sea tides, and 3) diurnal variations related to glacier surface melt. -from Authors

Walters, R. A.; Dunlap, W. W.

1987-01-01

188

Analysis of glacier facies using satellite techniques  

USGS Publications Warehouse

Landsat-derived reflectance is lowest for exposed ice and increases markedly at the transient snow line. Above the slush zone is a gradual increase in near-infrared reflectance as a result of decreasing grain-size of the snow, which characterizes drier snow. Landsat data are useful in measuring the areal extent of the ice facies, the slush zone within the wet-snow facies, the snow facies (combined wet-snow, percolation and dry-snow facies), and the respective position of the transient snow line and the slush limit. In addition, fresh snowfall and/or airborne contaminants, such as soot and tephra, can limit the utility of Landsat data for delineation of the glacier facies in some cases. -from Authors

Williams, Jr, R. S.; Hall, D. K.; Benson, C. S.

1991-01-01

189

Warm Oceans, Fast Glaciers: the connections  

Microsoft Academic Search

Over the last decade many outlet glaciers from the Greenland Ice Sheet have accelerated and thinned, and in a number of cases their termini have retreated. There is much in common from glacier to glacier that emerges as these changes are studied, yet the actual physical mechanisms remain unclear. One can show that the spatial patterns and timing of outlet

M. Truffer; M. A. Fahnestock; J. M. Amundson

2009-01-01

190

Tidal flexure of Jakobshavns Glacier, West Greenland  

Microsoft Academic Search

Jakobshavns Glacier, a floating outlet glacier on the West Greenland coast, was surveyed during July 1976. The vertical displacements of targets along two profiles perpendicular to the fjord wall bounding the north margin of the glacier were analyzed to determine the effect of flexure caused by tidal oscillations within the fjord. An analysis based on the assumption that vertical displacements

Craig S. Lingle; Terence J. Hughes; Ronald C. Kollmeyer

1981-01-01

191

Tidal Flexure of Jakobshavns Glacier, West Greenland  

Microsoft Academic Search

Jakobshavns Glacier, a floating outlet glacier on the West Greenland coast, was surveyed during July 1976. The vertical displacements of targets along two profiles perpendicular to the fjord wall bounding the north margin of the glacier were analyzed to determine the effect of flexure caused by tidal oscillations within the fjord. An analysis based on the assumption that vertical displacements

Craig S. Lingle; Terence J. Hughes; Ronald C. Kollmeyer

1981-01-01

192

Muir Glacier and Muir Inlet 1980  

USGS Multimedia Gallery

This ship-deck-based August 1980 photograph of Muir Glacier and Muir Inlet, Glacier Bay National Park and Preserve, St. Elias Mountains, Alaska, shows the nearly 200-ft-high retreating tidewater end of Muir Glacier with part of its face capped by a few angular pinnacles of ice, called séracs....

193

Get Close to Glaciers with Satellite Imagery.  

ERIC Educational Resources Information Center

Discusses the use of remote sensing from satellites to monitor glaciers. Discusses efforts to use remote sensing satellites of the Landsat series for examining the global distribution, mass, balance, movements, and dynamics of the world's glaciers. Includes several Landsat images of various glaciers. (TW)

Hall, Dorothy K.

1986-01-01

194

Flow velocities of Alaskan glaciers  

NASA Astrophysics Data System (ADS)

Our poor understanding of tidewater glacier dynamics remains the primary source of uncertainty in sea level rise projections. On the ice sheets, mass lost from tidewater calving exceeds the amount lost from surface melting. In Alaska, the magnitude of calving mass loss remains unconstrained, yet immense calving losses have been observed. With 20% of the global new-water sea level rise coming from Alaska, partitioning of mass loss sources in Alaska is needed to improve sea level rise projections. Here we present the first regionally comprehensive map of glacier flow velocities in Central Alaska. These data reveal that the majority of the regional downstream flux is constrained to only a few coastal glaciers. We find regional calving losses are 17.1?Gt?a-1, which is equivalent to 36% of the total annual mass change throughout Central Alaska.

Burgess, Evan W.; Forster, Richard R.; Larsen, Christopher F.

2013-07-01

195

Glacier sensitivity to climate change in the Nepalese Himalaya quantified using higher-order modelling  

NASA Astrophysics Data System (ADS)

Recent studies of glaciers in the eastern Himalaya have identified rapid changes in ice volume with small changes in climate indicating that these glaciers are highly sensitive to primary climate variables (e.g. daily variations in air temperature and monsoon precipitation). However, quantifying Himalayan glacier sensitivity to climate change is challenging due to: (1) a lack of information about how glaciological and geomorphological factors influence the balance of large debris-covered glaciers; (2) the local modification of meteorological variables by the interaction of high topography with regional atmospheric circulation systems; and (3) the simple representation of ice dynamics in many numerical glacier models which limits their usefulness in regions with steep terrain. To quantify the sensitivity of Himalayan glaciers to climate change we apply the integrated second-order shallow ice approximation (iSOSIA) [Egholm et al. 2011, Journal of Geophysical Research-Earth Surface] to large debris-covered glaciers on the southern slopes of Mt. Everest in the Khumbu Himal, Nepal. iSOSIA considers both the longitudinal and transverse stresses that drive mountain glacier flow in regions with steep terrain--a more suitable approach for Himalayan glaciers than those models based on approximations developed for shallow ice sheets. We apply iSOSIA at a 100-m resolution on a regular grid using a daily timestep to Nepalese glaciers including Khumbu, Ngozumpa and Lhotse. Our mass balance model development has focused on the dynamic representation of snow avalanching onto the glacier surfaces as this accounts for up to 75% of accumulation. We investigate Himalayan glacier sensitivities to primary climatological, glaciological and geological variables including air temperature, supraglacial debris cover, and catchment hypsometry. Furthermore, we aim to improve the representation of climate in glacier models for the Himalaya by testing a range of methods to describe these variables: (1) simple elevation-dependent rates for accumulation and ablation with empirical values for melt along a flow line beneath supraglacial debris; (2) climate-elevation relationships derived from local automatic weather stations in the Khumbu valley; and (3) 3-D surface energy balance calculations using regional meteorological data. Once we have described glacier-climate sensitivities in the Khumbu Himal, we will use these results to predict the likely magnitude and timescales of glacier mass loss under IPCC future climate change scenarios, and quantify the uncertainties associated with these predictions. Future work will consider: how glacier hydrology modifies variations in ice dynamics; how the spatial distribution of supraglacial debris modifies glacier balance sensitivity; how rock debris is transported within and on these glaciers; and how rates of rock debris delivery from hillslopes affects glacier balance and dynamics. Fieldwork in Nepal is planned for 2014 to collect data from debris-covered Khumbu Glacier with which to validate our numerical model.

Rowan, A. V.; Egholm, D. L.; Glasser, N. F.; Quincey, D. J.

2013-12-01

196

Recent Changes in Arctic Glaciers, Ice Caps, and the Greenland Ice Sheet: Cold Facts About Warm Ice  

NASA Astrophysics Data System (ADS)

One of the major manifestations of Arctic change can be observed in the state of balance of Arctic glaciers and ice caps and the Greenland ice sheet. These ice masses are estimated to contain nearly 3 million cubic kilometers of ice, which is more than six times greater than all the water stored in the Earth's lakes, rivers, and snow combined and is the equivalent of over 7 meters of sea level. Most of these ice masses have been shrinking in recent in years, but their mass balance is highly variable on a wide range of spatial and temporal scales. On the Greenland ice sheet most of the coastal regions have thinned substantially as melt has increased and some of its outlet glaciers have accelerated. Near the equilibrium line in West Greenland, we have seen evidence of summer acceleration that is linked to surface meltwater production, suggesting a relatively rapid response mechanism of the ice sheet change to a warming climate. At the same time, however, the vast interior regions of the Greenland ice sheet have shown little change or slight growth, as accumulation in these areas may have increased. Throughout much of the rest of the Arctic, many glaciers and ice caps have been shrinking in the past few decades, and in Canada and Alaska, the rate of ice loss seems to have accelerated during the late 1990s. These recent observations offer only a snapshot in time of the long-term behavior, but they are providing crucial information about the current state of ice mass balance and the mechanisms that control it in one of the most climatically sensitive regions on Earth. As we continue to learn more through a combination of remote sensing observations, in situ measurements and improved modeling capabilities, it is important that we coordinate and integrate these approaches effectively in order to predict future changes and their impact on sea level, freshwater discharge, and ocean circulation.

Abdalati, W.

2005-12-01

197

Glacier recession in Iceland and Austria  

NASA Technical Reports Server (NTRS)

It has been possible to measure glacier recession on the basis of Landsat data, in conjunction with comparisons of the magnitude of recession of a glacier margin with in situ measurements at fixed points along the same margin. Attention is presently given to the cases of Vatnajokull ice cap, in Iceland, and the Pasterze Glacier, in Austria, on the basis of satellite data from 1973-1987 and 1984-1990, respectively. Indications of a trend toward negative mass balance are noted. Nevertheless, while most of the world's small glaciers have been receding, some are advancing either due to local climate or the tidewater glacier cycle.

Hall, Dorothy K.; Williams, Richard S., Jr.; Bayr, Klaus J.

1992-01-01

198

Light Iceland Glacier Recession 1973 to 2000  

NSDL National Science Digital Library

This animation shows glacier recesion at the Breidamerkurjokull glacier in Iceland. The data from 1973 is taken from Landsat 1 and the 2000 data is from Landsat 7. The Breidamerkurjokull glacier in Iceland has been measured by Landsat to be receding since 1973. The glacierologists in Iceland and here at NASAs Goddard Space Flight Center have measured the recession throughout the entire glacier and found different rates of recession in different areas. In genral, the glacier seems to be receding at about 2% annually. It is extremely controversial whether or not this recession is caused by global warming.

Perkins, Lori; Hall, Dorothy

2001-04-09

199

Glacier recession in Iceland and Austria  

NASA Astrophysics Data System (ADS)

It has been possible to measure glacier recession on the basis of Landsat data, in conjunction with comparisons of the magnitude of recession of a glacier margin with in situ measurements at fixed points along the same margin. Attention is presently given to the cases of Vatnajokull ice cap, in Iceland, and the Pasterze Glacier, in Austria, on the basis of satellite data from 1973-1987 and 1984-1990, respectively. Indications of a trend toward negative mass balance are noted. Nevertheless, while most of the world's small glaciers have been receding, some are advancing either due to local climate or the tidewater glacier cycle.

Hall, Dorothy K.; Williams, Richard S., Jr.; Bayr, Klaus J.

1992-03-01

200

The effect of glaciers on streamflow variations.  

USGS Publications Warehouse

The effect of temperate glaciers on runoff variations is examined for the North Cascade Mountains of Washington State. An algorithm is presented that calculates the coefficient of variation of runoff for any arbitrary glacier cover. The results suggest that a minimum in year-to-year variation occurs for basins about 36% glacierized. On a month-to-month basis, maximum variation occurs in July and August for basins with less than 10% glacier cover but is a minimum for basins with glacier covers greater than 30%. -from Authors

Fountain, A. G.; Tangborn, W. V.

1985-01-01

201

The role of snowmelt and glacier melt on runoff in a glacierized catchment: a multi-tracer experiment  

NASA Astrophysics Data System (ADS)

The release of water as snowmelt and ice melt in high elevation catchments has significant social and economic impacts for population living in mountain areas. This is even more critical under the current conditions of glacier retreat as a consequence of global warming. Therefore, it is important to understand the role of ice and snow meltwater on runoff dynamics and groundwater recharge in glacierized environments. This task can be effectively accomplished by integrating isotopic and other tracers that are widely recognized as useful tools for the identification of the main water sources contributing to streamflow. In this work, we collected water samples from different sources in the Saldur catchment (Eastern Italian Alps). The catchment (area: 62 km², elevation range: 1600-3700 m a.s.l.) hosts a small glacier (2.8 km²) in its upper portion. Samples of rainfall, snow, snowmelt, glacier melt, stream water (main stream and tributaries) and spring water have been manually collected between April-October 2011 and April-November 2012 approximately on a monthly basis. Furthermore, 24-hour samplings with hourly collection frequency were performed at two cross sections during five melt-runoff events. The composition in stable water isotopes was determined by laser spectroscopy and mass spectrometry. Electrical conductivity (EC) and water temperature were measured in the field. Additionally, deuterium excess (DE) was computed for all samples based on the relationship between deuterium and 18-oxygen. The isotopic composition of rainfall and snow shows marked altitudinal and seasonal variations. A strong positive correlation is also evident in the relationship between DE of spring waters and elevation. Rainfall and snow samples fall perfectly on the Global Meteoric Water Line, revealing a predominant Atlantic origin of air masses producing precipitation in the study area. EC and water temperature linearly increase with the distance from the glacier snout, suggesting a decreasing influence of snow and glacier melt water (cold and little conductive) and an increasing contribution of non-glacierized areas moving downstream. Stream water shows a strong daily variability in isotopic composition and EC correlated well with discharge and air temperature, suggesting the relevant contribution of meltwater on runoff. Moreover, a seasonal trend is also observable in stream water and groundwater, with the most isotopically enriched and highest EC values found at low flow conditions (no melting periods), in early spring and late autumn. In agreement with these observations, end-member mixing analysis shows that summer precipitation plays a minor role on runoff temporal variability compared to glacier melt and snowmelt. Two- and three-component hydrograph separation for the summer melt-runoff events confirms the significant contribution of melting-event water (up to 73% for the upper station) and the importance of snowmelt and glacier melt (up to 37% and 28%, respectively) as water sources for streamflow at the daily scale in the study catchment. These results underline the critical role played by meltwater stored in glaciers and snow on water availability in mountain regions. Moreover, this works reveals the usefulness of a multi-tracer approach for the analysis of the main contributors to streamflow in glacierized catchments. Keywords: water stable isotopes, deuterium excess, electrical conductivity, snowmelt, glacier melt.

Penna, Daniele; Engel, Michael; Mao, Luca; Dell'Agnese, Andrea; Bertoldi, Giacomo; Comiti, Francesco

2013-04-01

202

Modeling energy and mass balance of Shallap Glacier, Peru  

NASA Astrophysics Data System (ADS)

We calculated the distributed surface mass and energy balance of Shallap Glacier, Cordillera Blanca, Peru (9° S, 77° W, 4700-5700 m a.s.l., ∼ 7 km2) on hourly time steps for two years (September 2006-August 2008) using a process-based model and meteorological measurements as input. Model parameter combinations were optimized against 21 temporal readings of 20 stakes in the ablation zone of the glacier. Uncertainty caused by model input parameters and parameterization schemes was estimated using a leave-one-out cross-validation scheme and yields values of root mean square deviation (RMSD) of surface height change < 1m (< 10% of the measured amplitude) for all stakes. With the best parameter combination (smallest RMSD) applied, the modeled annual surface mass balance of the glacier was -0.32 ± 0.4 m w.e. for September 2006-August 2007 and 0.51 ± 0.56 m w.e. for September 2007-August 2008. While the mass balance above 5000 m was similar in both years (? 0.35 ± 0.68 m w.e.) due to similar annual sums of solid precipitation, a difference of ∼ 2 ± 0.68 m w.e. was calculated for the lower parts of the glacier. This difference is associated with more frequent occurrence of higher snow line altitudes during the first year, which was mainly caused by a higher fraction of liquid precipitation due to higher mean air temperatures. As the net shortwave budget was found to be the main source for ablation throughout the year at Shallap Glacier, lower surface albedo caused by higher snow line altitudes explains most of the difference in modeled ablation and mass balance between the two years.

Gurgiser, W.; Marzeion, B.; Nicholson, L.; Kaser, G.; Ortner, M.

2013-08-01

203

Spatially heterogeneous wastage of Himalayan glaciers  

PubMed Central

We describe volumetric changes in three benchmark glaciers in the Nepal Himalayas on which observations have been made since the 1970s. Compared with the global mean of glacier mass balance, the Himalayan glaciers showed rapid wastage in the 1970s–1990s, but similar wastage in the last decade. In the last decade, a glacier in an arid climate showed negative but suppressed mass balance compared with the period 1970s–1990s, whereas two glaciers in a humid climate showed accelerated wastage. A mass balance model with downscaled gridded datasets depicts the fate of the observed glaciers. We also show a spatially heterogeneous distribution of glacier wastage in the Asian highlands, even under the present-day climate warming.

Fujita, Koji; Nuimura, Takayuki

2011-01-01

204

UV - GLACIER NATIONAL PARK MT  

EPA Science Inventory

Brewer 134 is located in Glacier NP, measuring ultraviolet solar radiation. Irradiance and column ozone are derived from this data. Ultraviolet solar radiation is measured with a Brewer Mark IV, single-monochrometer, spectrophotometer manufactured by SCI-TEC Instruments, Inc. of ...

205

Icebergs and Glaciers: Unit Outlines  

NSDL National Science Digital Library

This article assembles free resources from the Icebergs and Glaciers issue of the Beyond Penguins and Polar Bears cyberzine into a unit outline based on the 5E learning cycle framework. Outlines are provided for Grades K-2 and 3-5.

Fries-Gaither, Jessica

206

Numerical modelling of glacier systems  

Microsoft Academic Search

The aim of the project is to develop a scheme to model the dynamics of any given glacier system from the input data of bedrock distribution and accumulation or ablation (or balance) distribution as functions of time. The emphasis is on matching reality to provide a practical means of interpreting the history of change of an ice mass. The full

W. F. Budd; D. Jenssen

207

Mountain Glaciers and Ice Caps  

USGS Publications Warehouse

Projections of future rates of mass loss from mountain glaciers and ice caps in the Arctic focus primarily on projections of changes in the surface mass balance. Current models are not yet capable of making realistic forecasts of changes in losses by calving. Surface mass balance models are forced with downscaled output from climate models driven by forcing scenarios that make assumptions about the future rate of growth of atmospheric greenhouse gas concentrations. Thus, mass loss projections vary considerably, depending on the forcing scenario used and the climate model from which climate projections are derived. A new study in which a surface mass balance model is driven by output from ten general circulation models (GCMs) forced by the IPCC (Intergovernmental Panel on Climate Change) A1B emissions scenario yields estimates of total mass loss of between 51 and 136 mm sea-level equivalent (SLE) (or 13% to 36% of current glacier volume) by 2100. This implies that there will still be substantial glacier mass in the Arctic in 2100 and that Arctic mountain glaciers and ice caps will continue to influence global sea-level change well into the 22nd century.

Ananichheva, Maria; Arendt, Anthony; Hagen, Jon-Ove; Hock, Regine; Josberger, Edward G.; Moore, R. Dan; Pfeffer, William Tad; Wolken, Gabriel J.

2011-01-01

208

Relationships between fjord bathymetries and recent glacier behavior: gaining new insight from IceBridge flights over Greenland  

NASA Astrophysics Data System (ADS)

The geometry of glacial fjords may play a large role in determining the stability of outlet glaciers. Sloping seafloors will feedback on a moving grounding line and shallow sills and deep continental shelf troughs will allow greater interaction with the surrounding ocean water. To better understand the role of fjord bathymetry in the glacier system, Operation IceBridge (OIB) has flown a suite of radar, lidar, gravity and magnetic instruments along the flow lines of previously inaccessible outlet glaciers and their fjords around the Greenlandic coast. Here, we combine newly collected surface elevation, ice thickness data, and gravity and magnetic anomalies from OIB flights, along with ship-based bathymetric profiles, into a single dataset. The combination of these new data are used in the construction of forward models that provide the framework for performing gravity inversions, finally resulting in many new bathymetric charts of previously unmapped fjords in Greenland. These newly created fjord bathymetries are compared to several important characteristics their outlet glaciers and ocean waters. We investigate the importance of glacier parameters such as surface velocity and area changes, as well as newly available oceanographic data from within the fjord, on recent changes in glacier behavior. Are faster flowing glaciers found in fjords with deep sills and a greater exchange with continental shelf water? Comparisons of these glacier-fjord relationships are also separated by region and by glacier type. Are glaciers in the southeast mostly changing in a similar way even though their bed geometries are quite different? These broad correlations are a starting point in an effort to investigate the role of bed geometry in the relationship between external forcing and the observed recent change of many of Greenland's largest outlet glaciers.

Porter, D.; Boghosian, A.; Tinto, K. J.; Cochran, J. R.; Bell, R. E.

2012-12-01

209

A direct measured glacier thinning in the southern Tibetan Plateau (Xixiabangma, Yangbajing, Naimon'nyi Glacier)  

NASA Astrophysics Data System (ADS)

Various work confirmed the fast retreating of Tibetan Plateau glacier in recent decades due to global warming, especially the area shrinkage by remote sensing method. In recent years, more concern is focused on the effect of glacier melting on available water resource surrounding the glacier region. Consequently, the glacier ice volume change is of more importance in this sense. In this work, we present a result from directly measured glacier surface altitude change by differential GPS. By comparing the preciously measured altitude change from 2007 to 2011 at three glaciers in the southern Tibetan Plateau, we can give a reliable glacier thinning ratio in the past few years. The measured results from Gurenhekou Glacier, Yangbajing, show the ice depth loss is 3.96m in past 4 years from 2007 to 2011. In Kangwure glacier, Xixiabangma, the average depth loss is 2.70m in 3 years, and thus the annual glacier depth loss is 0.90m based on the observation from September 2007 to August 2010. The glacier depth loss is 1.4m on Naimon'nyi Glacier, one of the largest glaciers in west Himalayas, with an average annual loss of 0.7meter. Although the monitoring period is still limited, the quite similar ice losing ratio (0.7-1.0 m per year) in the southern Himalayas indicating the quite homogenous ice losing in different regions and with different glacier size and orientation. This work also finds that both ablation zone and accumulation zone are losing their ice, indicating the glacier flowing is also involves in the glacier thinning rather than the surface melting. This result also emphasizes the importance of GPS measurement compared to the stake-based mass balance observation. We are stilling working on even longer period monitoring and more glaciers to get more representative data to evaluate the glacier melting trends in the Tibetan Plateau.

Tian, L.; Zong, J.; Yao, T.; Ma, L.; Pu, J.

2012-12-01

210

Accelerating Ice Loss from the Fastest Greenland and Antarctic Glaciers  

NASA Technical Reports Server (NTRS)

Ice discharge from the fastest glaciers draining the Greenland and Antarctic ice sheets . Jakobshavn Isbrae (JI) and Pine Island Glacier (PIG). continues to increase, and is now more than double that needed to balance snowfall in their catchment basins. Velocity increase probably resulted from decreased buttressing from thinning (and, for JI, breakup) of their floating ice tongues, and from reduced basal drag as grounding lines on both glaciers retreat. JI flows directly into the ocean as it becomes afloat, and here creep rates are proportional to the cube of bed depth. Rapid thinning of the PIG ice shelf increases the likelihood of its breakup, and subsequent rapid increase in discharge velocity. Results from a simple model indicate that JI velocities should almost double to >20 km/a by 2015, with velocities on PIG increasing to >10 km/a after breakup of its ice shelf. These high velocities would probably be sustained over many decades as the glaciers retreat within their long, very deep troughs. Resulting sea ]level rise would average about 1.5 mm/a.

Thomas, R.; Frederick, E.; Li, J.; Krabill, W.; Manizade, S.; Paden, J.; Sonntag, J.; Swift, R.; Yungel, J.

2011-01-01

211

Hasty retreat of glaciers in northern Patagonia  

NASA Astrophysics Data System (ADS)

Mapping glacier extent from optical satellite data has become a most efficient tool to create or update glacier inventories and determine glacier changes over time. A most valuable archive in this regard is the nearly 30-year time series of Landsat Thematic Mapper (TM) data that is freely available (already orthorectified) for most regions in the world from the USGS. One region with a most dramatic glacier shrinkage and a missing systematic assessment of changes, is the Palena province in Chile, located south of Puerto Montt in northern Patagonia. A major bottleneck for accurate determination of glacier changes in this region is related to the huge amounts of snow falling in this very maritime region, hiding the perimeter of glaciers throughout the year. Consequently, we found only three years with Landsat scenes that can be used to map glacier extent through time. We here present the results of a glacier change analysis from six Landsat scenes (path-rows 232-89/90) acquired in 1985, 2000 and 2011 covering the Palena district in Chile and neighbouring regions. Clean glacier ice was mapped automatically with a standard technique (TM3/TM band ratio) and manual editing was applied to remove wrongly classified lakes and to add debris-covered glacier parts. The digital elevation model (DEM) from ASTER (GDEM2) was used to derive drainage divides, determine glacier specific topographic parameters, and analyse the area changes in regard to topography. The scene from the year 2000 has the best snow conditions and was used to eliminate seasonal snow in the other two scenes by digital combination of the binary glacier masks and neighbourhood analysis. The derived mean relative area loss over the entire study area is 25%, showing a large spatial variability and a strong dependence on elevation. While small mountain glaciers at high elevations and steep slopes show only little change over the 26-year period, ice at low elevations from large valley glaciers shows a dramatic decline (area and thickness loss). Some glaciers retreated more than 3 km over this time period or even disappeared completely. Typically, these glaciers lost contact to the accumulation areas of tributaries and melted away as dead ice. Furthermore, numerous proglacial lakes formed or expanded rapidly, increasing the local hazard potential. On the other hand, some glaciers located on or near to (still active) volcanoes have also slightly advanced over the same time period. Observed trends in temperature (decreasing) are in contrast to the observed strong glacier shrinkage, indicating that also other factors must play a role.

Paul, Frank; Mölg, Nico

2014-05-01

212

Rock glacier dynamics and paleoclimatic implications  

NASA Astrophysics Data System (ADS)

Many rock glaciers contain massive ice that may be useful in paleoclimate studies. Interpreting geochemical ice-core records from rock glaciers requires a thorough understanding of rock glacier structure and dynamics. High-precision surface-velocity data were obtained for the Galena Creek rock glacier, Absaroka Mountains, Wyoming. Surface velocities range from 0 to 1.00 m/yr and vary across the rock glacier in a manner similar to true glaciers. We used Glen's flow law to calculate the thickness of the deforming ice layer. The modeled ice thickness ranges from 0 to 50 m, and is confirmed by direct observations. This agreement shows that rock glacier movement can be entirely explained by deformation of massive ice within the rock glacier; neither basal sliding nor deformation of basal debris is necessary. Recovered ice cores (to depths of 25 m) contain thin debris layers associated with summer ablation in the accumulation zone. The ages of four samples of organic material removed from several debris layers inthe southern half of the rock glacier range from 200 ± 40 to 2250 ± 35 14C yr B.P., demonstrating that the rock glacier formed well before the Little Ice Age and may contain ice dating to the middle Holocene or earlier.

Konrad, S. K.; Humphrey, N. F.; Steig, E. J.; Clark, D. H.; Potter, N., Jr.; Pfeffer, W. T.

1999-12-01

213

Velocity map of the Thwaites Glacier catchment, West Antarctica  

NASA Astrophysics Data System (ADS)

The two-dimensional surface velocity of Thwaites Glacier, West Antarctica, was mapped with 23 ascending- and 22 descending-orbit European Remote-sensing Satellite synthetic aperture radar (ERS SAR) interferograms (time range 1995-2000). The velocity map covers 175 500 km2 from the Amundsen Coast to the southern turning point of the satellite orbit and comprises > 80% of the Thwaites catchment. Relative velocity errors are <10% except for rare regions (about 5% of the total area) of unfavorable look geometry. Six individual tributaries were identified; their center-line velocities increase from 0 at the catchment boundary to ~0.3 km a-1 when they join the main glacier trunk. On the main trunk, velocity increases to ~1.8 km a-1 at the grounding line and 3.6 km a-1 on the floating tongue. As at neighboring Pine Island Glacier, no strong longitudinal velocity gradients are found except near the grounding line. Within expected error bounds, the flow pattern appears temporally stationary, i.e.flowlines agree with the delineation of flow suggested by the pattern of velocity magnitude. A potential temporal shift of tributary boundaries must consequently be <4.4 m a-1.

Lang, Oliver; Rabus, T. Bernhard; Dech, W. Stefan

214

Glacier Change Detection in the Hindu Kush of Afghanistan  

NASA Astrophysics Data System (ADS)

A half century of intermittently collected cryospheric and hydrologic data in Afghanistan has involved diverse field surveys, aerial photography, and satellite imagery that enable change detection in the war-torn, drought-stricken region. Afghanistan relies heavily upon snow-and ice-melt for vital irrigation and ground-water recharge, yet the past two decades of war have only exacerbated the originally already deficient information collection and analysis of such data. Glacier field studies and base-line inventory work initiated in the pre-war 1960-1970 period are now providing limited change detection information for the vital physical analysis necessary in the reconstruction of the country. Five case study areas were selected for renewed assessment over the intervening half century, from the western-most ice masses of the Koh-i-Foladi region in central Afghanistan, through the Mir Samir and Sakhi regions of the central Hindu Kush, to the Keshnikhan and Pamir areas of the Wakhan Corridor. Certain incompatibilities or ambiguities exist between Soviet-era and Western-derived data sets. In general, however, glaciers of Afghanistan are continuing to downwaste and retreat, with smaller ice masses disappearing altogether, presumably as the climatic snowline continues to rise above the peaks, a trend first noticed in the 1960s. Glacier survival in the lower central areas is now in part determined by topographic shielding from solar radiation high in shadowed cirques, or being preserved beneath increasing debris covers, whereas in the higher regions to the northeast, fewer changes to the larger, higher altitude glaciers are apparent. Renewed assessment of all Afghanistan glaciers is now underway as a part of the USGS- and NASA-supported GLIMS (Global Land-Ice Measurements from Space) project, and is viewed as an important element in the primary geodata collection and hazard assessment necessary for aiding in rebuilding the infrastructure of the beleaguered nation.

Shroder, J. F.; Bishop, M. P.

2004-12-01

215

Modeling energy and mass balance of Shallap Glacier, Peru  

NASA Astrophysics Data System (ADS)

We calculated the distributed surface mass and energy balance of Shallap Glacier, Cordillera Blanca, Peru (9° S, 77° W, 4700-5700 m a.s.l., ~ 7 km2), on hourly time steps for two years (September 2006-August 2008) using a process-based model and meteorological measurements as input. Model parameter combinations were optimized against 21 temporal readings of 20 stakes in the ablation zone of the glacier. Uncertainty caused by model input parameters and parameterization schemes was estimated using a leave-one out cross-validation scheme, which yields values of root mean square deviation (RMSD) of surface height change < 1 m (< 10% of the measured amplitude) for all stakes. With the best parameter combination (smallest RMSD) applied, the modeled annual surface mass balance of the glacier was -0.32 ± 0.4 m w.e. (water equivalent) for September 2006-August 2007 and 0.51 ± 0.56 m w.e. for September 2007-August 2008. While the mass balance above 5000 m was similar in both years (? 0.33 ± 0.68 m w.e.) due to similar annual sums of solid precipitation, a difference of 1.97 ± 0.68 m w.e. was calculated for the lower parts of the glacier. This difference is associated with more frequent occurrence of higher snow line altitudes during the first year, which was mainly caused by a higher fraction of liquid precipitation due to higher mean air temperatures. As the net shortwave budget was found to be the main source for ablation throughout the year at Shallap Glacier, lower surface albedo especially caused by lower solid precipitation amounts explains most of the difference in modeled ablation and mass balance between the two years.

Gurgiser, W.; Marzeion, B.; Nicholson, L.; Ortner, M.; Kaser, G.

2013-11-01

216

Food web structure in a harsh glacier-fed river.  

PubMed

Glacier retreat is occurring across the world, and associated river ecosystems are expected to respond more rapidly than those in flowing waters in other regions. The river environment directly downstream of a glacier snout is characterised by extreme low water temperature and unstable channel sediments but these habitats may become rarer with widespread glacier retreat. In these extreme environments food web dynamics have been little studied, yet they could offer opportunities to test food web theories using highly resolved food webs owing to their low taxonomic richness. This study examined the interactions of macroinvertebrate and diatom taxa in the Ödenwinkelkees river, Austrian central Alps between 2006 and 2011. The webs were characterised by low taxon richness (13-22), highly connected individuals (directed connectance up to 0.19) and short mean food chain length (2.00-2.36). The dominant macroinvertebrates were members of the Chironomidae genus Diamesa and had an omnivorous diet rich in detritus and diatoms as well as other Chironomidae. Simuliidae (typically detritivorous filterers) had a diet rich in diatoms but also showed evidence of predation on Chironomidae larvae. Food webs showed strong species-averaged and individual size structuring but mass-abundance scaling coefficients were larger than those predicted by metabolic theory, perhaps due to a combination of spatial averaging effects of patchily distributed consumers and resources, and/or consumers deriving unquantified resources from microorganisms attached to the large amounts of ingested rock fragments. Comparison of food web structural metrics with those from 62 published river webs suggest these glacier-fed river food web properties were extreme but in line with general food web scaling predictions, a finding which could prove useful to forecast the effects of anticipated future glacier retreat on the structure of aquatic food webs. PMID:23613751

Clitherow, Leonie R; Carrivick, Jonathan L; Brown, Lee E

2013-01-01

217

Recent Observations and Structural Analysis of Surge-Type Glaciers in the Glacier Bay Area  

NASA Astrophysics Data System (ADS)

The Chugach-St.-Elias Mountains in North America hold the largest non-polar connected glaciated area of the world. Most of its larger glaciers are surge-type glaciers. In the summer of 2003, we collected aerial photographic and GPS data over numerous glaciers in the eastern St. Elias Mountains, including the Glacier Bay area. Observed glaciers include Davidson, Casement, McBride, Riggs, Cushing, Carroll, Rendu, Tsirku, Grand Pacific, Melbern, Ferris, Margerie, Johns Hopkins, Lamplugh, Reid, Burroughs, Morse, Muir and Willard Glaciers, of which Carroll, Rendu, Ferris, Grand Pacific, Johns Hopkins and Margerie Glaciers are surge-type glaciers. Our approach utilizes a quantitative analysis of surface patterns, following the principles of structural geology for the analysis of brittle-deformation patterns (manifested in crevasses) and ductile deformation patterns (visible in folded moraines). First results will be presented.

Mayer, H.; Herzfeld, U. C.

2003-12-01

218

Rapid thinning and collapse of lake calving Yakutat Glacier, Southeast Alaska  

NASA Astrophysics Data System (ADS)

Glaciers around the globe are experiencing a notable retreat and thinning, triggered by atmospheric warming. Tidewater glaciers in particular have received much attention, because they have been recognized to contribute substantially to global sea level rise. However, lake calving glaciers in Alaska show increasingly high thinning and retreat rates and are therefore contributors to sea level rise. The number of such lake calving systems is increasing worldwide as land-terminating glaciers retreat into overdeepened basins and form proglacial lakes. Yakutat Glacier in Southeast Alaska is a low elevation lake calving glacier with an accumulation to total area ratio of 0.03. It experienced rapid thinning of 4.43 +/- 0.06 m w.e. yr-1 between 2000-2010 and terminus retreat of over 15 km since the beginning of the 20th century. Simultaneously, adjacent Yakutat Icefield land-terminating glaciers thinned at lower but still substantial rates (3.54 +/- 0.06 m w.e. yr -1 for the same time period), indicating lake calving dynamics help drive increased mass loss. Yakutat Glacier sustained a ˜3 km long floating tongue for over a decade, which started to disintegrate into large tabular icebergs in 2010. Such floating tongues are rarely seen on temperate tidewater glaciers. The floating ice was weakened by surface ablation, which then allowed rifts to form and intersect. Ice velocity from GPS measurements showed that the ice on the floating tongue was moving substantially faster than grounded ice, which was attributed to rift opening between the floating and grounded ice. Temporal variations of rift opening were determined from time-lapse imagery, and correlated well with variations in ice speeds. Larger rift opening rates occurred during and after precipitation or increased melt episodes. Both of these events increased subglacial discharge and could potentially increase the subaqueous currents towards the open lake and thus increase drag on the ice underside. Simultaneously, increased water input may cause lake level in rifts to rise resulting in faster rift propagation and spreading. Similar formation and disintegration of floating tongues are expected to occur in the glacier's future, as the ice divide lies below the current lake level. In addition to calving retreat, Yakutat Glacier is rapidly thinning, which lowers its surface and therefore exposes the ice to warmer air temperatures causing increased thinning. Even under a constant climate, this positive feedback mechanism would force Yakutat Glacier to quickly retreat and mostly disappear. Simulations of future mass loss were run for two scenarios, keeping the current climate and forcing it with a projected warming climate. Results showed that over 95% of the glacier ice will have disappeared by 2120 or 2070 under a constant vs projected climate, respectively. For the first few decades, the glacier will be able to maintain its current thinning rate by retreating and thus losing areas of lowest elevation. However, once higher elevations have thinned substantially, the glacier cannot compensate any more to maintain a constant thinning rate and transfers into an unstable run-away situation. To stop this collapse and transform Yakutat Glacier into equilibrium in its current geometry, air temperatures would have to drop by 1.5 K or precipitation would have to increase by more than 50%. An increase in precipitation alone is unlikely to lead to a stable configuration, due to the very small current accumulation area.

Trussel, Barbara Lea

219

Google Earth Tours of Glacier Change  

NSDL National Science Digital Library

To prepare for this assignment students have already used Google Earth to examine beach erosion, but they have not yet created any new content with Google Earth. Students are already competent navigators and are accustomed to the perspective views used in Google Earth. In this assignment students first go through a prepared Google Earth tour on Juneau Icefield glaciers, and answer questions about glacier features. Then students create their own Google Earth tour, using placemarks to identify key features of their glacier.

Pelto, Mauri

220

Southern Alaska as an Example of the Long-Term Consequences of Mountain Building Under the Influence of Glaciers  

NASA Technical Reports Server (NTRS)

Southern Alaska is a continent-scale region of ongoing crustal deformation within the Pacific-North American plate boundary zone. Glaciers and glacial erosion have dictated patterns of denudation in the orogen over the last approx. 5 My. The orogen comprises three discrete topographic domains from south to north, respectively: (1) the Chugach/St. Elias Range; (2) the Wrangell Mountains; and (3) the eastern Alaska Range. Although present deformation is distributed across the orogen, much of the shortening and uplift are concentrated in the Chugach/St. Elias Range. A systematic increase in topographic wavelength of the range from east to west reflects east-to-west increases in the width of a shallowly-dipping segment of the plate interface, separation of major upper plate structures, and a decrease in the obliquity of plate motion relative to the plate boundary. Mean elevation decays exponentially from approx. 2500 m to approx. 1100 m from east to west, respectively. Topographic control on the present and past distribution of glaciers is indicated by close correspondence along the range between mean elevation and the modern equilibrium line altitude of glaciers (ELA) and differences in the modern ELA, mean annual precipitation and temperature across the range between the windward, southern and leeward, northern flanks. Net, range- scale erosion is the sum of: (1) primary bedrock erosion by glaciers and (2) erosion in areas of the landscape that are ice-marginal and are deglaciated at glacial minima. Oscillations between glacial and interglacial climates controls ice height and distribution, which, in turn, modulates the locus and mode of erosion in the landscape. Mean topography and the mean position of the ELA are coupled because of the competition between rock uplift, which tends to raise the ELA, and enhanced orographic precipitation accompanying mountain building, which tends to lower the ELA. Mean topography is controlled both by the 60 deg latitude and maritime setting of active deformation and by the feedback between shortening and uplift, glacial erosion, and orographic effects on climate accompanying mountain building.

Meigs, Andrew; Sauber, Jeanne

2000-01-01

221

Recent glacier retreat over Kerguelen archipelago (49°S, 69°E) derived from field data, satellite imagery and modelling  

NASA Astrophysics Data System (ADS)

Situated in the Indian Ocean at 49° S, 69° E, Kerguelen archipelago represents a unique sub-polar observational site. Located at low altitude and on islands, the glaciers are particularly sensitive to oceanic and atmospheric variations (e.g. Poggi, 1977a,b; Vallon, 1987). The cryosphere on Kerguelen showed important fluctuations during the last 2 centuries (Frenot et al., 1993). After a small stable period until 1961, the ice cap showed a huge and extremely quick retreat, losing 20% of its surface during the last 40 years (Berthier et al., 2009). Relating directly this acceleration with the fluctuations of temperature and precipitation inferred from direct meteorological measurements is attractive and was generally performed (e.g. Frenot et al., 1993, 1997; Berthier et al., 2009). However, it was recently discovered that the drastic temperature change may be mainly due to changes in meteorological station characteristics in 1973 (Météo France, personal communication), challenging previous interpretation. The analysis of field data collected on Ampere glacier since 2010 presented here provides a first approach in our aim to understand the recent rapid retreat of its cryosphere. In this area, short term mass balance data from previous studies (Vallon 1977a,b, 1987) were compared to recent mass balance measurements. The analysis revealed that the spatial distribution of SMB significantly changed in 40 years. Collecting spatially distributed data of the surface characteristics and ablation was crucial to better interpret our field data. Recent variations (from 2000 to 2012) of the equilibrium line altitude (ELA) of Cook ice cap derived from MODIS imagery confirmed that the ELA rose about 100m since 2000. Additionally, we analysed meteorological and reanalysis data over Kerguelen from 1950 to 2012, in order to assess the causes and processes involved in the retreat of the ice cap, and present additional SMB and ELA estimates from a simple positive degree-day model. We concluded that the parameter with the largest variation was precipitation, which was associated to a decrease in cloud cover. The direct impact of these changes was a rise of the 0°C level that led to a reduction of the occurrence of solid precipitation at low elevation. These retroactions demonstrate that Kerguelen's glaciers are extremely sensitive to small climatic changes. These results on glaciological processes of Ampere glacier are an important base to constrain modelling approaches to assess past, present and future ice cap variations. In this framework, regional scale simulations of mass balance processes over Kerguelen archipelago have been initiated with a downscaling scheme (SMHiL) and with the regional climate model MAR (Modèle Atmosphérique Régional).

Verfaillie, Deborah; Favier, Vincent; Dumont, Marie; Jomelli, Vincent; Gilbert, Adrien; Brunstein, Daniel; Frenot, Yves

2013-04-01

222

The GAMDAM Glacier Inventory: a quality controlled inventory of Asian glaciers  

NASA Astrophysics Data System (ADS)

We present a new glacier inventory for the high mountain Asia named "Glacier Area Mapping for Discharge from the Asian Mountains" (GAMDAM). Glacier outlines were delineated manually using more than 226 Landsat ETM+ scenes from the period 1999-2003, in conjunction with a digital elevation model (DEM) and high-resolution Google Earth imagery. Geolocations are consistent between the Landsat imagery and DEM due to systematic radiometric and geometric corrections made by the United States Geological Survey. We performed repeated delineation tests and rigorous peer review of all scenes used in order to maintain the consistency and quality of the inventory. Our GAMDAM Glacier Inventory (GGI) includes 82776 glaciers covering a total area of 87507 ± 13126 km2 in the high mountain Asia. Thus, our inventory represents a greater number (+4%) of glaciers but significantly less surface area (-31%) than a recent global glacier inventory (Randolph Glacier Inventory, RGI). The employed definition of the upper boundaries of glaciers, glacier recession since the 1970s, and misinterpretation of seasonal snow cover are likely causes of discrepancies between the inventories, though it is difficult to evaluate these effects quantitatively. The GGI will help improve the temporal consistency of the RGI, which incorporated glacier outlines from the 1970s for the Tibetan Plateau, and will provide new opportunities to study Asian glaciers.

Nuimura, T.; Sakai, A.; Taniguchi, K.; Nagai, H.; Lamsal, D.; Tsutaki, S.; Kozawa, A.; Hoshina, Y.; Takenaka, S.; Omiya, S.; Tsunematsu, K.; Tshering, P.; Fujita, K.

2014-06-01

223

Antarctica: measuring glacier velocity from satellite images  

SciTech Connect

Many Landsat images of Antarctica show distinctive flow and crevasse features in the floating part of ice streams and outlet glaciers immediately below their grounding zones. Some of the features, which move with the glacier or ice stream, remain visible over many years and thus allow time-lapse measurements of ice velocities. Measurements taken from Landsat images of features on Byrd Glacier agree well with detailed ground and aerial observations. The satellite-image technique thus offers a rapid and cost-effective method of obtaining average velocities, to a first order of accuracy, of many ice streams and outlet glaciers near their termini.

Lucchitta, B.K.; Ferguson, H.M.

1986-11-28

224

Antarctica: Measuring glacier velocity from satellite images  

USGS Publications Warehouse

Many Landsat images of Antarctica show distinctive flow and crevasse features in the floating part of ice streams and outlet glaciers immediately below their grounding zones. Some of the features, which move with the glacier or ice stream, remain visible over many years and thus allow time-lapse measurements of ice velocities. Measurements taken from Landsat images of features on Byrd Glacier agree well with detailed ground and aerial observations. The satellite-image technique thus offers a rapid and cost-effective method of obtaining average velocities, to a first order of accuracy, of many ice streams and outlet glaciers near their termini.

Lucchitta, B. K.; Ferguson, H. M.

1986-01-01

225

Internationally coordinated glacier monitoring: strategy and datasets  

NASA Astrophysics Data System (ADS)

Internationally coordinated monitoring of long-term glacier changes provide key indicator data about global climate change and began in the year 1894 as an internationally coordinated effort to establish standardized observations. Today, world-wide monitoring of glaciers and ice caps is embedded within the Global Climate Observing System (GCOS) in support of the United Nations Framework Convention on Climate Change (UNFCCC) as an important Essential Climate Variable (ECV). The Global Terrestrial Network for Glaciers (GTN-G) was established in 1999 with the task of coordinating measurements and to ensure the continuous development and adaptation of the international strategies to the long-term needs of users in science and policy. The basic monitoring principles must be relevant, feasible, comprehensive and understandable to a wider scientific community as well as to policy makers and the general public. Data access has to be free and unrestricted, the quality of the standardized and calibrated data must be high and a combination of detailed process studies at selected field sites with global coverage by satellite remote sensing is envisaged. Recently a GTN-G Steering Committee was established to guide and advise the operational bodies responsible for the international glacier monitoring, which are the World Glacier Monitoring Service (WGMS), the US National Snow and Ice Data Center (NSIDC), and the Global Land Ice Measurements from Space (GLIMS) initiative. Several online databases containing a wealth of diverse data types having different levels of detail and global coverage provide fast access to continuously updated information on glacier fluctuation and inventory data. For world-wide inventories, data are now available through (a) the World Glacier Inventory containing tabular information of about 130,000 glaciers covering an area of around 240,000 km2, (b) the GLIMS-database containing digital outlines of around 118,000 glaciers with different time stamps and (c) the Randolph Glacier Inventory (RGI), a new and globally complete digital dataset of outlines from about 180,000 glaciers with some meta-information, which has been used for many applications relating to the IPCC AR5 report. Concerning glacier changes, a database (Fluctuations of Glaciers) exists containing information about mass balance, front variations including past reconstructed time series, geodetic changes and special events. Annual mass balance reporting contains information for about 125 glaciers with a subset of 37 glaciers with continuous observational series since 1980 or earlier. Front variation observations of around 1800 glaciers are available from most of the mountain ranges world-wide. This database was recently updated with 26 glaciers having an unprecedented dataset of length changes from from reconstructions of well-dated historical evidence going back as far as the 16th century. Geodetic observations of about 430 glaciers are available. The database is completed by a dataset containing information on special events including glacier surges, glacier lake outbursts, ice avalanches, eruptions of ice-clad volcanoes, etc. related to about 200 glaciers. A special database of glacier photographs contains 13,000 pictures from around 500 glaciers, some of them dating back to the 19th century. A key challenge is to combine and extend the traditional observations with fast evolving datasets from new technologies.

Hoelzle, Martin; Armstrong, Richard; Fetterer, Florence; Gärtner-Roer, Isabelle; Haeberli, Wilfried; Kääb, Andreas; Kargel, Jeff; Nussbaumer, Samuel; Paul, Frank; Raup, Bruce; Zemp, Michael

2014-05-01

226

Evaluation of Lateglacial temperatures in the Southern Alps of New Zealand based on glacier modelling at Irishman Stream, Ben Ohau Range  

NASA Astrophysics Data System (ADS)

Climate proxy records from the middle to high latitude Southern Hemisphere indicate that a Lateglacial (15,000-11,500 years ago) climate reversal, approximately coeval with the Antarctic Cold Reversal (ACR), interrupted a warming trend during deglaciation. In New Zealand, some palaeoclimate proxy records indicate a cool episode during the ACR (ca 14,500-12,500 years ago), while others do not express a significant change in climate. Recently published moraine maps and ages present an opportunity to improve the palaeoclimate interpretation through numerical modelling of glaciers. We use a coupled energy-balance and ice-flow model to quantify palaeoclimate from past glacier extent constrained by mapped and dated moraines in the headwaters of Irishman Stream, a high-elevation catchment in the Southern Alps. First, a suite of steady-state model runs is used to identify the temperature and precipitation forcing required to fit the modelled glacier to well-dated Lateglacial moraine crests. Second, time-dependent glacier simulations forced by a nearby proxy temperature record derived from chironomids are used to assess the fit with the glacial geomorphic record. Steady-state experiments using an optimal parameter set demonstrate that the conditions under which the 13,000 year old moraine formed were 2.3-3.2 °C colder than present with the range in temperature corresponding to a ±20% variance in precipitation relative to the present-day. This reconstructed climate change relative to the present-day corresponds to an equilibrium-line altitude of ca 2000 ± 40 m above sea level (asl), which is ca 400 m lower than present. Time-dependent simulations of glacier length produce ice advance to within 100 m of the 13,000 year old terminal moraine, indicating that the chironomid-based temperature forcing and moraine record provide consistent information about past climate. Our results, together with other climate proxy reconstructions from pollen records and marine sediment cores, support the notion that temperatures during the ACR in New Zealand were ˜2-3 °C cooler than today.

Doughty, Alice M.; Anderson, Brian M.; Mackintosh, Andrew N.; Kaplan, Michael R.; Vandergoes, Marcus J.; Barrell, David J. A.; Denton, George H.; Schaefer, Joerg M.; Chinn, Trevor J. H.; Putnam, Aaron E.

2013-08-01

227

The effect of black carbon on reflectance of snow in the accumulation area of glaciers in the Baspa basin, Himachal Pradesh, India  

NASA Astrophysics Data System (ADS)

Himalayan glaciers are being extensively debated in scientific and public forums, as changes in their distribution can significantly affect the availability of water in many rivers originating in the region. The distribution of glaciers can be influenced by mass balance, and most of the glaciers located in the Pir Panjal and Greater Himalayan mountain ranges are losing mass at the rate of almost a meter per year. The Equilibrium Line Altitude (ELA) has also shifted upward by 400 m in the last two decades. This upward migration of ELA and the loss in mass could have been influenced by changes in temperature, precipitation and by the deposition of black carbon in the accumulation area of glaciers. The deposition of black carbon can reduce the albedo of snow in the accumulation area leading to faster melting of snow and causing more negative mass balance. In this investigation, a change in reflectance in the accumulation area of the Baspa basin is analysed for the year 2009, as the region has experienced extensive forest fires along with northern Indian biomass burning. The investigation has shown that: (1) The number of forest fires in the summer of 2009 was substantially higher than in any other year between 2001 and 2010; (2) the drop in reflectance in the visible region from April to May in the accumulation area was significantly higher in the year 2009 than in any other year from 2000 to 2012; (3) the temperature of the region was substantially lower than the freezing point during the active fire period of 2009, indicating the small influence of liquid water and grain size; (4) the drop in reflectance was observed only in the visible region, indicating role of contamination; (5) in the visible region, a mean drop in reflectance of 21± 5% was observed during the active fire period in the accumulation area. At some places, the drop was as high as 50 ± 5%. This can only be explained by the deposition of black carbon. The study suggests that a change in snow albedo in the accumulation area due to the deposition of black carbon from anthropogenic and natural causes can influence the mass balance of the glaciers in the Baspa basin, Himachal Pradesh, India.

Kulkarni, A. V.; Vinay Kumar, G.; Negi, H. S.; Srinivasan, J.; Satheesh, S. K.

2013-04-01

228

Deriving surface motion of mountain glaciers in the Tuomuer-Khan Tengri Mountain Ranges from PALSAR images  

NASA Astrophysics Data System (ADS)

Glaciers flow velocity is an important parameter for the study of glacier dynamics, mass balance and climate change, and can provide precursory warning of glacier melting induced flooding, debris flowing, etc. The Tuomuer-Khan Tengri Mountain Range is one of the largest glaciated areas in Tian Shan Mountain. However, the knowledge of glacier motion in this area is still rather limited. Using the method of robust Offset-tracking and four pairs of PALSAR images covering the Tuomuer-Khan Tengri Mountain Range, this paper estimates the displacement fields of the mountain glaciers in this area for each pair. The displacement fields are then mapped into daily glacier flow velocities by dividing the acquiring intervals of each pair. Using a series of checkpoints selected in stationary areas where the displacements can be assumed to be zero, we evaluate the estimation error of the displacement fields and find that most of them are less than 2.17 cm/day. The displacement fields are analyzed in detail with regards to glacier bed terrain and glacial temperature and thickness. We find that they are in excellent accordance with the flow characteristic of typical mountain glaciers. The velocity changes among the observation years have been carefully examined. This along with the associated runoff measurements makes us conclude that the glaciers in the Tuomuer-Khan Tengri Range are assumedly in dynamic equilibrium between intensified melting and increased precipitation and glaciation, and their velocity will maintain stable in the near future. We also find that the altitudes of the velocity peaks are close to the recorded snowline, which indicates that detecting the changes of velocity peaks' position might provide a reference for monitoring the changes of the snowlines.

Li, Jia; Li, Zhiwei; Zhu, Jianjun; Ding, Xiaoli; Wang, Changcheng; Chen, Jianli

2013-02-01

229

Advances in Modelling of Valley Glaciers  

NASA Astrophysics Data System (ADS)

For glaciological conditions typical of valley glaciers, the central idea of this research lies in understanding the effects of high-order mechanics and parameterizing these for simpler dynamical and statistical methods in glaciology. As an effective tool for this, I formulate a new brand of dynamical models that describes distinct physical processes of deformational flow. Through numerical simulations of idealized glacier domains, I calculate empirical correction factors to capture the effects of longitudinal stress gradients and lateral drag for simplified dynamical models in the plane-strain regime. To get some insights into real glacier dynamics, I simulate Haig Glacier in the Canadian Rocky Mountains. As geometric effects overshadow dynamical effects in glacier retreat scenarios, it appears that high-order physics are not very important for Haig Glacier, particularly for evaluating its fate. Indeed, high-order and reduced models all predict that Haig Glacier ceases to exist by about AD2080 under ongoing climate warming. This finding regarding the minimal role of high-order physics may not be broadly valid, as it is not true in advance scenarios at Haig Glacier and it may not be representative of other glaciological settings. Through a 'bulk' parameterization of high-order physics, geometric and climatic settings, sliding conditions, and transient effects, I also provide new insights into the volume-area relation, a widely used statistical method for estimating glacier volume. I find a steady-state power-law exponent of 1:46, which declines systematically to 1:38 after 100 years of sustained retreat, in good accord with the observations. I recommend more accurate scaling relations through characterization of individual glacier morphology and degree of climatic disequilibrium. This motivates a revision of global glacier volume estimates, of some urgency in sea level rise assessments.

Adhikari, Surendra

230

Recent Surface Changes in Southern Greenland Outlet Glaciers from NASA's Airborne Topographic Mapper Experiments  

NASA Astrophysics Data System (ADS)

In summer 2008, NASA deployed its Airborne Topographic Mapper (ATM), along with other airborne science instruments, to several locations around the southern periphery of the Greenland ice sheet, with the aim of quantifying recent changes in a number of outlet glaciers. The ATM also joined with a Swansea University (United Kingdom) team in order to provide geodetic reference ties on the bare bedrock surrounding a dozen outlet glaciers, most of them in southeastern Greenland. The goal of this phase of the effort was to make possible the computation of volumetric change of these glaciers using a decades-long series of oblique aerial photographs, combined with the geodetic reference provided by the ATM's rock overflights. Finally, we supported a National Science Foundation and University of Kansas effort to fly a large, dense grid over the greater Jakobshavn basin to obtain bedrock topography using their 150 MHz depth-sounding radar. In the process of this, we obtained our own extensive surface-topography measurements over the same grid. Here we present initial results from these efforts, including changes in the surface topography of the Jakobshavn and Helheim glacier basins, and along the flowlines of Kangerdlugssuaq and other outlet glaciers in the southeast of Greenland. Finally we summarize initial, or baseline, measurements along the flowlines of a number of glaciers never mapped before by the ATM, which we flew as part of our other efforts and which will pay dividends when the ATM returns to refly the lines in future campaigns.

Krabill, W. B.; Sonntag, J. G.

2008-12-01

231

Ground-penetrating radar observations of winter snow accumulation on Alaska Glaciers.  

NASA Astrophysics Data System (ADS)

Understanding the spatial variability of winter snow in glacierized watersheds is vital for estimating glacier changes, forecasting freshwater delivery to riverine and marine ecosystems and informing Earth loading models for studies of seasonal variations in crustal uplift. Accurately reproducing snow distribution within glacier-models still remains a challenge due to the difficulty obtaining in-situ measurements and large local or regional variability in snow thicknesses. Between March and July 2012, high frequency (200-500 MHz) Ground-Penetrating Radar (GPR) surveys designed to obtain spatially distributed measurements of snow accumulation, were collected on a number of different glaciers in south-central Alaska, USA. The surveys span a range of climatic zones including continental and maritime glaciers. Several modes of travel were employed, including helicopter-borne, snowmobile and ski-towed. Preliminary results from the Valdez Glacier suggest that the agreement between 200 MHz-GPR-derived snow-depth and 17 manually measured snow-depths is ± 10% using an estimated radar velocity of 0.22 m/ns, as one example. Additionally, GPR profiles in the accumulation areas showed firn-stratigraphy of previous summer surfaces, thus, making it possible to distinguish the elevation of the firn line and indicating that in the accumulation zone it may be possible to estimate annual net mass balance if density can be estimated. In this presentation we will illustrate the characteristics of snow accumulation on this suite of Alaska Glaciers as derived by GPR and discuss our results in terms of the usefulness and challenges associated with using GPR to determine the winter and annual mass balance of these glaciers.

Gusmeroli, A.; Wolken, G. J.; Arendt, A. A.; Campbell, S. W.; O'Neel, S.; Marshall, H.

2012-12-01

232

Daily and seasonal glacier velocity change on Kronebreen, Svalbard, as measured using FORMOSAT-2 imagery and in situ continuous GPS  

NASA Astrophysics Data System (ADS)

Glacier response to climate change is often heralded by changes in the velocity field. Remote sensing can be used to map changes in glacier speed. Visible satellite imagery provides high resolution products in convenient to use format, but is hampered by the presence of clouds. The high-resolution (2-m pixel nominal resolution in panchromatic mode) FORMOSAT-2 satellite has a daily revisit capability, allowing programmed acquisitions to capture occasional periods with few or no clouds. Here we use FORMOSAT-2 to derive glacier-wide velocities on the lower 10 km of Kronebreen, Svalbard's fastest-moving glacier, which has peak summer season speeds of up to 2 m d^{-1}. We present FORMOSAT-derived velocity fields for the summer melt seasons of 2007 to 2011, obtained using 4-8 images, the exact number depending on the year. We also compare the data from 2009 onward to 3-hourly measurements of speed made using a number of in situ code-phase GPS units deployed at various points on the glacier tongue. The FORMOSAT-derived data have good spatial resolution and show how velocity increases start at the front of the glacier and move upstream. The GPS data have high temporal resolution and show how the glacier reacts to meltwater inputs. The GPS data are also used to verify the spatial variability of the remote-sensing data since the receivers are located along the flow line as well as on a transect across the flow line.

Kohler, J.; Berthier, E.; Reijmer, C. H.; Nuth, C.

2011-12-01

233

Earth tide forcing of glacier drainage  

Microsoft Academic Search

Fourier analysis reveals that winter electrical self potential (SP), water pressure (PW), and electrical conductivity (EC) time series collected beneath Haut Glacier d'Arolla, Switzerland, are forced by earth and atmospheric tides. Forcing is dominant during periods of expanding bedrock, consistent with glacier substrate deformation periodically driving water from the ice body into the bed. This may modify the strength of

Bernd Kulessa; Bryn Hubbard; Giles H. Brown; Julia Becker

2003-01-01

234

Muir Glacier and Muir Inlet 2003  

USGS Multimedia Gallery

This photo was taken in September 2003; in the 23 years between photographs, Muir Glacier has retreated more than a mile and ceased to have a tidewater terminus. Since 1980, Muir Glacier has thinned by more than 600 ft, permitting a view of a mountain with a summit elevation of greater than 4000 ft,...

235

Scientific visualization of glacier changes for public communication: the example of Findelengletscher, Switzerland  

NASA Astrophysics Data System (ADS)

The melting of glaciers and ice caps has been recognized as one of the best natural indicators for global climate change. In Switzerland, the early onset of both glacier research and detailed mapping of the country resulted in a wealth of historical material documenting glacier changes over the past 160 years. Fife years ago, the Universities of Zurich and Fribourg, along with the Swiss energy utility Axpo, launched the Glacier Laserscanning Experiment Obervallis (GLAXPO). In this project three laserscanning flights were performed on Findelengletscher in order to create high resolution Digital Elevation Models (DEM). These DEM provide a precise mapping of the glacier surface topography and serve as reference surface for the co-registration of past DEMs computed from digitized historical maps. In addition to that distributed numerical glacier models were run with ensembles of climate change scenarios in order to calculate glacier changes over the 21st century. The present work makes use of this great data pool for a scientifically correct visualization of 3-dimensional changes of Findelengletscher from AD 1850 to 2100 for public communication. We therefore collected ten different historical maps with the earliest dating from 1862 (plane survey sheet of the Dufour map). The pre-processing included georeferencing and digitalization of contour lines for the creation of different historical DEMs. Afterwards all historical DEMs were co-registered to one of the latest high resolution laserscanning DEM (from 2005). In between years with available DEMs, surface changes were interpolated linearly to create a sequence for the computer animation. For future developments, modeled glacier elevation changes where added/subtracted from the latest DEM (from 2010). Finally, two animations, showing glacier changes from 1850-2010 and 2010-2100, were composed and rendered in the animation program Visual Nature Studio 3. In cooperation with professional booth and model builders, these animations were set up as a glacier exhibit including an interactive touchscreen, a large panoramic view of the Findelen Valley, and an additional interactive monitor providing related background information in French and German. Beginning of 2013, the glacier exhibit was launched as permanent part of the Axporama visitor center and ready for more than 10,000 public visitors a year.

Rastner, Philipp; Jörg, Philipp Claudio; Huss, Matthias; Zemp, Michael

2013-04-01

236

Glacier surges past and present  

NASA Astrophysics Data System (ADS)

Investigations of the glacial geologic record commonly use modern analogues to underpin reconstructions of former environments. While this approach is very powerful, it is not without problems and is vulnerable to changing paradigms (or fashions) in glaciology. A well-known example is the ascendancy of the 'deforming bed' model in the 1980s and 1990s, which was subsequently challenged by the 'ploughing bed' model. These models have contrasting implications for till genesis and subglacial sediment transport, but rigorous testing is hampered by the difficulty of directly observing modern glacier beds and the lack of unambiguous diagnostic criteria for interpreting ancient tills. We address this issue by examining sediment-landform assemblages formed by surging glaciers in Svalbard. Surges leave a distinctive imprint on fjord floors, including fluted subglacial till, crevasse-fill ridges, thrust block moraines, and extensive proglacial mud flows. The latter have been interpreted as either masses of extruded subglacial till or the collapsed fronts of oversteepened thrust moraines. The 'extrusion hypothesis' implies significant subglacial sediment flux towards the margin, consistent with a metres-thick deforming layer, whereas the 'moraine failure' hypothesis implies dominantly proglacial transport. We show that both fjord-floor and terrestrial 'mud aprons' consist of masses of marine sediment which were pushed in front of the advancing glacier, while undergoing more or less continuous gravitational failure. The subaqueous moraines and mud flows are therefore interpreted as end-member glacitectonic landforms, formed by similar processes to thrust-block moraines. These results indicate highly episodic glacial sediment transport in Svalbard fjords, accomplished largely by ice-push during surges. The survival of transverse (moraine) ridges below megaflutings in some fjords suggests that subglacial sediment transport is relatively unimportant, and that the 'ploughing model' best describes the behaviour of the ice-bed interface during surges. We suggest that similar glacitectonic processes may have been important for delivering sediment to the margins of Pleistocene marine ice sheets.

Benn, D.; Kristensen, L.

2009-04-01

237

Iceland Glacier Recession 1997 to 2000  

NSDL National Science Digital Library

This animation is a close up zoom into largest area of glacier recesion at the Breidamerkurjokull glacier in Iceland. The data from 1997 is taken from Landsat 5 and the 2000 data is from Landsat 7. The Breidamerkurjokull glacier in Iceland has been measured by Landsat to be receding since 1973. In 1997, Landsat 5 took several other images of the glacier. It was thought by some glacierologists that this particular glacier was receding quicker in the late 1990s than it did in the late 1980s or 1970s. After careful analysis Goddards Glacierologist, Dorothy Hall, concluded that the recession from 1997 to 2000 occurs at a similar rate to the recession between 1973 and 2000. It is extremely controversial whether or not this recession is caused by global warming.

Perkins, Lori; Hall, Dorothy

2001-04-09

238

GLACIER PEAK ROADLESS AREA, WASHINGTON.  

USGS Publications Warehouse

A mineral survey outlined areas of mineral-resource potential in the Glacier Peak Roadless Area, Washington. Substantiated resource potential for base and precious metals has been identified in four mining districts included in whole or in part within the boundary of the roadless area. Several million tons of demonstrated base- and precious-metal resources occur in numerous mines in these districts. Probable resource potential for precious metals exists along a belt of fractured and locally mineralized rock extending northeast from Monte Cristo to the northeast edge of the roadless area.

Church, S. E.; Johnson, F. L.

1984-01-01

239

Title: Climate-glacier Relationship of Retreating Alaskan Glaciers Author: Elliott Mazur and Umesh K. Haritashya  

NASA Astrophysics Data System (ADS)

Portage, Whittier, Eklutna, as well as many other well-known "tourism glaciers" in the vicinity of Anchorage, Alaska are known to have retreated in the past 20 years. This begs the question, "what of the other lesser-known glaciers? Do they follow the same patterns and minimal glacier models?" Glaciers such as Byron, Leonard, Matanuska, Raven and Spencer may fit a minimal model. Information on Byron and Leonard is sparse, as both have become hanging glaciers. Other glaciers, such as Raven, are small enough to be deemed insignificant, yet may have information to give. Consequently our objective is to study five Alaskan glaciers and determine wide-ranging variability to changing regional climate. To do this we obtained field geo-location data and characterized glaciers based on the satellite imagery and climate reevaluation. Our result shows that glaciers are retreating and thinning irrespective of their aspects, location and altitudinal variability. Moreover, our presentation establishes the strong climate-glacier relationship and defines retreating snowline patterns over the last few decades.

Mazur, E. M.

2012-12-01

240

Seasonal variability of organic matter composition in an Alaskan glacier outflow: insights into glacier carbon sources  

NASA Astrophysics Data System (ADS)

Glacier ecosystems are a significant source of bioavailable, yet ancient dissolved organic carbon (DOC). Characterizing DOC in Mendenhall Glacier outflow (southeast Alaska) we document a seasonal persistence to the radiocarbon-depleted signature of DOC, highlighting ancient DOC as a ubiquitous feature of glacier outflow. We observed no systematic depletion in ? 14C-DOC with increasing discharge during the melt season that would suggest mobilization of an aged subglacial carbon store. However, DOC concentration, ? 13C-DOC, ? 14C-DOC and fluorescence signatures appear to have been influenced by runoff from vegetated hillslopes above the glacier during onset and senescence of melt. In the peak glacier melt period, the ? 14C-DOC of stream samples at the outflow (?181.7 to ?355.3‰) was comparable to the ? 14C-DOC for snow samples from the accumulation zone (?207.2 to ?390.9‰), suggesting that ancient DOC from the glacier surface is exported in glacier runoff. The pre-aged DOC in glacier snow and runoff is consistent with contributions from fossil fuel combustion sources similar to those documented previously in ice cores and thus provides evidence for anthropogenic perturbation of the carbon cycle. Overall, our results emphasize the need to further characterize DOC inputs to glacier ecosystems, particularly in light of predicted changes in glacier mass and runoff in the coming century.

Spencer, Robert G. M.; Vermilyea, Andrew; Fellman, Jason; Raymond, Peter; Stubbins, Aron; Scott, Durelle; Hood, Eran

2014-05-01

241

Black soot and the survival of Tibetan glaciers  

PubMed Central

We find evidence that black soot aerosols deposited on Tibetan glaciers have been a significant contributing factor to observed rapid glacier retreat. Reduced black soot emissions, in addition to reduced greenhouse gases, may be required to avoid demise of Himalayan glaciers and retain the benefits of glaciers for seasonal fresh water supplies.

Xu, Baiqing; Cao, Junji; Hansen, James; Yao, Tandong; Joswia, Daniel R.; Wang, Ninglian; Wu, Guangjian; Wang, Mo; Zhao, Huabiao; Yang, Wei; Liu, Xianqin; He, Jianqiao

2009-01-01

242

Glacier Change and an Updated Glacier Inventory of Mongolia using Landsat 8  

NASA Astrophysics Data System (ADS)

Mountain glaciers and ice caps around the world are recognized as significant contributors to both global sea level and local and regional water resources, especially for arid regions. However, the remote and rugged nature of glaciers in many parts of Asia hinders their study. To complicate the picture, not only are glaciers in High Mountain / Central / North Asia exhibiting considerable regional variability in mass balance, but different measurement methods are painting significantly different pictures of glacier health. Mongolia provides a subset of the global glacier inventory which exemplifies low data availability and seemingly contradictory results. Based on previous studies, Mongolia is home to ~500 glaciers totaling ~650 km2, but these figures are quite rough. Regional glacier mass balance estimates vary from -2 × 1 Gt / yr to 3 × 6 Gt / yr. However, the glaciers are important to the local environment and agriculture, as Mongolian glaciers are estimated to store 10% of Mongolia's fresh water. The glaciers have lost ~6% of their area from the 1960s to the 1990s. Most recent studies of high mountain Asia (the large group of glaciated ranges between the Tien Shan, Qilian Mountains, and the Himalayas) show accelerated losses in recent years. Therefore, from within this uncertainty, we harness newly available data from Landsat 8's Operational Land Imager (OLI) to build an updated glacier inventory for Mongolia. Prior regional studies have focused of a variety of sub-ranges across many different epochs within the Altai (i.e. Munkh Khairkhan, Tavan Bogd, Turgen, Kharkhiraa, Munkhkhairkhan, Sair, and Tsambagarav Mountains); here, we unify the picture of recent change for all of Mongolia's glaciers (i.e., the additional glaciated areas eastward of the Altai). In addition to highlighting the ease and utility of Landsat 8's OLI, we will take advantage of a further suite of data (i.e. Landsat archival imagery, ICESat, ASTER, SPOT-5, or submeter imagery) to further document glacier change in the Mongolian Altai.

Pope, A.; Scambos, T. A.

2013-12-01

243

Rotational Equilibrium  

NSDL National Science Digital Library

In this activity, learners explore the concept of rotational equilibrium. Learners work in teams to estimate and determine the force within a mobile design. Learners solve algebraic equations, apply graphing techniques, compare results and discuss findings. Designing the mobile requires learners to solve a set of two linear algebraic equations. Learners solve the equations using three different methods: by substitution, by graphing the equations and finding the intersection, and by using determinants.

Ieee

2013-07-08

244

Utilizing physical sediment variability in glacier-fed lakes for continuous glacier reconstructions during the Holocene, northern Folgefonna, western Norway  

Microsoft Academic Search

The maritime plateau glacier of northern Folgefonna in western Norway has a short (subdecadal) response time to climatic shifts, and is therefore well suited for reconstructing high-resolution glacier fluctuations. The reconstruction presented here is based on physical parameters of glaciolacustrine sediments retrieved from two glacier-fed lakes and a peat bog north of the ice cap. Bulk density and modelled glacier

Jostein Bakke; øyvind Lie; Atle Nesje; Svein Olaf Dahl; øyvind Paasche

2005-01-01

245

Interaction between glacier and glacial lake in the Bhutan, Himalaya  

NASA Astrophysics Data System (ADS)

Recession of mountain glaciers in the Himalayas has been reported in the context of global warming. Associated with the glacier retreat, supraglacial lakes have been formed on the termini of debris-covered glaciers. Although it has been said that lake-terminating glaciers flow faster than land-terminating glaciers, observational evidence was scarce. We observationally investigated the influence of the presence/absence of glacial lakes on changes in surface elevation through glacier dynamics in two debris-covered glaciers, Thorthormi Glacier (land-terminating) and Lugge Glacier (lake-terminating), in the Lunana region, the Bhutan Himalaya. We surveyed the surface elevation of debris-covered areas of the two glaciers in 2004 and 2011 by a differential GPS. Change in surface elevation of the lake-terminating Lugge Glacier was much more negative than that of the land-terminating Thorthormi Glacier. Considering almost flat slope and location at lower elevation, however, larger ice thinning rate of the Thorthormi Glacier should have been expected than the Lugge Glacier. We measured surface flow speed of the two glaciers during 2009-2010 by multitemporal orthorectified The Panchromatic Remote-sensing Instrument for Stereo Mapping (PRISM) images of ALOS. Surface flow speed of the Thorthormi Glacier was faster in the upper reaches and reduced toward the downstream. In contrast, the flow speed at the Lugge Glacier measured in the same periods was greatest at the lower most part. Observed spatial distribution of surface flow speed at both glaciers are evaluated by a two-dimensional numerical flow model. The model shows that contribution of basal sliding to surface flow velocity is large in the lower part of both glaciers. Particularly in the Thorthormi Glacier, approximately 100% of surface flow velocity attribute to basal sliding. Calculated emergence velocity at the Thorthormi Glacier is larger than that at the Lugge Glacier. This result suggests that decreasing in flow velocity towards the terminus in the Thorthormi Glacier causes compressive flow and thus counterbalances surface melting, resulting in inhibition of the surface lowering. In contrast, the extensional flow of the Lugge Glacier accelerated the surface lowering. In this study we show the observational evidences, in which the glacier lake formation makes contrast the thinning rates of glaciers in the Bhutan Himalaya. If the supraglacial lake on Thorthormi Glacier expands, the surface lowering will be accelerated in the future.

Tsutaki, S.; Fujita, K.; Yamaguchi, S.; Sakai, A.; Nuimura, T.; Sugiyama, S.; Komori, J.; Takenaka, S.; Tshering, P.

2012-12-01

246

The state and fate of Himalayan glaciers.  

PubMed

Himalayan glaciers are a focus of public and scientific debate. Prevailing uncertainties are of major concern because some projections of their future have serious implications for water resources. Most Himalayan glaciers are losing mass at rates similar to glaciers elsewhere, except for emerging indications of stability or mass gain in the Karakoram. A poor understanding of the processes affecting them, combined with the diversity of climatic conditions and the extremes of topographical relief within the region, makes projections speculative. Nevertheless, it is unlikely that dramatic changes in total runoff will occur soon, although continuing shrinkage outside the Karakoram will increase the seasonality of runoff, affect irrigation and hydropower, and alter hazards. PMID:22517852

Bolch, T; Kulkarni, A; Kääb, A; Huggel, C; Paul, F; Cogley, J G; Frey, H; Kargel, J S; Fujita, K; Scheel, M; Bajracharya, S; Stoffel, M

2012-04-20

247

Glacier surge triggered by massive rock avalanche: Teleseismic and satellite image study of long-runout landslide onto RGO Glacier, Pamirs  

NASA Astrophysics Data System (ADS)

Glacier surges are thought to result from changes in resistance to sliding at the base of the ice mass. The reasons for such changes in basal conditions are not entirely understood, and this is in part because empirical constraints are severely limited. Recent work in the Karakoram and Pamir mountains, home to the majority of Earth's surging mountain glaciers, has boosted observational data, but has led to diametrically opposed interpretations of their glacier surging mechanics, ranging from thermal to hydrological switching. In this context we describe a surge of the RGO (Russian Geographical Society) Glacier in the Pamirs triggered by a massive rock avalanche off Mt Garmo in 2001. Initial reports pegged the RGO Glacier landslide as having been triggered in 2002 by strong ground motion originating from a nearby tectonic earthquake. We used multitemporal satellite imagery to establish failure must have struck in August-September 2001. This revised date was confirmed by reexamining teleseismic data recorded at stations in central Asia: it became clear that a landslide seismic source of magnitude Msw?5.4 on 2001/09/02 had been misinterpreted as two tectonic sources located within kilometers of Mt Garmo. Exploiting a new technique we have developed for inverting long-period seismic waveforms, we show that a mass of rock and ice around 2.8×{}1011 kg collapsed to the SSE from an elevation of around 5800m, accelerated to a peak speed of about 60m/s, collided with the valley wall ˜ 2 km to the south and turned east to run out a further 6km over significant fractions of the accumulation and ablation zones of the RGO Glacier. Based on this estimate of landslide mass, we deduce that the supraglacial debris blanket generated by this rock avalanches averaged about 20m in thickness. By this reckoning, the Mt Garmo landslide is one of the largest in the last 33 years. Next we mapped the velocity field of the RGO Glacier over time using multitemporal satellite imagery. We performed image correlation velocimetry (sometimes known as feature tracking or optical flow velocimetry) using around 120 Landsat 7 ETM+ scenes spanning 1999 through 2012. Reliable velocity fields were generated even after the loss of scan-line correction (SLC-off scenes) in 2003. Our preliminary results reveal two phases of glacier surge. The first began within a few months of the rock avalanche during the winter of 2001, with ice flow speeds rising by more than an order of magnitude to nearly 1000m/y mid-glacier at the landslide toe, and propagating as a wave down-glacier in less than a year. This phase ended in 2002-3. The second, milder surge phase began in 2005 and ended in 2007. Each phase led to an advance of the terminus over several 100m. We interpret surge initiation as being the direct consequence of rock avalanche deposition on the glacier. To explore the apparent link between rock avalanching and glacier surging, we have developed a 2D thermomechanical, higher-order, flowline model coupled to a basal hydrology scheme. We conclude with a discussion of the behavior of this model when heavily perturbed by abrupt debris deposition, and we explore whether the occurrence of landslide-triggered surging can in any way advance our understanding of glacier surge mechanics in general.

Stark, C. P.; Wolovick, M.; Ekstrom, G.

2012-12-01

248

Alaska PaleoGlacier Atlas: A Geospatial Compilation of Pleistocene Glacier Extents  

NSDL National Science Digital Library

The Alaska PaleoGlacier (APG) Atlas is a recently released, web-based summary of Pleistocene glaciation across Alaska. Students can access a gallery of maps depicting the extent of glaciers during the late Wisconsin glaciation in Alaska as well as the maximum extent reached during the last 3 million years by valley glaciers, ice caps, and the northwestern Cordilleran Ice Sheet. a set of links is also provided to sites on galcial geology and glacial geospatial data.

Manley, William

249

Testing Environmental Records From Ice Cores of a Temperate Alpine Glacier  

NASA Astrophysics Data System (ADS)

Low-latitude temperate alpine glaciers are largely overlooked but potentially useful archives of paleoenvironmental data; although smaller and shorter-lived than polar glaciers, their position adjacent to areas of dense population makes these glaciers attractive research targets. The Palisade Glacier is the largest glacier in the Sierra Nevada, and thus most likely to contain a reasonably unaltered physical and chemical record for the region. We collected two ice cores, ~4-m and 6-m long, from the uppermost bench on the glacier in August, 2003. Subsamples of the ice cores were analyzed for stable isotopes (d18O and dD), trace elemental abundance, and mass-accumulation stratigraphy. In addition, we sampled snow pits near the coring site in early July and early August 2003, and late June 2004 to constrain physical and isotopic changes in the snowpack through the summer meltseason. A SNOTEL site in the same drainage basin provides local records of daily precipitation and temperature, approximately 2000 feet below Palisade Glacier Our results suggest that despite recent thinning, the Palisade glacier preserves both isotopic and elemental stratigraphy. Annual layers are most apparent in the trace element concentrations, which indicate the cores preserve 4-5 years of accumulation, probably from the mid-to late1990's. A heavy concentration of the dust at the surface, combined with snow accumulation records from nearby SNOTEL sites, indicate that all snow from the previous 6 years (since winter of 1997/98, the last above-average snow year in the basin) was lost to ablation. Significantly lower visible dust concentrations in the underlying layers indicate that the core site had net accumulation during the preceding 4 years, in agreement with the SNOTEL record. Stable isotopes co-vary in the cores, coincident with the dust stratigraphy. In addition, the dD/d18O ratios closely resemble the trend of the global meteoric water line, suggesting that post-depositional melting and fractionation have been minimal. These results lend further support to previous studies (e.g., Naftz et al., 1993; Steig et al., 1998) that indicate that small temperate glaciers can preserve valuable, if complex, records of past environmental change. Further coring is needed to confirm our results, and to test viability of deeper ice in this or other glaciers.

Gillespie, A. J.; Clark, D. H.; Steig, E. J.; McConnell, J.

2004-12-01

250

Predicting the response of seven Asian glaciers to future climate scenarios using a simple linear glacier model  

Microsoft Academic Search

Observations from seven Central Asian glaciers (35–55°N; 70–95°E) are used, together with regional temperature data, to infer uncertain parameters for a simple linear model of the glacier length variations. The glacier model is based on first order glacier dynamics and requires the knowledge of reference states of forcing and glacier perturbation magnitude. An adjoint-based variational method is used to optimally

Diandong Ren; David J. Karoly

2008-01-01

251

Predicting the response of seven Asian glaciers to future climate scenarios using a simple linear glacier model  

Microsoft Academic Search

Observations from seven Central Asian glaciers (35-55°N 70-95°E) are used, together with regional temperature data, to infer uncertain parameters for a simple linear model of the glacier length variations. The glacier model is based on first order glacier dynamics and requires the knowledge of reference states of forcing and glacier perturbation magnitude. An adjoint-based variational method is used to optimally

Diandong Ren; David J. Karoly

2008-01-01

252

Glacier acceleration, glacial earthquakes, and ice loss at Helheim Glacier, Greenland  

NASA Astrophysics Data System (ADS)

Satellite observations during the last decade have shown dramatic changes in flow speed at Greenland's outlet glaciers, often accompanied by retreats of several km in calving-front location and increasing numbers of glacial earthquakes. Geodetic, seismological, and oceanographic data collected as part of a multidisciplinary field experiment at Helheim Glacier, East Greenland, over three summer seasons (2006--2008), together with satellite imagery, place new constraints on the processes responsible for these changes. Analysis of high-rate GPS data from 2007 reveals several large, sudden increases in flow speed at Helheim Glacier. These abrupt accelerations are detected along the length of the glacier (~20~km) spanned by the GPS network, and coincide in time with major calving events and teleseismically detected glacial earthquakes. The calving events are implicated in the earthquake source process. Further, our results link changes in glacier velocity directly to calving-front behavior at Greenland's large outlet glaciers, on timescales as short as minutes to hours. No large earthquakes occurred at Helheim Glacier during the 2006 field campaign, providing the opportunity for comparison between seismically active and quiescent modes of glacier behavior. Data recorded in 2008 include near-field broadband seismic recordings and time-lapse photography, allowing us to refine our understanding of both the glacial earthquake source process and the glacier response to major ice loss events.

Nettles, M.; Larsen, T. B.; Elósegui, P.; Hamilton, G. S.; Stearns, L. A.; Ahlstrøm, A. P.; Davis, J. L.; Andersen, M. L.; de Juan, J.; Khan, S. A.; Stenseng, L.; Ekström, G.; Forsberg, R.; Schild, K. M.

2008-12-01

253

Research Team Discovers First Evidence of Microbes Living in a Rock Glacier  

NSDL National Science Digital Library

This NSF press release reports that scientists have discovered evidence of microbial activity in a rock glacier high above tree line in the Rocky Mountains, a barren environment previously thought to be devoid of life. Included in this NSF press release are links to all NSF affiliated pages.

The National Science Foundation (NSF)

254

Erosion and transport by Byrd Glacier, Antarctica during the Last Glacial Maximum  

NASA Astrophysics Data System (ADS)

Glacial till samples from seven, modern-Holocene Byrd Glacier moraines were characterized using particle size analysis, sand petrography and detrital zircon geochronology and compared to Ross Sea tills deposited during the Last Glacial Maximum. The goal was to identify the paleoflow path for Byrd Glacier and assess the use of multiple provenance techniques. The coarse sand fraction of Byrd Glacier tills is dominated by lithic fragments of adjacent bedrock outcrops, except samples from the Lonewolf Nunataks, which have a higher proportion of mineral to lithic fragments, as well as a recognizable exotic component. Cluster analysis shows that Byrd Glacier tills, with the exception of the two Lonewolf Nunataks sites, do not cluster strongly with Ross Sea samples because they have a higher proportion of lithic fragments. This indicates that comminution must be an active subglacial process beneath East Antarctic outlet glaciers. Byrd Glacier tills are also typically coarser grained that Ross Sea tills and their maturity is a reflection of both glacial processes and rock type. Measured U/Pb ages of detrital zircons from Byrd Glacier tills range from Triassic to Archean (240-3540 Ma) with a dominance of grains 530-600 Ma. Ross Sea till samples show spatial variability in U/Pb age distributions, with the core sites west of the 180° longitude line showing similarity to most Byrd Glacier tills, whereas core NBP9407-39, east of 180° long., is dominated by ˜100 Ma grains. Ross Sea tills also contain a recognizable detrital zircon fraction eroded inland of the Transantarctic Mountains. Both provenance methods indicate that the ice flow line for Byrd Glacier during the LGM was to the east of Ross Island and extended on either side of Ross Bank, with the majority of ice flowing to the Ross Sea's Central Basin. Our analysis shows that sand petrography and detrital zircon U/Pb age spectra provide complementary datasets that produce similar ice flow reconstructions and reveal valuable information about glacial processes and ice covered bedrock.

Licht, K. J.; Palmer, E. F.

2013-02-01

255

Glaciers, Water and Wind, Oh My!  

NSDL National Science Digital Library

This hands-on activity explores five different forms of erosion (chemical, water, wind, glacier and temperature). Students rotate through stations and model each type of erosion on rocks, soils and minerals.

Integrated Teaching and Learning Program, College of Engineering, University of Colorado at Boulder

2012-04-23

256

Icebergs and Glaciers - Issue 15, August 2009  

NSDL National Science Digital Library

This issue of the free online magazine, Beyond Penguins and Polar Bears, contains content knowledge and instructional resources about icebergs and glaciers and the scientific principles of density and buoyancy.

University, The O.

257

Common Misconceptions about Icebergs and Glaciers  

NSDL National Science Digital Library

This article describes some common misconceptions that elementary students may have about icebergs and glaciers (including density and buoyancy). It also includes suggestions for formative assessment and teaching for conceptual change.

Fries-Gaither, Jessica

258

In Brief: Glacier photo database update  

NASA Astrophysics Data System (ADS)

More than 1200 photographs of Greenland glaciers have been digitized and are now available at the Online Glacier Photograph Database, housed at the National Snow and Ice Data Center (NSIDC) in Boulder, Colo. The database includes 50 photographs taken between 1890 and 1996 of glaciers in Colorado and New Zealand as well as a series of photos of New Zealand's Franz Josef Glacier taken between 1951 and 1964. NSIDC has partnered with the NOAA Climate Database Modernization Program and the National Geophysical Data Center to scan selected photographs that compose the online database. For information about these updates or to access the data, visit the Web site: http://nsidc.org/data/g00472.html.

Showstack, Randy

2007-11-01

259

Radar Sounding of Fast-Flowing Glaciers  

Microsoft Academic Search

A major challenge in radio glaciology is sounding of fast-flowing glaciers such as Jakobshavn, Helheim, and Kangardlussuq in Greenland. Weak ice-bed echoes from fast-flowing glaciers are masked by off-vertical surface clutter. We need fine resolution both in the along-track and cross-track directions to reduce surface clutter. Synthetic Aperture Radar (SAR) techniques can be used to improve resolution in the along-track

S. Gogineni; C. Leuschen; J. Li; L. Smith; J. Plummer; A. Hoch

2008-01-01

260

USGS Repeat Photography Project: Glacier National Park  

NSDL National Science Digital Library

This project, conducted by the United States Geological Survey (USGS), documents changes over time in the landscape of Glacier National Park, particularly the retreat of the park's glaciers. The project involves pairing historic photos from the park's archives with recent photos to illustrate how the landscape has changed. Users can view and download the photos in pairs with dates and a caption describing the scene and the changes that have taken place.

261

Glacier Inventory: A Case in Semiarid Chile  

Microsoft Academic Search

\\u000a Glaciers are the most important water reservoirs found in the Andes. While the scientific community has conducted more extensive\\u000a glaciological studies in southern Chile, it is only recently that attention has been focused on northern Chile. In the Chilean\\u000a “Norte Chico” region, where glaciation is restricted to the highest summits, the sparse glacier network provides the majority\\u000a of water to

Jorge Marín; José Araos

262

Fuzzy Cognitive Maps for Glacier Hazards Assessment: Application to Predicting the Potential for Glacier Lake Outbursts  

NASA Astrophysics Data System (ADS)

Glaciers and ice sheets are among the largest unstable parts of the solid Earth. Generally, glaciers are devoid of resources (other than water), are dangerous, are unstable and no infrastructure is normally built directly on their surfaces. Areas down valley from large alpine glaciers are also commonly unstable due to landslide potential of moraines, debris flows, snow avalanches, outburst floods from glacier lakes, and other dynamical alpine processes; yet there exists much development and human occupation of some disaster-prone areas. Satellite remote sensing can be extremely effective in providing cost-effective and time- critical information. Space-based imagery can be used to monitor glacier outlines and their lakes, including processes such as iceberg calving and debris accumulation, as well as changing thicknesses and flow speeds. Such images can also be used to make preliminary identifications of specific hazardous spots and allows preliminary assessment of possible modes of future disaster occurrence. Autonomous assessment of glacier conditions and their potential for hazards would present a major advance and permit systematized analysis of more data than humans can assess. This technical leap will require the design and implementation of Artificial Intelligence (AI) algorithms specifically designed to mimic glacier experts’ reasoning. Here, we introduce the theory of Fuzzy Cognitive Maps (FCM) as an AI tool for predicting and assessing natural hazards in alpine glacier environments. FCM techniques are employed to represent expert knowledge of glaciers physical processes. A cognitive model embedded in a fuzzy logic framework is constructed via the synergistic interaction between glaciologists and AI experts. To verify the effectiveness of the proposed AI methodology as applied to predicting hazards in glacier environments, we designed and implemented a FCM that addresses the challenging problem of autonomously assessing the Glacier Lake Outburst Flow Potential and Impound Water Upstream Flow Potential. The FCM is constructed using what is currently our understanding of how glacier lake outbursts occur, whereas the causal connection between concepts is defined to capture the expertise of glacier scientists. The proposed graph contains 27 nodes and a network of connections that represent the causal link between concepts. To test the developed FCM, we defined three scenarios representing glacier lake environmental conditions that either occurred or that are likely to occur in such highly dynamic environments. For each case, the FCM has been initialized using observables extracted from hypothesized remote sensing imagery. The map, which converges to a fixed point for all of the test scenarios within 15 iterations, shows reasoning consistent with that of glacier experts. The FCM-based cognitive approach has the potential to be the AI core of real-time operational hazards assessment and detection systems.

Furfaro, R.; Kargel, J. S.; Fink, W.; Bishop, M. P.

2010-12-01

263

A data set of worldwide glacier length fluctuations  

NASA Astrophysics Data System (ADS)

Glacier fluctuations contribute to variations in sea level and historical glacier length fluctuations are natural indicators of past climate change. To study these subjects, long-term information of glacier change is needed. In this paper we present a data set of global long-term glacier length fluctuations. The data set is a compilation of available information on changes in glacier length worldwide, including both measured and reconstructed glacier length fluctuations. All 471 length series start before 1950 and cover at least four decades. The longest record starts in 1535, but the majority of time series start after 1850. The number of available records decreases again after 1962. The data set has global coverage including records from all continents. However, the Canadian Arctic is not represented in the data set. The available glacier length series show relatively small fluctuations until the mid-19th century, followed by a global retreat. The retreat was strongest in the first half of the 20th century, although large variability in the length change of the different glaciers is observed. During the 20th century, calving glaciers retreated more than land-terminating glaciers, but their relative length change was approximately equal. Besides calving, the glacier slope is the most important glacier property determining length change: steep glaciers have retreated less than glaciers with a gentle slope.

Leclercq, P. W.; Oerlemans, J.; Basagic, H. J.; Bushueva, I.; Cook, A. J.; Le Bris, R.

2014-04-01

264

Geostatistical evaluation of satellite radar altimetry for high-resolution mapping of Lambert Glacier, Antarctica  

NASA Technical Reports Server (NTRS)

The potential of satellite radar altimetry for high-resolution mapping of Antarctic ice streams is evaluated, using retracked and slope-corrected data from the Lambert Glacier and Amery Ice Shelf area, East Antarctica, acquired by Geosat during the Exact Repeat Mission (ERM), 1986-89. The map area includes lower Lambert Glacier north of 72.18 deg S, the southern Amery Ice Shelf, and the grounded inland ice sheet on both sides. The Geosat ERM altimetry is found to provide substantially more complete coverage than the 1978 Seasat altimetry, due to improved tracking. Variogram methods are used to estimate the noise levels in the data as a function of position throughout the map area. The spatial structure in the data is quantified by constructing experimental variograms using altimetry from the area of the grounding zone of Lambert Glacier, which is the area chiefly of interest in this topographically complex region. Kriging is employed to invert the along-track height measurements onto a fine-scale 3 km grid. The unsmoothed along-track Geosat ERM altimetry yields spatially continuous maps showing the main topographic features of lower Lambert Glacier, upper Amery Ice Shelf and the adjacent inland ice sheet. The probable position of the grounding line of Lambert Glacier is identified from a break in slope at the grounded ice/floating ice transition. The approximate standard error of the kriged map is inferred from the data noise levels.

Herzfeld, Ute C.; Lingle, Craig S.; Lee, Li-Her

1993-01-01

265

Glaciers in the Earth's Hydrological Cycle: Assessments of Glacier Mass and Runoff Changes on Global and Regional Scales  

NASA Astrophysics Data System (ADS)

Changes in mass contained by mountain glaciers and ice caps can modify the Earth's hydrological cycle on multiple scales. On a global scale, the mass loss from glaciers contributes to sea-level rise. On regional and local scales, glacier meltwater is an important contributor to and modulator of river flow. In light of strongly accelerated worldwide glacier retreat, the associated glacier mass losses raise concerns over the sustainability of water supplies in many parts of the world. Here, we review recent attempts to quantify glacier mass changes and their effect on river runoff on regional and global scales. We find that glacier runoff is defined ambiguously in the literature, hampering direct comparison of findings on the importance of glacier contribution to runoff. Despite consensus on the hydrological implications to be expected from projected future warming, there is a pressing need for quantifying the associated regional-scale changes in glacier runoff and responses in different climate regimes.

Radi?, Valentina; Hock, Regine

2014-05-01

266

Modeling of subaqueous melting of Greenland tidewater glaciers using an ocean general circulation model  

NASA Astrophysics Data System (ADS)

Ice discharge from the Greenland Ice Sheet is mainly through tidewater glaciers that terminate in the ocean and whose near-vertical calving front is submerged in seawater. Subaqueous melting at the calving front is not only a direct mechanism for mass loss but also a possible trigger of glacier acceleration. We modified the Massachusetts Institute of Technology general circulation model (MITgcm) to include a subaqueous melting contribution at the calving front and the outflow of subglacial runoff at the glacier grounding line. Previous 2-D sensitivity studies showed that subaqueous melting is strongly dependent on subglacial runoff: it ceases when subglacial runoff is zero and increases sub-linearly with the flux of subglacial runoff. Subaqueous melting increases quadratically with ocean thermal forcing when subglacial runoff is low, but only linearly when subglacial runoff is high in the sensitivity experiments. We now apply this model to Store Glacier fjord in West Greenland, where oceanographic data (temperature, salinity, current velocity and sea floor bathymetry) were collected in August 2010. We run 3-D simulations with bathymetry measurement, and integrate the model with JRA25 atmospheric forcing, ECCO2 oceanic boundary conditions, and RACMO subglacial runoff. Subglacial channels are assumed to exist at discrete locations at the grounding line. The model results are compared with the oceanographic observation. This study helps us evaluate the ocean impact on subaqueous melting of Greenland tidewater glaciers and in turn on glacier mass balance. This work is performed at UCI under a contact with NASA Cryosphere ScienceProgram. We thank Michiel can den Broeke for RACMO daily subglacial runoff data.

Xu, Y.; Rignot, E. J.; Menemenlis, D.; Koppes, M. N.

2011-12-01

267

Glacier changes since Local Last Glacial Maximum in the South-West slope of Nevado Hualcán, Cordillera Blanca, Peru, deduced from moraine mapping and GIS-based analysis  

NASA Astrophysics Data System (ADS)

Anticipating and assessing hazards and risks associated with the shrinking of surface and subsurface ice in cold mountain chains is facilitated by empirical-quantitative data on present and past rates of change, as well as by a general understanding of related landforms and landscape evolution through time. Rock/ice avalanches and devastating outburst floods from glacial lakes indeed constitute a major cause of severe damage in populated mountain areas such as the Cordillera Blanca whose combination of tectonic, topographic and glaciological characteristics make it a threatened region. This study focuses on the Río Chucchún catchment above the city of Carhuaz, which was recently affected by a flood/debris flow from a rock/ice avalanche impacting a recently grown lake (Laguna 513). Traces left by past glaciations strongly affect the current geomorphodinamic behaviour of the catchment. For instance, a prominent sediment-filled glacial overdeepening behind Younger Dryas (YD) moraines (Pampa de Shonquil) with its retention function strongly influenced the chain of processes initiated by the outburst of Laguna 513. The aim of this study is to reconstruct earlier glacial phases in the SW slope of Nevado Hualcán (Río Chucchún catchment), in order to compile quantitative information on surface areas and Equilibrium Line Altitudes (ELAs). To do so, glacier stages were assigned to five different glacial phases, through photointerpretation and moraine cartography: 2003; 1962; Hualcán-I-LIA (15th to 18th centuries); Hualcán-II-YD (~12,5 ka BP); and Hualcán-III-LLGM (~34 to 21 ka BP). Glacial stages Hualcán-I-LIA, Hualcán-II-YD and Hualcán-III-LLGM present relative dating based on previous studies from different authors in the Peruvian Andes. Once glaciers were delimited, their surface areas and Equilibrium Line Altitudes (ELAs) were calculated. For ELA estimation three different methods were used: the mid-range elevation, the Accumulation Area Ratio (AAR), and the Area x Altitude Balance Ratio (AABR). The results show a decrease in surface area with respect to Hualcán-III-LLGM of 16% for Hualcán-II-YD; 50% for Hualcán-I-LIA; and 74% for 2003. With respect to 2003, ELAs shifted ~520 m since the Local Last Glacial Maximum (LLGM), ~470 m since a marked late-glacial stage (YD?), ~130 m since the Little Ice Age (LIA) and about ~100 m since 1962. If the changes are exclusively attributed to temperature effects, warming since LLGM can be estimated at some 3°C and since the maximum glacier extent of LIA at about 0.8°C. Such values are rather close to mean global temperature change during the corresponding intervals. Most of the ELA shift since LIA appears to have taken place during recent decades characterized by very rapid glacier shrinkage, although air temperature does not seem to have risen considerably during the last 30 years. These results along with other environmental and social approaches will contribute to a better understanding of impacts from climate change and glacier shrinkage in order to develop adaptation, mitigation and disaster risk reduction strategies in the Peruvian Andes.

Giráldez, Claudia; Palacios, David; Haeberli, Wilfried; Úbeda, Jose; Schauwecker, Simone; Torres, Judith

2014-05-01

268

Changing features of the climate and glaciers in China's monsoonal temperate glacier region  

Microsoft Academic Search

Climatic data, ice core records, the tree ring index, and recorded glacier variations have been used to reconstruct a history of climatic and glacial changes in the monsoonal temperate glacier region of southwestern China during the last 400 years. The region's temperature has increased in a fluctuating manner during the twentieth century after two cold stages of the Little Ice

Yuanqing He; Zhonglin Zhang; Wilfred H. Theakstone; Tuo Chen; Tandong Yao; Hongxi Pang

2003-01-01

269

Decay of a long-term monitored glacier: Careser Glacier (Ortles-Cevedale, European Alps)  

NASA Astrophysics Data System (ADS)

The continuation of valuable, long-term glacier observation series is threatened by the accelerated mass loss which currently affects a large portion of so-called "benchmark" glaciers. In this work we present the evolution of the Careser Glacier, from the beginning of systematic observation at the end of the 19th century to its current condition in 2012. In addition to having one of the longest and richest observation records among the Italian glaciers, Careser is unique in the Italian Alps for its 46 yr mass balance series that started in 1967. In the present study, variations in the length, area and volume of the glacier since 1897 are examined, updating and validating the series of direct mass balance observations and adding to the mass balance record into the past using the geodetic method. The glacier is currently strongly out of balance and in rapid decay; its average mass loss rate over the last 3 decades was 1.5 m water equivalent per year, increasing to 2.0 m water equivalent per year in the last decade. Although these rates are not representative at a regional scale, year-to-year variations in mass balance show an unexpected increase in correlation with other glaciers in the Alps, during the last 3 decades. If mass loss continues at this pace, the glacier will disappear within a few decades, putting an end to this unique observation series.

Carturan, L.; Baroni, C.; Becker, M.; Bellin, A.; Cainelli, O.; Carton, A.; Casarotto, C.; Dalla Fontana, G.; Godio, A.; Martinelli, T.; Salvatore, M. C.; Seppi, R.

2013-12-01

270

The GLIMS geospatial glacier database: A new tool for studying glacier change  

Microsoft Academic Search

The Global Land Ice Measurement from Space (GLIMS) project is a cooperative effort of over sixty institutions world-wide with the goal of inventorying a majority of the world's estimated 160000 glaciers. Each institution (called a Regional Center, or RC) oversees the analysis of satellite imagery for a particular region containing glacier ice. Data received by the GLIMS team at the

Bruce Raup; Adina Racoviteanu; Siri Jodha Singh Khalsa; Christopher Helm; Richard Armstrong; Yves Arnaud

2007-01-01

271

Nonlocal thermodynamic equilibrium response matrix  

Microsoft Academic Search

A connection between atomic kinetics and non-equilibrium thermodynamics has been recently established using a collisional-radiative model modified to include line absorption. The net emission can be expressed as a symmetric non-local thermodynamic-equilibrium response-matrix. This connection is extended to models used in hydrodynamic codes to simulate laser–plasma interactions. A new, exact and, general formula is obtained for the response-matrix and an

G. Faussurier; R. M. More

2003-01-01

272

Evaluating the performance of a glacier erosion model applied to Peyto Glacier, Alberta, Canada  

NASA Astrophysics Data System (ADS)

Glaciers are effective agents of erosion for many mountainous regions, but primary rates of erosion are difficult to quantify due to unknown conditions at the glacier bed. We develop a numerical model of subglacial erosion and passively couple it to a vertically integrated ice flow model (UBC regional glaciation model). The model accounts for seasonal changes in water pressure at the glacier bed which affect rates of abrasion and quarrying. We apply our erosion model to Peyto Glacier, and compare estimates of glacier erosion to the mass of fine sediment contained in a lake immediately down valley from the glacier. A series of experiments with our model and ones based on subglacial sliding rates are run to explore model sensitivity to bedrock hardness, seasonal hydrology, changes in mass balance, and longer-term dimensional changes of the glacier. Our experiments show that, as expected, erosion rates are most sensitive to bedrock hardness and changes in glacier mass balance. Silt and clay contained in Peyto Lake primarily originate from the glacier, and represent sediments derived from abrasion and comminution of material produced by quarrying. Average specific sediment yield during the period AD1917-1970 from the lake is 467×190 Mg km-2yr-1 and reaches a maximum of 928 Mg km-2yr-1 in AD1941. Converting to a specific sediment yield, modelled average abrasion and quarrying rates during the comparative period are 142×44 Mg km-2yr-1 and 1167×213 Mg km-2yr-1 respectively. Modelled quarrying accounts for approximately 85-95% of the erosion occurring beneath the glacier. The basal sliding model estimates combined abrasion and quarrying. During the comparative period, estimated yields average 427×136 Mg km-2yr-1, lower than the combined abrasion and quarrying models. Both models predict maximum sediment yield when Peyto Glacier reached its maximum extent. The simplistic erosion model shows higher sensitivity to climate, as seen by accentuated sediment yield peaks during the Little Ice Age. In all of our experiments to date, modelled sediment yield closely follow maximum ice cover. In contrast, sediment yields obtained from the lake indicate that maximum sediment delivery to the lake lagged maximum ice cover and occurred during a period of rapid glacier retreat. We interpret this lag to indicate removal of stored sediments beneath the glacier and subaerial erosion from recently exposed sediments in the glacier forefield rather than an increase in primary erosion of bedrock.

Vogt, R.; Mlynowski, T. J.; Menounos, B.

2013-12-01

273

Helical axis stellarator equilibrium model  

SciTech Connect

An asymptotic model is developed to study MHD equilibria in toroidal systems with a helical magnetic axis. Using a characteristic coordinate system based on the vacuum field lines, the equilibrium problem is reduced to a two-dimensional generalized partial differential equation of the Grad-Shafranov type. A stellarator-expansion free-boundary equilibrium code is modified to solve the helical-axis equations. The expansion model is used to predict the equilibrium properties of Asperators NP-3 and NP-4. Numerically determined flux surfaces, magnetic well, transform, and shear are presented. The equilibria show a toroidal Shafranov shift.

Koniges, A.E.; Johnson, J.L.

1985-02-01

274

A new method for deriving glacier centerlines applied to glaciers in Alaska and northwest Canada  

NASA Astrophysics Data System (ADS)

This study presents a new method to derive centerlines for the main branches and major tributaries of a set of glaciers, requiring glacier outlines and a digital elevation model (DEM) as input. The method relies on a "cost grid-least-cost route approach" that comprises three main steps. First, termini and heads are identified for every glacier. Second, centerlines are derived by calculating the least-cost route on a previously established cost grid. Third, the centerlines are split into branches and a branch order is allocated. Application to 21 720 glaciers in Alaska and northwest Canada (Yukon, British Columbia) yields 41 860 centerlines. The algorithm performs robustly, requiring no manual adjustments for 87.8% of the glaciers. Manual adjustments are required primarily to correct the locations of glacier heads (7.0% corrected) and termini (3.5% corrected). With corrected heads and termini, only 1.4% of the derived centerlines need edits. A comparison of the lengths from a hydrological approach to the lengths from our longest centerlines reveals considerable variation. Although the average length ratio is close to unity, only ~ 50% of the 21 720 glaciers have the two lengths within 10% of each other. A second comparison shows that our centerline lengths between lowest and highest glacier elevations compare well to our longest centerline lengths. For > 70% of the 4350 glaciers with two or more branches, the two lengths are within 5% of each other. Our final product can be used for calculating glacier length, conducting length change analyses, topological analyses, or flowline modeling.

Kienholz, C.; Rich, J. L.; Arendt, A. A.; Hock, R.

2014-03-01

275

Climate sensitivity of Tibetan Plateau glaciers - past and future implications  

NASA Astrophysics Data System (ADS)

The Tibetan Plateau is one of the most extensively glaciated, non-Polar regions of the world, and its mountain glaciers are the primary source of melt water for several of the largest Asian rivers. During glacial cycles, Tibetan Plateau glaciers advanced and retreated multiple times, but remained restricted to the highest mountain areas as valley glaciers and ice caps. Because glacier extent is dominantly controlled by climate, the past extent of Tibetan glaciers provide information on regional climate. Here we present a study analyzing the past maximum extents of glaciers on the Tibetan Plateau with the output of a 3D glacier model, in an effort to quantify Tibetan Plateau climate. We have mapped present-day glaciers and glacial landforms deposited by formerly more extensive glaciers in eight mountain regions across the Tibetan Plateau, allowing us to define present-day and past maximum glacier outlines. Using a high-resolution (250 m) higher-order glacier model calibrated against present-day glacier extents, we have quantified the climate perturbations required to expand present-day glaciers to their past maximum extents. We find that a modest cooling of at most 6°C for a few thousand years is enough to attain past maximum extents, even with 25-75% precipitation reduction. This evidence for limited cooling indicates that the temperature of the Tibetan Plateau remained relatively stable over Quaternary glacial cycles. Given the significant sensitivity to temperature change, the expectation is perhaps that a future warmer climate might result in intense glacier reduction. We have tested this hypothesis and modeled the future glacier development for the three mountain regions with the largest present-day glacier cover using a projected warming of 2.8 to 6.2°C within 100 years (envelope limits from IPCC). These scenarios result in dramatic glacier reductions, including 24-100% ice volume loss after 100 years and 77-100% ice volume loss after 300 years.

Heyman, Jakob; Hubbard, Alun; Stroeven, Arjen P.; Harbor, Jonathan M.

2013-04-01

276

The History of the Glacier Facies Concept  

NASA Astrophysics Data System (ADS)

The concept of glacier facies developed as a result of physical measurements made in Greenland on repeated traverses that went inland from the west coast at two latitudes (77 N and 70 N) and north to south along the crest of the ice sheet. Snow pits and shallow cores showed discontinuities in physical characteristics that defined the facies boundaries. Some refinement have resulted from research in Antarctica and on Alaskan mountain glaciers. Thirty years after the facies were defined, based on field measurements, it was found that radar data (SAR) from satellites show the boundary between the percolation and dry snow facies in Greenland. They also show the percolation facies of the Greenland ice sheet to be the brightest radar reflector on earth. The dry snow facies is rare except on the major ice sheets (Greenland and Antarctica), but it is present on mountains that exceed 4000 m in Alaska and the Yukon. In particular, Mt. Wrangell, Alaska was selected for continued study of glacier facies because it has a large and accessible area above 4000 m. Mt. Wrangell has proven to have the full spectrum of glacier facies, and these can be seen on the SAR map of Alaska. Refinements in the definition of the lower end of the wet snow facies, to deal with a slush zone and a superimposed ice zone, resulted from Fritz Mueller's research on Axel Heiberg Island and from studies on the McCall Glacier of Alaska. Minor refinements in defining the dry snow facies resulted from comparing Antarctica and Greenland in places where mean annual temperature and accumulation rates were essentially equal. The glacier facies concept also provides a way of comparing the two polar regions and of speculating on the glacier facies that existed on the Pleistocene continental ice sheets.

Benson, C. S.

2001-12-01

277

Predicting the Effect of Mountain Glacier Recession on Water Resources: A Modeling Study on the Bow Glacier, Alberta  

NASA Astrophysics Data System (ADS)

Meltwater from alpine glaciers provides critical water supply for vulnerable populations in the western Andes, the Himalayas and the eastern Canadian Rockies. Glacier recession is of major concern in these climate-sensitive regions where we seek to predict changes in watershed hydrology in selected glacierized river basins. The overarching research question of this investigation asks: How have changes in headwater glaciers affected water supply reliability in those parts of the world where streamflow dynamics are most affected by glacier sources? Our approach uses a process-based model that incorporates snow, glaciers, soil, groundwater, vegetation, and topography. The model is a newly modified version of the spatially distributed hydrology model, DHSVM, in which we have added a dynamic glacier submodel. The glacier submodel is initialized with satellite remote sensing-derived maps of glacier extent and a digital elevation model. It assumes conservation of mass, solving the continuity equation for ice and assumes Glen's ice creep law, a sliding law, and the shallow ice approximation. The glacier model can also handle transport and melt-out of debris cover, ice rheology, and isostatic adjustment for long model runs. Using the Bow Glacier, Alberta as an example, this presentation will focus on recent advances in the integrated modeling of glacier and snowmelt runoff and state-of-the-art remote sensing of glacier extent from ASTER and Landsat.

Nolin, A. W.; Lettenmaier, D. P.; Clarke, G. K.; Naz, B. S.; Burns, P. J.

2011-12-01

278

Pine Island Glacier, Antarctica, MISR Multi-angle Composite  

article title:  Pine Island Glacier, Antarctica, MISR Multi-angle Composite     ... iceberg has finally separated from the calving front of Antarctica's Pine Island Glacier. Scientists first detected a rift in the ...

2013-12-17

279

Optical Flow for Glacier Motion Estimation  

NASA Astrophysics Data System (ADS)

Quantitative measurements of glacier flow over time are an important ingredient for glaciological research, for example to determine the mass balances and the evolution of glaciers. Measuring glacier flow in multi-temporal images involves the estimation of a dense set of corresponding points, which in turn define the flow vectors. Furthermore glaciers exhibit rather difficult radiometry, since their surface usually contains homogeneous areas as well as weak texture and contrast. To date glacier flow is usually observed by manually measuring a sparse set of correspondences, which is labor-intensive and often yields rather irregular point distributions, with the associated problems of interpolating over large areas. In the present work we propose to densely compute motion vectors at every pixel, by using recent robust methods for optic flow computation. Determining the optic flow, i.e. the dense deformation field between two images of a dynamic scene, has been a classic, long-standing research problem in computer vision and image processing. Sophisticated methods exist to optimally balance data fidelity with smoothness of the motion field. Depending on the strength of the local image gradients these methods yield a smooth trade-off between matching and interpolation, thereby avoiding the somewhat arbitrary decision which discrete anchor points to measure, while at the same time mitigating the problem of gross matching errors. We evaluate our method by comparing with manually measured point wise ground truth.

Vogel, C.; Bauder, A.; Schindler, K.

2012-07-01

280

Exploration of Uncertainty in Glacier Modelling  

NASA Technical Reports Server (NTRS)

There are procedures and methods for verification of coding algebra and for validations of models and calculations that are in use in the aerospace computational fluid dynamics (CFD) community. These methods would be efficacious if used by the glacier dynamics modelling community. This paper is a presentation of some of those methods, and how they might be applied to uncertainty management supporting code verification and model validation for glacier dynamics. The similarities and differences between their use in CFD analysis and the proposed application of these methods to glacier modelling are discussed. After establishing sources of uncertainty and methods for code verification, the paper looks at a representative sampling of verification and validation efforts that are underway in the glacier modelling community, and establishes a context for these within overall solution quality assessment. Finally, an information architecture and interactive interface is introduced and advocated. This Integrated Cryospheric Exploration (ICE) Environment is proposed for exploring and managing sources of uncertainty in glacier modelling codes and methods, and for supporting scientific numerical exploration and verification. The details and functionality of this Environment are described based on modifications of a system already developed for CFD modelling and analysis.

Thompson, David E.

1999-01-01

281

Progresses in the ice formation of glaciers in China  

Microsoft Academic Search

Glaciers, formed by snowfall and characterized by movement and size, are the most sensitive indicators to climate change.\\u000a The ice formation of glaciers (the processes, mechanisms and results of transformation from snow to ice) can indicate the\\u000a growth condition, the formation process and the physical characteristics of glaciers. Its spatial variation can also reflect\\u000a glacier change, and further reveal climate

Xiangying Li; Shiyin Liu; Donghui Shangguan; Aigang Lu

2008-01-01

282

Glacier Bay, Alaska, from the Ground, Air and Space  

NSDL National Science Digital Library

This video contains a mix of live action video, stills, and computer animations of the Glacier Bay National Park in Glacier Bay, Alaska. Satellite mapping and imagery are used to show changes in the Glacier Bay area over a period of several years. Specific image processing techniques are discussed in relation to determining the evolution of glacier terminus points and in obtaining elevation data and how it is used to create fly-by visualizations of the area.

Starr, Cindy; Strong, Jim; Oneil, Pamela; Acuna, Andy; Hall, Dorothy; Benson, Carl

1996-02-23

283

Decay of a long-term monitored glacier: the Careser glacier (Ortles-Cevedale, European Alps)  

NASA Astrophysics Data System (ADS)

The continuation of valuable, long-term glacier observation series is threatened by the accelerated mass loss which currently affects a large portion of so-called "benchmark" glaciers. In this work we present the evolution of the Careser glacier, from the beginning of systematic observation at the end of the nineteenth century to its current condition in 2012. In addition to having one of the longest and richest observation record among the Italian glaciers, Careser is unique in the Italian Alps for its 45 yr mass balance series started in 1967. In the present study, variations in the length, area and volume of the glacier since 1897 are examined, updating the series of direct mass balance observations and extending it into the past using the geodetic method. The glacier is currently strongly out of balance and in rapid decay; its average mass loss rate over the last three decades was -1.5 m water equivalent per year, increasing to -2.0 m water equivalent per year in the last decade. If mass loss continues at this pace, the glacier will disappear within a few decades, putting an end to this unique observation series.

Carturan, L.; Baroni, C.; Becker, M.; Bellin, A.; Cainelli, O.; Carton, A.; Casarotto, C.; Dalla Fontana, G.; Godio, A.; Martinelli, T.; Salvatore, M. C.; Seppi, R.

2013-07-01

284

Asynchroneity of maximum glacier advances in the central Spanish Pyrenees  

Microsoft Academic Search

The deglaciation history of the Escarra and Lana Mayor glaciers (Upper Gállego valley, central Spanish Pyrenees) had been reconstructed on the basis of detailed geomorphological studies of glacier deposits, sedimentological and palynological analyses of glacial lake sediments and an accelerator mass spectrometry (AMS) 14C chronology based on minimum ages from glacial lake deposits. The maximum extent of the Pyrenean glaciers

José M. García-Ruiz; Blas L. Valero-Garcés; Carlos Martí-Bono; Penélope González-Sampériz

2003-01-01

285

Extracting a Climate Signal from 169 Glacier Records  

Microsoft Academic Search

I constructed a temperature history for different parts of the world from 169 glacier length records. Using a first-order theory of glacier dynamics, I related changes in glacier length to changes in temperature. The derived temperature histories are fully independent of proxy and instrumental data used in earlier reconstructions. Moderate global warming started in the middle of the 19th century.

J. Oerlemans

2005-01-01

286

Chemical weathering in the foreland of a retreating glacier  

Microsoft Academic Search

Chemical denudation rates and strontium isotope ratios in streams vary substantially and systematically in the foreland of the retreating Bench Glacier in south-central Alaska. To study weathering of young glacier sediments, we sampled 12 streams draining a chronosequence of till and moraine soils derived from Cretaceous metagraywacke–metapelite bedrock. Both sediment age and vegetation cover increase with distance from the glacier.

Suzanne Prestrud Anderson; James I Drever; Carol D Frost; Pete Holden

2000-01-01

287

Snow and glacier mapping with polarimetric SAR  

NASA Technical Reports Server (NTRS)

The objective of this study was to examine the capability of mapping snow and glaciers in alpine regions using synthetic aperture radar (SAR) imagery when topographic information is not available. The topographic effects on the received power for a resolution cell can be explained by the change in illumination area and incidence angle in a slant-rante representation of SAR imagery. The specific polarization signatures and phase difference between HH and VV components are relatively independent of the illuminated are, and the incidence angle has only a small effect on these parameters. They provide a suitable measurement data set for snow and glacier mapping in a high-relief area. The results show that the C-band images of the enhancement factor, the phase difference between HH and VV scattering components, and the normalized cross product of VV scattering elements provide the capability to discriminate among snow with different wetnesses, glaciers, and rocky regions.

Shi, Jiancheng; Dozier, Jeff; Rott, Helmut; Davis, Robert E.

1991-01-01

288

Response of glaciers in northwestern North America to future climate change: an atmosphere\\/glacier hierarchical modeling approach  

Microsoft Academic Search

The response of glaciers to changing climate is explored with an atmosphere\\/glacier hierarchical modeling approach, in which global simulations are downscaled with an Arctic MM5 regional model which provides temperature and precipitation inputs to a glacier mass-balance model. Themass balances of Hubbardand BeringGlaciers, south-central Alaska, USA, aresimulated for October 1994-September 2004. The comparisons of the mass-balance simulations using dynamically-downscaled vs

Jing Zhang; Uma S. Bhatt; Wendell V. Tangborn; Craig S. Lingle

2007-01-01

289

Comparative metagenome analysis of an Alaskan glacier.  

PubMed

The temperature in the Arctic region has been increasing in the recent past accompanied by melting of its glaciers. We took a snapshot of the current microbial inhabitation of an Alaskan glacier (which can be considered as one of the simplest possible ecosystems) by using metagenomic sequencing of 16S rRNA recovered from ice/snow samples. Somewhat contrary to our expectations and earlier estimates, a rich and diverse microbial population of more than 2,500 species was revealed including several species of Archaea that has been identified for the first time in the glaciers of the Northern hemisphere. The most prominent bacterial groups found were Proteobacteria, Bacteroidetes, and Firmicutes. Firmicutes were not reported in large numbers in a previously studied Alpine glacier but were dominant in an Antarctic subglacial lake. Representatives of Cyanobacteria, Actinobacteria and Planctomycetes were among the most numerous, likely reflecting the dependence of the ecosystem on the energy obtained through photosynthesis and close links with the microbial community of the soil. Principal component analysis (PCA) of nucleotide word frequency revealed distinct sequence clusters for different taxonomic groups in the Alaskan glacier community and separate clusters for the glacial communities from other regions of the world. Comparative analysis of the community composition and bacterial diversity present in the Byron glacier in Alaska with other environments showed larger overlap with an Arctic soil than with a high Arctic lake, indicating patterns of community exchange and suggesting that these bacteria may play an important role in soil development during glacial retreat. PMID:24712530

Choudhari, Sulbha; Lohia, Ruchi; Grigoriev, Andrey

2014-04-01

290

Recent climate trends, Glacier Bay, Alaska  

NASA Astrophysics Data System (ADS)

Glaciers and ice caps respond to changes in regional climate at decadal scales and can thus serve as indicators of regional climate change. Many of the tidewater and terrestrial glaciers in Glacier Bay, Alaska have been in a state of rapid retreat since the late 1700s, with highly disparate rates of recession occurring in the western versus eastern arms, yet the combination of environmental and glaciological factors that must exist to catalyze these rapid changes is not clearly understood. The Cold Regions Research and Engineering Laboratory (CRREL) initiated the first systematic analyses of weather and precipitation patterns across Glacier Bay National Park in 2000 by establishing 26 meteorological stations with the long-term objective of better understanding regional and global factors, that control terrestrial and marine physical systems. Initial temperature and precipitation trends show rapid seasonal and annual shifts. This is consistent with apparent paleo-trends in climate and glacier advance and recession over the last 9K years, as well as the historical record that indicate the area is climatically sensitive. Comparisons of summer and winter precipitation totals show a precipitation gradient increasing northward from the lower bay to the head of Muir Inlet (east arm), and decreasing northwestward in the West Arm. Monthly averages of air temperatures span about 3.5 C between the warmest and coldest sites near sea level. Winter temperatures averaged more than 1 C colder in the West Arm than the East. We also found large gradients of increasing rainfall from north to south in the east arm, from north to south in the Western arm. Average temperatures in October decreased westward in the northern half of the Park and were milder at sites within the larger southern Bay. Continuing a long-term climate-monitoring program in Glacier Bay will assist with quantifying climate trends in the context of glacial movement, helping to determine the overall sensitivity of the regional glacial system to regional climate signals.

Kopczynski, S. E.; Bigl, S. R.; Lawson, D. E.; Finnegan, D. C.

2003-12-01

291

Geodetic observations of short-time-scale changes in glacier flow at Helheim and Kangerdlugssuaq Glaciers, East Greenland  

Microsoft Academic Search

Evidence obtained by several workers during the past few years has shown that the major outlet glaciers in Greenland can both accelerate and decelerate more rapidly than previously appreciated. Some abrupt accelerations at the largest outlet glaciers, including Jakobshavn Isbrae and Helheim and Kangerdlugssuaq Glaciers, have been linked to large-scale calving events and glacial earthquakes (Nettles et al., 2008; Amundson

M. Nettles; P. Elosegui; T. Larsen; J. L. Davis; G. S. Hamilton; L. A. Stearns; M. L. Andersen; J. de Juan; E. Malikowski; I. Gonzalez; M. Okal; B. Johns; G. Ekstrom; A. Ahlstrøm; L. Stenseng; S. A. Khan; K. M. Schild; R. Forsberg; S. A. Veitch

2009-01-01

292

Glacier volume response time and its links to climate and topography based on a conceptual model of glacier hypsometry  

NASA Astrophysics Data System (ADS)

Glacier volume response time is a measure of the time taken for a glacier to adjust its geometry to a climate change. It has been previously proposed that the volume response time is given approximately by the ratio of glacier thickness to ablation at the glacier terminus. We propose a new conceptual model of glacier hypsometry (area-altitude relation) and derive the volume response time where climatic and topographic parameters are separated. The former is expressed by mass balance gradients which we derive from glacier-climate modelling and the latter are quantified with data from the World Glacier Inventory. Aside from the well-known scaling relation between glacier volume and area, we establish a new scaling relation between glacier altitude range and area, and evaluate it for seven regions. The presence of this scaling parameter in our response time formula accounts for the mass balance elevation feedback and leads to longer response times than given by the simple ratio of glacier thickness to ablation at the terminus. Volume response times range from decades to thousands of years for glaciers in maritime (wet-warm) and continental (dry-cold) climates respectively. The combined effect of volume-area and altitude-area scaling relations is such that volume response time can increase with glacier area (Axel Heiberg Island and Svalbard), hardly change (Northern Scandinavia, Southern Norway and the Alps) or even get smaller (The Caucasus and New Zealand).

Raper, S. C. B.; Braithwaite, R. J.

2009-08-01

293

Glacier volume response time and its links to climate and topography based on a conceptual model of glacier hypsometry  

NASA Astrophysics Data System (ADS)

Glacier volume response time is a measure of the time taken for a glacier to adjust its geometry to a climate change. It is currently believed that the volume response time is given approximately by the ratio of glacier thickness to ablation at the glacier terminus. We propose a new conceptual model of glacier hypsometry (area-altitude relation) and derive the volume response time where climatic and topographic parameters are separated. The former is expressed by mass balance gradients which we derive from glacier-climate modelling and the latter are quantified with data from the World Glacier Inventory. Aside from the well-known scaling relation between glacier volume and area, we establish a new scaling relation between glacier altitude range and area, and evaluate it for seven regions. The presence of this scaling parameter in our response time formula accounts for the mass balance elevation feedback and leads to longer response times than given by the simple ratio of glacier thickness to ablation. Volume response times range from decades to thousands of years for glaciers in maritime (wet-warm) and continental (dry-cold) climates, respectively. The combined effect of volume-area and altitude-area scaling relations is such that volume response time can increase with glacier area (Axel Heiberg Island and Svalbard), hardly change (Northern Scandinavia, Southern Norway and the Alps) or even get smaller (The Caucasus and New Zealand).

Raper, S. C. B.; Braithwaite, R. J.

2009-03-01

294

Glacier area and length changes in Norway from repeat inventories  

NASA Astrophysics Data System (ADS)

In this study, we assess glacier area and length changes in mainland Norway from repeat Landsat TM/ETM+ derived inventories and digitized topographic maps. The multi-temporal glacier inventory consists of glacier outlines from within three time ranges: 1947 to 1985 (GIn50), 1988 to 1997 (GI1990), and 1999 to 2006 (GI2000). For the northernmost regions, we include an additional inventory (GI1900), based on historic maps surveyed between 1895 to 1907. Area and length changes are assessed per glacier unit, for 36 subregions, and for three main parts of Norway: southern, central and northern Norway. The results show a decrease of the glacierized area from 2994 km2 in GIn50, to 2668 km2 in GI2000 (totally 2722 glacier units), corresponding to an area reduction of -326 km2, or -11% of the initial GIn50 area. This is equivalent to an average change rate of -11 km2 a-1 over the past 30 years. The average length change for the full epoch (within GIn50 and GI2000) is -240 m, corresponding to an average length change rate of -8 m a-1. Overall, the comparison reveals both area and length reduction as a general pattern, even though some glaciers have advanced. The three northernmost glacier regions show the strongest retreat rates, whereas the central part of Norway shows the lowest change rates. Glacier area and length changes indicate that glaciers in maritime areas in southern Norway have retreated more than glaciers in the interior, and glaciers in the north have retreated more than southern glaciers. These observed spatial trends in glacier change are related to a combination of several geographical factors like glacier geometry and elevation, and other climatic aspects, such as continentality and the North Atlantic Oscillation.

Winsvold, S. H.; Andreassen, L. M.; Kienholz, C.

2014-06-01

295

The Increasing of Glacial Runoff in Response to Climate Warming in Glacier No.1 at the Headwaters of the Urumqi River, Tianshan Mountains  

NASA Astrophysics Data System (ADS)

Based on hydrological observations and calculations of water balance?the annual meltwater runoff of Glacier No.1 which locates at the Headwaters of the Urumqi River, Tianshan Mountains has been computed. It shows an elevated trend during the last several decades.The mean meltwater runoff depth is 936.6mm during the period of 1986 to 2001, comparing to 508.4mm during the period of 1958 to 1985. Data analysis shows that the proportion of liquid precipitation which can form runoff over the glacier surface has also been raised ,with the annual mean air temperature at the glacier terminus in the period of 1986 to 2001 increased by 0.5? to the period of 1958 to 1985.We also found that the ablation occurred in the position corresponding approximately to the equilibrium altitude in the glacier kept pace well with the glacier meltwater runoff. We conclude that the ablation on that altitude can represent the glacial meltwater runoff to a certain extent. Considering the climate shift in northwest of China, it is necessary to realize the glacial meltwater runoff sensitivity to climate change. We applied the degree-day model which has performed well for reconstructing mass balance of this glacier to simulate glacial meltwater runoff.

Li, Jing; Liu, Shiyin

2010-05-01

296

Pre-survey of the 79°N Glacier (Nioghalvfjerdsbrae), Greenland, using airborne radio echo sounding and laser altimetry  

NASA Astrophysics Data System (ADS)

The 79°N Glacier is an outlet glacier of the only large ice stream of Greenland, the North-East Greenland Ice Stream. In contrast to tidewater glaciers this glaciers forms a floating tongue which is comparable to the ice shelves in Antarctica. In 2016 a field campaign aims to derive the basal melt rates and to investigate if warm water masses are draining from the Fram Strait underneath the floating tongue of the 79°N Glacier. In preparation for the future field campaign a combined radio echo sounding and laser scanner survey was flown in 2013 along the floating tongue and upstream the grounding line. Here, we present an analysis of the radio echo sounding from that airborne campaign and previous datasets acquired using a 150 MHz system. We infer the location of the grounding line and the ice thickness. Additionally, we have used laser scanner data to determine the local DEM. Using the laser scanner data, we also estimated the surface roughness of the ice, as the floating tongue is experiencing an extended summer melt season in which rivers and ponds form. Furthermore, we present the plans for the field campaign in 2016.

Steinhage, Daniel; Helm, Veit; Belke-Brea, Maria; Humbert, Angelika

2014-05-01

297

A complex relationship between calving glaciers and climate  

USGS Publications Warehouse

Many terrestrial glaciers are sensitive indicators of past and present climate change as atmospheric temperature and snowfall modulate glacier volume. However, climate interpretations based on glacier behavior require careful selection of representative glaciers, as was recently pointed out for surging and debris-covered glaciers, whose behavior often defies regional glacier response to climate [Yde and Paasche, 2010]. Tidewater calving glaciers (TWGs)mountain glaciers whose termini reach the sea and are generally grounded on the seaflooralso fall into the category of non-representative glaciers because the regional-scale asynchronous behavior of these glaciers clouds their complex relationship with climate. TWGs span the globe; they can be found both fringing ice sheets and in high-latitude regions of each hemisphere. TWGs are known to exhibit cyclic behavior, characterized by slow advance and rapid, unstable retreat, largely independent of short-term climate forcing. This so-called TWG cycle, first described by Post [1975], provides a solid foundation upon which modern investigations of TWG stability are built. Scientific understanding has developed rapidly as a result of the initial recognition of their asynchronous cyclicity, rendering greater insight into the hierarchy of processes controlling regional behavior. This has improved the descriptions of the strong dynamic feedbacks present during retreat, the role of the ocean in TWG dynamics, and the similarities and differences between TWG and ice sheet outlet glaciers that can often support floating tongues.

Post, A.; O'Neel, S.; Motyka, R. J.; Streveler, G.

2011-01-01

298

Pine Island glacier ice shelf melt distributed at kilometre scales  

NASA Astrophysics Data System (ADS)

By thinning and accelerating, West Antarctic ice streams are contributing about 10% of the observed global sea level rise. Much of this ice loss is from Pine Island Glacier, which has thinned since at least 1992, driven by changes in ocean heat transport beneath its ice shelf and retreat of the grounding line. Details of the processes driving this change, however, remain largely elusive, hampering our ability to predict the future behaviour of this and similar systems. Here, a Lagrangian methodology is developed to measure oceanic melting of such rapidly advecting ice. High-resolution satellite and airborne observations of ice surface velocity and elevation are used to quantify patterns of basal melt under the Pine Island Glacier ice shelf and the associated adjustments to ice flow. At the broad scale, melt rates of up to 100 m yr-1 occur near the grounding line, reducing to 30 m yr-1 just 20 km downstream. Between 2008 and 2011, basal melting was largely compensated by ice advection, allowing us to estimate an average loss of ice to the ocean of 87 km3 yr-1, in close agreement with 2009 oceanographically constrained estimates. At smaller scales, a network of basal channels typically 500 m to 3 km wide is sculpted by concentrated melt, with kilometre-scale anomalies reaching 50% of the broad-scale basal melt. Basal melting enlarges the channels close to the grounding line, but farther downstream melting tends to diminish them. Kilometre-scale variations in melt are a key component of the complex ice-ocean interaction beneath the ice shelf, implying that greater understanding of their effect, or very high resolution models, are required to predict the sea-level contribution of the region.

Dutrieux, P.; Vaughan, D. G.; Corr, H. F. J.; Jenkins, A.; Holland, P. R.; Joughin, I.; Fleming, A. H.

2013-09-01

299

Rheology of rock glaciers: a preliminary assessment  

Microsoft Academic Search

Movement of rock debris under the influence of gravity, i.e., mass movement, generates a range of phenomena from soil creep, through solifluction,debris flows and rock glaciers to rock falls. Whereas the resultant forms of these phenomena are different, common elements in the mechanics of movement are utilized in the basic interpretation of the processes of formation. Measurements of morphologic variables

J. R. Giardino; J. D. Vitek; E. R. Hoskins

1985-01-01

300

Resource Use in Glacier Bay National Preserve.  

National Technical Information Service (NTIS)

The report is a baseline description of resource use in the Dry Bay area, which in 1981 became Glacier Bay National Preserve. The study involved the joint cooperation of the NPS and the Subsistence Division of the Alaska Dept. of Fish and Game. The main p...

G. Gmelch

1982-01-01

301

Stream temperature response to glacier retreat (Invited)  

NASA Astrophysics Data System (ADS)

Stream temperature is a fundamental aspect of aquatic habitat, and there has been increasing concern in recent years that climatic change and glacier retreat will result in increased water temperatures, with potentially negative influences on cold and cool water species such as salmonids. A statistical model was developed to predict the maximum weekly average stream temperature based on data from 418 sites located throughout British Columbia, Canada. Catchment-scale glacier coverage was a significant predictor in the model, and example calculations indicate that plausible decreases in glacier coverage over the next few decades have the potential to result in warming that would be sufficient to cause shifts in fish species assemblages. However, this space-for-time substitution rests on assumptions that may not be valid, especially in the context of a changing climate, leading to a need to develop and apply physically based models. Reach-scale energy budget analyses indicate that parameterizations of energy fluxes used in current stream temperature models are not appropriate for steep channels with cascading flow. In particular, the sensible and latent heat fluxes are more efficient than in lower-gradient channels, and the albedo is enhanced by aeration. Over longer time scales, development of riparian forest has the potential to mitigate the effect of glacier retreat in alpine areas by shading the stream, but it may take centuries for functional riparian forest to develop at higher elevation sites.

Moore, R. D.

2013-12-01

302

Slow Erosion by a Fast Glacier  

Microsoft Academic Search

The dramatic imprints left on landscapes by Quaternary glaciations provide abundant evidence that glaciers can be efficient erosive agents. Understanding their erosive capability is key to unravelling the complex coupling of climate and the dynamics of the solid earth. Recent studies have focused on quantifying rates of glacial erosion to provide key data for understanding the physics that drives glacial

A. D. Huerta; J. P. Winberry

2007-01-01

303

Triaxial experinlents on iceberg and glacier ice  

Microsoft Academic Search

Triaxial experiments, at confining pressures in the range 0- 13.79 MPa, have been performed on glacial ice collected from four icebergs and one glacier. Tests were conducted at strain rates in the range of 5 x 10 .'J to 5 x 10 2 S I and at four temperatures in the range of 10 to -16 °C. Depending on test

R. E. GAG

304

Changes in the Surface Area of Glaciers in Northern Eurasia  

NASA Astrophysics Data System (ADS)

Glaciers are widely recognized as key indicators of climate change. Recent evidence suggests an acceleration of glacier mass loss in several key mountain regions. Glacier recession implies the landscape changes in the glacial zone, origin of new lakes and activation of natural disaster processes, catastrophic mudflows, ice avalanches, outburst floods, and etc. The presence of glaciers in itself threats to human life, economic activity and growing infrastructure. Economical and recreational human activity in mountain regions requires relevant information on snow and ice objects. Absence or inadequacy of such information results in financial and human losses. A more comprehensive evaluation of glacier changes is imperative to assess ice contributions to global sea level rise and the future of water resources from glacial basins. One of the urgent steps is a full inventory of all ice bodies, their volume and changes The first estimation of glaciers state and glaciers distribution in the big part of Northern Eurasia has been done in the USSR Glacier Inventory published in 1966 -1980 as a part of IHD activity. The Inventory is based on topographic maps and air photos and reflects the status of the glaciers in 1957-1970y. There is information about 23796 glaciers with area of 78222.3 km2 in the Inventory. It covers 23 glacier systems on Northern Eurasia. In the 80th the USSR Glacier Inventory has been transformed in the digital form as a part of the World Glacier Inventory. Recent satellite data provide a unique opportunity to look again at these glaciers and to evaluate changes in glacier extent for the second part of XX century. In the paper we report about 15 000 glaciers outlines for Caucasus, Pamir, Tien-Shan, Altai, Syntar-Khayata, Cherskogo Range, Kamchatka and Russian Arctic which have been derived from ASTER and Landsat imagery and could be used for glacier changes evaluation. The results show that glaciers are retreating in all these regions. There is, however, a rather large variability in degree of reduction very much depending on special local conditions and this was particularly notable with regard to smaller glaciers.

Khromova, T.; Nosenko, G.

2012-12-01

305

Earthly and Otherworldly Glaciers on Mars: Expressed Subsurface Subpolar Ice and "Plate Tectonic" South Polar Ices  

NASA Astrophysics Data System (ADS)

DIRTY SUBPOLAR GLACIERS: Deeply etched internal structures of debris-covered glaciers or rock glaciers occur widely on Mars at middle latitudes. Differentially sublimated folds, crevasses, medial moraines and flow lines are expressed now as a variety of pits, troughs, hummocks, and ridges; they reveal much about the extent of sublimation and the history of flow and accumulation that originally gave rise to these structures. In many regards, they appear like usual terrestrial debris-covered glaciers (including rock glaciers). These sublimated remnant structures are not uniformly distributed on the planet; they exhibit a definite relationship to latitude. The more deeply etched icy flows occur generally in the latitude belt from 30 to 40 degrees (north and south), where possibly very little ice remains near the surface. Between 40 and 55 degrees, most of these partly sublimated flows appear to be still icy. Poleward of that, many of them show very little evidence of any sublimational loss of ice, and instead appear as thick mantling blankets sometimes having subtle flow lines. Inferences for the distribution of ground ice and the role of sublimation are similar to those inferred from the distribution and morphology of small polygons; these results are also consistent with theoretical models of the distribution of ground ice and with Mars Odyssey neutron spectroscopy of the distribution of hydrogen in the upper meter of Mars. A peculiar aspect of dirty glaciers on Mars is their current lack of an evident zone of atmospherically driven accumulation; instead, accumulation of some dirty glaciers appears to be due to load-driven expression of ice originating probably in massive crustal layers; for others, atmospheric accumulation may occur at other times during the obliquity cycle of Mars. SOUTH POLAR ICE SHEET: Previously I have reported on evidence for flowing, faulting, folding south polar ice, with the evidence for the more ductile types of deformation concentrated within the area of perennial CO2 ice. This part of the polar cap exhibits strong evidence for convergent flow tending to close the quasi-spiral structured troughs, as predicted by finite-element modelers. A rich phenomenology accompanies this closure. In some cases, good evidence exists for one icy sheet overriding another. Elastic plate flexural responses, with attendant small-scale tectonism, is quite common, as is evidence for ductile deformation. Analogs drawn from Earth's lithosphere provide compelling explanations for some of these features. Smooth, topographically enclosed flat areas in the south polar deposits may be the surface expressions of subglacial lakes or refrozen lakes.

Kargel, J. S.

2003-12-01

306

Jökulhlaup triggering: Observations at Kennicott Glacier, Alaska  

NASA Astrophysics Data System (ADS)

Jökulhlaups, sudden releases of water impounded by a glacier, produce large floods unrelated to weather events. We draw on observations from 90 years of annual jökulhlaups from Hidden Creek Lake, Kennicott Glacier, Alaska and from detailed monitoring in 1999 and 2000, to examine conditions that trigger outburst floods. For the class of jökulhlaups caused by subglacial drainage, the trigger must be related to formation of subglacial conduits, a pivotal problem in glaciology. Hidden Creek Lake water level at drainage has declined over the last century, during which time the glacier has thinned. The water level trend is mirrored by a tendency toward earlier release dates in the summer. These observations suggest that a minimum threshold lake level must be exceeded for drainage to occur, and that this threshold is related to ice thickness. The release date varies by over a month, however, and lake level varies by as much as 10 m over spans of a few years, which indicates that more is involved than simple exceedance of a threshold. Kennicott Glacier impounds several other small lakes. In two summers with fairly complete observations of their behavior, these lakes drained in sequence from nearest to furthest from the terminus. More frequent observations have been made of drainage of one of these lakes: Erie Lake, located roughly the same distance from the terminus as Hidden Creek Lake, along a major tributary to the Kennicott Glacier, usually drains within days of Hidden Creek Lake. These patterns are consistent with a trigger that is related to glacier-wide evolution of the hydrologic system, rather than each drainage reflecting purely local conditions. Perhaps there is a linkage between timing of outbursts and seasonal upglacier extension of the subglacial conduit system. While we have no direct information on annual evolution of the conduit system at Kennicott Glacier, some have suggested that conduits and the snowline move upglacier in tandem. In 1999 and 2000, the snowline had retreated far upglacier, beyond Hidden Creek Lake, before it drained. Estimated melt rates in the days preceding Hidden Creek Lake outbursts, calculated with a degree day model, show no pattern: lake drainage has occurred during times of both low and high melt production. Jökulhlaup triggering appears to be controlled by a number of conditions, among them the height of the ice barrier, organization of the subglacial hydrologic system, and specific, probably transient, conditions within that system at the time of drainage.

Anderson, S. P.; Walder, J. S.; Fountain, A. G.; Anderson, R. S.; Trabant, D. C.

2003-12-01

307

Ice flow dynamics of Alaska glaciers  

NASA Astrophysics Data System (ADS)

Understanding long-term ice dynamic response to climate change remains of the utmost importance with respect to constraining sea level rise (SLR) projections for 2100. SLR contributions from Alaska approximate those from Greenland and may be dominated by mass losses from changes in flow dynamics. But due to a lack of data on flow dynamics, projections for future mass change in Alaska only consider surface mass balance. Here we present the first regionally extensive dataset of mountain glacier flow velocities in Alaska---covering 28,022 km2 of ice. This dataset reveals that more than 50% of the mass flux in Alaska comes from only eleven key glacier systems that have high mass fluxes due to high balance velocities and are not necessarily linked to tidewater glacier retreat. In south central Alaska, we find that the rate of mass loss from tidewater calving is equivalent to 75% of the total net mass loss annually; thus surface mass balance alone is inadequate to project future statewide mass losses. Our dataset also enables a close examination of a surge (periodic acceleration) event on Bering Glacier, the largest surging glacier in the world. There, velocities exceed quiescent speeds by 18 times over two periods lasting a total of 3 years. Results suggest that downstream propagation of the surge is closely linked to the evolution of the driving stress during the surge because driving stress appears to be tied to the spatial variability of resistive stress provided by the bed. Finally, we are able to examine regional changes in wintertime flow velocities and find that wintertime flow speed is inversely correlated with summertime positive degree days. We propose that this relationship is the result of a negative feedback mechanism whereby increased meltwater production enlarges subglacial conduit systems that are more effective at discharging water from subglacial cavities. As cavities close during the fall, less remaining water reduces bed separation during winter and thus engenders slower sliding velocities. We find this mechanism exerts a secondary control on glacier surge triggering, encouraging/discouraging initiation after cold/warm summers. This mechanism could have important ice dynamic implications when forced by a changing climate. Increases in summertime temperatures could result in a gradual slowing of land terminating ice, thus providing a negative feedback (self correcting) mechanism that could slightly slow projected mass losses from land terminating glaciers.

Burgess, Evan Windam

308

Meltwater Induced Glacier Landslides - Waxell Ridge, AK  

NASA Astrophysics Data System (ADS)

Within the past year, two large landslides have originated from south-facing peaks on Waxell Ridge, the bedrock massif that separates the Bagley Icefield from Bering Glacier, Alaska. Each involves a near-summit hanging glacier. In each instance, the presence of meltwater appears to be a triggering factor. The largest of the two, which occurred on September 14, 2005, originated from just below the summit of 3,236-m-high Mt Steller and landed on the surface of Bering Glacier, nearly 2,500 m below. The Alaska Volcano Observatory estimated the volume of this landslide, which consisted of rock, glacier ice, and snow, to be approximately 50 million cubic meters. Unlike most large Alaskan glacier-related landslides, this one was not triggered by an earthquake. However, the energy that the slide released was intense enough to generate a seismic signal that was recorded around the world with magnitudes of 3.8 to greater than 5. The slide extended ~10 km down the Bering Glacier from the point of impact. Much of the surface on which the slide occurred had a slope >50 degrees. The second landslide, located ~6 km to the west of Mt Steller, originated from a secondary summit of a 2,500- m-high unnamed peak. The date of its occurrence is unknown, but its toe sits on winter 2005-2006 snow. Both slides have been examined from helicopter and fixed-wing overflights, and with a variety of vertical and oblique aerial photographs. Oblique aerial photographs obtained of the Mt Steller slide on September 15, 2005 depict a 10-15-m-diameter moulin or englacial stream channel in the truncated 30-m-thick glacier ice that comprises the east wall of the landslide scarp. The presence of this unusual glacial-hydrologic feature at an elevation above 3,000 m, suggests that a large volume of water had recently been flowing on Mt Steller's east ridge and that the water might have had a role in triggering the landslide. Similarly, there is evidence of an englacial channel on the west flank of the summit scarp of the second slide. The presence of large volumes of meltwater close to the crest of Waxell Ridge raises questions about regional climate change and its role in the future generation of landslides at higher elevations. This presentation summarizes the findings produced from the analysis of aerial photography and field observations made between September 2005 and September 2006.

Molnia, B. F.; Angeli, K. M.; Bratton, D. A.; Keeler, R. H.; Noyles, C.

2006-12-01

309

The first glacier inventory for entire Greenland  

NASA Astrophysics Data System (ADS)

Detailed glacier data is becoming more and more important in the last decades to solve several research issues. One of the most prominent questions in this regard is the potential contribution of glaciers and icecaps (GIC) to global sea-level rise. Primarily, estimates are uncertain due to the globally still incomplete information about glacier location and size, as well as large uncertainties in future climate scenarios. Recent studies that calculate global sea-level rise from GIC have developed simplified approaches using information from glacier inventories or gridded data sets and a range of different global climate models and emission scenarios. However, for several strongly glacierized regions very rough assumptions about the ice distribution have to be made and an urgent demand for a globally complete glacier inventory is expressed. The GIC on Greenland are one of the regions with lacking information. Within the EU FP7 project ice2sea we mapped the GIC on Greenland using Landsat TM/ETM+ imagery acquired around the year 2000, along with an additional dataset in the North (DCW - Digital Chart of the World). A digital elevation model (DEM) with 90 m resolution (GIMP DEM) was used to derive drainage divides and henceforth topographic parameters for each entity. A major challenge in this regard is the application of a consistent strategy to separate the local GIC from the ice sheet. For this purpose we have defined different levels of connectivity (CL) of the local GIC with the ice sheet: CL0: Not connected. CL1: Connected but separable (either with drainage divides in the accumulation region or in touch only - and thus separable - in the ablation region). CL2: Connected but non-separable (the local GIC contribute to the flow of an ice sheet outlet in the ablation area). Up to now close to 12'000 GIC (only CL0 and CL1) with a total area of about 129'000 km2 have been mapped considering only entities larger than 0.1 km2. The area of the ice sheet itself is approximately 1'684'000 km2. The entire ice-covered area on Greenland is thus 1'813'000 km2. We will present the results of the GIC mapping along with an analysis of glacier inventory statistics.

Rastner, P.; Bolch, T.; Mölg, N.; Le Bris, R.; Paul, F.

2012-04-01

310

An investigation into the mechanisms controlling seasonal speedup events at a High Arctic glacier  

NASA Astrophysics Data System (ADS)

Seasonal variations in ice motion have been observed at several polythermal ice masses across the High Arctic, including the Greenland Ice Sheet. However, such variations in ice motion and their possible driving mechanisms are rarely incorporated in models of the response of High Arctic ice masses to predicted climate warming. Here we use a three-dimensional finite difference flow model, constrained by field data, to investigate seasonal variations in the distribution of basal sliding at polythermal John Evans Glacier, Ellesmere Island, Canada. Our results suggest that speedups observed at the surface during the melt season result directly from changes in rates of basal motion. They also suggest that stress gradient coupling is ineffective at transmitting basal motion anomalies to the upper part of the glacier, in contrast to findings from an earlier flow line study at the same glacier. We suggest that stress gradient coupling is limited through the effect of high drag imposed by a partially frozen bed and friction induced by valley walls and significant topographic pinning points. Our findings imply that stress gradient coupling may play a limited role in transmitting supraglacially forced basal motion anomalies through Arctic valley and outlet glaciers with complex topographic settings and highlight the importance of dynamically incorporating basal motion into models predicting the response of the Arctic's land ice to climate change.

Bingham, Robert G.; Hubbard, Alun L.; Nienow, Peter W.; Sharp, Martin J.

2008-06-01

311

The landform and sediment assemblage produced by a tidewater glacier surge in Kongsfjorden, Svalbard  

NASA Astrophysics Data System (ADS)

This paper describes the landform and sediment assemblage produced by a surge (in 1948) of the Kongsvegen/Kronebreen tidewater glacier complex in northwest Spitsbergen. The main geomorphological products of this advance are two large thrustmoraine complexes on opposite sides of the fjord, and a system of geometrical ridges revealed on glacier decay. The thrust-moraines are composed largely of diamicton, sandy and muddy gravel, gravelly sand, sand and mud, with minor laminites. All of these appear to be derived from the fjord floor and represent both fine fjord basin sediments and coarse grounding-line fan deposits. Thrusting was the principal mode of emplacement of the sediment onto the adjacent land areas during the 1948 advance. However, the geomorphology of the thrust-moraine complexes on either side of the fjord is quite different, reflecting a transpressive regime on the southwest side (mainly long ridges) and a normal compressive regime on the northeast side (short ridges and pinnacles of a 'hummocky' nature). The advance which produced the moraine complex has previously been attributed to a surge of Kongsvegen, but the glaciological and geomorphological evidence suggests that the advance involved both Kongsvegen and Kronebreen. Comparison of the landform assemblage produced by this event with that produced by other tidewater glacier surges demonstrates the diverse range of landform assemblages associated with glacier surges, or other episodes of rapid flow, within glaciomarine environments.

Bennett, Matthew R.; Hambrey, Michael J.; Huddart, David; Glasser, Neil F.; Crawford, Kevin

1999-08-01

312

Modelling bed overdeepenings for the glaciers in the Himalaya-Karakoram region using GlabTop2  

NASA Astrophysics Data System (ADS)

Calculating ice thickness distribution and bed topographies for large glacier samples is an essential task to estimate stored ice volumes with their potential for sea level rise and to model possible future retreat scenarios of glacier evolution under conditions of continued warming. Modelling such bed topographies to become exposed in the near future by continued glacier retreat also enables modelling of future landscapes with their landforms, processes and interactions. As the erosive power of glaciers can form numerous and sometimes large closed topographic bed depressions, many overdeepenings are commonly found in formerly glaciated mountain ranges. Where such overdeepend parts are becoming exposed and filled with water rather than sediments new lakes can come into existence. GlabTop (Glacier bed Topography) has been used to model ice thickness distribution and bed topographies of large glacier samples. It is an ice dynamical approach, based on the assumption of perfect plasticity of ice, which relates glacier thickness to its local surface slope via the basal shear stress estimated for each glacier based on an empirical relation between shear stress and elevation range as a governing factor of mass turnover. From comparison with radio-echo soundings in the Swiss Alps, the uncertainty range of local ice thicknesses calculated with GlabTop is estimated at about ±30%. The spatial variability of ice depths, i.e. the glacier-bed topography, primarily depends on surface slope as provided by DEMs and is quite robust. For the entire Swiss Alps, GlabTop revealed a considerable number (more than 500) of (partly large) overdeepenings in the modelled glacier beds with a total area of about 50-60 km2 and a total volume of about 1.5-2.5 km3. A number of lakes have formed in such modelled overdeepenings during the past years and decades. To calculate bed topographies with their overdeepenings for the 28'100 glaciers of the Himalaya-Karakoram region the GlabTop-approach was modified and named GlabTop2. While the original approach relied on so called glacier branch lines that had to be digitized manually, GlabTop2 is fully automated and requires only a DEM and glacier outlines as an input. The result is the same: ice thickness distribution and bed topographies, which can be used for volume calculations and for model simulations concerning glacier retreat scenarios and future landscapes. According to the model output there are about 15'000 overdeepenings covering an area of about 2000 km2 and having a total volume of about 120 km3 (3-4% of the now existing glacier volume) in the Himalaya-Karakoram region. In a statistical analysis concerning the morphological characteristics of these overdeepenings, mean and maximum values of the parameters surface area, length, width, depth, volume, frontal/adverse slope and their statistical interrelations are determined with their corresponding uncertainty ranges and compared with a corresponding analysis for the Swiss Alps. While the modelled overdeepenings based on model runs with different data input differ in shape, the locations of the overdeepenings are robust and the values for the extracted parameters are comparable.

Linsbauer, Andreas; Frey, Holger; Haeberli, Wilfried; Machguth, Horst

2014-05-01

313

Surge of a Complex Glacier System - The Current Surge of the Bering-Bagley Glacier System, Alaska  

NASA Astrophysics Data System (ADS)

Understanding fast glacier flow and glacial accelerations is important for understanding changes in the cryosphere and ultimately in sea level. Surge-type glaciers are one of four types of fast-flowing glaciers --- the other three being continuously fast-flowing glaciers, fjord glaciers and ice streams --- and the one that has seen the least amount of research. The Bering-Bagley Glacier System, Alaska, the largest glacier system in North America, surged in 2011 and 2012. Velocities decreased towards the end of 2011, while the surge kinematics continued to expand. A new surge phase started in summer and fall 2012. In this paper, we report results from airborne observations collected in September 2011, June/July and September/October 2012 and in 2013. Airborne observations include simultaneously collected laser altimeter data, videographic data, GPS data and photographic data and are complemented by satellite data analysis. Methods range from classic interpretation of imagery to analysis and classification of laser altimeter data and connectionist (neural-net) geostatistical classification of concurrent airborne imagery. Results focus on the characteristics of surge progression in a large and complex glacier system (as opposed to a small glacier with relatively simple geometry). We evaluate changes in surface elevations including mass transfer and sudden drawdowns, crevasse types, accelerations and changes in the supra-glacial and englacial hydrologic system. Supraglacial water in Bering Glacier during Surge, July 2012 Airborne laser altimeter profile across major rift in central Bering Glacier, Sept 2011

Herzfeld, U. C.; McDonald, B.; Trantow, T.; Hale, G.; Stachura, M.; Weltman, A.; Sears, T.

2013-12-01

314

Measurement of the Dissociation-Equilibrium Constants for Low Affinity Antibiotic Binding Interaction with Bacterial Ribosomes by the T2 (CPMG) and Line-Broadening Methods  

NASA Astrophysics Data System (ADS)

In this study the dissociation constants of the low antibiotic-ribosomes interaction were determined by the T2 (CPMG), the Carr-Purcell-Meiboom-Gill spin-echo decay rate and the line-broadening methods. Three MLSB antibiotics were studied, a macrolide roxithromycin, a ketolide HMR 3647 and a lincosamide clindamycin for their weak interaction with three bacterial ribosomes, E. coli, Staphylococcus aureus sensitive and resistant to erythromycin. Nous avons mesuré la constante de dissociation, Kd correspondant à l'interaction faible antibiotique-ribosome bactérien pour des antibiotiques de différentes classes, un macrolide (roxithromycine), un kétolide (HMR 3647) et une lincosamide (clindamycine) avec des ribosomes de différentes souches bactériennes (E. coli, Staphylococcus aureus sensible ou résistant à l'erythromycin) par deux méthodes : l'une basée sur la variation des largeurs de raies et l'autre sur les temps de relaxation transversaux T2 en utilisant une séquence CPMG.

Verdier, L.; Gharbi-Benarous, J.; Bertho, G.; Mauvais, P.; Girault, J.-P.

1999-10-01

315

52 glaciers and one lake: how to reconstruct past regional glacier variability  

NASA Astrophysics Data System (ADS)

Sediment records from distal glacier-fed lakes have been used in numerous reconstructions of past glacier activity, where the basic assumption is that the amount of minerogenic material deposited in the lake is directly proportional to the amount of upstream glacier erosion. However, the minerogenic component of the sediments in a distal glacier-fed lake is commonly derived from several different sources, not only subglacial erosion. Furthermore, glacier reconstructions tend to focus on individual mountain glaciers, which due to local effects might not always reflect regional scale glacier variability. Presently, certain high-resolution analysis techniques allow for fast multi-proxy analyses of sediment cores, which improve the basis for inferring the provenance of lake sediments; however, the only way of actually testing such inferences is to identify the different sediment sources in the adjacent catchment and characterize them using the same proxy measurements as in the lake core. Multi-proxy sedimentary fingerprinting techniques are labor-intensive, however, and proxies such as bulk geochemistry may prove of little use in differentiating between source areas if the bedrock lithology is uniform across the catchment. Here we present a simple method based on environmental magnetism that allow for tracking lake sediments to their sources in catchments where the bedrock lithology is uniform. Unlike ferro- and ferrimagnetic minerals, the magnetic susceptibility of paramagnetic minerals is inversely proportional to temperature. Thus, by measuring the bulk magnetic susceptibility (chi-Bulk) of a sediment sample both at room temperature (293K) and after freezing in liquid nitrogen (77K), the relative contribution from paramagnetic minerals to the total chi-Bulk can be inferred from the ratio of chi-Bulk77K over chi-Bulk293K. Theoretically, a ratio of 3.8 will indicate a purely paramagnetic sample, whereas progressively lower values reflect an increasing contribution from ferro- or ferrimagnetic minerals. We found that in the catchment of Nerfloen, a distal lake draining a large (440 km2) catchment in western Norway that contains 52 separate glaciers, there was a systematic decrease in the chi-Bulk77K/chi-Bulk293K-ratio with increasing altitude and proximity to the glaciers. We have not studied the magnetic mineralogy of our samples in detail, but infer from our data that the relative amount of paramagnetic minerals increase as soil formation progresses, thereby creating the contrasting ratios between samples collected at different altitudes. In the lake core we observe rapid shifts between sedimentary regimes dominated by high- and low-altitude source areas, which can best be explained by regional-scale growth and decay of mountain glaciers in the lake catchment.

Vasskog, Kristian; Paasche, Øyvind; Nesje, Atle; Boyle, John F.; Birks, H. John B.

2014-05-01

316

Chronology for fluctuations in late pleistocene Sierra Nevada glaciers and lakes  

SciTech Connect

Mountain glaciers, because of their small size, are usually close to equilibrium with the local climate and thus should provide a test of whether temperature oscillations in Greenland late in the last glacial period are part of global-scale climate variability or are restricted to the North Atlantic region. Correlation of cosmogenic chlorine-36 dates on Sierra Nevada moraines with a continuous radiocarbon-dated sediment record from nearby Owens Lake shows that Sierra Nevada glacial advances were associated with Heinrich events 5, 3, and 1. 27 refs., 2 figs., 1 tab.

Phillips, F.M.; Zreda, M.G.; Plummer, M.A. [New Mexico Institute of Mining and Technology, Socorro, NM (United States)] [and others] [New Mexico Institute of Mining and Technology, Socorro, NM (United States); and others

1996-11-01

317

Spatially distributed reconstruction of the surface mass balance of Pasterze glacier, Austria, employing a full Stokes model  

NASA Astrophysics Data System (ADS)

The Pasterze glacier is the largest Austrian glacier (17.7 km², 2003) based in the 'Hohe Tauern' region of the Eastern Alps. In the period from 1980 to 1997, surface mass balance (SMB) measurements were carried out by the Verbund-Austrian Hydro Power (AHP) Company. Since 2004 SMB measurements of the Pasterze glacier were reinstalled by the ZAMG using the glaciological method (stakes, snow pits,…). Current specific SMB rates correspond to a mean surface ice loss of ~1.5 m per balance year. Since 2005 kinematics of the ablation stakes have been determined through regular differential GPS surveys. Based on the high spatial sampling by the installed ablation stake network (~50-60 stakes), a high quality ablation and flow velocity data set has been gathered for the ablation area of the Pasterze glacier. As a next step we deployed a full stress computational model (http://elmerice.elmerfem.org) to investigate the dynamics of Pasterze glacier. We employed a high resolution digital elevation model (DEM) of the bedrock and high quality DEM's of the surface taken at different times (1969, 1998, 2012) as input for diagnostic simulations. After tuning the model parameters (e.g. sliding) to the in-situ determined dynamics, we reconstructed the spatial SMB distribution of the glacier and compared it to the measurements. The reconstruction of the SMB from diagnostic simulations can be an effective technique in order to - on top of measurements that usually are confined to centre-lines of glaciers - get additional information on the spatial SMB distribution by utilizing easier accessible surface DEM's as well as for SMB homogenization approaches.

Binder, Daniel; Zwinger, Thomas; Hauser, Beate; Hynek, Bernhard; Schöner, Wolfgang; Weyss, Gernot

2014-05-01

318

Seismic image of the ice–bedrock contact at the Lobbia glacier, Adamello Massif, Italy  

Microsoft Academic Search

In the framework of a geophysical study to investigate the ice thickness on the Lobbia Glacier located in the Adamello Massif, Italy, we used multifold seismic data to constrain a joint gravity survey covering an area of about 3.7 km2. Two seismic lines were recorded above the maximum ice thickness as estimated from single-fold seismic data and gravity data collected

L. Levato; L Veronese; A Lozej; E Tabacco

1999-01-01

319

Glacier Changes in the Bhutanese Himalaya - Present and Future  

NASA Astrophysics Data System (ADS)

Glacierized change in the Himalayas affects river-discharge, hydro-energy and agricultural production, and Glacial Lake Outburst Flood potential, but its quantification and extent of impacts remains highly uncertain. Here we present conservative, comprehensive and quantitative predictions for glacier area and meltwater flux changes in Bhutan, monsoonal Himalayas. In particular, we quantify the uncertainties associated with the glacier area and meltwater flux changes due to uncertainty in climate data, a critical problem for much of High Asia. Based on a suite of gridded climate data and a robust glacier melt model, our results show that glacier area and meltwater change projections can vary by an order of magnitude for different climate datasets. The most conservative results indicate that, even if climate were to remain at the present-day mean values (1980-2000), almost 10% of Bhutan's glacierized area would vanish and the meltwater flux would drop by as much as 30%. New mapping of glacierized area from 2000-2010 shows a significant change in glacierized area of 4-6%. Thus the conservative steady-state area changes predicted by the model are already being realized. Under the conservative scenario of an additional 1°C regional warming, glacier retreat is predicted to continue until about 25% of Bhutan's glacierized area will have disappeared and the annual meltwater flux, after an initial spike, would drop by as much as 65%.

Rupper, S.; Schaefer, J. M.; Burgener, L. K.; Maurer, J.; Smith, R.; Cook, E.; Putnam, A. E.; Krusic, P.; Tsering, K.; Koenig, L.

2012-12-01

320

Land Cover Change Impacts on Tropical Mountain Climate and Glaciers  

NASA Astrophysics Data System (ADS)

Glacier loss has traditionally been investigated as a dependent of larger-scale climate change. Here we attempt to quantify the "home-made" effect of local land cover change (LCC) on glacier mass loss, using glacier shrinkage on Kilimanjaro (East Africa) as a test case, which has been extensively studied in terms of multi-scale climatic controls. A new approach that enables to downscale large-scale climate dynamics to the glacier's mass balance (MB) in a fully physical way (Moelg and Kaser 2011, J. Geophys. Res. 116) allows us to isolate this local effect from the large-scale forcings. The novel element concerns the linking of a process-based glacier MB model and a limited-area (mesoscale) atmospheric model (LAM) without statistical downscaling at their interface. We perform sensitivity studies by varying the land cover distribution (1976 or present) at the lower boundary of the LAM, in order to determine (1) the resultant changes in atmospheric state and dynamics over the mountain and (2) their effect on glacier MB. Results are expected to demonstrate how forcings of glacier shrinkage are partitioned between large-scale flow and local (partly human-controlled) LCC and, in a wider context, which glacier types are vulnerable to local LCC. The study can also serve as a template for attribution of glacier changes anywhere in the world, and thus help to correctly interpret the climate signal that receding glaciers exhibit.

Moelg, T.; Grosshauser, M.; Hemp, A.; Hofer, M.; Marzeion, B.

2011-12-01

321

Assessing streamflow sensitivity to variations in glacier mass balance  

NASA Astrophysics Data System (ADS)

We examine long-term streamflow and mass balance data from two Alaskan glaciers located in climatically distinct basins: Gulkana Glacier, a continental glacier located in the Alaska Range, and Wolverine Glacier, a maritime glacier located in the Kenai Mountains. Both glaciers lost mass, primarily as a result of summer warming, and both basins exhibit increasing streamflow over the 1966-2011 study interval. We estimated total glacier runoff via summer mass balance, and separated the fraction related to annual mass imbalances. In both climates, the fraction of streamflow related to annual mass balance averages less than 20%, substantially smaller than the fraction related to total summer mass loss (>50%), which occurs even in years of glacier growth. The streamflow fraction related to changes in annual mass balance has increased only in the continental environment. In the maritime climate, where deep winter snowpacks and frequent rain events drive consistently high runoff, the magnitude of this streamflow fraction is small and highly variable, precluding detection of any existing trend. Changes in streamflow related to annual balance are often masked by interannual variability of maritime glacier mass balance, such that predicted scenarios of continued glacier recession are more likely to impact the quality and timing of runoff than the total basin water yield.

Oneel, S.; Hood, E. W.; Arendt, A. A.; Sass, L. C.; March, R. S.

2013-12-01

322

A study of discrete glacier motion  

NASA Astrophysics Data System (ADS)

Knowledge of process which control glacial dynamics are imperative in quantifying the response of a glacier or ice sheet to external forcing. This dissertation focuses mainly upon the characterization of sliding ice over a bed in an unstable fashion. I investigate unstable sliding through instances where it is observed in passive seismology as well as a focused laboratory study. The laboratory study attempts to isolate specific aspects of the sliding interface, which could lead to unstable sliding. Implications of unstable sliding with regards to erosion are also dealt with. Initially the TAMSEIS array is used to observe a unique set of seismicity originating at the base of David Glacier Antarctica in which ˜ 20,000 events were located over a ˜300 day period as the ice slid over an asperity. Tidal effects at the terminus modulated the interevent spacing and magnitude of events allowing for a basic analysis of healing process between a glacier and its bed. The 300 day period of repeat seismicity is hypothesized to arise from advection of debris rich ice over the asperity. Next the erosion implications of stick slip sliding are investigated. Sudden advancement associated with seismic energy generation is hypothesized to rapidly expand water filled cavities, which form in lee of bedrock highs. The rapid expansion creates a drop in water pressure within the cavity resulting in a pressure gradient leading to rapid fracture of bedrock. During the interseismic period of a stick slipping glacier the static coefficient of friction transfers a larger shear stress to the bed than the dynamic coefficient of friction from stably sliding glacier would. Next laboratory experimentation is conducted using a biaxial shearing apparatus in order to test the hypothesis that debris rich ice can affect the stability regime of a sliding glacier. This is preformed on a suite of ice-debris samples with range entrained debris percentages and temperatures. Both synthetic ice constructed in the laboratory and natural ice taken from the base of Engabreen Glacier were tested. Transition from a velocity strengthening to velocity weakening interface was observed for a constant velocity if the debris amount was increased thus validating the initial hypothesis. These exterminations were followed by a set of experiments in which the biax was de-stiffened in order to replicate the elastic strain, which would be accumulated at the base of a glacier. When driven under conditions previously identified in the unstable slip regime unstable sliding did occur. This allowed for exploration unstable slip parameters. Specifically comparisons of stress drop with recurrence interval, and peak-sliding velocity was investigated. Next POLENET seismic data was used to investigate a set of repeating ruptures occurring near the Executive Committee Range of Marie Byrd Land Antarctica, a known source of volcanic activity. Surface velocities as low as V ? 30 m yr--1 in this region exist indicating the source of glacially generated seismicity was atypical. A proposed source of a sudden addition of basal melt water from an increase in geothermal heat flux is hypothesized to result in the seismic signature observed. Lastly the POLENET dataset was used to investigate calving events located at the terminus of Thwaites Glacier. The seismicity displayed a monochromatic signal. A new calving mechanism, which could produce such a source of seismicity, is theorized as resonating within the block, which is being calved off.

Zoet, Lucas K.

323

The GLIMS Glacier Database: Status and Future Directions  

NASA Astrophysics Data System (ADS)

The Global Land Ice Measurements from Space (GLIMS) initiative has built a database of glacier outlines and related attributes, derived primarily from satellite imagery, such as from ASTER and Landsat. Each snapshot of a glacier is from a specific time, and the database is designed to store multiple snapshots representative of different times. The database continues to expand both spatially and temporally: the number of glaciers represented, as well as the number of outlines from different times per glacier, are both increasing. As of August 2011, the database, located at NSIDC, contains outlines for approximately 95 000 glaciers, covering 290 000 km2. More datasets are expected soon, such as from GlobGlacier (e.g. all European Alps, western Greenland, Sweden, Baffin Island), and the Regional Centers for Svalbard, Argentina, Nepal, China, and others. Though the database does not yet cover the world's glaciers completely, approximately 670 glaciers have outlines from more than one time. This database increasingly enables analysis of global and regional glacier area and its distribution, glacier change, distribution of glaciers by different properties (e.g. morphology, debris-cover),and other yet-to-be imagined possibilities. In spite of steady progress, there remain some geographic areas that are not yet covered, including southernmost South America, Arctic Russia, the the periphery of most of Greenland and Antarctica. For applications such as sea level change studies that require complete global coverage of glaciers with at least moderate resolution, it is imperative that these gaps be filled soon. This will be addressed through adapting existing datasets to the GLIMS data model, using new satellite data and methods as they develop, and building analysis capacity worldwide to get more researchers involved in high accuracy glacier mapping.

Armstrong, R. L.; Racoviteanu, A.; Raup, B. H.; Khalsa, S. S.

2011-12-01

324

Glacier volume changes at Mt. Everest/Qomolangma 1962 - 2007  

NASA Astrophysics Data System (ADS)

The larger glaciers at Mt. Everest are heavily covered with supra-glacial debris like many other glaciers in the Himalaya. Most glacier change studies concentrate on area change only. However, the melting of debris-covered glaciers is most recognisable through downwasting. Hence, multi-temporal DEM analysis is needed to study the reaction of these glaciers to climate change in detail. We generated a time series of DEMs based on stereo corona (years 1962 and 1972) aerial images (1984), ASTER (2001) and Cartosat-1 data (2007) for the southern side of Mt. Everest (investigated glaciers: Khumbu, Nuptse, Lhotse, Lhotse Nup, Lhotse Shar and Imja) and two DEMs for the northern side (Rongbuk Glacier) based on a topographic map (1974) and ASTER data (2003). IceSat GLAS data, topographic maps and field GPS measurements are used for validation. The Cartosat-1 DEM was chosen to be the master DEM due to the highest accuracy and the other DEMs were co-registered to it. The characteristics of the downwasting are similar for all investigated glaciers: The downwasting is pronounced in the upper part with thin debris-cover and less pronounced but still recognisable in the lower parts with thick debris-cover. The highest surface lowering at the southern side is found at the possible transition zone between the active and stagnant glacier parts. The average downwasting for the investigated Eastern Rongbuk Glacier seems to be little higher (0.81 ± 0.53 m/a) than the value for Khumbu Glacier (0.42 ± 0.21 m/a). Both the accumulation and ablation area of Khumbu Glacier showed a surface lowering. Volume loss is detected for all glaciers and investigated time periods.

Bolch, Tobias; Piezconka, Tino; Chen, Feng; Kang, Shichang; Buchroithner, Manfred

2010-05-01

325

Retreat of Pine Island Glacier controlled by marine ice-sheet instability  

NASA Astrophysics Data System (ADS)

Over the last 40 years Pine Island Glacier in West Antarctica has thinned at an accelerating rate, so that it is currently the largest single contributor to sea-level rise in Antarctica. In recent years, the grounding line, which separates the grounded ice sheet from the floating ice shelf, has retreated by tens of kilometres. At present, the grounding line is crossing a retrograde bedrock slope that lies well below sea level, raising the possibility that the glacier is susceptible to the marine ice sheet instability mechanism. Here, using three state-of-the-art ice flow models, we show that Pine Island Glacier's grounding line is likely engaged in an unstable 40 kilometre retreat. The associated mass loss increases substantially over the course of our simulations from the average value of 20 Gt a-1 observed for the 1992-2011 period , up to and above 100 Gt a-1 equivalent to 3.5-10 mm eustatic sea-level rise over the following 20 years. Mass loss remains elevated from then on, ranging from 60 to 120 Gt a-1.

Durand, Gael; Favier, Lionel; Cornford, Stephen; Gudmundsson, Hilmar; Gagliardini, Olivier; Gillet-Chaulet, Fabien; Zwinger, Thomas; Payne, Anthony; Le Brocq, Anne

2014-05-01

326

Recent changes of very small glaciers in the Swiss Alps  

NASA Astrophysics Data System (ADS)

Present knowledge about Alpine glaciers is not representative in terms of glacier size distribution. More than 80% of all Swiss glaciers are smaller than 0.5 km2 and hence belong to the class of very small glaciers. In the context of fast glacier wastage in the European Alps, the near-future development of the size class distribution will most probably be in favour of very small glaciers which will comparably increase in number. However, there has been little research carried out about very small glaciers so far. It is not clear whether findings and theoretical concepts elaborated for medium and large valley glaciers (> 3 km2) can be directly transferred to very small glaciers, whose accumulation patterns are, for instance, characteristically exceptional because winter precipitation is multiplied by wind drift and avalanching. The extent of glaciers in the European Alps has recently been mapped and inventoried spatio-temporally consistently. Nevertheless, such glacier outlines derived by satellite remote-sensing techniques are not accurate enough for the special case of investigating changes in very small glaciers. Therefore, glacier outlines are digitized manually using high-resolution (25 cm) orthophotographs covering the entire Swiss Alps acquired twice for every scene (both in the early and late noughties). In contrast to the known shortcomings of satellite remote-sensing based approaches, the margins of very small glaciers are (with few exceptions) clearly distinguishable on these orthophotos, even in shaded, snow- or debris-covered areas. For the eastern Swiss Alps (east of the rivers Reuss and Ticino), about one third of all glaciers has vanished since 1973. The total area presently still glacierized amounts to 140 km2, whereof very small glaciers cover only 25% but account for almost 90% of the total number of glaciers. Retreat rates are highest for very small glaciers but seem to be stabilizing or even decreasing since the early noughties, implying that many of them have retreated far back into shaded cirques and below headwalls. Downwasting and disintegration into different ice patches has become the dominant process of mass loss. Furthermore, we evaluate changes in ice volume over the last three decades for a large set of Swiss glaciers by combining the glacier outlines for the late noughties with a new precision DEM (swissALTI3D) for the same date with outlines and elevation information from around 1980. Ice volume changes are compared to measured and estimated total glacier ice volume in order to quantify relative volume losses over the last decades. Moreover, annual surface mass balance was determined for three very small glaciers complementing the analysis of recent changes in this glacier size class. Very small glaciers in the Swiss Alps show fast mass loss but the picture is not uniform both in space and time.

Fischer, Mauro; Huss, Matthias; Hoelzle, Martin

2013-04-01

327

Microbial Energetics Beneath the Taylor Glacier, Antarctica  

NASA Astrophysics Data System (ADS)

Subglacial microbiology is controlled by glacier hydrology, bedrock lithology, and the preglacial ecosystem. These factors can all affect metabolic function by influencing electron acceptor and donor availability in the subglacial setting leaving biogeochemical signatures that can be used to determine ecosystem processes. Blood Falls, an iron-rich, episodic subglacial outflow from the Taylor Glacier in the McMurdo Dry Valleys Antarctica provides an example of how microbial community structure and function can provide insight into subglacial hydrology. This subglacial outflow contains cryoconcentrated, Pliocene-age seawater salts that pooled in the upper Taylor Valley and was subsequently covered by the advance of the Taylor Glacier. Biogeochemical measurements, culture-based techniques, and genomic analysis were used to characterize microbes and chemistry associated with the subglacial outflow. The isotopic composition of important geochemical substrates (i.e., ?34Ssulfate, ?33Ssulfate, ?18Osulfate, ?18Owater, ?14SDIC) were also measured to provide more detail on subglacial microbial energetics. Typically, subglacial systems, when driven to anoxia by the hydrolysis of organic matter, will follow a continuum of redox chemistries utilizing electron acceptors with decreasing reduction potential (e.g., Fe (III), sulfate, CO2). Our data provide no evidence for sulfate reduction below the Taylor Glacier despite high dissolved organic carbon (450 ?M C) and measurable metabolic activity. We contend that, in the case of the Taylor Glacier, the in situ bioenergetic reduction potential has been 'short-circuited' at Fe(III)-reduction and excludes sulfate reduction and methanogenesis. Given the length of time that this marine system has been isolated from phototrophic production (~2 Mya) the ability to degrade and consume increasingly recalcitrant organic carbon is likely an important component to the observed redox chemistry. Our work indicates that glacier hydrology imparts strong feedbacks on the availability of oxygen as an electron acceptor and may be a robust regulator of the in situ metabolism. This biogeochemical regulation in turn affects the chemical nature of subglacial efflux. Blood Falls demonstrates that measurements of geochemistry and microbial diversity can support models of subglacial hydrology.

Mikucki, J. A.; Turchyn, A. V.; Farquhar, J.; Priscu, J. C.; Schrag, D. P.; Pearson, A.

2007-12-01

328

Velocity Estimates of Fast-Moving Outlet Glaciers on the Greenland Ice Sheet  

NASA Technical Reports Server (NTRS)

In recent years, airborne laser altimetry has been used with great success to investigate the mass balance characteristics of the Greenland ice sheet. One spinoff of this activity has been the application of these measurements to the study of surface velocities in some of Greenland's fast-moving drainage glaciers. This is accomplished by tracking the motion of elevation features, primarily crevasses, in pairs of aircraft laser altimetry surveys. Detailed elevation measurements are made along or across glaciers of interest with a scanning swath of 150 to 200 meters, and the surveys are repeated several days later, typically to within better than 50 meters of the previous flight line. Surface elevation features are identified in each image, and their offsets are compared yielding detailed velocities over narrow regions. During the 1998 field season, repeat flights were made over three glaciers for the purpose of estimating their surface velocities. These were the Kangerdlugssuaq and Helheim glaciers on the east coast and the Jakobshavn Isbrae on the west coast. Each flows at such high speeds (on the order of a few kilometers per year) that their flow rates are difficult to assess by means of radar interferometry. The flexibility of the aircraft platform, however, allows for detailed measurements of the elevation and flow of these drainage areas, which are responsible for a significant portion of the ice discharge from the Greenland ice sheet. Velocity estimates for transects that span these glaciers will be presented, and where the ice thickness values are available (provided by researchers from the University of Kansas) the fluxes will be calculated.

Abdalati, Waleed; Krabill, W. B.

1998-01-01

329

Till deformation beneath Black Rapids Glacier, Alaska, and its implication on glacier motion  

NASA Astrophysics Data System (ADS)

The motion of a glacier is largely determined by the nature of its bed. The basal morphology and its reaction to the overlying ice mass have been subject to much speculation, because the glacier bed is usually difficult to access, and good field data are sparse. In spring 1997 a commercial wireline drill rig was set up on Black Rapids Glacier, Alaska, to extract cores of basal ice, subglacial till, and underlying bedrock. One of the boreholes was equipped with three tiltmeters to monitor till deformation, and a piezometer to record pore water pressure. The surface velocity and ice deformation in a borehole were also measured. The drill successfully reached bedrock twice after penetrating a till layer, some 5 to 7 m in thickness, confirming an earlier seismic interpretation. The till consisted of a sandy matrix containing clasts up to boulder size. Bedrock and till lithology indicated that all the drill holes were located to the north of the Denali Fault, a major tectonic boundary along which the glacier flows. The mean annual surface velocity of the glacier was 60 ma-1 , of which 20 to 30 ma-1 were ice deformation, leaving 30 to 40 ma-1 of basal motion. The majority of this basal motion occurred at a depth of more than 2 m in the till, contradicting previously held ideas about till deformation. Basal motion could occur as sliding of till over the underlying bedrock, or on a series of shear layers within the till. This finding has implications for the interpretation of the geologic record of former ice sheets, for geomorphology, and for glacier dynamics. The effect of a thick till layer on ice flow and on quantities observable at the glacier surface was calculated. These include velocity changes on secular, seasonal, and shorter time scales. A mechanism for uplift events and dye tracing responses was suggested. An easy surface observation that could serve to clearly distinguish a glacier underlain by till from the more traditional view of a glacier underlain by bedrock could not be identified.

Truffer, Martin

330

Monitoring glaciers and indications of subglacial volcanic activity using small-scale Top-Hat reflectors - An IsViews experiment on Myrdalsjökull, Iceland  

NASA Astrophysics Data System (ADS)

Subglacial volcanic eruptions often provide indications of activity some time before the actual catastrophic event. Surface undulations appear on top of the ice cap and meltwater torrents can occur at the glacier margin. Even large scale uplifts of ice caps have been observed. Within the project IsViews a processing chain, based on high spatially and temporally resolved remote sensing imagery, will be developed in order to automatically identify such early indications. The main data used for this analysis are acquired by the TerraSAR-X, TanDEM-X and RapidEye satellites. First investigations concerning the feasibility of the near real-time warning system and the general baseline conditions are carried out on two large plateau glaciers in southern Iceland, namely Mördalsjökull and Vatnajökull. Within the 2013 IsViews field work an experiment was started in order to test a new way of glacier monitoring. Two test sites were established on the Mördalsjökull ice cap (one at the equilibrium line and one below), each consisting of a permanent GPS station and two nearby RADAR reflectors. These RADAR reflectors are specially designed Top-Hat reflectors, which are cheap to manufacture, small (50 cm diameter) and lightweight and therefore easy to handle, transport and deploy. Their special design makes them visible in SAR images independent of orientation, so different acquisition geometries and even different sensors can be used. The drawback of the small, low reflecting Top-Hat can be overcome by using the newly implemented Staring Spotlight Mode of the German SAR Satellite TerraSAR-X, providing an unprecedented resolution of down to 20 cm in the azimuth direction. The reflectors, as point targets, allow absolute positioning within the cm-level in the TerraSAR-X data. Time series of SAR data can be used to derive position and altitude changes of the reflector itself and possibly even melting rates by exploiting the different signal paths. The visibility of the Top-Hat reflectors has been confirmed in various test acquisitions shortly after their deployment, and initial position measurements have been carried out. Further acquisitions will be recorded once the reflectors emerge from the winter snow cover, and correlation of the measurements will be performed once the data of the GPS stations are received in March 2014. The ease of deploying these new reflectors combined with the high-resolution capabilities of the TerraSAR-X satellite provides new monitoring possibilities, not only for glacial flow dynamics but also for rock movements and deformation of infrastructure.

Minet, Christian; Duque Biarge, Sergi; Jaenicke, Julia; Münzer, Ulrich; Mayer, Christoph; Franke, Jonas; Guðmundsson, Águst; Parizzi, Alessandro; Fritz, Thomas; Eineder, Michael

2014-05-01

331

Basaltic micrometeorites from the Novaya Zemlya glacier  

NASA Astrophysics Data System (ADS)

A large number of micrometeorites (MMs) was recovered from glacier deposits located at the north-eastern passive margin of the Novaya Zemlya glacier sheet. Melted, scoriaceous, and unmelted micrometeorites (UMMs) are present. Unmelted micrometeorites are dominated mostly by chondritic matter, but also a few achondritic MMs are present. Here we report the discovery of four UMMs that, according to their texture, mineralogy, and chemistry, are identified as basaltic breccias. Mineral chemistry and Fe/Mn ratios of two basaltic micrometeorites indicate a possible relationship with eucrites and/or mesosiderites, whereas two others seem to have parents, which appear not to be present in our meteorite collections. The basaltic breccia UMMs constitute 0.5% of the total population of the Novaya Zemlya MM suite. This content should be lowered to 0.25% because the Novaya Zemlya MM collection appears to be biased with carbonaceous UMMs being underrepresented.

Badjukov, Dmitry D.; Brandstätter, Franz; Raitala, Jouko; Kurat, Gero

2010-09-01

332

Present and future contribution of glacier storage change to runoff from macroscale drainage basins in Europe  

Microsoft Academic Search

Glaciers make a significant runoff contribution in macroscale drainage basinsThe impact of glacial melt water is recognizable with very small glacierizationThe retreat of alpine glaciers plays an important role in future water shortage

Matthias Huss

2011-01-01

333

Bacteria in Snow and Glacier Ice  

Microsoft Academic Search

By definition, the cryosphere is the portion of the Earth where water is in solid form as snow or ice. It includes vast areas\\u000a of sea ice, freshwater ice, glaciers, ice sheets, snow cover and permafrost. Because of the extremely harsh climatic conditions,\\u000a these frozen environments had been considered for a long time to be devoid of life or serving

Vanya Miteva

334

Glacier Bay, Alaska, from the Ground, Air, and Space  

NASA Technical Reports Server (NTRS)

This tape uses a combination of video, three-dimensional computer imaging, and still photographs to provide a descriptive overview of the life-cycle and environmental effects of glaciers. An historical prospective of researchers and the contribution that they have made to the understanding of glaciers and Glacier Bay is presented. The data collected from these scientists have been documented and used by means of scientific visualization in the hope of learning how glacial activity relates to climate changes.

Hall, Dorothy K.

1997-01-01

335

GLACIER PEAK WILDERNESS STUDY AREA, WASHINGTON.  

USGS Publications Warehouse

Geologic, geochemical, gravity, aeromagnetic, and mine and prospect surveys were conducted to evaluate the mineral-resource potential of the Glacier Peak Wilderness study area and proposed additions in Washington. In the study area, six areas containing several base and precious metals have been identified that have substantiated mineral-resource potential, two of which are in areas recommended for wilderness addition. An additional 10 areas have probable mineral-resource potential. The most important demonstrated resource identified is the porphyry copper-molybdenum deposit at Glacier Peak mine near the center of the wilderness study area, where a deposit totaling 1. 9 billion tons of mineralized rock has been delineated by drilling. A possible geothermal potential exists on the east side of the Glacier Peak volcano, and a possible 24-million-cu-yd cinder resource is identified at the White Chuck Cinder Cone in the wilderness study area, but both are remote and no resources were identified. No other energy resource potential was identified in this study.

Church, S. E.; Stotelmeyer, R. B.

1984-01-01

336

New Species in New Guinea / Melting Glaciers  

NSDL National Science Digital Library

The first segment of this radio broadcast discusses a recent expedition to the isolated Foja mountain range in western New Guinea, which has discovered several new species of birds, 20 new frog species, and four new butterfly species, as well as a rare bird which had not been seen for sixty years, and unusual plants. One of the explorers discusses the efforts to map the diversity of the island and the challenges in preserving such ecological treasures. This segment is 12 minutes and 21 seconds in length. The second segment consists of a conversation with researchers who travel the world documenting the retreat of mountain glaciers. Topics include efforts to build a global database of ice cores to document changes; a discussion of increased water flow from glaciers; the logistics of drilling ice cores at high altitude and moving them to a university lab; how annual snowfall is recorded in ice cores; and how retreating glaciers are exposing plants that were covered for six thousand years. This segment is 35 minutes and 20 seconds in length.

337

Non-Equilibrium Stability Theory.  

National Technical Information Service (NTIS)

Contents: Introduction; Local equilibrium; Classical stability theory of thermodynamic equilibrium; Equilibrium stability theory and entropy balance equation; Explicit form of the equilibrium stability conditions; Stability of non-equilibrium states; The ...

P. Glansdorff I. Prigogine

1969-01-01

338

Global Terrestrial Network for Glaciers: Databases and Web interfaces  

NASA Astrophysics Data System (ADS)

The Global Terrestrial Network for Glaciers (GTN-G) is an umbrella organization with links to the Global Climate Observing System (GCOS), Global Terrestrial Observing System (GTOS), and UNESCO (all organizations under the United Nations), for the curation of several glacier-related databases. It is composed of the World Glacier Monitoring Service (WGMS), the U.S. National Snow and Ice Data Center (NSIDC), and the Global Land Ice Measurements from Space (GLIMS) initiative. The glacier databases include the World Glacier Inventory (WGI), the GLIMS Glacier Database, the Glacier Photograph Collection at NSIDC, and the Fluctuations of Glaciers (FoG) and Mass Balance databases at WGMS. We are working toward increased interoperability between these related databases. For example, the Web interface to the GLIMS Glacier Database has also included queryable layers for the WGI and FoG databases since 2008. To improve this further, we have produced a new GTN-G web portal (http://www.gtn-g.org/), which includes a glacier metadata browsing application. This web application allows the browsing of the metadata behind the main GTN-G databases, as well as querying the metadata in order to get to the source, no matter which database holds the data in question. A new glacier inventory, called the Randolph Glacier Inventory 1.0, has recently been compiled. This compilation, which includes glacier outlines that do not have the attributes or IDs or links to other data like the GLIMS data do, was motivated by the tight deadline schedule of the sea level chapter of the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). Now served from the GLIMS website (http://glims.org/), it is designed to serve that narrowly focused research goal in the near term, and in the longer term will be incorporated into the multi-temporal glacier database of GLIMS. For the required merging of large sets of glacier outlines and association of proper IDs that tie together outlines that pertain to the same glacier (perhaps at different points in time), we at NSIDC have written software to examine geospatial relationships between the sets of outlines and assign attributes and linkages accordingly.

Raup, B.; Armstrong, R.; Fetterer, F.; Gartner-Roer, I.; Haeberli, W.; Hoelzle, M.; Khalsa, S. J. S.; Nussbaumer, S.; Weaver, R.; Zemp, M.

2012-04-01

339

Inventory of Glaciers in the North Cascades, Washington  

USGS Publications Warehouse

Perennial bodies of ice in the North Cascades having areas of at least 0.1 km2 (square kilometer) are tabulated and classified. The inventory, a contribution to the International Hydrological Decade, includes 756 glaciers, covering 267 km2, about half of the glacier area in the United States south of Alaska. Listings include each glacier's location, drainage basin, area, length, orientation, altitude, and classification as to form, source, surface, nature of terminus, and activity. These glaciers contribute annually about 800 million cubic meters of water to streamflow in the State of Washington.

Post, Austin; Richardson, Don; Tangborn, Wendell V.; Rosselot, F. L.

1971-01-01

340

Magnetospheric equilibrium with anisotropic pressure  

SciTech Connect

Self-consistent magnetospheric equilibrium with anisotropic pressure is obtained by employing an iterative metric method for solving the inverse equilibrium equation in an optimal flux coordinate system. A method of determining plasma parallel and perpendicular pressures from either analytic particle distribution or particle distribution measured along the satellite's path is presented. The numerical results of axisymmetric magnetospheric equilibrium including the effects of finite beta, pressure anisotropy, and boundary conditions are presented for a bi-Maxwellian particle distribution. For the isotropic pressure cases, the finite beta effect produces an outward expansion of the constant magnetic flux surfaces in relation to the dipole field lines, and along the magnetic field the toroidal ring current is maximum at the magnetic equator. The effect of pressure anisotropy is found to further expand the flux surfaces outward. Along the magnetic field lines the westward ring current can be peak away from the equator due to an eastward current contribution resulting from pressure anisotropy. As pressure anisotropy increases, the peak westward current can become more singular. The outer boundary flux surface has significant effect on the magnetospheric equilibrium. For the outer flux boundary resembling dayside compressed flux surface due to solar wind pressure, the deformation of the magnetic field can be quite different from that for the outer flux boundary resembling the tail-like surface. 23 refs., 17 figs.

Cheng, C.Z.

1991-07-01

341

Getz Ice Shelf, West Antarctica: Little glacier speed increase despite basal ice shelf melting  

NASA Astrophysics Data System (ADS)

The Getz Ice Shelf, stretching along ~500 km of coastline in the Amundsen Sea Sector of West Antarctica, occupies a region of changing climatic and oceanic conditions. Climatically, the region is influenced by the Amundsen Sea Low, a mean atmospheric circulation feature of West Antarctica that has slowly increased in intensity over the past several decades. Oceanographically, the shelf is affected by intrusions of Antarctic Circumpolar Deep Water, which are currently melting the shelf from below at a rate of 4.3 × 0.4 meters of water per year. Recent results from gravity-based assessments of mass change in the region indicate significant mass loss for the entire Getz ice drainage area, and altimetry studies of grounded ice in the Getz Ice Shelf catchment area show significant elevation loss since the 1990s. Our study examines the history of ice velocities from 1972-present on the Getz Ice Shelf, with particular attention to the ice shelf edge and the grounding zone area during the last decade. The shelf and grounded ice are characterized by relatively narrow zones of faster outflow and steep grounded ice surface slopes. The fastest outflow speeds are found toward the western edge at DeVicq Glacier, typically 800-1000 ma-1 near the ice edge and 400-800 ma-1 at the grounding line. Slower speeds towards the east are generally 250-500 ma-1 at the ice edge and 150-400 ma-1 near the grounding line. Despite significant basal melt and thinning of grounded ice, the Getz Ice Shelf has exhibited only modest accelerations: ~20% near the grounding line in the DeVicq Glacier region, ~35% at the far eastern edge, and <10% across central sections of the shelf. This contrasts with the nearly 50% flow speed increase of Pine Island Glacier between 1972 and 2012, and >100% for the adjacent Smith Glacier between 1992 and 2008. We postulate that steep slopes in the grounded ice flow just above the grounding line imply high basal shear stresses for the feeder glaciers and therefore relative insensitivity to thinning of the shelf. With steep initial surface slope, the increase in driving stress caused by grounding line melting is minor. We also examine the potential connection between the measured elevation loss of grounded ice feeding the Getz Ice Shelf with changes (decreases) in annual snow accumulation associated with the evolution of the Amundsen Sea Low.

Alley, K. E.; Scambos, T. A.

2013-12-01

342

Analysis of a 24-Year photographic record of Nisqually glacier, Mount Rainier National Park, Washington  

USGS Publications Warehouse

A systematic coverage of Nisqually Glacier by photographs taken from a network of stations on the ground was begun in 1942 to explore the value and limitations of such photographs as an aid in glacier study. Principles developed may be of value elsewhere, especially for the program 'Measurement of Glacier Variations on a World-Wide Basis' of the International Hydrological Decade. Nisqually Glacier in Mount Rainier National Park, Wash., covers 2.5 square miles (6.5 square kilometers) (1961) and extends from an altitude of about 14,300 feet (4,400 meters) near the top of Mount Rainier down to 4,700 feet (1,400 meters), in a horizontal distance of 4.1 miles (6.6 kilometers). Analyses were made of the annual photographs taken by the writer for 24 years from about 20 stations. A number of pictures taken sporadically from 1884 to 1941 by others were also available for use in the study. Where possible, the results obtained from photographs were compared with those from the available engineering surveys. Such detailed analysis of an extensive photographic coverage of a single glacier may be unique. Photographs illustrating the retreat and advance of the glacier's west ice margin in a reach extending for about a mile (1.6 kilometers) downstream from Wilson Glacier show that, by 1965, most of the ice thickness lost in that area between 1890 and 1944 had been recovered. Withering of the stagnant valley tongue down glacier from the nunatak is portrayed, as is its spectacular reactivation in the 1960's by a vigorous advance of fresh ice. Some of the visible characteristics of advancing and receding termini are noted. Annual values of the glacier's surface slope (5 to 10 degrees) at a cross profile were measured on photographs with respect to a projected vertical line identifiable in each picture. The results were found to average about 2 degrees less than those obtained from the 5-year topographic maps, but they are thought to be a little more accurate owing to lack of a sufficiently small contour interval on the maps for this special purpose. Year-to-year variations in the surface slope and other characteristics from place to place along the glacier are portrayed by pictures to a degree not economically attainable by any other means. Annual changes in the glacier's thickness at two locations were determined from photographs and found to agree well with the results of stadia surveys. A summary of conclusions reached in regard to other data or features of the glacier that were illustrated by annual photographs follows: 1. Toward the end of the ablation season, position of the annual snowline ranged between altitudes of about 5,800 and 7,300 feet (1,750 and 2,250 meters). The altitude limits within which firn was observed on the glacier were about 6,000 and 7,300 feet (1,850 and 2,250 meters). 2. Sources from which debris reaches the glacier are evident. 3. Medial moraines and other persistent patterns sometimes overlooked in the field are more noticeable in photographs. Ice-cored moraines and patterns of multiple lateral moraines are visible. 4. The extent, severity, and nature of crevassing in an area reflect the dynamic condition of the glacier at that location. 5. Erosion has caused certain bedrock areas or features on canyon walls to become unrecognizable within less than 15 years. 6. Effects of the 1932 and 1955 outburst floods on the stream channel and trees for a mile (1.6 kilometers) or so below the glacier are shown in comparison with ordinary, lesser floods. Visible effects include degradation, widening and changes in configuration of the channel, formation of small terraces, removal of vegetation from the flood plain, and the deposition of huge boulders on the stream banks and flood plain. Some photographic procedures recommended for use in a program of this type are described in the section on "Recommended Photographic Procedures."

Veatch, Fred M.

1969-01-01

343

Geometric and oceanographic controls on melting beneath Pine Island Glacier  

NASA Astrophysics Data System (ADS)

beneath the floating section of Pine Island Glacier have revealed the presence of a subglacial ridge which rises up to 300 m above the surrounding bathymetry. This topographic feature probably served as a steady grounding line position until sometime before the 1970s, when an ongoing phase of rapid grounding line retreat was initiated. As a result, a large ocean cavity has formed behind the ridge, strongly controlling the ocean circulation beneath the ice shelf and modulating the ocean water properties that cause ice melting in the vicinity of the grounding line. In order to understand how melt rates have changed during the various phases of cavity formation, we use a high-resolution ocean model to simulate the cavity circulation for a series of synthetic geometries. We show that the height of the ridge and the gap between the ridge and ice shelf strongly control the inflow of warm bottom waters into the cavity, and hence the melt rates. Model results suggest a rapid geometrically controlled increase of meltwater production at the onset of ice thinning, but a weak sensitivity to geometry once the gap between the ridge and ice shelf has passed a threshold value of about 200 m. This provides evidence for a new, coupled, ice-ocean feedback acting to enhance the initial retreat of an ice stream from a bedrock high. The present gap is over 200 m, and our results suggest that observed variability in melt rates is now controlled by other factors, such as the depth of the thermocline.

De Rydt, J.; Holl