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1

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

2

A new approach to calculating Holocene winter precipitation by combining glacier equilibrium-line altitudes and pine-tree limits: a case stud from Hardangerjokulen, central southern Norway  

Microsoft Academic Search

At Hardangerjøkulen, central southern Norway, detailed knowledge of the number, age and magnitude of Holocene glacier fluctuations is used to reconstruct variations in equilibrium-line altitude (ELA) for the last 10 000 years. Present and past ELAs are based on an accumulation-area ratio (AAR) of 0.7 and are adjusted for land uplift. A synchronous relationship between advanced glacier positions and the

Svein Olaf Dahl; Atle Nesje

1996-01-01

3

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

4

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

5

Present and late Pleistocene equilibrium line altitudes in the Mt Everest region — an application of the glacier inventory  

Microsoft Academic Search

UNESCO's pilot glacier inventory of the Mt Everest area was extended to include some 450 glaciers. After evaluation of various methods to establish the ELA, the pattern of the ELA isolines was analysed in relation to the orography, precipitation and temperature. The dominant role played by precipitation is recognized, and the unusually low mean AAR value of 0.41 is explained.

F. Mùller

6

Changes in glacier equilibrium-line altitude in the western Alps from 1984 to 2010: evaluation by remote sensing and modeling of the morpho-topographic and climate controls  

NASA Astrophysics Data System (ADS)

We present time series of equilibrium-line altitude (ELA) measured from the end-of-summer snow line altitude computed using satellite images, for 43 glaciers in the western Alps over the 1984-2010 period. More than 120 satellite images acquired by Landsat, SPOT and ASTER were used. In parallel, changes in climate variables, summer cumulative positive degree days (CPDD) and winter precipitation, were analyzed over the same time period using 22 weather stations located inside and around the study area. Assuming a continuous linear trend over the study period: (1) the average ELA of the 43 glaciers increased by about 170 m; (2) summer CPDD increased by about 150 PDD at 3000 m a.s.l.; and (3) winter precipitation remained rather stationary. Summer CPDD showed homogeneous spatial and temporal variability; winter precipitation showed homogeneous temporal variability, but some stations showed a slightly different spatial pattern. Regarding ELAs, temporal variability between the 43 glaciers was also homogeneous, but spatially, glaciers in the southern part of the study area differed from glaciers in the northern part, mainly due to a different precipitation pattern. A sensitivity analysis of the ELAs to climate and morpho-topographic variables (elevation, aspect, latitude) highlighted the following: (1) the average ELA over the study period of each glacier is strongly controlled by morpho-topographic variables; and (2) the interannual variability of the ELA is strongly controlled by climate variables, with the observed increasing trend mainly driven by increasing temperatures, even if significant nonlinear, low-frequency fluctuations appear to be driven by winter precipitation anomalies. Finally, we used an expansion of Lliboutry's approach to reconstruct fluctuations in the ELA of any glacier of the study area with respect to morpho-topographic and climate variables, by quantifying their respective weight and the related uncertainties in a consistent manner within a hierarchical Bayesian framework. This method was tested and validated using the ELA measured on the satellite images.

Rabatel, A.; Letréguilly, A.; Dedieu, J.-P.; Eckert, N.

2013-09-01

7

Changes in glacier Equilibrium-Line Altitude (ELA) in the western Alps over the 1984-2010 period: evaluation by remote sensing and modeling of the morpho-topographic and climate controls  

NASA Astrophysics Data System (ADS)

We present time series of equilibrium-line altitude (ELA) measured from the end-of-summer snowline altitude computed using satellite images, for 43 glaciers in the western Alps over the 1984-2010 period. More than 120 satellite images acquired by Landsat, SPOT and ASTER were used. In parallel, changes in climate parameters (summer cumulative positive degree days, CPDD, and winter precipitation) were analyzed over the same time period using 22 weather stations located inside and around the study area. Assuming a continuous linear trend over the study period: (1) the average ELA of the 43 glaciers increased by about 170 m; (2) summer CPDD increased by about 150 PDD at 3000 m a.s.l.; and (3) winter precipitation remained rather stationary. Summer CPDD showed homogeneous spatial and temporal variability; winter precipitation showed homogeneous temporal variability, but some stations showed a slightly different spatial pattern. Regarding ELAs, temporal variability between the 43 glaciers was also homogeneous, but spatially, glaciers in the southern part of the study area differed from glaciers in the northern part, mainly due to a different precipitation pattern. A sensitivity analysis of the ELAs to climate and morpho-topographic parameters (elevation, aspect, latitude) highlighted the following: (1) the average ELA over the study period of each glacier is strongly controlled by morpho-topographic parameters; and (2) the interannual variability of the ELA is strongly controlled by climate parameters, with the observed increasing trend mainly driven by increasing temperatures, even if significant nonlinear low frequency fluctuations appear to be driven by winter precipitation anomalies. Finally, we used an expansion of Lliboutry's approach to reconstruct fluctuations in the ELA of any glacier of the study area with respect to morpho-topographic and climate parameters, by quantifying their respective weight and the related uncertainties in a consistent manner within a hierarchical Bayesian framework. This method was tested and validated using the ELA measured on the satellite images.

Rabatel, A.; Letréguilly, A.; Dedieu, J.-P.; Eckert, N.

2013-06-01

8

An automatic method to create flow lines for determination of glacier length: A pilot study with Alaskan glaciers  

NASA Astrophysics Data System (ADS)

Glacier length is a key parameter in global glacier inventories, but difficult to determine in a consistent way and subject to frequent change. Its vector representation (a flow line) is a most important input for modeling 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. We here present a new algorithm that is based on Python scripting and additional libraries (GDAL and 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 Neighbor 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 dataset for 20 glaciers. This comparison revealed for 17 out of the 20 glaciers a length value within the range of the manual digitizations. Other potential methods performed less well. Combined with previous glacier outlines from the same region (Digital Line Graph) we automatically determined length changes for 390 glaciers over a c. 50 year period.

Le Bris, Raymond; Paul, Frank

2013-03-01

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

Remote sensing of glaciers and ice sheets  

NASA Astrophysics Data System (ADS)

This chapter summarizes research on satellite remote sensing of glaciers and ice sheets. It covers a number of topics, including studies of the equilibrium line; characteristic glacier surface zones or glacier facies; glacier velocity; glacier mapping; change detection; surface features; and snow pack characteristics. Finally, we briefly outline new opportunities for northern hydrology with the utilization of recent and planned spaceborne sensors such as MODIS, ENVISAT MERIS and ASAR, ICESat, and CryoSat.

Winther, Jan-Gunnar; Bindschadler, Robert; König, Max; Scherer, Dieter

11

Glaciers  

NASA Astrophysics Data System (ADS)

Glaciers are among the most beautiful natural wonders on Earth, as well as the least known and understood, for most of us. Michael Hambrey describes how glaciers grow and decay, move and influence human civilization. Currently covering a tenth of the Earth's surface, glacier ice has shaped the landscape over millions of years by scouring away rocks and transporting and depositing debris far from its source. Glacier meltwater drives turbines and irrigates deserts, and yields mineral-rich soils as well as a wealth of valuable sand and gravel. However, glaciers also threaten human property and life. Our future is indirectly connected with the fate of glaciers and their influence on global climate and sea level. Including over 200 stunning photographs, the book takes the reader from the High-Arctic through North America, Europe, Asia, Africa, New Zealand and South America to the Antarctic. Michael Hambrey is Director of the Centre for Glaciology at the University of Wales, Aberystwyth. A past recipient of the Polar Medal, he was also given the Earth Science Editors' Outstanding Publication Award for the first edition of Glaciers (Cambridge, 1995). Hambrey is also the author of Glacial Environments (British Columbia, 1994). JÜrg Alean is Professor of Geography at the Kantonsschule ZÜrcher Unterland in BÜlach, Switzerland.

Hambrey, Michael; Alean, Jürg

2004-12-01

12

Glaciers  

NSDL National Science Digital Library

Glaciers are found on every continent except Australia. This interactive feature provides an introduction to these moving streams of ice, which cover about 10 percent of Earth's land surface and hold between two and three percent of its water. Topics include what glaciers are, where and why they form, what influences their growth and decline, and how an apparently solid mass appears to flow like a river. There is also a brief description of some types of glaciers. A background essay and discussion questions are included.

2010-09-28

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

Glaciers and hydrological changes in the Tien Shan: simulation and prediction  

Microsoft Academic Search

In this study, we estimated the current glacier state and forecast the potential impact of global and regional climate change on the glaciers and glacier runoff in the Tien Shan. General (G) and detailed (D) simulations were developed based on assessment of the Tien Shan glacier recession between 1943 and 2003 using an iterative stepwise increase in the equilibrium line

V B Aizen; E M Aizen; V A Kuzmichonok

2007-01-01

15

Basal drag pattern and grounding line sensitivity of the ice flow of Totten Glacier, East Antarctica  

NASA Astrophysics Data System (ADS)

Increased ice thinning has been detected on Totten Glacier, East Antarctica, but the cause of thinning and its timing are unclear. Most of the observed changes are taking place in the proximity of the grounding line. In this work, we apply an inverse method part of the JPL/UCI Ice Sheet System Model (ISSM) to infer the spatial pattern of basal drag on Totten Glacier from satellite radar interferometry observations of ice motion combined with a gridded thickness map using IceBridge data. A particularity of Totten Glacier is that its grounding line migrates back and forth over more than 15 km along the glacier sides as a result of changes in oceanic tides. We use the model set up and our observations of grounding line migration to study the impact of oceanic tides and changes in ice shelf bottom melting on the ice speed of the glacier. We conclude on the likelihood that observed glacier thinning is indeed controlled by its grounding line dynamics and whether the current rate of ice thinning might be explained from a change in thermal forcing from the ocean. Preliminary results are presented. This work is performed at University of California, Irvine under a contract with NASA Cryosphere Science Program.

Li, X.; Rignot, E. J.; Morlighem, M.; Seroussi, H. L.; Larour, E. Y.; Mouginot, J.; Scheuchl, B.; Young, D. A.; Blankenship, D. D.

2011-12-01

16

Brief communication "Historical glacier length changes in West Greenland"  

NASA Astrophysics Data System (ADS)

Past glacier fluctuations provide insight into glacier dynamics, climate change, and the contribution of glaciers to sea-level rise. Here, the length fluctuations since the 19th century of 18 local glaciers in West and South Greenland are presented, extending and updating the study by Weidick (1968). The studied glaciers all showed an overall retreat with an average of 1.2 ± 0.2 km over the 20th century, indicating a general rise of the equilibrium line along the west coast of Greenland during the last century. Furthermore, the average rate of retreat was largest in the first half of the 20th century.

Leclercq, P. W.; Weidick, A.; Paul, F.; Bolch, T.; Citterio, M.; Oerlemans, J.

2012-11-01

17

Glaciers in Equilibrium - Results from the McMurdo Dry Valleys, Antarctica  

NASA Astrophysics Data System (ADS)

Since 1993 the mass balance of two glaciers in the McMurdo Dry Valleys, Antarctica (163° E 77.5° S) has been measured. The magnitude of annual mass gain or loss does not exceed 10 cm water equivalent averaged over each glacier, consistent with the local climate of a polar desert. The overall trend in mass balance shows that the glaciers are in approximate balance with the current climate and no obvious trends exist in either the winter or summer balances. These are similar to a set of mass balance measurements made in another part of the dry valleys during the 1970s (Chinn, 1985). Recent analysis of the climate of the dry valleys shows this region is cooling at a rate of 0.7° C per decade during this period since 1986, which is reflected in the overall lowering of lake levels, decreased primary productivity of the lakes, and declining number of invertebrates (Doran et al., 2002). Although an unusually warm period occurred in the summer of 2001-2002, annual temperatures continue to cool. This region seems to be isolated from the warming elsewhere in Antarctica and the cooling in this part of the Ross Sea region may be due to El Nino forcing (Bertler et al, 2004). The sluggish behavior of the glaciers results from a low mass exchange and an apparent climatic buffering, which supports evidence from the geologic record that these glaciers have not advanced more than a few hundred meters over the past 3 million years (Hall et al., 1993). Many of the glaciers, however, are advancing which probably results from a slow time-scale response from warming conditions in the past millennium.

Fountain, A. G.; Nylen, T. H.; Doran, P. T.

2004-12-01

18

Glacier fluctuations in the Kenai Fjords, Alaska, U.S.A.: An evaluation of controls on Iceberg-calving glaciers  

SciTech Connect

The histories of four iceberg-calving outlet-glacier systems in the Kenai Fjords National Park underscore the importance of fiord depth, sediment supply, and fiord geometry on glacier stability. These parameters, in turn, limit the reliability of calving glacier chronologies as records of climatic change. Tree-ring analysis together with radiocarbon dating show that the Northwestern and McCarty glaciers, with large drainage basins, were advancing in concert with nearby land-terminating glaciers about A.D. 600. After an interval of retreat and possible nonclimatically induced extension during the Medieval Warm Period, these ice margins advanced again through the Little Ice Age and then retreated synchronously with the surrounding land-terminating glaciers about A.D. 1900. In contrast, Holgate and Aialik glaciers, with deeper fiords and smaller basins, retreated about 300 yr earlier. Reconstructions of Little Ice Age glaciers suggest that equilibrium-line altitudes of Northwestern and McCarty glaciers were, respectively, 270 and 500 m lower than now. Furthermore, the reconstructions show that these two glaciers were climatically sensitive when at their terminal moranies. However, with ice margins at their present recessional positions and accumulation area ratios between 0.8 and 0.9, only McCarty Glacier shows evidence of advance. Aialik and Holgate glaciers were climatically insensitive during the Little Ice Age maxima and remain insensitive to climate. 40 refs., 7 figs., 2 tabs.

Wiles, G.C. [Columbia Univ., Palisades, NY (United States); Calkin, P.E. [Univ. of New York, Buffalo, NY (United States); Post, A. [Geological Survey, Vashon, WA (United States)

1995-08-01

19

Snow-Line Changes on Irian Jaya Glaciers Between 1971 and 2000 Record Temperature Changes in the Lower Troposphere (600 mb) of the Far Western Tropical Pacific  

NASA Astrophysics Data System (ADS)

Long-term fluctuations in the size and surface mass balance of glaciers in the wet tropics dominantly reflect temperature change in the lower troposphere. Hence, altitudinal changes in the snow- or equilibrium-line (ELA) on these glaciers approximate the height history of the mean annual 0oC isotherm. We report here changes in the size and mass balance of glaciers in the far western tropical Pacific region of Irian Jaya (4o S, 137o E) between 1971 and 2000. In 1971, the glaciers occupied about 12km2 of the Puncak Jaya region between 4400 and 4900 m above sea level (masl) (600 mb). By 2001, ice area was reduced to about 2 km2. Relying primarily on photogrammetric observations provided by PT Freeport Indonesia, we estimate that, between 1972 and 1995, the average ELA for the principle glaciers rose about 70 m from 4650 masl to 4724 masl based on clearly visible snow-lines. Between 1995 and 1997, the ELA appears to have risen an additional 50 m, reaching 4780 masl. Though net snow accumulation for 1995-1997 varied laterally across the glacier surfaces, almost all ice surfaces lowered for 1995-1997. Between 1997 and 2000, net balances were substantially more positive than for 1995-1997, indicating ELA lowering by 10s of meters. Patches of net surface-elevation increase and decrease were only partially related to altitude. Significant areas of net positive balance were apparent down to 4740 masl. Assuming that there was no long-term trend in precipitation in this region, we infer that regional temperature increase drove the ELA rise on these glaciers. If the lapse rate on Puncak Jaya held at 0.7oC/100 m, then the ELA changes signify a net warming of the lower troposphere of nearly 0.9 oC between 1971 and 1997. The apparent net ELA lowering from 1997 to 2000 is consistent with nearly offsetting warming and cooling in this interval measured by PT Freeport Indonesia. For 1971-2000, the ELA-based temperature trends mimick those derived from tropical radiosonde data. Hence, the geological record of past ELA changes in New Guinea presents the opportunity to reconstruct regional lower tropospheric conditions back in time.

Prentice, M. L.; Brackett, T.

2002-05-01

20

Climate Change in the Russian Altai Mountains and its Influence on Tree Line and Glacier Dynamics  

NASA Astrophysics Data System (ADS)

The mountain ecosystems are highly sensitive to climate changes. The Russian Altai Mountains are located in the Inner Asia on the border of Russia, Mongolia, China and Kazakhstan. The Department of Geography and Geoecology of SPbSU has been organizing annual field expeditions to this region during the last 20 yrs. The uniqueness of the Altai landscapes lies in its great variety as these mountains are higher than 4 km and located on the zonal border between steppes and semi-deserts and between continental and sharply continental climates. This research deals with space-time features of regional climate changes and the dynamics of high-altitude landscapes. The 1940-2004 time series of seasonal air temperature and precipitation from 14 weather stations from 300 to 2600 m a.s.l. were statistically analyzed applying regression, correlation, spectral and cluster analyses. To extend time series over the past 350-400 yrs, mean summer temperature and precipitation were reconstructed applying dendroclimatological methods and using the WSL Dendro data base. Comparing to the Northern Hemisphere tendency of temperature increase in the second half of the 20th century over the Altai has been observed generally earlier, since 1950s. Maximum warming rate in the last quarter of the 20th century is typical to winter in the Altai (0,85°/10 yrs) as well as the entire Northern Hemisphere. Synchronous changes in the Altai and the Northern Hemisphere are observed in all seasons only in 1975-2004. At the turn of the XX-XXI centuries warming rates slow down in the region while temperature level is still high. These changes are partly associated with circulation epochs. Spectral analysis revealed important role of natural cyclical recurrence in climate changes, for example quasi-biennial, solar and Brückner cycles. According to dendrochronological reconstruction mean summer temperature increased from the end of the Little Ice Age (LIA) to its maximum in the 1990s by approximately 2°C, to the average for the period 1986-2004 - about 1,3°C. As tree line against the other belt borders strongly limited by summer temperature its eventual dynamics since the end of the LIA over the Altai were estimated and tree line position at different stages of modern regional warming was reconstructed. Theoretical evaluation shows that mean summer temperature increase of 1.3°C from the end of the LIA causes tree line to rise maximum by 180-280 m in different localities of the Altai. Glacial complexes of mountain massifs Mongun-Taiga, Tavan-Boghd-Ola, Turgeni-Nuru and Harhira-Nuru located in the South-Eastern Altai are represented by small glaciers mostly on northern and eastern leeward slopes. Being situated in region with dry climatic conditions (250-400 mm/year) glaciers survive only in negative forms of relief with high concentration of snow. Accumulation coefficient is mainly from 2 to 3, and on cirque glaciers is from 6 to 8. Now glaciers retreat rapidly (17% of area loss for the period of 1995-2010 for Mongun-Taiga, 12% in 2002-2009 for Tavan-Boghd-Ola), especially valley glaciers (2-10 m/yr), the number of glaciers increase due to disintegration of larger glaciers. Small forms of glaciation disappear or transform into snow patches and rock glaciers.

Syromyatina, M.; Moskalenko, I.; Ganushkin, D.; Chistyakov, K.

2011-12-01

21

Variations of the tree line and glaciers in the Central and Eastern Altai regions in the Holocene  

NASA Astrophysics Data System (ADS)

Variations in the tree line position and glacier activity in the Central and Eastern Altai regions in the Holocene were reconstructed on the basis of analysis of sixty radiocarbon and eighteen dendrochronological dates. The tree line was higher than now in the Early and Middle Holocene, and the climate was warmer and, likely, more humid. Glaciers advanced in the forests 300, 1400, and 3000-6000 years ago. In the last millennium the forest decline at the upper tree limit occurred in 1206-1256, 1445-1501, and 1642-1736.

Nazarov, A. N.; Solomina, O. N.; Myglan, V. S.

2012-06-01

22

Complex Behaviour of Glaciers in Ladakh Mountains (J & K State, India) : Case Study  

NASA Astrophysics Data System (ADS)

The Ladakh Mountains house approximately 4500 glaciers in its two major basins, namely Indus (1800 glaciers) and Shyok (2700 glaciers).Glaciers in Indian Himalaya have been under monitor for past about five decades. Monitoring of scores of glaciers have been both in terms of documentary record and field studies of the glaciers in northwest Himalaya. The studies suggest that glaciers of Ladakh mountains show an extremely different behavior as compared to the glaciers of rest of northwest Himalaya. Four glaciers, namely Durung Drung, Kangriz, Machoi and Siachen, representing the Indus and Shyok basin are dealt herein. Sufficient documentary and field evidences of these four glaciers support the view that glaciers housed in Ladakh mountains contradict the commonly accepted concept of fast melting glaciers in Himalaya (Ganjoo and Koul 2009; Ganjoo et al. 2010). The studies further suggest that the secular movement of glaciers in Ladakh mountains is a complex phenomena of several micro and macro-climatic factors, terrain morphology, and tectonics (Ganjoo 2009, Koul and Ganjoo 2010). The change in the morphology of glaciers is not necessarily related with the change in climate as commonly believed and hyped. Ganjoo, R.K. (2009) Holocene Tectonics and Climate of Durung Drung Glacier Basin, Zanskar Himalaya, India (Abstract). The 5th International Symposium on Tibetan Plateau and 24th Himalaya- Karakorum-Tibet Workshop, Aug. 11-14, Beijing, China. Ganjoo, R.K. and Koul, M.N. (2009) Is the Siachen glacier melting? Current Science, 97(3), 309-310. Ganjoo, RK; Koul, MN; Ajai; Bahuguna, IM (2010) Glaciers of Nubra valley, Karakorum mountains, Ladakh (India) vis-à-vis climate change (abstract). 7th Annual Meeting of Asia Oceania Geosciences Society, Hyderabad. Koul, M.N. and Ganjoo, R.K. (2010) Impact of inter- and intra-annual variation in weather parameters on mass balance and equilibrium line altitude of Naradu glacier (Himachal Pradesh), NW Himalaya, India. Climatic Change, 99, 119-139.

Ganjoo, R. K.

2011-12-01

23

Holocene climatic changes in Iceland: evidence from modelling glacier length fluctuations at Sólheimajökull  

Microsoft Academic Search

We use a coupled energy-balance\\/glacier-flow model to reconstruct Holocene climate from a 5000-yr record of glacier length fluctuations at Sólheimajökull, an outlet glacier in southern Iceland. The climatic reconstruction is presented in terms of Equilibrium-Line Altitude and is translated to envelopes of possible temperature and precipitation changes. The reconstruction is highly resolved between AD 1700 and 1990: the 20th Century

Andrew N. Mackintosh; Andrew J. Dugmore; Alun L. Hubbard

2002-01-01

24

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

25

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

26

Constraining Glacier Sensitivity across the Andes: A Modeling Experiment  

NASA Astrophysics Data System (ADS)

Valley glaciers are sensitive indicators of climate change. Records of former glacial fluctuations have been extensively used to reconstruct paleoclimatic conditions at different temporal and spatial scales. These reconstructions typically do not account for variations in regional climate conditions. Based on modeling results, it has been suggested these regional climate conditions could play an important role modulating the magnitude of glacier response for large scale climate perturbations. The climatically diverse Andes mountain range represents an ideal setting to test hypothesis of glacier sensitivity variability. Here, we quantify glacier sensitivity to climate change in different climatic regimes across the Andean. By applying a regional Surface Energy Mass Balance model (SEMB), we analyze the change in the Equilibrium Line Altitude (ELA) for a sample of 234 glaciers, under different climatic perturbations. Our results suggest that ELAs of Andean glaciers respond linearly to changes in temperature, with rates that oscillate between 153 and 186 m/°C. For example, with a perturbation of -6°C (~Global LGM), our model predicts a drop in the ELA of 916 m for the least sensitive glaciers and 1117 m for the more sensitive ones. This glacier sensitivity variability exhibits a very distinctive spatial distribution. The most sensitive glaciers are located in Central Chile (south of 31°C), and the Western Cordillera of Peru (north of 13°S). In contrast, lower sensitivity glaciers are situated in the inner Tropics, Eastern Cordillera of Peru and Bolivia (south of 13°S), and part of southern Patagonia and Tierra del Fuego. When analyzing the response of glaciers to changes in accumulation, our results suggest that under a scenario of increasing precipitation, glacier behavior is nonlinear. A statistical cluster analysis of glacier sensitivity divides our 234 glaciers into three distinct groups. The most sensitive glaciers correspond to those situated in western Cordillera of Peru and Bolivia (south of 15°S), the north of Chile-Argentina (north of 19°S), and Central Chile, between 27° and 38°S. Similar to our results with temperature, the inner tropical glaciers are the least responsive to precipitation changes. With our regional approach, we expect to explore the mechanisms responsible for the spatial variability of glacier sensitivity across the Andes, thus improving our understanding of climate-glacial dynamic interaction. These mechanisms will provide a framework to study the causes of past episodes of glacial fluctuations and ultimately to predict the response of glaciers to future climate change scenarios.

Sagredo, E. A.; Rupper, S.; Lowell, T. V.

2011-12-01

27

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

28

Mountain and subpolar glaciers show an increase in sensitivity to climate warming and intensification of the water cycle  

Microsoft Academic Search

The time-series of all available records of seasonal and annual glacier mass balances, equilibrium line altitude, accumulation area ratio and change in surface area of about 300 glaciers have been compiled, digitized, quality checked and analyzed over the period of almost four decades (1961–1998). These time-series show significant changes towards loss in glacier area and volume in global scale with

Mark Dyurgerov

2003-01-01

29

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

30

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

31

Holocene climate and glacier variability at Hallet and Greyling Lakes, Chugach Mountains, south-central Alaska  

Microsoft Academic Search

Evidence from lake sediments and glacier forefields from two hydrologically isolated lake basins is used to reconstruct Holocene\\u000a glacier and climate history at Hallet and Greyling Lakes in the central Chugach Mountains of south-central Alaska. Glacial\\u000a landform mapping, lichenometry, and equilibrium-line altitude reconstructions, along with changes in sedimentary biogenic-silica\\u000a content, bulk density, and grain-size distribution indicate a dynamic history of

Nicholas P. McKay; Darrell S. Kaufman

2009-01-01

32

Polar versus temperate grounding-line sedimentary systems and marine glacier stability during sea level rise by global warming  

Microsoft Academic Search

Marine-ending glaciers may retreat with global warming as sea level rises by ocean thermal expansion. If the sea floor rises by sediment accumulation, then glaciers may not feel the effect of sea level rise. A submersible ROV and other techniques have been used to collect data from temperate and polar glaciers to compare sediment production and mass balance of their

R. D. Powell; A. R. Pyne; L. E. Hunter; N. R. Rynes

1992-01-01

33

Velocity change and ice discharge from Antarctic Peninsula Glaciers  

NASA Astrophysics Data System (ADS)

Satellite radar interferometry data from ERS-1/2 acquired in 1996 were employed to map the ice velocity of the outlet glaciers discharging ice along the eastern flank of the Peninsula from 64 south to 71 south, and along the former Wordie Ice Shelf in the west. Differential radar interferometry was employed to map the position of the glacier grounding lines. Estimates of ice thickness at the grounding line were obtained from hydrostatic equilibrium using existing topographic maps, or from direct measurement from radio echo sounding by BAS in 1994-2000 and CECS/NASA in 2002. The resulting glacier fluxes were compared to snow accumulation compiled by Turner et al. (2002) to deduce first-order estimates of the glacier mass balance. In places where ice shelves are known to have been retreating, we compared the 1996 velocities with older measurements as well as more recent estimates from ERS-1/2 (2000), Radarsat (2000-2003) and Aster (2002). On Fleming Glacier, we find a large increase in flow speed from 1972 to 1996, with no further increase after 1996, which suggests that the glacier did respond to the collapse of Wordie Ice Shelf several decades ago. On Drygakski glacier in the east, we confirm a large acceleration of the glacier following the collapse of Larsen B, as revealed by Rott et al. (2002), which is continuing to this date. We conclude on the effect of retreating ice shelves on the evolution of inland ice in this sector of Antarctica and on its impact on sea level rise.

Rignot, E.; Pritchard, H.; Vaughan, D.; Rivera, A.; Kanagaratnam, P.; Casassa, G.; Thomas, R.

2003-12-01

34

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

35

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.

36

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

37

Modeling the Climatic Controls and Topographic Form of Modern and Late Pleistocene Tropical Peruvian Glaciers  

NASA Astrophysics Data System (ADS)

Glaciers in the tropical highlands are important and highly sensitive indicators of global climate change over different time scales. Simulating glacier extent from basic climatic and topographic input elucidates understanding of present glacier-climate processes, climate control over past glacial extent, and future impacts of changing climate. We apply a physically based, 2-D, glacier model to reconstruct steady-state glacier forms and mass distributions for a range of tropical climatic conditions in the Cordillera Blanca, Peru (8-10°S). The model is based on gridded digital elevation data, computes the effects of topography on the largest component of surface energy balance, shortwave solar insolation, calculates 2-D, in the horizontal-plane, distribution of snow accumulation using a surface mass and energy balance approach, and reconstructs resultant glacier shape with a 2-D flow model. We are able to reconstruct modern glacier extent to match satellite imagery using climate data assimilated from over 30 Andean stations located between 9-11°S, including current observations at glacier elevations, and compute a modern equilibrium line at ˜5000 m asl. We then apply the model in an inverse approach to infer paleoclimate conditions for late Pleistocene moraine positions mapped in specific valleys with global positioning system positions and dated by radiocarbon dates on lake and peat sediments. Simulations confirm that with no precipitation changes, a cooling of 4.5°C is required to achieve equilibrium glacier shapes terminating at moraine positions bounding Laguna Queshque (4300 m asl 9°50'S; 77°25'W). Alternatively, increasing precipitation by 1.5 times the modern values requires a temperature reduction of 3.75°C for the model to reach the same ELA position. A model sensitivity analysis highlights the importance of both moisture availability and temperature changes in driving tropical Andean glacier fluctuations. Results also indicate that temperature reductions of 1°C are required to reconstruct equilibrium glacier shapes to match the modern glacier tongue in the Queshque valley. Under modern climate conditions, the remaining valley glacier volume will disappear within three decades.

Mark, B. G.; Stansell, N.; Fairman, J. G.; Plummer, M. A.; Rodbell, D. T.

2010-12-01

38

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

39

World Glacier Monitoring Service  

NSDL National Science Digital Library

The World Glacier Monitoring Service site contains online issues of Fluctuations of Glaciers and the Glacier Mass Balance Bulletin; glacier inventory data describing the spatial variability and glacier fluctuation data documenting changes in time; explanations of glacier monitoring strategy using glacier mass balance, length change, inventories, and data analysis; and a bibliography of related work.

40

Glacier fluctuations in the Southern Alps of New Zealand determined from snowline elevations  

SciTech Connect

Preliminary analysis of 452 determinations of end-of-summer glacier snowline altitudes (ELAs) made over 17 yr on up to 47 glaciers show good correlation with major climatic events, and conform well with fluctuations of glacier termini when reaction times are taken into consideration. With snowline altitudes used as surrogates for annual mass balance values, there is a recent trend to increased mass balances, i.e. a climate {open_quotes}cooling,{close_quotes} which follows a long period of predominantly glacial recession. Snowline trend surfaces plotted for the Southern Alps of New Zealand show considerable warping with variable departures from the steady-state equilibrium-line altitude each year. The current resurgence of the more active glaciers should continue in the near future. 39 refs., 10 figs., 1 tab.

Chinn, T.J.H. [Institute of Geological & Nuclear Sciences Ltds., P.B. Dunedin (New Zealand)

1995-05-01

41

New Tools for Analyzing Glacier Changes From Space  

NASA Astrophysics Data System (ADS)

Efforts to compile a comprehensive global glacier inventory, such as that being undertaken by the Global Land Ice Measurements from Space (GLIMS) project, require ready access to high-resolution satellite imagery as well as tools for performing analyses on these data. In this paper we describe a study of ice extent and volume changes for the Petrov glacier system of the Akshiyrak Range in the interior Tien Shan of Central Asia. Glacier outlines were digitized from an orthorectified ASTER imagery using a freeware tool, GLIMSView. A digital elevation model (DEM) was extracted from an ASTER scene acquired in October 2002. From these results we determine ice area as a function of elevation using GIS tools. The resulting hypsography is then used in conjunction with field measurements of mass balance for another glacier in the same range to estimate the mass balance for the Petrov glacier as a function of observed equilibrium line altitude, and thus to predict how climate change will impact the hydrology of the region.

Khalsa, S. S.; Dyurgerov, M. B.; Raup, B.; Scharfen, G.; Barry, R. G.

2003-12-01

42

Spatial distribution of glacial erosion rates in the St. Elias range, Alaska, inferred from a realistic model of glacier dynamics  

NASA Astrophysics Data System (ADS)

Glaciers have been principal erosional agents in many orogens throughout much of the recent geological past. A modern example is the St. Elias Mountains in southeastern Alaska; it is a highly convergent, complex orogen, which has been glaciated for much of its history. We examine the Seward-Malaspina Glacier system, which comprises two of the largest temperate glaciers in the world. We focus on the pattern of erosion within its narrow passage through the St. Elias Mountains, the Seward Throat. Measured glacier surface velocities and elevations provide constraints for a full-stress numerical flowband model that enables us to quantitatively determine the glacier thickness profile, which is not easily measured on temperate glaciers, and the basal characteristics relevant for erosion. These characteristics at the bed, namely the water pressure, normal and shear stresses, and sliding velocity, are then used to infer the spatial variation in erosion rates using several commonly invoked erosion laws. The calculations show that the geometry of the glacier basin exerts a far stronger control on the spatial variation of erosion rates than does the equilibrium line altitude, which is often assumed to be important in studies of glaciated orogens. The model provides a quantitative basis for understanding why erosion rates are highest around the Seward Throat, which is generally consistent with local and large-scale geological observations and thermochronologic evidence. Moreover, model results suggest how glacier characteristics could be used to infer zones of active or recent uplift in ice-mantled orogens.

Headley, Rachel; Hallet, Bernard; Roe, Gerard; Waddington, Edwin D.; Rignot, Eric

2012-09-01

43

Glacier Caves  

NSDL National Science Digital Library

Created by Charlie Anderson Jr. of the International Glaciospeleological Survey, Glacier Caves provides numerous fantastic photographs of glaciers, caves, and volcanoes located mainly in Northwestern United States. Visitors can sort through the images by topic or by location. Users can find various materials on eruptions, special features, and explorations of many famous Northwestern mountains including Mount St. Helens, Mount Hood, and Mount Rainer. The site features links to volcano web cameras.

44

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

45

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

46

Plasma Equilibrium in a Magnetic Field with Stochastic Field-Line Trajectories  

NASA Astrophysics Data System (ADS)

The nature of plasma equilibrium in a magnetic field with stochastic field lines is examined, expanding upon the ideas first described by Reiman et al. The magnetic partial differential equation (PDE) that determines the equilibrium Pfirsch-Schlüter currents is treated as a passive stochastic PDE for ?j/B. Renormalization leads to a stochastic Langevin equation for ? in which the resonances at the rational surfaces are broadened by the stochastic diffusion of the field lines; even weak radial diffusion can significantly affect the equilibrium, which need not be flattened in the stochastic region. Particular attention is paid to satisfying the periodicity constraints in toroidal configurations with sheared magnetic fields. A numerical scheme that couples the renormalized Langevin equation to Ampere's law is described. A. Reiman et al, Nucl. Fusion 47, 572--8 (2007). J. A. Krommes, Phys. Reports 360, 1--351.

Krommes, J. A.; Reiman, A. H.

2008-11-01

47

Spatial variation of glacial erosion rates in the St. Elias range, Alaska, inferred from a realistic model of glacier dynamics  

NASA Astrophysics Data System (ADS)

Glaciers have been principal erosional agents in many tectonically active orogens throughout much of the recent geological past. The St. Elias Mountains in southeastern Alaska are a surface expression of a highly convergent, complex orogen that was likely glaciated for much of its history. We examine the Seward-Malaspina Glacier system, part of one of the largest temperate glacier systems in the world, and focus on the Seward Throat, which is a narrow passage of the glacier through the St. Elias Mountains. It is within this region that we examine the pattern of erosion where ice velocities are exceptionally high. The glacier surface velocities and elevations, which are known, provide constraints for a numerical, full-stress flowband model that enables us to infer the glacier thickness, which is not easily measured on temperate glaciers, and the corresponding sliding velocity and other basal properties. This in turn allows us to produce one of the first studies of the current spatial distribution of erosion under an active glacier; erosion rates are inferred using the flow model guided by glaciological observations and several commonly invoked erosion laws that depend upon the sliding velocity and basal shear stress. The spatial variation of current erosion rates is strongly controlled by the geometry of the glacier and less influenced by other factors, such as the equilibrium line altitude or the choice of erosion law. Inferred erosion rates are highest within the narrow, central portion of the Seward Throat, consistent with both local and regional geological observations. The numerical model used in conjunction with surface glaciological measurements is a powerful tool for investigating ice thickness, basal properties, and the spatial variation of glacial erosion rates for many temperate glaciers, where little is known aside from surface properties. The glaciological data and model results have potential use for inferring local regions of active uplift in the vicinity of the Seward Throat and for investigating the role of glacial erosion within the broader tectonic setting of the St. Elias Mountains.

Headley, R. M.; Hallet, B.; Roe, G.; Waddington, E. D.

2011-12-01

48

Recent changes detected on two glaciers at the northern part of James Ross Island, Antarctica  

NASA Astrophysics Data System (ADS)

Antarctic Peninsula is one of the regions, which have been exposed to the most rapid warming of the Earth since 1950. Consequences of climate changes are clearly documented by recent disintegration of ice shelves on both sides of the Antarctic Peninsula as well as by the retreat of land-based glaciers. James Ross Island, located close to the northernmost tip of the Antarctic Peninsula, represents an excellent place to study changes in the glacier mass-balance and their sensitivity to a regional warming trend. Two different types of glaciers of the Ulu Peninsula, the Whisky Glacier and the Davies Dome have been studied. Multi-temporal remote sensing data (aerial photographs, Landsat MSS, TM and ETM+ and Aster satellite optical and thermal multispectral data) and field survey allowed detecting changes in extent (2-D) as well as calculating glacier mass-balance changes (3-D) for these two glaciers from 1977 to 2009. The Whisky Glacier is a well-delimited valley glacier located mostly below the local Equilibrium line altitude (ELA). The glacier with high-flow velocities is fed by an intensive snow accumulation caused by prevailing southwestern winds. The Whisky Glacier covers an area of 2.3 km2 and its altitude varies from 215 to 475 m a.s.l. The Davies Dome is a flat-bottom dome glacier. Significant parts of its surface are located above the ELA and limited flow velocities are characteristic for the most parts of its body. However, the Davies Dome has a single 500-700 m wide southwestern outlet flowing towards the Whisky Bay. The Davies Dome extends an area of 6.7 km2 and its altitude ranges from 0 to 514 m a.s.l. Both glaciers experienced massive extension of their ice tongues towards the Brandy Bay during the mid Holocene. Lateral moraines located in front of the both glaciers heading down to the left coast of the Brandy Bay document this event. According to the remote sensing data and field investigations both glaciers have retreated since 1977. Between 2006 and 2009 repeated mapping of the Davies Dome was carried out and the results showed that the largest retreat ranging from 10 to 20 m occurred in the NW flat part of the glacier. Digital elevation models calculated on bases of aerial stereo-photographs from 1979 and 2006 allowed us to define mass-balance changes of the studied glaciers. Ground Penetrating Radar measurements taken on both glaciers helped with mass-balance investigations, furthermore, made it possible to increase the accuracy of the 3-D models. Annual mass balance measurements on the Davies Dome indicated a mean ablation about 20 cm between 2006 and 2009. On the Whisky Glacier, a network of 20 ablation stakes was established just recently (February 2009). Therefore, another 3-year investigation is necessary to bring comparable results. Acknowledgments: This research has been undertaken within a framework of the project No. 205/09/1876 funded by the Czech Science Foundation and by the R & D project VaV SP II 1a9/23/07.

Nývlt, Daniel; Kopa?ková, Veronika; Láska, Kamil; Engel, Zbyn?k.

2010-05-01

49

Glacier Photograph Collection  

NSDL National Science Digital Library

These repeat photographs (also known as glacier pairs) are of special interest to scientists studying glaciers and climate. Glacier photographs taken from the same vantage point, but years apart in time, can reveal dramatic changes in the glacier terminus position, as a glacier either advances or retreats. Most glaciers around the world have retreated at unprecedented rates over the last century. These pairs of photographs can provide striking visual evidence of climate change.

Center, National S.

50

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

51

Evaluation of proposed early-Holocene advances of alpine glaciers in the North Cascade Range, Washington State, USA: constraints provided by palaeoenvironmental reconstructions  

Microsoft Academic Search

Many palaeoenvironmental reconstructions from across western North America indicate that the early to mid-Holocene was warmer and drier than present. The wide distribution of these records suggests that relatively mild and arid conditions were regionally ubiquitous during the early Holocene. In contrast, two recently proposed advances of alpine glaciers in the Cascade Range of Washington State, corresponding to equilibrium-line altitude

Mel A. Reasoner; P. Thompson Davis; Gerald Osborn

2001-01-01

52

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

53

Estimating Glacier Retreat through Satellite Based Observation In the Beas Basin, Himachal Pradesh, India  

NASA Astrophysics Data System (ADS)

Glaciers are now well recognized as the most reliable indicators of climate (IPCC, 2007), more particularly in the regions where there is an acute paucity in the availability of meteorological database. Subsequently it can be said that monitoring the glaciers is important to assess the overall reservoir health (Kulkarni et al., 2007). Almost negligible studies have been conducted to investigate the deglaciation status in the Indian Himalaya. A change detection analysis of the areal cover of glaciers in the Beas basin, India with the aid of remote sensing techniques in the present study concludes that the Beas basin has witnessed a loss of about 22.49 km2in the last four decades which is about 22% of the area. Another major aspect of this study is the noticeable retreat of the glaciers in the period 1972-1989. The glaciers in the Beas basin show larger area loss in this period as compared to the loss in area during the 1990s and later. Thus, it can be said that in spite of the alarming scenario of a continued recession of the glaciated terrain in the Beas basin, the pace of retreat has been observed to slow down after the 1990s. The loss has been more significant in the glaciers comprising of the area of 2-5 km2range as compared to the other categories. Glaciers in the area range more than 5 km2and less than 2 km2show less variation reflecting not much of significant loss. The total number of glaciers increased in the period of last four decades although not very significantly, indicating fragmentation. The glaciers in the range 0.5-2 km2 show a higher tendency towards fragmentation. The average elevation of the glaciers in the basin underwent an upward shift from 4565 m in the year 1972 to 4629 m in the year 2006 which is a reason for concern. The gradual upward shifting of contours over a period of almost four decades can be a consequence of a shift in Equilibrium Line Altitude (ELA) which has been constantly moving upwards showing a retreat of glaciers in the region. Moreover, it is also indicative of a negative mass balance.

Dutta, Shruti; Ramanathan, Al.; Linda, Anurag

2010-05-01

54

Recent changes on Greenland outlet glaciers  

NASA Astrophysics Data System (ADS)

Aircraft laser-altimeter surveys during the 1990s showed near-coastal parts of the Greenland ice sheet to be thinning; despite slow thickening at higher elevations, the ice sheet lost mass to the ocean. Many outlet glaciers thinned more rapidly than could be explained by increased melting during the recent warmer summers, indicating dynamic imbalance between glacier velocity and upstream snow accumulation. Results from more recent surveys, presented here, show that thinning rates have increased in most coastal regions. For almost half of the surveys, these increases might have resulted from increases in summer melting, but rapid thinning on others is indicative of dynamic changes that increased with time. In particular, thinning rates on the three fastest glaciers increased to tens of m a-1 after 2000, and other observations show an approximate doubling in their velocities. The deep beds of these glaciers appear to have a strong influence on rates of grounding-line retreat and thickness change, with periods of glacier acceleration and rapid thinning initiated by flotation and break-up of lightly grounded glacier snouts or break-up of floating ice tongues. Near-simultaneous thinning of these widely separated glaciers suggests that warming of deeper ocean waters might be a common cause. Nearby glaciers without deep beds are thinning far more slowly, suggesting that basal lubrication as a result of increased surface melting has only a marginal impact on Greenland outlet-glacier acceleration

Thomas, R.; Frederick, E.; Krabill, W.; Manizade, S.; Martin, C.

55

Columbia Glacier Terminus  

USGS Multimedia Gallery

View of Columbia Glacier's terminus as it enters the waters of Prince William Sound. Columbia Glacier is one of Alaska's many tidewater glaciers, and it has been the focus of numerous studies due to its unusually high rate of retreat. The glacier has retreated nearly 20 km (12.43 mi) since 1980. In ...

2010-07-14

56

South Cascade Glacier bibliography  

SciTech Connect

South Cascade Glacier, in Washington State, resides in a well-defined basin with mainly unglacierized divides making it ideal for most glaciological and hydrological studies. This bibliography is divided into three cateogories: (1) studies done about South Cascade Glacier specifically; (2) studies that use data from South Cascade Glacier but do not focus on or give insight to the glacier itself; and (3) instrumentation studies and non-glacier projects including snow studies done in the basin. (ACR)

Fountain, A.G.; Fulk, M.A.

1984-01-01

57

Unveiling the climate memory of an Arctic polythermal glacier: a combined radar and thermomechanical modeling approach  

NASA Astrophysics Data System (ADS)

Based on borehole temperature measurements and radio-echo sounding surveys on McCall Glacier, Alaska (USA) we were able to identify and map the Cold Transition Surface (CTS) marking the limit between cold and warm ice of a polythermal glacier. In the accumulation area, the ice column is observed to be warm throughout, while in the ablation area, the amount of cold ice at the top of the ice column increases downstream, hence lowering the CTS. High englacial temperatures in the accumulation are explained by the latent heat release due to percolating meltwater and precipitation, hence warming the ice column. With increasing atmospheric temperatures and increasing ablation rates, reduction of the perennial snowpack results in surface runoff and ice cooling. Using a transient thermomechanically-coupled higher-order glacier model, the timing of the cooling was determined from which past equilibrium-line altitudes (ELA) were constructed, which are in accord with ELAs measured since the 1950s (IGY). The paper therefore shows that (i) mapping of the CTS allows reconstructing the recent climate history of polythermal glaciers, and (ii) with a warming climate, McCall Glacier tends to cool down in a counterintuitive way.

Delcourt, C.; Van Liefferinge, B.; Pattyn, F.; Nolan, M.

2011-12-01

58

Sea-level rise from glaciers and ice caps: A lower bound  

Microsoft Academic Search

One of the most easily measured dimensions of a glacier, the accumulation area, is linked to future changes in glacier volume and consequent changes in sea level. Currently observed accumulation areas are too small, forcing glaciers to lose 27% of their volume to attain equilibrium with current climate. As a result, at least 184 ± 33 mm of sea-level rise

David B. Bahr; Mark Dyurgerov; Mark F. Meier

2009-01-01

59

Sea-level rise from glaciers and ice caps: A lower bound  

Microsoft Academic Search

One of the most easily measured dimensions of a glacier, the accumulation area, is linked to future changes in glacier volume and consequent changes in sea level. Currently observed accumulation areas are too small, forcing glaciers to lose 27% of their volume to attain equilibrium with current climate. As a result, at least 184 +\\/- 33 mm of sea-level rise

David B. Bahr; Mark Dyurgerov; Mark F. Meier

2009-01-01

60

Modeling magnetohydrodynamics and non-equilibrium SoHO/UVCS line emission of CME shocks  

NASA Astrophysics Data System (ADS)

Aims: We provide a guideline to interpret the UltraViolet Coronograph Spectrometer (UVCS) emission lines (in particular O VI and Si XII) during shock wave propagation in the outer solar corona. Methods: We use a numerical magnetohydrodynamic (MHD) model performing a set of simulations of shock waves generated in the corona and from the result we compute the plasma emission for the O VI and Si XII, including the effects of Non Equilibrium Ionization (NEI). We analyze the radiative and spectral properties of our model with the support of a detailed radiation model, including Doppler dimming and an analytical model for shocks, and, finally, we synthesize the expected O VI 1032 Å line profile. Results: We explain several spectral features of the observations like the absence of discontinuities in the O VI emission during the shock passage, the brightening of Si XII emission, and the width of the lines. We also use our model to give very simple and general predictions for the strength of the line wings due to the ions shock heating and on the line shape for Limb Coronal Mass Ejections (CMEs) or Halo CMEs. Conclusions: The emission coming from the post-shock region in the solar corona roughly agrees with the emission from a simple planar and adiabatic shock, but the effect of thermal conduction and the magnetic field may be important depending on the event parameters. Doppler dimming significantly influences the O VI emission while Si XII line brightens mainly because of the shock compression. Significant shock heating is responsible for the wide and faint component of the O VI line usually observed, which may be taken as a shock signature in the solar corona.

Pagano, P.; Raymond, J. C.; Reale, F.; Orlando, S.

2008-04-01

61

Investigation of the Ice-Water Vapor Equilibrium Along the Sublimation Line  

NASA Astrophysics Data System (ADS)

An accurate knowledge of the thermodynamic properties of water at low temperature plays an important role in atmospheric processes, chemical physics, and metrological applications. Preliminary investigations of the water vapor-ice equilibrium along the sublimation line have been carried out at Istituto Nazionale di Ricerca Metrologica (INRIM). The measurements covered the temperature range from -50 °C to 0 °C, corresponding to a saturation vapor pressure from about 4 Pa to 611 Pa. The measurements were performed using a small gold-plated cell kept in a liquid bath at a constant temperature with millikelvin stability. The sample cell was connected to a manifold where the pressure was measured using two capacitive diaphragm pressure gauges. The paper reports the water sample preparation, measuring method, and measurement corrections. Measurement results are discussed and uncertainty sources estimated. The resulting expanded relative uncertainty ( k = 2) varies from 0.038 % at 0 °C to 0.70 % at -50 °C.

Fernicola, V.; Rosso, L.; Giovannini, M.

2012-09-01

62

Shear viscosities away from the melting line: A comparison of equilibrium and nonequilibrium molecular dynamics  

SciTech Connect

Doubts about the validity of the nonequilibrium molecular dynamics (NEMD) methods of computing shear viscosity have persisted, partly because of the apparent disagreement (approx.25%) between NEMD and equilibrium Green--Kubo (GK) results for the Lennard-Jones system near its triple point. This region of the phase diagram near the melting line is the so-called ''molasses'' regime where the tail of the shear-stress autocorrelation function is quite large, deviating from ''exponential'' decay at a level of about 10%. In order to see whether the effects of the ''molasses tail'' might be obscuring a more profound difference between NEMD and GK results, we have carried out independent NEMD and GK calculations for a state in the LJ fluid far away from this troublesome molasses region, namely at a temperature twice critical and a density between the triple and critical points. We find the NEMD and GK results for the linear shear viscosity to be in good agreement.

Holian, B.L.; Evans, D.J.

1983-04-15

63

A theory of glacier surges  

NASA Astrophysics Data System (ADS)

We propose a model of glacier flow that is capable of explaining temperate glacier surges. The laws of conservation of mass and momentum are supplemented by the prescription of a sliding law that gives the basal shear stress ? as a function of the basal velocity u and the effective pressure N. The effective drainage pressure N is determined by a simple study of the subglacial hydraulic system. Following Röthlisberger, we determine N = NR for the case of drainage through a single subglacial tunnel. Alternatively, following Kamb, we find that the corresponding theory for a linked-cavity drainage system yields N = NK < NR. Furthermore, the stability of each drainage system depends on the velocity u, such that for large enough u, there is a transition from tunnel to cavity drainage. Consequently, one can write N = N(u). We then find that the sliding law ? = ?(u) is multivalued, and hence so also is the flux/depth relation Q = Q(H). An analysis of the resulting system of equations is sketched. For large enough accumulation rates, a glacier will undergo regular relaxation oscillations, resembling a surge. The surge is triggered at the point of maximum stress; from this point two hydraulic transition fronts travel up and down glacier to calculable boundary points. The speed of propagation is the order of 50 metres an hour. At these fronts, the tunnel drainage system collapses, and a high water pressure cavity drainage system is installed. This activated zone has high velocities and quickly relaxes (surges) to a quasi-equilibrium state. This relaxation is much like opening a sluice gate, in that a large wave front propagates forward. Behind this wave front, the velocity can decay oscillatorily, and thus the flow can be compressive. We conclude with some discussion of the effects of seasonal variation and of prospects for the current theory's applicability to soft-bedded glaciers.

Fowler, A. C.

1987-08-01

64

Afghanistan Glacier Diminution  

Microsoft Academic Search

Glaciers in Afghanistan represent a late summer - early fall source of melt water for late season crop irrigation in a chronically drought-torn region. Precise river discharge figures associated with glacierized drainage basins are generally unavailable because of the destruction of hydrological gauging stations built in pre-war times although historic discharge data and prior (1960s) mapped glacier regions offer some

J. F. Shroder; M. Bishop; U. Haritashya; J. Olsenholler

2008-01-01

65

Glaciers in 21st Century Himalayan Geopolitics  

NASA Astrophysics Data System (ADS)

Glaciers are ablating rapidly the world over. Nowhere are the rates of retreat and downwasting greater than in the Hindu Kush-Himalaya (HKH) region. It is estimated that over the next century, 40,000 square kilometers of present glacier area in the HKH region will become ice free. Most of this area is in major valleys and the lowest glaciated mountain passes. The existence and characteristics of glaciers have security impacts, and rapidly changing HKH glaciers have broad strategic implications: (1) Glaciers supply much of the fresh water and hydroelectric power in South and Central Asia, and so glaciers are valuable resources. (2) Shared economic interests in water, hydroelectricity, flood hazards, and habitat preservation are a force for common cause and reasoned international relations. (3) Glaciers and their high mountains generally pose a natural barrier tending to isolate people. Historically, they have hindered trade and intercultural exchanges and have protected against aggression. This has further promoted an independent spirit of the region's many ethnic groups. (4) Although glaciers are generally incompatible with human development and habitation, many of the HKH region's glaciers and their mountains have become sanctuaries and transit routes for militants. Siachen Glacier in Kashmir has for 17 years been "the world's highest battlefield," with tens of thousands of troops deployed on both sides of the India/Pakistan line of control. In 1999, that conflict threatened to trigger all-out warfare, and perhaps nuclear warfare. Other recent terrorist and military action has taken place on glaciers in Kyrgyzstan and Tajikistan. As terrorists are forced from easily controlled territories, many may tend to migrate toward the highest ground, where definitive encounters may take place in severe alpine glacial environments. This should be a major concern in Nepali security planning, where an Army offensive is attempting to reign in an increasingly robust and brutal Maoist insurgency. (5) Glacier lakes are in many cases very fragile and their natural dams routinely rupture, causing devastating floods. A rising regional terrorist threat in several countries could target these dams and precipitate calamitous and terrifying results. (6) Over the next century, retreating glaciers may open new corridors for trade and human migration across the Himalaya and pave the way for possible new economic, military and political alliances in the region. (7) Glacier retreat might open new sanctuaries for terrorists and open new corridors for possible ground-based military offensive action across the HKH ranges. The documentation of glacier characteristics that may influence their trafficability, and projections of future glacier extent and behavior are relevant to wide ranging concerns of the region's inhabitants. Satellite remote sensing and mapping of glaciers is one approach to defining and monitoring the problems and opportunities presented by HKH glaciers. Global Land Ice Measurements from Space (GLIMS) is a joint USGS/NASA Pathfinder project that has formed a global consortium of glaciologists in several regional centers that are mapping and monitoring the HKH glaciers using repeat-pass ASTER and Landsat ETM+ data. We are currently building a comprehensive satellite multispectral image and GIS database that is providing detailed information on the state and rates of change of each glacier in the HKH region and other areas of the world. Merging these results with DEMs allows a predictive capability that could be useful in policy development and security planning.

Kargel, J. S.; Wessels, R.; Kieffer, H. H.

2002-05-01

66

Statistical Equilibrium Calculation of OH: Interpretation of the 1612 MHz Absorption Line in HCL2  

NASA Astrophysics Data System (ADS)

We have recently observed four hyperfine components of the ground state ?-doublet-type transition of OH toward several positions in the Taurus Molecular Cloud with the Effelsberg 100 m radio telescope. We have found that the 1612 MHz line appears in absorption toward the eastern position of HCL2, where the [CI](3P1-3P0) emission shows a local peak. Furthermore, the spectrum observed toward the other positions in HCL2 shows two velocity components. The higher velocity component is seen in absorption, whereas the lower velocity component is seen in emission. In order to understand the above results, we have made statistical equilibrium calculations of the OH molecule. It is found that the 1612 MHz line appears in absorption only when the gas kinetic temperature is higher than 40 K. Thus, intensities of the four hyperfine components of OH can be a good thermometer. The combination of emission and absorption observed in HCL2 would reflect a cloud structure like cold dense cores surrounded by a warm less-dense envelope.

Inokuma, H.; Sakai, N.; Maezawa, H.; Menten, K.; Yamamoto, S.

2013-10-01

67

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.

68

Worthington Glacier Project  

NSDL National Science Digital Library

Funded by the National Science Foundation (NSF), the Worthington Glacier Project is a collaboration between researchers at the University of Wyoming and the University of Colorado. The objective of this project is to understand glacier flow dynamics "by comparing detailed measurements of glacier motion with numerical models for glacier flow." Summaries and diagrams are provided of the discussed topics: Borehole Video Observations, Radio-Echo Sounding, Crevassing, Surface Flow Field, Englacial Flow Field, 3-D Flow Field, and In-Situ Stress. Images of the Worthington Glacier fieldwork, future research, and publications are also available at the site.

69

Timing and paleoclimatic significance of Holocene glacier fluctuations in the Cordillera Vilcabamba of southern Peru  

NASA Astrophysics Data System (ADS)

Past fluctuations in climatically sensitive tropical glaciers provide important insight into regional paleoclimatic trends and forcings, but well-dated chronologies are scarce, particularly during the Holocene. We have established precise cosmogenic 10Be surface exposure ages of moraine sequences in the Cordillera Vilcabamba (13°20’S latitude), located in the outer tropics of southern Peru. Results indicate the dominance of two major glacial culminations and associated climatic shifts in the Vilcabamba, including an early Holocene glacial interval and a somewhat less extensive glaciation late in the ‘Little Ice Age’ (LIA) period. Lichenometric measurements on the youngest moraines support the 10Be ages, but uncertainties in the lichen ages arise from the lack of a local lichen growth curve. The Peruvian glacier chronologies differ from a recently-developed New Zealand record but are broadly correlative with well-dated glacial records in Europe, suggesting climate linkages between the tropics and the North Atlantic region. For the latest Holocene, our leading hypothesis is that climate forcings involving southward migration of the Atlantic Intertropical Convergence Zone can explain concurrent glaciations in tropical South America and northern high latitudes, but the influence of other climate drivers such as the El Niño/Southern Oscillation may have also played a role. Estimated differences between equilibrium-line altitudes (ELAs) on modern glaciers and those inferred for expanded latest Holocene glaciers reveal an ELA rise of 165-200 m since the LIA, suggesting that temperatures 1.1-1.3°C cooler than present could have sustained glaciers at their LIA maximum positions if temperature was the only control, and thus providing an upper bound on temperature depression during the LIA. However, further work is required to constrain the likely role of precipitation changes. These new Peruvian glacier chronologies and ELA reconstructions complement ice core and lacustrine paleoclimate records in the vicinity, thereby increasing spatial and temporal coverage for identifying patterns of climate change in the tropical Andes during the Holocene.

Licciardi, J. M.; Taggart, J. R.; Schaefer, J. M.; Lund, D. C.

2009-12-01

70

Feedbacks and mechanisms affecting the global sensitivity of glaciers to climate change  

NASA Astrophysics Data System (ADS)

Mass loss by glaciers has been an important contributor to sea level rise in the past and is projected to contribute a substantial fraction of total sea level rise during the 21st century. Here, we use a model of the world's glaciers in order to quantify equilibrium sensitivities of global glacier mass to climate change, and to investigate the role of changes in glacier hypsometry for long term mass changes. We find that 21st century glacier mass loss to a~large degree is governed by the glaciers responding to 20th century climate change. This limits the influence of 21st century climate change on glacier mass loss, and explains why there are relatively small differences in glacier mass loss under greatly different scenarios of climate change. Because of the geographic distribution of glaciers, both temperature and precipitation anomalies experienced by glaciers are vastly stronger than on global average. The projected increase in precipitation partly compensates for the mass loss caused by warming, but this compensation is negligible at higher temperature anomalies since an increasing fraction of precipitation at the glacier sites it liquid. Loss of low-lying glacier area, and more importantly, eventual complete disappearance of glaciers, strongly limit the projected sea level contribution from glaciers in coming centuries. The adjustment of glacier hypsometry to changes in the forcing reduces the sensitivity of global glacier mass to changes in global mean temperature by a factor of two to three. This result is a second reason for the relatively weak dependence of glacier mass loss on future climate scenario, and helps explain why glacier mass loss in the first half of the 20th century was of the same order of magnitude as in the second half of the 20th century, even though the rate of warming was considerably smaller.

Marzeion, B.; Jarosch, A. H.; Gregory, J. M.

2013-06-01

71

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

72

Afghanistan Glacier Diminution  

NASA Astrophysics Data System (ADS)

Glaciers in Afghanistan represent a late summer - early fall source of melt water for late season crop irrigation in a chronically drought-torn region. Precise river discharge figures associated with glacierized drainage basins are generally unavailable because of the destruction of hydrological gauging stations built in pre-war times although historic discharge data and prior (1960s) mapped glacier regions offer some analytical possibilities. The best satellite data sets for glacier-change detection are declassified Cornona and Keyhole satellite data sets, standard Landsat sources, and new ASTER images assessed in our GLIMS (Global Land Ice Measurements from Space) Regional Center for Southwest Asia (Afghanistan and Pakistan). The new hyperspectral remote sensing survey of Afghanistan completed by the US Geological Survey and the Afghanistan Ministry of Mines offers potential for future detailed assessments. Long-term climate change in southwest Asia has decreased precipitation for millennia so that glaciers, rivers and lakes have all declined from prehistoric and historic highs. As many glaciers declined in ice volume, they increased in debris cover until they were entirely debris-covered or became rock glaciers, and the ice was protected thereby from direct solar radiation, to presumably reduce ablation rates. We have made a preliminary assessment of glacier location and extent for the country, with selected, more-detailed, higher-resolution studies underway. In the Great Pamir of the Wakhan Corridor where the largest glaciers occur, we assessed fluctuations of a randomly selected 30 glaciers from 1976 to 2003. Results indicate that 28 glacier-terminus positions have retreated, and the largest average retreat rate was 36 m/yr. High albedo, non-vegetated glacier forefields formed prior to 1976, and geomorphological evidence shows apparent glacier-surface downwasting after 1976. Climatic conditions and glacier retreat have resulted in disconnection of tributary glaciers to their main trunk, the formation of high-altitude lakes, and an increased frequency and size of proglacial lakes that are, however, genrally unavailable for irrigation sources. Similar conditions of glacier diminution have occurred in almost all other high altitude parts of the country. Generally decreased precipitation in all seasons, coupled with decreased glacier storage of potential melt-water, augers continued severe problems for beleaguered Afghanistan agriculture, along with concomitant social problems as a result.

Shroder, J. F.; Bishop, M.; Haritashya, U.; Olsenholler, J.

2008-12-01

73

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

74

Thoughts on some outstanding issues in the physics of equilibrium wetting and conceptual understanding of contact lines  

NASA Astrophysics Data System (ADS)

Equilibrium wetting is a fundamental phenomenon, relevant to many scientific areas. Since the pioneering work on equilibrium wetting of Thomas Young (1805) [1], researchers strived to advance our understanding of this fundamental problem. Despite its apparent simplicity, equilibrium wetting phenomenon still holds many unanswered questions and represents a challenge to modern physicists and engineers. The relationship between quantities amenable to measurements, like macroscopic wetting contact angle, and other surface ener- gies and physical properties remains to be fully elucidated. Wetting is a physical problem which spans over two length scales, inner region ("microscopic") length scale and outer region ("macroscopic"). The three-phase contact line, where the macroscopic region meets the micro- scopic one, and underlying surface forces, represents a challenge to fully understand and model. In this paper, a brief review of the basics of wetting and existing concepts is first presented. Then two important questions are discussed in the light of the latest experimental findings: first the relevance of the continuum concept when describing interfaces near the three-phase contact line, and second the effect of adsorption on interfacial energies and its use to explain some interesting observations like the dependence of equilibrium contact angle on pressure and size of droplets. These recent observations raise some fundamental questions about how the three-phase contact line is conceptualised.

Sefiane, K.

2011-08-01

75

The thermophysics of glaciers  

SciTech Connect

This volume presents the results of experimental and theoretical work on the thermodynamics of ice sheets and glaciers. The author has carried out extensive field work in both the Soviet Union and Antarctica over the last 25 years and has contributed to the understanding of the thermophysics of glaciers. The topics covered in this volume embrace heat flow measurement and temperature distributions in glaciers, the thermal drilling of glaciers, the melting and freezing of ice sheets, and other thermophysical problems. Also included are topics of relevance to glacial engineering.

Zotikov, I.A.

1986-01-01

76

Influence of CO2 line profiles on radiative and radiative-convective equilibrium states of the Venus lower atmosphere  

NASA Astrophysics Data System (ADS)

Influence of CO2 line profiles on vertical temperature distributions in the radiative and radiative-convective equilibria is examined in the Venus atmosphere. The CO2 opacity obtained by the Voigt (Lorentz) profile without the line cutoff is shown to be excessive since this opacity gives surface temperatures of about 860-1020 K in the radiative-convective equilibrium. On the other hand, the opacity obtained by the extremely sub-Lorentzian profiles of Pollack et al. (1993) and Tonkov et al. (1996) are underestimated; the surface temperature obtained with this opacity remains 600 K even in the radiative equilibrium. In this case, convection does not take place below the cloud layer because of the cloud opacity. It is also shown that Fukabori et al.'s (1986) and Meadows and Crisp's (1996) profiles, both of which have intermediate absorption coefficients, give temperature distributions close to the observed one in the radiative-convective equilibrium. In these cases, the convection layer extends from the surface to 30-50 km altitudes. Then, the temperature distribution below the cloud layer is determined by a dry adiabatic lapse rate and the temperature near the cloud bottom. The surface temperature in the radiative-convective equilibrium is strongly affected by the temperature near the cloud bottom in this situation. The detailed structure of the H2SO4 cloud must be taken into account to construct a realistic radiative transfer model.

Takagi, M.; Suzuki, K.; Sagawa, H.; Baron, P.; Mendrok, J.; Kasai, Y.; Matsuda, Y.

2010-06-01

77

Patterns of Glacier Change in the American West  

NASA Astrophysics Data System (ADS)

We examine a century of glacier area change in the American West, exclusive of Alaska, using historic photography, historic maps, and recent aerial photos. Of the approximately 3200 glaciers and permanent snow masses, we track about 400 glaciers across a region that spans from Washington to California and Colorado to Montana. All glaciers have retreated since 1900 with the greatest change in Montana (Lewis Range) and the Sierra Nevada of California, and the least change in Washington including the North Cascades and the Olympic Peninsula. The pattern since 1970s is more complex, with the majority of glaciers having retreated since the 1970s, some vastly more than others. The glaciers that exhibit relatively little retreat are largely restricted to the high stratovolcanoes >3500m in elevation. In these cases we infer elevated snow accumulation at higher elevations compensates for increased ablation (melt) at lower elevations. In addition, many of the most stable glaciers are debris covered in their lower elevations, due to rock fall from the relatively weak volcanic edifice. Small glaciers, <1 km2, show great variability in their behavior, with a few glaciers at equilibrium or slightly advancing, to the majority retreating, with some losing 67% of their area. These differences are more difficult to explain. We infer that local climatic/topographic influences play a dominant role in the magnitude of change while regional climate patterns control the sign of the change. Temporal patterns of glacier change are very similar across broad regions while the magnitude of that change is particular to individual glaciers.

Fountain, A. G.; Basagic, H. J.; Hoffman, M. J.

2008-12-01

78

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

79

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

80

Photographer Overlooking Columbia Glacier  

USGS Multimedia Gallery

Photographer Tad Pfeffer capturing images of Columbia Glacier in Prince William Sound, Alaska. He is looking down-glacier towards the ice front, which faces open water in the fjord. This open water is extremely rare, and has not happened again since 2005. The fjord is typically covered with iceberg ...

2010-07-14

81

The Morteratsch Glacier  

Microsoft Academic Search

During my stay in the Engadine this summer I took the opportunity of making a few observations relative to the movement of the Morteratsch Glacier, which may be of interest to some of your readers. These observations were taken inside the artificial cave of the above glacier in preference to the surface, as I thereby obtained a more direct measurement

Hugo Leupold

1881-01-01

82

Mini Glacier Meltdown  

NSDL National Science Digital Library

This activity (located on page 3 of the PDF) is a full inquiry investigation about the different causes of glacial melt. Groups of learners will design their own experiment using frozen "glaciers", bricks and different energy sources (fans, and lights) to test how different conditions affect the rate of melting. The results might be surprising. Relates to linked video, DragonflyTV GPS: Glaciers.

Twin Cities Public Television, Inc.

2007-01-01

83

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

84

20 years of glacier mass balance monitoring in the french alps from remote sensing imagery  

NASA Astrophysics Data System (ADS)

This study presents a synthesis of recent progress and challenges in Remote Sensing of glaciers variations at a local scale, using optical and SAR data. Times series on glaciers changes are available from satellite since 20 years and the accuracy of new methodologies allows to spatialise glaciers parameters monitoring at a global scale for a direct climate application. It can also offer a contribution to the worldwide glacier monitoring in the 21th century, because only 65 samples are investigated over the world. We focused this work on the mass balance parameter, because the annual mass balance is very sensitive to climatic fluctuations and the correlation between these parameters is widely recognized. The aim of this work is to clarify the relationship between the computed pattern mass balance and the fields' measurements on 6 outlet glaciers of the French Alps ; located between latitude of 45^o 87'N and 44^o 56'N along longitude of 06^o 30', with ice field elevation ranging from 4000 to 1400 m and flowing out in all directions. These glaciers have been monitored since decades for some of them. Optical satellite measurements are easy to interpret for snow-covered and iced areas, but no data are available under dark and cloudy conditions. The main advantages of radar-based methods are the following : one hand the SAR method is less sensitive to atmospheric effects than the optical method, on the other hand measurements can be recorded at night, when snow is under frozen conditions in summer period. Combining high resolution SAR and optical data, we produced a yearly map of the snow-line altitude between accumulation and ablation areas, correlated in the French Alps to the Equilibrium Line Altitude (ELA). Using two yearly consecutive images taken at the end of the hydrological year (fall season), the ELA variations were transformed into mass balance fluctuations with a mean value of the altitudinal gradient of the annual mass balance. The results were compared successfully in a identical order of magnitude with the specific mass balance observations, ground-based methods using stakes over each glacier surface.

Dedieu, J. P.; Rabatel, A.; Vincent, C.

2003-04-01

85

Modeling Glacier Erosion Through Time  

NSDL National Science Digital Library

Prior to this lab, students will have read and learned about valley glacier processes, glacier mass balance, warm-based and cold-based glaciers, and can identify various glacier landforms formed by erosion. They will also have had an introductory lecture on ice physics, but that is not necessary to complete this activity.

Connor, Cathy L.

86

Numerical modeling of the temperature and flow field of McCall Glacier, Alaska, constrained by borehole temperature data  

NASA Astrophysics Data System (ADS)

During IPY, an extensive field programme was set up on McCall Glacier, Alaska including borehole drilling to the bed at three locations. These holes were instrumented with a continuously-logging thermistor strings. Despite the low mean annual air temperatures (-10°C), temperate ice throughout the borehole in the accumulation area was observed, explained by the latent heat release due to refreezing of surface melt water in the firn. A 200m deep hole drilled in a cirque further down-glacier (2123m) shows that it is actually cooling substantially: the site has switched from accumulation to ablation area, ablating the firn away completely. This allows cold air temperatures to penetrate deeper in the ice, gradually cooling the upper part of the glacier. A third hole in the ablation area (1717m) is the coldest of all, though temperate at the bed because of large frictional heating rates due to basal sliding. Using a 3D higher-order thermodynamical model we simulated the time-dependent increase in equilibrium line altitude and associated reduction of the accumulation area. The temperature profiles were used as constraints to control the change from warm to cold conditions in the upper part of the glacier. Further constraints stem from accumulation/ablation measurements as well as repeat surface velocity measurements along the central flowline of the glacier. Results of these experiments show that the cooling trend in the lower cirque is going on for at least 40 years, which is corroborated by previous mass balance reconstructions of the glacier.

Delcourt, Charlotte; Pattyn, Frank; Nolan, Matt

2010-05-01

87

Rapid ASTER imaging facilitates timely assessment of glacier hazards and disasters  

Microsoft Academic Search

Glacier- and permafrost-related hazards increasingly threaten human lives, settlements, and infrastructure in high-mountain regions. Present atmospheric warming particularly affects terrestrial systems where surface and sub-surface ice are involved. Changes in glacier and permafrost equilibrium are shifting beyond historical knowledge. Human settlement and activities are extending toward danger zones in the cryospheric system. A number of recent glacier hazards and disasters

Andy Kääb; Rick Wessels; Wilfried Haeberli; Christian Huggel; Jeffrey S. Kargel; Siri Jodha Singh Khalsa

2003-01-01

88

Uncovering glacier dynamics beneath a debris mantle  

NASA Astrophysics Data System (ADS)

Debris-covered glaciers (DCGs) have an extensive sediment mantle whose low albedo influences their surface energy balance to cause a buffering effect that could enhance or reduce ablation rates depending on the sediment thickness. The last effect suggests that some DCGs may be less sensitive to climate change and survive for longer than debris-free (or 'clean') glaciers under sustained climatic warming. However, the origin of DCGs is debated and the precise impact of the debris mantle on their flow dynamics and surface geometry has not been quantified. Here we investigate these issues with a numerical model that encapsulates ice-flow physics and surface debris evolution and transport along a glacier flow-line, as well as couples these with glacier mass balance. We model the impact of surface debris on ablation rates by a mathematical function based on published empirical data (including Ostrem's curve). A key interest is potential positive feedback of ablation on debris thickening and lowering of surface albedo. Model simulations show that when DCGs evolve to attain steady-state profiles, they reach lower elevations than clean glaciers do for the same initial and climatic conditions. Their mass-balance profile at steady state displays an inversion near the snout (where the debris cover is thickest) that is not observed in the clean-glacier simulations. In these cases, where the mantle causes complete buffering to inhibit ablation, the DCG does not reach a steady-state profile, and the sediment thickness evolves to a steady value that depends sensitively on the glacier surface velocities. Variation in the assumed englacial debris concentration in our simulations also determines glacier behaviour. With low englacial debris concentration, the DCG retreats initially while its mass-balance gradient steepens, but the glacier re-advances if it subsequently builds up a thick enough debris cover to cause complete buffering. We identify possible ways and challenges of testing this model with field observations of DCGs, given the inherent difficulty that such glaciers may not be in steady state.

Lefeuvre, P.-M.; Ng, F. S. L.

2012-04-01

89

Saddle-point equilibrium lines between fcc and bcc phases in Al and Ca from first principles  

NASA Astrophysics Data System (ADS)

Phase equilibrium lines (denoted ph-eq lines) of face-centered-cubic (fcc) and body-centered-cubic (bcc) phases, as well as saddle-point equilibrium lines (denoted sp-eq lines) in Al and Ca are studied by first-principles total-energy calculations. For a non-vibrating crystal of Al we determine the transition pressure pt = 2.62 Mbar from fcc to bcc phase. The sp-eq line lies between the two ph-eq lines, merges with the bcc-eq line at V = 61 au3/atom (p = 1.64 Mbar) and with the fcc-eq line at V = 42.4 au3/atom (p = 5.50 Mbar), gives the Gibbs free energy barrier ?G = 0.64 mRy/atom at pt. The bcc phase is unstable below 1.64 Mbar, while the fcc phase is unstable above 5.50 Mbar. In a non-vibrating crystal of Ca two sp-eq lines (denoted sp1-eq line and sp2-eq line, respectively) are found corresponding to two phase transitions: one is from fcc to bcc at pt1 = 89.6 kbar, the other is from bcc to fcc at pt2 = 787 kbar. The sp1-eq line merges with the bcc-eq line at V = 231 au3/atom (p = 50 kbar) and with the fcc-eq line at V = 183 au3/atom (p = 174 kbar), gives a barrier of ?G1 = 0.62 mRy/atom at pt1. The sp2-eq line merges with the bcc-eq line at V = 90 au3/atom (p = 981 kbar) and with the fcc-eq line at V = 110 au3/atom (p = 624 kbar), gives a barrier of ?G2 = 1.1 mRy/atom at pt2. The bcc phase is stable in the range from 50 kbar to 981 kbar but unstable outside this range, while the fcc phase is unstable in the range from 174 to 624 kbar but stable outside this range. This work confirms all the features of the sp-eq line described in our recent work [S.L. Qiu, P.M. Marcus, J. Phys.: Condens. Matter 24, 225501 (2012)] and finds two additional features: (1) there are two sp-eq lines corresponding to the two phase transitions between fcc and bcc phases in Ca; (2) fcc phase of Ca is unstable between the two merge points on the fcc-eq line but stable beyond them, while bcc phase of Ca is stable between the two merge points on the bcc-eq line but unstable beyond them.

Qiu, S. L.; Marcus, P. M.

2013-10-01

90

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

91

Metastable extensions of phase equilibrium lines and singular points of simple substance  

SciTech Connect

The thermodynamic properties of crystal, liquid, and gas in the stable and metastable states have been determined by molecular dynamics simulation of a system of 2048 Lennard-Jones particles. The spinodals of a superheated crystal, a superheated liquid, and a supersaturated vapor have been approximated; the spinodal for a supercooled liquid turns out to be nonexistent. The liquid-vapor, liquid-crystal, and crystal-vapor equilibrium curves and their extensions beyond the triple point have been calculated. It has been shown that, as distinct from the metastable extension of the saturation curve, which terminates at the zero isotherm, the metastable melting and sublimation curves terminate at, respectively, the stretched liquid and superheated crystal spinodals. The properties of the critical end points of metastable equilibrium of extended phases are considered.

Baidakov, V. G., E-mail: bai@itp.uran.ru; Protsenko, S. P. [Russian Academy of Sciences, Institute of Thermal Physics, Ural Division (Russian Federation)

2006-12-15

92

Modelling Greenland Outlet Glaciers.  

National Technical Information Service (NTIS)

The objective of this project was to develop simple yet realistic models of Greenland outlet glaciers to better understand ongoing changes and to identify possible causes for these changes. Several approaches can be taken to evaluate the interaction betwe...

C. vanderVeen

2001-01-01

93

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

94

Moving Model Glacier  

NSDL National Science Digital Library

In this goopy activity, learners will model glacial movement with âgak,â a white glue and liquid starch mixture. Each fist-sized gob of gak represents a yearâs worth of snow, accumulating to form a âglacierâ on a model landscape. Learners will record the gakâs rate of travel as well as make observations of other glacier behaviors. Relates to the linked video, DragonflyTV GPS: Glaciers.

Twin Cities Public Television, Inc.

2007-01-01

95

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

96

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

97

A decade of energy and mass balance investigations on the glacier Kongsvegen, Svalbard  

NASA Astrophysics Data System (ADS)

Kongsvegen is an Arctic glacier located in northwest Spitzbergen. We use meteorological observations made near the average equilibrium line of Kongsvegen during the decade 2001 to 2010 to drive a glacier energy and mass balance model. Average daily and seasonal cycles are analyzed over the course of a full decade, as well as the interannual variations of the meteorological parameters and of the mass and energy balance components. The calculated average of net radiation is close to zero and the sensible heat flux is the most important and continuous source of energy at the surface. The latent heat flux is a weak source of energy as well. The resultant flux constellation yields a surplus of energy accumulating throughout the decade (9.5 W m-2) and fosters a negative specific surface mass balance throughout the investigated decade (-1.8 m w. eq.). The most significant mass loss occurred during the middle of the decade (2004 until 2006), with positive surface mass balances observed afterward when significant amounts of superimposed ice were formed. This development is well correlated to the total surface mass balance of the glacier. Application of monthly temperature and precipitation perturbations corroborates earlier studies indicating a high sensitivity of the mass balance to energy fluxes depending on temperature conditions during summer.

Karner, F.; Obleitner, F.; Krismer, T.; Kohler, J.; Greuell, W.

2013-05-01

98

Recent Acceleration of Thwaites Glacier.  

National Technical Information Service (NTIS)

The first velocity measurements for Thwaites Glacier were made by R. J. Allen in 1977. He compared features of Thwaites Glacier and Iceberg Tongue on aerial photography from 1947 and 1967 with 1972 Landsat images, and measured average annual displacements...

J. G. Ferrigno

1993-01-01

99

Glacier fluctuations, global temperature and sea-level change  

NASA Astrophysics Data System (ADS)

The current world-wide glacier retreat is a clear sign of global warming. In addition, glaciers contribute to sea-level rise as a consequence of the current retreat. In this thesis we use records of past glacier fluctuations to reconstruct past climate variations and the glacier contribution to sea-level change. Firstly, a coherent data set of world-wide glacier fluctuations over the past centuries is compiled. Most available information of glacier fluctuations concerns glacier length fluctuations. There is currently a large number of sources available, varying from field observations, satellite images and aerial photography to reconstructions from historical documents and geological evidence. The data set, resulting from the compilation of available data, contains 374 length records of glaciers from all continents and is described in Chapter 2. In Chapter 3, a climatic interpretation of the length fluctuations of Glaciar Frías is presented. This glacier in North Patagonia has the longest detailed length record in southern South America. The glacier behaviour is modelled with a simplified mass balance model that is coupled with a flow line model. A warming of North Patagonian climate with 1.16 °Csince the mid 17th century, or a decrease in precipitation of 34%, would best explain the observed retreat since 1639. Driving the glacier model with existing climate reconstructions shows that the uncertainties in these reconstructions are rather large. In addition, it appears that the length fluctuations are mainly driven by variations in temperature rather than variations in precipitation. The development of such detailed models is not feasible for all glaciers in the length fluctuations data set. In the next chapter a simplified approach is used to reconstruct global and hemispheric temperature for the period 1600-2000 from world-wide glacier length fluctuations. The reconstructions show that global temperature was more or less constant from 1600 until the middle of the 19th century. Since then, temperature rises until 2000, with a period of slight cooling from 1940 to 1970. Glacier-based reconstructions are completely independent from both other proxy-based reconstructions and from the instrumental record. Still, the reconstructed temperature agrees well with the instrumental record of the 20th century and it is in broad agreement with existing temperature reconstructions. However, according to the glacier length reconstruction the global warming starts in the middle of the 19th century instead of in the beginning of the 20th century, as indicated by several other reconstructions. The data set of glacier length changes can also be used to estimate the glacier contribution to sea-level change. In Chapter 5, a global glacier length signal is calculated from the available glacier length records. The global length signal is scaled to global volume change, which is calibrated on mass balance and geodetic observations of the period 1950-2005. The reconstructed glacier contribution is 8.4 ± 2.1 cm for the period 1800-2005 and 9.1 ± 2.3 cm for the period 1850-2005. These estimates are significantly higher than earlier estimates. Glacier retreat accounts for half the observed sea-level rise since the middle of the 19th century.

Leclercq, P. W.

2012-02-01

100

The GLIMS Glacier Database  

NASA Astrophysics Data System (ADS)

The Global Land Ice Measurements from Space (GLIMS) project has built a geospatial and temporal database of glacier data, composed of glacier outlines and various scalar attributes. These data are being 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. We have implemented two web-based interfaces to the database; one enables exploration of the data via interactive maps (web map server), while the other allows searches based on text-field constraints. The web map server is an Open Geospatial Consortium (OGC) compliant Web Map Server (WMS) and Web Feature Server (WFS). This means that other web sites can display glacier layers from our site over the Internet, or retrieve glacier features in vector format. All components of the system are implemented using Open Source software: Linux, PostgreSQL, PostGIS (geospatial extensions to the database), MapServer (WMS and WFS), and several supporting components such as Proj.4 (a geographic projection library) and PHP. These tools are robust and provide a flexible and powerful framework for web mapping applications. As a service to the GLIMS community, the database contains metadata on all ASTER imagery acquired over glacierized terrain. Reduced-resolution of the images (browse imagery) can be viewed either as a layer in the MapServer application, or overlaid on the virtual globe within Google Earth. The interactive map application allows the user to constrain by time what data appear on the map. For example, ASTER or glacier outlines from 2002 only, or from Autumn in any year, can be displayed. The system allows users to download their selected glacier data in a choice of formats. The results of a query based on spatial selection (using a mouse) or text-field constraints can be downloaded in any of these formats: ESRI shapefiles, KML (Google Earth), MapInfo, GML (Geography Markup Language) and GMT (Generic Mapping Tools). This "clip-and-ship" function allows users to download only the data they are interested in. Our flexible web interfaces to the database, which includes various support layers (e.g. a layer to help collaborators identify satellite imagery over their region of expertise) will facilitate enhanced analysis to be undertaken on glacier systems, their distribution, and their impacts on other Earth systems.

Raup, B. H.; Khalsa, S. S.; Armstrong, R.

2007-12-01

101

Jakobshavns Glacier drainage basin - A balance assessment  

NASA Astrophysics Data System (ADS)

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.

1984-03-01

102

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

103

Fundamentals of Glacier Dynamics  

NASA Astrophysics Data System (ADS)

Glaciers form when snow melts and refreezes, or is compressed, to form ice. Spreading under their own weight, they flow seaward, channeled along preferred routes by the shape or composition of the underlying bedrock. Though we don't know why, some ice streams flow rapidly within slower-moving ice in Greenland and Antarctica. Glaciers exist on all continents except Australia, and at high enough elevations, they can be found even at the equator. Many are melting as global temperatures rise, but about 99% of glacier ice is in Greenland and Antarctica, where it is partly protected from global warming by low temperatures. Nevertheless, the coastal ice sheet in Greenland has thinned recently for unknown reasons, and we still don't know whether the far larger Antarctic ice sheet is growing or shrinking.

Thomas, Robert H.

104

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

105

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

106

The health of glaciers: Recent changes in glacier regime  

USGS Publications Warehouse

Glacier wastage has been pervasive during the last century; small glaciers and those in marginal environments are disappearing, large mid-latitude glaciers are shrinking slightly, and arctic glaciers are warming. Net mass balances during the last 40 years are predominately negative and both winter and summer balances (accumulation and ablation) and mass turnover are increasing, especially after 1988. Two principal components of winter balance time-series explain about 50% of the variability in the data. Glacier winter balances in north and central Europe correlate with the Arctic Oscillation, and glaciers in western North America correlate with the Southern Oscillation and Northern Hemisphere air temperature. The degree of synchronization for distant glaciers relates to changes in time of atmospheric circulation patterns as well as differing dynamic responses.

Meier, M. F.; Dyurgerov, M. B.; McCabe, G. J.

2003-01-01

107

Equilibrium of the human body and the gravity line: the basics  

Microsoft Academic Search

Introduction  Bipedalism is a distinguishing feature of the human race and is characterised by a narrow base of support and an ergonomically\\u000a optimal position thanks to the appearance of lumbar and cervical curves.\\u000a \\u000a \\u000a \\u000a \\u000a Materials  The pelvis, adapted to bipedalism, may be considered as the pelvic vertebra connecting the spine to the lower limbs. Laterally,\\u000a the body’s line of gravity is situated very

J. C. Le Huec; R. Saddiki; J. Franke; J. Rigal; S. Aunoble

108

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

109

Monitoring of Gangotri glacier using remote sensing and ground observations  

NASA Astrophysics Data System (ADS)

In this study, Gangotri glacier was monitored using Indian Remote Sensing (IRS) LISS-III sensor data in combination with field collected snow-meteorological data for a period of seven years (2001-2008). An overall decreasing trend in the areal extent of seasonal snow cover area (SCA) was observed. An upward shifting trend of wet snow line was observed in the beginning of melt period, i.e., in May and dominant wet snow conditions were observed between May and October. Snow meteorological parameters collected in the Gangotri sub-basin suggest reduction in fresh snowfall amount during winter, increase in rainfall amount during summer, decrease in snowfall days, increase in rainfall days and rising trend of average temperature. The prevailing wet snow condition on glacier has caused scouring of slopes which led the excessive soil/debris deposition on the glacier surface. This was observed as one of the major factor for activating fast melting and affecting the glacier health significantly. Apart from climatic conditions, terrain factors were observed for changing the glacio-morphology. The significant changes on the glacier surface were observed in the regions of abrupt slope change. The above factors affecting the Gangotri glacier health were also validated using high resolution satellite imageries and field visit. A deglaciation of 6% in overall area of Gangotri glacier was observed between the years 1962 and 2006.

Negi, H. S.; Thakur, N. K.; Ganju, A.; Snehmani

2012-08-01

110

Glaciers and Glaciation  

NSDL National Science Digital Library

This site contains lecture notes to accompany one chapter/lecture of a physical geology course using the text, The Dynamic Earth: An Introduction to Physical Geology, 4th Edition, by Brian J. Skinner and Stephen C. Porter. Subtopics include glaciers, glacial deposits, glacial features, glaciation, and glacial ages.

Nelson, Stephen

111

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.

112

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

113

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

114

Latest Pleistocene and Holocene alpine glacier fluctuations in Scandinavia  

NASA Astrophysics Data System (ADS)

During the early Holocene abrupt, decadal to centennial-scale climate variations caused significant glacier variations in Norway. Increased freshwater inflow to the North Atlantic and Arctic Oceans has been suggested as one of the most likely mechanisms to explain the abrupt and significant Lateglacial and early Holocene climatic events in NW Europe. The largest early Holocene glacier readvances occurred ~11,200, 10,500, 10,100, 9700, 9200 and 8400-8000 cal. yr BP. The studied Norwegian glaciers apparently melted away at least once during the early/mid-Holocene. The period with the most contracted glaciers in Scandinavia was between 6600 and 6000 cal. yr BP. Subsequent to ~6000 cal. yr BP the glaciers started to advance and the most extensive glaciers existed at about ~5600, 4400, 3300, 2300, 1600 cal. yr BP, and during the ‘Little Ice Age'. Times with overall less glacier activity were apparently around 5000, 4000, 3000, 2000, and 1200 cal. yr BP. It has been proposed that several glacier advances occurred in Scandinavia (including northern Sweden) at ~8500-7900, 7400-7200, 6300-6100, 5900-5800, 5600-5300, 5100-4800, 4600-4200, 3400-3200, 3000-2800, 2700-2000, 1900-1600, 1200-1000, and 700-200 cal. yr BP. Glaciers in northern Sweden probably reached their greatest ‘Little Ice Age' extent between the 17th and the beginning of the 18th centuries. Evidence for early Holocene glacier advances in northern Scandinavia, however, has been questioned by more recent, multi-disciplinary studies. The early to mid-Holocene glacier episodes in northern Sweden may therefore be questioned. Most Norwegian glaciers attained their maximum ‘Little Ice Age' extent during the mid-18th century. Cumulative glacier length variations in southern Norway, based on marginal moraines dated by lichenometry and historic evidence, show an overall retreat from the mid-18th century until the 1930s-40s. Subsequently, most Norwegian glaciers retreated significantly. Maritime outlet glaciers with short frontal time lags (<10-15 years) started to advance in the mid-1950s, whereas long outlet glaciers with longer frontal time lags (>15-20 years) continued their retreat to the 1970s and 1980s. However, maritime glaciers started to advance as a response to higher winter accumulation during the first part of the 1990s. After 2000 several of the observed glaciers have retreated remarkably fast (annual frontal retreat >100 m) mainly due to high summer temperatures. The general glacier retreat during the early Holocene and the Neoglacial advances after 6000 cal. yr BP are in line with orbital forcing, due to the decrease of Northern Hemisphere summer solar insolation and the increase in winter insolation. In addition, regional weather modes, such as the North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO), play a significant role with respect to decadal and multi-decadal climate variability.

Nesje, A.

2009-04-01

115

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

116

Columbia Glacier in 1984: disintegration underway  

Microsoft Academic Search

Columbia Glacier is a large, iceberg-calving glacier near Valdez, Alaska. The terminus of this glacier was relatively stable from the time of the first scientific studies in 1899 until 1978. During this period the glacier terminated partly on Heather Island and partly on a submerged moraine shoal. In December, 1978, the glacier terminus retreated from Heather Island, and retreat has

M. F. Meier; L. A. Rasmussen; D. S. Miller

1985-01-01

117

The Natural Variability of Glaciers  

NASA Astrophysics Data System (ADS)

Glaciers respond to both the natural variability that is intrinsic to a constant climate and also to the trends and shifts that constitute actual climate change. Over the last ten years a series of studies has shown, for a variety of climatic and glacier settings, that the standard deviation (1 sigma) of natural glacier-length fluctuations may range from 300 to 600 m. By definition of the standard deviation, a glacier will spend approximately 5% of its time outside ±2? (and 1% of its time outside of ±3?). Thus, fluctuations of several kilometers can be expected to occur every few centuries, even without any climate change. Because these magnitudes rival those commonly interpreted as reflecting Holocene climate changes, it is vital to improve our understanding of these natural glacier fluctuations. The physical basis for this behavior is presented. The magnitude and duration of natural glacier fluctuations depends straightforwardly on the geometry and average climate of the glacier setting, and the probability distribution of interannual climate variability. Such dependence can be demonstrated in a simple linear glacier model. The analyses are supplemented by detailed dynamical flowline modeling of glaciers around Mt. Baker in Washington State, and Franz Josef glacier in New Zealand.

Roe, G.

2012-04-01

118

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

119

How Key GEOSS Datasets Contribute to the Global Monitoring and Assessment of Glaciers  

NASA Astrophysics Data System (ADS)

An early and dramatic indicator of global climate change has been the recession of mountain glaciers. The potential impacts on water resources and global sea level rise has led to an increased interest in accurate monitoring and assessment of glaciers worldwide. Past glacier inventories recorded scalar information such as area and terminus location for glaciers in easily accessible regions of the Earth. A modern glacier inventory must be truly global, attempting to assess all of the Earth's estimated 160,000 glaciers, and contain actual glacier extents with area distribution by elevation. These data are required in order to begin modeling the response of this portion of the cryosphere to future climate change. Fortunately, the two key data sets required to produce this global inventory of glaciers were recently made available as contributions to GEOSS by GEO Member nations. These are the multispectral imagery in the Landsat archive, contributed by the U.S.A., and the Global Digital Elevation Model (GDEM) jointly contributed by the Ministry of Economy, Trade, and Industry (METI) of Japan and the United States National Aeronautics and Space Administration (NASA). This talk will describe how the Global Land Ice Monitoring from Space (GLIMS) project is utilizing these GEOSS resources by enabling GLIMS collaborators to derive detailed glacier outlines, transient snow lines, area-elevation distributions, and other pertinent information that will enhance our understanding of the current state, recent evolution, and future fate of the glaciers worldwide.

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

2009-12-01

120

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

121

Line-by-line radiative excitation model for the non-equilibrium atmosphere: Application to CO[sub 2] 15-[mu]m emission  

SciTech Connect

We describe a new line-by-line (LBL) algorithm for radiative excitation in infrared bands in a non-local thermodynamic equilibrium (non-LTE) planetary atmosphere. Specifically, we present a predictive model for the terrestrial CO[sub 2] 15[mu]m emission that incorporates this generic algorithm, and validate the model by comparing its results with emission spectra obtained in a limb-scanning rocket experiment. The unique features of the reactive-excitation algorithm are discussed in this paper. These features contribute to accurate radiative transfer results and reliable atmospheric cooling rates. For altitudes above 40 km, we present results of model calculations of CO[sub 2]([nu][sub 2]) vibrational temperatures, 15-[mu]m limb spectral radiances, and cooling rates, for the main band and for weaker hot and isotopic bands. We calculate the excitation and deexcitation rates due to different processes. We compare the predicted limb radiance with earthlimb spectral scans obtained in the SPIRE rocket experiment over Poker Flat, Alaska, and get excellent agreement as a function of both wavelength and tangent height. This constitutes the first validation of a long-wavelength CO[sub 2] non-LTE emission model using an actual atmospheric data set and verifies the existence of certain aeronomic features that have only been predicted by models and constrains the previously unknown value of the very important rate constant for deactivation of the CO[sub 2] bending mode by atomic oxygen to the range of 5-6 [times] 10[sup [minus]12] cm[sup 3]/(mol s) at mesospheric and lower thermospheric temperatures. We discuss the significance of this large value for terrestrial and Venusian thermospheres and the convergence rate of the iterative scheme, the model's sensitivity to the background atmosphere, the importance of the lower boundary surface contribution, and the effects of the choice of the layer thickness and the neglect of line overlap. 86 refs., 20 figs., 5 tabs.

Wintersteiner, P.P. (ARCON Corp., Waltham, MA (United States)); Picard, R.H.; Sharma, R.D.; Winick, J.R. (Hanscom Air Force Base, MA (United States))

1992-11-20

122

Glaciers and Glaciation  

NASA Astrophysics Data System (ADS)

Scientific interest in glaciers and glaciation dates back at least 200 years, but the knowledge explosion of the past 20 years has been truly breathtaking. Milutin Milankovitch's once unpopular belief that periodic variations of Earth's orbit regulate the timing of the glacial cycle is now embraced as mainstream orthodoxy. The detailed record of Ice Age climate preserved within the Greenland and Antarctic ice sheets is slowly being decoded and completely upsets the comfortable assumption that extreme climate change necessarily proceeds at a slow pace. Hoary discussion of the processes of glacial erosion and sedimentation has been replaced by serious attempts to observe the mechanical and hydrological processes active beneath mountain glaciers and polar ice streams.

Clarke, Garry K. C.

123

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

124

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

125

Glacier Evolution in the Altai Mountains, South-West Siberia, for the Last Half Century (with use of Geo-Informational Catalogue)  

Microsoft Academic Search

To systemize and analyze the information for the period from 1835 to present on altitudinal distributions of glaciers, exposition, their numbers and surface areas in basins, volumes, genetic classification, location of lower and upper level of glaciers, average firn line position and main morphometric characteristics, DataBase on glacier dynamics in the Altai Mountains (AGDB) has been developed in ArcGIS Format

A. B. Surazakov; Y. K. Narojniy; S. A. Nikitin; V. B. Aizen

2003-01-01

126

Mapping Pine Island Glacier's Sub-ice Cavity with Airborne Gravimetry  

Microsoft Academic Search

Pine Island Glacier, located on Antarctica's Amundsen Sea coast, is among the main contributors to mass loss from the West Antarctic Ice Sheet. Over the past several decades, Pine Island Glacier has experienced rapid thinning, acceleration, and grounding line retreat. The circulation of relatively warm and dense circum polar deep water beneath the floating ice shelf in front of Pine

M. Studinger; C. Allen; W. Blake; L. Shi; S. Elieff; W. B. Krabill; J. G. Sonntag; S. Martin; P. Dutrieux; A. Jenkins; R. E. Bell

2010-01-01

127

Insights into the Thwaites Glacier grounding zone from Operation IceBridge aerogravity  

Microsoft Academic Search

Operation IceBridge acquired 1500 km of geophysical data, at 10 km spacing, in front of the Thwaites Glacier grounding line during the 2009 season. The gravity anomalies recorded by the survey have been used to model the bathymetry of the sea floor in front of the glacier, an area inaccessible to previous surveys. The resulting map reveals previously unseen detail

K. J. Tinto; R. E. Bell; J. R. Cochran; S. Elieff; N. Frearson

2010-01-01

128

Muir Glacier in Glacier Bay National Monument 2004  

USGS Multimedia Gallery

This August 2004 photo further documents the significant changes that have occurred during the 63 years between photographs A and C, and during the 54 years between photographs B and C. Muir Glacier has retreated out of the field of view and is now nearly 5 miles to the northwest. Riggs Glacier has ...

129

Pine Island Glacier - basal properties and sliding laws  

NASA Astrophysics Data System (ADS)

The dynamics of the Antarctic Ice Sheet can be well seen and studied on the behavior of Pine Island Glacier. Despite the long time believe in a slow response of the ice sheet to changing atmospheric and oceanic forcing, Pine Island has shown acceleration, thinning and a significant grounding line retreat in the past decades. These ongoing processes are coinciding with a concentrated mass loss in the area around Pine Island Glacier, the Amundsen Sea Embayment. The area is of additional interest due to its retrograde bed slope below the glacier. The postulated instability of the setting turns the glacier into an even more suitable object for modeling studies. Plenty of working groups have conducted modeling studies of Pine Island Glacier with varying model complexity and diverse focuses. We want to add to this by conducting model experiments with a diagnostic 3D full-stokes model of Pine Island Glacier. The model is thermo-mechanically coupled and implemented with the commercial finite-element package COMSOL Multiphysics©. We use remotely sensed surface velocity data to validate our results. The focus of our work lies on the basal properties below the glacier and the connection to sliding behavior. We believe that this is a crucial part, as different basal conditions might cause different responses to ongoing changes in the area. Recent studies presented evidence for the existence of a water saturated sediment basin below the main trunk of the glacier. We conduct a variety a numerical experiments with which we test different approaches of combining information about the basal properties with sliding laws.

Wilkens, Nina; Humbert, Angelika

2013-04-01

130

Rapid ASTER imaging facilitates timely assessment of glacier hazards and disasters  

NASA Astrophysics Data System (ADS)

Glacier- and permafrost-related hazards increasingly threaten human lives, settlements, and infrastructure in high-mountain regions. Present atmospheric warming particularly affects terrestrial systems where surface and sub-surface ice are involved. Changes in glacier and permafrost equilibrium are shifting beyond historical knowledge. Human settlement and activities are extending toward danger zones in the cryospheric system. A number of recent glacier hazards and disasters underscore these trends. Difficult site access and the need for fast data acquisition make satellite remote sensing of crucial importance in high-mountain hazard management and disaster mapping.

Kääb, Andy; Wessels, Rick; Haeberli, Wilfried; Huggel, Christian; Kargel, Jeffrey S.; Khalsa, Siri Jodha Singh

131

Chernobyl fallout on Alpine glaciers  

SciTech Connect

Measurements of the gross beta activity of snow samples from four Alpine glaciers contaminated by radioactive fallout from the Chernobyl nuclear accident and a gamma-spectrum analysis of selected samples are reported. The results are discussed with respect to possible risks to the population from using meltwater from these glaciers as drinking water.

Ambach, W.; Rehwald, W.; Blumthaler, M.; Eisner, H.; Brunner, P.

1989-01-01

132

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

133

Explaining Glaciers, Accurately  

NSDL National Science Digital Library

What happens when a geology graduate student and two fourth-grade teachers collaborate on lessons for the classroom? They discover interesting and practical ways to explore geology and other scientific concepts, that's what! Here they share the glacial erosion lessons that grew out of the geologist's frustration at finding glacial erosion labs erroneously showing glaciers eroding by pushing rocks. Their goal was to find a way to show and explain glacial erosion more accurately and in a way that elementary age students could understand.

Tate, Mari; Faw, Mary; Scott, Nancy

2009-04-01

134

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

135

Contribution of SAR interferometry (InSAR) to the study of alpine glaciers. The example of Forni Glacier (Central Alps, Italy): preliminary results  

NASA Astrophysics Data System (ADS)

Aiming at reconstructing superficial velocity and volumetric variations of alpine glaciers, SAR interferometry (InSAR) technique is, for the first time in Italy, applied jointly with the glaciological classic field methods. This methodology with its quantitative results provides, together with other space geodesy techniques like GPS, some fundamental elements for the estimation of the climate forcing and the evaluation of the future glacier trend. InSAR is usually applied to antarctic glaciers and to other wide extralpine glaciers, detectable by the SAR orbits; in the Italian Alps, the limited surface area of the glaciers and the deformation of radar images due to strong relief effect, reduce the applicability of this tecnique. The chosen glacier is suitable for this kind of study both for its large size and for the many field data collected and available for the interferometric results validation. Forni Glacier is the largest valley glacier in the Italian Alps and represents a good example of long term monitoring of a valley glacier in the Central Alps. It is a north facing valley glacier formed by 3 ice streams, located in Italian Lombardy Alps (46 23 50 N, 10 35 00 E). In 2002 its area was approximately 13 km2, extending from 2500 to 3684 m a.s.l., with a maximum width of approximately 7500 m and a maximum length of about 5000 m. Available data include mass-balance measurements on the glacier tongue (from the hydrological year 1992-1993 up to now), frontal variations data from 1925 up to now, topographical profiling by means of GPS techniques and profiles of the glacier bed by geoelectrical surveys (VES) (Guglielmin et alii, 1995) and by seismic surveys (Merlanti et alii, 2001). In order to apply radar interferometry on this glacier eight ERS SAR RAW images have been purchased, in addition to the Digital Elevation Model from IGM (Geographic Military Institute), and repeat pass interferometry used. Combining the different passes, differential interferograms are computed and velocity map obtained. The validation of interferometric data was possible comparing them with the field glaciological data obtained by GPS velocity surveys in the years 1992-1993 (Vittuari and Smiraglia, unpublished) and 1996-1997, which resulted of about 20m/y. The InSAR results give further contributions in the estimation of the velocity field of Forni Glacier for a deeper understanding of the different flow lines of the glacier. Problems related to relief effect, loss of coherence, geometry of satellite imagery and geocoding, are also discussed.

Sterzai, P.; Mancini, F.; Corazzato, C.; D Agata, C.; Diolaiuti, G.

2003-04-01

136

Polythermal Glacier Hydrology: A Review  

NASA Astrophysics Data System (ADS)

The manner by which meltwater drains through a glacier is critical to ice dynamics, runoff characteristics, and water quality. However, much of the contemporary knowledge relating to glacier hydrology has been based upon, and conditioned by, understanding gleaned from temperate valley glaciers. Globally, a significant proportion of glaciers and ice sheets exhibit nontemperate thermal regimes. The recent, growing concern over the future response of polar glaciers and ice sheets to forecasts of a warming climate and lengthening summer melt season necessitates recognition of the hydrological processes in these nontemperate ice masses. It is therefore timely to present an accessible review of the scientific progress in glacial hydrology where nontemperate conditions are dominant. This review provides an appraisal of the glaciological literature from nontemperate glaciers, examining supraglacial, englacial, and subglacial environments in sequence and their role in hydrological processes within glacierized catchments. In particular, the variability and complexity in glacier thermal regimes are discussed, illustrating how a unified model of drainage architecture is likely to remain elusive due to structural controls on the presence of water. Cold ice near glacier surfaces may reduce meltwater flux into the glacier interior, but observations suggest that the transient thermal layer of near surface ice holds a hydrological role as a depth-limited aquifer. Englacial flowpaths may arise from the deep incision of supraglacial streams or the propagation of hydrofractures, forms which are readily able to handle varied meltwater discharge or act as locations for water storage, and result in spatially discrete delivery of water to the subglacial environment. The influence of such drainage routes on seasonal meltwater release is explored, with reference to summer season upwellings and winter icing formation. Moreover, clear analogies emerge between nontemperate valley glacier and ice sheet hydrology, the discussion of which indicates how persistent reassessment of our conceptualization of glacier drainage systems is required. There is a clear emphasis that continued, integrated endeavors focused on process glaciology at nontemperate glaciers are a scientific imperative to augmenting the existing body of research centered on ice mass hydrology.

Irvine-Fynn, Tristram D. L.; Hodson, Andrew J.; Moorman, Brian J.; Vatne, Geir; Hubbard, Alun L.

2011-11-01

137

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

138

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

139

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

140

Determination of the Liquid Line of Descent of Anhydrous Tholeiitic Magmas at High Prese - Results from Equilibrium and Fractional Crystallisation Experiments at 1.0 GPa  

Microsoft Academic Search

Tholeiitic magmas are the most common eruptive products on the earth surface; petrology indicates that the majority of them differentiate in deep-seated magma chambers probably located in the lower crust or at the crust-mantle-boundary. To quantify the liquid line of descent of dry mantle-derived tholeiitic magmas and to understand the end-member processes of equilibrium and fractional crystallisation respectively at high

S. Villiger; P. Ulmer; A. Thompson; O. Muentener

2003-01-01

141

Recent evolution and mass balance of Cordón Martial glaciers, Cordillera Fueguina Oriental  

NASA Astrophysics Data System (ADS)

Past and present glacier changes have been studied at Cordón Martial, Cordillera Fueguina Oriental, Tierra del Fuego, providing novel data for the Holocene deglaciation history of southern South America and extrapolating as well its future behavior based on predicted climatic changes. Regional geomorphologic and stratigraphic correlations indicate that the last glacier advance deposited the ice-proximal ("internal") moraines of Cordón Martial, around 330 14C yr BP, during the Late Little Ice Age (LLIA). Since then glaciers have receded slowly, until 60 years ago, when major glacier retreat started. There is a good correspondence for the past 100 years between the surface area variation of four small cirque glaciers at Cordón Martial and the annual temperature and precipitation data of Ushuaia. Between 1984 and 1998, Martial Este Glacier lost 0.64 ± 0.02 × 10 6 m 3 of ice mass (0.59 ± 0.02 × 10 6 m 3 w.e.), corresponding to an average ice thinning of 7.0 ± 0.2 m (6.4 ± 0.2 m w.e), according to repeated topographic mapping. More detailed climatic data have been obtained since 1998 at the Martial Este Glacier, including air temperature, humidity and solar radiation. These records, together with the monthly mass balance measured since March 2000, document the annual response of the Martial Este Glacier to the climate variation. Mass balances during hydrological years were positive in 2000, negative in 2001 and near equilibrium in 2002. Finally, using these data and the regional temperature trend projections, modeled for different future scenarios by the Atmosphere-Ocean Model (GISS-NASA/GSFC), potential climatic-change effects on this mountain glacier were extrapolated. The analysis shows that only the Martial Este Glacier may survive this century.

Strelin, Jorge; Iturraspe, Rodolfo

2007-10-01

142

Scaling the Teflon Peaks: Granite, Glaciers, and the Highest Relief in North America  

NASA Astrophysics Data System (ADS)

We use a combination of field observations, remote sensing, and digital elevation data to demonstrate how the topographic character of the Alaska Range (Alaska, USA) has been influenced by the exhumation of Tertiary granitic plutons among more erodible sedimentary and metamorphic rocks. Observations that the mean elevations of many tectonically active mountain ranges follow closely the elevation of the mean Cenozoic snowline or glacial equilibrium line (ELA), rather than rates of tectonic rock uplift, have led to the “glacial buzzsaw hypothesis” - that terrain raised above the ELA is rapidly denuded by glaciers. The Alaska Range stands in prominent exception to this observation. Much of the range is developed on pervasively fractured sedimentary and metamorphic rocks and has local relief of 1000-1500 m. In contrast, early and mid-Tertiary plutons of relatively intact granite support most of the range's impressive mountains (including Mt. McKinley, or Denali, the highest mountain in North America at 6194 m), with 2500-5000 m of local relief. Moreover, these plutons are where the range's modern glaciers originate, as the high peaks protrude in some cases kilometers above modern snowlines. These glaciers flow off of the plutons onto the surrounding, softer rocks, where mean summit elevations are similar to modern snowline elevations. We exploit the Denali massif and the Kichatna Mountains to its west to illustrate the direct ways in which exhumation of granite plutons affects glacial erosion, glacier long profiles, the glacial drainage network, and the effectiveness of periglacial processes. We use simple scaling calculations to explore the potential feedbacks of relief enhancement - specifically, that of avalanching from steep valley walls - on the health of the glaciers occupying the valleys, and describe ways in which peaks can be preserved and allowed to grow to great heights. Our work indicates that most of the Alaska Range has developed in accordance with the glacial buzzsaw hypothesis, except where resistant granite has been exhumed among the weaker rocks. Differential erosion has progressively localized divides on the plutons as they were exhumed, leading to focused glaciation there. However, glacier long profiles provide evidence that glacial incision is less efficient on the granite. Cirques cannot form on the steep valley walls that are maintained by detachment of rock slabs along sheeting joints. The strong granites can therefore sustain steep walls that act as Teflon, efficiently shedding snow to the valley below. These avalanches can greatly enhance the health and the erosive power of the modern glaciers in parts of the range. During glaciations, mass is removed efficiently from the surrounding sedimentary landscape, promoting isostatic uplift of the granitic massifs. We conclude that, in places such as Denali, unusual combinations of tectonic uplift rate and rock strength have enacted a set of feedbacks that allowed the development of the highest relief in North America by enhancing glacial erosion in the valleys while preserving the peaks.

Ward, D.; Anderson, R. S.; Haeussler, P. J.

2010-12-01

143

An update on surge-type glaciers and spatial constraint of surge behavior in the Alaska Range  

NASA Astrophysics Data System (ADS)

The Alaska Range is host to many surge-type glaciers as originally identified by Post in the 1960s. A reanalysis of Post's Alaska Range surge-type glacier inventory and updates by Wilbur and Clarke has been compiled from the literature, USGS maps, nadir and oblique aerial photographs and satellite imagery with a combined time span of 1949 to 2011. Glaciers in the Alaska Range show a spectrum of surge behavior, from episodic "pulsing" (or acceleration) of a tributary glacier into a major glacier trunk, to full glacier participation resulting in kilometers of displacement. To address this spectrum a classification scheme was developed and applied to show both magnitude of surge behavior and provide a confidence index of surge-type glacier identification. Of the 356 glaciers in the Alaska Range with a surface area greater than 1 km2, 28 glaciers comprising 38% of the total glacier surface area show some degree of surge behavior. 19 major surge events have been observed or temporally constrained with imagery. To better spatially constrain surge behavior, tributary branches of surge-type glaciers were assessed individually for surge participation. The extent of displacement from the most recent surge was identified from surface expressions where possible. Pre- and post-surge moraine structures for glaciers known to have major surges since the 1990s were mapped, illustrating ice displacement and the evolution of glacier geometry during the quiescent phase. Moraine geometries of Black Rapids and Susitna glaciers were also mapped. Both are well studied glaciers whose predicted surges have not occurred. Elevation data collected along a centerline of Yanert Glacier before and after a surge in 2000-01 show a mass transfer of (6.2 ± 0.3) x 10^8 m3. These data also show the location of the hinge line or boundary between reservoir and receiving areas. Using these data as well as additional direct hinge line measurements made in the Alaska Range and elsewhere in Alaska, a 70/30 surface area ratio between the reservoir and receiving areas was derived. This ratio was applied to surge-type glaciers in the Alaska Range lacking direct hinge line measurements. We propose that knowing the location of the hinge line can aid surge forecasting.

Herreid, S. J.; Truffer, M.; Harrison, W. D.; Hock, R. M.

2011-12-01

144

Middle Sister and Hayden Glacier  

USGS Multimedia Gallery

The North face of Middle Sister and Hayden Glacier, in Three Sisters Wilderness, Deschutes National Forest, Oregon. This Picture was taken while climbing Middle Sister. Middle Sister is also known as "Hope" and is an extinct stratovolcano....

2009-12-08

145

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

146

New boundary conditions for the West Antarctic ice sheet: Subglacial topography beneath Pine Island Glacier  

NASA Astrophysics Data System (ADS)

Predictions about future changes in the Amundsen Sea sector of the West Antarctic ice sheet (WAIS) have been hampered by poorly known subglacial topography. Extensive airborne survey has allowed us to derive improved subglacial topography for the Pine Island Glacier basin. The trunk of this glacier lies in a narrow, 250-km long, 500-m deep sub-glacial trough, suggesting a long-lived and constrained ice stream. Two tributaries lie in similar troughs, others lie in less defined, shallower troughs. The lower basin of the glacier is surrounded by bedrock, which, after deglaciation and isostatic rebound, could rise above sea level. This feature would impede ice-sheet collapse initiated near the grounding line of this glacier, and prevent its progress into the deepest portions of WAIS. The inland-slope of the bed beneath the trunk of the glacier, however, confirms potential instability of the lower basin, containing sufficient ice to raise global sea by ~24 cm.

Vaughan, David G.; Corr, Hugh F. J.; Ferraccioli, Fausto; Frearson, Nicholas; O'Hare, Aidan; Mach, Dieter; Holt, John W.; Blankenship, Donald D.; Morse, David L.; Young, Duncan A.

2006-05-01

147

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

148

Glacier Sensitivity Across the Andes  

NASA Astrophysics Data System (ADS)

Most of the research on causes driving former glacial fluctuations, and the climatic signals involved, has focused on the comparisons of sequences of glacial events in separate regions of the world and their temporal-phasing relationship with terrestrial or extraterrestrial climate-forcing mechanisms. Nevertheless the climatic signals related with these glacial advances are still under debate. This impossibility to resolve these questions satisfactorily have been generally attributed to the insufficiently precise chronologies and unevenly distributed records. However, behind these ideas lies the implicit assumption that glaciers situated in different climate regimes respond uniformly to similar climatic perturbations. This ongoing research is aimed to explore the climate-glacier relationship at regional scale, through the analysis of the spatial variability of glacier sensitivity to climatic change. By applying a Surface Energy Mass Balance model (SEMB) developed by Rupper and Roe (2008) to glaciers located in different climatic regimes, we analyzed the spatial variability of mass balance changes under different baseline conditions and under different scenarios of climatic change. For the sake of this research, the analysis is being focused on the Andes, which in its 9,000 km along the western margin of South America offers an unparalleled climatic diversity. Preliminary results suggest that above some threshold of climate change (a hypothetical uniform perturbation), all the glaciers across the Andes would respond in the “same direction” (advancing or retreating). Below that threshold, glaciers located in some climatic regimes may be insensitive to the specific perturbation. On the other hand, glaciers located in different climatic regimes may exhibit a “different magnitude” of change under a uniform climatic perturbation. Thus, glaciers located in the dry Andes of Perú, Chile and Argentina are more sensitive to precipitation changes than variations in temperatures, while glaciers located in the wet Patagonian Andes seem to exhibit an opposite behavior. In an intermediate position are those glaciers located in the Tropical Andes, and Tierra del Fuego, which even though still more sensitive to temperature, they can be affected by temperature changes as well. With this regional approach towards the comprehension of climate-glacial dynamic interaction, we expect to contribute to the understanding the causes and mechanism driving former episodes of glacial fluctuations, and in turn, to the development of future scenarios of climate change.

Sagredo, E. A.; Lowell, T. V.; Rupper, S.

2010-12-01

149

Glacier discharge and climate variations  

NASA Astrophysics Data System (ADS)

Different studies account for the warming in the polar regions that consequently would affect Glacier Discharge (GD). Since changes in GD may cause large changes in sensible and latent heat fluxes, we ask about the relationships between GD and climate anomalies, which have not been quantified yet. In this study we apply different statistical methods such as correlation, Singular Spectral Analysis and Wavelet to compare the behaviour of GD data in two Experimental Pilot Catchments (CPE), one (CPE-KG-62°S) in the Antarctica and the other (CPE-KVIA-64°N) in the Arctic regions. Both CPE's are measuring sub- and endo-glacier drainage for recording of glacier melt water run-off. The CPE-KG-62°S is providing hourly GD time series since January 2002 in Collins glacier of the Maxwell Bay in King George Island (62°S, 58°W). The second one, CPE-KVIA-64°N, is providing hourly GD time series since September 2003 in the Kviarjökull glacier of the Vatnajökull ice cap in Iceland (64°N, 16°W). The soundings for these measurements are pressure sensors installed in the river of the selected catchments for the ice cap (CPE-KG-62°S) and in the river of the glacier for (CPE-KVIA-64°N). In each CPE, the calibration function between level and discharge has been adjusted, getting a very high correlation coefficient (0.99 for the first one and 0.95 for the second one), which let us devise a precise discharge law for the glacier. We obtained relationships between GD with atmospheric variables such as radiation, temperature, relative humidity, atmospheric pressure and precipitation. We also found a negative response of GD to El Niño teleconnection index. The results are of great interest due to the GD impact on the climate system and in particular for sea level rise.

Dominguez, M. Carmen; Rodriguez-Puebla, Concepcion; Encinas, Ascension H.; Visus, Isabel; Eraso, Adolfo

2010-05-01

150

Borehole video analysis of a temperate glacier' englacial and subglacial structure: Implications for glacier flow models  

Microsoft Academic Search

Video observations made in 16 boreholes drilled through a deforming valley glacier affirm that temperate glacier ice may be reasonably well represented as homogeneous in glacier flow models, but raise warnings about the complexities of basal boundary conditions and glacier sliding. Discrete englacial structures, including clear-ice layers, voids, and water conduits, compose a total of <3% of the ice mass.

Joel T. Harper; Neil F. Humphrey

1995-01-01

151

Imbalance and accelerated melting of glaciers and ice caps  

NASA Astrophysics Data System (ADS)

Most glaciers and ice caps (GIC) are out of balance with the current climate. In order to return to equilibrium, these GIC must retreat to higher elevations, losing mass and making a 21st-century sea-level contribution comparable to that of ice sheets. Here, we present data for 140 GIC from 1970-2009 and show that most glaciers and ice caps are farther from balance than previously believed. For the first decade of the 21st century (2000-2009), GIC in this data set have a mean accumulation-area ratio (AAR, the fractional glacier area where accumulation exceeds ablation) of 35%, far below the mean equilibrium value of 56%. If these AARs are assumed to be representative, the Earth's GIC are committed to the future loss of ~40% of their volume, simply to be in balance with the climate of the past decade. Accounting for geographic sampling biases, estimated volume losses are somewhat reduced, but are still substantially larger than previous published values. Extrapolation of recent trends suggests that if recent climate trends continue for the next several decades, the Earth's GIC will ultimately lose more than half their volume.

Mernild, S. H.; Lipscomb, W. H.

2012-04-01

152

Significant total mass contained in small glaciers  

NASA Astrophysics Data System (ADS)

A single large glacier can contain hundreds of millions of times the mass of a small glacier. Nevertheless, small glaciers are so numerous that their contribution to the world's total ice volume is significant and may be a notable source of error if excluded. With current glacier inventories, total volume errors on the order of 10 % are possible at both global and regional scales. However, errors of less than 1 % require glaciers that are smaller than those available in some inventories. Such accuracy requires a global list of all glaciers and ice caps (GIC) as small as 1 km2, and for regional estimates requires substantially smaller sizes. For some regions, volume errors of less than 5 % require a complete list of all glaciers down to the smallest conceivable sizes. For this reason, sea-level rise estimates and other total mass and total volume analyses cannot ignore the world's smallest glaciers without careful justification.

Bahr, D. B.; Radi?, V.

2012-02-01

153

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

154

Surface mass balance of Greenland mountain glaciers and ice caps  

NASA Astrophysics Data System (ADS)

Mountain glaciers and ice caps contribute roughly half of eustatic sea-level rise. Greenland has thousands of small mountain glaciers and several ice caps > 1000 sq. km that have not been included in previous mass balance calculations. To include small glaciers and ice caps in our study, we use Polar WRF, a next-generation regional climate data assimilation model is run at grid resolution less than 10 km. WRF provides surface mass balance data at sufficiently high resolution to resolve not only the narrow ice sheet ablation zone, but provides information useful in downscaling melt and accumulation rates on mountain glaciers and ice caps. In this study, we refine Polar WRF to simulate a realistic surface energy budget. Surface melting is calculated in-line from surface energy budget closure. Blowing snow sublimation is computed in-line. Melt water re-freeze is calculated using a revised scheme. Our results are compared with NASA's Gravity Recovery and Climate Experiment (GRACE) and associated error is calculated on a regional and local scale with validation from automated weather stations (AWS), snow pits and ice core data from various regions along the Greenland ice sheet.

Benson, R. J.; Box, J. E.; Bromwich, D. H.; Wahr, J. M.

2009-12-01

155

Extreme Short-term Variability in Southeast Greenland Outlet Glacier Dynamics  

NASA Astrophysics Data System (ADS)

Widespread acceleration, retreat and dynamically-induced thinning of marine-terminating outlet glaciers along Greenland’s southeastern coast peaked earlier in the decade and then appeared to subside between 2005 and 2007, prompting speculation that these glaciers have stabilized. Rapid thinning, however, continued in 2008 and 2009, before again changing to thickening by 2010. Individual glaciers exhibit remarkable variability over this period; the largest glacier of Koge Bugt fjord thinned over 100m between 2003 and 2005, thickened by nearly 100m in a single year between 2006 and 2007, thinning again by over 60m the following year. We hypothesize that this extreme volatility in behavior is likely due to thinning of the glacier trunk to flotation, so that small variations in thickness and basal effective pressure lead to large variations in basal slip. Variability in motion and thickness is likely exacerbated by basal topography, glacier shape and changing oceanographic conditions within the fjord. We analyze a decade of ice thickness, speed and front position data for southeast Greenland outlet glaciers and concurrent climate ocean and climate data to assess the cause(s) of this extreme short-term variability and implications for future glacier stability and predictions of ice sheet mass balance. Boxplot of annual ice thinning rate (positive implies thickening) for the 31 largest glaciers along the southeast Greenland coast (not all glaciers have data for all years). Red lines denote the median, the edges of the boxes are the 75th percentiles, and the whiskers extend to the most extreme non-outlier data points. Outliers are plotted individually as red crosses.

Howat, I. M.; McFadden, E. M.; Ahn, Y.; Joughin, I. R.; Smith, B. E.

2010-12-01

156

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

157

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

158

Dislocation equilibrium conditions revisited  

Microsoft Academic Search

If there is an equilibrium arrangement of a given collection of dislocations, each having a fixed size and shape, in an externally loaded or unloaded elastic body, the corresponding potential energy will be stationary with respect to infinitesimal perturbations of the dislocation positions. This leads to the dislocation equilibrium conditions: the Peach–Koehler forces along the dislocation line of each dislocation

V. A. Lubarda

2006-01-01

159

Monitoring Popocatepetl volcano's glaciers (Mexico): case study of glacier extinction  

Microsoft Academic Search

Popocatépetl volcano is located 60 km southeast of Mexico City and is one of the three ice-clad volcanoes in Mexico. The two glaciers of Popocatépetl became extinct after a strong retreat due to the combination of at least three causes: global change, change in regional meteorological conditions (induced by the vicinity to highly polluted areas) and local enforcement (namely volcanic

H. Delgado; P. Julio; C. Huggel; M. Brugman

2003-01-01

160

GLIMS Glacier Database: Status and Challenges  

NASA Astrophysics Data System (ADS)

GLIMS (Global Land Ice Measurements from Space) is an international initiative to map the world's glaciers and to build a GIS database that is usable via the World Wide Web. The GLIMS programme includes 70 institutions, and 25 Regional Centers (RCs), who analyze satellite imagery to map glaciers in their regions of expertise. The analysis results are collected at the National Snow and Ice Data Center (NSIDC) and ingested into the GLIMS Glacier Database. The database contains approximately 80 000 glacier outlines, half the estimated total on Earth. In addition, the database contains metadata on approximately 200 000 ASTER images acquired over glacierized terrain. Glacier data and the ASTER metadata can be viewed and searched via interactive maps at http://glims.org/. As glacier mapping with GLIMS has progressed, various hurdles have arisen that have required solutions. For example, the GLIMS community has formulated definitions for how to delineate glaciers with different complicated morphologies and how to deal with debris cover. Experiments have been carried out to assess the consistency of the database, and protocols have been defined for the RCs to follow in their mapping. Hurdles still remain. In June 2008, a workshop was convened in Boulder, Colorado to address issues such as mapping debris-covered glaciers, mapping ice divides, and performing change analysis using two different glacier inventories. This contribution summarizes the status of the GLIMS Glacier Database and steps taken to ensure high data quality.

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

2008-12-01

161

Mountain glacier identification from SAR images  

NASA Astrophysics Data System (ADS)

Because the terrain of mountain glacier is usually very rugged, it is hard to measure glaciers and estimated their changes in larger area by conventional measuring method. With fast development of remote sensing technique, synthetic aperture radar (SAR) interferometry is used for glacier monitoring with the ability of all-time and all-weather. Although interferometric coherence is a very good index to glacier, it is difficult to distinguish glacier area from non-glacier area when their coherence is similar. In this case, interferometric phase can play an important role to identify glacier. In this paper, phase texture analysis method is proposed to extract glacier. 8 texture features were analyzed based on co-occurrence matrix (COM), including mean, variance, homogeneity, contrast, dissimilarity, entropy, second moment, and correlation. Among them, variance, contrast and dissimilarity can distinguish glacier from non-glacier clearly most, so they are chosen for RGB combination. Then the RGB combination image is classified into several land covers by maximum likelihood classification (MLC). With post-classification processing, glacier area can be extracted accurately. Landsat TM images validate the proposed method.

Wu, Hong'an; Zhang, Yonghong; Zhong, Weifan; Sun, Guangtong

2011-11-01

162

Regional and global volumes of glaciers derived from statistical upscaling of glacier inventory data  

NASA Astrophysics Data System (ADS)

Very few global-scale ice volume estimates are available for mountain glaciers and ice caps, although such estimates are crucial for any attempts to project their contribution to sea level rise in the future. We present a statistical method for deriving regional and global ice volumes from regional glacier area distributions and volume area scaling using glacier area data from ˜123,000 glaciers from a recently extended World Glacier Inventory. We compute glacier volumes and their sea level equivalent (SLE) for 19 glacierized regions containing all mountain glaciers and ice caps on Earth. On the basis of total glacierized area of 741 × 103 ± 68 × 103 km2, we estimate a total ice volume of 241 × 103 ± 29 × 103 km3, corresponding to 0.60 ± 0.07 m SLE, of which 32% is due to glaciers in Greenland and Antarctica apart from the ice sheets. However, our estimate is sensitive to assumptions on volume area scaling coefficients and glacier area distributions in the regions that are poorly inventoried, i.e., Antarctica, North America, Greenland, and Patagonia. This emphasizes the need for more volume observations, especially of large glaciers and a more complete World Glacier Inventory in order to reduce uncertainties and to arrive at firmer volume estimates for all mountain glaciers and ice caps.

Radi?, Valentina; Hock, Regine

2010-03-01

163

The contribution of glacier melt to streamflow  

SciTech Connect

Ongoing and projected future changes in glacier extent and water storage globally have lead to concerns about the implications for water supplies. However, the current magnitude of glacier contributions to river runoff is not well known, nor is the population at risk to future glacier changes. We estimate an upper bound on glacier melt contribution to seasonal streamflow by computing the energy balance of glaciers globally. Melt water quantities are computed as a fraction of total streamflow simulated using a hydrology model and the melt fraction is tracked down the stream network. In general, our estimates of the glacier melt contribution to streamflow are lower than previously published values. Nonetheless, we find that globally an estimated 225 (36) million people live in river basins where maximum seasonal glacier melt contributes at least 10% (25%) of streamflow, mostly in the High Asia region.

Schaner, Neil; Voisin, Nathalie; Nijssen, Bart; Lettenmaier, D. P.

2012-09-13

164

Accelerating ice loss from the fastest Greenland and Antarctic glaciers  

NASA Astrophysics Data System (ADS)

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-1 by 2015, with velocities on PIG increasing to >10 km a-1 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-1.

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

2011-05-01

165

Stagnant air temperature and receding glaciers - a puzzling question in the Cordillera Blanca, Peru  

NASA Astrophysics Data System (ADS)

The tropical Andes have been recognized as one of the most vulnerable regions to climate change. Recent research shows that climatic changes in the region are not uniform. However, in many sites, critical information on observed trends are missing and unclear, representing barriers to design and implement appropriate climate change adaptation measures. Here, we analysed air temperature trends in the Cordillera Blanca, Peru. Long temperature data series between 1964 and 2011 are available for five meteorological stations at elevations of over 3000 m asl. in the area of the Cordillera Blanca, the Cordillera Huayash and the Cordillera Central and for three additional stations near the coast, at the foothills of the Cordillera Negra. We found that - after a strong positive trend between 1965 and 1980 of about 0.5°C per decade - mean annual air temperature in the area of the Cordillera Blanca did not show any significant increase during the last about 30 years, what could be confirmed by even more stations. Additionally, also four stations situated between approx. 4000 and 4800 m asl. do not show a trend in the last decade. These findings are consistent with the ERA-Interim reanalysis data for the 500 hPa pressure level, but are not confirmed by the NCEP/NCAR Reanalysis data. The stagnant temperature in the studied area stands in contrast to the temperature trends e.g. in the Peruvian Altiplano, where no break in the increasing trend of air temperature is observed. At some stations of the Cordillera Blanca, there was even a decreasing trend observed since 1980, at least for minimum air temperature. We argue here that this might be linked with a decadal mode of the ocean-atmosphere-land climate system counteracting to the anthropogenic warming of the atmosphere during the last about 30 years. These findings are in sharp contrast to the general pattern of the tropics characterized by an increasing freezing level height during the last few decades. Astonishingly enough, glaciers of the Cordillera Blanca were all the same receding heavily within the last 30 years. Considering that the response time of these quite small mountain glaciers are in the order of a few years, this glacier wastage seems to be contra-intuitive. One reason for this might be that equilibrium line altitudes (ELAs) are - already today - quite high in relation to a steady state ELA. If this decadal mode turns temperature forcing from negative to positive and comes in-line with anthropogenic warming in the Cordillera Blanca region, glacier wastage may accelerate dramatically, and peak water may be delayed for the next one or two decades. Diminishing of water resources coming from glaciers may be thereafter even more abrupt than solely estimated based on CMIP5 climate model scenarios, with important consequences on climate change adaptation.

Schauwecker, Simone; Rohrer, Mario; Huggel, Christian; Salzmann, Nadine; Acuña, Delia; Giráldez, Claudia; Jacques, Martín; Vuille, Mathias; Gómez, Jesús; Cochachin, Alejo

2013-04-01

166

MOVEMENT OF WATER IN GLACIERS  

Microsoft Academic Search

A network of passages situated along three-grain intersections enables water to percolate through temperate glacier ice. The deformability of the ice allows the passages to expand and contract in response to changes in pressure, and melting of the passage walls by heat generated by viscous dissipation and carried by above-freezing water causes the larger passages gradually to increase in size

R. L. SHREVE

1972-01-01

167

Glacier Lakes Ecosystem Experiments Site.  

National Technical Information Service (NTIS)

The Glacier Lakes Ecosystem Experiment Site (GLEES), a 600 ha research watershed at 3200-3400 m elevation in the Snowy Range of SE Wyoming, has been established to examine the effects of atmospheric deposition on alpine and subalpine ecosystems. This docu...

R. C. Musselman

1994-01-01

168

Jakobshavn Glacier Ice Flow (WMS)  

NSDL National Science Digital Library

Since measurements of Jakobshavn Isbrae were first taken in 1850, the glacier has gradually receded, finally coming to rest at a certain point for the past 5 decades. However, from 1997 to 2003, the glacier has begun to recede again, this time almost doubling in speed. The finding is important for many reasons. For starters, as more ice moves from glaciers on land into the ocean, it raises sea levels. Jakobshavn Isbrae is Greenlands largest outlet glacier, draining 6.5 percent of Greenlands ice sheet area. The ice streams speed-up and near-doubling of ice flow from land into the ocean has increased the rate of sea level rise by about .06 millimeters (about .002 inches) per year, or roughly 4 percent of the 20th century rate of sea level increase. This animation shows a time-lapse sequence of the ice flowing toward the ocean. In recent years, even ice that has traditionally remained in place is now being pulled down to the edge of land.

Sokolowsky, Eric; Kekesi, Alex; Abdalati, Waleed

2005-03-30

169

Microbial Habitat on Kilimanjaro's Glaciers  

NASA Astrophysics Data System (ADS)

Kilimanjaro glaciers captured a history of microbial diversity and abundance of supraglacial habitats. We show that a majority of bacterial clones, as determined by bacterial 16S rRNA gene sequencing, are most closely related to those isolated from cold-water environments.

Ponce, A.; Beaty, S. M.; Lee, C.; Lee, C.; Noell, A. C.; Stam, C. N.; Connon, S. A.

2011-03-01

170

Snow line altitude evolution in the Franco-Italian Alps over the 1984-2010 period reconstructed using optical remote sensing images  

NASA Astrophysics Data System (ADS)

For mid-latitude mountain glaciers, the snow line altitude (SLA) at the end of the hydrological year is a good indicator of the equilibrium line altitude and thus of the annual mass balance. This enables SLA evolution to be reconstructed for long time periods from remote sensing data, as the snow line is generally easy to identify using aerial photographs and satellite images. Consequently, this enables researchers to study the climate-glacier relationship at the massif scale, particularly in remote areas where no direct measurements are available. In this study, we present series of reconstructed SLA for approximately 50 glaciers in the Franco-Italian Alps over the period 1984-2010. More than 130 images have been used, registred by the following satellites: Landsat 4TM, 5TM, 7 ETM+, SPOT 1 to 5 and ASTER, with spatial resolutions ranging between 2.5 and 30 m. To facilitate the identification of the snow line on the Landsat and SPOT-ASTER images, we used a combination of the spectral bands 542 and 431, respectively, with radiometric thresholds for bands 2, 4 and 1, 3. On each image, the snow line has been manually delineated. Its average altitude has been calculated for only the central part of the glaciers to avoid border effects on the glacier banks, which could generate snow line position dependence on local conditions (shadows from surrounding slopes, additional snow input by avalanches or due to wind drift). A comparison between SLA time-series and in-situ measurements of glacier mass balance was set for three French glaciers where direct mass balance measurements are available over the whole time-period (Argentière, Saint Sorlin and Gébroulaz glaciers). Results show high correlation (0.74 < r2 < 0.98, p < 0.01, n = 27), underlying the quality of the SLA dataset and strenghtening the interest of the SLA as a key indicator of the climate-glacier relationship. Considering the complete time period, the average SLA of the studied glaciers has increased by about 160 m (ranging between 0 and 380 m depending of the glacier). However, this increase is in the range of the interannual variability (±112 m). Considering each glacier individually, a meridional effect appears; the SLA is about 100 m higher for the glaciers located in the southern sector of the study area (i.e. the Ecrins Massif at 44°50' N), than for the those located in the nothern sector (i.e. the Mont Blanc Massif at 45°55' N). Considering summer temperatures and winter accumulation, this observation can be attributed to warmer and drier conditions in the southern Alps. However, this meridional effect does not affect the evolution of SLA over the study period. Exposure appears to be the most important factor controlling the SLA evolution, with glaciers exposed to the East experiencing the most important SLA increase. Finally, we present a preliminary study regarding the sensitivity of the SLA to both winter accumulation and summer temperatures.

Rabatel, A.; Dedieu, J.; Letréguilly, A.; Thibert, E.; Six, D.; Vincent, C.

2011-12-01

171

Triple scale segmentation of non-equilibrium system simulated by macro–micro-atomic line model with mesoscopic transitions  

Microsoft Academic Search

The concept of restraining stress ahead of a macro-crack was first applied to the development of a dual scale line crack model. The local stress intensity is said to be lowered due to the restraint represented by the opposing intensity of the strip zone, the size of which determines the amount of restraint. The description used for this effect may

G. C. Sih; X. S. Tang

2005-01-01

172

Impacts of debris cover on glaciers: research priorities and relation to glacier-climate interactions on clean-ice glaciers.  

NASA Astrophysics Data System (ADS)

Debris covered glaciers are a common feature in many high mountain environments. The presence of surficial debris fundamentally alters a number of glacier processes, and consequently the manner in which glaciers respond to climate. Incomplete understanding of these altered processes hampers (a) the use of records of glacier change as a means of unraveling former climate conditions, (b) the production of glacier runoff projections and (c) development of high quality hazard assessments of the future development of debris covered glaciers and associated ice dammed lakes. This presentation summarizes four key ways in which debris cover alters the behaviour of glaciers in ways that are relevant to solving both scientific and more practical problems: (1) surface energy balance and sensitivity to climate (2) ablation gradient of debris covered glaciers and their long profile evolution under changing climate conditions (3) differential ablation and the development of supraglacial ponds (4) sedimentary record of moraine deposition and impacts of this on climatic reconstruction and long term moraine stability The presentation concludes by outlining priority list of research required specifically on debris covered glaciers and how this could be integrated within research programs assessing the response of clean ice glaciers to ongoing climate change.

Nicholson, L. I.

2012-04-01

173

Assessing Geometric Controls on Tidewater Glacier Sensitivity to Frontal Perturbations Using a Numerical Ice Flow Model  

NASA Astrophysics Data System (ADS)

Marine-terminating glaciers worldwide have undergone rapid changes in their dynamics in response to external forcing. Observations from the Greenland coast, however, reveal that outlet glaciers in close proximity to each other, likely sharing a similar external forcing, can exhibit dramatically different behavior. These behavioral differences may result from differences in glacier shape, such as the presence of basal overdeepenings and lateral constrictions near the terminus. Understanding how shape influences glacier response to forcing at the terminus is critical for predicting future change. The dependence of ice flow on shape is non-linear and complex and, therefore, best examined using numerical methods. We employ a numerical ice flow model to investigate how the shape of marine-terminating glaciers (i.e. basal topography, thickness and width) influences the dynamic response to perturbations in the stress boundary condition at the front caused by front retreat and thinning. Governing model equations are compiled from various numerical models derived for a lightly grounded outlet glaciers, grounded retreat through basal over-deepenings, and calving of marine-terminating outlet glaciers. The model is designed for tidewater glaciers confined to narrow channels so that the stress balance components consist of substantial longitudinal and lateral stresses in addition to basal drag. Emphasis is placed on conditions at the grounding zone, as it is particularly sensitive to changes in basal drag and longitudinal stress. The effect of ice softening at the shear margins as a result of glacial acceleration is also considered. Boundary conditions at the front are categorized by two different calving criteria: (1) the buoyancy stress criterion prescribed by Durand et al. (2009), and (2) the modified flotation criterion derived by Vieli et al. (2001). The model is applied to a range of glacier bed and width geometries and perturbed from steady state by prescribing increased longitudinal stress at the ice/water boundary. Results from our model are compared to recent glaciological observations to determine if an ice-flow numerical model with simplified geometry can reasonably describe observed glacier dynamics. Durand, G., O. Gagliardini, B. de Fleurian, T. Zwinger, and E. Le Meur (2009), Marine ice sheet dynamics: Hysteresis and neutral equilibrium, Journal of Geophysical Research, 114(F03009), doi: 10.1029/2008JF001170. Vieli, A., M. Funk, and H. Blatter (2001), Flow dynamics of tidewater glaciers: a numerical modelling approach, Journal of Glaciology, 47(159), 595-606.

McFadden, E. M.; Howat, I. M.

2010-12-01

174

Snow micro-structure at Kongsvegen glacier, Svalbard  

NASA Astrophysics Data System (ADS)

Measurements of physical snow properties have been performed at several sites at Kongsvegen glacier, which is a key Arctic glacier in western Spitzbergen (79N, 13E). The data were collected at six locations along the flow line of the glacier at different elevations (161 to 741m asl.) and describe snow that was deposited during winter 2010/11. We basically consider the vertical profiles of snow temperature, density, hardness, grain size and crystal shapes derived from standard stratigraphic methods (snow pits)and measurements using advanced instruments like Snow Micropen® and NIR imagery. Some parameters were measured repeatedly and with different instruments which proves a high quality as well as long-term and spatial representativeness of the data. The general snow conditions at the end of winter are characterized by a linear increase of snow depth and water equivalent with elevation. Snow hardness also increases with elevation while density remains remarkably constant. At most sites the snow temperature, density, hardness and grain size increase from the surface towards the snow-ice interface. The surface and the bottom layers stand out by specific changes in snow signature (crystal types) and delineate the bulk of the snow pack which itself features a rather complex layering. Comparison of the high-resolution profiles measured at different elevations at the glacier suggests some principal correlations of the signatures of hardness, grain size and crystal type. Thus, some major features (e.g. particularly hard layers) can be traced along the glacier, but the high-resolution layering can not straightforwardly be related from one site to the other. This basically reflects a locally different history of the snow pack in terms of precipitation events and post-depositional snow metamorphism. The issue is investigated more quantitatively by enhanced statistical processing of the observed signatures and simulation of the history of individual layers. These studies are supported by meteorological measurements at the snow observation sites.

Bilgeri, F.; Karner, F.; Steinkogler, W.; Fromm, R.; Obleitner, F.; Kohler, J.

2012-04-01

175

Low-latitude mountain glacier evidence for abrupt climate changes  

NASA Astrophysics Data System (ADS)

Clear evidence that a widespread warming of Earth's climate system is now underway comes from low latitude mountain glaciers. Proxy temperature histories reconstructed from ice cores, and the rapidly accelerating loss of both the total ice area and ice volume on a near global scale suggest that these glaciers responding to increasing rates of melting. In situ observations reveal the startling rates at which many tropical glaciers are disappearing. For example, the retreat of the terminus of the Qori Kalis Glacier in Peru is roughly 200 meters per year, 40 times faster than its retreat rate in 1978. Similarly, in 1912 the ice on Mount Kilimanjaro covered 12.1 km2, but today it covers only 2.6 km2. If the current rate of retreat continues, the perennial ice fields may disappear within the next few decades, making this the first time in the past 11,700 years that Kilimanjaro will be devoid of the ice that shrouds its summit. Tropical glaciers may be considered ``the canaries in the coal mine'' for the global climate system as they integrate and respond to key climatological variables, such as temperature, precipitation, cloudiness, humidity, and incident solar radiation. A composite of the decadally-averaged oxygen isotopic records from three Andean and three Tibetan ice cores extending back over the last two millennia shows an isotopic enrichment in the 20th century that suggests a large-scale warming is underway at lower latitudes. Multiple lines of evidence from Africa, the Middle East, Europe and South America indicate an abrupt mid-Holocene climate event in the low latitudes. If such an event were to occur now with a global human population of 6.3 billion people, the consequences could be severe. Clearly, we need to understand the nature and cause of abrupt climate events.

Thompson, L. G.; Mosley-Thompson, E. S.; Lin, P.; Davis, M. E.; Mashiotta, T. A.; Brecher, H. H.

2004-12-01

176

Motion patterns of glaciers in the eastern Wrangell Mountains, Alaska, seen on ERS-1 SAR Interferograms  

NASA Astrophysics Data System (ADS)

Mt. Wrangell, an active volcano, rises 4,317 meters from the Copper River Valley lowlands. The summit and the surrounding mountainous areas, i.e., the Wrangell Mountains, are covered by numerous alpine glaciers. To get a clearer picture of the glacial dynamics and mass balance in the area, and their changes in relation to volcanic heating and climate changes, we study the motion patterns of glaciers in the eastern Wrangell Mountains using the European Remote Sensing satellite, ERS-1, SAR images acquired in early 1994 when the satellite repeated its orbits every three days. Pairs of coherent single-look complex SAR images acquired 3 days apart are co-registered precisely and interferograms are formed after the difference of the phase values of individual pixels on the two SAR images are calculated pixel by pixel. Differential Interferometric SAR (DInSAR) technique has been used to remove the impact of topography on interferograms using an existing digital elevation model (DEM). The resulting interferograms reveal glacier motion patterns at sub-wavelength (centimeter) sensitivity. Adjustment of displacement for surface slope and motion direction is necessary because the direct measurement is made along the radar line-of-sight. The dense fringes parallel to the sidewalls of glaciers suggest strong shear between the central lines and sidewalls of glaciers. Nabesna glacier moves at a velocity about 0.4-0.6 m/day. A similar velocity about 0.5 m/day is derived for the upper section of Chisana Glacier. Near its terminus, Jacksina Glacier has a velocity a few centimeters a day. Investigation is in progress.

Li, S.; Benson, C.; Gens, R.; Lingle, C.

2006-12-01

177

Calendar-dated, early 'Little Ice Age' glacier advance at Robson Glacier, British Columbia, Canada  

Microsoft Academic Search

Dendrochronological studies at Robson and Bennington Glaciers have provided the first calendar dating of an early 'Little Ice Age' glacier advance in North America. Dates derived from in-situ stumps indicate that Robson Glacier began over-riding forest between c. AD 1142 and 1150 and continued until at least AD 1350. The highest rates of glacier advance (c. 3.8 m yr-1 )

B. H. Luckman

1995-01-01

178

Glacier Surge Mechanism: 1982-1983 Surge of Variegated Glacier, Alaska  

Microsoft Academic Search

The hundredfold speedup in glacier motion in a surge of the kind that took place in Variegated Glacier in 1982-1983 is caused by the buildup of high water pressure in the basal passageway system, which is made possible by a fundamental and pervasive change in the geometry and water-transport characteristics of this system. The behavior of the glacier in surge

Barclay Kamb; C. F. Raymond; W. D. Harrison; Hermann Engelhardt; K. A. Echelmeyer; N. Humphrey; M. M. Brugman; T. Pfeffer

1985-01-01

179

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

180

GLACIER VIEW ROADLESS AREA, WASHINGTON.  

USGS Publications Warehouse

Surveys indicate little promise for the occurrence of metallic mineral resources in the Glacier View Roadless Area, Washington. Small, thin lenses of coal may be present at depth near the western edge of the area, but larger coal deposits occur at or near the surface outside the roadless area. Oil and gas may be in the subsurface, but the evaluation of the potential requires additional information obtainable only by drilling.

Evarts, Russell, C.; Barnes, Donald, J.

1984-01-01

181

Understanding dynamic changes of marine terminating outlet glaciers through combining observations and numerical modelling, the case of Crane Glacier, Antarctic Peninsula (Invited)  

NASA Astrophysics Data System (ADS)

The recently observed rapid dynamic thinning and acceleration of marine based outlet glaciers in Greenland and Antarctica has in many cases been related to the retreat or removal of a buttressing floating tongue or ice shelf. The recent collapse of the Larsen B ice shelf provides an ideal natural experiment to study the stability and dynamic response of marine tributary glaciers to such ice shelf removal. A prognostic numerical flow line model is applied to Crane Glacier, a former tributary of the Larsen B in order to investigate its post-collapse dynamic adjustment and future stability. The model includes basal, lateral and longitudinal stresses and a robust treatment of groundingline motion. Through model perturbation experiments we explore the sensitivity and dynamic response of Crane Glacier to the removal of the ice shelf and compare these model results with remotly sensed velocity and surface elevation change data. We find that Crane Glacier is only sensitive to the removal of the shelf in close proximity of the grounding line (~10km) which explains the 3 year delay in peak thinning to the ice shelf collapse in 2002. The modelled rapid adjustment and upstream propagation of thinning and acceleration agrees well in terms of timescales and timing with observations, however, the modelling underestimates the magnitude of the dynamic changes and suggests that the thinning/groundinline-retreat feedback alone does not explain the observed thinning rates.

Vieli, A.; Nick, F.

2009-12-01

182

How well do observations on bench mark glaciers represent a glacier system?  

NASA Astrophysics Data System (ADS)

The main source of uncertainty in knowledge of the global glacier regime is the limited number of direct mass balance observations. Since the spatial variability of glacier properties is huge the few benchmark glaciers chosen for continuous observations are unlikely to adequately represent the glacier system to which they belong. It is not feasible to suggest that the number of field-based observations will substantially increase in the future. Therefore, observations from space-based sensors will become more widely used to study the characteristics and status of the world's glaciers. In this paper we examine how the restricted number of mass balance observations in one well-monitored glacier system may be used to characterize the entire system, and examine the potential and limitations of monitoring glacier systems from space. We have developed a "template method" whereby mass balance measurements on a benchmark glacier can be extrapolated to estimate the mass balance of its glacier system. We test this method by applying it to the Scandinavia Glacier System (SGS), where standard and continuous mass balance observations have been carried out since the mid-20th century on several tens of glaciers. We analyze spatial variability of glacier mass balance, accumulation area ratio, ELA and hypsography for twenty benchmark glaciers in SGS to better understand the behavior of this glacier system, and connect the standard field measurement results to estimations of ELA from Landsat imagery. From this we estimate the mass balance of SGS, and predict extreme values in relation to climate change. We have found that only a few glaciers in this system may adequately represent the regime of SGS, and that those commonly believed to be representative are actually not. We quantify the uncertainty in the extrapolation.

Khalsa, S. S.; Raup, B. H.; Dyurgerov, M.

2005-12-01

183

Determination of the Liquid Line of Descent of Anhydrous Tholeiitic Magmas at High Prese - Results from Equilibrium and Fractional Crystallisation Experiments at 1.0 GPa  

NASA Astrophysics Data System (ADS)

Tholeiitic magmas are the most common eruptive products on the earth surface; petrology indicates that the majority of them differentiate in deep-seated magma chambers probably located in the lower crust or at the crust-mantle-boundary. To quantify the liquid line of descent of dry mantle-derived tholeiitic magmas and to understand the end-member processes of equilibrium and fractional crystallisation respectively at high pressure, the following experimental approaches were chosen. Equilibrium crystallisation experiments were performed using a single starting composition and temperature increments of 30 ^oC. An approximation to pure fractional crystallisation was achieved by a stepwise approach: The liquid compositions are determined from each experiment; subsequent experiments are performed at lower temperature starting with the liquid composition of the previous, higher temperature experiment. All experiments were performed at 1.0 GPa using an end-loaded piston-cylinder-apparatus and NaCl-pyrex-MgO-assemblies. To prevent iron loss to the sample container and to constrain fO_2 at the C-CO_2 equilibrium, a Pt-graphite double capsule technique was applied. A first series of equilibrium crystallisation experiments was performed with a starting composition, which corresponds to an experimentally produced liquid in equilibrium with a fertile lherzolite at 1.5 GPa and 1350 ^oC (Hirose and Kushiro, 1993, EPSL). In these experiments olivine (ol) and spinel (spl) crystallised at 1270 ^oC followed by clinopyroxene (cpx) at 1240 ^oC. At 1210 ^oC ol disappeared and orthopyroxene (opx) crystallised with cpx and spl. At 1180 ^oC two pyroxenes but no spl were present. Between 1150 ^oC and 1060 ^oC cpx, opx and spl represented the solid phases. No plagioclase (plg) was observed in this series. In order to test potential feldspar nucleation problems a second series of experiments was conducted with 0.5 wt% of pure anorthite (an) seeds added. With this starting material plg is stable with cpx, opx, and spl at 1120 ^oC and 1090 ^oC. Between 1270 ^oC and 1150 ^oC opx, cpx and spl crystallised. The chosen starting composition is probably nearly multiply saturated and, therefore, the small change in composition resulting from the addition of anorthite leads to the disappearance of olivine from the assemblage. A third series of experiments has been initiated, simulating fractional crystallisation. To ensure that the starting composition is saturated in ol, natural ol crystals were added to the original starting material. At 1300 ^oC ol is stable with melt. The solid phases are ol, cpx, opx and spl at 1270 ^oC and cpx and opx at 1240 ^oC. In this series plg first occurs at 1210 ^oC together with cpx, opx and spl. At 1180 ^oC cpx, plg and spi and at 1150 ^oC cpx, plg, spi and ol crystallised. The experimental results are compared with natural ultramafic to mafic cumulates (dunites, websterites, gabbronorites and gabbros) that occur in lower crustal cumulate series such as the Layered Series of the well exposed Ivrea Zone (Northern Italy; Rivalenti et al. 1984, TMPM).

Villiger, S.; Ulmer, P.; Thompson, A.; Muentener, O.

2003-04-01

184

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

185

Geomorphological and sedimentological record of accelerated deglaciation of small mountain glacier, Ragnarbreen, Svalbard  

NASA Astrophysics Data System (ADS)

Most of the Svalbrad glaciers have been in retreat since the end of the Little Ice Age (LIA). Hence, they give a good opportunity to study the geomorphological and sedimentological record of deglaciation. The aim of the study is to describe main landsystem elements of Ragnar glacier and relate them to different stages of the glacier recession. The Ragnar glacier is located in the Svalbard archipelago, in the central part of the West Spitsbergen Isle, in the north branch of Billefjorden. Ragnar is a small (~ 6 km2), outlet glacier, which current clean ice edge has retreated ca. 1500 m from the position related to the maximum LIA extent. Fieldworks of the study comprised detailed geomorphological mapping and sedimentary works. Four main elements of the landsystem of the Ragnar glacier can be distinguished: 1) Clean glacier surface. Currently, the ice surface of Ragnar glacier is almost completely debris-free and with only several supraglacial streams. 2) Ice-marginal lake. The lake started to form after 1980 year. Since that time, its length has reached 1000 m. Distant (from the ice-edge) part of the lake is shallow (< 2 m) with several small islands. Part proximal to the current ice edge is deeper (up to 16 m) and devoid of islands. At the bottom of the lake some ice (probable of glacier origin) was detected. 3) Lateral moraines - were developed along the both valley sides, from frontal moraine complex - to ca. 2 km upward the glacier valley. 4) Frontal moraine complex. This complex comprises of several chains of ridges and depressions and is relatively distinct - elevated about 35 m above the valley bottom. The elements of the landsystem of the Ragnar glacier have undergone several transformations since the LIA maximum: 1) Formation of the frontal moraine complex can be related to the state of dynamic equilibrium of the glacier during the LIA maximum. During formation of the complex and shortly after it the main depositional agents were intense debris flows, which are recorded by thick covers of the old debris flow deposits. Nowadays, despite of ice-cores, frontal moraine complex is much more stable than the lateral moraines or ice-marginal lake. 2) As a consequence of lowering of the clean glacier surface and formation of the distinct lateral moraines, the debris delivering from the valley sides is limited only to very narrow zone of the glacier (i.e. only to the lateral moraine). 3) Accelerated recession of the ice mouth and limitation in delivery of debris from sides of the valley caused that amount of deposits released in the ice front is small. 4) Increasing amount of water flowing from the glacier was blocked by frontal moraine complex and the ice marginal lake was created. 5) The debris cover on the lateral moraines is relatively thin. In addition, as a consequence of the clean ice surface lowering, slopes of the lateral moraines are very steep. It causes that mass movement processes (especially debris flows) are ubiquitous. Contemporary, lateral moraines are the elements undergoing the most intense transformations. Observations made in the Ragnar marginal zone revealed spatial-temporal changes in distribution of the sediments and landforms. They also add some premises that in the first stage of deglaciation debris flow and other mass wasting processes are most common. In the later phase glaciolacustrine and glaciofluvial deposition also plays important role in transformation of landforms and sediments.

Ewertowski, Marek

2010-05-01

186

Climate during the Last Glacial Maximum in the Wasatch Mountains Inferred from Glacier Mass-Balance and Ice-Flow Modeling  

NASA Astrophysics Data System (ADS)

The Wasatch Mountains of northern Utah contained numerous valley glaciers east and immediately downwind of Lake Bonneville during the Last Glacial Maximum (LGM). While the extent and chronology of glaciation in the Wasatch Mountains and the rise and fall of Lake Bonneville are becoming increasingly well understood, inferences of climatic conditions during the LGM for this area and elsewhere in the Rocky Mountains and northern Great Basin have yielded a wide range of temperature depression estimates. For example, previous estimates of temperature depression based on glacier and lake reconstructions in this region generally range from 7° to 9° C colder than modern. Glacier modeling studies for Little Cottonwood Canyon (northern Wasatch Mountains) suggest that such temperature depressions would have been accompanied by precipitation increases of about 3 to 1x modern, respectively (McCoy and Williams, 1985; Laabs et al., 2006). However, interpretations of other proxies suggest that temperature depression in this area may have been significantly greater, up to 13° C (e.g., Kaufman 2003), which would likely have been accompanied by less precipitation than modern. To address this issue, we reconstructed ice extent in the American Fork Canyon of the Wasatch Mountains and applied glacier modeling methods of Plummer and Phillips (2003) to infer climatic conditions during the LGM. Field mapping indicates that glaciers occupied an area of more than 20 km2 in the canyon and reached maximum lengths of about 9 km. To link ice extent to climatic changes, a physically based, two- dimensional numerical model of glacier mass balance and ice flow was applied to these valleys. The modeling approach allows the combined effects of temperature, precipitation and solar radiation on net mass balance of a drainage basin to be explored. Results of model experiments indicate that a temperature depression of less than 9° C in the American Fork Canyon would have been accompanied by greater precipitation than modern, whereas greater temperature depressions would have required less-than-modern precipitation to sustain glaciers in the Wasatch Mountains. Without independent estimates of either temperature or precipitation for the LGM, model results do not provide a unique combination of these two variables based on simulated ice extent. However, the reconstructed pattern of glaciation in the Wasatch and Uinta Mountains indicates a sharp westward decline in glacier equilibrium- line altitudes in valleys immediately downwind of Lake Bonneville (Munroe et al, 2006), which suggests that precipitation in the Wasatch Mountains was enhanced during the LGM. Therefore, model results can be used to set limits on the temperature and precipitation. We estimate that, if temperatures during the LGM were 6° to 8° C less than modern, precipitation was 3 to 1.5x modern. Such precipitation increases would reflect the importance of Lake Bonneville as a moisture source for valleys in the Wasatch Mountains, as suggested by previous studies.

Bash, E. A.; Laabs, B. J.

2006-12-01

187

Global glacier changes: a revised assessment of committed mass losses and sampling uncertainties  

NASA Astrophysics Data System (ADS)

Most glaciers and ice caps (GIC) are out of balance with the current climate. To return to equilibrium, GIC must thin and retreat, losing additional mass and raising sea level. Because glacier observations are sparse and geographically biased, there is an undersampling problem common to all global assessments. Here, we further develop an assessment approach based on accumulation-area ratios (AAR) to estimate committed mass losses and analyze the undersampling problem. We compiled all available AAR observations for 144 GIC from 1971 to 2010, and found that most glaciers and ice caps are farther from balance than previously believed. Accounting for regional and global undersampling errors, our model suggests that GIC are committed to additional losses of 32 ± 12% of their area and 38 ± 16% of their volume if the future climate resembles the climate of the past decade. These losses imply global mean sea-level rise of 163 ± 69 mm, assuming total glacier volume of 430 mm sea-level equivalent. To reduce the large uncertainties in these projections, more long-term glacier measurements are needed in poorly sampled regions.

Mernild, S. H.; Lipscomb, W. H.; Bahr, D. B.; Radi?, V.; Zemp, M.

2013-10-01

188

Global glacier retreat: a revised assessment of committed mass losses and sampling uncertainties  

NASA Astrophysics Data System (ADS)

Most glaciers and ice caps (GIC) are out of balance with the current climate. To return to equilibrium, GIC must thin and retreat, losing additional mass and raising sea level. Because glacier observations are sparse and geographically biased, there is an undersampling problem common to all global assessments. Here, we further develop an assessment approach based on accumulation-area ratios (AAR) to estimate committed mass losses and analyze the undersampling problem. We compiled all available AAR observations for 144 GIC from 1971-2010 and found that most glaciers and ice caps are farther from balance than previously believed. Accounting for regional and global undersampling errors, our model suggests that GIC are committed to additional losses of 30 ± 11% of their area and 38 ± 17% of their volume if the future climate resembles the climate of the past decade. These losses imply global mean sea-level rise of 163 ± 73 mm, assuming total glacier volume of 430 mm sea-level equivalent. To reduce the large uncertainties in these projections, more long-term glacier measurements are needed in poorly sampled regions.

Mernild, S. H.; Lipscomb, W. H.; Bahr, D. B.; Radi?, V.; Zemp, M.

2013-05-01

189

Automated Glacier Surface Velocity using Multi-Image/Multi-Chip (MIMC) Feature Tracking  

NASA Astrophysics Data System (ADS)

Remote sensing from space has enabled effective monitoring of remote and inhospitable polar regions. Glacier velocity, and its variation in time, is one of the most important parameters needed to understand glacier dynamics, glacier mass balance and contribution to sea level rise. Regular measurements of ice velocity are possible from large and accessible satellite data set archives, such as ASTER and LANDSAT-7. Among satellite imagery, optical imagery (i.e. passive, visible to near-infrared band sensors) provides abundant data with optimal spatial resolution and repeat interval for tracking glacier motion at high temporal resolution. Due to massive amounts of data, computation of ice velocity from feature tracking requires 1) user-friendly interface, 2) minimum local/user parameter inputs and 3) results that need minimum editing. We focus on robust feature tracking, applicable to all currently available optical satellite imagery, that is ASTER, SPOT and LANDSAT etc. We introduce the MIMC (multiple images/multiple chip sizes) matching approach that does not involve any user defined local/empirical parameters except approximate average glacier speed. We also introduce a method for extracting velocity from LANDSAT-7 SLC-off data, which has 22 percent of scene data missing in slanted strips due to failure of the scan line corrector. We apply our approach to major outlet glaciers in west/east Greenland and assess our MIMC feature tracking technique by comparison with conventional correlation matching and other methods (e.g. InSAR).

Ahn, Y.; Howat, I. M.

2009-12-01

190

Uses of Several Photographic Methods to Detect Changes of Glaciers in Arctic Alaska  

NASA Astrophysics Data System (ADS)

We have employed several photographic methods to detect changes on glaciers in Arctic Alaska. On Okpilak and McCall Glaciers in the eastern Brooks Range, we have re-occupied photo-locations from 1906 and 1958 respectively. These photos unambiguously document that a large loss of ice mass has been on-going here over the past 100 years. The Okpilak Glacier photos also unambiguously reveal that retreat from the most recently exposed moraines did not begin until near the turn of the century, supporting lichenometric evidence that the change in weather patterns that marked the end of the Little Ice Age here occurred sometime around 1890. A time-series of photos from this photo-site since 1906 reveals the influence of glacier geometry on volume loss rates. Comparing these photos with modern survey data has also allowed us to better quantify the ice loss observed. On McCall Glacier, we have employed time-lapse photography in several ways. By installing a camera on a ridge high above the glacier, we can watch the snow-line move up-glacier in summer. By placing a camera in the accumulation area in front of a large ruler, we can record the rate of snow accumulation throughout the year. By placing a camera in front of our weather stations located on the glacier surface, we can both improve our interpretations of the weather data as well as help troubleshoot the causes for equipment malfunctions. Because shading plays such an important role in patterns of surface mass balance in these steep mountain valleys, we have used both optical and infrared time-series of photos to document both shading and the resulting impact on surface temperature within the valley. We are also using these time-series to help validate models of surface energy balance that incorporate shading.

Nolan, M.; Takahashi, S.

2004-12-01

191

FLUCTUATIONS OF CRILLON GLACIER SYSTEM, SOUTHEAST ALASKA  

Microsoft Academic Search

Crillon Glacier system (Lat. 58° 37? N, Long. 137° 23?w) consisting of two long feeding arms and a common T-shaped ending along the Fairweather Fault, with two cliffed termini, has been advancing. La Perouse's sketch map in 1786 suggests that North and South Crillon Glaciers were back far enough to have separate termini in Lituya Bay, so they must have

RICHARD P. GOLDTHWAIT; IAN C. Mc KELLAR; CASPAR CRONK

1963-01-01

192

Glaciers in 21st Century Himalayan Geopolitics  

Microsoft Academic Search

Glaciers are ablating rapidly the world over. Nowhere are the rates of retreat and downwasting greater than in the Hindu Kush-Himalaya (HKH) region. It is estimated that over the next century, 40,000 square kilometers of present glacier area in the HKH region will become ice free. Most of this area is in major valleys and the lowest glaciated mountain passes.

J. S. Kargel; R. Wessels; H. H. Kieffer

2002-01-01

193

A Lower Bound for Sea Level Rise from Glaciers and Ice Caps  

NASA Astrophysics Data System (ADS)

Most glaciers and ice caps (GIC) are out of balance with the current climate. In order to return to equilibrium, these GIC must retreat to higher elevations, losing mass and raising sea level. The required mass losses can be derived from the accumulation-area ratio (AAR), the fractional glacier area where accumulation exceeds ablation. Here, we present an updated data set for 142 GIC from 1970-2009 and show that most glaciers and ice caps are farther from balance than previously believed. For the first decade of the 21st century (2000-2009), GIC in this data set have a mean AAR of 35%, far below the mean equilibrium value of 56%. Assuming that these AARs are representative, the Earth's glaciers and ice caps must lose about 40% of their volume, raising mean sea level by about 240 mm, to be in balance with the climate of the past decade. Extrapolation of recent trends suggests that if climate change continues unabated for the next two to three decades, the Earth's GIC will eventually lose more than 75% of their volume.

Lipscomb, W. H.; Mernild, S. H.; Bahr, D.; Zemp, M.

2011-12-01

194

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

195

Englacial Drainage Systems in Himalayan Debris-covered Glaciers, and Implications for Supraglacial Lake Evolution  

NASA Astrophysics Data System (ADS)

Rates of mass loss on Himalayan debris-covered glaciers are controlled by a complex web of processes, including melting below debris, melting of exposed ice, and calving around supraglacial lakes. Ablation rates around lakes are typically one to two orders of magnitude higher than beneath supraglacial debris, so the extent and lifespan of supraglacial lakes exert strong controls on rates of glacier downwasting. Using a combination of speleological observations of englacial conduits and ASTER image analysis, we show that there is a close coupling between lake evolution and englacial hydrology. Surface meltwater on Himalayan glaciers commonly drains via shallow englacial conduits, formed by the incision of surface streams that become isolated from the surface by roof closure ('cut and closure'). Cut-and-closure conduits are typically beneath less than 30 m of ice, where low rates of creep closure allow them to persist for several years even after active enlargement has ceased. How conduits affect lake life cycle depends on whether lakes are 'perched' or at 'base level'. Moraine dams at debris-covered glacier snouts determine hydrological base level for the drainage system. Lakes at elevations above the moraine dam (perched lakes) can drain when connections are made to active or relict englacial conduits, which offer lines of high hydraulic conductivity through otherwise impermeable ice. Englacial drainage of warm lake water can then cause significant conduit enlargement, roof collapse and glacier surface subsidence. Regions of subsidence, particularly where bare ice is exposed, can then act as nuclei for the formation of new supraglacial lakes. In contrast, base-level lakes cannot drain englacially. Conduits connecting with base-level lakes, however, can encourage rapid lake growth and integration, by providing lines of enhanced internal ablation. Links between englacial and supraglacial hydrology and conduit formation and collapse result in strongly non-linear mass loss of debris-covered glaciers in the Himalayas, and may be important on debris-covered glaciers in other regions.

Benn, D.; Gulley, J.; Thompson, S. S.

2011-12-01

196

Modelling The Energy And Mass Balance Of A Black Glacier  

Microsoft Academic Search

A distributed energy balance hydrologic model has been implemented to simulate the melting season of the Belvedere glacier, situated in the Anza river basin (North- Western Italy) for a few years. The Belvedere Glacier is an example of SblackS glacier, ´ since the ablation zone is covered by a significant debris layer. The glacierSs termi- nus has an altitude of

G. Grossi; S. Taschner; R. Ranzi

2002-01-01

197

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

198

Simulation and forecast of the Tien Shan glacier's changes  

Microsoft Academic Search

Two mathematical models: glacial-covered areas\\/glacier numbers and glacial volume changes developed based on assessment of the glacier recession that occurred in a Tien Shan glacial massif for the last 60 years. According to estimations performed in the Akshiirak glacierized massif for the period from 1943 to 1977, change in mean altitude (Hm) of each individual glacier in the massif is

V. B. Aizen; V. A. Kuzmichenok; E. M. Aizen; A. B. Surazakov

2006-01-01

199

Proccedings of the Third Glacier Bay Science Symposium 1993.  

National Technical Information Service (NTIS)

The Third Glacier Bay Science Symposium was held at Glacier Bay Lodge in Glacier Bay National Park and Preserve, Alaska, on September 15-18, 1993. Like its predecessors, this meeting was jointly sponsored by the National Park Service, Friends of Glacier B...

D. R. Engstrom

1993-01-01

200

The influence of supraglacial debris cover on glacier hydrology: Miage Glacier, Italy.  

NASA Astrophysics Data System (ADS)

The Miage Glacier is a debris-covered glacier in the western Italian Alps. An integrated study of its hydrology, including dye tracing, glacier velocity measurements and water chemistry analysis of the proglacial stream was performed throughout the 2010 and 2011 ablation seasons. These data were used to elucidate the structure and seasonal evolution of the hydrological system. Slower and smaller streams were found to occur on the more thickly debris covered lower glacier, which gave traces indicative of an inefficient subglacial system. This may be due to the uneven topography of the lower glacier, which is characterised by small supraglacial catchments with low ablation rates. The largest streams were found draining the debris free upper glacier, and these gave faster and more peaked returns. This means that unlike on clean glaciers, the tracer velocity was faster with increasing distance up-glacier. The glacier responds dynamically to variations in meltwater input over periods of a few days at the beginning of the melt season, as well as after cooler weather in July. The delaying influence of the debris cover is highlighted in the reduced amplitude of diurnal variations in meltwater discharge, especially early in the season when the upper glacier is snow covered.

Fyffe, C. L.; Brock, B. W.; Kirkbride, M. P.; Mair, D. W. F.

2012-04-01

201

Quantifying global warming from the retreat of glaciers  

SciTech Connect

Records of glacier fluctuations compiled by the World Glacier Monitoring Service can be used to derive an independent estimate of global warming during the last 100 years. Records of different glaciers are made comparable by a two-step scaling procedure; one allowing for differences in glacier geometry, the other for differences in climate sensitivity. The retreat of glaciers during the last 100 years appears to be coherent over the globe. On the basis of modeling of the climate sensitivity of glaciers, the observed glacier retreat can be explained by a linear warming trend of 0.66 kelvin per century.

Oerlemans, J. (Utrecht Univ. (Netherlands))

1994-04-08

202

Shrinking Alpine glaciers spell trouble for Europe's rivers  

NASA Astrophysics Data System (ADS)

Within the frosted peaks of the Swiss Alps, the cycle of winter precipitation accumulation and springtime melt provides a seasonal flow of water to much of western Europe. Research into the freshwater contributions of Alpine glaciers has predominantly looked to measure water released directly from glacier melt. A glacier's overall water storage, however, which takes into account the snow that resides on the glacier's surface, more accurately describes the role Swiss glaciers play in feeding European streams. A new analysis by Huss that investigated the effects of changing Swiss glacier storage on the flows of four of Europe's largest rivers suggests that glaciers may be more important than previously realized.

Schultz, Colin

2011-10-01

203

Climate Change and Glacier Retreat: Scientific Fact and Artistic Opportunity  

Microsoft Academic Search

Mountain glaciers continue to retreat rapidly over most of the globe. In North America, at Glacier National Park, Montana, recent research results from Sperry Glacier (2005-2007) indicate negative mass balances are now 3-4 times greater than in the 1950s. A geospatial model of glacier retreat in the Blackfoot-Jackson basin suggested all glaciers would be gone by 2030 but has proved

D. B. Fagre

2008-01-01

204

Glaciers in Patagonia: Controversy and prospects  

NASA Astrophysics Data System (ADS)

Lately, glaciers have been subjects of unceasing controversy. Current debate about planned hydroelectric facilities—a US$7- to $10-billion megaproject—in a pristine glacierized area of Patagonia, Chile [Romero Toledo et al., 2009; Vince, 2010], has raised anew the matter of how glaciologists and global change experts can contribute their knowledge to civic debates on important issues. There has been greater respect for science in this controversy than in some previous debates over projects that pertain to glaciers, although valid economic motivations again could trump science and drive a solution to the energy supply problem before the associated safety and environmental problems are understood. The connection between glaciers and climate change—both anthropogenic and natural—is fundamental to glaciology and to glaciers' practical importance for water and hydropower resources, agriculture, tourism, mining, natural hazards, ecosystem conservation, and sea level [Buytaert et al., 2010; Glasser et al., 2011]. The conflict between conservation and development can be sharper in glacierized regions than almost anywhere else. Glaciers occur in spectacular natural landscapes, but they also supply prodigious exploitable meltwater.

Kargel, J. S.; Alho, P.; Buytaert, W.; Célleri, R.; Cogley, J. G.; Dussaillant, A.; Guido, Z.; Haeberli, W.; Harrison, S.; Leonard, G.; Maxwell, A.; Meier, C.; Poveda, G.; Reid, B.; Reynolds, J.; Rodríguez, C. A. Portocarrero; Romero, H.; Schneider, J.

2012-05-01

205

Step-wise changes in glacier flow speed coincide with calving and glacial earthquakes at Helheim Glacier, Greenland  

NASA Astrophysics Data System (ADS)

Geodetic observations show several large, sudden increases in flow speed at Helheim Glacier, one of Greenland's largest outlet glaciers, during summer, 2007. These step-like accelerations, detected along the length of the glacier, coincide with teleseismically detected glacial earthquakes and major iceberg calving events. No coseismic offset in the position of the glacier surface is observed; instead, modest tsunamis associated with the glacial earthquakes implicate glacier calving in the seismogenic process. Our results link changes in glacier velocity directly to calving-front behavior at Greenland's largest outlet glaciers, on timescales as short as minutes to hours, and clarify the mechanism by which glacial earthquakes occur.

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.

2008-12-01

206

Glacier Monitoring: Opportunities, Accomplishments, and Limitations.  

NASA Astrophysics Data System (ADS)

Glaciers and ice caps, exclusive of the two major ice sheets, have been monitored for more than a century. Initially sparked by interest in the effect of glaciers on the landscape and their sensitive response to changes of climate, glacier study is now additionally motivated because of impacts on cold-regions ecology and hydrology as well as global sea-level rise. Glacier observations in many areas provide the only real data on climate change in the mountains. A substantial number of mass balance programs were initiated during the 1960s that improved our understanding of spatial and temporal changes in climate, and provided a basis for projecting future changes to glaciers and sea level. These results show a general increase in both snow accumulation and ice melting during the last 40 years (but with net wastage predominating), and a marked increase in the sensitivity of ice wastage to air temperature since the late 1980s. The World Data Center system provided unrestricted exchange of data among glaciologists during the `cold war.' The World Glacier Monitoring Service together with the National Snow and Ice Data Center and several individuals now provide ready access to glacier data. Remaining problems include inadequate access to digital data, a size bias to small glaciers, some traditional methodologies which limit the usefulness of the results, slow incorporation of new technologies, complexity of incorporating glacier dynamics in mass balance analysis, and insufficient attention by some investigators to reporting observational error. Perhaps the most difficult problems are the extension of limited data to the synthesis of broad regional or global conclusions, and a general dwindling of support for monitoring activities.

Meier, M. F.; Dyurgerov, M. B.

2001-12-01

207

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

208

Long-term mass and energy balance monitoring of Himalayan glaciers (GLACIOCLIM project) : some results for Chhota Shigri Glacier (India), Mera and Changri Nup glaciers (Nepal)  

NASA Astrophysics Data System (ADS)

Two white Himalayan glaciers, Chhota Shigri Glacier (16 km2, 32°N, India, arid-monsoon transition climate) and Mera Glacier (10 km2, 27°N, Nepal, Indian monsoon climate) have been monitored for mass, energy and hydrological balances since 2002 and 2007 respectively. Both glaciers belong now to the GLACIOCLIM observatory aiming at monitoring over a long term selected glaciers representative of different climates of the world. Additionally, a debris-covered glacier, Changri Nup Glacier (4 km2, 28°N, Nepal) has been monitored for mass and energy balances since 2009. During the period 2002-2011, Chhota Shigri Glacier experienced a negative glacier-wide mass balance (MB) of -0.59 ± 0.40 m water equivalent per year (w.e. yr-1), measured with the glaciological method. A recent study of the dynamic behaviour of the glacier showed that the glacier has probably experienced a period of near zero or slightly positive mass balance in the 1990s, before shifting to an imbalance in the 21st century. There is no sign of large recession of glaciers in Lahaul and Spiti region (Northern India) over the last 2 decades, the ice wastage being only limited to the last decade. On Mera Glacier, between 2007 and 2011, the cumulative mass balance is very close to zero. Melting is mainly driven by the radiative fluxes, the albedo being a key variable of the surface energy balance. The turbulent fluxes are only important in winter, when melting is insignificant and sublimation high.

Wagnon, P.; Ramanathan, A. L.; Arnaud, Y.; Azam, F.; Vincent, C.

2012-04-01

209

Modeled Climate-Induced Glacier Change in Glacier National Park, 1850--2100  

NSDL National Science Digital Library

This peer-reviewed article from BioScience journal is about the glacier change in Glacier National park. The glaciers in the Blackfoot--Jackson Glacier Basin of Glacier National Park, Montana, decreased in area from 21.6 square kilometers (km2) in 1850 to 7.4 km2 in 1979. Over this same period global temperatures increased by 0.45 degrees C (+/- 0.15 degrees C). We analyzed the climatic causes and ecological consequences of glacier retreat by creating spatially explicit models of the creation and ablation of glaciers and of the response of vegetation to climate change. We determined the melt rate and spatial distribution of glaciers under two possible future climate scenarios, one based on carbon dioxide--induced global warming and the other on a linear temperature extrapolation. Under the former scenario, all glaciers in the basin will disappear by the year 2030, despite predicted increases in precipitation; under the latter, melting is slower. Using a second model, we analyzed vegetation responses to variations in soil moisture and increasing temperature in a complex alpine landscape and predicted where plant communities are likely to be located as conditions change.

MYRNA H. P. HALL and DANIEL B. FAGRE (;)

2002-02-01

210

Climatology of Andean glaciers: A framework to understand glacier response to climate change  

NASA Astrophysics Data System (ADS)

Recent glacial and climate models suggest that glaciers located in contrasting climates could respond with different magnitudes to identical climatic perturbations. This implies that to understand the response of glaciers to a particular climate perturbation or to compare glacial fluctuations between different regions, climate conditions that permit glaciers to exist must be taken into account. In this study we systematize, classify, and identify the spatial distribution of the climates that permit the occurrence of present-day glaciers in the climatically diverse Andes. A first approximation suggests that a sample of 234 Andean glaciers exist under three distinctive combinations of temperature and precipitation conditions: i) cold and dry, ii) intermediate, and iii) warm and wet conditions. Cluster analysis (CA) and Principal Component analysis (PCA) of temperature, precipitation, and humidity reveal seven climatic configurations that support present-day Andean glaciers and suggest that these configurations have a distinctive geographical distribution. The groups are: 1) inner tropics and Tierra del Fuego, 2) wetter outer tropics, 3) drier outer tropics, 4) subtropics, 5) central Chile-Argentina (semi-arid), 6) northern and central Patagonia, and 7) southern Patagonia. This classification provides a basis to examine the spatial variability of glacier sensitivity to climate change, to unravel the causes of past glacial fluctuations, to understand the climatic signals driving present-day glacier fluctuations, and perhaps to predict the response of glaciers to future climate changes.

Sagredo, E. A.; Lowell, T. V.

2012-04-01

211

Glacier Change in the Western Himalayas: A Case Study of Suru Glacier, Northern India  

NASA Astrophysics Data System (ADS)

Mountain glaciers are considered as primary indicators to monitor the impact of climate change on regional temperature and precipitation patterns. They are linked to the atmosphere through mass and energy exchange which determine accumulation and ablation throughout the year. Since the advent of satellite remote sensing and its data availability to researchers from 1972 onwards, mapping and monitoring of glaciers become more popular because of its improved multi-spectral, multi-temporal and multi-spatial resolution. The investigated Suru Glacier is located in the upper Zanskar catchment, a major southern tributary of the Indus valley in the western Himalayan Range, Northwest India. The 8 km long glacier ranges from about 4700 m up to 5800 m a.s.l. To detect the changes of Suru Glacier remote sensing data such as Corona from 1972, diverse IRS and Landsat data, as well as an additional topographic map from 1962 were used. In order to calculate the volumetric changes of the glacier, dGPS measurements were carried out in 2007 and 2008. These measurements were then related and compared to a digital elevation model, which was generated from the topographic map, and to a SRTM-DEM (version 4, 2000). The co-registered data show a glacier retreat of about 120 m between 1962 and 2009. Apart from the recession of the glacier snout a certain downwasting of the glacier is detectable.

Schmidt, Susanne; Nüsser, Marcus; Nathawat, M. S.; Ghosh, S.; Pandey, A. C.

2010-05-01

212

New airborne laser altimetry over the Thwaites Glacier catchment, West Antarctica  

Microsoft Academic Search

A new airborne altimetry data set collected over Thwaites Glacier, one of Antarctica's most active ice streams, demonstrates the improvement in publicly available digital elevation models (DEMs) of the Antarctic ice sheet. The airborne altimetry comprises 35,000 line km sampled at 20 m along track. The full data set has a relative error of ±20 cm; a reference subset has

Duncan A. Young; Scott D. Kempf; Donald D. Blankenship; John W. Holt; David L. Morse

2008-01-01

213

Timing of recent accelerations of Pine Island Glacier, Antarctica  

USGS Publications Warehouse

We have used Interferometric Synthetic Aperture Radar (InSAR) data and sequential Landsat imagery to identify and temporally constrain two acceleration events on Pine Island Glacier (PIG). These two events are separated by a period of at least seven years (1987 - 1994). The change in discharge between two flux gates indicates that the majority of the increase in discharge associated with the second acceleration originates well inland (>80 km) from the grounding line. An analysis indicates that changes in driving stress consistent with observed thinning rates are sufficient in magnitude to explain much of the acceleration.

Joughin, I.; Rignot, E.; Rosanova, C. E.; Lucchitta, B. K.; Bohlander, J.

2003-01-01

214

Climate change: Shrinking glaciers under scrutiny  

NASA Astrophysics Data System (ADS)

Melting glaciers contribute to sea-level rise, but measuring their mass loss over time is difficult. An analysis of satellite data on Earth's changing gravity field does just that, and delivers some unexpected results.

Bamber, Jonathan

2012-02-01

215

International Symposium on Fast Glacier Flow.  

National Technical Information Service (NTIS)

Cryospheric Sciences Program "International Symposium on Fast Glacier Flow" (PI, C. Lingle) provided partial support for publication of Annals of Glaciology 36 by the International Glaciological Society. Annals of Glaciology is a peer-reviewed j...

C. S. Lingle

1990-01-01

216

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.

217

Towards a complete World Glacier Inventory  

NASA Astrophysics Data System (ADS)

The need for an inventory of the world's glaciers evolved during the International Hydrological Decade (1965-74). As a result, guidelines were established in the mid 1970s to compile a worldwide detailed inventory of existing perennial snow and ice masses. Following these international guidelines, several countries started compiling national glacier inventories based primarily on aerial photographs and maps. In the 1980s, the World Glacier Inventory (WGI) database was launched together with a status report about global and regional glacierised surface areas for the second half of the 20th century. These estimates were based on the detailed inventory data together with preliminary estimates of the remaining glacierised regions derived from early satellite imagery. In the late 1990s, the Global Land Ice Measurements from Space (GLIMS) database was initiated to continue the inventory task with space-borne sensors. In the WGI, glaciers are represented by geographical point coordinates. The GLIMS database includes digital outlines. Both include exact time stamps and tabular information on glacier classifications, length, area, orientation, and altitude range. Both are regularly updated with newly available data: the WGI stores point information for the second half of the 20th century whereas the GLIMS includes digital outlines for the 21st century. Since these detailed glacier inventories are not (yet) globally complete, there have been several efforts towards preliminary estimates of the overall global glacier coverage. A first, well elaborated one was included in the original status report of the WGI, published in 1989, and was refined in 2005 with information from other sources by Dyurgerov and Meier. Other studies used the detailed WGI, or an extended format by Cogley, for regional or global up-scaling of glacier extents. In 2003, Cogley published a global map of percentage glacier coverage per 1°x1° grid box (GGHydro) that is widely used for modeling at global scale. A first globally and almost complete map with (generalized) digital outlines of all ice covered regions (incl. Greenland but excluding Antarctica) was derived from ESRI's Digital Chart of the World (DCW) and other sources by Raup and colleagues in 2000. Most recently, Arendt and colleagues produced the Randolph dataset which combines available outlines from the GLIMS, DCW, and WGI datasets as well as from many other (often unpublished) sources by using the highest quality version in each region. However, while having the advantage of being almost complete, these global estimates lack time stamps and attributes for individual glaciers. The present work provides a brief review of the various efforts, its methodological differences, and findings towards the completion of a World Glacier Inventory.

Zemp, Michael

2013-04-01

218

A data set of world-wide 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 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 world-wide, 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 1534, 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 glacier length series show relatively small fluctuations until the mid-19th century followed by a global retreat that 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.

2013-09-01

219

Stars equilibrium  

NSDL National Science Digital Library

What causes the fusion reaction in a star's core? This activity page, part of an interactive laboratory series for grades 8-12, introduces students to processes inside a star. Students read about the equilibrium process in a star, in which outward gas pressure equals inward gravitational pressure. Then, an interactive lab activity offers students the opportunity to predict temperature, pressure, and gravity changes that occur during equilibrium. The chemical reactions of the fusion process are presented, and more specific detailed reactions are available in a pop-up box. Student practice quizzes about the equilibrium process and pressure and gravity interactions inside the star are included, as are answers. Copyright 2005 Eisenhower National Clearinghouse

University of Utah. Astrophysics Science Project Integrating Research and Education (ASPIRE)

2003-01-01

220

Increased flow speed on a large East Antarctic outlet glacier caused by subglacial floods  

NASA Astrophysics Data System (ADS)

Changes in the velocity of large outlet glaciers and ice streams in Greenland and Antarctica are important for ice-sheet mass balance and hence sea level. Mass loss in large parts of both ice sheets is being driven by the recent accelerations of outlet glaciers in response to unknown or poorly constrained climatic or internal perturbations in their boundary conditions. Surprisingly active networks of subglacial lake drainage have recently been found beneath the Antarctic ice sheet and tentatively linked to the onset of fast ice flow. Here we report an observed acceleration of ice velocity on Byrd Glacier, East Antarctica, of about 10% of the original speed between December 2005 and February 2007. The acceleration extended along the entire 75km glacier trunk and its onset coincided with the discharge of about 1.7km3 of water from two large subglacial lakes located about 200km upstream of the grounding line. Deceleration coincided with the termination of the flood. Our findings provide direct evidence that an active lake drainage system can cause large and rapid changes in glacier dynamics.

Stearns, Leigh A.; Smith, Benjamin E.; Hamilton, Gordon S.

2008-12-01

221

Impacts of Change in Glacier Ice  

NSDL National Science Digital Library

This is a five-activity module that explores the evidence for and impacts of melting glacial ice, with resources from major institutions and scientists who study glaciers -- primarily in Arctic areas. The suite of activities includes both glaciers and melting ice, as well as the impact of melt water downstream. Each activity follows the 5E model of Engagement, Exploration, Explanation, Elaboration, and Evaluation.

Grant, Alaska S.

222

Recent changes on Greenland outlet glaciers  

Microsoft Academic Search

Aircraft laser-altimeter surveys during the 1990s showed near-coastal parts of the Greenland ice sheet to be thinning; despite slow thickening at higher elevations, the ice sheet lost mass to the ocean. Many outlet glaciers thinned more rapidly than could be explained by increased melting during the recent warmer summers, indicating dynamic imbalance between glacier velocity and upstream snow accumulation. Results

R. Thomas; E. Frederick; W. Krabill; S. Manizade; C. Martin

2009-01-01

223

ASTER Imaging and Analysis of Glacier Hazards  

Microsoft Academic Search

\\u000a Most scientific attention to glaciers, including ASTER and other satellite-derived applications in glacier science, pertains\\u000a to their roles in the following seven functions: (1) as signposts of climate change (Kaser et al. 1990; Williams and Ferrigno\\u000a 1999, 2002; Williams et al. 2008; Kargel et al. 2005; Oerlemans 2005), (2) as natural reservoirs of fresh water (Yamada and\\u000a Motoyama 1988; Yang

Jeffrey Kargel; Roberto Furfaro; Georg Kaser; Gregory Leonard; Wolfgang Fink; Christian Huggel; Andreas Kääb; Bruce Raup; John Reynolds; David Wolfe; Marco Zapata

224

Glacier, glacier lake and permafrost distribution in the Brahmaputra river basin  

NASA Astrophysics Data System (ADS)

Glacier distribution, glacier changes, glacier lakes and their changes, and mountain permafrost occurrence are investigated and compared to climate scenarios in order to assess the influence of melting glaciers and degrading permafrost on the long-term runoff of the Upper Brahmaputra River. In this contribution we derive glacier inventories for three test areas in the Upper Brahmaputra River Basin based on semi-automatic classification of Landsat data of 2000 and supplementary ASTER data. The resulting glacier outlines are intersected with the glacier outlines of the Chinese Glacier Inventory from about the 1970s-1980s and compared to selected Corona satellite data from the 1960s. In total, an area loss of about 18% was observed over the period investigated. We estimate the according ice volume loss to be on the order of 20%. Using the Chinese Glacier Inventory and our inventory results we upscale the above glacier change to the entire Upper Brahmaputra River Basin. Glacier lakes are mapped for the boundary region between Bhutan and Tibet using 1990 and 2000 Landsat imagery. Changes in lake area are compared to the observed glacier changes. The permafrost distribution in the study region is estimated using regionally adapted versions of two empirical models, both originally developed to estimate the permafrost distribution on a regional scale in the Swiss Alps. One model (PERMAKART) applies a topo-climatic key, based on the relation between altitude above sea level, aspect, and permafrost probability. The second model (PERMAMAP) is based on a linear spatial relation between the bottom temperature of the winter snow cover (BTS), the mean annual air temperature (MAAT) and the potential direct solar radiation. Adaptation of the models is done through the inclusion of ground based meteorological data and validated using distribution patterns of rock glaciers. The latter are mapped from high resolution satellite data such as CORONA and Quickbird imagery. Both, the observed glacier changes and the modelled permafrost distribution are compared to climate simulations in order to estimate the recent and near-future climate change impact on the glaciers and mountain permafrost in the Upper Brahmaputra River basin.

Kääb, A.; Frauenfelder, R.; Hoelzle, M.; Sossna, I.; Avian, M.

2009-04-01

225

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

226

Creating improved ASTER DEMs over glacierized terrain  

NASA Astrophysics Data System (ADS)

Digital elevation models (DEMs) produced from ASTER stereo imagery over glacierized terrain frequently contain data voids, which some software packages fill by interpolation. Even when interpolation is applied, the results are often not accurate enough for studies of glacier thickness changes. DEMs are created by automatic cross-correlation between the image pairs, and rely on spatial variability in the digital number (DN) values for this process. Voids occur in radiometrically homogeneous regions, such as glacier accumulation areas covered with uniform snow, due to lack of correlation. The same property that leads to lack of correlation makes possible the derivation of elevation information from photoclinometry, also known as shape-from-shading. We demonstrate a technique to produce improved DEMs from ASTER data by combining the results from conventional cross-correlation DEM-generation software with elevation information produced from shape-from-shading in the accumulation areas of glacierized terrain. The resulting DEMs incorporate more information from the imagery, and the filled voids more accurately represent the glacier surface. This will allow for more accurate determination of glacier hypsometry and thickness changes, leading to better predictions of response to climate change.

Raup, B. H.; Khalsa, S. S.; Armstrong, R.

2006-12-01

227

Glacier Dynamics Within a Small Alpine Cirque  

NASA Astrophysics Data System (ADS)

Cirques, with their steep walls and overdeepened basins, have captivated the imagination of scientists since the mid-1800s. Glaciers in cirques, by generating these spectacular amphitheater-shaped landforms, contribute significantly to erosion in the core of mountain ranges and are one of the principal agents responsible for the relief structure at high elevations. Yet comprehensive studies of the dynamics of cirque glaciers, and their link to erosional processes, have never been undertaken. To this end, we acquired an extensive new set of measurements at the West Washmawapta Glacier, which sits in a cirque on the east side of Helmet Mountain in the Vermillion Range of the Canadian Rockies. Ice thickness surveys with ground penetrating radar revealed that the glacier occupies a classic bowl-shaped depression complete with a nearly continuous riegel. Using GPS-derived surface velocities of a glacier-wide grid network and the tilt of one borehole, we calculated the complete force balance of the glacier. This analysis also produced a map of basal sliding velocity and a value for the viscosity of temperate ice. We will discuss the implications of these findings for the problem of how cirques are formed by glacial erosion.

Sanders, J. W.; Cuffey, K. M.; MacGregor, K. R.; Kavanaugh, J. L.; Dow, C. F.

2008-12-01

228

Diverse calving patterns linked to glacier geometry  

NASA Astrophysics Data System (ADS)

Iceberg calving has been implicated in the retreat and acceleration of glaciers and ice shelves along the margins of the Greenland and Antarctic ice sheets. Accurate projections of sea-level rise therefore require an understanding of how and why calving occurs. Unfortunately, calving is a complex process and previous models of the phenomenon have not reproduced the diverse patterns of iceberg calving observed in nature. Here we present a numerical model that simulates the disparate calving regimes observed, including the detachment of large tabular bergs from floating ice tongues, the disintegration of ice shelves and the capsizing of smaller bergs from grounded glaciers that terminate in deep water. Our model treats glacier ice as a granular material made of interacting boulders of ice that are bonded together. Simulations suggest that different calving regimes are controlled by glacier geometry, which controls the stress state within the glacier. We also find that calving is a two-stage process that requires both ice fracture and transport of detached icebergs away from the calving front. We suggest that, as a result, rapid iceberg discharge is possible in regions where highly crevassed glaciers are grounded deep beneath sea level, indicating portions of Greenland and Antarctica that may be vulnerable to rapid ice loss through catastrophic disintegration.

Bassis, J. N.; Jacobs, S.

2013-10-01

229

Glacier Fluctuation and Climate Change: the NOAA/NSIDC Glacier Photo Digitization Project  

NASA Astrophysics Data System (ADS)

The study of historic glacier photographs is an excellent source of information about climate change. Glaciers are sensitive to temperature and precipitation patterns associated with climate change. Ice cores from glaciers can provide a long-term climate record and aid current scientific research in understanding changes that have occurred over tens of thousands of years. Within recent history, a warming climate has resulted in the unfortunate retreat and disappearance of glaciers around the world. Comparisons of glacial area and mass balance over time can help scientists understand a glacier's response to climate change. The National Snow and Ice Data Center is the repository of several thousand glacier photographs taken and collected by the American Geographical Society. The dates of the photographs range from the 1880s to the 1970s and the collection consists of both aerial and terrestrial photos. The digitization of these photographs will help inform users of their existence and will provide easier access to the images. It will also be an important first step in a project to display matching images of the same glaciers over time, thus providing an instantaneous visual representation of climate change. A searchable online database is being created for several thousand photographs and their accompanying metadata. Images will be retrievable by glacier name, photographer name, state, geographic coordinates, and subject keywords. This work is being done with funding by the National Oceanic and Atmospheric Administration's (NOAA) Climate Database Modernization Program (CDMP), whose goal is to make major climate databases available on the web.

Mullins, T. L.; Armstrong, R.; Machado, A.; Wang, I.; Ballagh, L.; Paserba, A.; Edwards, M.; Yohe, L.; Fetterer, F.

2002-12-01

230

Basal Conditions for Pine Island and Thwaites Glaciers Determined using Satellite and Airborne Data  

NASA Astrophysics Data System (ADS)

We used models constrained by remotely sensed data for Pine Island and Thwaites glaciers to infer basal properties, which are difficult to observe directly. The results indicate strong basal melting in areas above the grounding lines of both glaciers where the speeds are fast and the basal shear stresses are high. Farther inland, both glaciers have mixed bed conditions with extensive apparent areas of both crystalline bed rock and weak till. In particular, there are weak areas along much of its main trunk that could prove unstable if Pine Island Glacier retreats past the band of strong bed just above its current grounding line. In agreement with earlier studies, our model shows a strong sensitivity to small perturbations in the grounding line position. These results also reveal a strong sensitivity to the assumed sliding model, with non-linear sliding laws producing substantially greater dynamic response than earlier simulations that assume a linear-viscous till. Finally, our results using a plastic-bed are at least compatible with the limited observational constraints, which is consistent with recent theoretical work that shows basal shear stress cannot grow without bound.

Joughin, I.; Bamber, J.; Blankenship, D.; Holt, J.; Scambos, T.; Vaughan, D.; Tulaczyk, S.

2008-12-01

231

Basal conditions for Pine Island and Thwaites Glaciers, West Antarctica, determined using satellite and airborne data  

NASA Astrophysics Data System (ADS)

We use models constrained by remotely sensed data from Pine Island and Thwaites Glaciers, West Antarctica, to infer basal properties that are difficult to observe directly. The results indicate strong basal melting in areas upstream of the grounding lines of both glaciers, where the ice flow is fast and the basal shear stress is large. Farther inland, we find that both glaciers have 'mixed' bed conditions, with extensive areas of both bedrock and weak till. In particular, there are weak areas along much of Pine Island Glacier's main trunk that could prove unstable if it retreats past the band of strong bed just above its current grounding line. In agreement with earlier studies, our forward ice-stream model shows a strong sensitivity to small perturbations in the grounding line position. These results also reveal a large sensitivity to the assumed bed (sliding or deforming) model, with non-linear sliding laws producing substantially greater dynamic response than earlier simulations that assume a linear-viscous till rheology. Finally, comparison indicates that our results using a plastic bed are compatible with the limited observational constraints and theoretical work that suggests an upper bound exists on maximum basal shear stress.

Joughin, Ian; Tulaczyk, Slawek; Bamber, Jonathan L.; Blankenship, Don; Holt, John W.; Scambos, Ted; Vaughan, David G.

232

Progressive unpinning of Thwaites Glacier from newly identified offshore ridge: Constraints from aerogravity  

NASA Astrophysics Data System (ADS)

A new bathymetric model from the Thwaites Glacier region based on IceBridge airborne gravity data defines morphologic features that exert key controls on the evolution of the ice flow. A prominent ridge with two distinct peaks has been identified 40 km in front of the present-day grounding line, undulating between 300-700 m below sea level with an average relief of 700 m. Presently, the Thwaites ice shelf is pinned on the eastern peak. More extensive pinning in the past would have restricted flow of floating ice across the full width of the Thwaites Glacier system. At present thinning rates, ice would have lost contact with the western part of the ridge between 55-150 years ago, allowing unconfined flow of floating ice and contributing to the present-day mass imbalance of Thwaites Glacier. The bathymetric model also reveals a 1200 m deep trough beneath a bight in the grounding line where the glacier is moving the fastest. This newly defined trough marks the lowest topographic pathway to the Byrd Subglacial Basin, and the most likely path for future grounding line retreat.

Tinto, K. J.; Bell, R. E.

2011-10-01

233

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

234

Methodological approaches to inferring end-of-winter snow distribution on alpine glaciers  

NASA Astrophysics Data System (ADS)

End-of-winter snow distribution is a key variable in terms of glacier mass balance. However, such measurements are typically rare and not adequately represented in today's mass balance models. A better understanding of processes governing preferential snow deposition and redistribution on glacierized surfaces is a prerequisite for a more reliable impact assessment of climate change on glaciers. We present measurements of snow accumulation distribution from the 2009/2010 season on Findelengletscher, Valais, Switzerland, a large alpine valley glacier (13.4 km2). Field data were obtained simultaneously in April 2010 from (a) manual snow probing, (b) airborne Ground Penetrating Radar (GPR) and (c) surface elevation changes given by two LIDAR (Light Detection and Ranging) Digital Elevation Models (DEM). In this study, we aim at combining and comparing these data sources of point, line and area type. In-situ snow probings serve as ground reference. This data set consists of 463 point values covering the entire glacier elevation range. Additionally, snow density was measured in 13 snow pits across the glacier. The 500 MHz GPR survey was carried out from helicopter along 12.7 km of linear tracks providing about 10,000 evaluated traces. The surface elevation change based on LIDAR DEMs of Oct. 2009 and Apr. 2010 is corrected for the glacier dynamics using ice emergence velocity estimated with the 5-year average surface mass balance and observed geometry changes. This data source provides fully distributed spatial information on snow depth on a 1x1 m resolution grid over the entire glacier. The LIDAR-derived snow depth distribution differs from in-situ snow probings and the GPR-based data particularly in crevassed areas and due to difficulties in the spatial correction of glacier dynamics. These deviations are assessed by localizing error magnitudes and by their dependency on elevation. The GPR-based measurements reveal general problems of scale when comparing them with point-based snow probings on a rough surface such as on a glacier. This is addressed by a variogram analysis to detect possible systematic biases. Further, we compute the winter mass balance from the raw LIDAR surface elevation change and snow density measurements as 0.620 m water equivalent (w.e.). Extrapolating the snow distribution from the in-situ snow probings yields a higher winter balance of 0.780 m w.e. and allows a cross-validation with the GPR- and LIDAR-based data sets. Our results show that surface elevation change from LIDAR DEMs provides valuable information on end-of-winter snow distribution but has to be carefully corrected for glacier dynamics. Although not being truly distributed, the GPR-based data is reliable and unaffected by glacier dynamics. Thus, helicopter-borne GPR offers a straightforward and efficient tool for mapping the snow distribution on alpine glaciers. Cross-comparison of the three data sets indicates that the conventional method of extrapolating snow distribution from point probings might be subject to a systematic bias.

Sold, L.; Huss, M.; Hoelzle, M.; Joerg, P.; Salzmann, N.; Zemp, M.

2012-04-01

235

The relative impacts of greenhouse gas and aerosol climate forcing on mountain glacier melt at the third pole  

NASA Astrophysics Data System (ADS)

The third pole region resides within a hot spot for atmospheric brown clouds owing to the widespread emissions of dust, soot, and organic carbon aerosols in South and East Asia. As much as one-half of the regional climate warming over South Asia in the later 20th and early 21st centuries has been attributed to the direct radiative heating of the troposphere by aerosol solar absorption. The other half is attributed to the global greenhouse gas forcing. While the increase in temperature and infrared back radiation attributable to greenhouse gas warming is expected to accelerate melting of Himalayan glaciers, aerosol radiative forcing, and the climate response to it, contribute a host of additional impacts on mountain glaciers, many of which exacerbate the melting. These impacts include atmospheric warming, increased infrared back radiation, reduced surface insolation, surface albedo modification by soot deposition, and reductions in monsoon precipitation. The contributions of each of these effects upon melting of Himalayan mountain glaciers is explored in a glacier mass model based on energy balance calculations. The surface energy balance from the base to the top of several glaciers is calculated based on remote sensing and in-situ time series of radiative fluxes and precipitation. The model is calibrated against recent in-situ measurements of glacier mass balance and equilibrium altitude where available. Perturbations to the radiative fluxes and precipitation are then imposed on the mass balance calculations based on published estimates of the aerosol radiative forcing magnitudes and observed changes in regional temperature and precipitation over the modern era. In light of the substantial uncertainty surrounding regional forcing values and mountain glacier characteristics, the study emphasizes sensitivity studies comparing the relative responses of glaciers to the components of aerosol and greenhouse gas forcing mentioned above. Of particular interest are: (a) the balance between aerosol radiative warming of the atmosphere and aerosol radiative cooling of the surface; (b) estimates of the magnitude of soot deposition required to cause melting rates comparable to those caused by regional warming; and (c) the relative contributions of aerosol warming of the atmosphere and the associated decrease in monsoon precipitation to total glacier mass change. The modeling framework presented here is offered as a means of providing additional quantitative constraints on recent speculation about the role of black carbon aerosols and the fate of the Himalayan glaciers.

Wilcox, E. M.

2010-12-01

236

Measured Climate Induced Volume Changes of Three Glaciers and Current Glacier-Climate Response Prediction  

NASA Astrophysics Data System (ADS)

Small but hydrologically significant shifts in climate have affected the rates of glacier volume change at the three U.S. Geological Survey Benchmark glaciers. Rate changes are detected as inflections in the cumulative conventional and reference-surface mass-balances of Wolverine and Gulkana Glaciers in Alaska and South Cascade Glacier in Washington. The cumulative mass balances are robust and have recently been corroborated by geodetic determinations of glacier volume change. Furthermore, the four-decade length of record is unique for the western hemisphere. Balance trends at South Cascade Glacier in Washington are generally in the opposite sense compared with Wolverine Glacier in Alaska; NCEP correlation of winter balance with local winter temperatures is positive at 0.59 for Wolverine and -0.64 for South Cascade Glacier. At Wolverine Glacier, the negative trend of cumulative mass balances, since measurements began in 1965, was replaced by a growth trend \\(positive mass balances\\) during the late 1970s and 1980s. The positive mass-balance trend was driven by increased precipitation during the 1976/77 to 1989 period. At Gulkana Glacier, the cumulative mass-balance trend has been negative throughout its measurement history, but with rate-change inflection points that coincide with the interdecadal climate-regime shifts in the North Pacific indices. At South Cascade Glacier, the mass-loss trend, observed since measurements began in 1953, was replaced by a positive trend between 1970 and 1976 then became strongly and continuously negative until 1997 when the rate of loss generally decreased. Since 1989, the trends of the glaciers in Alaska have also been strongly negative. These loss rates are the highest rates in the entire record. The strongly negative trends during the 1990s agree with climate studies that suggest that the period since the 1989 regime shift has been unusual. Volume response time and reference surface balance are the current suggested methods for analyzing the response of glaciers to climate. Volume response times are relatively simple to determine and can be used to evaluate the temporal, areal, and volumetric affects of a climate change. However, the quasi-decadal period between the recent climate-regime shifts is several times less than the theoretical volume readjustment response times for the benchmark glaciers. If hydrologically significant climate shifts recur at quasi-decadal intervals and if most glaciers' volume-response times are several times longer \\(true for all but a few small, steep glaciers\\), most medium and large glaciers are responding to the current climate and a fading series of regime shifts which, themselves, vary in magnitude. This confused history of driver trends prevent conventional balances from being simply correlated with climate. Reference-surface balances remove the dynamic response of glaciers from the balance trend by holding the surface area distribution constant. This effectively makes the reference surface balances directly correlated with the current climatic forcing. The challenging problem of predicting how a glacier will respond to real changes in climate may require a combination of the volume response time and reference surface mass balances applied to a long time-series of measured values that contain hydrologically significant variations.

Trabant, D. C.; March, R. S.; Cox, L. H.; Josberger, E. G.

2003-12-01

237

Accelerating ice loss from the fastest Greenland and Antarctic glaciers  

Microsoft Academic Search

Progressive increase in ice discharge from fastest Greenland\\/Antarctic glaciersKey imortance of floating ice shelves to future behavior of many similar glacierLikelihood of continued, very large increases in ice discharge

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

2011-01-01

238

Observations of Glacier Dynamics in the St. Elias Mountains (Invited)  

NASA Astrophysics Data System (ADS)

Alaska glaciers contribute more to sea level rise than any other glacierized mountain region in the world. Alaska is loosing ~84 Gt of ice annually, which accounts for ~0.23 mm/yr of SLR (Luthcke et al., 2008). The primary cause of such rapid mass loss is complex glacier flow dynamics, not increased melting due to temperature increases (Larsen et al., 2007). Indirect observations indicate these complex flow dynamics occur on many glaciers throughout Alaska, but no comprehensive measurements of flow velocities have been made. We are working to measure surface velocities on glaciers throughout Alaska using offset tracking with synthetic aperture radar (SAR). We focus on the flow dynamics on the Seward/Malaspina Glacier system and on surrounding St. Elias glaciers. Flow variations of approximately 80% are evident on the Seward during “quiescent” phases. An active surge is visible on the Agassiz Glacier and regional synchronous velocity fluctuations have been found.

Burgess, E. W.; Forster, R. R.; Hall, D. K.

2010-12-01

239

Glacial Hydrology: Bibliography on the Hydrology of Glacierized Areas.  

National Technical Information Service (NTIS)

Information on the runoff from glaciers and glacierized basins, its prediction for agricultural, power-supply and transportation purposes, and its control for irrigation and flood protection, are vital concerns to the peoples living in most mountain areas...

G. J. Young

1982-01-01

240

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

241

Contemporary sediment production and transfer in high-altitude glaciers  

Microsoft Academic Search

The nature of fine-grained sediment production and transfer in high-altitude debris-covered glaciers was studied by examining the Rakhiot and Chungphar glaciers in the Nanga Parbat Himalaya, Northern Pakistan. Transport pathways, from the source areas to the glacier snout, were mapped and samples collected for particle size analysis and scanning electron microscopy. Positive down-glacier trends in sediment fining and increased weathering

Lewis A. Owen; Edward Derbyshire; Christine H. Scott

2003-01-01

242

Dynamics and Evolution of Taylor Glacier, Antarctica  

NASA Astrophysics Data System (ADS)

Taylor Glacier is a high-stress outlet glacier of East Antarctica. It originates on the Taylor Dome, flows eastward through the Transantarctic Mountains, and terminates in the famous Dry Valleys of Victoria Land. Here we summarize results from extensive new studies on its 80 km long ablation zone. Radar surveys show the basal topography is dominated by a deeply eroded central trough. Force balance and flow analyses yield estimates for basal temperature and demonstrate that basal motion of this glacier is non-existent or minor. A full-stress three-dimensional model of ice flow with no approximations in the mathematical framework is used to examine in detail how the glacier negotiates the complex mountainous topography and how the nonlinearity of ice deformation is manifest. We have also measured the stable isotope profile of surface ice along the lower 27 km of the central flowline, and thereby inferred ages of the ice at some locations. Analysis of these data reveal time-dependent behavior of the glacier over millennial timescales. Time-dependent planview models of the system are used to explore past incursions of ice into Taylor Valley.

Cuffey, K. M.; Kavanaugh, J. L.; Morse, D. L.; Aciego, S.; Bliss, A.

2005-12-01

243

Geophysical imaging of alpine rock glaciers  

NASA Astrophysics Data System (ADS)

Slope instabilities caused by the disappearance of ice within alpine rock glaciers are an issue of increasing concern. Design of suitable counter-measures requires detailed knowledge of the internal structures of rock glaciers, which can be obtained using geophysical methods. We examine benefits and limitations of diffusive electromagnetics, geoelectrics, seismics and ground-penetrating radar (georadar) for determining the depth and lateral variability of the active layer, the distributions of ice and water, the occurrence of shear horizons and the bedrock topography. In particular, we highlight new developments in data acquisition and data analysis that allow 2-D or even 3-D structures within rock glaciers to be imaged. After describing peculiarities associated with acquiring appropriate geophysical datasets across rock glaciers and emphasizing the importance of state-of-the-art tomographic inversion algorithms, we demonstrate the applicability of 2-D imaging techniques using two case studies of rock glaciers in the eastern Swiss Alps. We present joint interpretations of geoelectric, seismic and georadar data, appropriately constrained by information extracted from boreholes. A key conclusion of our study is that the different geophysical images are largely complementary, with each image resolving a different suite of subsurface features. Based on our results, we propose a general template for the cost-effective and reliable geophysical characterization of mountain permafrost.

Maurer, Hansruedi; Hauck, Christian

244

Improving Mass Balance Modeling of Benchmark Glaciers  

NASA Astrophysics Data System (ADS)

The USGS monitors long-term glacier mass balance at three benchmark glaciers in different climate regimes. The coastal and continental glaciers are represented by Wolverine and Gulkana Glaciers in Alaska, respectively. Field measurements began in 1966 and continue. We have reanalyzed the published balance time series with more modern methods and recomputed reference surface and conventional balances. Addition of the most recent data shows a continuing trend of mass loss. We compare the updated balances to the previously accepted balances and discuss differences. Not all balance quantities can be determined from the field measurements. For surface processes, we model missing information with an improved degree-day model. Degree-day models predict ablation from the sum of daily mean temperatures and an empirical degree-day factor. We modernize the traditional degree-day model as well as derive new degree-day factors in an effort to closer match the balance time series and thus better predict the future state of the benchmark glaciers. For subsurface processes, we model the refreezing of meltwater for internal accumulation. We examine the sensitivity of the balance time series to the subsurface process of internal accumulation, with the goal of determining the best way to include internal accumulation into balance estimates.

van Beusekom, A. E.; March, R. S.; O'Neel, S.

2009-12-01

245

Regional Modeling of Thwaites Glacier: Dynamic Changes in the Amundsen Sea Embayment  

NASA Astrophysics Data System (ADS)

With ongoing changes on Thwaites Glacier and a large negative mass balance, the Amundsen Sea Embayment is likely to be an avenue for sustained cryospheric contributions to sea-level rise through the coming centuries. Over the past decade, Thwaites Glacier has lost large portions of its ice tongue. Its grounding line is retreating and its catchment is thinning and widening. Because it is a marine outlet glacier that flows over an upward sloping bed and has a deep trough that is connected to the interior of the West Antarctic ice sheet, any forcing that produces a sustained retreat off of the broad (~50 km along flow) and shallow (~ -500 m) sill on which its grounding line currently rests could potentially lead to rapid and significant changes in sea level. To simulate the evolution of Thwaites Glacier due to various forcings over the coming centuries, the SeaRISE experiments were conducted using a higher-order finite-element flowline model. The magnitude of the response to forcings at the terminus is dependent on the spatial resolution of the basal topography as well as on the basal rheology. Therefore, a thorough analysis of this region will require further field investigations.

Edwards, R. A.; Parizek, B. R.; Wolfe, D.; Bertini, G. T.; Walker, R. T.

2011-12-01

246

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

247

Surface mass balance of Greenland mountain glaciers and ice caps  

Microsoft Academic Search

Mountain glaciers and ice caps contribute roughly half of eustatic sea-level rise. Greenland has thousands of small mountain glaciers and several ice caps > 1000 sq. km that have not been included in previous mass balance calculations. To include small glaciers and ice caps in our study, we use Polar WRF, a next-generation regional climate data assimilation model is run

R. J. Benson; J. E. Box; D. H. Bromwich; J. M. Wahr

2009-01-01

248

Subpolar glaciers network as natural sensors of global warming evolution  

Microsoft Academic Search

In the expeditions carried out both to temperate and subpolar glaciers in both hemispheres, we have observed the existence of endoglacier and subglacier flows and drainages also in subpolar glaciers. Our main work hypothesis is centred on investigating the role played by subpolar glacier discharge in global warming, as we consider this discharge may represent that unknown third of sea

Adolfo Eraso

249

Assessing Glacier Hazards At Ghiacciaio Del Belvedere, Macugnaga, Italian Alps  

Microsoft Academic Search

The uppermost section of the Valle Anzasca behind and above the community of Macugnaga in the Italian Alps is one of the most spectacular high-mountain land- scapes in Europe, with gigantic rock walls and numerous steep hanging glaciers. Its main glacier, Ghiacciaio del Belvedere at the foot of the huge Monte Rosa east face, is a heavily debris-covered glacier flowing

W. Haeberli; M. Chiarle; G. Mortara; A. Mazza

2002-01-01

250

Glacier variation in boduizangbu basin in Southeast Tibet  

Microsoft Academic Search

Glacier variation, especially the alpine glacier, is a sensitive indicator of climatic change. Glacier plays a vital role in studying the global climate system. The climate of the Tibet plateau has direct and indirect effects on the lives and economic activities of approximately two-thirds of the world's population who live downstream of this elevated terrain. Despite this critical importance of

Xiaoli Wang; Songbing Zou; Shangzhe Zhou; Gao Xiang

2005-01-01

251

Marine Geophysical Surveying Along the Hubbard Glacier Terminus, Southeast Alaska  

Microsoft Academic Search

Tidewater glaciers are a challenging environment for marine investigations, owing to the dangers associated with calving and restrictions on operations due to dense floating ice. We report here on recent efforts to conduct marine geophysical surveys proximal to the ice face of Hubbard Glacier, in Disenchantment Bay, Alaska. Hubbard is an advancing tidewater glacier that has twice recently (1986 and

J. A. Goff; M. Davis; S. P. Gulick; D. E. Lawson; B. A. Willems

2010-01-01

252

The Role of Glaciers in the Hydrology of Nepal (Invited)  

Microsoft Academic Search

Glaciers are a component of the hydrologic regime of many large mountain ranges of the world, including the Himalaya. However, the hydrologic regime of Himalayan catchment basins and the role of glaciers in the hydrologic regime of this region are not well understood. Current concern regarding the impact of the retreat of Himalayan glaciers on water supplies poses an urgent

R. L. Armstrong; A. Racoviteanu; D. Alford

2010-01-01

253

Mapping Pine Island Glacier's Sub-ice Cavity with Airborne Gravimetry  

NASA Astrophysics Data System (ADS)

Pine Island Glacier, located on Antarctica’s Amundsen Sea coast, is among the main contributors to mass loss from the West Antarctic Ice Sheet. Over the past several decades, Pine Island Glacier has experienced rapid thinning, acceleration, and grounding line retreat. The circulation of relatively warm and dense circum polar deep water beneath the floating ice shelf in front of Pine Island Glacier is seen as the main cause for melt rates at the base of the ice shelf that exceed known melting beneath Antarctica’s largest ice shelves by two orders of magnitude. The interplay between basal melting beneath the floating ice shelf and the thinning and acceleration of grounded ice upstream remains poorly understood. Measurements from an autonomous underwater vehicle have shown that the circumpolar deep water flows directly into the sub-ice cavity below the Pine Island Glacier ice shelf (Jenkins et al. 2010). The precise shape and depth of the cavity, however, remain poorly understood. During 2009, NASA’s Operation IceBridge collected airborne gravity, ice-penetrating radar and laser altimetry data on a 5 km grid of flight lines over the floating ice shelf in front of Pine Island Glacier and the grounding line. The load carrying capability of NASA’s DC-8 long-range aircraft allowed us to acquire a comprehensive suite of airborne geophysical data that constrains the geometry of the sub-ice cavity for input into coupled ocean circulation and ice sheet models. Forward modeling and inversion of airborne gravity data confirmed the existence of a ridge previously discovered by the autonomous underwater vehicle. Preliminary analysis of the gravity data reveals a deep, sinuous channel that reaches all the way from the edge of the ice shelf to the grounding line, allowing warm water to reach the grounding line and cause basal melting of the ice shelf. The downward slope of the subglacial topography makes the thinning, acceleration, and grounding line retreat a potentially unstable process that could result in further acceleration of the process. A detailed understanding of the ocean ice interactions and the processes in the sub-ice cavity near the grounding line is critical for predicting the future behavior of Pine Island Glacier and West Antarctica’s contributions to sea-level rise.

Studinger, M.; Allen, C.; Blake, W.; Shi, L.; Elieff, S.; Krabill, W. B.; Sonntag, J. G.; Martin, S.; Dutrieux, P.; Jenkins, A.; Bell, R. E.

2010-12-01

254

Subglacial melting of glaciers by catchment streams is a missing link in temperate glacier mass balance  

NASA Astrophysics Data System (ADS)

The influence of snowmelt and rain water on subglacial hydrology and glacier mass balance of temperate valley glaciers is poorly understood. We present a thermo-hydraulic melt model to improve understanding of the potential influence that streams sourced from snowmelt and rain have on the subglacial hydrology and melting of the high-precipitation Franz Josef Glacier, New Zealand. The model simulates conduit expansion due to melting caused by heat advection and contraction to due ice deformation at an hourly time-step to obtain an annual melt rate along the length of individual subglacial conduits fed from terrestrial streams that enter the glacier from the ice-free sub-catchments surrounding it. These streams are fed by snowmelt and rainfall that enter the glacier well above 0°C (up to ~10°C at low altitudes). Our model is calibrated using terrestrial stream temperature data and is validated with field measurements of surface and proglacial meltwater temperatures, as well as internal water flow velocities. Modelled outputs based on the best available data from measurements and observations indicate that streams entering the Franz Josef Glacier contribute an estimated 7% to the total glacier melt. This is the equivalent of more than twice the surface rainfall heat flux, which shows that rain and snowmelt may melt significant quantities of ice within a glacier. Not accounting for this melting mechanism in glaciological models where streams enter glaciers may lead to: 1) an incorrect characterisation of the subglacial hydrological drainage system; and 2) a potentially serious bias error in mass balance estimations. The second implication is fundamentally important for model robustness given that glaciological models are increasingly being used to predict the effects of future climate change.

Alexander, David; Shulmeister, James; Davies, Tim; Callow, Nik

2013-04-01

255

A comparison of glacier melt on debris-covered glaciers in the northern and southern Caucasus  

NASA Astrophysics Data System (ADS)

The glacier coverage in the Caucasus Mountains underwent considerable changes during the last decades. Besides a reduction in glacier area which in some areas is comparable to area changes in the European Alps, also the concentration of supra-glacial debris increased on many glaciers. Only a few glaciers in the Caucasus are monitored on a regular basis, while for most areas no field measurements are available on a continuous basis. In this study the regional differences between the well studied Adyl-su basin on the northern slope of the Caucasus is compared with a similar basin in the South (Zopkhito basin). Special focus is laid on the effect of supra-glacial debris cover on the melt conditions during the ablation season. Systematic differences can be shown for the distribution and temporal increase of the debris cover on the glaciers. While in the Adyl-su basin an extensive debris cover on the glacier tongues is common, only some low lying glacier tongues in the Zopkhito basin show considerable supra-glacial debris. Also the temporal increase in debris cover is decidedly stronger in the North. Field experiments show that the thermal resistance of the debris cover is somewhat higher than in other glacerised regions in the world. A simple ablation model which includes the effect of the debris cover on ice melt indicates considerably stronger melt rates in the northern basin, despite the much more widespread debris distribution. This is due to the different meteorological conditions with more frequent cloud cover and precipitation in the South. Still ablation is strongly influenced in both basins by the occurrence of supra-glacial debris cover, reducing the total amount of melt on the glacier by about 20%. Especially in the lower tongue areas this effect mitigates the area loss of the glaciers considerably.

Lambrecht, A.; Mayer, C.; Hagg, W.; Popovnin, V.; Rezepkin, A.; Lomidze, N.; Svanadze, D.

2011-02-01

256

Reconstruction of surface area and volume variations of a small alpine valley glacier since the Little Ice Age the case-study of Dosdè Est Glacier (central Alps, Italy)  

NASA Astrophysics Data System (ADS)

Reconstructing past glacier fluctuations and understanding them to forecast future trend of water availability in the Alps is an aim of general interest. For this reason continuous monitoring on sample glaciers is required to collect mass balance data, area and volume changes, ice thickness variations. The case-study of Dosdè Est Glacier, Piazzi-Campo Group, Italian Alps, representative of Italian small valley glaciers, is a good example of long term documentation of the evolution of this kind of glacier in the Central Alps. Dosdè Est Glacier is a North facing valley glacier, located in Italian Lombardy Alps (46 23 30 N, 10 13 05 E). In 2002 its area was approximately 2 kmq, extending from 2580 to 3294 m a.s.l., with a maximum widht of about 1000 m and a maximum lenght of about 2000 m. Observations to monitor the evolution of the glacier and to reconstruct past areas and volumes involve (in descending order of accuracy) direct mass balance measurements since 1995, topographic surveys (GPS) since 1996, GPR survey in order to evaluate ice thickness in 1999, seismic prospection and geoelectrical survey (VES) in 1997, glacier terminus variations field measurements from 1934 up to now (thanks to CGI operators), reconstruction of the 20th century maximum and of the LIA maximum using the well preserved moraines. Since hydrological year 1995-1996, mass balance of the glacier has been surveyed every year by glaciological field method. The stakes position is calculated by GPS technique and is used also to evaluate glacier surface velocity. The net mass balance during the 7 years of measurements was almost always negative with only one positive value recorded in the year 2001. During the 7 years of measures Dosdè Est Glacier lost about 7 m of ice thickness, it means 14.000.000 mc w.e. The mean yearly value of mass balance on 7 years of measures is -0,85 m w.e. and the mass balance gradient is 0,60 m w.e./100 m of altitude. Since 1925 Dosdè Est Glacier terminus variations were measured yearly by operators of Italian Glaciological Committee. The glacier had a continuous and uninterrupted retreating phase from 1934 to 1972 (-525m, mean value -25 m/y). Then an advancing phase occured from 1973 to 1986 (+100m, mean value +7.7 m/y). After that year the glacier resumed a continuous and uninterrupted frontal retreat. From 1934 to 2000 the glacier retreated of 602 m (mean yearly value, -12.5 m/y) and -165 m from 1987 up to now (mean yearly value of -15.8 m/y). In the last years, the glacier has been topographically surveyed by GPS techniques: from 1999 to 2001 the terminus was mapped yearly, in 2002 a large number of point positions in GPS Kinematic (about 6000 points) were collected to calculate surface glacier DEM. The stakes position measurements allowed to calculate the displacements of the stakes which resulted of about 30 m/y, with an accuracy of + - 1,5 m. The surface topography of the glacier was mapped by GPS data; a kriging technique was applied to GPS data, using a grid with a 10 m spacing to interpolate the 6000 measured values of position. On Dosdè Est Glacier different geophysical surveys were applied in order to evaluate ice thickness and bedrock morphology. In 1997 geoeletrical survey (VES) was used; the maximum value of ice thickness was evaluated more than 50 m; in 1997 seismic reflection method was applied to evaluate the glacier thickness along 1 longitudinal line (L1) and 2 trasversal lines (T1 and T2) situated in the centre of the glacier (Merlanti et alii, 2001).The maximum ice thickness was of about 90 m with a mean value of about 50 m. Moreover in 1999 GPR technique was used to obtain high-resolution topography of the glacier bed. A Pulse Ekko (Sensor and Software Company) GPR operating at a frequency of 50 MHz was used. The maximum ice thickness calculated is of about 90 m in the central area of the glacier, according to seismic prospection data. A kriging technique was applied to the radar data, using a grid with a 10 m spacing to interpolate the values of ice thickness between the GPR profiles. A topographic

Diolaiuti, G.; D Agata, C.; Pavan, M.; Belo, M.; Smiraglia, C.

2003-04-01

257

ASTER Imaging and Analysis of Glacier Hazards  

NASA Astrophysics Data System (ADS)

Most scientific attention to glaciers, including ASTER and other satellite-derived applications in glacier science, pertains to their roles in the following seven functions: (1) as signposts of climate change (Kaser et al. 1990; Williams and Ferrigno 1999, 2002; Williams et al. 2008; Kargel et al. 2005; Oerlemans 2005), (2) as natural reservoirs of fresh water (Yamada and Motoyama 1988; Yang and Hu 1992; Shiyin et al. 2003; Juen et al. 2007), (3) as contributors to sea-level change (Arendt et al. 2002), (4) as sources of hydropower (Reynolds 1993); much work also relates to the basic science of glaciology, especially (5) the physical phenomeno­logy of glacier flow processes and glacier change (DeAngelis and Skvarca 2003; Berthier et al. 2007; Rivera et al. 2007), (6) glacial geomorphology (Bishop et al. 1999, 2003), and (7) the technology required to acquire and analyze satellite images of glaciers (Bishop et al. 1999, 2000, 2003, 2004; Quincey et al. 2005, 2007; Raup et al. 2000, 2006ab; Khalsa et al. 2004; Paul et al. 2004a, b). These seven functions define the important areas of glaciological science and technology, yet a more pressing issue in parts of the world is the direct danger to people and infrastructure posed by some glaciers (Trask 2005; Morales 1969; Lliboutry et al. 1977; Evans and Clague 1988; Xu and Feng 1989; Reynolds 1993, 1998, 1999; Yamada and Sharma 1993; Hastenrath and Ames 1995; Mool 1995; Ames 1998; Chikita et al. 1999; Williams and Ferrigno 1999; Richardson and Reynolds 2000a, b; Zapata 2002; Huggel et al. 2002, 2004; Xiangsong 1992; Kääb et al. 2003, 2005, 2005c; Salzmann et al. 2004; Noetzli et al. 2006).

Kargel, Jeffrey; Furfaro, Roberto; Kaser, Georg; Leonard, Gregory; Fink, Wolfgang; Huggel, Christian; Kääb, Andreas; Raup, Bruce; Reynolds, John; Wolfe, David; Zapata, Marco

258

Crustal and Lithospheric Structural Controls on Thwaites Glacier, West Antarctica  

NASA Astrophysics Data System (ADS)

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 Embayment ice streams of West Antarctica that the locations of subglacial water (and sediment) are critical to initiating fast flow. Subglacial water can be created in areas where the base of the ice is at the pressure melting point, particularly in areas that may have elevated geothermal heat flux. To fully understanding the thermal state of the base of the ice, we must determine the deeper geology of the continent below. We hypothesize that the crustal and lithospheric structure of the Thwaites Glacier catchment (TGC) impacts the behavior of Thwaites Glacier through spatially heterogeneous geothermal heat flux. Here we use airborne gravity results collected primarily by the University of Texas at Austin in 2004-2005 to test this hypothesis. The airborne gravity free-air and Bouguer anomalies can be used in two ways to estimate sub-ice earth structure. First, the long-wavelength Bouguer gravity anomalies reflect changes in Moho depth. Based on spectral estimates of the gravity anomalies for gross crustal structure, there are two crustal provinces in the TGC: the West Antarctic Rift System in the eastern side of the catchment with a Moho at approx. 27 km b.s.l., and the Marie Byrd Land crustal block in the western side of the catchment with a Moho at approx. 20 km b.s.l. To determine the spatial variability of crustal thickness across these crustal provinces, we invert the long-wavelength Bouguer anomalies for Moho depth. This method will also more precisely locate the boundary between the two provinces. Second, we use admittance/coherence techniques on the gravity and topography to estimate the elastic thickness (Te) of the lithosphere containing the crustal blocks. The elastic thickness of the lithosphere is related to the lithosphere's actual thickness and thus the temperature at the base of the lithosphere. Based on our crustal and lithospheric structure results, we will comment on both the potential heterogeneity of subglacial heat flux and the creation of deep sedimentary basins.

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

2007-12-01

259

Melting Himalayan Glaciers May Doom Towns  

NSDL National Science Digital Library

This news article describes how mountain lakes in Nepal and Bhutan have become so overfilled by water from melting glaciers that they are in danger of overflowing. Scientists from the United Nations Environment Program (UNEP), along with remote-sensing experts from the International Center for Integrated Mountain Development (ICIMOD), predict that in the next half decade or so, the Himalayas could experience intense flooding as mountain lakes overflow with water from glaciers and snowfields which are melting as a result of gradually rising global temperatures.

260

Sensitivity of 21st century sea level to ocean-induced thinning of Pine Island Glacier, Antarctica  

NASA Astrophysics Data System (ADS)

Pine Island Glacier (PIG), Antarctica, is rapidly losing mass, supporting arguments that it may play a major role in 21st century sea-level rise. Yet this glacier's quantitative contribution to sea level based on theoretical and computational models is poorly known. We have developed a basin-scale glaciological model to examine the sensitivity of PIG to a range of environmental forcings. While oceanic melt likely played the leading role in recent thinning and retreat, we find that the particular grounding-line geometry with an extended ice plain in the 1990s made it susceptible to such forcing. Our model further indicates that while the rate of grounding-line retreat should diminish soon, the glacier's mass loss may continue at rates similar to, or moderately elevated from, the present. While substantial, our model-derived maximum rate of 2.7 cm/century is considerably smaller than previous heuristically-derived bounds on the sea-level contribution.

Joughin, Ian; Smith, Benjamin E.; Holland, David M.

2010-10-01

261

Rapid erosion of soft sediments by tidewater glacier advance: Taku Glacier, Alaska, USA  

NASA Astrophysics Data System (ADS)

Taku Glacier in southeast Alaska has advanced 7.5 km over the last 115 years, overriding its own glaciomarine and outwash sediments. We have documented rapid erosion of these sediments by comparing radio echo soundings (RES) along five transects (2003-2005) to earlier RES surveys (1989 and 1994) and to early bathymetric surveys of the proglacial fjord. Erosion rates, $\\dot{E, reached 3.9 +/- 0.8 m a-1 (1989-2003) at a distance, L, of 5.4 km from the 2003 terminus, where ice thickness, H, is 610 m. $\\dot{E averaged 2.0 +/- 0.1 m a-1 (1940-2005) at L = 3 km (H = 350 m), and 1.5 +/- 0.2 m a-1 (1952-2005) at L = 1.5 km (H = 250 m). Detailed mapping over a 4 km2 area of the terminus revealed a deeply incised channel in line with a major outlet stream. Glaciofluvial processes must play the dominant role in the subglacial erosion and removal of these unlithified sediments.

Motyka, Roman J.; Truffer, Martin; Kuriger, Elsbeth M.; Bucki, Adam K.

2006-12-01

262

Sensitivity of glaciers and small ice caps to greenhouse warming.  

PubMed

Recent field programs on glaciers have supplied information that makes simulation of glacier mass balance with meteorological models meaningful. An estimate of world-wide glacier sensitivity based on a modeling study of 12 selected glaciers situated in widely differing climatic regimes shows that for a uniform 1 K warming the area-weighted glacier mass balance will decrease by 0.40 meter per year. This corresponds to a sea-level rise of 0.58 millimeter per year, a value significantly less than earlier estimates. PMID:17835895

Oerlemans, J; Fortuin, J P

1992-10-01

263

Contrasting response of South Greenland glaciers to recent climatic change  

SciTech Connect

A unique geographical configuration of glaciers exists in the Narsarsuaq district of South Greenland. Two large outlet glaciers divide into seven distributaries, such that each glacier system has land-terminating, tidewater-calving, and fresh-water-calving termini. Despite a similar climatic regime, these seven glaciers have exhibited strongly contrasting terminal behavior in historical time, as shown by historical records, aerial photographs, and fieldwork in 1989. The behavior of the calving glaciers cannot be accounted for with reference solely to climatic parameters. The combination of iceberg calving dynamics and topographic control has partially decoupled them from climatic forcing such that their oscillations relate more closely to glaciodynamic than glacioclimatic factors.

Warren, C.R.; Glasser, N.F. (Univ. of Edinburgh, Scotland (United Kingdom))

1992-05-01

264

Monitoring surging glaciers of the Pamirs, central Asia, from space  

NASA Astrophysics Data System (ADS)

The evolution of surging glaciers of the Pamirs, central Asia, has been studied using repeat remote-sensing surveys in the Institute of Geography, Russian Academy of Sciences, since the early 1970s. We use images obtained from national Resurs-F satellites (1972-91), as well as Landsat 7 and Terra (1999-2006), to provide a basis for monitoring of surging glaciers, aimed at developing their inventory, studying the causes and mechanisms of surges and examining the timing and extent of glacial catastrophes. The inventory from the early 1990s allows identification of 215 glaciers with a dynamically unstable regime. We discovered 51 surging glaciers. Up until 2006, 10 more surges had occurred. We use stereoscopic deciphering and photogrammetric processing of consecutive satellite images to study the morphology and ice-velocity changes of several compound surging glaciers. We analyze the results of monitoring of Bivachny and Oktyabr'sky glaciers from 1972 to 1991 and Sugran glacier from 1972 to 2006. Two surges of Sugran glacier occurred during this time: an internal surge in 1976-80, and a surge with glacier tongue advance as far as 4.5 km in 2000-05. The role of damming in compound glacier systems is examined. Satellite-based monitoring is now the only method for obtaining initial information about the state and fluctuations of such glaciers.

Kotlyakov, V. M.; Osipova, G. B.; Tsvetkov, D. G.

265

Improving estimation of glacier volume change: a GLIMS case study of Bering Glacier System, Alaska  

NASA Astrophysics Data System (ADS)

The Global Land Ice Measurements from Space (GLIMS) project has developed tools and methods that can be employed by analysts to create accurate glacier outlines. To illustrate the importance of accurate glacier outlines and the effectiveness of GLIMS standards we conducted a case study on Bering Glacier System (BGS), Alaska. BGS is a complex glacier system aggregated from multiple drainage basins, numerous tributaries, and many accumulation areas. Published measurements of BGS surface area vary from 1740 to 6200 km2, depending on how the boundaries of this system have been defined. Utilizing GLIMS tools and standards we have completed a new outline (3630 km2) and analysis of the area-altitude distribution (hypsometry) of BGS using Landsat images from 2000 and 2001 and a US Geological Survey 15-min digital elevation model. We compared this new hypsometry with three different hypsometries to illustrate the errors that result from the widely varying estimates of BGS extent. The use of different BGS hypsometries results in highly variable measures of volume change and net balance (bn). Applying a simple hypsometry-dependent mass-balance model to different hypsometries results in a bn rate range of -1.0 to -3.1 m a-1 water equivalent (W.E.), a volume change range of -3.8 to -6.7 km3 a-1 W.E., and a near doubling in contributions to sea level equivalent, 0.011 mm a-1 to 0.019 mm a-1. Current inaccuracies in glacier outlines hinder our ability to correctly quantify glacier change. Understanding of glacier extents can become comprehensive and accurate. Such accuracy is possible with the increasing volume of satellite imagery of glacierized regions, recent advances in tools and standards, and dedication to this important task.

Beedle, M. J.; Dyurgerov, M.; Tangborn, W.; Khalsa, S. J. S.; Helm, C.; Raup, B.; Armstrong, R.; Barry, R. G.

2008-04-01

266

Glacier regime on the northern slope of the Himalaya (Xixibangma glaciers)  

Microsoft Academic Search

The mass–energy exchange components and ice thickness of the Xixibangma glacier massif were evaluated during the Chinese–Russian glaciological expedition to the northern Himalaya in 1991. Long-term data from two Chinese meteorological stations were used to analyze the glacier-climatic regime in the surrounding area. It was determined that solar radiation income during the summer–autumn monsoon is half that theoretically possible because

V. B Aizen; E. M Aizen; S. A Nikitin

2002-01-01

267

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

268

Glacier melting in a stratified ocean: Observations from outlet glaciers in Greenland (Invited)  

NASA Astrophysics Data System (ADS)

Submarine melting is an important balance term for tidewater outlet glaciers in Greenland, and has emerged as a potential trigger for their recent acceleration, necessitating its inclusion in future prognostic ice-sheet models. Yet, our present understanding of the process is limited, largely because of a lack of measurements. Most existing studies pertain to tidewater glaciers terminating in fjords with shallows sills that allow the inflow of a single oceanic water mass. Greenland’s fjords, on the other hand, are characterized by deep sills and a vigorous fjord/shelf exchange which allows both cold, fresh Arctic waters and warm, salty Atlantic waters, present on the shelf, to come in contact with the ice. As a result, submarine melting of outlet glaciers in Greenland occurs in strongly stratified waters. Here, we present oceanographic measurements from three major East Greenland glaciers, including winter measurements, which show that this stratification and, in particular, the density contrast between the Arctic and Atlantic waters, give rise to multiple overturning melt cells (as opposed to a single estuarine cell) at the ice-edge. The resulting heat transport and melt rate vary strongly with depth suggesting that the ocean waters around Greenland exert a strong control on the vertical profile of the glacier’s terminus.

Straneo, F.; Sutherland, D. A.; Hamilton, G. S.; Cenedese, C.; Stearns, L. A.

2010-12-01

269

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

270

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.

2013-04-01

271

Calibration of hydrological models in glacierized catchments  

NASA Astrophysics Data System (ADS)

Glacierized catchments are important source regions for water, and detailed knowledge of water availability is a prerequisite for good resource management strategies. Reliable and physically consistent runoff simulations become even more important if climate change impacts on alpine water resources are to be assessed. However, hydrological modeling of glacierized catchments is challenging ice melt which represents an additional source of water. Thus, adequate calibration strategies are needed especially in data scarce regions. An important question is how powerful a limited amount of data might be for model calibration. Accordingly, we analyzed the calibration power of limited discharge measurements, mass balance observations and the combination of by means of both Monte Carlo analyzes and multi-criteria model performance evaluation. Ensembles of 100 parameter sets were selected by evaluating the simulations based on a limited and discrete number of discharge measurements, glacier mass balance, and the combination of discharge and mass balance observations. Using these ensembles then the runoff was simulated and evaluated for the entire runoff series. The results for the Vernagtferner catchment and the Venter Ache catchment in Austria indicated that a single annual glacier mass balance observation contained useful information to constrain hydrological models. Combining mass balance observations with a few discharge data improved the internal consistency and significantly reduced the uncertainties compared to parameter set selections based on discharge measurements alone. Information on discharge was required for at least 3 days during the melting season to obtain good ensemble predictions.

Konz, Markus; Seibert, Jan; Braun, Ludwig; Burlando, Paolo

2010-05-01

272

Geology Fieldnotes: Glacier National Park, Montana  

NSDL National Science Digital Library

Glaciers have played an important role in shaping this park, which is part of the Rocky Mountain chain and shares a border with Canada's Waterton Lakes National Park. Information on this site includes park geology, visitor information, photographs, and links to other resources.

273

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

274

Response of Italian Glaciers to Climatic Variations  

NASA Astrophysics Data System (ADS)

The glaciers of the southern alpine slope have been investigated using a variety of different methods. The most common ones are: a) glacial inventories, which consist of an overall description, the geographical location, the classification, and the area and volumetric measurements. Four such inventories, all focussed on the Italian Alps, were carried out in 1925, 1958, 1976 and in 1989 [1, 2]. The first one is the result of the consultation of I.G.M. topographic maps, the second comes from measurements in the field, and the latter two come from aerophotogrammetric observations. The data base for the last one was provided by Italy Flight 1988; b) annual glacial campaigns, during which snout variations of the ablating tongue are measured. The operation, carried out by land surveys, refers to a sample of about 15% of the total population of glaciers, and it includes almost all the glacial bodies of major dimension and importance [3]; c) mass balances, with the calculation of the volumetric variation of the glacier in time and its role in the local climatic evolution. Only a few sample glaciers, located in different parts of the Alpine range, are taken into consideration.

Biancotti, A.; Motta, M.

275

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

276

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

1996-11-01

277

Progressive unpinning of Thwaites Glacier from newly identified offshore ridge: Constraints from aerogravity  

Microsoft Academic Search

A new bathymetric model from the Thwaites Glacier region based on IceBridge airborne gravity data defines morphologic features that exert key controls on the evolution of the ice flow. A prominent ridge with two distinct peaks has been identified 40 km in front of the present-day grounding line, undulating between 300-700 m below sea level with an average relief of

K. J. Tinto; R. E. Bell

2011-01-01

278

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

279

Holocene glacier fluctuations recorded in eastern Jotunheimen, southern Norway  

NASA Astrophysics Data System (ADS)

Sediment records from proglacial lake Russvatnet in eastern Jotunheimen central southern Norway comprise a complex combination of direct glacier-derived material from glaciers in the catchment as well as material from a variety of different episodic mass movement processes. To disentangle the sedimentary units we utilize a multi proxy approach analyzing sediment cores from Russvatnet and extract the glacier-derived signal from the complex multi-process record. The prevailing wintertime westerlies in the North Atlantic region leads to a strong west-east precipitation gradient across southern Norway, and the study area is, at present, located in the precipitation shadow of the Jotunheimen mountains. Comparing our reconstructed record of Holocene glacier activity with independent pollen-based reconstructions of temperature, we deduce the varying influence of temperature and winter precipitation on glacier fluctuations, and thus gain information on the dominating climate regime and strength/influence of the westerlies during the Holocene. During the Holocene thermal maximum (around 7000 cal. yr BP), the glacier signal is weak and glaciers were probably small. At about 4500 cal. yr BP glacier activity increased and results indicate a significant correlation between the reconstructed glacier fluctuations and summer temperatures over the following 2000 years (c. 4500-2500 cal. yr BP), arguably indicating a continental climate regime. After c. 2500 cal. yr BP there is no significant correlation between glacier variability and summer temperature, indicating a relative higher influence of a maritime climate regime, and a relative increase in winter precipitation.

Støren, E.; Dahl, S. O.

2012-04-01

280

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

281

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

282

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

283

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

284

New boundary conditions for the West Antarctic Ice Sheet: Subglacial topography of the Thwaites and Smith glacier catchments  

NASA Astrophysics Data System (ADS)

Airborne radar sounding over the Thwaites Glacier (TG) catchment and its surroundings provides the first comprehensive view of subglacial topography in this dynamic part of the West Antarctic Ice Sheet (WAIS) and reveals that TG is underlain by a single, broad basin fed by a dendritic pattern of valleys, while Smith Glacier lies within an extremely deep, narrow trench. Subglacial topography in the TG catchment slopes inland from a broad, low-relief coastal sill to the thickest ice of the WAIS and makes deep connections to both Pine Island Glacier and the Ross Sea Embayment enabling dynamic interactions across the WAIS during deglaciation. Simple isostatic rebound modeling shows that most of this landscape would be submarine after deglaciation, aside from an island chain near the present-day Ross-Amundsen ice divide. The lack of topographic confinement along TG's eastern margin implies that it may continue to widen in response to grounding line retreat.

Holt, John W.; Blankenship, Donald D.; Morse, David L.; Young, Duncan A.; Peters, Matthew E.; Kempf, Scott D.; Richter, Thomas G.; Vaughan, David G.; Corr, Hugh F. J.

2006-05-01

285

Glacier and climate change in Pakistan and Afghanistan  

NASA Astrophysics Data System (ADS)

Climate change predictions and water resource related issuesin Afghanistan and Pakistan have led to the need for detailed assessments and understanding of glacier fluctuations, and the determination of the dominant controlling factors governing glacier sensitivity to climate change. Consequently, we studied glacier fluctuations and the role of topography in an attempt to understand glacier fluctuations.Specifically we used ASTER imagery, Landsat ETM data, and an SRTM digital elevation model, together with Google Earth™ high-resolution imagery to examine terminus fluctuations, ice velocity variations, and local- and meso-scale topographic parameters that are related to irradiance variations, ablation, and glacial geomorphology.Multispectral satellite imagery were utilized to estimate advance and retreat rates, along with glacier profile velocities. Geomorphometric analysis was utilized to generateglacier altitude profiles of hypsometry, slope, curvature, and topographic shielding. Our results reveal that glacier response to climate change is highly variable in Pakistan, as many glaciers are advancing as well as retreating, while others exhibit a stationary terminus. It is important to note that advances in the Karakoram do not appear to be restricted to glaciers at high elevations, suggesting climate forcing. Glaciers in the Hindu Raj and Hindu Kush are retreating, with fewer glaciers advancing, indicating the possibility of a spatial trend from West to East in Pakistan. There is a dramatic diminution of Hindu Kush ice in Afghanistan. In the Karakoram, many new surging glaciers have been identified with flow velocities ranging from 200-1000 m/yr. Non- surging glaciers also exhibit relative high velocities there. Spatial patternsof relief appear to be associated with glacier debris cover, as snow/ice avalanchescontribute debris and ice mass. In addition, patterns of topographic shielding are highly variable, revealing variations in the diffuse-skylight irradiance component. Altitudinal slope and azimuth variations alsodictate significant variations in the direct-irradiance component. Consequently, glaciers within the same region receive very different amounts of surface irradiance, causing ablation variation that accounts for highly variable terminus fluctuations. Furthermore, altitudinal variations in glacier surface and topographic conditions can potentially be used to characterize glaciers and their dynamics, in terms of climate sensitivity and geomorphological influence. Collectively, our results suggest climate forcing in the Karakoram, and topographic control of glacier fluctuations.

Shroder, J.; Bishop, M.; Burgett, A.

2012-04-01

286

Sedimentological and Geochemical Aspects of Sediment and Water from Ten Alaskan Valley Glaciers.  

National Technical Information Service (NTIS)

The characteristics of superglacial sediments, suspended stream sediments, and meltwater from ten Alaskan valley glaciers were determined. The glaciers are eroding five different types of bedrock. Superglacial sediments from six glaciers are relatively un...

R. M. Slatt

1970-01-01

287

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

288

36 CFR 13.1132 - What types of commercial fishing are authorized in Glacier Bay?  

Code of Federal Regulations, 2010 CFR

...2010-07-01 false What types of commercial fishing are authorized in Glacier Bay? 13...Regulations-Glacier Bay National Park and Preserve Commercial Fishing § 13.1132 What types of commercial fishing are authorized in Glacier Bay?...

2010-07-01

289

36 CFR 13.1132 - What types of commercial fishing are authorized in Glacier Bay?  

Code of Federal Regulations, 2010 CFR

...2009-07-01 false What types of commercial fishing are authorized in Glacier Bay? 13...Regulations-Glacier Bay National Park and Preserve Commercial Fishing § 13.1132 What types of commercial fishing are authorized in Glacier Bay?...

2009-07-01

290

Bathymetry and ocean properties beneath Pine Island Glacier revealed by Autosub3 and implications for recent ice stream evolution (Invited)  

NASA Astrophysics Data System (ADS)

The Antarctic ice sheet, which represents the largest of all potential contributors to sea level rise, appears to be losing mass at a rate that has accelerated over recent decades. Ice loss is focussed in a number of key drainage basins where dynamical changes in the outlet glaciers have led to increased discharge. The synchronous response of several independent glaciers, coupled with the observation that thinning is most rapid over their floating termini, is generally taken as an indicator that the changes have been driven from the ocean. Some of the most significant changes have been observed on Pine Island Glacier, where thinning, acceleration and grounding line retreat have all been observed, primarily through satellite remote sensing. Even during the relatively short satellite record, rates of change have been observed to increase. Between 20th and 30th January 2009 the Autosub3 autonomous underwater vehicle was deployed from host ship RVIB Nathaniel B Palmer on six sorties into the ocean cavity beneath Pine Island Glacier. Total track length was 887 km (taking 167 hours) of which 510 km (taking 94 hours) were beneath the glacier. Some of the main aims were to map both the seabed beneath and the underside of the glacier and to investigate how warm Circumpolar Deep Water (CDW) flows beneath Pine Island Glacier and determines its melt rate. Among the instruments carried by Autosub-3 were a Seabird CTD, with dual conductivity and temperature sensors plus a dissolved oxygen sensor and a transmissometer, a multi-beam echosounder that could be configured to look up or down, and two Acoustic Doppler Current Profilers (ADCPs): an upward-looking 300 kHz instrument and a downward-looking 150 kHz instrument, providing a record of ice draft and seabed depth along the vehicle track. The ADCP data reveal an apparently continuous ridge with an undulating crest that extends across the cavity about 30km in from the current ice front. This topographic feature blocks CDW inflow from the inner cavity and impacts the degree to which it mixes with the cooler melt water outflow. Swath soundings indicate that this ridge was a former grounding line, while satellite imagery from the early 1970’s hints that Pine Island Glacier might still have been in contact with the ridge at that time. These findings suggest that the changes observed by satellite over the past two decades are the continuation of a longer period of grounding line retreat.

Jenkins, A.; Dutrieux, P.; McPhail, S.; Perrett, J.; Webb, A.; White, D.; Jacobs, S. S.

2009-12-01

291

Satellite Image Atlas of Glaciers of the World: North America  

NSDL National Science Digital Library

This atlas contains Landsat images, aerial photographs, selected maps, and other data, which provide a baseline look (from the mid-1970's) at glaciation in Canada, the conterminous United States, and Mexico. The Landsat false-color imagery includes ice fields, outlet glaciers, valley glaciers, and cirque glaciers, as well as ice caps. Ice features are grouped by location and a full description is available for each.

292

Arthropod colonisation of a debris-covered glacier  

Microsoft Academic Search

The largest debris-covered glacier in the Alps (Miage Glacier, western Italian Alps) has been studied to explore the effects of debris-cover extent and depth on the spatial distribution of ground-dwelling arthropods. A multitaxa approach has been used to compare taxa richness and distribution to the functional role (dietary habits) of each taxon along the glacier tongue. Spiders and ground beetles

Mauro Gobbi; Marco Isaia; Fiorenza De Bernardi

2011-01-01

293

Microbial Life beneath a High Arctic Glacier  

Microsoft Academic Search

The debris-rich basal ice layers of a high Arctic glacier were shown to contain metabolically diverse microbes that could be cultured oligotrophically at low temperatures (0.3 to 4°C). These organisms included aerobic chemoheterotrophs and anaerobic nitrate reducers, sulfate reducers, and methanogens. Colonies purified from subglacial samples at 4°C appeared to be predominantly psychrophilic. Aerobic chemoheterotrophs were metabolically active in unfrozen

MARK L. SKIDMORE; JULIA M. FOGHT; MARTIN J. SHARP

2000-01-01

294

Significant contribution to total mass from very small glaciers  

NASA Astrophysics Data System (ADS)

A single large glacier can contain tens of millions of times the mass of a small glacier. Nevertheless, very small glaciers (with area ?1 km2) are so numerous that their contribution to the world's total ice volume is significant and may be a notable source of error if excluded. With current glacier inventories, total global volume errors on the order of 10% are possible. However, to reduce errors to below 1% requires the inclusion of glaciers that are smaller than those recorded in most inventories. At the global scale, 1% accuracy requires a list of all glaciers and ice caps (GIC, exclusive of the ice sheets) larger than 1 km2, and for regional estimates requires a complete list of all glaciers down to the smallest possible size. For this reason, sea-level rise estimates and other total mass and total volume analyses should not omit the world's smallest glaciers. In particular, upscaling GIC inventories has been common practice in sea level estimates, but downscaling may also be necessary to include the smallest glaciers.

Bahr, D. B.; Radi?, V.

2012-07-01

295

West Antarctic Glacier Ice Flows and Elevation Change  

NASA Video Gallery

This animation shows glacier changes detected by ATM, ICESat and ice bridge data in the highly dynamic Amundsen Embayment of West Antarctica. Integrating these altimetry sources allows us to estimate surface height changes throughout the drainage regions of the most important glaciers in the region. We see large elevation changes at the coast on Thwaites glacier, at the center of the images, and large and accelerating elevation changes extending inland from the coast on Pine Island and Smith glaciers, to the left and right of the images, respectively.

Holly Zell

2011-11-03

296

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

297

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.

298

Passive microwave (SSM/I) satellite predictions of valley glacier hydrology, Matanuska Glacier, Alaska  

USGS Publications Warehouse

We advance an approach to use satellite passive microwave observations to track valley glacier snowmelt and predict timing of spring snowmelt-induced floods at the terminus. Using 37 V GHz brightness temperatures (Tb) from the Special Sensor Microwave hnager (SSM/I), we monitor snowmelt onset when both Tb and the difference between the ascending and descending overpasses exceed fixed thresholds established for Matanuska Glacier. Melt is confirmed by ground-measured air temperature and snow-wetness, while glacier hydrologic responses are monitored by a stream gauge, suspended-sediment sensors and terminus ice velocity measurements. Accumulation area snowmelt timing is correlated (R2 = 0.61) to timing of the annual snowmelt flood peak and can be predicted within ??5 days. Copyright 2008 by the American Geophysical Union.

Kopczynski, S. E.; Ramage, J.; Lawson, D.; Goetz, S.; Evenson, E.; Denner, J.; Larson, G.

2008-01-01

299

Glacier ice-volume modeling and glacier volumes on Redoubt Volcano, Alaska  

USGS Publications Warehouse

Assessment of ice volumes and hydrologic hazards on Redoubt Volcano began four months before the 1989-90 eruptions removed 0.29 cubic kilometer of perennial snow and ice from Drift glacier. A volume model was developed for evaluating glacier volumes on Redoubt Volcano. The volume model is based on third-order polynomial simulations of valley cross sections. The third-order polynomial is an interpolation from the valley walls exposed above glacier surfaces and takes advantage of ice-thickness measurements. The fortuitous 1989-90 eruptions removed the ice from a 4.5-kilometer length of Drift glacier, providing a unique opportunity for verification of the volume model. A 2.5-kilometer length was chosen in the denuded glacier valley and the ice volume was measured by digitally comparing two new maps: one derived from the most recent pre-eruption 1979 aerial photographs and the other from post-eruption 1990 aerial photographs. The measured volume in the reference reach was 99 x 106 cubic meters, about 1 percent less than was estimated by the volume model. The volume estimate produced by this volume model was much closer to the measured volume than was the volume estimated by other techniques. The verified volume model was used to evaluate the total volume of perennial snow and glacier ice on Redoubt Volcano, which was estimated to be 4.1?0.8 cubic kilometers. Substantial snow and ice covers on volcanoes exacerbate the hydrologic hazards associated with eruptions. The volume on Redoubt Volcano is about 23 times the volume that was present on Mount St. Helens before its 1980 eruption, which generated lahars and floods.

Trabant, Dennis C.; Hawkins, Daniel B.

1997-01-01

300

Cryospheric Dynamics in the Central Chilean Andes: Multi-decadal Reconstruction and Multi-annual Monitoring of Rock Glaciers and a Debris-covered Glacier  

Microsoft Academic Search

In the semiarid Central Chilean Andes at 33.5°S, permafrost is widely present above 3500-4000 m a.s.l., especially in the form of ice-rich debris accumulations such as rock glaciers. While Chilean rock glacier are among the largest known rock glaciers, glaciers are mostly restricted to the highest summits and are affected by a significant retreat during the last decades. Rock glaciers

X. Bodin; F. Rojas; A. Brenning

2009-01-01

301

A new glacier inventory on southern Baffin Island, Canada, from ASTER data: II. Data analysis, glacier change and applications  

NASA Astrophysics Data System (ADS)

In part II of the paper we discuss the results obtained with the methods presented in part I. The analysis is separated in three sections: (1) a statistical analysis of the glacier inventory data (year 2000) and their mutual dependencies derived from the ASTER scene, (2) change assessment between the mapped LIA glacier extent and glacier outlines from 1975 and 2000, and (3) application of both data sets to derive further quantities (like volume change). The statistical analysis includes 664 glaciers and icecaps ranging in size from 0.02 to 125 km². The frequency distribution of the count and area per size class reveals that glaciers from 1-10 (count: 239), 10-50 (36) and >50 km² (8) cover each one third of the total area (2416 km²), while the 381 glaciers < 1 km² account only for 5%. There is a slight aspect dependency of the area covered towards the northern sectors (W-N-E). The mean elevation is 992 m (+/- 199 m) with a slight dependence on aspect (200 m lower for north facing glaciers), minimum and maximum elevation do strongly depend on glacier size, and mean slope is 18 (increasing towards smaller glaciers). For a sample of 264 glaciers area changes between LIA-1975-2000 have been calculated. The relative area change since the LIA (around 1920) is -7.3% to 1975 and -12.5% to 2000, which gives a slight increase in the rate of area loss for the latter period. Length changes reach up to 3.3 km from LIA to 2000 and show a high correlation with original glacier length (r=0.8). Mean glacier elevation has increased by 50 m which is about one half of what is expected due to the temperature increase since the 1920s and indicate that glacier geometries are not yet in balance with the current climate. Neglecting that glaciers might not be in a steady-state yet, we calculated for a sample of 194 glaciers the mean mass loss by combining the calculated cumulative length changes with the topographic glacier parameters from the inventory, yielding a mean mass balance of about -0.11 m w.e. per year.

Paul, F.; Svoboda, F.

2009-04-01

302

Improved log(gf) Values Of Selected Lines In Mn I And Mn II For Studies Of Non-equilibrium Effects In Stellar Photospheres  

NASA Astrophysics Data System (ADS)

The work presents transition probabilities with very low uncertainties for a selected set of multiplets of Mn I and Mn II. Multiplets are chosen which are accessible to ground-based observation, are relatively unblended and unsaturated in stellar spectra and which are amenable to accurate branching fraction determination. These lab measurements provide a foundation for studies of non-LTE and 3-dimensional effects in stellar photospheres. We report on new radiative lifetime measurements for 22 levels of Mn I from the e8D, z6P, z6D, z4F, e8S and e6S multiplets and 3 levels of Mn II from the z5P multiplet using time-resolved laser-induced fluorescence on a slow atomic beam. New branching fractions for transitions from these levels, measured using a Fourier-transform spectrometer, are also reported. When combined, these measurements yield transition probabilities for 47 transitions of Mn I and 12 transitions of Mn II. Comparisons are made to data from the literature and to simple Russell-Saunders or LS theory. Final recommended values, which are weighted averages of all available modern measurements and in some cases LS theory, are given for the transition probabilities. These recommended log(gf) values are accurate to +/- 0.02 dex with high ( 2 sigma) confidence. The companion paper applies these new lab results to studies of departures from both LTE in Mn I and Saha equilibrium between Mn I and Mn II on a variety of stellar photospheres. This research is supported in part by NASA Grant NNX08AQ09G and NSF Grant AST-0907732.

Den Hartog, Elizabeth; Lawler, J. E.; Sobeck, J.; Sneden, C.; Cowan, J. J.; Asplund, M.

2010-01-01

303

Extending Glacier Monitoring into the Little Ice Age and Beyond  

NASA Astrophysics Data System (ADS)

Glaciers are among the best natural proxies of climatic changes and, as such, a key variable within the international climate observing system. The worldwide monitoring of glacier distribution and fluctuations has been internationally coordinated for more than a century. Direct measurements of seasonal and annual glacier mass balance are available for the past six decades. Regular observations of glacier front variations have been carried out since the late 19th century. Information on glacier fluctuations before the onset of regular in situ measurements have to be reconstructed from moraines, historical evidence, and a wide range of dating methods. The majority of corresponding data is not available to the scientific community which challenges the reproducibility and direct comparison of the results. Here, we present a first approach towards the standardization of reconstructed Holocene glacier front variations as well as the integration of the corresponding data series into the database of the World Glacier Monitoring Service (www.wgms.ch), within the framework of the Global Terrestrial Network for Glaciers (www.gtn-g.org). The concept for the integration of these reconstructed front variations into the relational glacier database of the WGMS was jointly elaborated and tested by experts of both fields (natural and historical sciences), based on reconstruction series of 15 glaciers in Europe (western/central Alps and southern Norway) and 9 in southern South America. The reconstructed front variation series extend the direct measurements of the 20th century by two centuries in Norway and by four in the Alps and in South America. The storage of the records within the international glacier databases guarantees the long-term availability of the data series and increases the visibility of the scientific research which - in historical glaciology - is often the work of a lifetime. The standardized collection of reconstructed glacier front variations from southern Norway, the western Alps and the southern Andes allows a direct comparison between different glaciers. It is a first step towards a worldwide compilation and free dissemination of Holocene glacier fluctuation series within the internationally coordinated glacier monitoring.

Nussbaumer, S. U.; Gärtner-Roer, I.; Zemp, M.; Zumbühl, H. J.; Masiokas, M. H.; Espizua, L. E.; Pitte, P.

2011-12-01

304

A note on the water budget of temperate glaciers  

NASA Astrophysics Data System (ADS)

In this note, the total dissipative melting in temperate glaciers is studied. The analysis is based on the notion that the dissipation is determined by the loss of potential energy due to the downward motion of mass (ice, snow, meltwater and rain). A mathematical formulation of the dissipation is developed and applied to a simple glacier geometry. In the next step, meltwater production resulting from enhanced ice motion during a glacier surge is calculated. The amount of melt energy available follows directly from the lowering of the centre of gravity of the glacier. To illustrate the concept, schematic calculations are presented for a number of glaciers with different geometric characteristics. Typical dissipative melt rates, expressed as water-layer depth averaged over the glacier, range from a few centimetres per year for smaller glaciers to half a metre per year for Franz Josef Glacier, one of the most active glaciers in the world (in terms of mass turnover). The total generation of meltwater during a surge is typically half a metre. For Variegated Glacier a value of 70 cm is found, for Kongsvegen 20 cm. These values refer to water layer depth averaged over the entire glacier. The melt textit{rate} depends on the duration of the surge. It is generally an order of magnitude greater than water production by `normal' dissipation. On the other hand, the additional basal melt rate during a surge is comparable in magnitude with the water input from meltwater and precipitation. This suggests that enhanced melting during a surge does not grossly change the total water budget of a glacier. Basal water generated by enhanced sliding is an important ingredient in many theories of glacier surges. It provides a positive feedback mechanism that actually makes the surge happen. The results found here suggest that this can only work if water generated by enhanced sliding accumulates in a part of the glacier base where surface meltwater and rain have no or very limited access. This finding seems compatible with the fact that, on many glaciers, surges are initiated in the lower accumulation zone.

Oerlemans, J.

2013-09-01

305

Glaciohydraulic Supercooling and Basal Ice Formation at Outlet Glaciers of Vatnajökull and Oraefajokull, Iceland  

NASA Astrophysics Data System (ADS)

The hydrology of glaciers is affected by the subglacial environment and in particular overdeepenings that may result in supercooling of subglacial waters and the entrainment of debris into basal ice. Warm-based outlet glaciers of Vatnajökull and Oraefajökull, Iceland, are often characterized by overdeepenings in their terminal regions and up to 100-m long exposures of meters-thick, debris-laden (4 to 35% by vol.) basal zones. During the period 2002 to 2005, we collected bulk samples (300g) of the basal ice, englacial ice, melt water and frazil ice from a number of these outlet glaciers to evaluate probable origins of the basal zone and thus the role of basal topography and hydrology in its generation. Analyses of the 18O and D content show delta 18O and D values for the basal ice generally plot below the meteoric water line and are less negative then values for englacial ice. The difference between the mean delta 18O values of the basal and englacial ice is approximately 2.41 per mil, while the mean delta D values differ by about 11.12 per mil. The delta 18O and delta D values of frazil ice also generally plot below the meteoric water line and overlap those of the basal ice. Mean delta 18O values of frazil ice and meltwater differ by approximately 1.93 per mil, while the mean deuterium values differ by about 13.16 per mil. Little difference exists between the mean delta 18O and D values of meltwater and englacial ice. Tritium measured in basal ice ranges from 1.9 to 6.1 TU and averages 2.9 TU, whereas in englacial ice it is essentially 0. Both the physical properties and isotopic composition of the basal zone ice and debris in the outlet glaciers sampled is consistent with a glaciohydraulic supercooling origin resulting from subglacial discharge out of overdeepenings.

Lawson, D. E.; Larson, G. J.; Evenson, E. B.; Knudsen, O.

2007-12-01

306

The Equilibrium and Stability of the Multipole  

Microsoft Academic Search

The equilibrium and linear ballooning mode stability of a plasma in an axisymmetric closed field line device such as the multipole is investigated. Two models of the plasma are used, a kinetic model and an ideal MHD model, and the results are compared. Numerical calculations are made of the equilibrium and of ballooning mode stability criteria in the Wisconsin Levitated

Michael Wallace Phillips

1982-01-01

307

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

308

Localized basal motion of a polythermal Arctic glacier: McCall Glacier, Alaska, USA  

NASA Astrophysics Data System (ADS)

We analyzed the ice flow of McCall Glacier, Alaska, USA, by numerical glacier modeling and radio-echo sounding (RES). Model experiments were carried out with a higher-order numerical ice-flow model, and results were validated with measurements of annual ice velocities and compared with previous estimates of ice-flow dynamics. During the 2003 summer campaign, detailed RES measurements were carried out along the central flowline of the ablation area with a 5 MHz (central frequency) ice-penetrating radar, where 10 m ice temperatures are approximately -7.5°C. The bed reflection power (BRP) beneath this central flowline abruptly increases at one location area, followed by a slow decrease down-glacier. The model experiments show that basal sliding (<50%) is necessary to match the observed annual mean surface velocities in the area that is characterized by high BRP values. However, when thermomechanical effects are taken into account, a temperate basal ice layer is apparent in the ablation area, which locally softens the ice and can explain to a certain extent the anomalous flow field. The model results confirm that the present temperature field is a remnant of a larger glacier geometry that was near steady state before the onset of enhanced surface thinning in the 1970s.

Pattyn, Frank; Nolan, Matt; Rabus, Bernhard; Takahashi, Shuhei

309

Anisotropy of the Reflected Radiation Field Over Melting Glacier Ice  

Microsoft Academic Search

In this article we analyze the anisotropy of the reflected radiation field over melting glacier ice using 118 ground-based radiance measurements in Landsat TM Bands 2 and 4. The measurements were carried out on the tongue of the Morteratschgletscher, Switzerland. On the basis of directional measurements several bidirectional reflectance distribution functions (BRDFs) were derived for dirty and clean glacier ice

Wouter H. Knap; Carleen H. Reijmer

1998-01-01

310

Jökulhlaups: A reassessment of floodwater flow through glaciers  

Microsoft Academic Search

In glaciated catchments, glacier-generated floods (Jökulhlaups) put human activity at risk with large, sporadic Jökulhlaups accounting for most flood-related fatalities and damage to infrastructure. In studies of Jökulhlaup hydrodynamics the view predominates that floodwater travels within a distinct conduit eroded into the underside of a glacier. However, some Jökulhlaups produce subglacial responses wholly inconsistent with the conventional theory of drainage.

Matthew J. Roberts

2005-01-01

311

JÖkulhlaups: A reassessment of floodwater flow through glaciers  

Microsoft Academic Search

In glaciated catchments, glacier-generated floods (jökulhlaups) put human activity at risk with large, sporadic jökulhlaups accounting for most flood-related fatalities and damage to infrastructure. In studies of jökulhlaup hydrodynamics the view predominates that floodwater travels within a distinct conduit eroded into the underside of a glacier. However, some jökulhlaups produce subglacial responses wholly inconsistent with the conventional theory of drainage.

Matthew J. Roberts

2005-01-01

312

Dynamics of tidewater glaciers: comparison of three models  

Microsoft Academic Search

A minimal model of a tidewater glacier based solely on mass conservation is compared with two one-dimensional numerical flowline models, one with the calving rate proportional to water depth, and the other with the flotation criterion as a boundary condition at the glacier terminus. The models were run with two simplified bed geometries and two mass-balance formulations. The models simulate

F. M. Nick; J. Oerlemans

2006-01-01

313

Melting on glaciers: environmental controls examined with orbiting radar  

Microsoft Academic Search

Direct, in situ measurements of glacier mass balance are expensive. Remote sensing would be an attractive alternative if remotely observable quantities could be interpreted in terms of mass gain or loss. A system developed recently for the analysis of Radarsat browse images is used here to explore temporal and environmental controls of melting on glaciers on Axel Heiberg Island, Nunavut,

J. Graham Cogley; M. A. Ecclestone; D. T. Andersen

2001-01-01

314

What influences climate and glacier change in southwestern China?  

Microsoft Academic Search

The subject of climate change in the Tibetan Plateau (TP) and Himalayas has taken on increasing importance because of the availability of water resources from their mountain glaciers (Immerzeel et al 2010). Many of the glaciers over these regions have been retreating, while some are advancing and stable (Yao et al 2004, Scherler et al 2011). Other studies report that

Teppei J. Yasunari

2011-01-01

315

Hydrologic monitoring of supercooled meltwater from Icelandic glaciers  

NASA Astrophysics Data System (ADS)

Knowledge of how glaciers entrain sediment is central to understanding processes of glacier movement and products of glacial sediment deposition. Previous work has shown that if the total hydraulic potential of subglacial meltwater increases more rapidly than the resulting mechanical energy can be transformed into sensible heat, then supercooling and ice growth will result. This process causes frazil ice to grow onto adjacent glacier ice, which acts to trap sediment in flowing meltwater eventually producing sedimentary inclusions within glacier ice. Supercooling has been recognised as a sediment entrainment mechanism at glaciers in Alaska, and more recently at several temperate Icelandic glaciers. Here we present short-period temperature measurements and field evidence of glaciohydraulic supercooling from three Icelandic glaciers. Temperature measurements demonstrate that supercooling occurs over a range of hydrological conditions and that the process does not operate continuously at all instrumented sites. Measurements of supercooling during a small jökulhlaup are also presented. Progressive accretion of supercooled meltwater creates sediment-laden ice exposures adjacent to active artesian vents. Understanding controls on the efficacy and pervasiveness of hydraulic supercooling is important for decoding the sedimentary record of modern and ancient glaciers and ice sheets.

Tweed, Fiona S.; Roberts, Matthew J.; Russell, Andrew J.

2005-11-01

316

36 CFR 7.3 - Glacier National Park.  

Code of Federal Regulations, 2010 CFR

...Medicine entrance to Two Medicine Lake; from West Glacier entrance to the Camas Entrance; U.S. Highway 2 from Walton to Java; and the Going-to-the-Sun Road from West Glacier entrance to Lake McDonald Lodge and from St. Mary entrance to...

2010-07-01

317

Mass fluxes and dynamics of Moreno Glacier, Southern Patagonia Icefield  

Microsoft Academic Search

Accumulation, ablation, calving, and flow dynamics of Moreno Glacier, one of the main outlet glaciers of the Southern Patagonia Icefield, were studied based on field campaigns and on spaceborne radar imagery acquired by SIR-C\\/X-SAR. Ice velocities and ablation were measured through two summers and one winter. The ice depth was sounded seismically at a transect 8 km above the calving

Helmut Rott; Martin Stuefer; Andreas Siegel; Pedro Skvarca; Alfons Eckstaller

1998-01-01

318

Widespread acceleration of tidewater glaciers on the Antarctic Peninsula  

Microsoft Academic Search

Over the last half century, the Antarctic Peninsula (AP) has been among the most rapidly warming regions on Earth. This has led to increased summer snowmelt, loss of ice shelves, and retreat of 87% of marine and tidewater glacier fronts. Tidewater-glacier flow is sensitive to changes in basal water supply and to thinning of the terminus, and faster flow leads

H. D. Pritchard; D. G. Vaughan

2007-01-01

319

Low-latitude mountain glacier evidence for abrupt climate changes  

Microsoft Academic Search

Clear evidence that a widespread warming of Earth's climate system is now underway comes from low latitude mountain glaciers. Proxy temperature histories reconstructed from ice cores, and the rapidly accelerating loss of both the total ice area and ice volume on a near global scale suggest that these glaciers responding to increasing rates of melting. In situ observations reveal the

L. G. Thompson; E. S. Mosley-Thompson; P. Lin; M. E. Davis; T. A. Mashiotta; H. H. Brecher

2004-01-01

320

Calving on tidewater glaciers amplified by submarine frontal melting  

NASA Astrophysics Data System (ADS)

While it has been shown repeatedly that ocean conditions exhibit an important control on the behaviour of grounded tidewater glaciers, modelling studies have focused largely on the effects of basal and surface melting. Here, a finite-element model of stresses near the front of a tidewater glacier is used to investigate the effects of frontal melting on calving, independently of the calving criterion used. Applications of the stress model to idealized scenarios reveal that undercutting of the ice front due to frontal melting can drive calving at up to ten times the mean melt rate. Factors which cause increased frontal melt-driven calving include a strong thermal gradient in the ice, and a concentration of frontal melt at the base of the glacier. These properties are typical of both Arctic and Antarctic tidewater glaciers. The finding that frontal melt near the base is a strong driver of calving leads to the conclusion that water temperatures near the bed of the glacier are critically important to the glacier front, and thus the flow of the glacier. These conclusions are robust against changes in the basal boundary condition and the choice of calving criterion, as well as variations in the glacier size or level of crevassing.

O'Leary, M.; Christoffersen, P.

2012-08-01

321

Calving on tidewater glaciers amplified by submarine frontal melting  

NASA Astrophysics Data System (ADS)

While it has been shown repeatedly that ocean conditions exhibit an important control on the behaviour of grounded tidewater glaciers, modelling studies have focused largely on the effects of basal and surface melting. Here, a finite-element model of stresses near the front of a tidewater glacier is used to investigate the effects of frontal melting on calving, independently of the calving criterion used. Applications of the stress model to idealized scenarios reveal that undercutting of the ice front due to frontal melting can drive calving at up to ten times the mean melt rate. Factors which cause increased frontal melt-driven calving include a strong thermal gradient in the ice, and a concentration of frontal melt at the base of the glacier. These properties are typical of both Arctic and Antarctic tidewater glaciers. The finding that frontal melt near the base is a strong driver of calving leads to the conclusion that water temperatures near the bed of the glacier are critically important to the glacier front, and thus the flow of the glacier. These conclusions are robust against changes in the basal boundary condition and the choice of calving criterion, as well as variations in the glacier size or level of crevassing.

O'Leary, M.; Christoffersen, P.

2013-01-01

322

Sensitivity and response of Bhutanese glaciers to atmospheric warming  

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. However, the most conservative results indicate that, even if climate were to remain at the present-day mean values, almost 10% of Bhutan's glacierized area would vanish and the meltwater flux would drop by as much as 30%. Under the conservative scenario of an additional 1°C regional warming, glacier retreat is going 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, Summer; Schaefer, Joerg M.; Burgener, Landon K.; Koenig, Lora S.; Tsering, Karma; Cook, Edward R.

2012-10-01

323

Dominant Bacteria and Biomass in the Kuytun 51 Glacier ? †  

PubMed Central

Dominant bacteria in the different habitats in the Kuytun 51 Glacier were investigated using a 16S rRNA gene clone library sequencing technique. Results showed diverse bacteria on the glacial surface, with the dominant phyla being Proteobacteria, Cyanobacteria, and Bacteroidetes. UniFrac data showed distinct community patterns between the Kuytun and Himalayan Rongbuk glaciers.

Xiang, Shu-Rong; Shang, Tian-Cui; Chen, Yong; Jing, Ze-Fan; Yao, Tandong

2009-01-01

324

Sierra Nevada Rock Glaciers: Biodiversity Refugia in a Warming World?  

Microsoft Academic Search

Rock glaciers and related periglacial rock-ice features (RIFs) are common landforms in high, dry mountain ranges, and widely distributed throughout canyons of the Sierra Nevada, California, USA (Millar & Westfall, in press). Due to insulating rock carapaces, active rock glaciers (ice-cored) have been documented to maintain ice longer, and thus contribute to more enduring hydrologic output, under past warming climates

C. I. Millar; R. D. Westfall

2007-01-01

325

AK-03 ALASKA: AK-03 Columbia Glacier "Cliff" (Narrated)  

NSDL National Science Digital Library

A video from the Extreme Ice Survey in which Dr. Tad Pfeffer and photographer Jim Balog discuss the dynamics of the Columbia glacier's retreat in recent years through this time-lapse movie. Key point: glacier size is being reduced not just by glacial melting but due to a shift in glacial dynamics brought on by climate change.

Balog, James; Pfeffer, Tad; Survey, Extreme I.

326

Large fluctuations in speed on Greenland's Jakobshavn Isbræ glacier  

Microsoft Academic Search

It is important to understand recent changes in the velocity of Greenland glaciers because the mass balance of the Greenland Ice Sheet is partly determined by the flow rates of these outlets. Jakobshavn Isbræ is Greenland's largest outlet glacier, draining about 6.5 per cent of the ice-sheet area, and it has been surveyed repeatedly since 1991 (ref. 2). Here we

Ian Joughin; Waleed Abdalati; Mark Fahnestock

2004-01-01

327

Reanalysis of the USGS Alaskan benchmark glacier dataset  

NASA Astrophysics Data System (ADS)

Resolving the relationship between glacier surface-forcing (climate) and glacier geometry changes is accomplished through mass-balance estimates which can be made with remote sensing methods or field-based observations. The small scale of Alaskan glaciers has prevented remote sensing methods until recently, and field data are essential for validating new techniques. Field data provide the only long duration record that can be studied with respect to climate. The United States Geological Survey has maintained a 44-year mass-balance program at Alaska’s Gulkana Glacier and Wolverine Glacier. We have reanalyzed the Alaskan benchmark glaciers mass balance time series so that all data are treated similarly and systematically. Both glaciers are undergoing sustained mass loss with an increasing rate in recent years. However, the magnitude of the calculated loss depends on the number and location of the data collection sites. We explore the sensitivity of the glacier-wide balance estimates to the method of integration used on the necessarily point data. The robustness of the balance is strengthened with use of independent photogrammetric measurements.

van Beusekom, A. E.; O'Neel, S.; March, R. S.; Sass, L. C.

2010-12-01

328

Global distributions of glacier properties: A stochastic scaling paradigm  

Microsoft Academic Search

Many problems in global climate and Earth systems science require knowledge of regional- or global-scale distributions of glacier properties, which includes mass balance, ice velocity, flux, thickness, volume, and surface area, among others. With roughly 160,000 glaciers worldwide, obtaining information on the global probability distributions of most ice properties is expensive and often infeasible. Only surface area distributions are relatively

David B. Bahr

1997-01-01

329

Global distributions of glacier properties: A stochastic scaling paradigm  

Microsoft Academic Search

Many problems in global climate and Earth systems science require knowledge of regional- or global-scale distributions of glacier properties, which includes mass balance, ice velocity, flux, thickness, volume, and surface area, among others. With roughly 160,000 glaciers worlwide, obtaining information on the global probability distributions of most ice properties is expensive and often infeasible. Only surface area distributions are relatively

David B. Bahr

1997-01-01

330

Source-to-sink study of erosion at Grinnell Glacier, Glacier National Park, Montana  

NASA Astrophysics Data System (ADS)

Cirques have been used as proxies for past climatic conditions, yet the detailed physical processes that act to form cirques remain poorly understood. In July 2005, we continued a field study at Grinnell Glacier in Montana to examine the relevant glacial and geomorphic processes driving cirque development. As in July 2004, we installed a grid of nine velocity poles to measure ice motion using differential GPS, and several temperature sensors and snow stakes to monitor snow and ice melt across Grinnell Glacier. We supplemented these data with time-series of 15-minute measurements of snow and ice melt recorded by an ultrasonic ranging sensor. Air temperature and snowmelt correlate well, with diurnal fluctuations in melt corresponding to diurnal temperature fluctuations. The ultrasonic sensor recorded an average melt rate of snow over the 24-day period of observation of 3.5 cm d-1 (water equivalent), with average daily rates as high as 6 cm d-1. Melt rates declined as snowmelt revealed debris-covered ice below. These observations suggest that debris-cover may play an important role in insolating Grinnell Glacier from summer melt, particularly in coming decades as debris concentrations are expected to rise. Average velocity near the center of the glacier, where ice thickness was ~44 meters, was ~5 cm d-1 during this time. Our measurements span the period of earthquake activity that occurred in Montana July 25-27. Iceberg calving was associated with the ground shaking. Downstream from Grinnell Glacier, we collected 5 lake cores to document sedimentation rates in Swiftcurrent and Josephine Lakes, source areas for erosion in the drainage basin, and environmental change due to forest fires and changes in vegetation. Two cores from Swiftcurrent Lake and one core from Lake Josephine are >5 m in length, providing us one of the first high-resolution lake records in Glacier National Park. While the core analysis remains a work-in-progress, preliminary work indicates that the cores document changes in charcoal abundance, organic matter, and sedimentation rates during the Quaternary. Future work will focus on determining erosion rates of Grinnell Glacier based on sedimentation rates in downstream sediment cores.

Riihimaki, C. A.; MacGregor, K. R.

2005-12-01

331

Mapping the World's glaciers from space: Results from the ESA project GlobGlacier  

NASA Astrophysics Data System (ADS)

The ESA project GlobGlacier aims at making a substantial contribution to current efforts of mapping the World's glaciers from satellite data using (semi-)automated techniques. For this purpose a number of key regions have been identified in close cooperation with the user group of the project and based on a set of criteria (e.g. filling the gaps in current inventories, or their potential contribution to sea-level rise). Apart from glacier outlines and terminus positions, a couple of further data products are created by the project: late summer snowlines (LSSL), topographic information, elevation changes and velocity fields. While most of the products are created from optical sensors like Landsat TM/ETM+ as available from the glovis.usgs.gov website, some of them will also utilize radar sensors and LIDAR data. The inventory data are mainly created for the year 2000 (+/- a few years) to have a good temporal match with the SRTM DEM. In selected regions, multi-temporal data sets will be used for change assessment. The new data sets will be integrated in the existing databases of GLIMS and WGMS. With this contribution we provide an overview of the current status of the project as well as its major achievements. Outlines for several thousand glaciers have already been created in many of the key regions. This includes parts of Alaska (Chigmit Mts., Kenai Peninsula, Chugach Mts.), Arctic Canada (Devon, Bylot, Baffin Island), West Greenland (Disko Island, Nuussuaq, Svartenhuk), Norway (Svartisen, Jostedalsbreen), India (Kashmir) and the European Alps. The products LSSL, topography and elevation changes were also produced for several hundred glaciers and surface velocity fields have been derived for more than 50 glaciers from radar and optical sensors. Topographic information for each glacier is obtained from freely available DEMs (e.g. SRTM, ASTER GDEM) and elevation changes are derived from DEM differencing as well as repeat track altimetry using the GLAS and RA-2 instruments. Some of the key regions act as integration sites where more than one product is created.

Paul, Frank

2010-05-01

332

Mass balance modelling of a debris cover glacier: the case study of Miage Glacier, Italy  

NASA Astrophysics Data System (ADS)

The growing interest in the response of glaciers to a changing climate has put large attention on the development of models of glaciers response, and mass balance models in particular, and efforts are been made to improve their accuracy and predictive skills. A key component that is receiving increasing attention is the role played by debris cover on the response of glaciers. Thin layers of debris enhance melt by increasing absorption of shortwave radiation, while thicker covers reduce melt by insulating it. This has an effect on the surface energy balance, melt rates under debris, runoff production, mass balance and ultimately glacier flow. An accurate representation of the effect of debris seems therefore important, also in view of the significant increase of the debris cover extent over glaciers associated to a warming climate. Distributed debris energy-balance (EB) models have been recently developed to account for the melt rate enhancing/reduction due to a thin/thick debris layer, respectively. Application of EB models at the glacier and regional scale however is associated with an increase of computational efforts and large uncertainties related to the spatial changes in the debris cover properties (thickness and conductivity) as well as extrapolation of the input meteorological data such as wind, temperature and radiative fluxes. In this paper we present a model for simulations of past and future mass balance of debris covered glaciers that relies on more limited input data than required by a full EB model. The model is tested against simulations from an EB model. The new debris enhanced temperature-index model (DETI) accounts for the debris thickness feedback (Ostrem curve) through a parameterisation that includes variable debris thickness. The model is developed and then used for continuous simulations on the extensively debris-covered Miage Glacier, Italy. First, we run the distributed debris energy balance model for the ablation season 2005, when all the meteorological variables required as input to the physically based approach are available. To evaluate the performance of the empirical approach, we then compare the energy balance model outputs against the simulations of the new DETI model. The model outputs are also validated against ablation stake readings at 22 locations. Second, the empirical approach is run for the period 2005-2011 and continuous time series of glacier mass balance are compared to those obtained with the same empirical approach with simple reduction coefficients. Accumulation is modelled by spatially distributing precipitation with a gradient and accounting for redistribution of snow by gravity. Our main result is that an empirical approach accounting for the warming/insulating effect as a function of the debris thickness, as the DETI model, is able to simulate the glacier melt rate similarly to the more complex energy-balance model. We also show a clear difference with respect to the model with simple reduction parameters that does not take into account the variable effect of debris thickness.

Carenzo, Marco; Pellicciotti, Francesca; Mabillard, Johan; Reid, Tim; Brock, Ben; Burlando, Paolo

2013-04-01

333

Glacier Erosion and Response to Climate in Chilean Patagonia  

NASA Astrophysics Data System (ADS)

A vibrant dimension in current research on landscape evolution is the potential impact of climate change on erosion rates due to differences in efficiency of glacial and non-glacial erosion processes. The climate-sensitive rate and spatial distribution of erosion can be as important as the tectonic environment in determining the development of mountain ranges. To evaluate properly how glacial erosion influences orogenic processes and reflects climate variability, it is necessary to understand how ice dynamics control erosion rates. The Patagonian Andes are a unique laboratory for documenting glacial erosion in a range of precipitation and thermal regimes, as zonal atmospheric circulation in the region creates strong latitudinal gradients. We will present relevant findings from two tidewater glaciers in Chilean Patagonia: San Rafael glacier, which drains the northern portion of the North Patagonian Icefield (46.6S, 74W), and Marinelli glacier, the largest glacier in the Cordillera Darwin of Tierra del Fuego (54.6S, 69W). Both glaciers have been in steady retreat during the latter half of the 20th century, and both calve into a fjord or lagoon, which provides an efficient trap for the sediment eroded by the glacier and deposited at the calving front. The reconstructed flux of ice into the glaciers is compared to the retreat of the ice fronts and to the sediment flux to examine the influence of ice dynamics on the rate of glacier erosion. NCEP-NCAR Reanalysis climate data, adjusted to local conditions by correlation with automatic weather stations installed at the glacier termini and coupled to a model of orographic enhancement of precipitation over the glacier basin, were used to reconstruct the daily precipitation input into and ablation output from the glaciers during the last 50 years. The sediment flux out of the glaciers during this period was calculated from acoustic reflection profiles of the sediments accumulated in the proglacial fjords, and used to infer erosion rates. Preliminary results indicate 1) that high rates of retreat of the ice front occur during years in which the total input of snow into the glacier is balanced by the total ablation, and hence the residual flux of ice at the terminus is insufficient to compensate for the calving, and 2) that the highest basin- wide erosion rates reflect years in which total ice accumulation is lower and retreat rates are high. Interestingly, basin-wide erosion rates from these glaciers are up to an order of magnitude higher than long- term exhumation rates derived from detrital apatite thermochronometry in the basins, indicating that current rates of erosion far exceed long-term rates, and are reflective of periods of warming climate and enhanced glacial retreat.

Koppes, M.; Hallet, B.; Stewart, R.

2006-12-01

334

Was there a 1930's Meltdown of Greenland Glaciers?  

NASA Astrophysics Data System (ADS)

While climate warming is suggested to have caused acceleration of Greenland Ice Sheet outlet glaciers, recent warming, however, is not without precedent. Examination of Greenland's meteorological stations confirms that 1920s through 1940s surface-air temperature anomalies were at least as equal in magnitude to the recent "global warming" decade, yet observations have not yet been compiled to confirm a similar glacier response. Mining The Ohio State University Libraries, this work compiles historical observations of glacier front positions and surface velocities from maps, photographs and other documentary evidence from mid 19th century Arctic expeditions. Of the glaciers reviewed, an acceleration and retreat indeed occurred between 1920 and 1940. The research put forth is thus consistent with a dynamical response in Greenland's outlet glaciers to the "roaring twenties" warming.

Box, J. E.; Herrington, A.

2007-12-01

335

The physical basis of glacier volume-area scaling  

USGS Publications Warehouse

Ice volumes are known for only a few of the roughly 160,000 glaciers worldwide but are important components of many climate and sea level studies which require water flux estimates. A scaling analysis of the mass and momentum conservation equations shows that glacier volumes can be related by a power law to more easily observed glacier surface areas. The relationship requires four closure choices for the scaling behavior of glacier widths, slopes, side drag and mass balance. Reasonable closures predict a volume-area scaling exponent which is consistent with observations, giving a physical and practical basis for estimating ice volumes. Glacier volume is insensitive to perturbations in the mass balance scaling, but changes in average accumulation area ratios reflect significant changes in the scaling of both mass balance and ice volume. Copyright 1997 by the American Geophysical Union.

Bahr, D. B.; Meier, M. F.; Peckham, S. D.

1997-01-01

336

Exploring tidewater glacier retreat using past and current observations at Columbia Glacier, Alaska. (Invited)  

NASA Astrophysics Data System (ADS)

Since fulfilling Austin Post’s prediction of impending retreat in the late 1970s, Columbia Glacier has repeatedly surprised both casual and careful observers with its ability for rapid change. Over the last three decades, Columbia Glacier has lost approximately 18 km of its original 66 km length, while thinning by approximately 50% at the present terminus. The total ice volume lost to the Gulf of Alaska Estimates upwards of 120 km3 constrain the total ice volume lost to the Gulf of Alaska. Recently, the terminus supported a ~1.5 km long floating tongue for over than a year, contradicting the common assumption that the mechanical properties of temperate ice prohibit flotation over sustained time intervals. The rich history of study offers an opportunity to better understand tidewater glacier retreat, and a valuable analog to the dynamic instability underway at several ice sheet outlet glaciers. Current research aims to improve processing resolution of existing aerial photographic data, while complimenting the 30-year photogrammetric record with a suite of field observations. Recent instrumentation includes: oblique time lapse and still imagery, semi-permanent GPS, airborne radar, mass balance, passive seismology and LiDAR. This presentation will focus on innovative methods developed in recent field seasons, sharing insight each has provided into the retreat process . 1The Columbia Glacier Consortium consists of: Fabian Walter (SIO), Kenichi Matsuoka (NPI), Ben Smith (UW), Ethan Welty (CU-Boulder), Chris Larsen (UAF), Dave Finnegan (CRREL), Dan McNamara (USGS), Yushin Ahn (OSU), Julie Markus (OSU), Adam LeWinter (EIS).

O'Neel, S.; Pfeffer, W. T.; Howat, I. M.; Conway, H.; Columbia Glacier Consortium

2010-12-01

337

Re-establishing seasonal mass balance observation at Abramov Glacier, Kyrgyzstan, from 1968 - 2012  

NASA Astrophysics Data System (ADS)

The Abramov Glacier, located in the Pamir Alay in Kyrgyzstan, was subject to intense studies in the frame of various scientific programs under the former USSR. With the breakdown of the Soviet Union, the monitoring was abruptly abandoned in the late nineties. Well documented and continuous seasonal mass balance observations are available for 1968-1994. However, some inconsistencies between different publications lead to in-homogeneous data sets. Recently, the project CATCOS (Capacity Building and Twinning for Climate Observing Systems) was launched, aiming among other goals to re-establish mass balance observation on selected glaciers in Kyrgyzstan. At Abramov Glacier, a new stake network, an automatic weather station (AWS) and two automatic terrestrial cameras with instantaneous data transfer over satellite were installed in 2011. Measurements were repeated and intensified in 2012 and will be subject of a third field campaign in summer 2013. A complete re-analysis of the long-term mass balance series from 1968 to 1994 delivers corrected mass balance data for Abramov Glacier. To homogenize in-situ mass balance records, a spatially distributed mass balance model driven with local daily temperature and precipitation data was calibrated to each seasonal mass balance survey. The model resolves seasonal mass-balance measurements to a daily timescale and performs spatial inter- and extrapolation of data points based on a consistent algorithm, taking into account the principal factors of mass balance distribution. Summarizing the annually optimized parameters over the entire study period provides a robust model parameter set for years with less extensive direct measurements. From 1994 to 2011, neither direct point measurements nor meteorological data are available. In order to run the calibrated model developed for the 1960's to 90's, climate input variables were taken from bias corrected Re-analysis data (NCEP/NCAR and JRA). Evaluation of the model results was achieved through observations of snow-lines on Landsat images throughout each mass balance year. Automatic cameras, installed in August 2011 took repeated oblique photographs of the glacier on a daily basis. Snow-line evolution was analysed on the orthorectified and georeferenced images and complementary on Landsat imagery. Meteorological variables collected in 2012 from the newly installed AWS were used to run the calibrated mass balance model for the hydrological year 2011/2012. All available mass balance point measurements were used for optimization. Evaluation against snow-line observations on terrestrial photographs and satellite images are promising.

Barandun, Martina; Huss, Matthias; Azisov, Erlan; Gafurov, Abror; Hoelzle, Martin; Merkushkin, Aleksandr; Salzmann, Nadine; Usubaliev, Ryskul

2013-04-01

338

Worldwide dataset of glacier thickness observations compiled by literature review  

NASA Astrophysics Data System (ADS)

The volume of glaciers and ice caps is still poorly known, although it is expected to contribute significantly to changes in the hydrological cycle and global sea level rise over the next decades. Studies presenting worldwide estimations are mostly based on modelling and scaling approaches and are usually calibrated with only few measurements. Direct investigations of glacier thickness, a crucial parameter for ice volume calculations, are rather sparse but nevertheless available from all around the globe. This study presents a worldwide compilation of glacier thickness observation data. Literature review revealed mean and/or maximum thickness values from 442 glaciers and ice caps, elevation band information and point measurements for 10 and 14 glaciers, respectively. Resulting in a dataset containing glaciers and ice caps with areas ranging from smaller than 0.1 km2 (e.g. Pizolgletscher, Switzerland) to larger than 10'000 km2 (e.g. Agassiz Ice Cap, Canada), mean ice thicknesses between 4 m (Blaueis, Germany) and 550 m (Aletschgletscher, Switzerland) and 64 values for ice masses with entries from different years. Thickness values are derived from various observation methods and cover a survey period between 1923 and 2011. A major advantage of the database is the included metadata, giving information about specific fields, such as the mean thickness value of Aletschgletscher, which is only valid for the investigation area Konkordiaplatz and not over the entire glacier. The relatively small collection of records in the two more detailed database levels reflects the poor availability of such data. For modelling purposes, where ice thicknesses are implemented to derive ice volumes, this database provides essential information about glacier and ice cap characteristics and enables the comparison between various approaches. However, the dataset offers a great variety of locations, thicknesses and surface areas of glaciers and ice caps and can therefore help to compare, calibrate and validate existing models and analyses to improve the broader understanding of sea-level rise contribution from glaciers and ice caps worldwide.

Naegeli, Kathrin; Gärtner-Roer, Isabelle; Hagg, Wilfried; Huss, Matthias; Machguth, Horst; Zemp, Michael

2013-04-01

339

Inter-annual and intra-seasonal flow variability of Hubbard Glacier - an advancing tidewater glacier in SE Alaska  

Microsoft Academic Search

Hubbard Glacier is an advancing tidewater glacier in southeast Alaska. Its continued advance raises the possibility that Russell Fjord will become a dammed freshwater lake and a potential flood hazard to the town of Yakutat and its fishery. In order to predict the closure of Russell Fjord, a program of glaciological, oceanographic and meteorological measurements is underway. We will describe

L. A. Stearns; G. S. Hamilton; D. E. Lawson; D. C. Finnegan

2010-01-01

340

Integrated research on mountain glaciers: Current status, priorities and future prospects  

Microsoft Academic Search

Mountain glaciers are sensitive probes of the local climate, and, thus, they present an opportunity and a challenge to interpret climates of the past and to predict future changes. Furthermore, glaciers can constitute hazards, including: glacier outburst floods; changes in the magnitude and timing of runoff in the mountains and adjacent regions; and, through worldwide loss of glacier ice, a

Lewis A. Owen; Glenn Thackray; Robert S. Anderson; Jason Briner; Darrell Kaufman; Gerard Roe; William Pfeffer; Chaolu Yi

2009-01-01

341

In Situ ATP Bioluminescent Measurements in Subglacial Environments - The Engabreen Glacier in the Norwegian Arctic  

Microsoft Academic Search

Engabreen is a northern outlet glacier from the western Svartisen ice cap on the Nordland coast of Norway just inside the Arctic Circle. A unique feature of the glacier is a man-made tunnel system within the bedrock beneath the glacier that offers scientists direct access to the glacier-bedrock interface. This unique facility - called the Engabreen Subglacial Laboratory - is

D. C. Cullen; J. L. Wadham; R. Pancost; S. Kelly; M. J. Barnett; M. Jackson

2007-01-01

342

Solar-radiation-maintained glacier recession on Kilimanjaro drawn from combined ice-radiation geometry modeling  

Microsoft Academic Search

In the context of investigating modern glacier recession on Kilimanjaro, which began around 1880, this study addresses the glacier regime of the vertical ice walls that typically form the margins of Kilimanjaro's summit glaciers. These walls have suffered a continuous lateral retreat during the twentieth century. To evaluate the role of solar radiation in maintaining glacier recession on Kilimanjaro, a

Thomas Mölg; Douglas R. Hardy; Georg Kaser

2003-01-01

343

ADAPTING TO THE REALITY OF CLIMATE CHANGE AT GLACIER NATIONAL PARK, MONTANA, USA  

Microsoft Academic Search

The glaciers of Glacier National Park (GNP) are disappearing rapidly and likely will be gone by 2030. These alpine glaciers have been continuously present for approximately 7,000 years so their loss from GNP in another 25 years underscores the significance of current climate change. There are presently only 27 glaciers remaining of the 150 estimated to have existed when GNP

Daniel B. Fagre

344

Cold Debris Entrainment at Taylor Glacier, Antarctica: Implications for Its Basal Thermal Regime  

Microsoft Academic Search

Taylor Glacier is an outlet glacier from the East Antarctic Ice Sheet, draining continental flow through Taylor Valley and toward McMurdo Sound. As is the case for most glaciers from the Dry Valleys, Taylor Glacier was less extensive than at present during the last glacial maximum and has since expanded, reaching now its maximum Holocene extension. Bonney drift, which can

D. Samyn; S. J. Fitzsimons; R. D. Lorrain

2005-01-01

345

Hubbard Glacier Update: Another Closure of Russell Fjord in the Making?  

Microsoft Academic Search

Hubbard Glacier is located near the community of Yakutat in southeastern Alaska. It is the largest non-polar temperate tidewater glacier in the world and has been advancing since 1890 AD, currently at a rate of 35 m a-1. Hubbard Glacier has twice closed off Russell Fjord creating enormous glacier dam lakes, once in 1986 and again 2002. Both dams failed

R. J. Motyka; D. Lawson; D. Finnegan; G. Kalli; C. Lingle

2007-01-01

346

Assessing the Impact of Retreating Glaciers on Dry-Season Discharge in a Tropical Andean Watershed  

Microsoft Academic Search

Receding glaciers in the tropical Andes are causing concerns for future water supply in a region with thermal homogeneity and a strongly seasonal precipitation cycle. Dry season runoff from glacierized catchments is buffered by glacier melt that is not completely replaced by seasonal precipitation. Our objective is to trace the changing contribution of glacier meltwater to stream flow and to

B. G. Mark; J. M. McKenzie

2006-01-01

347

Glacier annual balance measurement, prediction, forecasting and climate correlations, North Cascades, Washington 1984-2006  

NASA Astrophysics Data System (ADS)

North Cascade glacier annual balance measured on 10 glaciers from 1984-2006 yielded mean annual balance (ba) of -0.54 m/a, and -12.38 m cumulatively. This is a significant loss for glaciers that average 30-60 m in thickness, representing 20-40% of their entire volume. Two observed glaciers, Lewis Glacier and Spider Glacier, no longer exist. The ba of North Cascade glaciers is reliably calculated based on 1 April snowpack water equivalent and ablation season temperature. 1 May forecasting of ba using the Pacific Decadal Oscillation and the Multivariate El Nino Southern Oscillation circulation indices correctly determined the sign of mass balance in 42 of 47 years. Glacier annual balance forecasting is an important step for summer water resource management in glacier runoff dominated stream systems. The forecast for North Cascade glaciers in 2007 is for a negative annual balance.

Pelto, M. S.

2007-06-01

348

Glacier Sliding With Cavitation Over Irregular Beds  

NASA Astrophysics Data System (ADS)

Pressurised subglacial water affects the sliding of glaciers over hard beds through the process of cavitation. In particular, it is widely recognised that sliding velocities depend not only on shear stress but also on the difference pe between overburden and drainage pressures. However, the precise form which such a sliding law should take is unclear, and many modellers opt for a heuristic power-law ub = C? bn pe-m. Here we show how Iken's (J. Glaciol., 27, 407-422) notion of a `critical pressure' at which sliding becomes unstable can be re-interpreted as an upper bound on the amount basal shear stress which a hard bed can support. Such an upper bound clearly contradicts the sliding law above. Motivated by the need to construct a more realistic sliding law which is not in conflict with Iken's bound, we present an analysis of hard bed sliding in the presence of cavitation which extends Fowler's (Proc. R. Soc. L. Ser. A., 407, 147--170) treatment to the case of irregular beds with many different bump sizes. Our results imply that generalised power-law sliding laws should not be used indiscriminately, particularly when discussing surge-type glacier flow. Furthermore, our results highlight the need to incorporate improved drainage models into the theory of hard bed sliding.

Schoof, C.

2002-12-01

349

Gravity analyses for the crustal structure and subglacial geology of West Antarctica, particularly beneath Thwaites Glacier  

NASA Astrophysics Data System (ADS)

The West Antarctic Ice Sheet (WAIS) is mostly grounded in broad, deep basins (down to 2.5 km below sea level) that are stretched between five crustal blocks. The geometry of the bedrock, being mostly below sea level, induces a fundamental instability in the WAIS through the possibility of runaway grounding line retreat. The crustal environment of the WAIS further influences the ice sheet's fast flow through conditions at the ice-bedrock boundary. This study focuses on understanding the WAIS by examining the subglacial geology (such as volcanoes and sedimentary basins) at the ice-bedrock boundary and the continent's deeper crustal structure- primarily using airborne gravity anomalies. The keystone of this study is a 2004-2005 aerogeophysical survey over one of the most negative mass balance glaciers on the continent: Thwaites Glacier (TG). The gravity anomalies derived from this dataset- as well as gravity-based modeling and spectral crustal boundary depth estimates- reveal a heterogeneous crustal environment beneath the glacier. The widespread Mesozoic rifting observed in the Ross Sea Embayment (RSE) of West Antarctica extends beneath TG, where the crust is ˜27 km thick and cool. Adjacent to TG, spectrally-derived shallow Moho depths for the Marie Byrd Land (MBL) crustal block can be explained by thermal support from warm mantle. I assemble here new compilations of free-air and Bouguer gravity anomalies across West Antarctica (from both airborne and satellite datasets) and re-interpret the extents of West Antarctic crustal block and their boundaries with the rift system. Airy isostatic gravity anomalies reveal that TG is relatively sediment starved, in contrast to the sediment-rich RSE. TG's fast flow velocities could be sustained in this sediment poor environment if higher heat flux in MBL was providing an ample source of subglacial melt water to the glacier. The isostatic anomalies also indicate that TG's outlet rests on a bedrock sill that will impede future grounding line retreat (up to ˜100 km) and temporarily stabilize the glacier.

Diehl, Theresa Marie

350

Multi-decadal glacier surface lowering in the Antarctic Peninsula  

NASA Astrophysics Data System (ADS)

From approximately 400 glaciers of the western Antarctic Peninsula, no in situ records of mass balance exist and their recent contribution to sea level is consequently poorly constrained. We seek to address this shortcoming by using surface elevations from USGS and BAS airborne (1948-2005) and ASTER spaceborne (2001-2010) stereo imagery, combined by using a rigorous semi-automated registration approach, to determine multi-decadal glacier surface elevation changes in the western Antarctic Peninsula for 12 glaciers. All observed glaciers show near-frontal surface lowering and an annual mean lowering rate of 0.28 ± 0.03 m/yr at the lower portion of the glaciers during the ˜4 decades following the mid-1960s, with higher rates for the glaciers in the north-west parts of the Antarctic Peninsula. Increased lowering of up to 0.6 m/yr can be observed since the 1990s, in close correspondence to increased atmospheric positive degree days. In all cases, surface lowering reduces to zero within 5 km of the glacier front at around 400 m altitude. This lowering may have been at least partially compensated for by increased high-altitude accumulation.

Kunz, Matthias; King, Matt A.; Mills, Jon P.; Miller, Pauline E.; Fox, Adrian J.; Vaughan, David G.; Marsh, Stuart H.

2012-10-01

351

Glacier calving, dynamics, and sea-level rise. Final report  

SciTech Connect

The present-day calving flux from Greenland and Antarctica is poorly known, and this accounts for a significant portion of the uncertainty in the current mass balance of these ice sheets. Similarly, the lack of knowledge about the role of calving in glacier dynamics constitutes a major uncertainty in predicting the response of glaciers and ice sheets to changes in climate and thus sea level. Another fundamental problem has to do with incomplete knowledge of glacier areas and volumes, needed for analyses of sea-level change due to changing climate. The authors proposed to develop an improved ability to predict the future contributions of glaciers to sea level by combining work from four research areas: remote sensing observations of calving activity and iceberg flux, numerical modeling of glacier dynamics, theoretical analysis of the calving process, and numerical techniques for modeling flow with large deformations and fracture. These four areas have never been combined into a single research effort on this subject; in particular, calving dynamics have never before been included explicitly in a model of glacier dynamics. A crucial issue that they proposed to address was the general question of how calving dynamics and glacier flow dynamics interact.

Meier, M.F.; Pfeffer, W.T.; Amadei, B.

1998-08-01

352

Mass balance, runoff and surges of Bering Glacier, Alaska  

NASA Astrophysics Data System (ADS)

The historical net, ablation and accumulation daily balances, as well as runoff of Bering Glacier, Alaska are determined for the 1951-2011 period with the PTAA (precipitation-temperature-area-altitude) model, using daily precipitation and temperature observations collected at the Cordova and Yakutat weather stations, together with the area-altitude distribution of the glacier. The model mean annual balance for this 61 yr period is -0.6 m w.e., the accumulation balance is +1.4 and the ablation balance is -2.0 m w.e. Average annual runoff is 2.5 m w.e. Periodic surges of this glacier transport large volumes of ice to lower elevations where the ablation rate is higher, producing more negative balances and increasing runoff. Runoff from Bering Glacier (derived from simulated ablation and precipitation as rain) is highly correlated with four of the glacier surges that have occurred since 1951. Ice volume loss for the 1972-2003 period measured with the PTAA model is 2.7 km3 w.e. a-1 and closely agrees with losses for the same period measured with the geodetic method. It is proposed that the timing and magnitude of daily snow accumulation and runoff, both of which are controlled by the glacier's area-altitude distribution and are calculated with the PTAA model, can be used to determine the probability that a glacier will surge.

Tangborn, W.

2013-05-01

353

Exploring the links between transient water inputs and glacier velocity in a small temperate glacier in southeastern Alaska  

NASA Astrophysics Data System (ADS)

Glaciers along the Gulf of Alaska are thinning and retreating rapidly and over the last century this loss of ice has contributed measurably to global sea level rise. An important control on the rate at which ice is being lost is basal motion because higher glacier velocities increase the rate at which ice is delivered to ablation zones. Recent research has focused on understanding the effects of sub-glacial water storage on glacier basal motion. In this study, we examined how water inputs from large rainfall events as well as a glacier lake outburst flood affected the velocity of the Lemon Creek Glacier in southeastern Alaska. Lemon Creek Glacier is a moderately sized (~16~km2) temperate glacier at the margin of the Juneau Icefield. An ice- marginal lake forms at the head of the glacier and catastrophically drains once or twice every melt season. We have instrumented the glacier with two meteorological stations: one at the head of the glacier near the ice-marginal lake and another several kilometers below the terminus. These stations measure temperature, relative humidity, precipitation, incoming solar radiation and wind speed and direction. Lake stage in the ice- marginal lake was monitored with a pressure transducer. In addition, Lemon Creek was instrumented with a water quality sonde at the location of a US Geological Survey gaging station approximately 3 km downstream from the glacier terminus. The sonde provides continuous measurements of water temperature, dissolved oxygen, turbidity and conductivity. Finally, two Trimble NetRS dual frequency, differential GPS units were deployed on the glacier at approximately 1/3 and 2/3 down the centerline of the glacier. All of the instruments were run continuously from May-September 2008 and captured the outburst flood associated with the ice-marginal lake drainage as well as several large (>3~cm) rainfall events associated with frontal storms off of the Gulf of Alaska in late summer. Taken together, these data allow us to test the hypothesis that water inputs which overwhelm subglacial drainage networks result in increased rates of basal motion.

Habermann, M.; Hood, E.; Heavner, M.; Motyka, R.

2008-12-01

354

Borehole and Ice Feature Annotation Tool (BIFAT): A program for the automatic and manual annotation of glacier borehole images  

NASA Astrophysics Data System (ADS)

We present a stand-alone software platform, Borehole and Ice Feature Annotation Tool (BIFAT), for the examination, annotation and analysis of glacier borehole images. This tool aids in the lengthy and often subjective process of annotating layers and other features in optical and acoustic glacier borehole televiewer logs. Since these view 360° around the full circumference of an exploratory borehole, intersecting planes are reconstructed on the televiewer image as sinusoids, the amplitude and phase of which can be used to calculate, respectively, the dip and direction of dip of each of these planes. The program suite aids in the annotation and examination of such planes, as well as a number of other features, including clusters and inclusions. BIFAT also provides an automatic layer detection option to aid and speed up the often lengthy process of identifying planar features in glacier borehole images, and a semi-automatic inclusion detection tool. The software shows promising results in rock borehole images and in the detection of planar layers in line-scan ice core images. We describe the capability and operation of BIFAT, and illustrate its application with reference to the automatic identification and annotation of sections from optical televiewer (OPTV) borehole logs from a variety of ice masses including Roi Baudouin, Dronning Maud Land, Antarctica and Tsanfleuron Glacier, Switzerland. The software is freely available for download from http://users.aber.ac.uk/byh/iceoptv.

Malone, Terry; Hubbard, Bryn; Merton-Lyn, Derek; Worthington, Paul; Zwiggelaar, Reyer

2013-04-01

355

New glacier inventory of Salzburg 2007/09  

NASA Astrophysics Data System (ADS)

Glacier inventories are an important data basis for several investigations such as length-, area- and volume changes in the course of climate change. The new glacier inventory of Salzburg is part of the third Austrian glacier inventory (GI3) and is valid for the years 2007 and 2009 depending on each mountain range. The first inventory (GI1) was compiled in 1969 and the second one (GI2) represents the glacier state from 1998 to 2002. In Salzburg, 150 glaciers are located in the six mountain ranges: Ankogel, Glockner, Granatspitz, Sonnblick (Goldberg), Hochkönig and Venediger. The basis for the new mapping were orthophotos of 2007 and 2009 and the DEM of the southern part of Salzburg. On the basis of former inventories area-, height- and volume changes have been calculated. The biggest loss of glacier area per mountain range was found in the Ankogel range and on Hochkönig because of the disrupted structure of the thin glaciers. Referring to the absolute values, the largest changes took place in the Glockner- and Venediger mountain range with -10.11 km2 and -9.72 km2 during the period between GI1 (1969) and GI3 (2007/2009) respectively. Due to the lack of DEMs (only the southern part was available) volume changes have been calculated for about half of all glaciers in Salzburg. These are located at the Glockner, Granatspitz and Sonnblick mountain range and showed -0.335 km3 on average changes in height of 9.3 m. An extrapolation of these changes to all of the 150 glaciers in Salzburg results in a loss of about 0.7 km3 between GI1 and GI3.

Stocker-Waldhuber, M.; Wiesenegger, H.; Fischer, A.

2012-04-01

356

Detection of glacier lake using ALOS PALSAR data at Bhutan  

NASA Astrophysics Data System (ADS)

The retreat of mountain glaciers and expansion of glacial lakes are the common issue related to global warming and it sometimes causes a sudden flood, which is called as Glacier Lake Outburst Flood (GLOF). GLOF event occurs frequently in 1960s at Himalayan glaciers. Satellite data is a sophisticated tool for this research because it is difficult to operate frequent field survey due to severe weather condition and hard accessibility. However, the optical sensor equipped on satellite has one serious problem, which is weather condition of target area. It is very difficult to acquire cloud-free data at Himalayan region on a regular schedule. Therefore, it is necessary to find another way to avoid this problem. Synthetic Aperture Radar (SAR) is one possible way because SAR can observe under all weather condition and SAR image is able to distinguish water surface and other landcovers because water surface is smoother than the other landcovers, especially in the case of L-band wavelength scale. On the other hand, SAR image has geometric and radiometric distortion due to its observation mechanism and topographic feature. Geometric distortion is able to correct by applying systematic orthorectification using DEM data. However, radiometric distortion is still remained. Recently, several radiometric terrain correction (RTC) methods are proposed. This method corrects the radiometric distortion due to local topographic slope. After RTC, radiometric distortion due to topographic relief is suppressed and backscatter brightness of the image after RTC almost depend on landcovers. In this study, we used L-band ALOS/PALSAR (SAR) data after applying RTC, ALOS/AVNIR-2 (Optical Sensor) data and SRTM-3 (DEM) data. PALSAR data is used for detection of glacier lake to set threshold of radar brightness. AVNIR-2 data is used for making glacier mask area because radar brightness of smooth glacier or icecap area is as dark as water surface on the PALSAR image. To avoid this misdetection, we applied glacier mask by AVNIR-2 data. SRTM-3 data has two ways to use. One is source data for orthorectification of PALSAR data and the other is selection of candidate for glacier lake. The selection criteria for glacier lake candidate are surface slope and topographic height. Surface slope is criterion for surface flatness and topographic height is criterion for existence condition of liquid water. We used these criteria in combination for detection of glacier lakes. Preliminary consistency comparison result with ICIMODs' glacier lake inventory detected several mistakes of ICIMOD's inventory. We also have a plan to validate these glacier lake detection results with manual interpretation results of glacial lakes using optical sensor which compiled under SATREPS (Science and Technology Research Partnership for Sustainable Development) project by JICA and JST.

Yamanokuchi, T.; Tadono, T.; Tomiyama, N.

2010-12-01

357

The Chemical Equilibrium Problem.  

National Technical Information Service (NTIS)

It has long been known that the problem of determining the equilibrium composition of a solution of chemically reacting species could be formulated as a constrained minimum problem. Previous methods for solving the chemical equilibrium problem in this for...

J. H. Bigelow

1968-01-01

358

Analysis of the glacier retreat in the French Alps since the 1960s based on the new glacier inventory  

NASA Astrophysics Data System (ADS)

One of the most obvious impacts of climate change in high mountain areas is the glacial retreat. Since the French glacier inventory carried out by R. Vivian in the late 1960s within the context of the WGI, there was no updated data from the overall French alpine glaciers. We present here the first results of a new diachronic inventory of the French alpine glaciers based on different sources. Glacier outlines were manually delineated using 1/25,000 topographic maps of the french National Geographical Institute (IGN) from the end of the 1960s, and IGN 50-cm-pixel orthophotographs from 2006 to 2009. For Landsat 5 TM images (30 m resolution) dating from 1985-1986, and Landsat 5 TM and Landsat 7 ETM+ images (30 and 15 m resolutions) dating from 2003, an automatic delineation with the common NDSI method was used to determine glacier limits. Each glacier has been individually checked, with a special care for debris covered and shadowed areas to adjust the delineation, using a 542 spectral bands combination. For compounded glaciers, the same limits were manually adjusted for each period. Data were integrated into a GIS and a database including all the common items (surface area, minimal and maximal elevations, aspect, debris covered area, slope…) was generated. Topographic parameters were extracted from the IGN DEM (resolution of 25 m) for the topographic maps and Landsat images from the mid-80s, and the ASTER GDEM (resolution of 30 m) for the Landsat images of the early 2000s and the orthophotographs. . Current extension of the 593 French alpine glaciers is about 275 km2. It is ~20 % less than in 1985-1986 (end of the last glacial advance period), when glacier extension was 340 km2, and ~26 % less than at the end of the 1960s, when glacier coverage was about 375 km2. Different trends are observed across the French Alps, with a stronger glacial retreat in the southern massifs: for instance, glacier shrinkage in the Ecrins massif is more than three times stronger than in the French area of the Mont Blanc massif. The size distribution of the glaciers has changed within the last 40 years: the proportion of glaciers < 0.1 km2 increased from 31% to 51%, while glaciers 0.1-0,5 km2 and >1 km2 decreased from 41% to 31%, and 28 % to 18 %, respectively. The average minimal elevation of glacier fronts has risen from about 2670 m a.s.l. at the end of the 1960s to 2760 m (+ 90 m). Results from the analysis of the relationship between glaciers retreat and their aspect and elevation will be also presented. Finally, the reconstruction of glacier extensions at the end of the Little Ice Age, based on ancient maps and geomorphological study of the proglacial margins will be presented. As an example, glacier extension in the Vanoise massif has decreased by more than 50% since the end of the LIA.

Gardent, M.; Rabatel, A.; Dedieu, J. P.; Deline, P.; Schoeneich, P.

2012-04-01

359

Climate downscaling for estimating glacier mass balances in northwestern North America: Validation with a USGS benchmark glacier  

NASA Astrophysics Data System (ADS)

An atmosphere/glacier modeling system is described for estimating the mass balances of glaciers in both current and future climate in order to estimate their probable future contributions to rising sea level. Dynamically downscaled output from a regional atmospheric model, driven by global atmospheric reanalysis, is used to force a precipitation-temperature-area-altitude (PTAA) glacier mass balance model with daily maximum and minimum temperatures and precipitation. The modeling system is verified by hindcasting the mass balances of Gulkana Glacier, a U.S. Geological Survey (USGS) benchmark glacier in the Alaska Range, U.S.A., during a ten-year period from October 1994 to September 2004. The mass balances simulated with the atmosphere/glacier modeling system are comparable to the USGS measurements, and are also in good agreement with the meteorological station observation-forced PTAA simulations. The results suggest this is a promising approach for realistic estimation of the future mass balances of the glaciers of northwestern North America.

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

2007-11-01

360

Chemical denudation and silicate weathering in Himalayan glacier basins: Batura Glacier, Pakistan  

Microsoft Academic Search

The major ion, SiO2 and minor element contents of Batura Glacier meltwaters in the headwaters of the Indus Basin, Pakistan are examined. The data are used to examine the controls upon solute acquisition by runoff and to estimate solute yields. Solute yield calculations include estimation of the total and silicate-derived cationic denudation rates following the application of simple solute provenance

Andy Hodson; Phil Porter; Andy Lowe; Paul Mumford

2002-01-01

361

Rapid erosion of soft sediments by tidewater glacier advance: Taku Glacier, Alaska, USA  

Microsoft Academic Search

Taku Glacier in southeast Alaska has advanced 7.5 km over the last 115 years, overriding its own glaciomarine and outwash sediments. We have documented rapid erosion of these sediments by comparing radio echo soundings (RES) along five transects (2003–2005) to earlier RES surveys (1989 and 1994) and to early bathymetric surveys of the proglacial fjord. Erosion rates, $\\\\dot{E}$, reached 3.9

Roman J. Motyka; Martin Truffer; Elsbeth M. Kuriger; Adam K. Bucki

2006-01-01

362

Outlet Glacier-Ice Shelf-Ocean Interactions: Pine Island Glacier in the Amundsen Sea Embayment  

NASA Astrophysics Data System (ADS)

While the massive interior regions of the Antarctic and Greenland Ice Sheets are presently "resting quietly", the lower elevations of many outlet glaciers are experiencing dramatic adjustments due to changes in ice dynamics and/or surface mass balance. Oceanic and/or atmospheric forcing in these marginal regions often leads to mass deficits for entire outlet basins. Recent observations and theoretical studies indicate that the large and ongoing mass deficit in the Amundsen Sea sector of Antarctica is due to ice-ocean interactions and the subsequent propagation of these changes into the upstream reservoirs of the Pine Island and Thwaites Glaciers. Accurate assessments of future sea-level rise require careful consideration of potential forcings at the ice front as well as an understanding of the timing and extent of inland responses to those forcings. To this end, the higher-order flowline model used in this study incorporates both published data and 3-D model output as boundary and initial conditions to simulate the evolution of Pine Island Glacier over the centennial timescale. These SeaRISE experiments are focused on ice-flow sensitivity to changes in climate, subglacial sliding, and ocean-induced melting at the ice sheet perimeter.

Bertini, G. T.; Parizek, B. R.; Edwards, R. A.; Wolfe, D.; Walker, R. T.

2011-12-01

363

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

NASA Astrophysics Data System (ADS)

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 et al., 2008). Many questions regarding the dynamics of these glaciers remain unresolved, including the nature and cause of rapid deceleration events and the influence of surface melting and hydrology on variations in glacier speed. We have operated a GPS network on the surface of Helheim Glacier during the four summers of 2006--2009, as well as during the fall of 2008, late spring of 2009, and fall of 2009. Several auxiliary geophysical sensors have also been operated nearby. This short four-year period has revealed both glacier acceleration and deceleration, occurring on interannual to sub-hour timescales. The number of glacial earthquakes observed during this time period has also varied significantly. During the summer of 2009, we also operated a GPS network on Kangerdlugssuaq Glacier, obtaining a full season of high-time-resolution observations of glacier motion and deformation. The GPS data acquired during 2009 come primarily from a low-cost GPS receiver system designed by the authors to provide data security and near-real-time data delivery via a combination of radio and satellite telemetry. Here, we present results from the extended 2008/2009 seasons at Helheim and Kangerdlugssuaq in the context of our previous observations and longer-term observations of other workers.

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

2009-12-01

364

Chapman Cycle Equilibrium Calculator  

NSDL National Science Digital Library

The Chapman Cycle Equilibrium Calculator solves for the equilibrium solution of the chemical reactions in the Chapman Cycle, assuming a solar flux equivalent to that at the top of the Earth's atmosphere. A Newton-Rhapson method is used to find the solution, which requires an initial guess as to the equilibrium solution.

The Shodor Education Foundation, Inc.

365

Glaciers in a changing global climate: first results of worldwide glacier mass balance measurements 2000/2001  

NASA Astrophysics Data System (ADS)

Glacier signals from mountain areas are key elements of early detection strategies for dealing with possible man-induced climate change. The IPCC Third Assessment Report indeed defines mountain glaciers as one of the best natural indicators of atmospheric warming with the highest reliability ranking. In the chain of processes linking climate and glacier fluctuations, glacier length variation is the indirect/delayed response, whereas glacier mass change is the direct/undelayed reaction. Internationally coordinated long-term monitoring of glaciers started in 1894. The responsibility to collect and publish standardized data has been assumed since 1986 by the World Glacier Monitoring Service (WGMS). This work is primarily being carried out under the auspices of the International Commission on Snow and Ice (ICSI/IAHS) and the Federation of Astronomical and Geophysical Services (FAGS/ICSU). The WGMS maintains data exchange with the ICSU World Data Center A (WDC-A) for Glaciology in Boulder, Colorado. Corresponding data bases and measurement networks form an essential part of the Global Terrestrial Network for Glaciers (GTN-G: operated by the WGMS) as a pilot project within the Global Terrestrial Observing System (GTOS/GCOS). A network of 60 glacier mass balance observations provides information on presently observed rates of change in glacier mass, corresponding acceleration trends and regional distribution patterns. A preliminary calculation of the mass balance observations in 2000/2001 relating to 23 selected data sets provide a mean specific (annual) net balance of -367 mm w.e., 26 % of the observed balances were positive. The corresponding mean in six mountain ranges was -571 mm w.e. Such values indicate that mass losses in 2000/2001 have been less extreme than in the extraordinary years before but are still strongly negative. Over the past two decades glacier melt appears to continue at a considerable and possibly even an accelerating rate. The observed average changes in ice thickness interpreted as corresponding amounts of latent heat required for melting reflect an additional energy flux of a few W/m2 with an acceleration trend of some hundreds of a W/m2 per year. Such values are broadly consistent with model calculations. It should, however, be noted that the processes involved (energy balance, glacier dynamics) are complex and not fully understood.

Frauenfelder, R.; Hoelzle, M.; Haeberli, W.

2003-04-01

366

The mass balance and the flow of a polythermal glacier, McCall Glacier, Brooks Range, Alaska  

NASA Astrophysics Data System (ADS)

Studies of surface motion and geometry, ice thickness, and mass balance were carried out on the arctic McCall Glacier. They revealed characteristic processes of glacier flow and mass balance that independently reflect the polythermal temperature regime of the glacier, which consists of cold ice except for a discontinuous layer of temperate ice at the base. Analysis of the present flow of McCall Glacier showed the longitudinal stress coupling length to be significantly larger than on temperate glaciers. This is a consequence of the smaller mass balance gradients and associated lower strain rates of arctic glaciers. Furthermore, flow analysis suggests year-round basal sliding beneath a section of the lower glacier, which accounts for more than 70% of the total motion. This sliding anomaly is reflected in corresponding anomalies of the observed ice thickness and surface profiles. Changes in surface velocity, both on a decadal and on a seasonal scale, were also studied. Velocities during the short summer season increase by up to 75% above winter values as a result of enhanced basal sliding at the temperate glacier bed. The zone affected by this speed-up extends upglacier of any obvious sources of meltwater input to the bed. The mass balance of McCall Glacier exhibits a trend towards increasingly negative values. This is shown by both annual measurements during 1969-72 and 1993-96 and by comparing long-term values for two periods, 1957-71 and 1972-93. The contribution of refreezing surface water in the cold surface layers of firn and ice (internal accumulation) to the net accumulation was found to increase from about 40% in the 1970s to more than 90% in the 1990s. Comparative studies of long-term volume changes of neighboring glaciers showed that the McCall Glacier mass balance is regionally representative. Existing good correlations of the mass balance with meteorological parameters recorded by a weather station more than 400 km to the east furthermore suggest that McCall Glacier is representative on a synoptic scale and thus is a valuable indicator of climate change in the Arctic.

Rabus, Bernhard Theodor

367

Probing the till beneath Black Rapids Glacier, Alaska  

NASA Astrophysics Data System (ADS)

Black Rapids is a surge-type glacier in the Alaska Range which last surged in 1936. Seismic studies and wire-line drilling have shown that its central, most active part, is underlain by several meters of till, processes in which account for more than half of the present surface motion. We recently developed a 400 kg down-hole hammer system to place instrumented probes as deeply as possible into the till. The hammer is operated from the surface with a cathead and a composition rope. In 2002 we penetrated about 2.5 m into the till under 500 m of ice. To circumvent problems with probe placement and survival of communication with the surface, the probes are wireless and broadcast pressure and two axes of tilt data to a down-hole receiver placed slightly above the ice-till interface. Results from two probes in separate holes 4.1 m apart showed almost identical, complex patterns of tilt rate, relativey quiescent periods punctuated by rapid tilt events. One tilt event was accompanied by an almost 90 degree change in the direction of tilt. The tilt events show some correlation with motion events measured at the surface.

Harrison, W.; Trufffer, M.

2003-04-01

368

Tropical Glaciers: Recorders and Indicators of Climate Change  

NASA Astrophysics Data System (ADS)

Tropical climate is dominated on interannual time scales by monsoons and especially by ENSO, which is responsible for meteorological phenomena that directly or indirectly affect most regions on the planet and their populations. Common tropical teleconnections to the extra tropics include a stronger Aleutian low, stronger westerlies, variations in convective activity (flooding and drought), and modulation of tropical storm intensities. New ice core records from the Quelccaya and Coropuna ice caps provide 1700 years of continuous, annually-resolved records of climate and environmental variability expressed in the oxygen and hydrogen isotopic ratios, concentrations of mineral dust and various chemical species and net mass accumulation. These records provide an opportunity to examine the nature of tropical climate variability in greater detail, and to extract new information on ENSO and monsoon-linked climate phenomena. Quelccaya records display a prominent Little Ice Age isotopic depletion from 1520 to 1880 A.D. and a muted Medieval Warming between 1100 and 1300 AD. Drier conditions dominated from 300 to 500 AD, 1190 to 1470 AD and 1710 to 1910 with slightly wetter conditions from 500 to 1190 AD, and much wetter conditions from 1470 to 1710 A.D. and from 1910 A.D. to the present. The major cation and anion concentrations record other environmental changes over the past 1700 years. The longer tropical climate histories from Coropuna and Huascarán (Peru), Sajama (Bolivia), and Kilimanjaro (Tanzania) document abrupt climate disruptions such as the 4.2 ka drought and an extreme cold and wet period centered at 5.2 ka. The well documented ongoing ice loss on Quelccaya and Kilimanjaro paint a grim future for glacier histories from the tropics. The current melting of high-altitude, low-latitude ice fields is consistent with model predictions for a vertical amplification of temperature in the tropics. The ongoing glacier retreat in the Andes, Himalayas and Africa has implications for the people who live in these areas and hence are on the front lines of the climate change crisis.

Thompson, L. G.; Mosley-Thompson, E. S.; Buffen, A.; Urmann, D.; Davis, M. E.; Lin, P.

2008-12-01

369

Melting glaciers can change Earth's gravity field  

NASA Astrophysics Data System (ADS)

The Earth's rotation causes mass from the ductile mantle to bulge at the equator, making the radius of the Earth about 21 kilometers greater at the equator than at the poles. Over the past 20,000 or so years, the Earth has been becoming more round as it adjusts to the withdrawal of vast continental glaciers after the last ice age: Without the weight of ice pressing down, land has rebounded to give the Earth a more spherical shape. This in turn means that the Earth|'s geoid—the average gravity field across the globe—also became more round. However, in the early 1990s, scientists began to notice that postglacial rebound was starting to become offset by something else, causing the Earth's gravity field to cease changing shape.

Kumar, Mohi

2011-09-01

370

Glaciers and ice sheets as a biome.  

PubMed

The tundra is the coldest biome described in typical geography and biology textbooks. Within the cryosphere, there are large expanses of ice in the Antarctic, Arctic and alpine regions that are not regarded as being part of any biome. During the summer, there is significant melt on the surface of glaciers, ice caps and ice shelves, at which point microbial communities become active and play an important role in the cycling of carbon and other elements within the cryosphere. In this review, we suggest that it is time to recognise the cryosphere as one of the biomes of Earth. The cryospheric biome encompasses extreme environments and is typified by truncated food webs dominated by viruses, bacteria, protozoa and algae with distinct biogeographical structures. PMID:22000675

Anesio, Alexandre M; Laybourn-Parry, Johanna

2011-10-12

371

Glacier loss on Kilimanjaro continues unabated.  

PubMed

The dramatic loss of Kilimanjaro's ice cover has attracted global attention. The three remaining ice fields on the plateau and the slopes are both shrinking laterally and rapidly thinning. Summit ice cover (areal extent) decreased approximately 1% per year from 1912 to 1953 and approximately 2.5% per year from 1989 to 2007. Of the ice cover present in 1912, 85% has disappeared and 26% of that present in 2000 is now gone. From 2000 to 2007 thinning (surface lowering) at the summits of the Northern and Southern Ice Fields was approximately 1.9 and approximately 5.1 m, respectively, which based on ice thicknesses at the summit drill sites in 2000 represents a thinning of approximately 3.6% and approximately 24%, respectively. Furtwängler Glacier thinned approximately 50% at the drill site between 2000 and 2009. Ice volume changes (2000-2007) calculated for two ice fields reveal that nearly equivalent ice volumes are now being lost to thinning and lateral shrinking. The relative importance of different climatological drivers remains an area of active inquiry, yet several points bear consideration. Kilimanjaro's ice loss is contemporaneous with widespread glacier retreat in mid to low latitudes. The Northern Ice Field has persisted at least 11,700 years and survived a widespread drought approximately 4,200 years ago that lasted approximately 300 years. We present additional evidence that the combination of processes driving the current shrinking and thinning of Kilimanjaro's ice fields is unique within an 11,700-year perspective. If current climatological conditions are sustained, the ice fields atop Kilimanjaro and on its flanks will likely disappear within several decades. PMID:19884500

Thompson, L G; Brecher, H H; Mosley-Thompson, E; Hardy, D R; Mark, B G

2009-11-02

372

Glacier loss on Kilimanjaro continues unabated  

PubMed Central

The dramatic loss of Kilimanjaro's ice cover has attracted global attention. The three remaining ice fields on the plateau and the slopes are both shrinking laterally and rapidly thinning. Summit ice cover (areal extent) decreased ?1% per year from 1912 to 1953 and ?2.5% per year from 1989 to 2007. Of the ice cover present in 1912, 85% has disappeared and 26% of that present in 2000 is now gone. From 2000 to 2007 thinning (surface lowering) at the summits of the Northern and Southern Ice Fields was ?1.9 and ?5.1 m, respectively, which based on ice thicknesses at the summit drill sites in 2000 represents a thinning of ?3.6% and ?24%, respectively. Furtwängler Glacier thinned ?50% at the drill site between 2000 and 2009. Ice volume changes (2000–2007) calculated for two ice fields reveal that nearly equivalent ice volumes are now being lost to thinning and lateral shrinking. The relative importance of different climatological drivers remains an area of active inquiry, yet several points bear consideration. Kilimanjaro's ice loss is contemporaneous with widespread glacier retreat in mid to low latitudes. The Northern Ice Field has persisted at least 11,700 years and survived a widespread drought ?4,200 years ago that lasted ?300 years. We present additional evidence that the combination of processes driving the current shrinking and thinning of Kilimanjaro's ice fields is unique within an 11,700-year perspective. If current climatological conditions are sustained, the ice fields atop Kilimanjaro and on its flanks will likely disappear within several decades.

Thompson, L. G.; Brecher, H. H.; Mosley-Thompson, E.; Hardy, D. R.; Mark, B. G.

2009-01-01

373

Fast-flowing outlet glaciers on Svalbard ice caps  

SciTech Connect

Four well-defined outlet glaciers are present on the 2510 km{sup 2} cap of Vestfonna in Nordaustlandet, Svalbard. Airborne radio echo sounding and aerial-photograph and satellite-image analysis methods are used to analyze the morphology and dynamics of the ice cap and its component outlet glaciers. The heavily crevassed outlets form linear depressions in the ice-cap surface and flow an order of magnitude faster than the ridges of uncrevassed ice between them. Ice flow on the ridges is accounted for by internal deformation alone, whereas rates of outlet glacier flow require basal motion. One outlet has recently switched into and out of a faster mode of flow. Rapid terminal advance, a change from longitudinal compression to tension, and thinning in the upper basin indicate surge behavior. Observed outlet glacier discharge is significantly greater than current inputs of mass of the ice cap, indicating that present rates of flow cannot be sustained under the contemporary climate.

Dowdeswell, J.A. (Univ. of Cambridge (England)); Collin, R.L. (University College of Wales, Aberystwyth (England))

1990-08-01

374

The contribution potential of glaciers to Himalaya river runoff  

NASA Astrophysics Data System (ADS)

Glaciers are reported to crucially contribute to the water availability for large population numbers around the Himalaya. They are expected to change their water storage capacity under the changing climate conditions with major detrimental consequences for fresh water supply. The potential to modify river runoff of both the storage capacity in glaciers and its variability differs in different climate regimes and decreases downriver. The lack of appropriate data records and model performance leaves us with only vague ideas for most river systems. We present a simple method to assess the contribution potential of glaciers to river runoff from data sets available. Glacier contribution to runoff is shown together with population numbers downriver. Respective results are presented and discussed in simple plots and in a summary map.

Kaser, Georg; Grosshauser, Martin