Time-variant risk assessment of a hazard cascade at the example of a rockslide dam - a case study in the Upper Val Venosta / Vinschgau Valley, Italy

NASA Astrophysics Data System (ADS)

Kofler, Christian; Renner, Kathrin; Comiti, Francesco; Gems, Bernhard; Schneiderbauer, Stefan; Thiebes, Benni; Schlögel, Romy

2017-04-01

Earthquakes and heavy precipitation events represent the main triggering factors of mass movements such as landslides, rockslides or debris flows. The overall hazard potential is increased significantly if the mass movement subsequently interacts with an adjacent river course by creating a fully or partially blockage of the channel. These temporary dams can cause disastrous secondary hazards by backwater inundation or outburst floods. Therefore, the formation and failure of rockslide dams can be regarded and assessed as a cascade of hazards. Through the cascading effects, rockslide dams can affect areas at great distances up -or downstream of the site where the actual mass movement occurred. Moreover, the time span between the generation and the failure of a rockslide dam can vary from few minutes to several days or even decades. This type of cascading hazard is therefore subject to high temporal and spatial variability. Due to the difficulties assessing the probabilities of each part of the hazard cascade, there is a substantial uncertainty involved in the assessment of the overall hazard. Risk assessments, however, often do not account for this complexity when assessing the exposed elements. Especially the exposure of people, highly mobile in space and time, is often not taken into consideration. In this study, we propose a novel approach that combines both the dynamic components of the hazard and the exposure. The study area extends over the two municipalities of Stilfs/Stelvio and Prad am Stilsferjoch/Prato allo Stelvio in the Autonomous Province of Bozen/Bolzano (South Tyrol) in Northern Italy. Both municipalities are major tourist destinations in the region featuring two ski resorts, a national park and the well-known 'Stilfser Joch/Passo dello Stelvio' mountain pass. This implies a high daily and seasonal fluctuation of people, including commuters and tourists. The upper part of the slope above the village of Trafoi is at risk of a sudden failure of a large rock slide mass. Previous works modelled various slope failure scenarios and predicted rockslide run-out depositions of up to 75 m height in the channel of the Trafoi River. In this work, firstly the hazard induced by a potential rockslide dam was quantified. The backwater inundation was assessed by a GIS-based method and the downstream flood event was modelled with a combined 1D-2D hydrodynamic model. Secondly, the number of exposed people was estimated by a grid-based population model capable to simulate daily or seasonal movement patterns of people. Results show that peak discharge out of the breaching rockslide dam can reach up to 2550 m3s-1. Population modelling reveal that around 6640 people would be exposed to this hazard in winter time and 7250 in summer time. About one third of the persons would be tourists and one fourth were local commuters.

River-damming, late-Quaternary rockslides in the Ötz Valley region (Tyrol, Austria)

NASA Astrophysics Data System (ADS)

Dufresne, A.; Ostermann, M.; Preusser, F.

2018-06-01

The Ötz Valley and adjacent regions in Tyrol (Austria) have been repeatedly affected by large rockslope failures following deglaciation. Six rockslides, each over 107 m3 in volume, were emplaced into the Ötz and Inn valleys, five of which formed persistent rockslide dams. Even though catastrophic rockslope failures are short-lived events (commonly minutes) they can have long-lasting impacts on the landscape. For example, large fans have built in the Ötz Valley and knickpoints persist at the former dam sites even though the Ötz River has eroded through the deposits during the past thousands of years; exact age-constraints of rockslide dam failure, however, are still scarce. Empirical, geomorphic stability indices from the literature successfully identified the least and the most stable dams of this group, whereas the rest remain inconclusive with some indices variably placing the dams in the stable, unstable, and uncertain categories. This shows (a) that further index calibrations and (b) better age constraints on dam formation and failure are needed, and (c) that the exact processes of dam failure are not always trivial to pinpoint for ancient (partially) breached dams. This study is a contribution towards better constraining the nature and landscape impact of dam formation following large rockslope failures.

Modelling long term rockslide displacements with non-linear time-dependent relationships

NASA Astrophysics Data System (ADS)

De Caro, Mattia; Volpi, Giorgio; Castellanza, Riccardo; Crosta, Giovanni; Agliardi, Federico

2015-04-01

Rockslides undergoing rapid changes in behaviour pose major risks in alpine areas, and require careful characterization and monitoring both for civil protection and mitigation activities. In particular, these instabilities can undergo very slow movement with occasional and intermittent acceleration/deceleration stages of motion potentially leading to collapse. Therefore, the analysis of such instabilities remains a challenging issue. Rockslide displacements are strongly conditioned by hydrologic factors as suggested by correlations with groundwater fluctuations, snowmelt, with a frequently observed delay between perturbation and system reaction. The aim of this work is the simulation of the complex time-dependent behaviour of two case studies for which also a 2D transient hydrogeological simulation has been performed: Vajont rockslide (1960 to 1963) and the recent Mt. de La Saxe rockslide (2009 to 2012). Non-linear time-dependent constitutive relationships have been used to describe long-term creep deformation. Analyses have been performed using a "rheological-mechanical" approach that fits idealized models (e.g. viscoelastic, viscoplastic, elasto-viscoplastic, Burgers, nonlinear visco-plastic) to the experimental behaviour of specific materials by means of numerical constants. Bidimensional simulations were carried out using the finite difference code FLAC. Displacements time-series, available for the two landslides, show two superimposed deformation mechanisms: a creep process, leading to movements under "steady state" conditions (e.g. constant groundwater level), and a "dynamic" process, leading to an increase in displacement rate due to changes of external loads (e.g. groundwater level). For both cases sliding mass is considered as an elasto-plastic body subject to its self-weight, inertial and seepage forces varying with time according to water table fluctuation (due to snowmelt or changing in reservoir level) and derived from the previous hydrogeological analysis (see EGU2015-14374). All non-linearities are lumped into a thin layer representing the main rockslide basal shear zone. Due to the great number of parameters characterizing viscous rheological models we separated the modelling into different stages. Firstly, starting from available geotechnical data, we carried out shear strength reduction analysis for solving elasto-plastic critical parameters of the basal shear band. Then, according to the chosen approach, we applied different viscous rheological models in order to simulate steady and dynamic creep. We identified the Burgers-creep viscoplastic model (Mohr-Coulomb failure criterion coupled with general Burgers-creep time-dependent nucleus) as the most appropriate one for simulating the behavior of the two case studies and more generally of large rockslides that exhibit similar movements. Due to the adopted continuum numerical approach, the models reproduce only portions of displacements curves associated with first and secondary creep phenomena. The models have been calibrated and subsequently validated on long temporal series of monitoring data, and reliably simulate the in situ data.

Coastal cliffs, rock-slope failures and Late Quaternary transgressions of the Black Sea along southern Crimea

NASA Astrophysics Data System (ADS)

Pánek, Tomáš; Lenart, Jan; Hradecký, Jan; Hercman, Helena; Braucher, Règis; Šilhán, Karel; Škarpich, Václav

2018-02-01

Rock-slope failures represent a significant hazard along global coastlines, but their chronology remains poorly documented. Here, we focus on the geomorphology and chronology of giant rockslides affecting the Crimean Mountains along the Black Sea coast. Geomorphic evidence suggests that high (>100 m) limestone cliffs flanking the southern slopes of the Crimean Mountains are scarps of rockslides nested within larger deep-seated gravitational slope deformations (DSGSDs). Such pervasive slope failures originated due to lateral spreading of intensively faulted Late Jurassic carbonate blocks moving atop weak/plastic Late Triassic flysch and tuff layers. By introducing a dating strategy relying on the combination of the uranium-thorium dating (U-Th) of exposed calcareous speleothems covering the landslide scarps with the 36Cl exposure dating of rock walls, we are able to approximate the time interval between the origin of incipient crevices and the final collapse of limestone blocks that exposed the cliff faces. For the three representative large-scale rockslides between the towns of Foros and Yalta, the initiation of the DSGSDs as evidenced by the widening of crevices and the onset of speleothem accumulation was >300 ka BP, but the recent cliff morphology along the coast is the result of Late Pleistocene/Holocene failures spanning ∼20-0.5 ka BP. The exposures of rockslide scarps occurred mostly at ∼20-15, ∼8, ∼5-4 and ∼2-0.5 ka, which substantially coincide with the last major Black Sea transgressions and/or more humid Holocene intervals. Our study suggests that before ultimate fast and/or catastrophic slope failures, the relaxation of rock massifs correlative with karstification, cracks opening, and incipient sliding lasted on the order of 104-105 years. Rapid Late Glacial/Holocene transgressions of the Black Sea likely represented the last impulse for the collapse of limestone blocks and the origin of giant rockslides, simultaneously affecting the majority of the SW coast of the Crimean Peninsula.

The prehistoric Vajont rockslide: An updated geological model

NASA Astrophysics Data System (ADS)

Paronuzzi, Paolo; Bolla, Alberto

2012-10-01

This study presents the detailed reconstruction of the entire structure of the prehistoric Vajont rockslide (about 270-300 million m3 of rocks and debris) for the first time, describing the complex geometry and the characteristic superimposition of distinct rigid blocks on a very thick shear zone. The prehistoric Vajont rockslide was characterized by an enormous 'en masse' motion of a rigid overlying rock mass (100-130 m thick) that moved downslope, sliding onto a very thick shear zone (40-50 m thick, on average) made up of a chaotic assemblage of blocks, limestone angular gravel, and high plasticity clays (montmorillonitic clays). Coarse loose sediments, still exposed on the 9 October 1963 detachment surface, are always associated with large blocks made of strongly fractured rock masses (Fonzaso Formation: middle-upper Jurassic) preserving the stratification. The blocks of stratified and folded limestone sequences appear to be 'sheared off' from the underlying bedrock and can be considered as displaced rock masses planed off by the motion of the overlying rigid rock mass ('rock mass shavings'). The prehistoric Vajont rockslide was characterized by a multistage failure with a marked retrogressive evolution. The first rupture (Pian del Toc block) rapidly destabilized the upper slope, mobilizing a second rock mass block (Pian della Pozza block) that, in turn, determined the multiple rupture of the revealed shear zone material (Massalezza lobe). Even if the exact timing of the different phases is not known, the entire multistaged failure process was very rapid. At the end of the multistage retrogressive failure, the slope morphology of the northern toe of Mt. Toc was drastically changed and the large failed rock mass settled into the preexisting Vajont Valley assuming the unusual chair-like geometry. The Vajont rockslide represents a very significant example on how a complex geological situation, if not adequately analyzed and reconstructed, can lead to dangerous misinterpretations or even to erroneous engineering-geological and geotechnical models. Accurate fieldwork and modern technologies can be fundamental in solving such a very intriguing 'geological puzzle.'

Rock Slide Monitoring by Using TDR Inclinometers

NASA Astrophysics Data System (ADS)

Drusa, Marián; Bulko, Roman

2016-12-01

The geotechnical monitoring of the slope deformations is widespread at present time. In many geological localities and civil engineering construction areas, monitoring is a unique tool for controlling of negative factors and processes, also inform us about actual state of rock environment or interacting structures. It is necessary for risk assessment. In our case, geotechnical monitoring is controlling rockslide activity around in the future part of motorway. The construction of new highway route D1 from Bratislava to Košice crosses the territory which is affected by a massive rockslide close to Kraľovany village. There was a need to monitor the activity of a large unstable rockslide with deep shear planes. In this case of underground movement activity, the Department of Geotechnics of the University of Žilina installed inclinometers at the unstable area which worked on Time Domain Reflectometry (TDR) principle. Based on provided measurements, effectivity and suitability of TDR inclinometers for monitoring of deep underground movement activity is demonstrated.

Analysis of La Dehesa paleo-landslide. Central Pre-Andes of Argentina

NASA Astrophysics Data System (ADS)

Tapia Baldis, Carla; Rothis, Luis Martín; Perucca, Laura; Esper Angillieri, María; Vargas, Horacio; Ponce, David; Allis, Carlos

2018-04-01

The main objective of this paper is to consider the influence of Quaternary faults as likely triggering factor for rockslides occurrence in the Central Pre-Andes, a region with intense shallow seismic activity. A rockslide deposit was selected as study case, placed in the western flank of La Dehesa and Talacasto (DT) range (31°3‧37″ S and 68°46‧ 8″ W). Applied methodology includes the characterization of main discontinuities, reconstruction of the topography using a high-resolution digital elevation model, safety factor calculation along the sliding surface and, Newmark displacements estimation for three different hypothetical seismic scenarios, recreated from existing neotectonic local information. Equilibrium-limit method's results confirm that study case, La Dehesa rockslide (LDR), had a stable and safe slope's configuration under static conditions. However, a seismic horizontal coefficient between 0.2 and 0.3 decreases safety factor below the safety threshold. Newmark's displacements for different seismic reconstructed scenarios varies between 4.1 and 15.9 cm, values that agreed with a coherent failure process, likely triggered by Pleistocene to Holocene seismogenic sources in Central Pre-Andes. LDR trigger could be assigned mainly to an earthquake related to La Dehesa Quaternary fault (LDF) activity; however, similar movements produced by neighboring faults should not be discarded. LDR triggering related to climatic conditions is despised. Finally, the methodology presented in this work is easy to reproduce and may be applied to other rockslides located in the mountainous areas of the Central Pre-Andes of Argentina.

3D Numerical Simulation on the Rockslide Generated Tsunamis

NASA Astrophysics Data System (ADS)

Chuang, M.; Wu, T.; Wang, C.; Chu, C.

2013-12-01

The rockslide generated tsunami is one of the most devastating nature hazards. However, the involvement of the moving obstacle and dynamic free-surface movement makes the numerical simulation a difficult task. To describe both the fluid motion and solid movement at the same time, we newly developed a two-way fully-coupled moving solid algorithm with 3D LES turbulent model. The free-surface movement is tracked by volume of fluid (VOF) method. The two-step projection method is adopted to solve the Navier-Stokes type government equations. In the new moving solid algorithm, a fictitious body force is implicitly prescribed in MAC correction step to make the cell-center velocity satisfied with the obstacle velocity. We called this method the implicit velocity method (IVM). Because no extra terms are added to the pressure Poission correction, the pressure field of the fluid part is stable, which is the key of the two-way fluid-solid coupling. Because no real solid material is presented in the IVM, the time marching step is not restricted to the smallest effective grid size. Also, because the fictitious force is implicitly added to the correction step, the resulting velocity is accurate and fully coupled with the resulting pressure field. We validated the IVM by simulating a floating box moving up and down on the free-surface. We presented the time-history obstacle trajectory and compared it with the experimental data. Very accurate result can be seen in terms of the oscillating amplitude and the period (Fig. 1). We also presented the free-surface comparison with the high-speed snapshots. At the end, the IVM was used to study the rock-slide generated tsunamis (Liu et al., 2005). Good validations on the slide trajectory and the free-surface movement will be presented in the full paper. From the simulation results (Fig. 2), we observed that the rockslide generated waves are manly caused by the rebounding waves from two sides of the sliding rock after the water is dragging down by the solid downward motion. We also found that the turbulence has minor effect to the main flow field. The rock size, rock density, and the steepness of the slope were analyzed to understand their effects to the maximum runup height. The detailed algorithm of IVM, the validation, the simulation and analysis of rockslide tsunami will be presented in the full paper. Figure 1. Time-history trajectory of obstacle for the floating obstacle simulation. Figure 2. Snapshots of the free-surface elevation with streamlines for the rockslide tsunami simulation.

Characterization of the Jure (Sindhupalchok, Nepal) Landslide by TLS and field investigations

NASA Astrophysics Data System (ADS)

Jaboyedoff, Michel; Leibundgut, Geoffroy; Penna, Ivanna; Dahal, Ranjan Kumar; Sevkota, Sanjaya; Sudmeier, Karen

2015-04-01

On August 2nd 2014, a huge rockslide of approximately 5 million m3 blocked the Sun-Koshi River upstream of Jure village (Northeast of Kathmandu, Nepal). This landslide killed approximately 155 people, destroying approximately 120 houses completely and 37 partially. The main road leading to China was cut and the Sun-Koshi hydropower plant was affected. The landslide dammed the river, creating a 2 km long lake. During the whole month of August the authorities and the army managed to drain the lake in order to avoid a potential dam collapse and a disaster by flooding downstream. In addition, a road was built very quickly in the opposite slope of the rockslide. The main road was reopened in November 2014 crossing the rock avalanche deposit to reach China border. Rocky steep slope on right bank of lake is used for earthen road construction. After the quick draining of the lake water on October 5, 2014, many landslides were induced or reactivated on the slopes along the lake shore. Some are affecting the slopes over several hundred in uphill section. However, the roads are also promoting shallow landslides or old landslides reactivation. The DEM extracted from merging 16 terrestrial laser scanner (TLS) acquisitions permits to analyse the rock fall avalanche volume, scar structure and deposits. The rockslide was developed in phyllites, quartzite and sandstones. The stratification is folded but mainly subhorizontal in the scar area, while the scar is defined by several faults and visible joint sets. Using TLS and SRTM data the volume of the rockslide can be approximated at 5 million m3. From TLS data it is also possible to identify regional faults, which form the back scar with a dip of approximately 165°/60°. The discontinuity sets ~250°/60° and 075°/45° are forming oblique shallow wedges. In addition, subvertical joints which are cutting the whole scar are oriented north 145°. All these structures permits to define the volume involved in the rockslide. Satellite images since 2000 indicate an increasing rock fall and scarp development activity of the landslide before this catastrophic event and scarp development. In addition, it seems that some ephemeral springs developed below the unstable mass. The rockslide generated a rock avalanche, which is documented by the effect of volume on the travel distance. This Farböshung varies between 22° and 24° depending on the type of substratum, which is a bit above the standard values. The spreading of the rock mass can be also reproduced by simulations. It seems that the rockslide ran up the opposite slope and then receded as proposed by Crosta et al. (2003) for Val Pola. Furthermore the upper layer of soils on the failure area created an area of "mud splash" in the frontal part of the rock avalanche. Mud splash is supported by the mud and dust cover found in the trees on the opposite slope near the landslide dam. The analysis of this rock avalanche confirmed the general observation that can be made for present rockslides in general. It reactivated large scale instabilities. In addition, the location of such rockslide developed in complex structures accompanied by a degradation of the rock mass conditions. In addition, the impact of the lake on slope stability in and around the reservoir can be noticed. References: Crosta G.B., Imposimato S. and Roddeman D. G. (2003): Numerical modelling of large landslides stability and runout. Natural Hazards and Earth System Sciences, 3: 523-538 ICIMOD (2015): Eye on the Sun Koshi Landslide: Monitoring and Infrastructure Planning Key to Minimizing Scale of Disasters. http://www.icimod.org/?q=14356 NRSM (2014): Landslide on River Sun Koshi, Nepal. http://www.nrsc.gov.in/Nepal_Landslide.html Petley D. (2015): Sunkoshi landslide in Nepal - still no reduction in the lake. The landslide Blog.Blogs.agu.org. SANDRP (2015): Massive landslide blocks Sunkoshi River, Downstream Nepal-India under threat. http://sandrp.wordpress.com/2014/08/02/massive-landslide-blocks-sunkoshi-river-downstream-nepal-india-under-threat/

One hour of catastrophic landscape change in the upper Rhine River valley 9400 years ago

NASA Astrophysics Data System (ADS)

Clague, John; von Poschinger, Andreas; Calhoun, Nancy

2017-04-01

The Flims rockslide, which happened about 9400 years ago in the eastern Swiss Alps, is the largest postglacial terrestrial landslide in Europe. The landslide and the huge secondary mass flow it induced completely changed the floor and lower slopes of the Vorderrhein valley over a distance of several tens of kilometres, probably in one hour or less. The landslide began with the sudden detachment of 10-12 km3 of Jurassic and Cretaceous limestone from the north wall of the Vorderrhein valley. The detached rock mass rapidly fragmented as it accelerated and then struck the Rhein valley floor and the opposing valley wall. Tongues of debris traveled up and down the Vorderrhein. The impact liquefied approximately 1 km3 of valley-fill sediments, mainly fluvial and deltaic gravel and sand. The liquefied sediment moved as a slurry - the Bonaduz gravel - tens of kilometres downvalley from the impact site, carrying huge fragments of rockslide debris that became stranded on the valley floor, forming hills termed 'tumas'. Part of the flow was deflected by a cross-valley barrier and flowed 16 km up the Hinterrhein valley (the main tributary of the Vorderrhein), carrying tumas with it. Bonaduz gravel is >65 m thick and fines upward from massive sandy cobble gravel at its base to silty sand at its top. Sedimentologic and geomorphic evidence indicates that the liquefied sediment was transported as a hyperconcentated flow, possibly above a basal carpet of coarse diamictic sediment that behaved as a debris flow. The large amount of water involved in the Bonaduz flow indicates that at least part of the Flims rockslide entered a former lake in Vorderrhein valley. The rockslide debris impounded the Vorderrhein and formed Lake Ilanz, which persisted for decades or longer before the dam was breached in series of outburst floods. These floods further changed the valley floor below the downstream limit of the landslide. Today, Vorderrhein flows in a spectacular 8-km-long gorge incised up to 400 m in Flims rockslide debris; the river has yet to reach the base of the debris sheet.

The 2014 Lake Askja rockslide tsunami - optimization of landslide parameters comparing numerical simulations with observed run-up

NASA Astrophysics Data System (ADS)

Sif Gylfadóttir, Sigríður; Kim, Jihwan; Kristinn Helgason, Jón; Brynjólfsson, Sveinn; Höskuldsson, Ármann; Jóhannesson, Tómas; Bonnevie Harbitz, Carl; Løvholt, Finn

2016-04-01

The Askja central volcano is located in the Northern Volcanic Zone of Iceland. Within the main caldera an inner caldera was formed in an eruption in 1875 and over the next 40 years it gradually subsided and filled up with water, forming Lake Askja. A large rockslide was released from the Southeast margin of the inner caldera into Lake Askja on 21 July 2014. The release zone was located from 150 m to 350 m above the water level and measured 800 m across. The volume of the rockslide is estimated to have been 15-30 million m3, of which 10.5 million m3 was deposited in the lake, raising the water level by almost a meter. The rockslide caused a large tsunami that traveled across the lake, and inundated the shores around the entire lake after 1-2 minutes. The vertical run-up varied typically between 10-40 m, but in some locations close to the impact area it ranged up to 70 m. Lake Askja is a popular destination visited by tens of thousands of tourists every year but as luck would have it, the event occurred near midnight when no one was in the area. Field surveys conducted in the months following the event resulted in an extensive dataset. The dataset contains e.g. maximum inundation, high-resolution digital elevation model of the entire inner caldera, as well as a high resolution bathymetry of the lake displaying the landslide deposits. Using these data, a numerical model of the Lake Askja landslide and tsunami was developed using GeoClaw, a software package for numerical analysis of geophysical flow problems. Both the shallow water version and an extension of GeoClaw that includes dispersion, was employed to simulate the wave generation, propagation, and run-up due to the rockslide plunging into the lake. The rockslide was modeled as a block that was allowed to stretch during run-out after entering the lake. An optimization approach was adopted to constrain the landslide parameters through inverse modeling by comparing the calculated inundation with the observed run-up. By taking the minimum mean squared error between simulations and observations, a set of best-fit landslide parameters (friction parameters, initial speed and block size) were determined. While we were able to obtain a close fit with observations using the dispersive model, it proved impossible to constrain the landslide parameters to fit the data using a shallow water model. As a consequence, we conclude that in the present case, dispersive effects were crucial in obtaining the correct inundation pattern, and that a shallow water model produced large artificial offsets.

Blackhawk Landslide, California

NASA Image and Video Library

2016-09-30

The Blackhawk landslide, Lucerne Valley, California, is a lobe of marble breccia, 10 to 30 m thick, 3 km wide, and nearly 8 km long. Geologic evidence shows that the rockslide came down the gently inclined slope as a nearly monolithic sheet moving more than 100 km per hour. The accepted hypothesis is that the slide was lubricated by a layer of compressed air. At least two earlier similar but smaller rockslides have occurred in the area. The south-looking perspective view image was acquired on September 22, 2014, and is located at 34.4 degrees north, 116.7 degrees west. http://photojournal.jpl.nasa.gov/catalog/PIA21008

Structurally controlled 'teleconnection' of large-scale mass wasting (Eastern Alps)

NASA Astrophysics Data System (ADS)

Ostermann, Marc; Sanders, Diethard

2015-04-01

In the Brenner Pass area (Eastern Alps) , closely ahead of the most northward outlier ('nose') of the Southern-Alpine continental indenter, abundant deep-seated gravitational slope deformations and a cluster of five post-glacial rockslides are present. The indenter of roughly triangular shape formed during Neogene collision of the Southern-Alpine basement with the Eastern-Alpine nappe stack. Compression by the indenter activated a N-S striking, roughly W-E extensional fault northward of the nose of the indenter (Brenner-normal fault; BNF), and lengthened the Eastern-Alpine edifice along a set of major strike-slip faults. These fault zones display high seismicity, and are the preferred locus of catastrophic rapid slope failures (rockslides, rock avalanches) and deep-seated gravitational slope deformations. The seismotectonic stress field, earthquake activity, and structural data all indicate that the South-Alpine indenter still - or again - exerts compression; in consequence, the northward adjacent Eastern Alps are subject mainly to extension and strike-slip. For the rockslides in the Brenner Pass area, and for the deep-seated gravitational slope deformations, the fault zones combined with high seismic activity predispose massive slope failures. Structural data and earthquakes mainly record ~W-E extension within an Eastern Alpine basement block (Oetztal-Stubai basement complex) in the hangingwall of the BNF. In the Northern Calcareous Alps NW of the Oetztal-Stubai basement complex, dextral faults provide defacement scars for large rockfalls and rockslides. Towards the West, these dextral faults merge into a NNW-SSE striking sinistral fault zone that, in turn, displays high seismic activity and is the locus of another rockslide cluster (Fern Pass cluster; Prager et al., 2008). By its kinematics dictated by the South-Alpine indenter, the relatively rigid Oetztal-Stubai basement block relays faulting and associated mass-wasting over a N-S distance of more than 60 kilometers - from the Brenner Pass area located along the crestline of the Alps to mount Zugspitze near the northern fringe of the Northern Calcareous Alps. Major fault zones and intercalated rigid blocks thus can 'teleconnect' zones of preferred mass-wasting over large lateral distances in orogens. Reference: Prager, C., Zangerl, C., Patzelt, G., Brandner, R., 2008. Age distribution of fossil landslides in the Tyrol (Austria) and its surrounding areas. Natural Hazards and Earth System Science 8, 377-407.

Quaternary gravitational morpho-genesis of Central Apennines (Italy): Insights from the Mt. Genzana case history

NASA Astrophysics Data System (ADS)

Esposito, C.; Bianchi-Fasani, G.; Martino, S.; Scarascia-Mugnozza, G.

2013-10-01

This paper focuses on a study aimed at defining the role of geological-structural setting and Quaternary morpho-structural evolution on the onset and development of a deep-seated gravitational slope deformation which affects the western slope of Mt. Genzana ridge (Central Apennines, Italy). This case history is particularly significant as it comprises several aspects of such gravitational processes both in general terms and with particular reference to the Apennines. In fact: i) the morpho-structural setting is representative of widespread conditions in Central Apennines; ii) the deforming slope partially evolved in a large rockslide-avalanche; iii) the deformational process provides evidence of an ongoing state of activity; iv) the rockslide-avalanche debris formed a stable natural dam, thus implying significant variations in the morphologic, hydraulic and hydrogeological setting; v) the gravitational deformation as well as the rockslide-avalanche reveal a strong structural control. The main study activities were addressed to define a detailed geological model of the gravity-driven process, by means of geological, structural, geomorphological and geomechanical surveys. As a result, a robust hypothesis about the kinematics of the process was possible, with particular reference to the identification of geological-structural constraints. The process, in fact, involves a specific section of the slope exactly where a dextral transtensional structure is present, thus implying local structural conditions that favor sliding processes: the rock mass is intensively jointed by high angle discontinuity sets and the bedding attitude is quite parallel to the slope angle. Within this frame the gravitational process can be classified as a structurally constrained translational slide, locally evolved into a rockslide-avalanche. The activation of such a deformation can be in its turn related to the Quaternary morphological evolution of the area, which was affected by a significant topographic stress increase, testified by stratigraphic and morphologic evidence.

High-resolution seismic monitoring of rockslide activity in the Illgraben, Switzerland

NASA Astrophysics Data System (ADS)

Burtin, Arnaud; Hovius, Niels; Dietze, Michael; McArdell, Brian

2014-05-01

Rockfalls and rockslides are important geomorphic processes in landscape dynamics. They contribute to the evolution of slopes and supply rock materials to channels, enabling fluvial incision. Hillslope processes are also a natural hazard that we need to quantify and, if possible, predict. For these reasons, it is necessary to determine the triggering conditions and mechanisms involved in rockfalls. Rainfall is a well-known contributor since water, through soil moisture or pore pressure, may lead to the inception and propagation of cracks and can induce slope failure. Water can also affect slope stability through effects of climatic conditions such as the fluctuations of temperature around the freezing point. During the winter of 2012, we have recorded with a seismic array of 8 instruments substantial rockslide activity that affected a gully in the Illgraben catchment in the Swiss Alps. Three stations were positioned directly around the gully with a nearest distance of 400 m. The period of intense activity did not start during a rainstorm as it is common in summer but during a period of oscillation of temperatures around the freezing point. The activity did not occur in a single event but lasted about a week with a decay in time of the event frequency. Many individual events had two distinct seismic signals, with first, a short duration phase of about 10 s at frequencies below 5 Hz that we interpret as a slope failure signature, followed by a second long duration signal of > 60 s at frequencies above 10 Hz that we attribute to the propagation of rock debris down the slope. Thanks to the array of seismic sensors, we can study the fine details of this rockslide sequence by locating the different events, determining their distribution in time, and systematic quantification of seismic metrics (energy, duration, intensity...). These observations are compared to independent meteorological constrains and laser scan data to obtain an estimate of the volume mobilized by the event.

Landslide early warning based on failure forecast models: the example of Mt. de La Saxe rockslide, northern Italy

NASA Astrophysics Data System (ADS)

Manconi, A.; Giordan, D.

2015-02-01

We investigate the use of landslide failure forecast models by exploiting near-real-time monitoring data. Starting from the inverse velocity theory, we analyze landslide surface displacements on different temporal windows, and apply straightforward statistical methods to obtain confidence intervals on the estimated time of failure. Here we describe the main concepts of our method, and show an example of application to a real emergency scenario, the La Saxe rockslide, Aosta Valley region, northern Italy. Based on the herein presented case study, we identify operational thresholds based on the reliability of the forecast models, in order to support the management of early warning systems in the most critical phases of the landslide emergency.

Long term real-time GB_InSAR monitoring of a large rock slide

NASA Astrophysics Data System (ADS)

Crosta, G. B.; Agliardi, F.; Sosio, R.; Rivolta, C.; Mannucci, G.

2011-12-01

We analyze a long term monitoring dataset collected for a deep-seated rockslide (Ruinon, Lombardy, Italy). The rockslide has been actively monitored since 1997 by means of an in situ monitoring network (topographic benchmarks, GPS, wire extensometers) and since 2006 by a ground based radar. Monitoring data have been used to set-up and update the geological model, to identify rockslide extent and geometry, to analyse the sensitivity to seasonal changes and their impact on the reliability and early warning potential of monitoring data. GB-InSAR data allowed us to identify sectors characterized by different behaviours and associated to outcropping bedrock, thick debris cover, major structures. GB-Insar data have been used to set-up a "virtual monitoring network" by a posteriori selection of critical locations. Displacement time series extracted from GB-InSAR data provide a large amount of information even in debris-covered areas, when ground-based instrumentation fails. Such spatially-distributed, improved information, validated by selected ground-based measurements, allowed to establish new velocity and displacement thresholds for early warning purposes. The data are analysed to verify the dependency of the observed displacements on the line of sight orientation as well as on that of the framed resolution cell. Relationships with rainfall and morphological slope characteristics have been analysed to verify the sensitivity to rain intensity and amount and to distinguish among the different possible mechanisms.

Rockslide-debris avalanche of May 18, 1980, Mount St. Helens Volcano, Washington

USGS Publications Warehouse

Glicken, Harry

1996-01-01

This report provides a detailed picture of the rockslide-debris avalanche of the May 18, 1980, eruption of Mount St. Helens volcano. It provides a characterization of the deposit, a reinterpretation of the details of the first minutes of the eruption of May 18, and insight into the transport mechanism of the mass movement. Details of the rockslide event, as revealed by eyewitness photographs, are correlated with features of the deposit. The photographs show three slide blocks in the rockslide movement. Slide block I was triggered by a magnitude 5.1 earthquake at 8:32 a.m. Pacific Daylight Time (P.D.T.). An exploding cryptodome burst through slide block II to produce the 'blast surge.' Slide block III consisted of many discrete failures that were carried out in continuing pyroclastic currents generated from the exploding cryptodome. The cryptodome continued to depressurize after slide block III, producing a blast deposit that rests on top of the debris-avalanche deposit. The hummocky 2.5 cubic kilometer debris-avalanche deposit consists of block facies (pieces of the pre-eruption Mount St. Helens transported relatively intact) and matrix facies (a mixture of rocks from the old mountain and cryptodome dacite). Block facies is divided into five lithologic units. Matrix facies was derived from the explosively generated current of slide block III as well as from disaggregation and mixing of debris-avalanche blocks. The mean density of the old cone was measured to be abut 20 percent greater than the mean density of the avalanche deposit. Density in the deposit does not decrease with distance which suggests that debris-avalanche blocks were dilated at the mountain, rather than during transport. Various grain-size parameters that show that clast size converges about a mean with distance suggest mixing during transport. The debris-avalanche flow can be considered a grain flow, where particles -- either debris-avalanche blocks or the clasts within the blocks -- collided and created dispersive stress normal to the movement of material. The dispersive stress preserved the dilation of the material and allowed it to flow.

Satellite Monitoring of Pakistan's Rockslide-Dammed Lake Gojal

NASA Astrophysics Data System (ADS)

Kargel, Jeffrey S.; Leonard, Gregory; Crippen, Robert E.; Delaney, Keith B.; Evans, Stephen G.; Schneider, Jean

2010-10-01

On 4 January 2010, a rockslide 1200 meters long, 350 meters wide, and 125 meters high dammed the Hunza River in Attabad, northern Pakistan, and formed Lake Gojal. The initial mass movement of rock killed 20 people and submerged several villages and 22 kilometers of the strategic Karakoram Highway linking Pakistan and China. Tens of thousands of people were displaced or cut off from overland connection with the rest of the country. On 29 May, the lake overflow began to pour through a spillway excavated by Pakistani authorities. On approximately 20 July, the lake attained a maximum depth of 119 meters and a torrent at least 9 meters deep issued over the spillway, according to Pakistan's National Disaster Management Authority (NDMA). To date, the natural dam is holding and eroding slowly. However, the threat of a catastrophic outburst flood remains.

75 FR 75719 - U.S. Virgin Islands Disaster # VI-00007

Federal Register 2010, 2011, 2012, 2013, 2014

2010-12-06

... U.S. Virgin Islands (FEMA-1949-DR), dated 11/24/ 2010. Incident: Severe storms, flooding, rockslides, and mudslides associated with Tropical Storm Tomas. Incident Period: 11/08/2010 through 11/12/2010...

Rockslide susceptibility and hazard assessment for mitigation works design along vertical rocky cliffs: workflow proposal based on a real case-study conducted in Sacco (Campania), Italy

NASA Astrophysics Data System (ADS)

Pignalosa, Antonio; Di Crescenzo, Giuseppe; Marino, Ermanno; Terracciano, Rosario; Santo, Antonio

2015-04-01

The work here presented concerns a case study in which a complete multidisciplinary workflow has been applied for an extensive assessment of the rockslide susceptibility and hazard in a common scenario such as a vertical and fractured rocky cliffs. The studied area is located in a high-relief zone in Southern Italy (Sacco, Salerno, Campania), characterized by wide vertical rocky cliffs formed by tectonized thick successions of shallow-water limestones. The study concerned the following phases: a) topographic surveying integrating of 3d laser scanning, photogrammetry and GNSS; b) gelogical surveying, characterization of single instabilities and geomecanichal surveying, conducted by geologists rock climbers; c) processing of 3d data and reconstruction of high resolution geometrical models; d) structural and geomechanical analyses; e) data filing in a GIS-based spatial database; f) geo-statistical and spatial analyses and mapping of the whole set of data; g) 3D rockfall analysis; The main goals of the study have been a) to set-up an investigation method to achieve a complete and thorough characterization of the slope stability conditions and b) to provide a detailed base for an accurate definition of the reinforcement and mitigation systems. For this purposes the most up-to-date methods of field surveying, remote sensing, 3d modelling and geospatial data analysis have been integrated in a systematic workflow, accounting of the economic sustainability of the whole project. A novel integrated approach have been applied both fusing deterministic and statistical surveying methods. This approach enabled to deal with the wide extension of the studied area (near to 200.000 m2), without compromising an high accuracy of the results. The deterministic phase, based on a field characterization of single instabilities and their further analyses on 3d models, has been applied for delineating the peculiarity of each single feature. The statistical approach, based on geostructural field mapping and on punctual geomechanical data from scan-line surveying, allowed the rock mass partitioning in homogeneous geomechanical sectors and data interpolation through bounded geostatistical analyses on 3d models. All data, resulting from both approaches, have been referenced and filed in a single spatial database and considered in global geo-statistical analyses for deriving a fully modelled and comprehensive evaluation of the rockslide susceptibility. The described workflow yielded the following innovative results: a) a detailed census of single potential instabilities, through a spatial database recording the geometrical, geological and mechanical features, along with the expected failure modes; b) an high resolution characterization of the whole slope rockslide susceptibility, based on the partitioning of the area according to the stability and mechanical conditions which can be directly related to specific hazard mitigation systems; c) the exact extension of the area exposed to the rockslide hazard, along with the dynamic parameters of expected phenomena; d) an intervention design for hazard mitigation.

Prevention and remediation of rockslide at left portal of north tunnel of Da Nang - Qu ang Ngai expressway in Quang Nam, Vietnam

NASA Astrophysics Data System (ADS)

Thinh, Phi Hong; Tuan, Pham Quoc; Minh, Pham Ngoc

2016-03-01

Da Nang - Quang Ngai Expressway is one part of the North - South Expressway of Vietnam being 130km in length, 24.5m in width. The Tunnel is a section of 4 construction packages with station of 22+500km - 23+000km. The tunnel is designed to go through a small hill, altitude of about 120m above sea level and 500m long and has two bounds - called North and South Tunnel. The North Tunnel has two portals - left and right. Bedrock is sedimentary rock (alternation of sandstone and conglomerate). Authors have investigated the field, detected inaccuracy in geotechnical investigation report, applied discontinuity model and failure criterion for anisotropic rock, analyzed stability of rock slope and proposed a solution to prevent rockslide at the Left Portal of the North Tunnel of the Expressway.

Modelling of the Vajont rockslide displacements by delayed plasticity of interacting sliding blocks

NASA Astrophysics Data System (ADS)

Castellanza, riccardo; Hedge, Amarnath; Crosta, Giovanni; di Prisco, Claudio; Frigerio, Gabriele

2015-04-01

In order to model complex sliding masses subject to continuous slow movements related to water table fluctuations it is convenient to: i) model the time-dependent mechanical behaviour of the materials by means of a viscous-plastic constitutive law; ii) assume the water table fluctuation as the main input to induce displacement acceleration; iii) consider, the 3D constrains by maintaining a level of simplicity such to allow the implementation into EWS (Early Warning System) for risk management. In this work a 1D pseudo-dynamic visco-plastic model (Secondi et al. 2011), based on Perzyna's delayed plasticity theory is applied. The sliding mass is considered as a rigid block subject to its self weight, inertial forces and seepage forces varying with time. All non-linearities are lumped in a thin layer positioned between the rigid block and the stable bedrock. The mechanical response of this interface is assumed to be visco-plastic. The viscous nucleus is assumed to be of the exponential type, so that irreversible strains develop for both positive and negative values of the yield function; the sliding mass is discretized in blocks to cope with complex rockslide geometries; the friction angle is assumed to reduce with strain rate assuming a sort of strain - rate law (Dietrich-Ruina law). To validate the improvements introduced in this paper the simulation of the displacements of the Vajont rockslide from 1960 to the failure, occurred on October the 9th 1963, is perfomed. It will be shown that, in its modified version, the model satisfactorily fits the Vajont pre-collapse displacements triggered by the fluctuation of the Vajont lake level and the associated groundwater level. The model is able to follow the critical acceleration of the motion with a minimal change in friction properties.The discretization in interacting sliding blocks confirms its suitability to model the complex 3D rockslide behaviour. We are currently implementing a multi-block model capable to include the mutual influence of multiple blocks, characterized by different geometry and groundwater levels, shear zone properties and type of interconnection. Secondi M., Crosta G., Di Prisco C., Frigerio G., Frattini P., Agliardi F. (2011) "Landslide motion forecasting by a dynamic visco-plastic model", Proc. The Second World Landslide Forum, L09 - Advances in slope modelling, Rome, 3-9 October 2011, paper WLF2-2011-0571

Thermal regimes in bedrock and open fractures in the Nordnes rockslide, Norway

NASA Astrophysics Data System (ADS)

Hvidtfeldt Christiansen, Hanne; Harald Blikra, Lars

2010-05-01

The Nordnes rockslide site is located in the arctic part of the periglacial mountain landscape of Northern Norway at 69°30'N. It consists in the upper part of 1-10 m wide and 1-10 m deep open fractures. Extensive displacements measurements using GPS surveys, crackmeters, tiltmeter and lasers establish the intermunicipality monitoring programme, which shows ongoing deformation of the rockslide. In the rather special topographical setting of the open fractures we have during the International Polar Year 2007 to 2009 recorded the thermal regime of the upper part of the bedrock and of the air in the cracks for attempting to determine whether the recorded deformation can be geomorphologically controlled by bedrock surface expansion and contraction and/or by seasonal freezing or even by permafrost, or if only normal gravitational processes control the observed displacements. The upper 40 cm bedrock thermal conditions have been investigated in different exposures to identify the seasonal freezing depth and length, for determination of the influence of potential ice segregation processes causing weathering of the bedrock surfaces. The data show generally that that the bedrock surface is in the -3 to -8C freezing window for 3 to 6 months. Likewise 250 cm deep bedrock thermal monitoring have been carried out in three boreholes during one year at 900 m, 800 m and 625 m asl. extending over the area from the upper part of the unstable area and into the stable area above, for determination of the regional permafrost zone. These results in combination with thermal evidence from other deeper boreholes from the same setting in the same region show that seasonal freezing extends 5-10 m down, and that a potential active layer also is in the order of 5-10 m deep. The air temperatures in the cracks show significant cooling during winter, when the cracks have a thick snow cover, thus demonstrating the potential existence of permafrost in deeper part of the cracks and in the ground just around these. Automatic photography has been used for the last 4 years to study the seasonal snow cover duration and thickness in the open cracks. This shows that a thicker snow cover only develops in mid winter, with maximum amounts of snow in March and April, but also that not all snow melts during summer in the deeper parts of the open cracks. In addition we have found small pockets of ice in closed spaces of the bottom parts of the open crack, indicating the presence of permafrost. The combination of thermal data and the special seasonal variation in the rockslide deformations indicate that most likely refreezing of snow meltwater goes on in the open cracks for a considerable period from late summer, autumn and into the early winter, when the recorded rockslide deformation is largest. In late winter no significant deformation is recorded when the ground is constantly frozen, but there is a significant potential for ice segregation to occur where moisture is present in the rock.

Chasing a complete understanding of a rapid moving rock slide: the La Saxe landslide

NASA Astrophysics Data System (ADS)

Crosta, G. B.; Cancelli, P.; Tamburini, A.; Alberto, W.; Broccolato, M.; Castellanza, R.; Frattini, P.; Agliardi, F.; Rivolta, C.; Leva, D.

2012-04-01

Large deep seated slope deformations affect entire valley flanks and are characterized by slow to extremely slow present day displacement rates. Because of their extreme size, they are frequently characterized at their interior by secondary instabilities which can be classified as rockslides, that can originate large rock avalanches or can move at much faster rates with respect to the main mass. As a consequence local instabilities and reactivation of sectors of deep seated deformations should be carefully monitored and studied especially because they can affect strongly deformed and weakened rock masses. Because of these natural conditions and their preferential location in coincidence of slope steepening, these rockslides can undergo rapid evolution and activation putting the upmost urgency for monitoring, hazard and risk assessment. We present the case study of the La Saxe rockslide (Courmayeur, Aosta valley, Italy), located within a deep seated deformation affecting most of the 10 km long left hand flank of the Ferret valley (between 1340 m and 2300 m a.s.l.) and which underwent a major phase of acceleration in the last decade. The rockslide affects the extreme south western tip of the deep seated deformation at the outlet of Ferret valley, with an estimated volume of about 8 x 106 m3 of clay schists and thinly bedded black carbonates, intensely folded and faulted. An intense investigation activity has been performed in the last 2 years to reach a more complete understanding of the phenomenon. Boreholes have been drilled, logged, and instrumented to constrain the landslide volume, the rate of displacement at depth, and the water pressure. Displacement monitoring has been undertaken at successive steps by setting up sequentially: a distance measurement network (6 optical targets), a GPS network for periodic measurements (12 stations), a ground-based interferometer (GB-InSAR, LisaLab, by Ellegi, with 10 min acquisition intervals), a geodetic network based on a total station and 25 optical targets measured at 2 h intervals, a GPS network (7 stations) for quasi-real time measurements, four differential multiparametric borehole systems (DMS columns up to 100 m long). A geotechnical network has been also implemented including open pipe piezometers, borehole wire extensometers and inclinometric casings. This enormous monitoring effort is motivated by the extreme risk associated to this phenomenon, which is hanging over a famous touristic resort, a world famous cable way, the Mont Blanc highway, and in close proximity to the Mont Blanc tunnel. Rockslide characterization, failure surface definition, and groundwater flow investigations allowed for a series of slope stability analyses to be completed, together with modelling of the expected invasion area. Relationships with snowmelt have been ascertained and an early warning system based on real time measurements redundancy and all weather capabilities has been set up. LisaLab GB-InSAR equipment continuously provide spatially distributed displacement data which have been analysed to identify different failure scenarios and sensitivity of the landslide to triggering and controlling factors. Geodetic measurements are integrated with GB-InSAR data for verification and in depth 3D displacement reconstructions.

Characterization of the Vajont landslide (North-Eastern Italy) by means of reflection and surface wave seismics

NASA Astrophysics Data System (ADS)

Petronio, Lorenzo; Boaga, Jacopo; Cassiani, Giorgio

2016-05-01

The mechanisms of the disastrous Vajont rockslide (North-Eastern Italy, October 9, 1963) have been studied in great detail over the past five decades. Nevertheless, the reconstruction of the rockslide dynamics still presents several uncertainties, including those related to the accurate estimation of the actual landslide mass. This work presents the results of a geophysical characterization of the Vajont landslide body in terms of material properties and buried geometry. Both aspects add new information to the existing dataset and will help a better understanding of the rockslide failure mechanisms and dynamics. In addition, some general considerations concerning the intricacies of landslide characterization can be drawn, with due attention to potential pitfalls. The employed techniques are: (i) high resolution P-wave reflection, (ii) high resolution SH-wave reflection, (iii) controlled source surface wave analysis. We adopted as a seismic source a vibrator both for P waves and SH waves, using vertical and horizontal geophones respectively. For the surface wave seismic survey we used a heavy drop-weight source and low frequency receivers. Despite the high noise level caused by the fractured conditions of the large rock body, a common situation in landslide studies, we managed to achieve a satisfying imaging quality of the landslide structure thanks to the large number of active channels, the short receiver interval and the test of appropriate seismic sources. The joint use of different seismic techniques help focus the investigation on the rock mass mechanical properties. Results are in good agreement with the available borehole data, the geological sections and the mechanical properties of the rockmass estimated by other studies. In general the proposed approach is likely to be applicable successfully to similar situations where scattering and other noise sources are a typical bottleneck to geophysical data acquisition on landslide bodies.

Gravity-induced rock mass damage related to large en masse rockslides: Evidence from Vajont

NASA Astrophysics Data System (ADS)

Paronuzzi, Paolo; Bolla, Alberto

2015-04-01

The Vajont landslide is a well-known, reservoir-induced slope failure that occurred on 9 October 1963 and was characterized by an 'en masse' sliding motion that triggered various large waves, determining catastrophic consequences for the nearby territory and adjacent villages. During the Vajont dam construction, and especially after the disaster, some researchers identified widespread field evidence of heavy rock mass damage involving the presumed prehistoric rockslide and/or the 1963 failed mass. This paper describes evidence of heavy gravitational damage, including (i) folding, (ii) fracturing, (iii) faulting, and (iv) intact rock disintegration. The gravity-induced rock mass damage (GRMD) characterizes the remnants of the basal shear zone, still resting on the large detachment surface, and the 1963 failed rock mass. The comprehensive geological study of the 1963 Vajont landslide, based on the recently performed geomechanical survey (2006-present) and on the critical analysis of the past photographic documentation (1959-1964), allows us to recognize that most GRMD evidence is related to the prehistoric multistage Mt. Toc rockslide. The 1963 catastrophic en masse remobilization induced an increase to the prehistoric damage, reworking preexisting structures and creating additional gravity-driven features (folds, fractures, faults, and rock fragmentation). The gravity-induced damage was formed during the slope instability phases that preceded the collapse (static or quasi-static GRMD) and also as a consequence of the sliding motion and of the devastating impact between the failed blocks (dynamic GRMD). Gravitational damage originated various types of small drag folds such as flexures, concentric folds, chevron, and kink-box folds, all having a radius of 1-5 m. Large buckle folds (radius of 10-50 m) are related to the dynamic damage and were formed during the en masse motion as a consequence of deceleration and impact processes that involved the sliding mass. Prior to failure, unstable rock slopes can be affected by diffuse newly formed gravity-driven joints that are absent in the surrounding area and within the underlying bedrock, as the Vajont case history demonstrates (joint sets J9 and J10). These fractures, caused by critical tensile and shear stresses, represent an important mechanical clue to recognizing, on a geological basis, the instability condition of a rock slope under investigation. Owing to its complex geological evolution, the Vajont landslide is an outstanding example to help learn about cumulative GRMD effects that can accumulate over time when an ancient rockslide is further remobilized by a sudden en masse sliding motion.

Landslides and the weathering of granitic rocks

Treesearch

Philip B. Durgin

1977-01-01

Abstract - Granitic batholiths around the Pacific Ocean basin provide examples of landslide types that characterize progressive stages of weathering. The stages include (1) fresh rock, (2) corestones, (3) decomposed granitoid, and (4) saprolite. Fresh granitoid is subject to rockfalls, rockslides, and block glides. They are all controlled by factors related to...

Distribution and features of landslides induced by the 2008 Wengchuan Earthquake, Sichuan, China

NASA Astrophysics Data System (ADS)

Chigira, M.; Xiyong, W.; Inokuchi, T.; Gonghui, W.

2009-04-01

2008 Sichuan earthquake with a magnitude of Mw 7.9 induced numerous mass movements around the fault surface ruptures of which maximum separations we observed were 3.6 m vertical and 1.5 m horizontal (right lateral). The affected area was mountainous areas with elevations from 1000 m to 4500 m on the west of the Sichuan Basin. The NE-trending Longmenshan fault zone runs along the boundary between the mountains on the west and the Sichuan basin (He and Tsukuda, 2003), of which Yinghsiuwan-Beichuan fault was the main fault that generated the 2008 earthquake (Xu, 2008). The basement rocks of the mountainous areas range from Precambrian to Cretaceous in age. They are basaltic rocks, granite, phyllite, dolostone, limestone, alternating beds of sandstone and shale, etc. There were several types of landslides ranging from small, shallow rockslide, rockfall, debris slide, deep rockslide, and debris flows. Shallow rockslide, rock fall, and debris slide were most common and occurred on convex slopes or ridge tops. When we approached the epicentral area, first appearing landslides were of this type and the most conspicuous was a failure of isolated ridge-tops, where earthquake shaking would be amplified. As for rock types, slopes of granitic rocks, hornfels, and carbonate rocks failed in wide areas to the most. They are generally hard and their fragments apparently collided and repelled to each other and detached from the slopes. Alternating beds of sandstone and mudstone failed on many slopes near the fault ruptures, including Yinghsiuwan near the epicenter. Many rockfalls occurred on cliffs, which had taluses on their feet. The fallen rocks tumbled down and mostly stopped within the talus surfaces, which is quite reasonable because taluses generally develop by this kind of processes. Many rockslides occurred on slopes of carbonate rocks, in which dolostone or dolomitic limestone prevails. Deep-seated rockslide occurred on outfacing slopes and shallow rockslide and rockfall occurred on infacing slopes. Infacing slopes generally are steeper than outfacing slopes and hence surface rocks on infacing slopes tend to be loosened by gravity. Detachment surfaces of carbonate rocks are generally not smooth surfaces but are rough surfaces with dimple-like depressions, which are made by dissolution of these rocks. This feature is one of the most important causes to induce landslide in carbonate rocks. Many gravitational deformations were observed on phyllite slopes. Landslides on the west of Beichuan city is probably of weathered phyllite, which had been preceded by gravitational deformation beforehand. Taochishan landslide in Beichuan occurred on probable outfacing slope of phyllite. The Formosat II images on Google earth indicated that this landslide was also preceded by gravitational deformation, which appeared as spur-crossing depressions with upslope-convex traces on plan. Satellite images indicated that some landslides had long lobate forms, suggesting that they were flow. One of them was Shechadientsu landslide 34 km northeast of Dujiangyan, occurring across the probable earthquake fault rupture. It was 1.5 km long with a maximum width of 250 m and an apparent friction angle of 22°. The top of this landslide area was a steep cliff of Precambrian granite, which failed to go down a small valley. The volume of the slope failure was estimated much less than the volume of the deposit. The small valley had sporadic patches of bedrock consisting of alternating beds of sandstone and mudstone of Triassic in age. The bedrock was covered by bluish grey, clayey, water-saturated debris, which was not disturbed and in turn covered by water-saturated brownish debris with rubbles. The landslide deposits had wrinkles on the surface and streaks of same color rock fragments. In addition, cross section near the distal part had clearly defined reverse grading, in which larger rubbles with a maximum diameter of 5 m concentrated at the surface part. These characteristics strongly suggest that valley-fill sediments mobilized by the earthquake and flowed down the valley, getting higher at the outer side of the valley bent. The largest landslide with an estimated volume of 1 billion m3 occurred on an outfacing carbonate rock slope, which had been preceded by gravitational deformation appearing as a ridge-top depression. The second largest one occurred on a smooth outfacing slope that had been undercut.

A comparison of artifical and natural slope failures: the Santa Barbara earthquake of August 13, 1978.

USGS Publications Warehouse

Harp, E.L.; Keefer, D.K.; Wilson, R.C.

1980-01-01

The earthquake triggered rockfalls and rockslides from steep road cuts and coastal cliffs. The landslide reconnaissance survey which was carried out is described, with separate comments on each landslide site recorded. The general regional slope response to the earthquake is briefly considered. -R. House

The development of structures in analogue and natural debris avalanches

NASA Astrophysics Data System (ADS)

Paguican, Engielle Mae; van Wyk de Vries, Benjamin; Mahar Francisco Lagmay, Alfredo; Grosse, Pablo

2010-05-01

All types of rockslide-debris avalanches present a plethora of internal structures that are also well observed on the surface. Many of these are seen as faults and folds that can be used to determine deformation history and kinematics. We present two sets of simple and well-constrained experiments of reduced basal friction laboratory rockslides, equivalent to a highly deformed simple shear layer, with plug-flow. These follow the original ramp-slide work of Shea and van Wyk de Vries (Geosphere, 2008). The experiments used a curved ramp where materials accelerate until reaching a gently-sloped depositional surface and a constantly inclined ramp with a more regular slope and longer slides. A detailed description of deposit structures, their sequential formation and morphology is then used to investigate the transport type and deformation chronology from slide initiation to runout stopping of avalanches. Results using a curved ramp show accumulation and thickening at where the slope decreases. The thickened mass then further remobilises and advances by secondary collapse of the mass. Such a stop-start process may be important in many mountainous avalanches where there are rapid changes in slope. The constantly inclined ramp shows shearing and extensional structures at the levees and a set of compression and extension structures in the middle. We noted that frontal accumulation during flow occurs as materials at the front move slower relative to those in the medial and proximal zones. This also leads to secondary frontal collapse, and helps to maintain a thicker mass that can flow further. Descriptions and analyses of these structures are then applied to the kinematics and dynamics of natural examples. We study the 2006 Guinsaugon Rockslide event in the Philippines and find that frontal accumulation and secondary avalanching had also occurred and were important in determining the distribution and runout of the mass. Frontal bulking and collapse may also have occurred at the Tacna Avalanche, Peru and the Pajonales-Aracar event in Argentina.

The major mass movements of the Western Dolomites (Italy)

NASA Astrophysics Data System (ADS)

Ostermann, Marc; Gruber, Alfred

2014-05-01

Major gravitational slope deformations are widely disseminated in the Dolomite Mountains (NE-Italy), one of the world's most conspicuous landscapes and part of the UNESCO world heritage list. Because of their unique geological composition the Dolomites provide a natural laboratory where nearly all kind of mass wasting processes, in all dimensions, can be investigated. Simplified there are thick, rigid carbonatic successions (Triassic-Jurassic) resting on and interfingering with relatively weak successions of shallow marine clastic and of pelagic sediments. In some areas even volcanic successions and crystalline basement rocks are outcropped. Hugh rockslides and long run-out rock avalanches are limited to the carbonates and volcanic rocks. The superposition of Middle and Upper Triassic reefs, showing brittle deformation behaviour, above weak successions of evaporites, clays and marls, characterised by ductile deformation behaviour, leads to a classical "hard on soft" situation. The observable results are rockslides and rock avalanches of several hundred millions of m³ in volume, large scale rock toppling and rock flows and deep-seated gravitational slope deformations (DSGSD). Within the weak successions slow moving rotational landslides and large dimensional earthflows are very common. We focused our research on an area of about 40*40km within the Western and Northern Dolomites, where an inventory of the major gravitational mass movements has been compiled. We combined detailed geological maps with high resolution DEMs and extensive fieldwork data within a GIS-system. The different processes have been characterised and classified based on kinematic criteria, dimension and involved material. Altogether the database consists of 186 entries. Most frequently are landslides and earthflows (146) followed by catastrophic rockslides and rock avalanches (26) and DSGSDs (14). The spatial distribution of the mapped processes has been analysed in terms of the main geomorphological and geological characteristics, and of their clustering. For some of the most impressive sites age data has been established and allows a supra-regional comparison. For each type of investigated mass movement we present an exemplary case study that shows the most important features of the major slope failures within the Dolomites.

Qualitative landslide susceptibility assessment by multicriteria analysis: A case study from San Antonio del Sur, Guantánamo, Cuba

NASA Astrophysics Data System (ADS)

Castellanos Abella, Enrique A.; Van Westen, Cees J.

Geomorphological information can be combined with decision-support tools to assess landslide hazard and risk. A heuristic model was applied to a rural municipality in eastern Cuba. The study is based on a terrain mapping units (TMU) map, generated at 1:50,000 scale by interpretation of aerial photos, satellite images and field data. Information describing 603 terrain units was collected in a database. Landslide areas were mapped in detail to classify the different failure types and parts. Three major landslide regions are recognized in the study area: coastal hills with rockfalls, shallow debris flows and old rotational rockslides denudational slopes in limestone, with very large deep-seated rockslides related to tectonic activity and the Sierra de Caujerí scarp, with large rockslides. The Caujerí scarp presents the highest hazard, with recent landslides and various signs of active processes. The different landforms and the causative factors for landslides were analyzed and used to develop the heuristic model. The model is based on weights assigned by expert judgment and organized in a number of components such as slope angle, internal relief, slope shape, geological formation, active faults, distance to drainage, distance to springs, geomorphological subunits and existing landslide zones. From these variables a hierarchical heuristic model was applied in which three levels of weights were designed for classes, variables, and criteria. The model combines all weights into a single hazard value for each pixel of the landslide hazard map. The hazard map was then divided by two scales, one with three classes for disaster managers and one with 10 detailed hazard classes for technical staff. The range of weight values and the number of existing landslides is registered for each class. The resulting increasing landslide density with higher hazard classes indicates that the output map is reliable. The landslide hazard map was used in combination with existing information on buildings and infrastructure to prepare a qualitative risk map. The complete lack of historical landslide information and geotechnical data precludes the development of quantitative deterministic or probabilistic models.

Multi-temporal terrestrial laser scanning for identifying rockslide modifications: potentialities and problems

NASA Astrophysics Data System (ADS)

Castagnetti, Cristina; Bertacchini, Eleonora; Capra, Alessandro; Rivola, Riccardo

2013-04-01

The heart of this research is to provide an efficient methodology for a reliable acquisition and interpretation of Terrestrial Laser Scanner (TLS) data in the application field of landslide monitoring. In particular, rockslides, which are characterized by vertical walls of rock and by a complex morphology, are of great concern in the study. In these cases the airborne laser scanning is not able to provide useful and reliable description and the terrestrial laser scanning might be the only possible choice to obtain a good and reliable description of the geomorphology or to identify the changes occurred over time. The last purpose is still a challenging task when long distances are involved because the accurate and punctual identification of displacements is not possible due to the laser beam divergence. The final purpose of the research is a proposal of a methodology which is based on TLS technology for identifying displacements and extracting geomorphological changes. The approach is clearly based on a multi-temporal analysis which is computed on several repetitions of TLS surveys performed on the area of interest. To achieve best results and optimize the processing strategy, different methods about point clouds alignment have been tested together with algorithms both for filtering and post-processing. The case study is the Collagna Landslide that is located in the North Appennines (Reggio Emilia, Italy) on the right flank of Biola torrent. The large scale composite landslide area is made both by a wide rock slide sector and a more limited earth slide sector that, after high precipitation rates, disrupted the National Road 63 in December 2008. An integrated monitoring system is installed since 2009 and comprises both point-based technologies such as extensometers, total station and global positioning system, and also area-based technologies such as airborne laser scanner, long-range TLS and ground-based radar. This choice allows to couple the advantages of both approaches. The research focuses on TLS surveys for trying to detect displacements which might be responsible for instability. Four point clouds acquired in the last two years allow to monitor the spatial displacements of the whole slope, especially focusing on the rockslide sector. It is worth to underline an important aspect which contributes to highlight the significance of the work: the mean scanning distance is about 1.3 km. Few examples exist in literature about the use of very long-range TLS for displacements investigation. By sequentially analyzing TLS surfaces, displacement maps have been obtained for the rockslide area. Confirmation have been achieved by comparing results with movements of reflectors sited on the entire slope and continuously measured by total station. Such validation strengthens the idea that TLS has serious potentialities to be successfully used for analyzing instability. Comparing surfaces is not easy at all, thus a discussion about the encountered problems will be taken into account: any significant detail about potentialities and difficulties of the alignment strategy and the processing procedure will be given together with details about the specific algorithm implemented for filtering displacements by taking into account actual geomorphological conditions.

Landslide/reservoir interaction: 3D numerical modelling of the Vajont rockslide and generated water wave

NASA Astrophysics Data System (ADS)

Crosta, G.; Imposimato, S.; Roddeman, D.; Frattini, P.

2012-04-01

Fast moving landslides can be originated along slopes in mountainous terrains with natural and artificial lakes, or fjords at the slope foot. This landslides can reach extremely high speed and the impact with the immobile reservoir water can be influenced by the local topography and the landslide mass profile. The impact can generate large impulse waves and landslide tsunami. Initiation, propagation and runup are the three phases that need to be considered. The landslide evolution and the consequent wave can be controlled by the initial mass position (subaerial, partially or completely submerged), the landslide speed, the type of material, the subaerial and subaqueous slope geometry, the landslide depth and length at the impact, and the water depth. Extreme events have been caused by subaerial landslides: the 1963 Vajont rockslide (Italy), the 1958 Lituya Bay event (Alaska), the Tafjord and the Loen multiple events event (Norway), also from volcanic collapses (Hawaii and Canary islands). Various researchers completed a systematic experimental work on 2D and 3D wave generation and propagation (Kamphuis and Bowering, 1970; Huber, 1980; Müller, 1995; Huber and Hager, 1997; Fritz, 2002; Zweifel, 2004; Panizzo et al., 2005; Heller, 2007; Heller and Kinnear, 2010; Sælevik et al., 2009), using both rigid blocks and deformable granular" masses. Model data and results have been used to calibrate and validate numerical modelling tools (Harbitz, 1992; Jiang and LeBlond, 1993; Grilli et al., 2002; Grilli and Watts, 2005; Lynett and Liu, 2005; Tinti et al., 2006; Abadie et al., 2010) generally considering simplified rheologies (e.g. viscous rheologies) for subaerial subaqueous spreading. We use a FEM code (Roddeman, 2011; Crosta et al., 2006, 2009, 2010, 2011) adopting an Eulerian-Lagrangian approach to give accurate results for large deformations. We model both 2D and fully 3D events considering different settings. The material is considered as a fully deformable elasto-plastic continuum and water as nearly incompressible. In particular we modeled the Vajont rockslide both in 2D and 3D considering the landslide water interaction. More simulations have been performed to validate the model against 2D and 3D tank experiments considering different slope geometries and water depth.

Kinetic characteristics of debris flows as exemplified by field investigations and discrete element simulation of the catastrophic Jiweishan rockslide, China

NASA Astrophysics Data System (ADS)

Zou, Zongxing; Tang, Huiming; Xiong, Chengren; Su, Aijun; Criss, Robert E.

2017-10-01

The Jiweishan rockslide of June 5, 2009 in China provides an important opportunity to elucidate the kinetic characteristics of high-speed, long-runout debris flows. A 2D discrete element model whose mechanical parameters were calibrated using basic field data was used to simulate the kinetic behavior of this catastrophic landslide. The model output shows that the Jiweishan debris flow lasted about 3 min, released a gravitational potential energy of about 6 × 10^13 J with collisions and friction dissipating approximately equal amounts of energy, and had a maximum fragment velocity of 60-70 m/s, almost twice the highest velocity of the overall slide mass (35 m/s). Notable simulated characteristics include the high velocity and energy of the slide material, the preservation of the original positional order of the slide blocks, the inverse vertical grading of blocks, and the downslope sorting of the slide deposits. Field observations that verify these features include uprooted trees in the frontal collision area of the air-blast wave, downslope reduction of average clast size, and undamaged plants atop huge blocks that prove their lack of downslope tumbling. The secondary acceleration effect and force chains derived from the numerical model help explain these deposit features and the long-distance transport. Our back-analyzed frictions of the motion path in the PFC model provide a reference for analyzing and predicting the motion of similar geological hazards.

The geomorphic impact of catastrophic glacier ice loss in mountain regions

NASA Astrophysics Data System (ADS)

Evans, S. G.

2006-12-01

Perhaps the most dramatic manifestation of global warming is catastrophic glacier ice loss in mountain regions. The geomorphic impact of this process was first outlined by Evans and Clague in 1994 and includes mountain slope instability, glacier avalanching, the formation and failure of moraine dammed lakes, and the formation and failure of ice dammed lakes. The present paper is an update of the 1994 publication and has three components. First, a global review of recent glacier-related geomorphic events is undertaken. Second, an analysis of two cases from the Coast Mountains of British Columbia - the 1975 Devastation Glacier landslide and the 1983 Nostetuko Lake outburst resulting from the failure of a moraine dam illustrates the interaction of glacier ice loss and related geomorphic events. At Devastation Glacier, approximately 13 M m3 of altered Quaternary volcanic rock and glacier ice was lost from the west flank of Pylon Peak in the Mount Meager volcanic complex. The events were initiated by a catastrophic rockslide, involving altered Quaternary pyroclastic rocks, which continued down Devastation Creek valley as a high velocity debris avalanche. The overall length of the slide path was 7 km and the vertical height of the path was 1220 m yielding a fahrboschung of 10°. Other large landslides occurred in Devastation Creek valley in 1931 and 1947. Stability analysis of the initial failure shows that the 1975 rockslide was the result of a complex history of glacial erosion, loading and unloading of the toe of the slide mass caused by the Little Ice Age advance and subsequent retreat of Devastation Glacier. The shearing resistance along the base of the rockslide mass was reduced prior to 1975 by substantial previous slope displacements related to glacial ice loss. Some of this displacement is likely to have occurred as subglacial slope deformation since ice fall and crevasse patterns suggest the presence of slide like shearing displacements below the base of adjacent glacier ice. In the Nostetuko case, the analysis of large-scale digital elevation models indicate that the outburst of 6.5 M m3 of water was initiated by a 1.5 M m3 glacier avalanche from Cumberland Glacier which initiated the breach. 1.6 M m3 of moraine was removed during the sudden breach and injected into the headwaters of the Nostetuko River. Thirdly, an attempt is made to quantify the increase in denudation and related sediment flux in mountain landscapes subject to catastrophic glacier-ice loss.

Dynamic Fragmentation of Jointed Rock Blocks During Rockslide-Avalanches: Insights From Discrete Element Analyses

NASA Astrophysics Data System (ADS)

Zhao, Tao; Crosta, Giovanni Battista; Dattola, Giuseppe; Utili, Stefano

2018-04-01

The dynamic fragmentation of jointed rock blocks during rockslide avalanches has been investigated by discrete element method simulations for a multiple arrangement of a rock block sliding over a simple slope geometry. The rock blocks are released along an inclined sliding plane and subsequently collide onto a flat horizontal plane at a sharp kink point. The contact force chains generated by the impact appear initially at the bottom frontal corner of the rock block and then propagate radially upward to the top rear part of the block. The jointed rock blocks exhibit evident contact force concentration and discontinuity of force wave propagation near the joint, associating with high energy dissipation of granular dynamics. The corresponding force wave propagation velocity can be less than 200 m/s, which is much smaller than that of an intact rock (1,316 m/s). The concentration of contact forces at the bottom leads to high rock fragmentation intensity and momentum boosts, facilitating the spreading of many fine fragments to the distal ends. However, the upper rock block exhibits very low rock fragmentation intensity but high energy dissipation due to intensive friction and damping, resulting in the deposition of large fragments near the slope toe. The size and shape of large fragments are closely related to the orientation and distribution of the block joints. The cumulative fragment size distribution can be well fitted by the Weibull's distribution function, with very gentle and steep curvatures at the fine and coarse size ranges, respectively. The numerical results of fragment size distribution can match well some experimental and field observations.

Extracting source characteristics and dynamics of the August 2010 Mount Meager landslide from broadband seismograms

NASA Astrophysics Data System (ADS)

Allstadt, Kate

2013-09-01

methods can substantially improve the characterization of the dynamics of large and rapid landslides. Such landslides often generate strong long-period seismic waves due to the large-scale acceleration of the entire landslide mass, which, according to theory, can be approximated as a single-force mechanism at long wavelengths. I apply this theory and invert the long-period seismic waves generated by the 48.5 Mm3 August 2010 Mount Meager rockslide-debris flow in British Columbia. Using data from five broadband seismic stations 70 to 276 km from the source, I obtain a time series of forces the landslide exerted on the Earth, with peak forces of 1.0 × 1011 N. The direction and amplitude of the forces can be used to determine the timing and occurrence of events and subevents. Using this result, in combination with other field and geospatial evidence, I calculate an average horizontal acceleration of the rockslide of 0.39 m/s2 and an average apparent coefficient of basal friction of 0.38 ± 0.02, which suggests elevated basal fluid pressures. The direction and timing of the strongest forces are consistent with the centripetal acceleration of the debris flow around corners in its path. I use this correlation to estimate speeds, which peak at 92 m/s. This study demonstrates that the time series recording of forces exerted by a large and rapid landslide derived remotely from seismic records can be used to tie post-slide evidence to what actually occurred during the event and can serve to validate numerical models and theoretical methods.

DaDyn-RS: a tool for the time-dependent simulation of damage, fluid pressure and long-term instability in alpine rock slopes

NASA Astrophysics Data System (ADS)

Riva, Federico; Agliardi, Federico; Amitrano, David; Crosta, Giovanni B.

2017-04-01

Large mountain slopes in alpine environments undergo a complex long-term evolution from glacial to postglacial environments, through a transient period of paraglacial readjustment. During and after this transition, the interplay among rock strength, topographic relief, and morpho-climatic drivers varying in space and time can lead to the development of different types of slope instability, from sudden catastrophic failures to large, slow, long-lasting yet potentially catastrophic rockslides. Understanding the long-term evolution of large rock slopes requires accounting for the time-dependence of deglaciation unloading, permeability and fluid pressure distribution, displacements and failure mechanisms. In turn, this is related to a convincing description of rock mass damage processes and to their transition from a sub-critical (progressive failure) to a critical (catastrophic failure) character. Although mechanisms of damage occurrence in rocks have been extensively studied in the laboratory, the description of time-dependent damage under gravitational load and variable external actions remains difficult. In this perspective, starting from a time-dependent model conceived for laboratory rock deformation, we developed Dadyn-RS, a tool to simulate the long-term evolution of real, large rock slopes. Dadyn-RS is a 2D, FEM model programmed in Matlab, which combines damage and time-to-failure laws to reproduce both diffused damage and strain localization meanwhile tracking long-term slope displacements from primary to tertiary creep stages. We implemented in the model the ability to account for rock mass heterogeneity and property upscaling, time-dependent deglaciation, as well as damage-dependent fluid pressure occurrence and stress corrosion. We first tested DaDyn-RS performance on synthetic case studies, to investigate the effect of the different model parameters on the mechanisms and timing of long-term slope behavior. The model reproduces complex interactions between topography, deglaciation rate, mechanical properties and fluid pressure occurrence, resulting in different kinematics, damage patterns and timing of slope instabilities. We assessed the role of groundwater on slope damage and deformation mechanisms by introducing time-dependent pressure cycling within simulations. Then, we applied DaDyn-RS to real slopes located in the Italian Central Alps, affected by an active rockslide and a Deep Seated Gravitational Slope Deformation, respectively. From Last Glacial Maximum to present conditions, our model allows reproducing in an explicitly time-dependent framework the progressive development of damage-induced permeability, strain localization and shear band differentiation at different times between the Lateglacial period and the Mid-Holocene climatic transition. Different mechanisms and timings characterize different styles of slope deformations, consistently with available dating constraints. DaDyn-RS is able to account for different long-term slope dynamics, from slow creep to the delayed transition to fast-moving rockslides.

Exploring the Dynamics of the August 2010 Mount Meager Rock Slide-Debris Flow Jointly with Seismic Source Inversion and Numerical Landslide Modeling

NASA Astrophysics Data System (ADS)

Allstadt, K.; Moretti, L.; Mangeney, A.; Stutzmann, E.; Capdeville, Y.

2014-12-01

The time series of forces exerted on the earth by a large and rapid landslide derived remotely from the inversion of seismic records can be used to tie post-slide evidence to what actually occurred during the event and can be used to tune numerical models and test theoretical methods. This strategy is applied to the 48.5 Mm3 August 2010 Mount Meager rockslide-debris flow in British Columbia, Canada. By inverting data from just five broadband seismic stations less than 300 km from the source, we reconstruct the time series of forces that the landslide exerted on the Earth as it occurred. The result illuminates a complex retrogressive initiation sequence and features attributable to flow over a complicated path including several curves and runup against a valley wall. The seismically derived force history also allows for the estimation of the horizontal acceleration (0.39 m/s^2) and average apparent coefficient of basal friction (0.38) of the rockslide, and the speed of the center of mass of the debris flow (peak of 92 m/s). To extend beyond these simple calculations and to test the interpretation, we also use the seismically derived force history to guide numerical modeling of the event - seeking to simulate the landslide in a way that best fits both the seismic and field constraints. This allows for a finer reconstruction of the volume, timing, and sequence of events, estimates of friction, and spatiotemporal variations in speed and flow thickness. The modeling allowed us to analyze the sensitivity of the force to the different parameters involved in the landslide modeling to better understand what can and cannot be constrained from seismic source inversions of landslide signals.

Brief Communication: On the rapid and efficient monitoring results dissemination in landslide emergency scenarios: the Mont de La Saxe case study

NASA Astrophysics Data System (ADS)

Giordan, D.; Manconi, A.; Allasia, P.; Bertolo, D.

2015-09-01

Straightforward communication of monitoring results is of major importance in emergency scenarios relevant to large slope instabilities. Here we describe the communication strategy developed for the Mont de La Saxe rockslide threatening La Palud and Entrèves hamlets in the Courmayeur municipality (Aosta Valley, Italy). Starting from the definition of actions and needs of the landslide management team, including scientists, technicians, civil protection operators, decision makers, and politicians, we show that sharing and disseminating ad hoc information simplifies the understanding of the landslide evolution, as well as the correct communication of the level of criticality.

Use of statistical analysis of long term displacement rate time series for the definition of Early Warning thresholds. The case studies of the Ruinon and Mont de La Saxe landslides (N Italy)

NASA Astrophysics Data System (ADS)

Alberti, Stefano; Battista Crosta, Giovanni; Rivolta, Carlo

2016-04-01

Rockslides are characterized by complex spatial and temporal evolution. Forecasting their behaviour is a hard task, due to non-linear displacement trends and the significant effects of seasonal or occasional events. The displacement rate and the landslide evolution are influenced by various factors like lithology, structural and hydrological settings, as well as meteo-climatic factors (e.g. snowmelt and rainfall). The nature of the relationships among these factors is clearly non linear, site specific and even specific to each sector that can be individuated within the main landslide mass. In this contribution, total displacement and displacement rate time series are extracted from Ground-based Interferometric synthetic aperture radar (GB-InSAR) surveys, monitoring of optical targets by total stations, a GPS network and multi-parametric borehole probes. Different Early Warning domains, characterized by different velocity regimes (slow to fast domains) and with different sensitivity to external perturbations (e.g. snowmelt and rainfall), have been identified in previous studies at the two sites. The Mont de La Saxe rockslide (ca. 8 x 106 m3) is located in the Upper Aosta Valley, and it has been intensively monitored since 2009 by the Valle D'Aosta Geological Survey. The Ruinon landslide (ca. 15 x 106 to 20 x 106 m3) is located in the Upper Valtellina (Lombardy region) and monitoring data are available starting since 2006 and have been provided by ARPA Lombardia. Both phenomena are alpine deep-seated rockslides characterized by different displacement velocity, from few centimetres to over 1 meter per year, and which have undergone exceptional accelerations during some specific events. We experiment the use of normal probability plots for the analysis of displacement rates of specific points belonging to different landslide sectors and recorded during almost ten years of monitoring. This analyses allow us to define: (i) values with a specific probability value expressed in terms of percentiles; (ii) values for which a specific change in behaviour is observed which could be associated to a specific type of triggering event (e.g. rainfall intensity, duration or amount; snowmelt amount) . These values could be used to support the choice of threshold values for the management of Early Warning System, by considering also the minimization of false alarms. The analyses have been performed by using data averaged over different time intervals so to study the effects of noise on the threshold values. Analyses of false alarm triggered by the choice of different threshold values (i.e. different percentiles) have been performed and analysed. This could be an innovative approach to define velocity thresholds of Early Warning system and to analyse the quantitative data derived from remote sensing monitoring and filed surveys, by linking them to both spatial and temporal changes.

Geodiversity assessment for environmental management of geomorphosites: Derborence and Illgraben, Swiss Alps

NASA Astrophysics Data System (ADS)

Jaskulska, Alicja; Reynard, Emmanuel; Zwoliński, Zbigniew

2013-04-01

The concept of geodiversity was created relatively recently and has been accepted by geomorphologists and geologists worldwide. Nevertheless, despite the widespread use of the term, little progress has been made in its evaluation. Until now, only a few authors have undertaken, directly or indirectly, methodological issues related to the geodiversity estimation. In some studies, geodiversity maps were applied to investigate the spatial or genetic relationships with the richness of particular environmental elements like geosites, geomorphosites, geoarchaeological and palaeontological sites, etc. However, so far, the spatial differentiation of geodiversity values in areas already accepted as large geomorphosites has not been undertaken. This poster presents a new methodology developed to assess the geodiversity in geoinformation environments and tested in two geomorphosites located in the Swiss Alps: Derborence and Illgraben. Derborence is a quite isolated valley, where some big rockslides occurred in the past; the sharp rockslide landforms, high limestone cliffs and a lake dammed by the rockslide deposits attract tourists in summer. A part of the valley is a natural reserve managed by Pronatura (a national environmental association). Illgraben is a steep torrential system on the left bank of the Rhone River valley, characterized by high erosion rates and frequent occurrence of rockfalls and debris flows. The site is the largest active torrential system in Switzerland and is part of a Regional Nature Park. Both geomorphosites are recognized as geosites of national importance. The basis of the assessment is the selection of features of the geographical environment, which on one hand describe landforms, and on the other indicate geomorphometric differences. Firstly, seven factor maps were processed for each area: landform energy derived from a 25-meter digital elevation model, landform fragmentation generated from the Topographic Position Index (TPI), contemporary landform preservation derived from land use classification using high resolution ortho images, geological settings, geomorphological features, soils and hydrology elements. Input maps were then standardized by attributing grid geodiversity values in five classes to each raster map: very low geodiversity, low geodiversity, medium geodiversity, high geodiversity and very high geodiversity. Obtained maps result from map algebra operations carried out by multi criteria evaluation (MCE) with GIS-based Weighted Linear Combination (WLC) technique. The final geodiversity maps for each of the two geomorphosites were then compared with existing tourist trails and panoramic points to verify if there are any dependencies. Geosite inventories are a more or less qualitative selection of sites considered as important by the scientific community for their contribution to Earth history knowledge and more in general for the society. Some geosites, in particular geomorphosites, can be quite large (several sq. km), and sometimes heterogeneous. The proposed methodology, tested on two Swiss geomorphosites, allows the intrinsic geodiversity differentiation of large geosites to be assessed and the results could be used for other purposes such as the preservation of specific features within the geosite perimeter, spatial planning or tourist management.

Magnitude estimation and runout analysis of a rockslide for the construction of a defensive structure

NASA Astrophysics Data System (ADS)

Gigli, G.; Casagli, N.; Lombardi, L.; Nocentini, M.; Balducci, M.; Venanti, L.

2009-04-01

In the past few years the Maiolica (micritic limestone) quarry of Torgiovannetto (Perugia, Italy) has suffered an increasing amount of rockfalls. The rock mass has loosened progressively and a perimetral crack longer than 100 meters has appeared. The huge block bounded by this crack, two lateral discontinuities and a stratigraphic layer, threatens two roads at the base of the slope. Since these are very important and busy traffic routes the Department of Earth Sciences of the University of Firenze performed magnitude estimations and runout analyses regarding two different aspects: 1) investigate the trajectories of single falling blocks and; 2) forecast the runout distance and the debris intensity distribution in case a large rockslide occurs. The magnitude of a landslide is, actually, the most important input parameter for correctly estimating the trajectory, the runout distance and the kinetic energy of a landslide. A detailed and updated knowledge of the actual morphological conditions is a good starting point for defining as accurately as possible the extent of a moving block. Due to the very high urgency and precision required, a detailed survey of the quarry area has been performed by means of a High Accuracy & Long Range 3D laser scanner (RIEGLE, LMS-Z.420i). In order to avoid shadow zones and to obtain a comprehensive digital elevation model of the quarry area, a total of more than 30 million points were taken from three different scan positions. The resulting point cloud was dense enough to reveal the main structural features of the rock mass, including the discontinuities bounding the moving block, which has a calculated volume of 180 000 m3. With the aim of confirming the block volume and assessing the deformational field of the moving mass, a multitemporal ground-based interferometric SAR survey was performed. The results of the survey precisely confirm the geometry of the unstable block and also indicate that the displacements decrease from E to W, due to the greater lateral friction in the western portion of the wedge. This deformational behaviour has been confirmed by a wireless real time monitoring system installed for the time of failure forecast. Laboratory tests and stability analyses of the unstable wedge allowed us to hypothesize a sudden and brittle failure behavior, which can be associated to a long runout distance. Both empirical (energy line approach) and numerical methods (DAN-W and DAN3D softwares) were employed for estimating the runout distance and debris intensity distribution associated with the failure of the main block. The results of this analysis indicate that the potential rockslide will likely reach the nearest road. The estimated velocity, debris depth, and kinetic energy of the moving mass can be used to project defensive structures at the base of the artificial slope.

Brief Communication: On the rapid and efficient monitoring results dissemination in landslide emergency scenarios: the Mont de La Saxe case study

NASA Astrophysics Data System (ADS)

Giordan, D.; Manconi, A.; Allasia, P.; Bertolo, D.

2015-04-01

Straightforward communication of monitoring results is of major importance in emergency scenarios relevant to large slope instabilities. Here we describe the communication strategy developed for the Mont de La Saxe case study, a large rockslide threatening La Palud and Entrèves hamlets in the Courmayeur municipality (Aosta Valley, Italy). Starting from the definition of actions and needs of the Landslide Management Team, including scientists, technicians, civil protection operators, decision makers, and politicians, we show that sharing and disseminating ad hoc information simplifies the understanding of the landslide evolution, as well as the correct communication of the level of criticality.

3D SPH numerical simulation of the wave generated by the Vajont rockslide

NASA Astrophysics Data System (ADS)

Vacondio, R.; Mignosa, P.; Pagani, S.

2013-09-01

A 3D numerical modeling of the wave generated by the Vajont slide, one of the most destructive ever occurred, is presented in this paper. A meshless Lagrangian Smoothed Particle Hydrodynamics (SPH) technique was adopted to simulate the highly fragmented violent flow generated by the falling slide in the artificial reservoir. The speed-up achievable via General Purpose Graphic Processing Units (GP-GPU) allowed to adopt the adequate resolution to describe the phenomenon. The comparison with the data available in literature showed that the results of the numerical simulation reproduce satisfactorily the maximum run-up, also the water surface elevation in the residual lake after the event. Moreover, the 3D velocity field of the flow during the event and the discharge hydrograph which overtopped the dam, were obtained.

Frequency, triggering factors and possible consequences of mass movements on outlet glaciers in Iceland.

NASA Astrophysics Data System (ADS)

Saemundsson, Thorsteinn; Margeirsson, Guðbjörn

2016-04-01

During the last 15 years several mass movements of various size and origin, e.g. rock avalanches, rock slides and debris slides have been observed to have fall on outlet glaciers in Iceland. This should not come as a surprise in this type of glacial environment, but in a way it does. When looking at the history only few mass movements are recorded to have fall on outlet glaciers in Iceland, during the decades before the year 2000 or since 1960. This "lack of mass movements" can be explained by the fact that fewer observations and monitoring were done in the past, but is it so or are we seeing increasing activity? Looking at the distribution of the known mass movements, two activity periods cam be identified. The former one around 1970 and the second one starting around 2000 and is still ongoing. Both of these periods are characterized by warmer climate leading to retreating phases of glaciers. Two larger mass movements are known from these two retreating periods. The former one occurred in January 1967. Then a large rockslide fell on the snout and into the glacial lake of the Steinholtsjökull outlet glacier in the northern side of the Eyjafjallajökull ice cap. The rockslide broke up the snout of the glacier and caused large floodwave bursting down the Steinholtsdalur valley transporting large volume of sediments down its path. The later one occurred in 2007, when a large rockavalanche fell on the Morsárjökull outlet glacier, in the southern side of the Vatnajökull ice cap. The avalanche debris covered around 1/5 of the glacier surface. Today the retreat and thinning of glaciers in Iceland are extremely rapid. The consequences of such a rapid retreat are e.g. unstable valley slopes surrounding the outlet glaciers, both in loose sediments and bedrock, thawing of mountain permafrost and not least formation of glacial lakes in front of the rapid retreating ice margins. Such conditions can become extremely hazardous, as seen by the above mentioned examples, both for all infrastructure but not least for the rapidly increasing tourism in Iceland.

Mass movements on Venus - Preliminary results from Magellan cycle 1 observations

NASA Technical Reports Server (NTRS)

Malin, Michael C.

1992-01-01

A preliminary assessment of mass movements and their geomorphic characteristics as determined from visual inspection of Magellan cycle 1 synthetic aperture radar images is described. The primary data set was a catalog of over 200 ten-inch square photographic prints of full-resolution mosaic image data records. Venus exhibits unambiguous evidence of mass movements at a variety of scales. Mass movements appear mostly in the form of block and rock movements; there is little evidence of regolith and sediment movements. Unique Venusian conditions may play a role in the creation of some mass movement features. Dark (smooth) surfaces surrounding many rockslide avalanches are probably fine materials emplaced as part of the mass movement process, as airfall, surface-hugging density flows, or coarse-depleted debris flows. The size and efficiency of emplacement of landslide deposits on Venus are comparable to those seen on Mars, which in turn generally resemble terrestrial occurrences.

Staircase Falls Rockfall on December 26, 2003, and Geologic Hazards at Curry Village, Yosemite National Park, California

USGS Publications Warehouse

Wieczorek, Gerald F.; Snyder, James B.; Borchers, James W.; Reichenbach, Paola

2007-01-01

Since 1857, several hundred rockfalls, rockslides, and debris flows have been observed in Yosemite National Park. At 12:45 a.m. on December 26, 2003, a severe winter storm triggered a rockfall west of Glacier Point in Yosemite Valley. Rock debris moved quickly eastward down Staircase Falls toward Curry Village. As the rapidly moving rock mass reached talus at the bottom of Staircase Falls, smaller pieces of flying rock penetrated occupied cabins. Physical characterization of the rockfall site included rockfall volume, joint patterns affecting initial release of rock and the travel path of rockfall, factors affecting weathering and weakening of bedrock, and hydrology affecting slope stability within joints. Although time return intervals are not predictable, a three-dimensional rockfall model was used to assess future rockfall potential and risk. Predictive rockfall and debris-flow methods suggest that landslide hazards beneath these steep cliffs extend farther than impact ranges defined from surface talus in Yosemite Valley, leaving some park facilities vulnerable.

Science guides search and rescue after the 2006 Philippine landslide.

PubMed

Lagmay, Alfredo Mahar A; Tengonciang, Arlene Mae P; Rodolfo, Raymond S; Soria, Janneli Lea A; Baliatan, Eden G; Paguican, Engielle R; Ong, John Burtkenley T; Lapus, Mark R; Fernandez, Dan Ferdinand D; Quimba, Zareth P; Uichanco, Christopher L

2008-09-01

A rockslide-debris avalanche destroyed the remote village of Guinsaugon in Southern Leyte, Philippines, on 17 February 2006. Although search and rescue procedures were implemented immediately, the scale of the landslide and a lack of information about its nature resulted in unfocused and imprecise efforts in the early days of the operation. Technical support was only introduced five days after the event, provided by a team of volunteer geologists, geophysicists, and meteorologists. By the time search and rescue operations were transferred to specific target sites, however, the chances of finding survivors trapped under the rubble had diminished. In such critical situations, speed, accuracy, and the maximum appropriation of resources are crucial. We emphasise here the need for a systematic and technically informed approach to search and rescue missions in large-scale landslide disaster contexts, and the formulation of better disaster management policies in general. Standard procedures must be developed and enforced to improve how civil authorities respond to natural calamities.

Morphologic Evolution of the Mount St. Helens Crater Area, Washington

NASA Technical Reports Server (NTRS)

Beach, G. L.

1985-01-01

The large rockslide-avalanche that preceded the eruption of Mount St. Helens on 18 May 1980 removed approximately 2.8 cubic km of material from the summit and north flank of the volcano, forming a horseshoe-shaped crater 2.0 km wide and 3.9 km long. A variety of erosional and depositional processes, notably mass wasting and gully development, acted to modify the topographic configuration of the crater area. To document this morphologic evolution, a series of annual large-scale topographic maps is being produced as a base for comparitive geomorphic analysis. Four topographic maps of the Mount St. Helens crater area at a scale of 1:4000 were produced by the National Mapping Division of the U. S. Geological Survey. Stereo aerial photography for the maps was obtained on 23 October 1980, 10 September 1981, 1 September 1982, and 17 August 1983. To quantify topographic changes in the study area, each topographic map is being digitized and corresponding X, Y, and Z values from successive maps are being computer-compared.

Effects of the March 1964 Alaska earthquake on glaciers: Chapter D in The Alaska earthquake, March 27, 1964: effects on hydrologic regimen

USGS Publications Warehouse

Post, Austin

1967-01-01

The 1964 Alaska earthquake occurred in a region where there are many hundreds of glaciers, large and small. Aerial photographic investigations indicate that no snow and ice avalanches of large size occurred on glaciers despite the violent shaking. Rockslide avalanches extended onto the glaciers in many localities, seven very large ones occurring in the Copper River region 160 kilometers east of the epicenter. Some of these avalanches traveled several kilometers at low gradients; compressed air may have provided a lubricating layer. If long-term changes in glaciers due to tectonic changes in altitude and slope occur, they will probably be very small. No evidence of large-scale dynamic response of any glacier to earthquake shaking or avalanche loading was found in either the Chugach or Kenai Mountains 16 months after the 1964 earthquake, nor was there any evidence of surges (rapid advances) as postulated by the Earthquake-Advance Theory of Tarr and Martin.

Controls on size and occurrence of the largest sub-aerial landslide on Earth: Seymareh (Saidmarreh) landslide, Zagros fold-thrust belt, Iran

NASA Astrophysics Data System (ADS)

Roberts, N. J.; Evans, S. G.

2009-12-01

Gigantic (> 1 Gm3) landslides are high-magnitude, low-frequency extremes of mass movements. They are important factors in topographic evolution and hazard in mountain regions due to their magnitude. However, few examples exist for study because of their infrequency. Consequently, controls on the location and size gigantic landslides remain poorly understood. Re-examination of the Seymareh (Saidmarreh) rock avalanche, Zagros fold-thrust belt, shows it to be the largest sub-aerial landslide on Earth (initial failure volume 38 Gm3), thus representing the upper magnitude limit for terrestrial landslides. Detailed examination of the source area (including orbital remote sensing, geotechnical investigation and structural mapping) provides new insights into controls on the size and mobility of gigantic landslides. The gigantic Early Holocene rockslide initiated on the northeast limb of Kabir Kuh, the largest anticline in the Zagros fold-thrust belt, and involved the simultaneous failure of a rock mass measuring 15 km along strike. The rockslide transformed into a rock avalanche that ran-out 19.0 km, filling two adjacent valleys and overtopping an intervening low mountain ridge. The failure involved 220 m of competent jointed limestone (Asmari Formation) underlain by 580 m of weaker mudrock-dominated units. Geologic structure, geomechanical strength and topography of the source slope strongly controlled failure initiation. Extreme landslide dimensions resulted in part from extensive uniform pre-failure stability, produced by structural and topographic features related to the large scale of the Kabir Kuh anticline. High continuity bedding planes determined the large lateral extent along strike. Bedding normal joints, the breached nature of the anticline and fluvial undercutting at the slope toe accommodated expansive lateral, headscarp and toe release, respectively, necessary for extensive failure. Geomechanically weak units at depth aided the penetration of the failure surface into the source slope while low bedding dip (ca. 19°) allowed kinematic freedom of a particularly thick sequence to move downslope. Prevention of gradual rockmass removal by smaller-magnitude, more frequent denudation ensured its preservation for later simultaneous failure. The overall failure surface (11°) cut across weaker beds and finally breached the Asmari carapace by break-out at the base of the source slope. Relative relief of the source slope on Kabir Kuh was modest (1350 m on average) indicating that uniform structural and topographic conditions along strike, shallow bedding dips, and the geomechnical properties of the source rock mass were more important in determining the magnitude of the landslide that forms the upper magnitude limit for subaerial landslides.

Consequence assessment of large rock slope failures in Norway

NASA Astrophysics Data System (ADS)

Oppikofer, Thierry; Hermanns, Reginald L.; Horton, Pascal; Sandøy, Gro; Roberts, Nicholas J.; Jaboyedoff, Michel; Böhme, Martina; Yugsi Molina, Freddy X.

2014-05-01

Steep glacially carved valleys and fjords in Norway are prone to many landslide types, including large rockslides, rockfalls, and debris flows. Large rockslides and their secondary effects (rockslide-triggered displacement waves, inundation behind landslide dams and outburst floods from failure of landslide dams) pose a significant hazard to the population living in the valleys and along the fjords shoreline. The Geological Survey of Norway performs systematic mapping of unstable rock slopes in Norway and has detected more than 230 unstable slopes with significant postglacial deformation. This large number necessitates prioritisation of follow-up activities, such as more detailed investigations, periodic displacement measurements, continuous monitoring and early-warning systems. Prioritisation is achieved through a hazard and risk classification system, which has been developed by a panel of international and Norwegian experts (www.ngu.no/en-gb/hm/Publications/Reports/2012/2012-029). The risk classification system combines a qualitative hazard assessment with a consequences assessment focusing on potential life losses. The hazard assessment is based on a series of nine geomorphological, engineering geological and structural criteria, as well as displacement rates, past events and other signs of activity. We present a method for consequence assessment comprising four main steps: 1. computation of the volume of the unstable rock slope; 2. run-out assessment based on the volume-dependent angle of reach (Fahrböschung) or detailed numerical run-out modelling; 3. assessment of possible displacement wave propagation and run-up based on empirical relations or modelling in 2D or 3D; and 4. estimation of the number of persons exposed to rock avalanches or displacement waves. Volume computation of an unstable rock slope is based on the sloping local base level technique, which uses a digital elevation model to create a second-order curved surface between the mapped extent of the unstable rock slope. This surface represents the possible basal sliding surface of an unstable rock slope. The elevation difference between this surface and the topographic surface estimates the volume of the unstable rock slope. A tool has been developed for the present study to adapt the curvature parameters of the computed surface to local geological and structural conditions. The obtained volume is then used to define the angle of reach of a possible rock avalanche from the unstable rock slope by using empirical derived values of angle of reach vs. volume relations. Run-out area is calculated using FlowR; the software is widely used for run-out assessment of debris flows and is adapted here for assessment of rock avalanches, including their potential to ascend opposing slopes. Under certain conditions, more sophisticated and complex numerical run-out models are also used. For rock avalanches with potential to reach a fjord or a lake the propagation and run-up area of triggered displacement waves is assessed. Empirical relations of wave run-up height as a function of rock avalanche volume and distance from impact location are derived from a national and international inventory of landslide-triggered displacement waves. These empirical relations are used in first-level hazard assessment and where necessary, followed by 2D or 3D displacement wave modelling. Finally, the population exposed in the rock avalanche run-out area and in the run-up area of a possible displacement wave is assessed taking into account different population groups: inhabitants, persons in critical infrastructure (hospitals and other emergency services), persons in schools and kindergartens, persons at work or in shops, tourists, persons on ferries and so on. Exposure levels are defined for each population group and vulnerability values are set for the rock avalanche run-out area (100%) and the run-up area of a possible displacement wave (70%). Finally, the total number of persons within the hazard area is calculated taking into account exposure and vulnerability. The method for consequence assessment is currently tested through several case studies in Norway and, thereafter, applied to all unstable rock slopes in the country to assess their risk level. Follow-up activities (detailed investigations, periodic displacement measurements or continuous monitoring and early-warning systems) can then be prioritized based on the risk level and with a standard approach for whole Norway.

Clark's nutcracker spatial memory: the importance of large, structural cues.

PubMed

Bednekoff, Peter A; Balda, Russell P

2014-02-01

Clark's nutcrackers, Nucifraga columbiana, cache and recover stored seeds in high alpine areas including areas where snowfall, wind, and rockslides may frequently obscure or alter cues near the cache site. Previous work in the laboratory has established that Clark's nutcrackers use spatial memory to relocate cached food. Following from aspects of this work, we performed experiments to test the importance of large, structural cues for Clark's nutcracker spatial memory. Birds were no more accurate in recovering caches when more objects were on the floor of a large experimental room nor when this room was subdivided with a set of panels. However, nutcrackers were consistently less accurate in this large room than in a small experimental room. Clark's nutcrackers probably use structural features of experimental rooms as important landmarks during recovery of cached food. This use of large, extremely stable cues may reflect the imperfect reliability of smaller, closer cues in the natural habitat of Clark's nutcrackers. This article is part of a Special Issue entitled: CO3 2013. Copyright © 2013 Elsevier B.V. All rights reserved.

Multi-Dimensional Analysis of Large, Complex Slope Instability: Case study of Downie Slide, British Columbia, Canada. (Invited)

NASA Astrophysics Data System (ADS)

Kalenchuk, K. S.; Hutchinson, D.; Diederichs, M. S.

2013-12-01

Downie Slide, one of the world's largest landslides, is a massive, active, composite, extremely slow rockslide located on the west bank of the Revelstoke Reservoir in British Columbia. It is a 1.5 billion m3 rockslide measuring 2400 m along the river valley, 3300m from toe to headscarp and up to 245 m thick. Significant contributions to the field of landslide geomechanics have been made by analyses of spatially and temporally discriminated slope deformations, and how these are controlled by complex geological and geotechnical factors. Downie Slide research demonstrates the importance of delineating massive landslides into morphological regions in order to characterize global slope behaviour and identify localized events, which may or may not influence the overall slope deformation patterns. Massive slope instabilities do not behave as monolithic masses, rather, different landslide zones can display specific landslide processes occurring at variable rates of deformation. The global deformation of Downie Slide is extremely slow moving; however localized regions of the slope incur moderate to high rates of movement. Complex deformation processes and composite failure mechanism are contributed to by topography, non-uniform shear surfaces, heterogeneous rockmass and shear zone strength and stiffness characteristics. Further, from the analysis of temporal changes in landslide behaviour it has been clearly recognized that different regions of the slope respond differently to changing hydrogeological boundary conditions. State-of-the-art methodologies have been developed for numerical simulation of large landslides; these provide important tools for investigating dynamic landslide systems which account for complex three-dimensional geometries, heterogenous shear zone strength parameters, internal shear zones, the interaction of discrete landslide zones and piezometric fluctuations. Numerical models of Downie Slide have been calibrated to reproduce observed slope behaviour, and the calibration process has provided important insight to key factors controlling massive slope mechanics. Through numerical studies it has been shown that the three-dimensional interpretation of basal slip surface geometry and spatial heterogeneity in shear zone stiffness are important factors controlling large-scale slope deformation processes. The role of secondary internal shears and the interaction between landslide morphological zones has also been assessed. Further, numerical simulation of changing groundwater conditions has produced reasonable correlation with field observations. Calibrated models are valuable tools for the forward prediction of landslide dynamics. Calibrated Downie Slide models have been used to investigate how trigger scenarios may accelerate deformations at Downie Slide. The ability to reproduce observed behaviour and forward test hypothesized changes to boundary conditions has valuable application in hazard management of massive landslides. The capacity of decision makers to interpret large amounts of data, respond to rapid changes in a system and understand complex slope dynamics has been enhanced.

Drainage evolution in the debris avalanche deposits near Mount Saint Helens, Washington

NASA Technical Reports Server (NTRS)

Beach, G. L.; Dzurisin, D.

1984-01-01

The 18 May 1980 eruption of Mount St. Helens was initiated by a massive rockslide-debris avalanche which completely transformed the upper 25 km of the North Fork Toutle River valley. The debris was generated by one of the largest gravitational mass movements ever recorded on Earth. Moving at an average velocity of 35 m/s, the debris avalanche buried approximately 60 sq km of terrain to an average depth of 45 m with unconsolidated, poorly sorted volcaniclastic material, all within a period of 10 minutes. Where exposed and unaltered by subsequent lahars and pyroclastic flows, the new terrain surface was characterized predominantly by hummocks, closed depressions, and the absence of an identifiable channel network. Following emplacement of the debris avalanche, a complex interrelationship of fluvial and mass wasting processes immediately began operating to return the impacted area to an equilibrium status through the removal of material (potential energy) and re-establishment of graded conditions. In an attempt to chronicle the morphologic evolution of this unique environmental setting, a systematic series of interpretative maps of several selected areas was produced. These maps, which document the rate and character of active geomorphic processes, are discussed.

ShakeMap-based prediction of earthquake-induced mass movements in Switzerland calibrated on historical observations

USGS Publications Warehouse

Cauzzi, Carlo; Fah, Donat; Wald, David J.; Clinton, John; Losey, Stephane; Wiemer, Stefan

2018-01-01

In Switzerland, nearly all historical Mw ~ 6 earthquakes have induced damaging landslides, rockslides and snow avalanches that, in some cases, also resulted in damage to infrastructure and loss of lives. We describe the customisation to Swiss conditions of a globally calibrated statistical approach originally developed to rapidly assess earthquake-induced landslide likelihoods worldwide. The probability of occurrence of such earthquake-induced effects is modelled through a set of geospatial susceptibility proxies and peak ground acceleration. The predictive model is tuned to capture the observations from past events and optimised for near-real-time estimates based on USGS-style ShakeMaps routinely produced by the Swiss Seismological Service. Our emphasis is on the use of high-resolution geospatial datasets along with additional local information on ground failure susceptibility. Even if calibrated on historic events with moderate magnitudes, the methodology presented in this paper yields sensible results also for low-magnitude recent events. The model is integrated in the Swiss ShakeMap framework. This study has a high practical relevance to many Swiss ShakeMap stakeholders, especially those managing lifeline systems, and to other global users interested in conducting a similar customisation for their region of interest.

The extreme mobility of debris avalanches: A new model of transport mechanism

NASA Astrophysics Data System (ADS)

Perinotto, Hélène; Schneider, Jean-Luc; Bachèlery, Patrick; Le Bourdonnec, François-Xavier; Famin, Vincent; Michon, Laurent

2015-12-01

Large rockslide-debris avalanches, resulting from flank collapses that shape volcanoes and mountains on Earth and other object of the solar system, are rapid and dangerous gravity-driven granular flows that travel abnormal distances. During the last 50 years, numerous physical models have been put forward to explain their extreme mobility. The principal models are based on fluidization, lubrication, or dynamic disintegration. However, these processes remain poorly constrained. To identify precisely the transport mechanisms during debris avalanches, we examined morphometric (fractal dimension and circularity), grain size, and exoscopic characteristics of the various types of particles (clasts and matrix) from volcanic debris avalanche deposits of La Réunion Island (Indian Ocean). From these data we demonstrate for the first time that syn-transport dynamic disintegration continuously operates with the increasing runout distance from the source down to a grinding limit of 500 µm. Below this limit, the particle size reduction exclusively results from their attrition by frictional interactions. Consequently, the exceptional mobility of debris avalanches may be explained by the combined effect of elastic energy release during the dynamic disintegration of the larger clasts and frictional reduction within the matrix due to interactions between the finer particles.

The Ålesund slide, March 2008: Lidar analysis of an urban human-induced rockslide

NASA Astrophysics Data System (ADS)

Derron, M.-H.; Melchiorre, C.; Blikra, L.; Loye, A.; Pedrazzini, A.

2009-04-01

On March 26 2008, a 2400 m3 rock block slid from an excavated slope on a six floors house in the city of Aalesund (Western coast of Norway). The whole house was displaced horizontally on its basement on about 6 meters and the two lower floors of the building collapsed. Five persons died during the event. Almost 500 inhabitants living in the surroundings had to be evacuated for 6 to 8 days because of a gas leakage. The site has been scanned three times with a terrestrial lidar. In the first dataset, made a couple of days after the event, the block and the house are present. In the second dataset, acquired about 3 months later, the house had been removed but most of the sliding block is still in place. The last scan, made six months after the events, shows very well the sliding surface, as the block had been removed too. These three scans completed by field measurement and observations have been used: 1) to characterize the geometry and volume of the block, 2) to determine the displacement vector, 3) to perform a analysis of discontinuities and some kinematics tests, 4) to estimate the roughness and the waviness of the sliding surface.

Editorial: Introduction to the Special Issue ;Slope Tectonics: Inherited Structures, Morphology of Deformation and Catastrophic Failure;

NASA Astrophysics Data System (ADS)

Hermanns, R. L.; Oppikofer, T.; Jaboyedoff, M.; Clague, J. J.; Scarascia-Mugnozza, G.

2017-07-01

The "Conference on Slope Tectonics" has become an international scientific meeting point to present and discuss a variety of topics related to slope deformation and the deposits of related failures. The first conference took place on February 15-16, 2008 at University of Lausanne (Switzerland). It was followed by a second conference on September 6-10, 2011, in Austria (organized by the Geological Survey of Austria) and a third on September 8-12, 2014, in Norway (organized by the Geological Survey of Norway). The two later events included field trips. It has become a tradition that selected papers from these conference are published - papers from the first conference were published by the Geological Society as Special Publication 351 (Jaboyedoff, 2011), and those from the second conference were published in a special issue of Tectonophysics (Baron and Jaboyedoff, 2013). This special issue of Geomorphology is a collection of papers presented at the Norwegian Conference on Slope Tectonics. This collection of papers focuses on the role of tectonics in gravitationally induced rock-slope instabilities. The slopes either deform over long periods as deep-seated gravitational slope deformation (DSGSD) or more rapidly as rockslides or rock avalanches. The reconstruction of slope deformation is an integral part of the studies captured in this special issue.

Community Structure and Survival of Tertiary Relict Thuja sutchuenensis (Cupressaceae) in the Subtropical Daba Mountains, Southwestern China

PubMed Central

Tang, Cindy Q.; Yang, Yongchuan; Ohsawa, Masahiko; Momohara, Arata; Yi, Si-Rong; Robertson, Kevin; Song, Kun; Zhang, Shi-Qiang; He, Long-Yuan

2015-01-01

A rare coniferous Tertiary relict tree species, Thuja sutchuenensis Franch, has survived in the Daba Mountains of southwestern China. It was almost eliminated by logging during the past century. We measured size and age structures and interpreted regeneration dynamics of stands of the species in a variety of topographic contexts and community associations. Forest communities containing T. sutchuenensis were of three types: (1) the Thuja community dominated by T. sutchuenensis, growing on cliffs; (2) the Thuja-Quercus-Cyclobalanopsis community dominated by T. sutchuenensis, Quercus engleriana and Cyclobalanopsis oxyodon, along with Fagus engleriana and Carpinus fargesiana, on steep slopes; (3) the Thuja-Tsuga-Quercus community dominated by T. sutchuenensis, Tsuga chinensis, and Quercus spinosa, on crest ridges. The established seedlings/saplings were found in limestone crevices, on scarred cliff-faces, cliff-edges, fallen logs, canopy gaps and forest margins. The radial growth rate was 0.5-1.1 mm per year. Its growth forms were distorted. It had strong sprouting ability after disturbances. The T. sutchuenensis population thrives on cliffs where there is little competition from other species because of harsh conditions and rockslide disturbances. It is shade-intolerant but stress-tolerant. Its regeneration has depended on natural disturbances. PMID:25928845

DOE Office of Scientific and Technical Information (OSTI.GOV)

Glicken, H.

Large volcanic debris avalanches are among the world's largest mass movements. The rockslide-debris avalanche of the May 18, 1980, eruption of Mount St. Helens produced a 2.8 km/sup 3/ deposit and is the largest historic mass movement. A Pleistocene debris avalanche at Mount Shasta produced a 26 km/sup 3/ deposit that may be the largest Quaternary mass movement. The hummocky deposits at both volcanoes consist of rubble divided into (1) block facies that comprises unconsolidated pieces of the old edifice transported relatively intact, and (2) matrix facies that comprises a mixture of rocks from the old mountain and material pickedmore » up from the surrounding terrain. At Mount St. Helens, the juvenile dacite is found in the matrix facies, indicating that matrix facies formed from explosions of the erupting magma as well as from disaggregation and mixing of blocks. The block facies forms both hummocks and interhummock areas in the proximal part of the St. Helens avalanche deposit. At Mount St. Helens, the density of the old cone is 21% greater than the density of the avalanche deposit. Block size decreases with distance. Clast size, measured in the field and by sieving, coverages about a mean with distance, which suggests that blocks disaggregated and mixed together during transport.« less

Rapid evolution of the paraglacial Moosfluh rock slope instability (Swiss Alps) captured by Sentinel-1

NASA Astrophysics Data System (ADS)

Manconi, Andrea; Glueer, Franziska; Loew, Simon

2017-04-01

The Great Aletsch Region (GAR, Swiss Alps) has undergone to several cycles of glacial advancement and retreat, which have deeply affected the evolution of the surrounding landscape. Currently, this region is one of the places where the effects of climate change can be strikingly observed, as the Aletsch glacier is experiencing a remarkable retreat with rates in the order of 50 meters every year. In particular, a deep-seated slope instability located in the area called "Moosfluh" has shown during the past 20 years evidences of a slow but progressive increase of surface displacement. The moving mass associated to the Moosfluh rockslide affects an area of about 2 km2 and entails a volume estimated in the order of 150-200 Mm3. In the late summer 2016, an unusual acceleration of the Moosfluh rockslide was observed. Compared to previous years, when ground deformations were in the order of few centimeters, in the period September-October 2016 maximum velocities have reached locally 1 m/day. Such a critical evolution resulted in an increased number of local rock failures and caused the generation of several deep tensile cracks, hindering the access to hiking paths visited by tourists. Moreover, surface deformations have also affected the Moosfluh cable car station, located near the crest of the unstable slope. In this critical framework, the information available on ground was not enough to disentangle the spatial extent of the most active region. To investigate that, we have processed a number of Sentinel-1 SAR images acquired over the GAR. We paired images with maximum temporal baseline spanning 12 and 24 days, in order to preserve the highest possible interferometric coherence over the target area. Secondly, by stacking surface displacements obtained from the differential interferograms, we have increased the signal-to-noise ratio to produce velocity maps of the Moosfluh landslide over the period of interest. This approach has allowed us to constrain the lateral borders of the most active area, and to define a strategy for the installation of additional in-situ monitoring targets. Thus, we have improved our capability to monitor in near-real-time the evolution of surface displacement, as well as to provide a better interpretation of the ongoing critical phase and to define evolutionary scenarios. Space borne DInSAR for the analysis of unstable slopes is experiencing a new Era. In former times, the combination of poor temporal sampling and rapid evolution of surface displacements has hindered this technique from performing analysis on landslides during critical acceleration phases. Indeed, the time spanning between the acquisition of a robust SAR dataset and the availability of reliable results were in the order months or, in some cases, even years. Nowadays, by leveraging the unprecedented spatial and temporal coverage provided by the ESA Sentinel-1 A and B, the time spanning from data acquisition to the generation of ground displacements has been reduced to weeks or, in some cases, days. Thus, we can now obtain information current stage of the slope instability and also to catch the rapid evolution towards a potential catastrophic failure.

Monitoring and Early Warning of the 2012 Preonzo Catastrophic Rockslope Failure

NASA Astrophysics Data System (ADS)

Loew, Simon; Gschwind, Sophie; Keller-Signer, Alexandra; Valenti, Giorgio

2015-04-01

In this contribution we describe the accelerated creep stage and early warning system of a 210'000 m3 rock slope failure that occurred in May 2012 above the village of Preonzo (Swiss Alps). The very rapid failure occurred from a larger and retrogressive instability in high-grade metamorphic ortho-gneisses and amphibolites with a total volume of about 350'000 m3 located at an alpine meadow called Alpe di Roscioro. This instability showed clearly visible signs of movements since 1989 and accelerated creep with significant hydro-mechanical forcing since about 1999. Because the instability at Preonzo threatened a large industrial facility and important transport routes a cost-effective early warning system was installed in 2010. The alarm thresholds for pre-alarm, general public alarm and evacuation were derived from 10 years of continuous displacement monitoring with crack extensometers and an automated total station. These thresholds were successfully applied to evacuate the industrial facility and close important roads a few days before the catastrophic slope failure of May 15th, 2012. The rock slope failure occurred in two events, exposing a planar rupture plane dipping 42° and generating deposits in the mid-slope portion with a travel angle of 38°. Two hours after the second rockslide, the fresh colluvial deposits became reactivated in a devastating de-bris avalanche reaching the foot of the slope.

ToF-SIMS applied to historical archaeology in the Alps

NASA Astrophysics Data System (ADS)

Sodhi, R. N. S.; Mahaney, W. C.; Milner, M. W.

2006-07-01

The actual route Hannibal followed during the invasion of Italia in the Second Punic War is one of the major questions of antiquity, one that historians/archaeologists have long studied. There are six possible passes Hannibal could have used and one of the many bits of evidence in the ancient literature that might help answer this question is the location of fired rock, the result of a conflagration Hannibal is reputed to have employed to reduce the size of boulders in a two-tier blocking rockslide on the lee side (e.g. Italian) some distance down from the high col. The only route with fired rock along the roadway leading to the Po River Valley or the Dora Riparia is below the Col du Clapier, one of the possible northern routes. ToF-SIMS investigation of the 100-μm thick burned crust in hornblende schist interlaced with veins of quartz-feldspathic minerals yields various elements C, Mg, Na, Ca, Si, Ti, P, Al, Fe and their associated fragments. Hydrocarbon fragments are thought to be products of combustion whereas Ca and Na along with Mg-Fe silicates are derived from the country rock. Aeolian components along with clay minerals settled onto rock surfaces following firing. While the SIMS data clearly would not provide an age for the burnt rock, compositional evidence of the conflagration may relate to Hannibal's actual route.

Physical Modeling of Landslide Generated Tsunamis and the 50th Anniversary of the Vajont Dam Disaster

NASA Astrophysics Data System (ADS)

McFall, Brian C.; Mohammed, Fahad; Fritz, Hermann M.

2013-04-01

The Vajont river is an affluent of the Piave River located in the Dolomite Alps of the Veneto Region, about 100km north of Venice. A 265.5 m high double curved arch dam was built across a V-shaped gorge creating a reservoir with a maximum storage capacity of 0.169 km3. A maximum water depth of 250 m was reached by early September 1963 during the third filling attempt of the reservoir, but as creeping on the southern flank increased the third reservoir draw down was initiated. By October 9, 1963 the water depth was lowered to 240m as the southern flank of Vajont reservoir catastrophically collapsed on a length of more than 2km. Collapse occurred during reservoir drawdown in a final attempt to reduce flank creeping and the reservoir was only about two-thirds full. The partially submerged rockslide with a volume of 0.24 km3 penetrated into the reservoir at velocities up to 30 m/s. The wave runup in direct prolongation of slide axis reached the lowest houses of Casso 270m above reservoir level before impact corresponding to 245m above dam crest (Müller, 1964). The rockslide deposit came within 50m of the left abutment and towers up to 140m above the dam crest. The lateral spreading of the surge overtopped the dam crest by more than 100m. The thin arch dam withstood the overtopping and sustained no damage to the structural shell and the abutments. The flood wave dropped more than 500m down the Vajont gorge and into the Piave Valley causing utter destruction to the villages of Longarone, Pirago, Villanova, Rivalta and Fae. More than 2000 persons perished. The Vajont disaster highlights an extreme landslide tsunami event in the narrowly confined water body of a reservoir. Landslide tsunami hazards exist even in areas not exposed to tectonic tsunamis. Source and runup scenarios based on real world events are physically modeled in the three dimensional NEES tsunami wave basin (TWB) at Oregon State University (OSU). A novel pneumatic landslide tsunami generator (LTG) was deployed to simulate landslides with varying geometry and kinematics. The LTG consists of a sliding box filled with up to 1,350 kg of naturally rounded river gravel which is accelerated by means of four pneumatic pistons down the 2H: 1V slope, launching the granular landslide towards the water at velocities of up to 5 m/s. Topographical and bathymetric features can greatly affect wave characteristics and runup heights. Landslide tsunamis are studied in different topographic and bathymetric configurations: far field propagation and runup, a narrow fjord and curved headland configurations, and a conical island setting representing landslides off an island or a volcanic flank collapse. Water surface elevations were measured using an array of resistance wave gauges. The granulate landslide shape and front velocity were measured using above and underwater cameras. Three-dimensional landslide surfaces with surface velocities were reconstruction using a stereo particle image velocimetry (PIV) setup. The speckled pattern on the surface of the granular landslide allows for cross-correlation based PIV analysis. Wave runup was measured with resistance wave gauges along the slope and verified with video image processing. The measured landslide and tsunami data serve to validate and advance 3-dimensional numerical landslide tsunami and prediction models.

Geomorphic impacts, age and significance of two giant landslide dams in the Nepal Himalayas: Ringmo-Phoksundo (Dolpo District) and Dhampu-Chhoya (Mustang District).

NASA Astrophysics Data System (ADS)

Fort, Monique; Braucher, Regis; Bourlès, Didier; Guillou, Valery; Nath Rimal, Lila; Gribenski, Natacha; Cossart, Etienne

2014-05-01

Large catastrophic slope failures have recently retained much attention in the northern dry Himalayas (1). They play a prominent role in the denudation history of active orogens at a wide range of spatial and time scales (2), and they impact durably landforms and process evolution in upstream catchments. Their occurrence mostly results from three different potential triggers: earthquakes, post-glacial debuttressing, and permafrost melting. We focus on two examples of giant rock slope failures that occurred across and north of the Higher Himalaya of Nepal and assess their respective influence on the regional, geomorphic evolution. The Ringmo rockslide (4.5 km3) results from the collapse of a mountain wall (5148 m) cut into palaeozoic dolomites of the Tethysian Himalayas. It caused the damming of the Suli Gad River at the origin of the Phoksumdo Lake (3600 m asl). The presence of glacial till at the very base of the sequence suggests the rockslide event is post-glacial, a field assumption confirmed by cosmogenic dating. Two consistent 36Cl ages of 20,885 ±1675 argue for a single, massive event of paraglacial origin that fits well with the last chronologies available on the Last Glacial Maximum in the Nepal Himalaya. The persistence of the Phoksumdo Lake is due to its dam stability (i.e. high lime content of landslide components) and to low sediment flux from the arid, upper Suli Gad catchment. The Dhampu-Chhoya rock avalanche (about 1 km3, area extent 10 km2) was derived from the northward failure of the Kaiku ridge, uphold by north-dipping, upper crystallines of the Higher Himalaya. It dammed the Kali Gandaki River, with complex interactions with the Late Pleistocene ice tongues derived from the Dhaulagiri (8167 m) and Nilgiris (7061 m) peaks. Both the rock avalanche and glaciers controlled the existence and level of the "Marpha Lake" (lacustrine deposits up to Kagbeni). Again, consistent 10Be ages of 29,680 ± 1015 ka obtained from two large blocks (>1000 m3) suggest a single event, in full agreement with other 10Be dates obtained by a different team from the same site (3). This latter event occurred during glaciation, and was likely triggered in connection with the North Himalayan Fault and/or Thakkhola fault activity. Post-landslide dam evolution includes rapid dissection of lacustrine deposits (4), yet the braided pattern of the Kali Gandaki evidence the delay in headward erosion caused by landslide dam persistence. References: (1) Hewitt K., 2009. Catastrophic rock slope failures and late Quaternary developments in the Nanga Parbat-Haramosh Massif, Upper Indus basin, northern Pakistan. Quaternary Science Reviews, 28, 1055-1069; (2) Korup, O., Clague, J.J., 2009. Natural hazards, extreme events, and mountain topography. Quaternary Science Reviews 28, 977-990; (3) Zech R., Zech M, Kubik P.W., Kharki K., Zech W. (2009). Deglaciation and landscape history around Annapurna, Nepal, based on 10Be surface exposure dating, Quaternary Science Reviews, v. 28(11-12), pp.1106-1118; (4) Fort M., Cossart E. (2013) Erosion assessment in the middle Kali Gandaki (Nepal): A sediment budget approach. Journal of Nepal Geological Society, Vol. 46, pp. 25-40.

A hazard and risk classification system for catastrophic rock slope failures in Norway

NASA Astrophysics Data System (ADS)

Hermanns, R.; Oppikofer, T.; Anda, E.; Blikra, L. H.; Böhme, M.; Bunkholt, H.; Dahle, H.; Devoli, G.; Eikenæs, O.; Fischer, L.; Harbitz, C. B.; Jaboyedoff, M.; Loew, S.; Yugsi Molina, F. X.

2012-04-01

The Geological Survey of Norway carries out systematic geologic mapping of potentially unstable rock slopes in Norway that can cause a catastrophic failure. As catastrophic failure we describe failures that involve substantial fragmentation of the rock mass during run-out and that impact an area larger than that of a rock fall (shadow angle of ca. 28-32° for rock falls). This includes therefore rock slope failures that lead to secondary effects, such as a displacement wave when impacting a water body or damming of a narrow valley. Our systematic mapping revealed more than 280 rock slopes with significant postglacial deformation, which might represent localities of large future rock slope failures. This large number necessitates prioritization of follow-up activities, such as more detailed investigations, periodic monitoring and permanent monitoring and early-warning. In the past hazard and risk were assessed qualitatively for some sites, however, in order to compare sites so that political and financial decisions can be taken, it was necessary to develop a quantitative hazard and risk classification system. A preliminary classification system was presented and discussed with an expert group of Norwegian and international experts and afterwards adapted following their recommendations. This contribution presents the concept of this final hazard and risk classification that should be used in Norway in the upcoming years. Historical experience and possible future rockslide scenarios in Norway indicate that hazard assessment of large rock slope failures must be scenario-based, because intensity of deformation and present displacement rates, as well as the geological structures activated by the sliding rock mass can vary significantly on a given slope. In addition, for each scenario the run-out of the rock mass has to be evaluated. This includes the secondary effects such as generation of displacement waves or landslide damming of valleys with the potential of later outburst floods. It became obvious that large rock slope failures cannot be evaluated on a slope scale with frequency analyses of historical and prehistorical events only, as multiple rockslides have occurred within one century on a single slope that prior to the recent failures had been inactive for several thousand years. In addition, a systematic analysis on temporal distribution indicates that rockslide activity following deglaciation after the Last Glacial Maximum has been much higher than throughout the Holocene. Therefore the classification system has to be based primarily on the geological conditions on the deforming slope and on the deformation rates and only to a lesser weight on a frequency analyses. Our hazard classification therefore is primarily based on several criteria: 1) Development of the back-scarp, 2) development of the lateral release surfaces, 3) development of the potential basal sliding surface, 4) morphologic expression of the basal sliding surface, 5) kinematic feasibility tests for different displacement mechanisms, 6) landslide displacement rates, 7) change of displacement rates (acceleration), 8) increase of rockfall activity on the unstable rock slope, 9) Presence post-glacial events of similar size along the affected slope and its vicinity. For each of these criteria several conditions are possible to choose from (e.g. different velocity classes for the displacement rate criterion). A score is assigned to each condition and the sum of all scores gives the total susceptibility score. Since many of these observations are somewhat uncertain, the classification system is organized in a decision tree where probabilities can be assigned to each condition. All possibilities in the decision tree are computed and the individual probabilities giving the same total score are summed. Basic statistics show the minimum and maximum total scores of a scenario, as well as the mean and modal value. The final output is a cumulative frequency distribution of the susceptibility scores that can be divided into several classes, which are interpreted as susceptibility classes (very high, high, medium, low, and very low). Today the Norwegian Planning and Building Act uses hazard classes with annual probabilities of impact on buildings producing damages (<1/100, <1/1000, <1/5000 and zero for critical buildings). However, up to now there is not enough scientific knowledge to predict large rock slope failures in these strict classes. Therefore, the susceptibility classes will be matched with the hazard classes from the Norwegian Building Act (e.g. very high susceptibility represents the hazard class with annual probability >1/100). The risk analysis focuses on the potential fatalities of a worst case rock slide scenario and its secondary effects only and is done in consequence classes with a decimal logarithmic scale. However we recommend for all high risk objects that municipalities carry out detailed risk analyses. Finally, the hazard and risk classification system will give recommendations where surveillance in form of continuous 24/7 monitoring systems coupled with early-warning systems (high risk class) or periodic monitoring (medium risk class) should be carried out. These measures are understood as to reduce the risk of life loss due to a rock slope failure close to 0 as population can be evacuated on time if a change of stability situation occurs. The final hazard and risk classification for all potentially unstable rock slopes in Norway, including all data used for its classification will be published within the national landslide database (available on www.skrednett.no).

Analysis of Low-Light and Night-Time Stereo-Pair Images for Photogrammetric Reconstruction

NASA Astrophysics Data System (ADS)

Santise, M.; Thoeni, K.; Roncella, R.; Diotri, F.; Giacomini, A.

2018-05-01

Rockfalls and rockslides represent a significant risk to human lives and infrastructures because of the high levels of energy involved in the phenomena. Generally, these events occur in accordance to specific environmental conditions, such as temperature variations between day and night, that can contribute to the triggering of structural instabilities in the rock-wall and the detachment of blocks and debris. The monitoring and the geostructural characterization of the wall are required for reducing the potential hazard and to improve the management of the risk at the bottom of the slopes affected by such phenomena. In this context, close range photogrammetry is largely used for the monitoring of high-mountain terrains and rock walls in mine sites allowing for periodic survey of rockfalls and wall movements. This work focuses on the analysis of low-light and night-time images of a fixed-base stereo pair photogrammetry system. The aim is to study the reliability of the images acquired over the night to produce digital surface models (DSMs) for change detection. The images are captured by a high-sensitivity DLSR camera using various settings accounting for different values of ISO, aperture and time of exposure. For each acquisition, the DSM is compared to a photogrammetric reference model produced by images captured in optimal illumination conditions. Results show that, with high level of ISO and maintaining the same grade of aperture, extending the exposure time improves the quality of the point clouds in terms of completeness and accuracy of the photogrammetric models.

Brittle and Ductile Behavior in Deep-Seated Landslides: Learning from the Vajont Experience

NASA Astrophysics Data System (ADS)

Paronuzzi, Paolo; Bolla, Alberto; Rigo, Elia

2016-06-01

This paper analyzes the mechanical behavior of the unstable Mt. Toc slope before the 1963 catastrophic collapse, considering both the measured data (surface displacements and microseismicity) and the updated geological model of the prehistoric rockslide. From February 1960 up to 9 October 1963, the unstable mass behaved as a brittle-ductile `mechanical system,' characterized by remarkable microseismicity as well as by considerable surface displacements (up to 4-5 m). Recorded microshocks were the result of progressive rock fracturing of distinct resisting stiff parts made up of intact rock (indentations, undulations, and rock bridges). The main resisting stiff part was a large rock indentation located at the NE extremity of the unstable mass that acted as a mechanical constraint during the whole 1960-1963 period, inducing a progressive rototranslation toward the NE. This large constraint failed in autumn 1960, when an overall slope failure took place, as emphasized by the occurrence of the large perimetrical crack in the upper slope. In this circumstance, the collapse was inhibited by a reblocking phenomenon of the unstable mass that had been previously destabilized by the first reservoir filling. Progressive failure of localized intact rock parts progressively propagated westwards as a consequence of the two further filling-drawdown cycles of the reservoir (1962 and 1963). The characteristic brittle-ductile behavior of the Vajont landslide was made possible by the presence of a very thick (40-50 m) and highly deformable shear zone underlying the upper rigid rock mass (100-120 m thick).

Numerical modeling of the Mount Meager landslide constrained by its force history derived from seismic data

NASA Astrophysics Data System (ADS)

Moretti, L.; Allstadt, K.; Mangeney, A.; Capdeville, Y.; Stutzmann, E.; Bouchut, F.

2015-04-01

We focus on the 6 August 2010 Mount Meager landslide that occurred in Southwest British Columbia, Canada. This 48.5 Mm3 rockslide that rapidly changed into a debris flow was recorded by over 25 broadband seismic stations. We showed that the waveform inversion of the seismic signal making it possible to calculate the time history of the force applied by the landslide to the ground is very robust and stable, even when using only data from a single station. By comparing this force with the force calculated through numerical modeling of the landslide, we are able to support the interpretation of seismic data made using a simple block model. However, our study gives different values of the friction coefficients involved and more details about the volumes and orientation of the subevents and the flow trajectory and velocity. Our sensitivity analysis shows that the characteristics of the released mass and the friction coefficients all contribute to the amplitude and the phase of the force. Despite this complexity, our study makes it possible to discriminate the best values of all these parameters. Our results suggest that comparing simulated and inverted forces helps to identify appropriate rheological laws for natural flows. We also show that except for the initial collapse, peaks in the low-frequency force related to bends and runup over topography changes are associated with high-frequency generation, possibly due to an increased agitation of the granular material involved.

Characterization of Unstable Rock Slopes Through Passive Seismic Measurements

NASA Astrophysics Data System (ADS)

Kleinbrod, U.; Burjanek, J.; Fäh, D.

2014-12-01

Catastrophic rock slope failures have high social impact, causing significant damage to infrastructure and many casualties throughout the world each year. Both detection and characterization of rock instabilities are therefore of key importance. An analysis of ambient vibrations of unstable rock slopes might be a new alternative to the already existing methods, e.g. geotechnical displacement measurements. Systematic measurements have been performed recently in Switzerland to study the seismic response of potential rockslides concerning a broad class of slope failure mechanisms and material conditions. Small aperture seismic arrays were deployed at sites of interest for a short period of time (several hours) in order to record ambient vibrations. Each measurement setup included a reference station, which was installed on a stable part close to the instability. Recorded ground motion is highly directional in the unstable parts of the rock slope, and significantly amplified with respect to stable areas. These effects are strongest at certain frequencies, which were identified as eigenfrequencies of the unstable rock mass. In most cases the directions of maximum amplification are perpendicular to open cracks and in good agreement with the deformation directions obtained by geodetic measurements. Such unique signatures might improve our understanding of slope structure and stability. Thus we link observed vibration characteristics with available results of detailed geological characterization. This is supported by numerical modeling of seismic wave propagation in fractured media with complex topography.For example, a potential relation between eigenfrequencies and unstable rock mass volume is investigated.

Influence of filling-drawdown cycles of the Three Gorges reservoir on deformation and failure behaviors of anaclinal rock slopes in the Wu Gorge

NASA Astrophysics Data System (ADS)

Huang, Da; Gu, Dong Ming

2017-10-01

The upper Wu Gorge on the Yangtze River has been the site of tens of reservoir-induced landslides since the filling of the Three Gorges reservoir in 2003. These landslides have been occurring in heavily fractured carbonate rock materials along the rim of the reservoir in the Wu Gorge. A detailed investigation was carried out to examine the influence of reservoir operations (filling and drawdown) on slope stabilities in the upper Wu Gorge. Field investigations reveal many collapses of various types occurred at the toe of the anaclinal rock slopes, owing to the long-term intensive river erosion caused by periodic fluctuation of the reservoir level. Analysis of data from deformation monitoring suggests that the temporal movement of the slopes shows seasonal fluctuations that correlate with reservoir levels and drawdown conditions, with induced slope acceleration peaking when reservoir levels are lowest. This may illustrate that the main mechanism is the reservoir drawdown, which induces an episodic seepage force in the highly permeable materials at the slope toes, and thus leads to the episodic rockslides. The coupled hydraulic-mechanical (HM) modeling of the G2 landslide, which occurred in 2008, shows that collapse initiated at the submerged slope toe, which then caused the upper slope to collapse in a rock topple-rock slide pattern. The results imply that preventing water erosion at the slope toe might be an effective way for landslide prevention in the study area.

Integration of Geomatics Techniques for Digitizing Highly Relevant Geological and Cultural Heritage Sites: the Case of San Leo (italy)

NASA Astrophysics Data System (ADS)

Girelli, V. A.; Borgatti, L.; Dellapasqua, M.; Mandanici, E.; Spreafico, M. C.; Tini, M. A.; Bitelli, G.

2017-08-01

The research activities described in this contribution were carried out at San Leo (Italy). The town is located on the top of a quadrangular rock slab affected by a complex system of fractures and has a wealth of cultural heritage, as evidenced by the UNESCO's nomination. The management of this fragile set requires a comprehensive system of geometrical information to analyse and preserve all the geological and cultural features. In this perspective, the latest Geomatics techniques were used to perform some detailed surveys and to manage the great amount of acquired geometrical knowledge of both natural (the cliff) and historical heritage. All the data were also georeferenced in a unique reference system. In particular, high accurate terrestrial laser scanner surveys were performed for the whole cliff, in order to obtain a dense point cloud useful for a large number of geological studies, among others the analyses of the last rockslide by comparing pre- and post-event data. Moreover, the geometrical representation of the historical centre was performed using different approaches, in order to generate an accurate DTM and DSM of the site. For these purposes, a large scale numerical map was used, integrating the data with GNSS and laser surveys of the area. Finally, many surveys were performed with different approaches on some of the most relevant monuments of the town. In fact, these surveys were performed by terrestrial laser scanner, light structured scanner and photogrammetry, the last mainly applied with the Structure from Motion approach.

Assessment and Survey of Potential Catastrophic Landslides by Using Geomorphometric Analysis

NASA Astrophysics Data System (ADS)

Hsieh, Yu-Chung; Hou, Chin-Shyong; Hu, Jyr-Ching; Chan, Yu-Chang; Fei, Li-Yuan; Chen, Hung-Jen; Chiu, Cheng-Lung

2013-04-01

In recent years, extreme weather events have induced more frequent geological hazards in Taiwan. The heavy rainfall brought by the Typhoon Morakot has triggered a large amount of landslides. The most unfortunate case occurred in the Hsiaolin village which was totally demolished by a catastrophic landslide in less than a minute. The study of such catastrophic landslides is urgently needed to mitigate loss of lives and properties in the future. Traditionally, the study of landslides usually includes shallow landslides, rockslide, and debris flow etc. and is commonly made use of satellite images, aerial photos, coupled with field surveys. It is considered that the creep phase of a landslide is a progressive stage of failure and gives sufficient signals before turning into a catastrophic landslide. Due to lack of high quality terrain data, however, the research of catastrophic landslides has been time consuming with often unsatisfactory results. This study used high-resolution airborne LiDAR-derived DEM data from the Central Geological Survey, MOEA. Different geomorphometric analyses were applied to process the high resolution and high accuracy DEM data including the hillshade, aspect, slope, eigenvalue ratio (ER) & openness. Among the geomorphometric analyses, combining the characteristics of openness, slope and hillshade gives a clear advantage to distinguish and analyze regions of potential catastrophic landslides in many cases. Statistical and image processing techniques to quantify morphological and other aspects of the terrain surface are also employed. Our results indicate that over hundreds of potential catastrophic landslides may present in southern Taiwan after the Typhoon Morakot event. The quantitative methods used in this study highlight the terrain features of the creep phase of catastrophic landslides and is helpful for landslide feature interpretation and hazard assessment.

Large landslides associated with a diapiric fold in Canelles Reservoir (Spanish Pyrenees): Detailed geological-geomorphological mapping, trenching and electrical resistivity imaging

NASA Astrophysics Data System (ADS)

Gutiérrez, Francisco; Linares, Rogelio; Roqué, Carles; Zarroca, Mario; Carbonel, Domingo; Rosell, Joan; Gutiérrez, Mateo

2015-07-01

Detailed geomorphological-geological mapping in Canelles Reservoir, the Spanish Pyrenees, reveals the presence of several large landslides overlooked in previous cartographic works. One of the slope movements, designated as the Canelles landslide, corresponds to a 40 × 106 m3 translational landslide reactivated in 2006 by a severe decline in the reservoir water level. The geomorphic features mapped in the upper part of the Canelles landslide, including surface ruptures corroborated by electrical resistivity imaging and trenching, indicate multiple displacement episodes previous to the 2006 human-induced event. Consistently, the stratigraphic and structural relationships observed in a trench record at least two displacement events older and larger in magnitude than the 2006 reactivation. The oldest recorded event occurred in the 6th to 7th Centuries and the second in 1262-1679 yr AD. This latter episode might be correlative to the 1373 Ribagorza earthquake (Mw 6.2), which caused the reactivation of a landslide and the consequent destruction of a village in the adjacent valley. The available data indicate that over more than one millennium the kinematics of the landslide has been characterised by discrete small-displacement episodes. These data, together with the available literature on rapid rockslides, do not concur with the acceleration predicted by modelling in a previous investigation, which foresees a speed of 16 m s- 1 despite the low average dip of the sliding surface (9-10°). This case study illustrates that the trenching technique may provide valuable practical information on the past behaviour of landslides, covering a much broader time span than instrumental and historical records.

The role of tectonic damage and brittle rock fracture in the development of large rock slope failures

NASA Astrophysics Data System (ADS)

Brideau, Marc-André; Yan, Ming; Stead, Doug

2009-01-01

Rock slope failures are frequently controlled by a complex combination of discontinuities that facilitate kinematic release. These discontinuities are often associated with discrete folds, faults, and shear zones, and/or related tectonic damage. The authors, through detailed case studies, illustrate the importance of considering the influence of tectonic structures not only on three-dimensional kinematic release but also in the reduction of rock mass properties due to induced damage. The case studies selected reflect a wide range of rock mass conditions. In addition to active rock slope failures they include two major historic failures, the Hope Slide, which occurred in British Columbia in 1965 and the Randa rockslides which occurred in Switzerland in 1991. Detailed engineering geological mapping combined with rock testing, GIS data analysis and for selected case numerical modelling, have shown that specific rock slope failure mechanisms may be conveniently related to rock mass classifications such as the Geological Strength Index (GSI). The importance of brittle intact rock fracture in association with pre-existing rock mass damage is emphasized though a consideration of the processes involved in the progressive-time dependent development not only of though-going failure surfaces but also lateral and rear-release mechanisms. Preliminary modelling data are presented to illustrate the importance of intact rock fracture and step-path failure mechanisms; and the results are discussed with reference to selected field observations. The authors emphasize the importance of considering all forms of pre-existing rock mass damage when assessing potential or operative failure mechanisms. It is suggested that a rock slope rock mass damage assessment can provide an improved understanding of the potential failure mode, the likely hazard presented, and appropriate methods of both analysis and remedial treatment.

Numerical Modeling of Earthquake-Induced Landslide Using an Improved Discontinuous Deformation Analysis Considering Dynamic Friction Degradation of Joints

NASA Astrophysics Data System (ADS)

Huang, Da; Song, Yixiang; Cen, Duofeng; Fu, Guoyang

2016-12-01

Discontinuous deformation analysis (DDA) as an efficient technique has been extensively applied in the dynamic simulation of discontinuous rock mass. In the original DDA (ODDA), the Mohr-Coulomb failure criterion is employed as the judgment principle of failure between contact blocks, and the friction coefficient is assumed to be constant in the whole calculation process. However, it has been confirmed by a host of shear tests that the dynamic friction of rock joints degrades. Therefore, the friction coefficient should be gradually reduced during the numerical simulation of an earthquake-induced rockslide. In this paper, based on the experimental results of cyclic shear tests on limestone joints, exponential regression formulas are fitted for dynamic friction degradation, which is a function of the relative velocity, the amplitude of cyclic shear displacement and the number of its cycles between blocks with an edge-to-edge contact. Then, an improved DDA (IDDA) is developed by implementing the fitting regression formulas and a modified removing technique of joint cohesion, in which the cohesion is removed once the `sliding' or `open' state between blocks appears for the first time, into the ODDA. The IDDA is first validated by comparing with the theoretical solutions of the kinematic behaviors of a sliding block on an inclined plane under dynamic loading. Then, the program is applied to model the Donghekou landslide triggered by the 2008 Wenchuan earthquake in China. The simulation results demonstrate that the dynamic friction degradation of joints has great influences on the runout and velocity of sliding mass. Moreover, the friction coefficient possesses higher impact than the cohesion of joints on the kinematic behaviors of the sliding mass.

A computationally fast, reduced model for simulating landslide dynamics and tsunamis generated by landslides in natural terrains

NASA Astrophysics Data System (ADS)

Mohammed, F.

2016-12-01

Landslide hazards such as fast-moving debris flows, slow-moving landslides, and other mass flows cause numerous fatalities, injuries, and damage. Landslide occurrences in fjords, bays, and lakes can additionally generate tsunamis with locally extremely high wave heights and runups. Two-dimensional depth-averaged models can successfully simulate the entire lifecycle of the three-dimensional landslide dynamics and tsunami propagation efficiently and accurately with the appropriate assumptions. Landslide rheology is defined using viscous fluids, visco-plastic fluids, and granular material to account for the possible landslide source materials. Saturated and unsaturated rheologies are further included to simulate debris flow, debris avalanches, mudflows, and rockslides respectively. The models are obtained by reducing the fully three-dimensional Navier-Stokes equations with the internal rheological definition of the landslide material, the water body, and appropriate scaling assumptions to obtain the depth-averaged two-dimensional models. The landslide and tsunami models are coupled to include the interaction between the landslide and the water body for tsunami generation. The reduced models are solved numerically with a fast semi-implicit finite-volume, shock-capturing based algorithm. The well-balanced, positivity preserving algorithm accurately accounts for wet-dry interface transition for the landslide runout, landslide-water body interface, and the tsunami wave flooding on land. The models are implemented as a General-Purpose computing on Graphics Processing Unit-based (GPGPU) suite of models, either coupled or run independently within the suite. The GPGPU implementation provides up to 1000 times speedup over a CPU-based serial computation. This enables simulations of multiple scenarios of hazard realizations that provides a basis for a probabilistic hazard assessment. The models have been successfully validated against experiments, past studies, and field data for landslides and tsunamis.

Geologic columns for the ICDP-USGS Eyreville B core, Chesapeake Bay impact structure: Impactites and crystalline rocks, 1766 to 1096 m depth

USGS Publications Warehouse

Horton, J. Wright; Gibson, R.L.; Reimold, W.U.; Wittmann, A.; Gohn, G.S.; Edwards, L.E.

2009-01-01

The International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville drill cores from the Chesapeake Bay impact structure provide one of the most complete geologic sections ever obtained from an impact structure. This paper presents a series of geologic columns and descriptive lithologic information for the lower impactite and crystalline-rock sections in the cores. The lowermost cored section (1766-1551 m depth) is a complex assemblage of mica schists that commonly contain graphite and fibrolitic sillimanite, intrusive granite pegmatites that grade into coarse granite, and local zones of mylonitic deformation. This basement-derived section is variably overprinted by brittle cataclastic fabrics and locally cut by dikes of polymict impact breccia, including several suevite dikes. An overlying succession of suevites and lithic impact breccias (1551-1397 m) includes a lower section dominated by polymict lithic impact breccia with blocks (up to 17 m) and boulders of cataclastic gneiss and an upper section (above 1474 m) of suevites and clast-rich impact melt rocks. The uppermost suevite is overlain by 26 m (1397-1371 m) of gravelly quartz sand that contains an amphibolite block and boulders of cataclasite and suevite. Above the sand, a 275-m-thick allochthonous granite slab (1371-1096 m) includes gneissic biotite granite, fine- and medium-to-coarse-grained biotite granites, and red altered granite near the base. The granite slab is overlain by more gravelly sand, and both are attributed to debris-avalanche and/or rockslide deposition that slightly preceded or accompanied seawater-resurge into the collapsing transient crater. ?? 2009 The Geological Society of America.

Recognition of earthquake-related damage in archaeological sites: Examples from the Dead Sea fault zone

NASA Astrophysics Data System (ADS)

Marco, Shmuel

2008-06-01

Archaeological structures that exhibit seismogenic damage expand our knowledge of temporal and spatial distribution of earthquakes, afford independent examination of historical accounts, provide information on local earthquake intensities and enable the delineation of macroseismic zones. They also illustrate what might happen in future earthquakes. In order to recover this information, we should be able to distinguish earthquake damage from anthropogenic damage and from other natural processes of wear and tear. The present paper reviews several types of damage that can be attributed with high certainty to earthquakes and discusses associated caveats. In the rare cases, where faults intersect with archaeological sites, offset structures enable precise determination of sense and size of slip, and constrain its time. Among the characteristic off-fault damage types, I consider horizontal shifting of large building blocks, downward sliding of one or several blocks from masonry arches, collapse of heavy, stably-built walls, chipping of corners of building blocks, and aligned falling of walls and columns. Other damage features are less conclusive and require additional evidence, e.g., fractures that cut across several structures, leaning walls and columns, warps and bulges in walls. Circumstantial evidence for catastrophic earthquake-related destruction includes contemporaneous damage in many sites in the same area, absence of weapons or other anthropogenic damage, stratigraphic data on collapse of walls and ceilings onto floors and other living horizons and burial of valuable artifacts, as well as associated geological palaeoseismic phenomena such as liquefaction, land- and rock-slides, and fault ruptures. Additional support may be found in reliable historical accounts. Special care must be taken in order to avoid circular reasoning by maintaining the independence of data acquisition methods.

Influence of filling-drawdown cycles of the Vajont reservoir on Mt. Toc slope stability

NASA Astrophysics Data System (ADS)

Paronuzzi, Paolo; Rigo, Elia; Bolla, Alberto

2013-06-01

In the present work, the 1963 Vajont landslide has been back-analyzed in detail to examine the influence of reservoir operations (filling and drawdown) on Mt. Toc slope stability. The combined seepage-slope stability analyses carried out show that the main destabilizing factor that favored the 1963 Vajont landslide was the reservoir-induced water table that formed as a consequence of rapid seepage inflow within the submerged toe of the slope — decrease in the factor of safety (FOS) up to 12% compared to the initial slope stability condition, i.e., in the absence of the Vajont reservoir. Rainfall would only have been a decisive factor if the initial stability condition of the Mt. Toc slope had already been very close to failure (decrease in FOS caused by heavy or prolonged rainfall is about 3-4%, for the worst case scenario analyzed). The permeability of the shear zone material occurring at the base of the prehistoric Vajont rockslide has been evaluated at 5 × 10- 4 m/s, and back-calculated values of the friction angles Φ range from 17.5° to 27.5°. When considering mountain reservoirs, slope failures can occur during both filling and drawdown phases. In the Vajont case, owing to the highly permeable materials of the shear zone, slope stability decreased during filling and increased during drawdown. Another displacement-dependent phenomenon of a mechanical nature - progressive failure of the NE landslide constraint - has to be considered to understand the slope collapse that occurred during the last drawdown (26 September-9 October 1963). The results of the combined seepage-slope stability models indicate that permeability of bank-forming material and filling-drawdown rates of reservoirs can strongly influence slope stability. Slow lowering of the reservoir level is a necessary measure to reduce the occurrence of very dangerous transient negative peaks of FOS.

Monitoring of a steep rockfall area experiencing fast displacements in Kåfjord, Northern Norway

NASA Astrophysics Data System (ADS)

Dreiås Majala, Gudrun; Harald Blikra, Lars; Skrede, Ingrid; Kristensen, Lene

2016-04-01

An unstable rockfall area in Kåfjord, Northern Norway, was recognized during periodic monitoring campaigns in July and early September 2015. The LiSALab ground based Interferometric Synthethic Aperture Radar (GB InSAR) from Ellegi were used. A relatively sharply defined steep area of 1200 m2 (6.000 - 12.000 m3) was documented to be in movement. Norwegian Water Resources and Energy Directorate (NVE) was at this point performing mitigation work in terms of an embarkment within the rockfall run-out area. The monitoring system was reinstalled and adjusted to perform continuous monitoring with an early-warning aim. The section for rockslide management in NVE was responsible for the monitoring and the warning to the municipality and Police. The displacements increased from about 1 mm/day in July to 3 cm/day in mid September. People were evalcuated due to increased velocities the 16th of September. The displacements continued to increase in several stages, and with a distinct accelleration the 2nd of October. The velocity peaked in a short window to more than 200 cm/day, and it ended with a partly frontal and sideway collapse of the unstable area. However, large parts of the area stabilized again, and the run-out lengths from the small rockfalls were limited. The GB InSAR system operated exceptionally well during the event, and were able to follow continuously the displacements during the accelleration stage until collapse as the processing time window was frequently adjusted to the changes in velocity. We were also able to follow inidividual rockfalls from the images - primarily as the rockfall impact points on the slope below showed up clearly on the radar images. The area continued to stabilize due to falling temperatures, and the mitigation work were finished during the fall. The displacements seem to be correlated to the increasing temperatures in late summer and precipitation events.

Characterization of Unstable Rock Slopes Through Passive Seismic Measurements

NASA Astrophysics Data System (ADS)

Kleinbrod, Ulrike; Burjánek, Jan; Fäh, Donat

2014-05-01

Catastrophic rock slope failures have high social impact, causing significant damage to infrastructure and many casualties throughout the world each year. Both detection and characterization of rock instabilities are therefore of key importance. Analysing unstable rock slopes by means of ambient vibrations might be a new alternative to the already existing methods as for example geotechnical displacement measurements. A systematic measurement campaign has been initiated recently in Switzerland in order to study the seismic response of potential rockslides concerning a broad class of slope failure mechanisms and material conditions. First results are presented in this contribution. Small aperture seismic arrays were deployed at sites of interest for a short period of time (several hours) in order to record ambient vibrations. During each measurement a reference station was installed on a stable part close to the instability. The total number of stations used varies from 16 down to 2, depending on the site scope and resource availability. Instable rock slopes show a highly directional ground motion which is significantly amplified with respect to stable areas. These effects are strongest at certain frequencies which are identified as eigenfrequencies of the unstable rock mass. The eigenfrequencies and predominant directions have been estimated by frequency dependent polarization analysis. Site-to-reference spectral ratios have been calculated as well in order to estimate the relative amplification of ground motion at unstable parts. The retrieved results were compared with independent in-situ observations and other available data. The directions of maximum amplification are in most cases perpendicular to open cracks mapped on the surface and in good agreement with the deformation directions obtained by geodetic measurements. The interpretation of the observed wave field is done through numerical modelling of seismic wave propagation in fractured media with complex topography. For example, a potential relation between eigenfrequencies and unstable rock mass volume is investigated.

Catastrophic precipitation-triggered lahar at Casita volcano, Nicaragua: Occurrence, bulking and transformation

USGS Publications Warehouse

Scott, K.M.; Vallance, J.W.; Kerle, N.; Macias, J.L.; Strauch, W.; Devoli, G.

2005-01-01

A catastrophic lahar began on 30 October 1998, as hurricane precipitation triggered a small flank collapse of Casita volcano, a complex and probably dormant stratovolcano. The initial rockslide-debris avalanche evolved on the flank to yield a watery debris flood with a sediment concentration less than 60 per cent by volume at the base of the volcano. Within 2-5 km, however, the watery flow entrained (bulked) enough sediment to transform entirely to a debris flow. The debris flow, 6 km downstream and 1??2 km wide and 3 to 6 m deep, killed 2500 people, nearly the entire populations of the communities of El Porvenir and Rolando Rodriguez. These 'new towns' were developed in a prehistoric lahar pathway: at least three flows of similar size since 8330 14C years BP are documented by stratigraphy in the same 30-degree sector. Travel time between perception of the flow and destruction of the towns was only 2??5-3??0 minutes. The evolution of the flow wave occurred with hydraulic continuity and without pause or any extraordinary addition of water. The precipitation trigger of the Casita lahar emphasizes the nee d, in volcano hazard assessments, for including the potential for non-eruption-related collapse lahars with the more predictable potential of their syneruption analogues. The flow behaviour emphasizes that volcano collapses can yield not only volcanic debris avalanches with restricted runouts, but also mobile lahars that enlarge by bulking as they flow. Volumes and hence inundation areas of collapse-runout lahars can increase greatly beyond their sources: the volume of the Casita lahar bulked to at least 2??6 times the contributing volume of the flank collapse and 4??2 times that of the debris flood. At least 78 per cent of the debris flow matrix (sediment < -1??0??; 2 mm) was entrained during flow. Copyright c 2004 John Wiley & Sons, Ltd.

"Parco Archeologico Storico Naturale delle Chiese Rupestri del Materano": geomorphological fragility and slope instability in a rupestrian-heritage rich area (Basilicata, south Italy).

NASA Astrophysics Data System (ADS)

Francioso, R.; Sdao, F.; Tropeano, M.

2003-04-01

The Italian Ministry of Education, University and Research financed a research project about the study and the control of hydrogeological hazard of some sites belonging to the "Parco Archeologico Storico Naturale delle Chiese Rupestri del Materano"; the Park and the old city of Matera ("Sassi di Matera") was inserted in the UNESCO World Heritage list since 1993. The studied sites ("Belvedere Chiese Rupestri" and "Iazzo dell'Ofra" localities) are located along the top of the walls of the deep canyon (locally called "Gravina di Matera" and deeper than 100 m) which characterizes the area. Several valuable medieval rupestrian hand-hewn rock churches and sanctuaries are present along the canyon walls. The canyon cut weak rocks (Plio-Pleistocene calcarenites, in which churches and sanctuaries are excavated) and the underlying well-stratified limestones (Cretaceous calcilutites). Both rocks are abundantly and strongly fractured and disjointed by several different joint sets, and, on the left wall of the "Gravina di Matera" canyon, they are characterized by a mainly dipping-slope attitude. Consequently, rock blocks of different sizes formed (up to some tens of m^3 in volume), and are characterized by low stability condition. The considerable acclivity of the walls and the defects and intense fracturing state of rocks, especially along the edge, cause rapid falls, topples and rockslides of the blocks. This geomorphological fragility, confirmed by wide-spread signs of potential instability and by several rock blocks fell in the stream, causes the diffuse and significant structural-failures processes that involve most of the very fine rupestrian heritages. Our study, after the geological and geomorphological description of the sites and the editing of thematic maps, concentrates on the determination the present-day slope instability conditions. Moreover, the study demonstrated the notable genetic relationship between jointing, slope instability and failure type of carbonate blocks. The main results of this geological and geomorphological studies and thematic maps will be reported and discussed.

Integration of GB-InSAR, laser scanning and in situ monitoring on the rockslope instability of Mannen/Børa (western Norway)

NASA Astrophysics Data System (ADS)

Rouyet, Line; Kristensen, Lene; Derron, Marc-Henri; Michoud, Clément; Harald, Blikra Lars; Michel, Jaboyedoff

2013-04-01

This work is part of a master thesis about the use of Ground-Based InSAR for the monitoring of rock instabilities (University of Lausanne in cooperation with the Åknes/Tafjord Early Warning Centre in Norway). Main goals are (1) the evaluation of the GB-InSAR potential to investigate different kinds of instabilities, (2) the combination of data from GB-InSAR, conventional in situ devices and laser scanning to get information about instability behavior and geometry. The rockslope instability of Mannen/Børa is located in Møre of Romsdal County (western Norway). Mannen is a complex rockslide of 15-25 mill. m3 of volume, affecting the left side of the Romsdalen valley. Børa is a large plateau directly located on its south-eastern side and showing signs of activity. In this case, the analysis included GB-InSAR data of 2011 and 2012 campaigns in Børa compared with results of a permanent GB-InSAR in Mannen. The results of continuous monitoring in Mannen (GPS, extensometers, laser-reflectors and tiltmeters) since end of 2009, as well as periodical GPS campaigns on Børa plateau were integrated. The analysis showed a quite regular inter-annual velocity with seasonal effects in Mannen site and a slower movement in Børa. Moreover, it allowed highlighting an area in mid-slope, affected by high variations and periodical inversions of movement in the overlap sector between the two GB-InSAR. The first interpretation of this pattern involves networks of water flow across the slope. A novel point of this site is to have two GB-InSAR systems (one permanent and one temporary) imaging the rockslope with an overlap of views. GB-InSAR results were compared to other types of monitoring data, in terms of spatial coverage (punctual vs. large area), temporal scale (continuous monitoring vs. periodical campaigns) or recorded information (eg. 3D vs. 1D along the LOS). Moreover, a structural geology analysis based on terrestrial and airborne laser scanning data provided information about the geometry of rock instabilities and sliding surfaces.

Filling of Spirit Lake, Washington, May 18, 1980 to July 31, 1982

USGS Publications Warehouse

Meyer, William; Carpenter, Philip J.

1983-01-01

The rockslide/debris avalanche from the north face of Mount St. Helens that precipitated the volcano 's eruption on May 18, 1980 , blocked outflow from Spirit Lake, Washington. There has been no surface outflow since that time. From May 21, 1980, when the first measurement of lake level was made, to August 1, 1982, Spirit Lake has increased its volume from 122,800 acre-ft to 264 ,000 acre-ft, an increase of 115%. Lake level has risen approximately 54 ft during this period. Hydrologic and geologic properties of the debris dam are unknown, but the materials obviously are easily erodible. Steep walled channels up to 60 ft deep have been eroded into the dam and are extending headward toward the lowest points on the crest. In addition, it appears that the lower areas on the crest of the dam are underlain by ash cloud deposits of low density. Indications are that the debris dam could fail by headward erosion, by overtopping with rapid downcutting, or by ' piping ' and rapid erosion. Each type of failure can produce rapid release of stored lake water with very high discharge rates. On the basis of observed filling rates of the lake over the last two yr and precipitation records at four long-term, low altitude National Weather Service stations, it is expected that normal precipitation will fill the lake to the dam crest in December 1985. This estimate is also based on the assumption that loss of water from the lake by seepage continues at the present rate until December 1985. With normal precipitation during the coming yr (August 1982 through July 1983 the lake will fill to a level 50 ft below the lowest existing point on the crest of the debris dam, which is at 3,532 ft altitude. If precipitation exceeds normal by 1.5 times during this coming year, the lake level will be 40 ft below the 3 ,532-ft crest of the debris dam by the end of July 1983. This same lake level can be reached by the end of March 1983 if precipitation from October through March is twice the winter mean. (Author 's abstract)

Landslide management through the design and implementation of an early warning system

NASA Astrophysics Data System (ADS)

Intrieri, E.; Gigli, G.; Mugnai, F.; Fanti, R.; Casagli, N.

2012-04-01

Within the framework of landslide management, early warning systems (EWSs) are an alternative and cost-effective means to reduce the risk with a low environmental and economical impact. In some cases they can even be the only solution, for instance when a landslide is so large that it cannot possibly be stabilized, when in an area there are too many unstable slopes and there are not enough financial resources to take care of them all individually, or when the residual risk after remediation works is still unacceptable. An EWS for a rockslide (at Torgiovannetto, Central Italy) has been designed after a period during which monitoring, landslide characterization and the definition of risk scenarios have been carried out. It consists in a 182 000 m3 rock wedge threatening two roads which are important for local transportation. The present work encompasses and describes all the components of the EWS, including the geological knowledge, the risk scenarios, the kinematic characterization of the landslide, the choice and installation of the monitoring system, the setting of appropriate alarm levels, the definition of plans of civil protection and so on. The focus is on practical and logistical issues met in all these phases and the counter-measures adopted. At present the system consists in 13 wire extensometers, 1 thermometer, 1 rain gauge and 3 cameras, in part connected through a wireless sensor network. Should a velocity threshold be exceeded by two or more sensors, the attention level would be entered, causing improved monitoring and surveillance. In case the behaviour of the landslide changes and, by using expert judgement and forecasting methods, an imminent failure is hinted, then an alarm is issued and the upper road is closed. The EWS has been designed by stressing the importance of redundancy, simplicity, communication and minimizing the probability of false alarms. Although site-specific, this system can be useful when facing similar situations, in particular because, differently to many other works that focus only on social or technological issues, this one gives importance also to geological and procedural considerations. Therefore some solutions can be widely applicable, even in different contexts.

Three-Dimensional Simulation of Avalanche-Generated Impulse Waves and Evaluation of Lake-Lowering Scenarios at Lake Palcacocha, Peru

NASA Astrophysics Data System (ADS)

Chisolm, R. E.; McKinney, D. C.

2014-12-01

Accelerated retreat of Andean glaciers in recent decades due to a warming climate has caused the emergence and growth of glacial lakes. As these lakes continue to grow, they pose an increasing risk of glacial lake outburst floods (GLOFs). GLOFs can be triggered by moraine failures or by avalanches, rockslides, or ice calving into glacial lakes. For many decades Lake Palcacocha in the Cordillera Blanca, Peru has threatened citizens living in the city of Huaraz which was devastated by a GLOF in 1941. A safety system for Lake Palcacocha was put in place in the 1970's to control the lake level, but the lake has since grown to the point where it is once again dangerous. Overhanging ice from the glaciers above and a relatively low freeboard make the lake vulnerable to avalanches and landslides. Lake Palcacocha is used as a case study to investigate the impact of an avalanche event on the lake dynamics. Three-dimensional lake modeling in the context of glacial hazards is not common, but 3D simulations can enhance our understanding of avalanche-generated impulse waves and their downstream impacts. In this work, a 3D hydrodynamic model is used to simulate the generation of an impulse wave from an avalanche falling into the lake, wave propagation, and overtopping of the terminal moraine. These results are used as inputs to a downstream model to predict the impact from a GLOF. As lowering the level of the lake is the most likely mitigation alternative, several scenarios are considered to evaluate the impact from avalanche events with a reduction in the lake level. The results of this work can be used to evaluate the effectiveness of the current lake management system and potential lake-lowering alternatives. Use of a robust 3D lake model enables more accurate predictions of peak flows during GLOF events and the time scales of these events so that mitigation strategies can be developed that reduce the risk to communities living downstream of hazardous lakes.

Large Deformation Analysis of a High Steep Slope Relating to the Laxiwa Reservoir, China

NASA Astrophysics Data System (ADS)

Lin, Peng; Liu, Xiaoli; Hu, Senying; Li, Pujian

2016-06-01

The unstable rock slope in the Laxiwa reservoir area of the Yellow River upstream, China, shows the signs of gravitational and water-impounding induced large deformations over an area of 1.15 × 105 m2. Slope movements have been measured daily at more than 560 observation points since 2009, when the reservoir was first impounded. At two of these points, an average daily movement of around 60-80 mm has ever been observed since the beginning of the impounding. Based on the observed deformations and the geology of the site, a fluid-solid coupling model was then adopted to investigate the existing rockslide activity to better understand the mechanism underlying the large deformations. The results from the field observation, kinematic analysis and numerical modeling indicate that the slope instability is dominated by the strong structurally controlled unstable rock mass. Based on an integrated overview of these analyses, a new toppling mode, i.e. the so-called `conjugate block' mode, is proposed to explain the large deformation mechanism of the slope. The conjugate block is formed by a `dumping block' and toppling blocks. The large deformation of the slope is dominated by (1) a toppling component and (2) a subsiding bilinear wedge induced by planar sliding along the deep-seated faults. Following a thorough numerical analysis, it is concluded that small collapses of rock blocks along the slope will be more frequent with the impounding process continuing and the water level fluctuating during the subsequent operation period. Based on a shear strength reduction method and field monitoring, four controlling faults are identified and the instability of the loose structure in the surface layer is analyzed and discussed. The factor of safety against the sliding failure along the deep seated fractures in the slope is 1.72, which reveals that (1) the collapse of the free-standing fractured blocks cannot be ruled out and the volume of the unstable blocks may be greater than 100,000 m3; (2) the collapse of the whole slope, i.e. with the volume being greater than 92 million m3, or a very large collapse involving several million m3, is considered to be of very low likelihood, unless there are extreme conditions, such as earthquakes and exceptionally heavy rain.

Long-term multi-hazard assessment for El Misti volcano (Peru)

NASA Astrophysics Data System (ADS)

Sandri, Laura; Thouret, Jean-Claude; Constantinescu, Robert; Biass, Sébastien; Tonini, Roberto

2014-02-01

We propose a long-term probabilistic multi-hazard assessment for El Misti Volcano, a composite cone located <20 km from Arequipa. The second largest Peruvian city is a rapidly expanding economic centre and is classified by UNESCO as World Heritage. We apply the Bayesian Event Tree code for Volcanic Hazard (BET_VH) to produce probabilistic hazard maps for the predominant volcanic phenomena that may affect c.900,000 people living around the volcano. The methodology accounts for the natural variability displayed by volcanoes in their eruptive behaviour, such as different types/sizes of eruptions and possible vent locations. For this purpose, we treat probabilistically several model runs for some of the main hazardous phenomena (lahars, pyroclastic density currents (PDCs), tephra fall and ballistic ejecta) and data from past eruptions at El Misti (tephra fall, PDCs and lahars) and at other volcanoes (PDCs). The hazard maps, although neglecting possible interactions among phenomena or cascade effects, have been produced with a homogeneous method and refer to a common time window of 1 year. The probability maps reveal that only the north and east suburbs of Arequipa are exposed to all volcanic threats except for ballistic ejecta, which are limited to the uninhabited but touristic summit cone. The probability for pyroclastic density currents reaching recently expanding urban areas and the city along ravines is around 0.05 %/year, similar to the probability obtained for roof-critical tephra loading during the rainy season. Lahars represent by far the most probable threat (around 10 %/year) because at least four radial drainage channels can convey them approximately 20 km away from the volcano across the entire city area in heavy rain episodes, even without eruption. The Río Chili Valley represents the major concern to city safety owing to the probable cascading effect of combined threats: PDCs and rockslides, dammed lake break-outs and subsequent lahars or floods. Although this study does not intend to replace the current El Misti hazard map, the quantitative results of this probabilistic multi-hazard assessment can be incorporated into a multi-risk analysis, to support decision makers in any future improvement of the current hazard evaluation, such as further land-use planning and possible emergency management.

Structural controls on the large landslides triggered by the 14 November 2016, MW 7.8 Earthquake, Kaikoura, New Zealand

NASA Astrophysics Data System (ADS)

Massey, Chris

2017-04-01

The Kaikoura earthquake generated tens of thousands of landslides over a total area of about 10,000 km2, with the majority concentrated in a smaller area of about 3,500 km2. A noteworthy aspect of this event is the large number of landslides that occurred on the steep coastal cliffs south of Ward and extending to Oaro, north of Christchurch, which led to the closure of state highway routes. Another noteworthy feature of this earthquake is the large number (more than 190) of valley blocking landslides it generated. This was partly due to the presence of steep and confined slopes in areas of strong ground shaking. The largest valley blocking landslide has an approximate volume of 12(±2) M m3 and the debris travelled about 2.7 km down slope forming a dam on the Hapuku River. Given the sparse population in the vicinity of the landslides, only a few homes were impacted and there were no recorded deaths due to landslides. However, the long-term stability of cracked slopes and landslide "dams" from future strong earthquakes and significant rain events are an ongoing concern to central and local government agencies responsible for rebuilding homes and infrastructure. A particular concern is the potential for debris floods to affect downstream residences and infrastructure should some of the landslide dams breach catastrophically. The mapped landslide distribution reflects the complexity of the earthquake rupture—at least 13 faults ruptured to the ground surface or sea floor. The majority of landslides occurred in two geological and geotechnically distinct materials: Neogene sedimentary rocks (sandstones, limestones and siltstones) where first-time and reactivated rock-slides were the dominant landslide type, and Torlesse "basement" rocks (greywacke sandstones and argillite) where first-time rock and debris avalanches dominated. The largest landslides triggered by the earthquake are located either on or adjacent to faults that ruptured to the ground surface and so they are distributed across a wide area, and most have slide surfaces that correspond to geological discontinuities. Initial results from our landslide investigations suggest: predictive models relying only on ground-shaking estimates may underestimate the number and size of the larger landslides that occurred, surface faults may provide a plane of weakness or hydrological discontinuity, and adversely oriented surface faults may be indicative of the location of future large landslides.

Rock-avalanche dynamics revealed by large-scale field mapping and seismic signals at a highly mobile avalanche in the West Salt Creek valley, western Colorado

USGS Publications Warehouse

Coe, Jeffrey A.; Baum, Rex L.; Allstadt, Kate E.; Kochevar, Bernard; Schmitt, Robert G.; Morgan, Matthew L.; White, Jonathan L.; Stratton, Benjamin T.; Hayashi, Timothy A.; Kean, Jason W.

2016-01-01

On 25 May 2014, a rain-on-snow–induced rock avalanche occurred in the West Salt Creek valley on the northern flank of Grand Mesa in western Colorado (United States). The avalanche mobilized from a preexisting rock slide in the Green River Formation and traveled 4.6 km down the confined valley, killing three people. The avalanche was rare for the contiguous United States because of its large size (54.5 Mm3) and high mobility (height/length = 0.14). To understand the avalanche failure sequence, mechanisms, and mobility, we conducted a forensic analysis using large-scale (1:1000) structural mapping and seismic data. We used high-resolution, unmanned aircraft system imagery as a base for field mapping, and analyzed seismic data from 22 broadband stations (distances < 656 km from the rock-slide source area) and one short-period network. We inverted broadband data to derive a time series of forces that the avalanche exerted on the earth and tracked these forces using curves in the avalanche path. Our results revealed that the rock avalanche was a cascade of landslide events, rather than a single massive failure. The sequence began with an early morning landslide/debris flow that started ∼10 h before the main avalanche. The main avalanche lasted ∼3.5 min and traveled at average velocities ranging from 15 to 36 m/s. For at least two hours after the avalanche ceased movement, a central, hummock-rich core continued to move slowly. Since 25 May 2014, numerous shallow landslides, rock slides, and rock falls have created new structures and modified avalanche topography. Mobility of the main avalanche and central core was likely enhanced by valley floor material that liquefied from undrained loading by the overriding avalanche. Although the base was likely at least partially liquefied, our mapping indicates that the overriding avalanche internally deformed predominantly by sliding along discrete shear surfaces in material that was nearly dry and had substantial frictional strength. These results indicate that the West Salt Creek avalanche, and probably other long-traveled avalanches, could be modeled as two layers: a thin, liquefied basal layer, and a thicker and stronger overriding layer.

Field, Laboratory and Imaging spectroscopic Analysis of Landslide, Debris Flow and Flood Hazards in Lacustrine, Aeolian and Alluvial Fan Deposits Surrounding the Salton Sea, Southern California

NASA Astrophysics Data System (ADS)

Hubbard, B. E.; Hooper, D. M.; Mars, J. C.

2015-12-01

High resolution satellite imagery, field spectral measurements using a portable ASD spectrometer, and 2013 hyperspectral AVIRIS imagery were used to evaluate the age of the Martinez Mountain Landslide (MML) near the Salton Sea, in order to determine the relative ages of adjacent alluvial fan surfaces and the potential for additional landslides, debris flows, and floods. The Salton Sea (SS) occupies a pluvial lake basin, with ancient shorelines ranging from 81 meters to 113 meters above the modern lake level. The highest shoreline overlaps the toe of the 0.24 - 0.38 km3 MML deposit derived from hydrothermally altered granites exposed near the summit of Martinez Mountain. The MML was originally believed to be of early Holocene age. However, AVIRIS mineral maps show abundant desert varnish on the top and toe of the landslide. Desert varnish can provide a means of relative dating of alluvial fan (AF) or landslide surfaces, as it accumulates at determinable rates over time. Based on the 1) highest levels of desert varnish accumulation mapped within the basin, 2) abundant evaporite playa minerals on top of the toe of the landslide, and 3) the highest shoreline of the ancestral lake overtopping the toe of the landslide with gastropod and bivalve shells, we conclude that the MML predates the oldest alluvial fan terraces and lake sediments exposed in the Coachella and Imperial valleys and must be older than early Holocene (i.e. Late Pleistocene?). Thus, the MML landslide has the potential to be used as a spectral endmember for desert varnish thickness and thus proxy for age discrimination of active AF washes versus desert pavements. Given the older age of the MML landslide and low water levels in the modern SS, the risk from future rockslides of this size and related seiches is rather low. However, catastrophic floods and debris flows do occur along the most active AF channels; and the aftermath of such flows can be identified spectrally by montmorillonite crusts forming in recently flooded channels, as well as coarse-grained hyper-concentrated flow deposits that leave sorted (dark) heavy mineral concentrate behind. These observations, as well as supporting spectroscopic and change detection studies, will allow us to evaluate such hazards in this and similar inter-montane pluvial basins around the world.

Natural Hazard Public Policy Implications of the May 12, 2008 M7.9 Wenchuan Earthquake, Sichuan, China

NASA Astrophysics Data System (ADS)

Cydzik, K.; Hamilton, D.; Stenner, H. D.; Cattarossi, A.; Shrestha, P. L.

2009-12-01

The May 12, 2008 M7.9 Wenchuan Earthquake in Sichuan Province, China killed almost 90,000 people and affected a population of over 45.5 million throughout western China. Shaking caused the destruction of five million buildings, many of them homes and schools, and damaged 21 million other structures, inflicting devastating impacts to communities. Landslides, a secondary effect of the shaking, caused much of the devastation. Debris flows buried schools and homes, rock falls crushed cars, and rockslides, landslides, and rock avalanches blocked streams and rivers creating massive, unstable landslide dams, which formed “quake lakes” upstream of the blockages. Impassable roads made emergency access slow and extremely difficult. Collapses of buildings and structures large and small took the lives of many. Damage to infrastructure impaired communication, cut off water supplies and electricity, and put authorities on high alert as the integrity of large engineered dams were reviewed. During our field reconnaissance three months after the disaster, evidence of the extent of the tragedy was undeniably apparent. Observing the damage throughout Sichuan reminded us that earthquakes in the United States and throughout the world routinely cause widespread damage and destruction to lives, property, and infrastructure. The focus of this poster is to present observations and findings based on our field reconnaissance regarding the scale of earthquake destruction with respect to slope failures, landslide dams, damage to infrastructure (e.g., schools, engineered dams, buildings, roads, rail lines, and water resources facilities), human habitation within the region, and the mitigation and response effort to this catastrophe. This is presented in the context of the policy measures that could be developed to reduce risks of similar catastrophes. The rapid response of the Chinese government and the mobilization of the Chinese People’s Liberation Army to help the communities affected by the earthquake have allowed survivors to begin rebuilding their lives. However, the long-term impact of the earthquake continues to make headlines. Post-earthquake landslides and debris flows initiated by storm events have continued to impart devastation on the region. Events such as the Wenchuan Earthquake provide unique opportunities for engineers, scientists, and policy makers to collaborate for purposes of exploring the details of natural hazards and developing sound policies to protect lives and property in the future.

Dynamics of the Wulong landslide revealed by broadband seismic records

NASA Astrophysics Data System (ADS)

Li, Zhengyuan; Huang, Xinghui; Xu, Qiang; Yu, Dan; Fan, Junyi; Qiao, Xuejun

2017-02-01

The catastrophic Wulong landslide occurred at 14:51 (Beijing time, UTC+8) on 5 June 2009, in Wulong Prefecture, Southwest China. This rockslide occurred in a complex topographic environment. Seismic signals generated by this event were recorded by the seismic network deployed in the surrounding area, and long-period signals were extracted from 8 broadband seismic stations within 250 km to obtain source time functions by inversion. The location of this event was simultaneously acquired using a stepwise refined grid search approach, with an error of 2.2 km. The estimated source time functions reveal that, according to the movement parameters, this landslide could be divided into three stages with different movement directions, velocities, and increasing inertial forces. The sliding mass moved northward, northeastward and northward in the three stages, with average velocities of 6.5, 20.3, and 13.8 m/s, respectively. The maximum movement velocity of the mass reached 35 m/s before the end of the second stage. The basal friction coefficients were relatively small in the first stage and gradually increasing; large in the second stage, accompanied by the largest variability; and oscillating and gradually decreasing to a stable value, in the third stage. Analysis shows that the movement characteristics of these three stages are consistent with the topography of the sliding zone, corresponding to the northward initiation, eastward sliding after being stopped by the west wall, and northward debris flowing after collision with the east slope of the Tiejianggou valley. The maximum movement velocity of the sliding mass results from the largest height difference of the west slope of the Tiejianggou valley. The basal friction coefficients of the three stages represent the thin weak layer in the source zone, the dramatically varying topography of the west slope of the Tiejianggou valley, and characteristics of the debris flow along the Tiejianggou valley. Based on the above results, it is recognized that the inverted source time functions are consistent with the topography of the sliding zone. Special geological and topographic conditions can have a focusing effect on landslides and are key factors in inducing the major disasters, which may follow from them. This landslide was of an unusual nature, and it will be worthwhile to pursue research into its dynamic characteristics more deeply.[Figure not available: see fulltext.

Geotechnical applications of LiDAR pertaining to geomechanical evaluation and hazard identification

NASA Astrophysics Data System (ADS)

Lato, Matthew J.

Natural hazards related to ground movement that directly affect the safety of motorists and highway infrastructure include, but are not limited to, rockfalls, rockslides, debris flows, and landslides. This thesis specifically deals with the evaluation of rockfall hazards through the evaluation of LiDAR data. Light Detection And Ranging (LiDAR) is an imaging technology that can be used to delineate and evaluate geomechanically-controlled hazards. LiDAR has been adopted to conduct hazard evaluations pertaining to rockfall, rock-avalanches, debris flows, and landslides. Characteristics of LiDAR surveying, such as rapid data acquisition rates, mobile data collection, and high data densities, pose problems to traditional CAD or GIS-based mapping methods. New analyses methods, including tools specifically oriented to geomechanical analyses, are needed. The research completed in this thesis supports development of new methods, including improved survey techniques, innovative software workflows, and processing algorithms to aid in the detection and evaluation of geomechanically controlled rockfall hazards. The scientific research conducted between the years of 2006-2010, as presented in this thesis, are divided into five chapters, each of which has been published by or is under review by an international journal. The five research foci are: (i) geomechanical feature extraction and analysis using LiDAR data in active mining environments; (ii) engineered monitoring of rockfall hazards along transportation corridors: using mobile terrestrial LiDAR; (iii) optimization of LiDAR scanning and processing for automated structural evaluation of discontinuities in rockmasses; (iv) location orientation bias when using static LiDAR data for geomechanical analysis; and (v) evaluating roadside rockmasses for rockfall hazards from LiDAR data: optimizing data collection and processing protocols. The research conducted pertaining to this thesis has direct and significant implications with respect to numerous engineering projects that are affected by geomechanical stability issues. The ability to efficiently and accurately map discontinuities, detect changes, and standardize roadside geomechanical stability analyses from remote locations will fundamentally change the state-of-practice of geotechnical investigation workflows and repeatable monitoring. This, in turn, will lead to earlier detection and definition of potential zones of instability, will allow for progressive monitoring and risk analysis, and will indicate the need for pro-active slope improvement and stabilization.

Assessment of the detectability of geo-hazards using Google Earth applied to the Three Parallel Rivers Area, Yunnan province of China

NASA Astrophysics Data System (ADS)

Voermans, Michiel; Mao, Zhun; Baartman, Jantiene EM; Stokes, Alexia

2017-04-01

Anthropogenic activities such as hydropower, mining and road construction in mountainous areas can induce and intensify mass wasting geo-hazards (e.g. landslides, gullies, rockslides). This represses local safety and socio-economic development, and endangers biodiversity at larger scale. Until today, data and knowledge to construct geo-hazard databases for further assessments are lacking. This applies in particular to countries with a recently emerged rapid economic growth, where there are no previous hazard documentations and where means to gain data from e.g. intensive fieldwork or VHR satellite imagery and DEM processing are lacking. Google Earth (GE, https://www.google.com/earth/) is a freely available and relatively simple virtual globe, map and geographical information program, which is potentially useful in detecting geo-hazards. This research aimed at (i) testing the capability of Google Earth to detect locations of geo-hazards and (ii) identifying factors affecting the diagnosing quality of the detection, including effects of geo-hazard dimensions, environs setting and professional background and effort of GE users. This was tested on nine geo-hazard sites following road segments in the Three Parallel Rivers Area in the Yunnan province of China, where geo-hazards are frequently occurring. Along each road site, the position and size of each geo-hazard was measured in situ. Next, independent diagnosers with varying professional experience (students, researchers, engineers etc.) were invited to detect geo-hazard occurrence along each of the eight sites via GE. Finally, the inventory and diagnostic data were compared to validate the objectives. Rates of detected geo-hazards from 30 diagnosers ranged from 10% to 48%. No strong correlations were found between the type and size of the geo-hazards and their detection rates. Also the years of expertise of the diagnosers proved not to make a difference, opposite to what may be expected. Meanwhile the amount of time spent by the diagnoser proved to be positively influencing the detectability. GE showed to be a useful tool in detecting mainly larger geo-hazards if diligently applied, and is therefore applicable to identify geo-hazard hotspots. The usability for further assessments such as sediment delivery estimations is questionable and further research should be carried out to give insight to its full potential.

Relating rock avalanche morphology to emplacement processes

NASA Astrophysics Data System (ADS)

Dufresne, Anja; Prager, Christoph; Bösmeier, Annette

2015-04-01

The morphology, structure and sedimentological characteristics of rock avalanche deposits reflect both internal emplacement processes and external influences, such as runout path characteristics. The latter is mainly predisposed by topography, substrate types, and hydrogeological conditions. Additionally, the geological setting at the source slope controls, e.g. the spatial distribution of accumulated lithologies and hence material property-related changes in morphology, or the maximum clast size and amount of fines of different lithological units. The Holocene Tschirgant rock avalanche (Tyrol, Austria) resulted from failure of an intensely deformed carbonate rock mass on the southeast face of a 2,370-m-high mountain ridge. The initially sliding rock mass rapidly fragmented as it moved towards the floor of the Inn River valley. Part of the 200-250 x 106 m3 (Patzelt 2012) rock avalanche debris collided with and moved around an opposing bedrock ridge and flowed into the Ötz valley, reaching up to 6.3 km from source. Where the Tschirgant rock avalanche spread freely it formed longitudinal ridges aligned along motion direction as well as smaller hummocks. Encountering high topography, it left runup ridges, fallback patterns (i.e. secondary collapse), and compressional morphology (successively elevated, transverse ridges). Further evidence for the mechanical landslide behaviour is given by large volumes of mobilized valley-fill sediments (polymict gravels and sands). These sediments indicate both shearing and compressional faulting within the rock avalanche mass (forming their own morphological units through, e.g. in situ bulldozing or as distinctly different hummocky terrain), but also indicate extension of the spreading landslide mass (i.e. intercalated/injected gravels encountered mainly in morphological depressions between hummocks). Further influences on its morphology are given by the different lithological units. E.g. the transition from massive dolomite/limestone sequences to weaker siliciclastic and evaporitic beds (sand-/siltstones, rauhwacken) can be pinpointed on LiDAR shaded relief images of the rock avalanche deposit. Hence, several morphological signatures are clearly related to differences in mechanical behaviour of the involved lithologies, whereas others reflect particular emplacement modes of the same rock unit: e.g. rockslide motion versus rock avalanche spreading. Reference Patzelt G. 2012. The rock avalanches of Tschirgant and Haiming (Upper Inn Valley, Tyrol, Austria), comment on the map supply. (German language only). Jahrbuch der Geologischen Bundesanstalt 152(1-4): 13-24.

Detection of early stage large scale landslides in forested areas by 2 m LiDAR DEM analysis. The example of Portainé (Central Pyrenees)

NASA Astrophysics Data System (ADS)

Guinau, Marta; Ortuño, Maria; Calvet, Jaume; Furdada, Glòria; Bordonau, Jaume; Ruiz, Antonio; Camafort, Miquel

2016-04-01

Mass movements have been classically detected by field inspection and air-photo interpretation. However, airborne LiDAR has significant potential for generating high-resolution digital terrain models, which provide considerable advantages over conventional surveying techniques. In this work, we present the identification and characterization of six slope failures previously undetected in the Orri massif, at the core of the Pyrenean range. The landforms had not been previously detected and were identified by the analysis of high resolution 2 m LiDAR derived bared earth topography. Most of the scarps within these failures are not detectable by photo interpretation or the analysis of 5 m resolution topographic maps owing to their small heights (ranging between 0.5 and 2 m) and their location within forest areas. 2D and 3D visualization of hillshade maps with different sun azimuths, allowed to obtain the overall picture of the scarp assemblage and to analyze the geometry and location of the scarps with respect to the slope and the structural fabric. Near 120 scarps were mapped and interpreted as part of slow gravitational deformation, incipient slow flow affecting a colluvium, rotational rock-sliding and slope creep. Landforms interpreted as incipient slow flow affecting a colluvium have headscarps with horse-shoe shape and superficial (< 20 m) basal planes whereas sackung features have open headscarps and basal planes that are likely located at 200-250 m maximum depth. Other distinctive features are toppling or extensive scarps, double ridges and rock rotational landslides. The sharpness of the scarps suggests their recent activity, which may pose a potential risk for the Port-Ainé sky resort users and facilities. These results suggest that the systematic analysis of 2 m LIDAR derived bared earth topography would significantly help in the rapid detection and mapping of early stage slope deformations in high mountain areas, which could contribute to 1) a better understanding of the spatial controlling factors and 2) obtaining rapid diagnosis of the state of the slopes, critical for the proper forecast of future catastrophic failures. This presentation is supported by the Spanish Ministry of Science and Innovation project CHARMA: CHAracterization and ContRol of MAss Movements. A Challenge for Geohazard Mitigation (CGL2013-40828-R).

Risk-based consequences of extreme natural hazard processes in mountain regions - Multi-hazard analysis in Tyrol (Austria)

NASA Astrophysics Data System (ADS)

Huttenlau, Matthias; Stötter, Johann

2010-05-01

Reinsurance companies are stating a high increase in natural hazard related losses, both insured and economic losses, within the last decades on a global scale. This ongoing trend can be described as a product of the dynamic in the natural and in the anthroposphere. To analyze the potential impact of natural hazard process to a certain insurance portfolio or to the society in general, reinsurance companies or risk management consultants have developed loss models. However, those models are generally not fitting the scale dependent demand on regional scales like it is appropriate (i) for analyses on the scale of a specific province or (ii) for portfolio analyses of regional insurance companies. Moreover, the scientific basis of most of the models is not transparent documented and therefore scientific evaluations concerning the methodology concepts are not possible (black box). This is contrary to the scientific principles of transparency and traceability. Especially in mountain regions like the European Alps with their inherent (i) specific characteristic on small scales, (ii) the relative high process dynamics in general, (iii) the occurrence of gravitative mass movements which are related to high relief energy and thus only exists in mountain regions, (iv) the small proportion of the area of permanent settlement on the overall area, (v) the high value concentration in the valley floors, (vi) the exposition of important infrastructures and lifelines, and others, analyses must consider these circumstances adequately. Therefore, risk-based analyses are methodically estimating the potential consequences of hazard process on the built environment standardized with the risk components (i) hazard, (ii) elements at risk, and (iii) vulnerability. However, most research and progress have been made in the field of hazard analyses, whereas the other both components are not developed accordingly. Since these three general components are influencing factors without any weighting within the risk concept, this has sufficient implications on the results of risk analyses. Thus, an equal and scale appropriated balance of those risk components is a fundamental key factor for effective natural hazard risk analyses. The results of such analyses inform especially decision makers in the insurance industry, the administration, and politicians on potential consequences and are the basis for appropriate risk management strategies. Thereby, results (i) on an annual or probabilistic risk comprehension have to be distinguished from (ii) scenario-based analyses. The first analyses are based on statistics of periodically or episodically occurring events whereas the latter approach is especially applied for extreme, non-linear, stochastic events. Focusing on the needs especially of insurance companies, the first approaches are appropriate for premium pricing and reinsurance strategies with an annual perspective, whereas the latter is focusing on events with extreme loss burdens under worst-case criteria to guarantee accordant reinsurance coverage. Moreover, the demand of adequate loss model approaches and methods is strengthened by the risk-based requirements of the upcoming capital requirement directive Solvency II. The present study estimates the potential elements at risk, their corresponding damage potentials and the Probable Maximum Losses (PMLs) of extreme natural hazards events in Tyrol (Austria) and considers adequatly the scale dependency and balanced application of the introduced risk components. Beside the introduced analysis an additionally portfolio analysis of a regional insurance company was executed. The geocoded insurance contracts of this portfolio analysis were the basis to estimate spatial, socio-economical and functional differentiated mean insurance values for the different risk categories of (i) buildings, (ii) contents or inventory, (iii) vehicles, and (iv) persons in the study area. The estimated mean insurance values were incorporated with additional GIS and statistic data to a comprehensive property-by-property geodatabase of the existing elements and values. This stock of elements and values geodatabase is furthermore the consistent basis for all natural hazard analyses and enables the comparison of the results. The study follows the general accepted moduls (i) hazard analysis, (ii) exposition analysis, and (iii) consequence analysis, whereas the exposition analysis estimates the elements at risk with their corresponding damage potentials and the consequence analysis estimates the PMLs. This multi-hazard analysis focuses on process types with a high to extreme potential of negative consequences on a regional scale. In this context, (i) floodings, (ii) rockslides with the potential of corresponding consequence effects (backwater ponding and outburst flood), (iii) earthquakes, (iv) hail events, and (v) winter storms were considered as hazard processes. Based on general hazard analyses (hazard maps) concrete scenarios and their spatial affectedness were determined. For the different hazard processes, different vulnerability approaches were considered to demonstrate their sensitivity and implication on the results. Thus, no absolute values of losses but probable loss ranges were estimated. It can be shown, that the most serious amount of losses would arise from extreme earthquake events with loss burdens up to more than € 7 bn. solely on buildings and inventory. Possible extreme flood events could lead to losses between € 2 and 2.5 bn., whereas a severe hail swath which affects the central Inn valley could result in losses of ca. € 455 mill. (thereof € 285 mill. on vehicles). The potential most serious rockslide with additional consequence effects would result in losses up to ca. € 185 mill. and extreme winter storms can induce losses between € 100 mill. and 150 mill..

The Tjellefonna fault system of Western Norway: Linking late-Caledonian extension, post-Caledonian normal faulting, and Tertiary rock column uplift with the landslide-generated tsunami event of 1756

NASA Astrophysics Data System (ADS)

Redfield, T. F.; Osmundsen, P. T.

2009-09-01

On February 22, 1756, approximately 15.7 million cubic meters of bedrock were catastrophically released as a giant rockslide into the Langfjorden. Subsequently, three ˜ 40 meter high tsunami waves overwhelmed the village of Tjelle and several other local communities. Inherited structures had isolated a compartment in the hanging wall damage zone of the fjord-dwelling Tjellefonna fault. Because the region is seismically active in oblique-normal mode, and in accordance with scant historical sources, we speculate that an earthquake on a nearby fault may have caused the already-weakened Tjelle hillside to fail. From interpretation of structural, geomorphic, and thermo-chronological data we suggest that today's escarpment topography of Møre og Trøndelag is controlled to a first order by post-rift reactivation of faults parallel to the Mesozoic passive margin. In turn, a number of these faults reactivated Late Caledonian or early post-Caledonian fabrics. Normal-sense reactivation of inherited structures along much of coastal Norway suggests that a structural link exists between the processes that destroy today's mountains and those that created them. The Paleozoic Møre-Trøndelag Fault Complex was reactivated as a normal fault during the Mesozoic and, probably, throughout the Cenozoic until the present day. Its NE-SW trending strands crop out between the coast and the base of a c. 1.7 km high NW-facing topographic 'Great Escarpment.' Well-preserved kinematic indicators and multiple generations of fault products are exposed along the Tjellefonna fault, a well-defined structural and topographic lineament parallel to both the Langfjorden and the Great Escarpment. The slope instability that was formerly present at Tjelle, and additional instabilities currently present throughout the region, may be viewed as the direct product of past and ongoing development of tectonic topography in Møre og Trøndelag county. In the Langfjorden region in particular, structural geometry suggests additional unreleased rock compartments may be isolated and under normal fault control. Although post-glacial rebound and topographically-derived horizontal spreading stresses might in part help drive present-day oblique normal seismicity, the normal-fault-controlled escarpments of Norway were at least partly erected in pre-glacial times. Cretaceous to Early Tertiary post-rift subsidence was interrupted by normal faulting at the innermost portion of the passive margin, imposing a strong tectonic empreinte on the developing landscape.

Characterization of large instabilities displacements using Ground-Based InSAR

NASA Astrophysics Data System (ADS)

Rouyet, L.; Kristensen, L.; Derron, M.-H.; Michoud, C.; Blikra, L. H.; Jaboyedoff, M.

2012-04-01

A master thesis in progress at the Lausanne University (IGAR) in cooperation with the Åknes/Tafjord Early Warning Centre in Norway aims to characterize various instabilities displacements using Ground-Based Interferometric Synthetic Aperture Radar system (GB-InSAR). The main goal is to evaluate the potential of GB-InSAR to determine displacement velocities and mechanical behaviours of several large rock instabilities in Norway. GB-InSAR data are processed and interpreted for three case studies. The first test site is the unstable complex area of Mannen located in the Romsdalen valley (Møre og Romsdal county), threatening infrastructures and potentially able to cause a debacle event downstream. Its total volume is estimated to 15-25 mill m3. Mannen instability is monitored permanently with GB-InSAR since February 2010 and shows displacements towards the radar up to -8 mm per month during the most sensitive period. Børa area located on the southwest side of Mannen instability shows also some signs of activity. It monitored temporarily between August and October 2011 and could help to understand the behaviour of Mannen site. The second, Indre Nordnes rockslide in Lyngenfjord (Troms county), is directly located above an important fjord in North Norway causing a significant risk of tsunami. The volume is estimated to be around 10-15 mill m3. The site was monitored temporarily between June and August 2011. The data show displacements towards the radar up to -12 mm in 2 weeks. The third case concerns rock falls along the road between Oppdølsstranda and Sunndalsøra (Møre og Romsdal county). Even if the volume of rock is less important than the first two cases, rock falls are an important problem for the road 70 underneath. Several campaigns are done between beginning of 2010 and end of 2011. In June 2011 an important rock fall occurs in an area where significant movements were previously detected by GB-InSAR. In order to understand the behaviour of these instabilities and compare the contributions of different techniques, data from other monitoring data such as GPS, extensometers, crackmeters, tiltmeters, laser reflectors and LiDAR are integrated in the analysis. This integration of data results in the production of a mechanical model of the instabilities. These data are also used to improve the knowledge about the method (parameters setting, processing, accuracy control), its limitations and characteristics depending on different contexts of studies. The problems such as atmospheric effects, loss of coherence between acquisitions and fringe interpretations are explored in order to improve the quality of results.

Using Landslide Failure Forecast Models in Near Real Time: the Mt. de La Saxe case-study

NASA Astrophysics Data System (ADS)

Manconi, Andrea; Giordan, Daniele

2014-05-01

Forecasting the occurrence of landslide phenomena in space and time is a major scientific challenge. The approaches used to forecast landslides mainly depend on the spatial scale analyzed (regional vs. local), the temporal range of forecast (long- vs. short-term), as well as the triggering factor and the landslide typology considered. By focusing on short-term forecast methods for large, deep seated slope instabilities, the potential time of failure (ToF) can be estimated by studying the evolution of the landslide deformation over time (i.e., strain rate) provided that, under constant stress conditions, landslide materials follow creep mechanism before reaching rupture. In the last decades, different procedures have been proposed to estimate ToF by considering simplified empirical and/or graphical methods applied to time series of deformation data. Fukuzono, 1985 proposed a failure forecast method based on the experience performed during large scale laboratory experiments, which were aimed at observing the kinematic evolution of a landslide induced by rain. This approach, known also as the inverse-velocity method, considers the evolution over time of the inverse value of the surface velocity (v) as an indicator of the ToF, by assuming that failure approaches while 1/v tends to zero. Here we present an innovative method to aimed at achieving failure forecast of landslide phenomena by considering near-real-time monitoring data. Starting from the inverse velocity theory, we analyze landslide surface displacements on different temporal windows, and then apply straightforward statistical methods to obtain confidence intervals on the time of failure. Our results can be relevant to support the management of early warning systems during landslide emergency conditions, also when the predefined displacement and/or velocity thresholds are exceeded. In addition, our statistical approach for the definition of confidence interval and forecast reliability can be applied also to different failure forecast methods. We applied for the first time the herein presented approach in near real time during the emergency scenario relevant to the reactivation of the La Saxe rockslide, a large mass wasting menacing the population of Courmayeur, northern Italy, and the important European route E25. We show how the application of simplified but robust forecast models can be a convenient method to manage and support early warning systems during critical situations. References: Fukuzono T. (1985), A New Method for Predicting the Failure Time of a Slope, Proc. IVth International Conference and Field Workshop on Landslides, Tokyo.

Active and passive seismic methods for characterization and monitoring of unstable rock masses: field surveys, laboratory tests and modeling.

NASA Astrophysics Data System (ADS)

Colombero, Chiara; Baillet, Laurent; Comina, Cesare; Jongmans, Denis; Vinciguerra, Sergio

2016-04-01

Appropriate characterization and monitoring of potentially unstable rock masses may provide a better knowledge of the active processes and help to forecast the evolution to failure. Among the available geophysical methods, active seismic surveys are often suitable to infer the internal structure and the fracturing conditions of the unstable body. For monitoring purposes, although remote-sensing techniques and in-situ geotechnical measurements are successfully tested on landslides, they may not be suitable to early forecast sudden rapid rockslides. Passive seismic monitoring can help for this purpose. Detection, classification and localization of microseismic events within the prone-to-fall rock mass can provide information about the incipient failure of internal rock bridges. Acceleration to failure can be detected from an increasing microseismic event rate. The latter can be compared with meteorological data to understand the external factors controlling stability. On the other hand, seismic noise recorded on prone-to-fall rock slopes shows that the temporal variations in spectral content and correlation of ambient vibrations can be related to both reversible and irreversible changes within the rock mass. We present the results of the active and passive seismic data acquired at the potentially unstable granitic cliff of Madonna del Sasso (NW Italy). Down-hole tests, surface refraction and cross-hole tomography were carried out for the characterization of the fracturing state of the site. Field surveys were implemented with laboratory determination of physico-mechanical properties on rock samples and measurements of the ultrasonic pulse velocity. This multi-scale approach led to a lithological interpretation of the seismic velocity field obtained at the site and to a systematic correlation of the measured velocities with physical properties (density and porosity) and macroscopic features of the granitic cliff (fracturing, weathering and anisotropy). Continuous passive seismic monitoring at the site, from October 2013 to present, systematically highlighted clear energy peaks in the spectral content of seismic noise on the unstable sector, interpreted as resonant frequencies of the investigated volume. Both spectral analysis and cross-correlation of seismic noise showed seasonal reversible variation trends related to air temperature fluctuations. No irreversible changes, resulting from serious damage processes within the rock mass, were detected so far. Modal analysis and geomechanical modeling of the unstable cliff are currently under investigation to better understand the vibration modes that could explain the measured amplitude and orientation of ground motion at the first resonant frequencies. Classification and location of microseismic events still remains the most challenging task, due to the complex structural and morphological setting of the site.

ALS-based hummock size-distance relationship assessment of Mt Shasta debris avalanche deposit, Northern California, USA

NASA Astrophysics Data System (ADS)

Tortini, Riccardo; Carn, Simon; van Wyk de Vries, Benjamin

2015-04-01

The failure of destabilized volcano flanks is a likely occurrence during the lifetime of a stratovolcano, generating large debris avalanches and drastically changing landforms around volcanoes. The significant hazards associated with these events in the Cascade range were demonstrated, for example, by the collapse of Mt St Helens (WA), which triggered its devastating explosive eruption in 1980. The rapid modification of the landforms due to these events makes it difficult to estimate the magnitude of prehistoric avalanches. However, the widespread preservation of hummocks along the course of rockslide-debris avalanches is highly significant for understanding the physical characteristics of these landslides. Mt Shasta is a 4,317 m high, snow-capped, steep-sloped stratovolcano located in Northern California. The current edifice began forming on the remnants of an ancestral Mt Shasta that collapsed ~300-380k years ago producing one of the largest debris avalanches known on Earth. The debris avalanche deposit (DAD) covers a surface of ~450 km2 across the Shasta valley, with an estimated volume of ~26 km3. We analyze ALS data on hummocks from the prehistoric Shasta valley DAD in northern California (USA) to derive the relationship between hummock size and distance from landslide source, and interpret the geomorphic significance of the intercept and slope coefficients of the observed functional relationships. Given the limited extent of the ALS survey (i.e. 40 km2), the high-resolution dataset is used for validation of the morphological parameters extracted from freely available, broader coverage DTMs such as the National Elevation Dataset (NED). The ALS dataset also permits the identification of subtle topographic features not apparent in the field or in coarser resolution datasets, including a previously unmapped fault, of crucial importance for both seismic and volcanic hazard assessment in volcanic areas. We present evidence from the Shasta DAD of neotectonic deformation along a north south tending fault and a comparison with the NED-derived DTM. This work aims to improve our understanding of the Shasta DAD morphology and dynamics, and provide insight into the cause and timing of events as well as the mode of emplacement of the DAD. The Cascade range includes numerous large extinct, dormant or active stratovolcanoes. Size-distance relationships will enable us to estimate the volume of the collapsed mass and the travel distance of the avalanche, and the knowledge of the link between basement structures and the Shasta DAD will elucidate the causes of edifice instability and may be used to target priority areas for volcanic hazard mapping.

A time series deformation estimation in the NW Himalayas using SBAS InSAR technique

NASA Astrophysics Data System (ADS)

Kumar, V.; Venkataraman, G.

2012-12-01

A time series land deformation studies in north western Himalayan region has been presented in this study. Synthetic aperture radar (SAR) interferometry (InSAR) is an important tool for measuring the land displacement caused by different geological processes [1]. Frequent spatial and temporal decorrelation in the Himalayan region is a strong impediment in precise deformation estimation using conventional interferometric SAR approach. In such cases, advanced DInSAR approaches PSInSAR as well as Small base line subset (SBAS) can be used to estimate earth surface deformation. The SBAS technique [2] is a DInSAR approach which uses a twelve or more number of repeat SAR acquisitions in different combinations of a properly chosen data (subsets) for generation of DInSAR interferograms using two pass interferometric approach. Finally it leads to the generation of mean deformation velocity maps and displacement time series. Herein, SBAS algorithm has been used for time series deformation estimation in the NW Himalayan region. ENVISAT ASAR IS2 swath data from 2003 to 2008 have been used for quantifying slow deformation. Himalayan region is a very active tectonic belt and active orogeny play a significant role in land deformation process [3]. Geomorphology in the region is unique and reacts to the climate change adversely bringing with land slides and subsidence. Settlements on the hill slopes are prone to land slides, landslips, rockslides and soil creep. These hazardous features have hampered the over all progress of the region as they obstruct the roads and flow of traffic, break communication, block flowing water in stream and create temporary reservoirs and also bring down lot of soil cover and thus add enormous silt and gravel to the streams. It has been observed that average deformation varies from -30.0 mm/year to 10 mm/year in the NW Himalayan region . References [1] Massonnet, D., Feigl, K.L.,Rossi, M. and Adragna, F. (1994) Radar interferometry mapping of deformation in the year after the Landers earthquake. Nature 1994, 369, 227-230. [2] Berardino, P., Fornaro, G., Lanari, R., Sansosti, E. (2002). A new algorithm for surface deformation Monitoring based on Small Baseline Differential SAR Interferograms. IEEE Transactions on Geoscience and Remote Sensing, 40 (11), 2375-2383. [3] GEOLOGICAL SURVEY OF INDIA (GSI), (1999) Inventory of the Himalayan glaciers. Special publication, vol. 34, pp. 165-168. [4] Chen, C.W., and Zebker, H. A., (2000). Network approaches to two-dimensional phase unwrapping: intractability and two new algorithms. Journal of the Optical Society of America, A, 17, 401-414.

Database on unstable rock slopes in Norway

NASA Astrophysics Data System (ADS)

Oppikofer, Thierry; Nordahl, Bo; Bunkholt, Halvor; Nicolaisen, Magnus; Hermanns, Reginald L.; Böhme, Martina; Yugsi Molina, Freddy X.

2014-05-01

Several large rockslides have occurred in historic times in Norway causing many casualties. Most of these casualties are due to displacement waves triggered by a rock avalanche and affecting coast lines of entire lakes and fjords. The Geological Survey of Norway performs systematic mapping of unstable rock slopes in Norway and has detected up to now more than 230 unstable slopes with significant postglacial deformation. This systematic mapping aims to detect future rock avalanches before they occur. The registered unstable rock slopes are stored in a database on unstable rock slopes developed and maintained by the Geological Survey of Norway. The main aims of this database are (1) to serve as a national archive for unstable rock slopes in Norway; (2) to serve for data collection and storage during field mapping; (3) to provide decision-makers with hazard zones and other necessary information on unstable rock slopes for land-use planning and mitigation; and (4) to inform the public through an online map service. The database is organized hierarchically with a main point for each unstable rock slope to which several feature classes and tables are linked. This main point feature class includes several general attributes of the unstable rock slopes, such as site name, general and geological descriptions, executed works, recommendations, technical parameters (volume, lithology, mechanism and others), displacement rates, possible consequences, hazard and risk classification and so on. Feature classes and tables linked to the main feature class include the run-out area, the area effected by secondary effects, the hazard and risk classification, subareas and scenarios of an unstable rock slope, field observation points, displacement measurement stations, URL links for further documentation and references. The database on unstable rock slopes in Norway will be publicly consultable through the online map service on www.skrednett.no in 2014. Only publicly relevant parts of the database will be shown in the online map service (e.g. processed results of displacement measurements), while more detailed data will not (e.g. raw data of displacement measurements). Factsheets with key information on unstable rock slopes can be automatically generated and downloaded for each site, a municipality, a county or the entire country. Selected data will also be downloadable free of charge. The present database on unstable rock slopes in Norway will further evolve in the coming years as the systematic mapping conducted by the Geological Survey of Norway progresses and as available techniques and tools evolve.

Satellite Monitoring and Characterization of the 2010 Rockslide-Dammed Lake Gojal, North Pakistan

NASA Astrophysics Data System (ADS)

Leonard, G. J.; Kargel, J. S.; Crippen, R. E.; Evans, S. G.; Delaney, K. B.; Schneider, J. F.

2010-12-01

On January 4, 2010, a landslide blocked the Hunza River at Attabad, northern Pakistan (36.308°N, 74.820°E). The landslide destroyed the village of Attabad killing 19 people, and formed a dam approximately 1200m long, 350 meters wide, and 125 meters high. The flow of the Hunza river was blocked for 144 days, forming Lake Gojal. In addition to inundating several villages and submerging 22 km of the regionally critical Karakoram Highway, >25,000 people have been displaced or remain cut off from overland connection with the rest of the country. Lake overtopping began on May 29 via a 15m deep spillway excavated through the saddle of the dam. Remarkably, the slowly eroding natural structure remains largely intact and currently represents a new geologic feature, although a threat remains from possible catastrophic outburst flooding. We have monitored growth of the lake with multi-temporal satellite imagery collected from ASTER (Advanced Spaceborne Thermal and Reflection Radiometer) and ALI (Advanced Land Imager) sensors. We applied NASA’s ASTER Global Digital Elevation Model (GDEM) and SRTM-3 digital terrain data, along with field data obtained onsite by Schneider, and by Pakistan’s NDMA to derive volumes of the growing lake. Lake size peaked during mid-summer when it was ~22 km long, 12 km2, 119m deep, and contained 540 to 620 Mm3 water (SRTM-3 and GDEM +5m global correction estimates respectively). Our estimates indicated lake volumes three to four times higher than media quotes, and before spillover, were used to improve predictions of possible flood discharge and disaster management planning. Estimates of valley inflow based on a 31-year hydrographic history (Archer, D., 2003, Jour. Hydrology 274, 198-210) are consistent with our volume infilling estimates. As early as April 14 our volume assessments, coupled with hydrographic and seepage data were used to project a spillover date range of May 28-June 2, bracketing the actual overflow date. Additionally, we have applied vegetation indices (NDVI), landcover classifications, and image differencing change detection techniques to obtain reconnaissance level characterizations of lake-flood affected areas, including flooding of agricultural lands. Our successful prediction of lake growth and initial estimates of affected lands highlights the effectiveness of GIS methods applied to modern satellite datasets, and indicates the importance of monitoring natural hazard events with remote sensing, which can provide rapid assessments and augment onsite observations for disaster management support.

On the rapid and efficient divulgation of monitoring results in landslide emergency scenarios

NASA Astrophysics Data System (ADS)

Giordan, Daniele; Allasia, Paolo; Manconi, Andrea; Bertolo, Davide

2014-05-01

In last decades, the availability of several technological systems to monitor different physical parameters that can be used to control a landslide evolution recorded an exponential growth. In particular, surficial and deep-seated displacements of an instable area, as well as meteorological or hydrological parameters can be nowadays acquired with high spatial and temporal resolutions. As a consequence, the application of complex monitoring systems produces large amounts of data. While this can be considered an important progress in the field of landslide monitoring applications, the availability of large volumes of high resolution and multiparametric information implies important challenges. In this context, two main criticalities are: i) the integrated management of dataset produced by different monitoring systems and ii) the correct divulgation of monitoring results. In this work, we present the results of a real case-study relevant to a complex emergency scenario, i.e. the Mont de La Saxe landslide, a large rockslide (with an estimated volume or more than 8 million of cubic meters) that threatens La Palud and Entrèves hamlets in the Courmayeur municipality (Aosta Valley, Italy). We developed a web-based system based on the ADVICE algorithm (Allasia et al., 2013) in order to manage several data sources. The system collects, analyzes and publishes the results obtained by monitoring instrumentations in near-real-time at each new measurement cycle. Moreover, by collecting all the data in an unique web-based platform reduces the problems of compatibility amongst different monitoring systems, which usually rely on customized software for the data processing, delaying the comparative analysis comparison amongst different data sources. This is indeed a crucial task for decision makers, in particular during the emergency phases. In addition, by using the developed web-based platform we aimed at coping with another important task, often not considered and/or underestimated, relevant to the landslide monitoring results, i.e. the divulgation. Starting from the analysis of different landslide scenarios, we identified and classified people belonging to emergency management teams into several categories according to their role, the level of knowledge of landslides, and/or of monitoring systems. Our aim is to define standards to share the monitoring results, in order to disseminate the information about the recent evolution of the landslide, as well as the level of criticality, within all the people involved (scientists, technicians, civil protection operators, decision makers, politicians, press, population). This task is particularly critical during the emergency phases, when a correct understanding of the situation is (in particular for the population) the first step for a successful emergency management. References: Allasia, P.; Manconi, A.; Giordan, D.; Baldo, M.; Lollino, G. ADVICE: A New Approach for Near-Real-Time Monitoring of Surface Displacements in Landslide Hazard Scenarios. Sensors 2013, 13, 8285-8302.

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

NASA Astrophysics Data System (ADS)

King, Lorenz; Duishonakunov, Murataly; Imbery, Stephan

2014-05-01

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

Pyroclastic flow generated by crater-wall collapse and outpouring of the lava pool of Arenal Volcano, Costa Rica

NASA Astrophysics Data System (ADS)

Alvarado, Guillermo E.; Soto, Gerardo J.

2002-01-01

The pyroclastic flow that issued from the Arenal summit crater on 28 August 1993 came from the collapse of the crater wall of the cone and the drainage of a lava pool. The 3-km-long pyroclastic flow, 2.2±0.8×106 m3 in volume, was confined to narrow valleys (30-100 m wide). The thickness of the pyroclastic deposit ranged from 1 to 10 m, and its temperature was about 400 °C, although single bombs were up to 1,000 °C. The deposit is clast-supported, has a bimodal grain size distribution, and consists of an intimate mixture of finely pulverized rock ash, lapilli, small blocks, and cauliflower bread-crusted bombs, in which are set meter-size lava fragments and juvenile and non-juvenile angular blocks, and bombs up to 7 m in diameter. Large faceted blocks make up 50% of the total volume of the deposit. The cauliflower bombs have deep and intricate bread-crust texture and post-depositional vesiculation. It is proposed that the juvenile material was produced entirely from a lava pool, whereas faceted non-juvenile blocks come from the crater-wall collapse. The concentration and maximum diameter of cauliflower bread-crusted bombs increases significantly from the base (rockslide + pyroclastic flow) to the top (the pyroclastic flow) of the deposit. An ash cloud deposited accretionary lapilli in the proximal region (outside of the pyroclastic flow deposit), and very fine ash fell in the distal region (between 5 and 30 km). The accretionary lapilli deposit is derived from the fine, elutriated products of the flow as it moved. A turbulent overriding surge blew down the surrounding shrubbery in the flow direction. The pyroclastic flow from August 1993, similar to the flows of June 1975, May 1998, August 2000, and March 2001, slid and rolled rather than being buoyed up by gas. They grooved, scratched, and polished the surfaces over which they swept, similar to a Merapi-type pyroclastic flow. However, the mechanism of the outpouring of a lava pool and the resulting flows composed of high- to moderate-vesiculated, cauliflower bread-crusted bombs and juvenile blocks have not been described before. High-frequency earthquake swarms, followed by an increase in low-frequency volcanic events, preceded the 1975, 1993, and 2000 eruptions 2-4 months before. These pyroclastic flow events, therefore, may be triggered by internal expansion of the unstable cone in the upper part because of a slight change in the pressure of the magma column (gas content and/or effusive rate). This phenomenon has important short-term, volcanic hazard implications for touristic development of some parts on the flanks of the volcano.

GIS and Multi-criteria evaluation (MCE) for landform geodiversity assessment

NASA Astrophysics Data System (ADS)

Najwer, Alicja; Reynard, Emmanuel; Zwoliński, Zbigniew

2014-05-01

In geomorphology, at the contemporary stage of methodology and methodological development, it is very significant to undertake new research problems, from theoretical and application point of view. As an example of applying geoconservation results in landscape studies and environmental conservation one can refer to the problem of the landform geodiversity. The concept of geodiversity was created relatively recently and, therefore, little progress has been made in its objective assessment and mapping. In order to ensure clarity and coherency, it is recommended that the evaluation process to be rigorous. Multi-criteria evaluation meets these criteria well. The main objective of this presentation is to demonstrate a new methodology for the assessment of the selected natural environment components in response to the definition of geodiversity, as well as visualization of the landforms geodiversity, using the opportunities offered by the geoinformation environment. The study area consists of two peculiar alpine valleys: Illgraben and Derborence, located in the Swiss Alps. Apart from glacial and fluvial landforms, the morphology of these two sites is largely due to the extreme phenomena(rockslides, torrential processes). Both valleys are recognized as geosites of national importance. The basis of the assessment is the selection of the geographical environment features. Firstly, six factor maps were prepared for each area: the landform energy, the landform fragmentation, the contemporary landform preservation, geological settings and hydrographic elements (lakes and streams). Input maps were then standardized and resulted from map algebra operations carried out by multi-criteria evaluation (MCE) with GIS-based Weighted Sum technique. Weights for particular classes were calculated using pair-comparison matrixes method. The final stage of deriving landform geodiversity maps was the reclassification procedure with the use of natural breaks method. The final maps of landform geodiversity were generated with the use of the same methodological algorithm and multiplication of each factor map by its given weight with consistency ratio = 0.07. However, the results that were obtained were radically different. The map of geodiversity for Derborence is characterized by much more significant fragmentation. Areas of low geodiveristy constitute a greater contribution. In the Illgraben site, there is a significant contribution of high and very high geodiversity classes. The obtained maps were reviewed during the field exploration with positive results, which gives a basis to conclude that the methodology used is correct and can be applied for other similar areas. Therefore, it is very important to develop an objective methodology that can be implemented for areas at the local and regional scale, but also giving satisfactory results for areas with a landscape different from the alpine one. The maps of landform geodiversity may be used for environment conservation management, preservation of specific features within the geosite perimeter, spatial planning or tourism management.

Landslide inventory map as a tool for landscape planning and management in Buzau Land Geopark

NASA Astrophysics Data System (ADS)

Tatu, Mihai; Niculae, Lucica; Popa, Răzvan-Gabriel

2015-04-01

Buzău Land is an aspiring Geopark in Romania, located in the mountainous region of the southern part of the Carpathian Bend Area. From a geologic point of view, the East Carpathians represent a segment of the Alpine - Carpathian orogene, and they are composed of numerous tectonic units put up throughout the Mesozoic and Cenozoic orogenesis. They represent a result of two compressional phases, (1) during Late Cretaceous and (2) during Early and Middle Miocene that were responsible for thrusting of internal units onto external units. The latter cover tectonically the Foredeep folded deposits. Landslides are one of the most widespread and dangerous natural hazards in this region, disrupting access routes and damaging property and habitats at least twice per year, in the rainy seasons. This hazard induces deep changes in the landscape and has serious economic consequences related to the damaging of infrastructure and isolation of localities. The proximity to the Vrancea seismogenic zone increases the risk of landslide triggering. A first step in observing the space and time tendency and amplitude of landslides, in order to distinguish the main vulnerabilities and estimate the risk, is to produce an inventory map. We shall present a landslide inventory map for the Buzău Land territory (~1036 km2), which is the primary base of information for further discussions regarding this phenomenon and an essential tool in observing the development of mass-wasting processes and in landscape planning. The inventory map is in accordance with the recommendations of the IAEG Commission on Landslides and other Mass-Movement, applied across the EU. Based on this work, we can already draw some remarks: - The Geopark territory mostly covers two major tectonic units of the East Carpathians: the external nappes and the folded foredeep; areas with landslide potential are common, but by far the highest landslide frequency is observed in the foredeep. This is related to the soft, argillaceous and sandy rock compositions. The magnitude of the phenomenon progressively diminishes towards the NW, where older and more coherent rocks are found. Here, mixed aspects (landslides with blocks) and rockslides are well expressed. - The spatial distribution of landslides is controlled by active tectonics, most of them being observed along faults. - Landslides are common in the vicinity of salt diapirs and especially on their flanks. - Deforestation in the area is mostly related to small scale, superficial mass movements (soil creeps especially). - The dynamics of the area brings continuous damage to the infrastructure. Our inventory map is the first step in characterizing and forecasting landslide activity in the Geopark and future research will offer tools for the sustainable development of the region. The research leading to these results has received funding from EEA Financial Mecanism 2009 - 2014 under the GeoSust project contract no 22 SEE/30.06.2014.

Change-point analysis of geophysical time-series: application to landslide displacement rate (Séchilienne rock avalanche, France)

NASA Astrophysics Data System (ADS)

Amorese, D.; Grasso, J.-R.; Garambois, S.; Font, M.

2018-05-01

The rank-sum multiple change-point method is a robust statistical procedure designed to search for the optimal number and the location of change points in an arbitrary continue or discrete sequence of values. As such, this procedure can be used to analyse time-series data. Twelve years of robust data sets for the Séchilienne (French Alps) rockslide show a continuous increase in average displacement rate from 50 to 280 mm per month, in the 2004-2014 period, followed by a strong decrease back to 50 mm per month in the 2014-2015 period. When possible kinematic phases are tentatively suggested in previous studies, its solely rely on the basis of empirical threshold values. In this paper, we analyse how the use of a statistical algorithm for change-point detection helps to better understand time phases in landslide kinematics. First, we test the efficiency of the statistical algorithm on geophysical benchmark data, these data sets (stream flows and Northern Hemisphere temperatures) being already analysed by independent statistical tools. Second, we apply the method to 12-yr daily time-series of the Séchilienne landslide, for rainfall and displacement data, from 2003 December to 2015 December, in order to quantitatively extract changes in landslide kinematics. We find two strong significant discontinuities in the weekly cumulated rainfall values: an average rainfall rate increase is resolved in 2012 April and a decrease in 2014 August. Four robust changes are highlighted in the displacement time-series (2008 May, 2009 November-December-2010 January, 2012 September and 2014 March), the 2010 one being preceded by a significant but weak rainfall rate increase (in 2009 November). Accordingly, we are able to quantitatively define five kinematic stages for the Séchilienne rock avalanche during this period. The synchronization between the rainfall and displacement rate, only resolved at the end of 2009 and beginning of 2010, corresponds to a remarkable change (fourfold increase in mean displacement rate) in the landslide kinematic. This suggests that an increase of the rainfall is able to drive an increase of the landslide displacement rate, but that most of the kinematics of the landslide is not directly attributable to rainfall amount. The detailed exploration of the characteristics of the five kinematic stages suggests that the weekly averaged displacement rates are more tied to the frequency or rainy days than to the rainfall rate values. These results suggest the pattern of Séchilienne rock avalanche is consistent with the previous findings that landslide kinematics is dependent upon not only rainfall but also soil moisture conditions (as known as being more strongly related to precipitation frequency than to precipitation amount). Finally, our analysis of the displacement rate time-series pinpoints a susceptibility change of slope response to rainfall, as being slower before the end of 2009 than after, respectively. The kinematic history as depicted by statistical tools opens new routes to understand the apparent complexity of Séchilienne landslide kinematic.

Movement of a large, slow-moving landslide in the North Island, New Zealand, controlled by porewater pressure and river flow

NASA Astrophysics Data System (ADS)

McColl, Samuel; Holdsworth, Charlotte; Massey, Chris

2017-04-01

New Zealand has 7000 mapped large (> 2 ha) landslides, most of which occur in the Neogene cover rocks, and many of which are active. Active landslides in New Zealand damage lifeline infrastructure, entire suburbs, agricultural land, and they deliver large but little-quantified sediment load to rivers. Despite their prevalence in the landscape and these impacts, much remains unknown of their initiation, movement patterns and processes, or their contributions to landscape evolution. This research assesses how toe cutting and rainfall at a daily to seasonal timescale drive movement of a large (50 hectare) slow-moving, translational rockslide that is severely damaging a farm in the Rangitikei catchment, central North Island. Geomorphological mapping has been undertaken to define the landslide boundary, drainage lines and to assess zones of movements. Since July 2015, 3-monthly GPS-occupations of a survey mark network, and hourly time-lapse photography of the toe of the landslide have been used to identify the distribution and patterns of landslide movement. Pixel-tracking software is being used to quantify movement at the toe from the time-lapse photography at an daily timescale. Movement data are being compared with river flow data (i.e. toe cutting potential) and local rainfall and groundwater from a nearby site (i.e. a proxy for porewater-pressure changes at the landslide). Results so far indicate movement of several mm to cm per year in the upper part of the landslide through a block sliding mechanism, increasing to several metres per year towards the toe where block-sliding transitions sharply to more mobile earth flow-slide behaviour. In the upper part of the landslide, vertical displacements are larger closer to earth flow-slide zone, expressed as decimetre to metre-scale scarps and mini-grabens. The failure surface is exposed at the toe, which is being actively cut by a major river, and reveals a highly remoulded landslide body 1-3 metres thick, overlaying intact sandstone. Based on existing structural data and the landslide surface morphology it is assumed that the landslide thickens to about 60 m towards the head. The geomorphology suggests extension and thinning of the landslide body - which corroborates the movement data showing movement rates at the head (mm per year) increasing downslope to some metres per year at the toe - and without a zone of compression at the toe, suggesting near-continuous toe-unloading. Movement is fastest in the winter-spring months when water tables are high due to reduced evapotranspiration and slightly greater rainfall. However, this period also coincides with a period of higher river flow and flood events (i.e. toe cutting), and the landslide appears to be particularly sensitive (i.e. surges forward) following high river flow events that cut the toe. This observation suggests that movement is driven by both local and catchment-scale rainfall events.

Regional analysis of distribution of pre and post 2015 Nepal Earthquake landslides

NASA Astrophysics Data System (ADS)

Valagussa, Andrea; Frattini, Paolo; Crosta, Giovanni; Valbuzzi, Elena

2016-04-01

A magnitude 7.8 earthquake struck Nepal on April 25, 2015. Three landslide inventories have been prepared in four districts: Dhading (1885 km2), Sindhupalchok (2488 km2), Rasuwa (1522 km2) and Nuwakot (1194 km2), that are located north of Kathmandu. These inventories extend 14 to 138 km SE from the epicenter of the main shock (April 25, 2015), 4.5 to 143 km NW from the epicenter of the main aftershock (May 12, 2015), and 34 to 136 km from the Main Frontal Thrust. The first inventory is a coseismic and post-seismic landslide inventory based on multi-temporal images (Google Earth, Google Crisis maps, Bing maps), and helicopter-based video. The second one is a pre-event shallow landslide inventory. In these two inventories the most abundant landslide types are: debris flows, shallow translational slides, and rockfalls. The third is a deep seated landslide inventory, in which the most represented landslide types are rock avalanches, slumps, rockslides and deep-seated gravitational slope deformations (DSGSD). All the landslides have been mapped as individual polygons. For the analysis we focus our attention on four districts: First we studied how the landslide frequency density changes as a function of topographic parameters (i.e. slope gradient, slope aspect, and elevation). The analyses have been based on the ASTER Global Digital Elevation Model (ASTER GDEM). For coseismic and post-seismic landslides we observed that the mean slope gradient at which the landslide occurs is higher with respect to the two other inventories (50° and 30/40° respectively). The slope aspect of coseismic and post-seismic landslides is also different, with a larger frequency of landslides towards SW, whereas in pre-event landslides the most common slope aspect is SE. This could be related to the direction of the seismic wave. At least the coseismic and post-seismic landslides occur, in mean, at an elevation lower than the pre-event landslides. We also analyzed the relationship between the landslide frequency density and the lithology in which each landslide occurs to better understand if a particular geological suite is more prone to give landslides, both in seismic and non-seismic conditions. The landslide density for the Deep Seated Landslides and the Pre-Event Shallow landslides does not shows particular changes with the lithology in which the landslide occurred. The Deep Seated Landslides seem to be more abundant in marbles with respect the others lithologies. The pre-event landslides seem to be more abundant in gneiss and shale. Different observations could be done for the coseismic and post-seismic landslides, which show a high value of density (5.13 landslides per km2) for schist, limestone and quartzite. Instead, the granites have a lower number of landslides, as observed for the two other inventories.

Detection of rainfall-induced landslides on regional seismic networks

NASA Astrophysics Data System (ADS)

Manconi, Andrea; Coviello, Velio; Gariano, Stefano Luigi; Picozzi, Matteo

2017-04-01

Seismic techniques are increasingly adopted to detect signals induced by mass movements and to quantitatively evaluate geo-hydrological hazards at different spatial and temporal scales. By analyzing landslide-induced seismicity, it is possible obtaining significant information on the source of the mass wasting, as well as on its dynamics. However, currently only few studies have performed a systematic back analysis on comprehensive catalogues of events to evaluate the performance of proposed algorithms. In this work, we analyze a catalogue of 1058 landslides induced by rainfall in Italy. Among these phenomena, there are 234 rock falls, 55 debris flows, 54 mud flows, and 715 unspecified shallow landslides. This is a subset of a larger catalogue collected by the Italian research institute for geo-hydrological protection (CNR IRPI) during the period 2000-2014 (Brunetti et al., 2015). For each record, the following information are available: the type of landslide; the geographical location of the landslide (coordinates, site, municipality, province, and 3 classes of geographic accuracy); the temporal information on the landslide occurrence (day, month, year, time, date, and 3 classes of temporal accuracy); the rainfall conditions (rainfall duration and cumulated event rainfall) that have resulted in the landslide. We consider here only rainfall-induced landslides for which exact date and time were known from chronicle information. The analysis of coeval seismic data acquired by regional seismic networks show clear signals in at least 3 stations for 64 events (6% of the total dataset). Among them, 20 are associated to local earthquakes and 2 to teleseisms; 10 are anomalous signals characterized by irregular and impulsive waveforms in both time and frequency domains; 33 signals are likely associated to the landslide occurrence, as they have a cigar-shaped waveform characterized by emerging onsets, duration of several tens of seconds, and low frequencies (1-10 Hz). For this last category of events, we have applied the approach proposed in Manconi et al. (2016), in order to evaluate the performance of automatic identification, location and first order classification of landslide events trough seismic data only. Our analysis may provide important insights for the development and calibration of landslide identification algorithms, which might be used to enhance the completeness of landslide catalogues by relying on quantitative data. Brunetti, M.T., Peruccacci, S., Antronico, L., Bartolini, D., Deganutti, A.M., Gariano, S.L., Iovine, G., Luciani, S., Luino, F., Melillo, M., Palladino, M.R., Parise, M., Rossi, M., Turconi, L., Vennari, C., Vessia, G., Viero, A., and Guzzetti, F.: Catalogue of Rainfall Events with Shallow Landslides and New Rainfall thresholds in Italy, in Lollino G, Giordan D, Crosta G B, Corominas J, Azzam R, Wasowski J, Sciarra N (eds.), Engineering Geology for Society and Territory - Volume 2, Springer International Publishing, Switzerland, 1575-1579, 2015. Manconi, A., Picozzi, M., Coviello, V., De Santis, F., and Elia, L.: Real-time detection, location, and characterization of rockslides using broadband regional seismic networks, Geophys. Res. Lett., 43, 6960-6967, doi:10.1002/2016GL069572, 2016.

Increased Melting of Glaciers during Cotopaxi volcano awakening in 2015

NASA Astrophysics Data System (ADS)

Ramon, Patricio; Vallejo, Silvia; Almeida, Marco; Gomez, Juan Pablo; Caceres, Bolivar

2016-04-01

Cotopaxi (5897 m), located about 50 km south of Quito (Ecuador), is one of the most active volcanoes in the Andes and its historical eruptions have caused a great impact on the population by the generation of lahars along its three main drainages (N, S, E). Starting on April 2015 the seismic monitoring networks and the SO2 gas detection network in May 2015 showed a significant increase from their background values, in June a geodetic instrument located in the NE flank started to record inflation; all this indicated the beginning of a new period of unrest. On August 14, five small phreatic explosions occurred, accompanied by large gas and ash emissions, ash falls were reported to the W of the volcano and to the S of Quito capital city. Three new episodes of ash and gas emissions occurred afterwards and towards the end of November 2015, the different monitoring parameters indicated a progressive reduction in the activity of the volcano. Since August 18 almost weekly overflights were made in order to conduct thermal (FLIR camera), visual and SO2 gas monitoring. Towards the end of August thermal measurements showed for the first time the presence of new thermal anomalies (13.5 to 16.3 °C) located in the crevices of the N glaciers, at the same time fumarolic gases were observed coming out from those fractures. On a flight made on September 3, the presence of water coming out from the basal fronts of the northern glaciers was clearly observed and the formation of narrow streams of water running downslope, while it was evident the appearance of countless new crevices in the majority of glacier ends, but also new cracks and rockslides on the upper flanks. All this led to the conclusion that an abnormal process was producing the melting of the glaciers around the volcano. Starting on September it was possible to observe the presence of small secondary lahars descending several streams and we estimated that many of them are due to increased glacier melting. Later observations made until the end of last year showed an increase of the phenomena already described. Thanks to the collaboration of the Military Geographic Institute of Ecuador (IGM), orthophotos of the volcano made on August 18 and then again on October 8, shows a decrease in the area covered by glaciers of about 0.49 km2 (annual projection of 3.51 km2), this value compared to the decrease of glacier areas since 1976, shows a very high rate of glacier melting, not explained exclusively by climate change phenomena. It is estimated that small volumes of magma reached surface levels through the volcano conduits causing increased circulation of hot fluids inside the edifice, which are apparently reaching the basal area of the glaciers and producing a major melting thereof. It is necessary to further investigate hazard due to the instability in the melting glaciers of Cotopaxi and their eventual collapse which could lead to greater secondary lahars.

3D granular deposits on rock avalanches: can the application of different operators and filtering techniques improve our understanding of the phenomena?

NASA Astrophysics Data System (ADS)

Longchamp, Celine; Abellan, Antonio; Derron, Marc-Henri; Jaboyedoff, Michel

2014-05-01

Rock avalanches are catastrophic events involving a great volume of material (>106 m3). The flowing mass can reach velocities up to ten meters per second and travel long distances on the order of kilometres, covering an area over 0.1 km2. These extremely destructive and uncontrollable events are very unusual in nature and the use of analogue modelling is of great importance in the understanding of the behaviour of such events. The main objective of this research is to analyse rock avalanche dynamics by means of a detailed structural analysis of the features observed in the avalanche. Data used for this research consist on 3D measurements of mass movements of different magnitudes, from decimetre level scale laboratory experiments to well-studied rock avalanches of several square kilometres magnitude, as follows: (1) Laboratory experiments are performed on a tilting plane in which a well-defined granular material is released, chute down a slope, propagate and finally stop on a horizontal surface. The deposits are then scanned by a 3D digitizer (Konica Minolta vivid 9i micro-LiDAR) in order to get a 3D geometrical model of the mass. Different grainsize (115, 545 and 2605 μm) and substratum roughness (simulate by aluminium and sandpapers with grainsize from 16 to 425 μm) were used in order to understand their influence on the motion of a granular mass; (2) A well know rock avalanche deposit, the Frank slide (Alberta, Canada), was also analysed from the available 3D LiDAR dataset. This deposit consists in a 30× 106 m3 rockslide-avalanche of Palaeozoic limestone that was widely studied by several authors before (e.g. Cruden and Hungr, 1986, Cruden and Krahn, 1973, etc). In order to better understand the fault and folding structures presented in the rock avalanche deposits, we applied a series of linear and non-linear Matlab operators and filtering techniques to the 3D datasets, including differences derivatives ('diff'), numerical gradient ('gradient'), discrete Laplacian ('del2') and median filter ('medfilt2') with different moving windows sizes (from 3x3 to 9x9 nearest neighbour). A detailed structural analysis of the deposit is performed in order to understand how the sliding mass behaves. The application of these filters on the datasets results in: (1) a precise mapping of the longitudinal and transversal displacement features observed at the surface of the deposits; and (2) a more accurate interpretation of the relative movements along the deposit (i.e. normal, strike-slip and thrust faults) by using cross-sections. Preliminary results shows how the use of filtering techniques reveal disguised features in the original point cloud and that similar displacement patterns are observable in both cases studies, regardless the size of the avalanche. Furthermore, we observed how different structural features including transversal fractures and folding patterns tend to show a constant wavelength proportional to the size of the avalanche event.

Geomorphic changes induced by the April-May 2015 earthquake sequence in the Pharak-Khumbu area (Nepal): preliminary assessments.

NASA Astrophysics Data System (ADS)

Fort, Monique

2016-04-01

Landsliding is a common process shaping mountain slopes. There are various potential landslide triggers (rainfall, bank erosion, earthquakes) and their effectiveness depends on their distribution, frequency and magnitude. In a Himalayan context, the effects of monsoon rainfall can be assessed every year whereas the unpredictability and low frequency of large earthquakes make their role in triggering slope instability more obscure. A 7.8 magnitude earthquake struck central Nepal (Gorkha District) on 25 April 2015 and was followed by many aftershocks exceeding magnitude 5, including another strong 7.3 magnitude earthquake on May 12, 2015 (Dolakha District). This seismic crisis provides an exceptional opportunity to assess the disruptions that earthquakes may cause in "regular" geomorphic systems controlled by rainfall. Here we present field observations carried out in the Pharak-Khumbu area (East Nepal, Dudh Kosi catchment) before and after the April-May 2015 earthquakes. The Pharak, a "middle mountains" (2000-4500 m) area, is affected by monsoon rains (3000 m/yr at 2500 m) and characterised by steep hillslopes, shaped by different geomorphic processes according to slope height and aspect, rock type and strength, inherited landforms, stream connectivity and current land use changes. This study focuses on the south of Lukla (Phakding District), and more specifically on the Khari Khola catchment and its surroundings. The area lies at the transition between the Higher Himalayan crystallines and the Lesser Himalayan meta-sediments. On the basis of our diachronic observations (March and November 2015), we surveyed and mapped new earthquake-induced slope instabilities such as rock falls, rockslides, landslides and debris flows and a combination of several of them. Interviews with local people also helped to assess the exact timing of some events. While the first M 7.8 earthquake produced significant impacts in the northern Khumbu area, the M 7.3 aftershock seems to have been more destructive in Pharak. In Pharak, the observed geomorphic changes are not as great as in the zone between the Gorkha and Dolaka Districts. Control factors are (1) slope steepness (>45°) and height (500-1000 m), both favouring landslide initiation near the ridge top and a series of cascading processes resulting in temporary valley damming, as observed near Nakchun, Bupsa and W of Kharikhola-Jubing; (2) lithology also appears significant: weak fractured bedrock supplied rock falls (upper Kharikhola catchment), whereas superficial deposits (alluvial, lacustrine, and colluvial soils, including landslide material) favoured larger failures (Paya, Cheubas), particularly because of (3) the proximity of the deeply incised stream network. The limited size and shallow depth of the newly generated slope failures are noteworthy. More generally, these geomorphic changes and their characteristics may be explained by the nature of the 2015 climate: while the 2014-2015 winter was unusually dry, snowfalls and rainfalls were abundant during March and April, hence increasing the pore pressure and the potential instability of slopes and/or snow cover. Conversely, the rather weak monsoon rainfall of the 2015 summer did not take advantage of the many cracks opened by seismic shaking. Yet this may leave only a short delay for large landslide development during the next monsoon seasons.

Testing failure surface prediction methods and deposit reconstruction for the landslides cluster occurring during Talas Typhoon (Japan)

NASA Astrophysics Data System (ADS)

Jaboyedoff, Michel; Chigira, Masahiro; Arai, Noriyuki; Derron, Marc-Henri; Rudaz, Benjamin; Tsou, Ching-Ying

2016-04-01

Talas Typhoon hit Japan from 2 to 5 September 2011. It induced more than 70 deep-seated landslides in Kii peninsula. The hi-resolution topography of these landslides have been acquired by aerial 1 m LiDAR digital elevation models (DEM) before (pre-DEM) and after (post-DEM) the events (data from Nara prefectural Government and the Kinki Regional development Bureau of Ministry of Land, Infrastructure, Transportation, and Tourism). This extraordinary opportunity allows us to test methods to construct failure surface geometries, buried valley topographies and/or to rebuild deposits surfaces. We tested the sloping base local level method (SLBL) on 5 deep seated landslides which occurred during Typhoon Talas (Akatani, Kitamata, Nagatono, Shimizu and Akatani-East; see Chigira et al., 2013). The SLBL corresponds to a quadratic surface with a constant second derivative in all x-y directions. This curvature can be based on the knowledge of the length of the landslide and its maximum thickness. We used mainly hillshade DEM, slope maps and Coltop schemes to define the limits of landslides and to interpret their structures. Different attempts were performed to reconstruct the failure surface and deposits depending on a priori knowledge. Basically the morphological features extracted from the pre-DEM were used to delineate the limits of the landslides. The curvature of the failure surface was obtained by "expert" interpretations. The failure surfaces obtained using SLBL are in good agreement with the failure surface observed on the post-DEM. The results are improved when (1) they are adjusted to obtain similar estimate of the volume deduced by Chigira et al. (2013), and when (2) the contours of the landslides used comes from an interpretation of both post and pre-DEM. In order to obtain the expansion coefficient some of these landslide, the missing volume of the deposits (by river erosion) were calculated using inverse SLBL. The coefficient of expansion ranges from 13% to 30%. The reconstruction of topography before the landslides in the scar or below the deposits gives also reliable results. Even if in many of the above cases the failure surface is controlled by structures (faults, joints, bedding, etc.), the quadratic surface used in SLBL seems to be a suitable solution to fit failure surfaces. If the structures are controlling large parts of the surface of failure, usually several of them are participating to the failure surfaces. It seems that this network of surfaces tends to adopt quadratic shapes when combined. Looking at other landslides or rockslide scar profiles around the world, the quadratic shape appears as very relevant. These study shows the efficiency of the SLBL method as a tool to estimate quickly the failure surface without a lot of knowledge. Preliminary investigations indicates that failure surface are roughly close to quadratic surface. References: Chigira M., Tsou C.-Y., Matsushi Y., Hiraishi N., Matsuzawa M. 2013.Topographic precursors and geological structures of deep-seated catastrophic landslides caused by Typhoon Talas. Geomorphology 201, 479-493

Karstic slope "breathing": morpho-structural influence and hazard implications

NASA Astrophysics Data System (ADS)

Devoti, Roberto; Falcucci, Emanuela; Gori, Stefano; Eliana Poli, Maria; Zanferrari, Adriano; Braitenberg, Carla; Fabris, Paolo; Grillo, Barbara; Zuliani, David

2016-04-01

The study refers to the active slope deformation detected by GPS and tiltmeter stations in the Cansiglio karstic plateau located in the western Carnic Prealps (NE Italy). The observed transient deformation clearly correlates with the rainfall, so that the southernmost border of the Plateau reacts instantly to heavy rains displaying a "back and forth" deformation up to a few centimeters wide, with different time constants, demonstrating a response to different catchment volumes. We carried out a field survey along the southern Cansiglio slope, to achieve structural characterization of the relief and to verify the possible relation between structural features and the peculiar geomorphological setting dominated by widespread karstic features. The Cansiglio plateau develops on the frontal ramp anticline of the Cansiglio thrust, an about ENE-WSW trending, SSE-verging, low angle thrust, belonging to the Neogene-Quaternary front of the eastern Southern Alps. The Cansiglio thrust outcrops at the base of the Cansiglio plateau, where it overlaps the Mesozoic carbonates on the Miocene-Quaternary terrigenous succession. All along its length cataclastic limestone largely outcrop. The Cansiglio thrust is bordered by two transfer zones probably inherited from the Mesozoic paleogeography: the Caneva fault in the west and the Col Longone fault in the east. The carbonatic massif is also characterized by a series of about northward steeply dipping reverse minor faults and a set of subvertical joints parallel to the axes of the Cansiglio anticline. Other NNW-SSE and NNE-SSW conjugate faults and fractures perpendicular to the Cansiglio southern slope are also identified. This structural setting affect pervasively the whole slope and may determine centimetre- to metre-scale rock prisms. Interestingly, along the topmost portion of the slope, some dolines and swallow holes show an incipient coalescence, that trends parallel to the massif front and to the deformation zones related to the reverse fault. Such a dolines alignment forms a ridge parallel elongated trench, about 4 km long, which is a typical morpho-structural feature of slopes undergoing large scale gravitational instability (deep seated gravitational slope deformations). The trench is interrupted towards the NE by several coalescent and slide scarps. Such geomorphic evidence testifies to the occurrence of landslides events (mainly rockslides and rock falls) that sourced from the top portion of the slope, as local collapses of the sector affected by the trench. Our observations, as a whole, suggest that morpho-structural framework of the Cansiglio south-eastern slope is highly influenced by tectonic features related to the complex tectonic deformation. The structural setting is locally favoring the nucleation of karstic landforms (dolines, swallow holes and ipokarstic features). Moreover, the presence of widespread tectonic features lead gravitational instability affecting the slope, linked to the high local relief of the mountain front, may trigger collapse of sectors of the slope in rock falls phenomena. In this perspective, therefore, the continuous "back and forth" movements of the slope observed by GPS time series analysis induced by rainfall may progressively weaken the slope and render it prone to landsliding.

Rock-slope failure activity and geological crises in western Norway

NASA Astrophysics Data System (ADS)

Hilger, Paula; Hermanns, Reginald L.; Myhra, Kristin S.; Gosse, John C.; Ivy-Ochs, Susan; Etzelmüller, Bernd

2017-04-01

In Norway a compilation of terrestrial cosmogenic nuclide (TCN) ages of rock-avalanche deposits suggests a close link of rock-slope failures related to deglaciation. Although ages spread over several thousand years at the end of the Late Pleistocene, 50% of all documented events occurred within 1000 years after deglaciation. It is therefore likely that debuttressing triggered most of the events. The same data set suggests that 25% of the events occurred during a period stretching until the Holocene thermal maximum (HTM). These events might be interpreted as possible reactions to additional factors such as the thawing of high-altitude permafrost. An example of a geological crisis following deglaciation and before the HTM are seven lobate rock-avalanche deposits mapped under the slope of the Vora mountain (1450 m asl.) in the Nordfjord area of western Norway. Three events of this rock-slope failure cluster date within a short time period of 2000 years, where modelling studies indicate that high-altitude permafrost was present. After the HTM rock-slope failures are distributed temporally and spatially rather evenly throughout the Holocene and western Norway. But there are two independent local clusters with frequent rock slides during a short time span. (1) At the active Mannen rock-slope instability several rock-avalanche and rockslide deposits were mapped on the valley bottom. Stratigraphic relations combined with TCN dating suggest that at least one event occurred when the valley bottom was below the marine limit. TCN ages of further four lobes cluster around 5.2 ka BP, which does not coincide with any other rock-avalanche occurrence in the region. The top of the north facing 1295 m high unstable slope concurs with the currently estimated permafrost boundary. Preliminary TCN ages of the sliding surface indicate that larger parts of the mountain did not become active until the climate maximum. It is likely that due to structural complexity not allowing for any easy kinematic failure process, it required several thousand years of rock-slope deformation prior to the multiple failures. (2) The youngest independent rock-avalanche cluster is historic with 5 rock avalanches sourcing from Ramnefjellet in 1905, 1936 (three events), and 1950 entering into Loen lake in western Norway. Subsequent displacement waves killed 61 people in 1905 and 73 people due to the first failure in 1936. The back scarp does not exceed 850 m elevation and lies hence below the present day and Little Ice Age permafrost limit. It is therefore unlikely that permafrost dynamics contribute to this sequence of rock-slope failures. Local clusters or a geological crisis by rock-slope failures seems to be related to different main factors, such as glacial debutressing, influence of ground thermal regime changes (Mannen) and probably more disconnected to major climate variability (Loen). For an integrated risk management it is therefore important to understand that large rock-slope failures do not necessarily have to occur in single events but can occur over several decades or centuries and thus complicate severely land use management after catastrophic events.

Gas and Dust Phenomena of Mega-earthquakes and the Cause

NASA Astrophysics Data System (ADS)

Yue, Z.

2013-12-01

A mega-earthquake suddenly releases a large to extremely large amount of kinetic energy within a few tens to two hundreds seconds and over ten to hundreds kilometer distances in the Earth's crust and on ground surface. It also generates seismic waves that can be received globally and co-seismic ground damages such co-seismic ruptures and landslides. However, such vast, dramatic and devastating kinetic actions in the Earth's crustal rocks and on the ground soils cannot be known or predicted by people at few weeks, days, hours, or minutes before they are happening. Although seismologists can develop and use seismometers to report the locations and magnitudes of earthquakes within minutes of their occurrence, they cannot predict earthquakes at present. Therefore, damage earthquakes have caused and would continue to cause huge disasters, fatalities and injuries to our human beings. This problem may indicate that it is necessary to re-examine the cause of mega-earthquakes in addition to the conventional cause of active fault elastic rebounding. In the last ten years, many mega-earthquakes occurred in China and around the Pacific Ocean and caused many casualties to human beings and devastating disasters to environments. The author will give a brief review on the impacts of the mega-earthquakes happened in recent years. He will then present many gas and dust related phenomena associated with the sudden occurrences of these mega earthquakes. They include the 2001 Kunlunshan Earthquake M8.1, 2008 Wenchuan Earthquake M8.0 and the 2010 Yushu Earthquake M7.1 in China, the 2010 Haiti Earthquake M7.0, the 2010 Mexicali Earthquake M7.2, the 2010 Chile Earthquake M8.8, the 2011 Christchurch earthquake M6.3 and the 2011 Japan Earthquake M9.0 around the Pacific Ocean. He will discuss the cause of these gas and dust related phenomena. He will use these phenomena and their common cause to show that the earthquakes were caused the rapid migration and expansion of highly compressed and dense natural (methane) gas suddenly escaped from deep crust traps along deep fault zones. References Yue, ZQ, 2009. The source of energy power directly causing the May 12 Wenchuan Earthquake: Huge extremely pressurized natural gases trapped in deep Longmen Shan faults. News Journal of China Society of Rock Mechanics and Engineering, 86 (2009 (2)), 45-50. Yue, ZQ, 2010. Features and mechanism of coseismic surface ruptures by Wenchuan Earthquake. in Rock Stress and Earthquake, edited by Furen Xie, Taylor & Francis Group, London, ISBN 978-0-415-60165-8, 761-768. Yue, ZQ, 2013a. Natural gas eruption mechanism for earthquake landslides: illustrated with comparison between Donghekou and Papandayan Rockslide-debris flows. in Earthquake-induced Landslides, K. Ugai et al. (eds.), Springer-Verlage Berlin, Chapter 51: pp. 485-494 Yue ZQ, 2013b. On incorrectness in elastic rebound theory for cause of earthquakes. Paper No. S20-003 of Session S20, Proceedings of the 13th International Conference on Fracture, June 16-21, Beijing. Yue ZQ, 2013c. On nature of earthquakes with cause of compressed methane gas expansion and migration in crustal rocks, in Proceedings of Fifth Biot Conference on Poromechanics in Memory of Karl von Terzaghi (1883-1963), July 10-12, Vienna, edited by C. Hellmich et al, @ASCE, pp. 507-516.

Landslides along Highways: GIS-based Inventory and Planning Issues

NASA Astrophysics Data System (ADS)

Jaeger, Ann-Kathrin; Klose, Martin; Damm, Bodo

2015-04-01

Highways rank as critical transportation infrastructures that are at risk of landslides in many areas worldwide (e.g., Hungr et al., 1999; Bhandary et al., 2013). Safe and affordable operations of traffic routes constitute the two main criteria for transportation planning in landslide-prone terrain. A right balancing of these often conflicting priorities requires profound knowledge of landslide locations across highway networks and the costs caused by landslides in the past (e.g., Saha et al., 2005). Much of the direct costs affecting transportation departments relate to capital investments for landslide repair or mitigation and operational expenditures in connection with maintenance works. A systematic collection and inventory of such data sets combined with an acquisition of hazard information on vulnerable road sections is still rarely the case in engineering practice. This is despite significant cost impacts and budgetary burdens, especially in peripheral mountain areas where financial resources are naturally limited (e.g., Klose et al., 2014). The present contribution introduces a regional inventory of landslides along highways in the Harz Mountains, NW Germany. As subset of a landslide database for the entire country, this focused GIS-based inventory has been compiled in close collaboration with the Lower Saxony Department of Transportation. The inventory includes data sets gathered by archive studies and relies on high-quality information sources such as maintenance protocols, geotechnical reports, and documents from tendering, controlling, and accounting. A mapping tool in ArcGIS format is used to specify and visualize road sections affected by landslides. This spatial information on hazard exposure is complemented by narrative risk profiles for landslide sites showing a long history of damage events. By summarizing the occurrence dates of landslides, the associated damages, and the types and costs of repair or prevention, such risk profiles are useful to assess landslide impacts and the effectiveness of measures for their mitigation. The landslide inventory is part of an ongoing study concerned with the problems of damage financing at low-volume roads in mountain areas with shrinking populations and fiscal deficits. Using the example of the Harz Mountains, a key research question refers to a comparison of the costs necessary to spend for safe road operations with the benefits from providing traffic connections to landslide-prone rural communities. This study combines the damage and loss data stored in the inventory with different data sets on traffic density, local population, and road financing. The research results contribute to the development of planning strategies for cost-efficient maintenance of highway infrastructures exposed to landslide hazards. References Bhandary, N.P., Yatabe, R., Dahal, R.K., Hasegawa, S., Inagaki, H., 2013. Areal distribution of large-scale landslides along highway corridors in central Nepal. Georisk 7, 1-20. Hungr, O., Evans, S.G., Hazzard, J., 1999. Magnitude and frequency of rock falls and rockslides along the main transportation corridors of southwestern British Columbia. Canadian Geotechnical Journal 36, 224-238 Klose, M., Damm, B., Terhorst, B., 2014b. Landslide cost modeling for transportation infrastructures: a methodological approach. Landslides, DOI 10.1007/s10346-014-0481-1. Saha, A.K., Arora, M.K., Gupta, R.P., Virdi, M.L., Csaplovics, E., 2005. GIS-based route planning in landslide-prone areas. International Journal of Geographical Information Science 19, 1149-1175.

Geology of the Knife River area, North Dakota

USGS Publications Warehouse

Benson, William Edward

1953-01-01

The Knife River area, consisting of six 15-minute quadrangles, includes the lower half of the Knife River valley in west-central North Dakota. The area, in the center of the Williston Basin, is underlain by the Tongue River member of the Fort Union formation (Paleocene) and the Golden Valley formation (Eocene). The Tongue River includes beds equivalent to the Sentinel Butte shale; the Golden Valley formation, which receives its first detailed description in this report, consists of two members, a lower member of gray to white sandy kaolin clay and an upper member of cross-bedded micaceous sandstone. Pro-Tongue River rocks that crop out in southwestern North Dakota include the Ludlow member of the Fort Union formation, the Cannonball marine formation (Paleocene) and the Hell Creek, Fox Hills, and Pierre formations, all upper Cretaceous. Post-Golden Valley rocks include the White River formation (Oligocene) and gravels on an old planation surface that may be Miocene or Pliocent. Surficial deposits include glacial and fluvial deposits of Pleistocene age and alluvium, dune sand, residual silica, and landslide blocks of Recent age. Three ages of glacial deposits can be differentiated, largely on the basis of three fills, separated by unconformities, in the Knife River valley. All three are of Wisconsin age and probably represent the Iowan, Tazewell, and Mankato substages. Deposits of the Cary substage have not been identified either in the Knife River area or elsewhere in southern North Dakota. Iowan glacial deposits form the outermost drift border in North Dakota. Southwest of this border are a few scattered granite boulders that are residual from the erosion of either the White River formation or a pre-Wisconsin till. The Tazewell drift border cannot be followed in southern North Dakota. The Mankato drift border can be traced in a general way from the South Dakota State line northwest across the Missouri River and through the middle of the Knife River area. The major land forms of southwestern North Dakota are: (1) high buttes that stand above (2) a gravel-capped planation surface and (3) a gently-rolling upland; below the upland surface are (4) remnants of a broad valley stage of erosion into which (5) modern valleys have been cut. The broad valley profiles of many streams continue east across the Missouri River trench and are part of a former drainage system that flowed into Hudson Bay. Crossing the divides are (6) large trenches, formed when the former northeast-flowing streams were dammed by the glacier and diverted to the southeast. The largest diversion valley is occupied by the Missouri River; another diversion system, now largely abandoned, extends from the Killdeer Mountains southwest to the mouth of Porcupine Creek in Sioux County. By analogy with South Dakota, most of the large diversion valleys are thought to have been cut in Illinoian time. Numerous diversion valleys of Illinoian to late Wisconsin age cut across the divides. Other Pleistocene land forms include ground and moraines, kames, and terraces. Land forms of Recent age include dunes, alluvial terraces, floodplains, and several types of landslide blocks. One type of landslide, called rockslide slump, has not previously been described. Drainage is well adjusted to the structure, most of the streams flowing down the axes of small synclines. The bedrock formations have been gently folded into small domes and synclines that interrupt a gentle northward regional dip into the Williston Basin. Three episodes of deformation affected southwestern North Dakota in Tertiary time: (1) intra-Paleocene, involving warping and minor faulting; (2) post-Eocene, involving uplift and tilting; (2) Oligocene, involving uplift and gentle folding. Mineral resources include ceramic clay, sand and gravel and lignite coal. The Knife River area is the largest lignite-producing district in the United States.

The MW 7.0 Haiti Earthquake of January 12, 2010: USGS/EERI Advance Reconnaissance Team Report

USGS Publications Warehouse

Eberhard, Marc O.; Baldridge, Steven; Marshall, Justin; Mooney, Walter; Rix, Glenn J.

2010-01-01

Executive Summary A field reconnaissance in Haiti by a five-member team with expertise in seismology and earthquake engineering has revealed a number of factors that led to catastrophic losses of life and property during the January 12, 2010, Mw 7.0 earthquake. The field study was conducted from January 26 to February 3, 2010, and included investigations in Port-au-Prince and the heavily damaged communities to the west, including Leogane, Grand Goave, Petite Goave, and Oliver. Seismology Despite recent seismic quiescence, Haiti has suffered similar devastating earthquakes in the historical past (1701, 1751, 1770 and 1860). Despite this knowledge of historical seismicity, Haiti had no seismograph stations during the main earthquake, so it is impossible to estimate accurately the intensity of ground motions. Nonetheless, the wide range of buildings damaged by the January 12, 2010, earthquake suggests that the ground motions contained seismic energy over a wide range of frequencies. Another earthquake of similar magnitude could strike at any time on the eastern end of the Enriquillo Fault, directly to the south of Port-au-Prince. Reconstruction must take this hazard into account. The four portable seismographs installed by the team recorded a series of small aftershocks. As expected, the ground motions recorded at a hard-rock site contained a greater proportion of high frequencies than the motions recorded at a soil site. Two of the stations continue to monitor seismic activity. A thorough field investigation of the mapped Enriquillo Fault south of the city of Leogane failed to find any evidence of surface faulting. This led the team to conclude that the earthquake was unlikely to have produced any surface rupture in the study area. Geotechnical Aspects Soil liquefaction, landslides and rockslides in cut slopes, and road embankment failures contributed to extensive damage in Port-au-Prince and elsewhere. A lack of detailed knowledge of the physical conditions of the soils (for example, lithology, stiffness, density, and thickness) made it difficult for us to quantitatively assess the role of ground-motion amplification in the widespread damage. Buildings The Haitian Ministry of Statistics and Informatics reported that one-story buildings represent 73 percent of the building inventory. Most ordinary, one-story houses have roofs made of sheet metal (82 percent), whereas most multistory houses and apartments have roofs made of concrete (71 percent). Walls made of concrete/block/stone predominate both in ordinary houses and apartments. It appears that the widespread damage to residences and commercial and government buildings was attributable to a great extent to the lack of earthquake-resistant design. In many cases, the structural types, member dimensions, and detailing practices were inadequate to resist strong ground motions. These vulnerabilities may have been exacerbated by poor construction practices. Reinforced concrete frames with concrete block masonry infill appeared to perform particularly poorly. Structures with light (timber or sheet metal) roofs performed better compared to structures with concrete roofs and slabs. The seismic performance of some buildings was adequate, and some of the damaged buildings appeared to have had low deformation demands. These observations suggest that structures designed and constructed with adequate stiffness and reinforcing details would have resisted the earthquake without being damaged severely. A damage survey of 107 buildings in downtown Port-au-Prince indicated that 28 percent had collapsed and another 33 percent were damaged enough to require repairs. A similar survey of 52 buildings in Leogane found that 62 percent had collapsed and another 31 percent required repairs. Bridges There was no evidence of bridge collapses attributable to the earthquake. Most bridges in Port-au-Prince are simple box culverts consisting of box girders 2.0 to 2.

The Serra de Tramuntana World Heritage Site (Mallorca, Spain). Landslide activity valuation by means of Persistent Scatterers Interferometry

NASA Astrophysics Data System (ADS)

Mateos, Rosa Maria; Bianchini, Silvia; Herrera, Gerardo; Garcia, Inmaculada; Sanabria, Margarita

2016-04-01

The Serra de Tramuntana, which forms the backbone of the north-west of Mallorca (Spain), was declared in 2011 World Heritage Site by UNESCO under the cultural landscape category. The particular landscape of this range is the fruit of the exchange of knowledge between cultures, with small-scale works performed collectively for a productive aim, conditioned by the limitations imposed by the physical medium. The steep topography of the chain, highly related to its geological complexity, and the Mediterranean climate, influence intense slope dynamics with the consequent multiple types of slope failures: rock slides, earth landslides and rockfalls, which cause significant damage and specifically to the road network (Mateos, 2013a). The human landscape marked by agricultural terraces (dry stone constructions) has significantly contributed to the slope stability in the range for centuries. In the present work, a landslide inventory map with 918 events has been updated and the landslides state of activity was analyzed exploiting 14 ALOS PALSAR satellite SAR (Synthetic Aperture Radar) images acquired during the period 2007-2010. Landslide activity maps were elaborated through the use of PSI (Persistent Scatterers Interferometry) technique (Bianchini et al., 2013). Besides assessing the PS visibility of the study area according to the relief, land use and satellite acquisition parameters, these maps evaluate, for every monitored landslide, the average velocities along the satellite Line Of Sight (VLOS) and along the maximum local steepest slope (VSLOPE), providing an estimate of their state of activity and their potential to cause damages. Additionally, a ground motion activity map is also generated, based on active PS clusters not included within any mapped landslide phenomenon. A confidence degree evaluation is carried out to attest the reliability of measured displacements to represent landslide dynamics. Results show that 42 landslides were identified as active (VSLOPE < -5mm/yr) and seven of them with a potential to produce moderate damage (VSLOPE < -10mm/yr). One of the largest landslides in the range is the Bàlitx landslide (50 million m3 in volume), located on the steep coastal side (Mateos et al., 2013b). Within the landslide body, Roman cistern and old terrace walls have been identified. Numerous geomorphological features identified in its displaced mass (cracks, shallow slides and rockfalls) reveal that the landslide has not yet reached a state of equilibrium. Additionally, field observations determine that the northeastern sector of Bàlitx shows major activity signs. DInSAR results reveal that the rate of movement for the Bàlitx landslide is extremely low (- 5mm /yr on average) that could be interpreted as the residual displacement of the deep-seated rockslide. A major activity has also been detected in the northeastern sector of Bàlitx with the PSI technique, where velocities rates are slightly over -5 mm/yr. The outcomes of this work reveal the usefulness of landslide activity maps for environmental planning activities in cultural heritage sites. References: Bianchini S, Herrera G, Mateos RM, Notti D, García-Moreno I, Mora O, Moretti S (2013). Landslide Activity Maps Generation by means of Persistent Scattered Interferometry. Remote Sensing 5:6198-6222. Mateos R.M., García-Moreno I., Herrera G., Mulas J (2013) a. Damage caused by recent mass-movements in Majorca (Spain), a region with a high risk due to tourism. Landslide Science and Practice. Claudio Margottini, Paolo Canuti and Kyoji Sassa (Editors). Volume 7: Social and Economic Impact and Policies. 105-113. Mateos RM, Rodríguez-Peces M, Azañón JM, Rodríguez-Fernández FJ, Roldán FJ, García-Moreno I, Gelabert B, García-Mayordomo J (2013)b. El deslizamiento de Bàlitx (Mallorca) y su posible origen sísmico. Procesos activos desde el Pleistoceno superior. Boletín Geológico y Minero, 124 (1): 41-61

Characterization and monitoring of the Séchilienne rock slope using 3D imaging methods (Isère, France)

NASA Astrophysics Data System (ADS)

Vulliez, Cindy; Guerin, Antoine; Abellán, Antonio; Derron, Marc-Henri; Jaboyedoff, Michel; Chanut, Marie-Aurélie; Dubois, Laurent; Duranthon, Jean-Paul

2016-04-01

The Séchilienne landslide located in the Romanche Valley (Isère, France) is a well instrumented mass movements of about 650 m high and 250 m wide, with a potential volume of about 3 million m3 in the most active part (Duranthon and Effendiantz, 2004 ; Kasperski et al., 2010). The slope, which is mainly composed of micaschist, is characterized by the presence of a NE-SW sub-vertical fracturing system involved in the destabilization of the area. The rock slope has been continuously moving since the eighties decade, with a growing acceleration during the period 2009-2013 followed by a progressive stabilization during the last years. The monitoring of the active part of the rock slide is currently carried out by an instrumentation system in order to prevent a large failure. In this work, we used different 3D techniques in order to monitor the whole rock slide displacements in three dimensions, as follows: (a) First of all, we used a Terrestrial Laser Scanning to obtain high resolution point clouds (8 cm point spacing) of the rock slope geometry. Nine different fieldwork campaigns were performed during the last six years, as follows: Aug. 2009, Jul. 2010, Nov. 2011, Nov. 2012, Jun. and Nov. 2013, Jul. and Oct. 2014, May 2015, which provided a set of 3D representations of the rock slope topography over time; (b) In addition, we used three Helicopter-based Laser Scanning campaigns carried out in Jan. 2011, Feb. 2012 and Mar. 2014 acquired by the Cerema (Chanut et al., 2014); (c) Finally, more than 600 photos were taken in Apr. 2015 in order to build a photogrammetric model of the area using Structure-from-Motion (SfM) workflow in Agisoft PhotoScan software. All types of data were complementary for the study of the movement and allowed us having a good spatial vision of the evolution of the most active part of the slope. A detailed structural analysis was performed from both LiDAR and SfM point clouds using Coltop3D (Jaboyedoff et al., 2007). Eight joint sets were detected, allowing us to estimate the susceptibility of the slope to three main failure mechanisms: planar sliding, wedge sliding and flexural toppling. Moreover, we carried out the 3D tracking of several homogenous rock compartments using the roto-translation matrix technique (Oppikofer et al., 2009) in order to quantify separately the translational and rotational components of displacements. Large-scale movements (from several dm to more than 10 m) were observed in the active area with a coupling between subsidence and toppling oriented towards the valley. Lateral structures that cut the rear active part also seem to be affected by a clockwise rotation around the topple axis. The acquisition of dense and accurate terrain information using LiDAR and SfM for studying the Séchilienne landslide has been useful for quantifying the 3D displacements and clarifying the failure mechanisms involved in the complex dynamic of the active part of the slope. Chanut, M-A., Dubois, L., Duranthon, J.P. (2014) Analyse de l'évolution du mouvement de terrain de Séchilienne à partir de données LiDAR. Journées Nationales de Géotechnique et de Géologie de l'Ingénieur JNGG2014 - Bauvais. Duranthon, J. P., & Effendiantz, L. (2004). Le versant instable des «Ruines» de Séchilienne. Bulletin des laboratoires des Ponts et Chaussées, 252, 253. Jaboyedoff, M., Metzger, R., Oppikofer, T., Couture, R., Derron, M. H., Locat, J., & Turmel, D. (2007). New insight techniques to analyze rock-slope relief using DEM and 3D-imaging cloud points: COLTOP-3D software, in: Rock mechanics: Meeting Society's Challenges and demands (Vol. 1, pp. 61-68). Kasperski, J., Potherat, P., & Duranthon, J. P. (2010). Le mouvement de versant de Séchilienne: point sur l'activité du phénomène, in: Rock Slope Stability (p. 13p). Oppikofer, T., Jaboyedoff, M., Blikra, L., Derron, M. H., & Metzger, R. (2009). Characterization and monitoring of the Åknes rockslide using terrestrial laser scanning, in: Natural Hazards and Earth SystemScience, 9(3), 1003-1019.

Effects of the earthquake of March 27, 1964 in the Copper River Basin area, Alaska: Chapter E in The Alaska earthquake, March 27, 1964: regional effects

USGS Publications Warehouse

Ferrians, Oscar J.

1966-01-01

The Copper River Basin area is in south-central Alaska and covers 17,800 square miles. It includes most of the Copper River Basin and parts of the surrounding Alaska Range and the Talkeetna, Chugach, and Wrangell Mountains. On March 27, 1964, shortly after 5:36 p.m. Alaska standard time, a great earthquake having a Richter magnitude of about 8.5 struck south-central Alaska. Computations by the U.S. Coast and Geodetic Survey place the epicenter of the main shock at lat 61.1° N. and long 147.7° W., and the hypocenter, or actual point of origin, from 20 to 50 kilometers below the surface. The epicenter is near the western shore of Unakwik Inlet in northern Prince William Sound; it is 30 miles from the closest point within the area of study and 180 miles from the farthest point. Releveling data obtained in 1964 after the earthquake indicates that broad areas of south-central Alaska were warped by uplift and subsidence. The configuration of these areas generally parallels the trend of the major tectonic elements of the region. Presumably a large part of this change took place during and immediately after the 1964 earthquake. The water level in several wells in the area lowered appreciably, and the water in many became turbid; generally, however, within a few days after the earthquake the water level returned to normal and the suspended sediment settled out. Newspaper reports that the Copper River was completely dammed and Tazlina Lake drained proved erroneous. The ice on most lakes was cracked, especially around the margins of the lakes where floating ice broke free from the ice frozen to the shore. Ice on Tazlina, Klutina, and Tonsina Lakes was intensely fractured by waves generated by sublacustrine landslides off the fronts of deltas. These waves stranded large blocks of ice above water level along the shores. River ice was generally cracked in the southern half of the area and was locally cracked in the northern half. In the area of study, the majority of the ground cracks occurred within a radius of 100 miles from the epicenter of the earthquake. Ground cracks formed in flood plains of rivers, in deltas, and along the toes of alluvial fans. They also occurred locally in low terraces adjacent to flood plains, in highway and other fill material, along the margins of lakes, along the faces of steep slopes of river bluffs and hillsides, and in areas cleared of vegetation for several years. The ground cracks were restricted to areas underlain by unconsolidated deposits where one or more of the following conditions existed: (1) permafrost was absent or deep lying, (2) the ground-water table was near the surface, (3) bedrock was relatively deep lying, and (4) slopes were steep. Because the earthquake occurred in March, seasonal frost was present throughout the area. Despite the diversity of local conditions, the origin of most of the ground cracks can be explained by the following mechanisms: (1) lateral extension, caused by materials moving toward an unconfined face such as a lakeshore, river bluff, hillside, or terrace escarpment; (2) horizontal compaction, caused by repeated alternate compression and dilation (in the horizontal direction) of materials in flat-lying areas where there are no unconfined faces; (3) differential vertical compaction, caused by the shaking of materials that vary laterally in thickness or character; and (4) combinations of the above. Snowslides, avalanches, and rockslides were restricted to the mountainous areas surrounding the Copper River Basin. They were especially numerous in the Chugach Mountains which are closest to the epicenter of the earthquake. The large amount of snow and rock debris that has cascaded onto the icefield and glaciers of these mountains, and, probably even more important, the overall disturbance to the ice field will affect the regimen of the glaciers. Most of the damage to manmade structures occurred in the southern half of the area, and, primarily because of the sparsity of population and manmade structures, property damage was not great and no lives were lost.

Micromechanical Analyses of Sturzstroms

NASA Astrophysics Data System (ADS)

Imre, Bernd; Laue, Jan; Springman, Sarah M.

2010-05-01

Sturzstroms are very fast landslides of very large initial volume. As type features they display extreme run out, pared with intensive fragmentation of the involved blocks of rock within a collisional flow. The inherent danger to the growing communities in alpine valleys below future potential sites of sturzstroms must be examined and results of predictions of endangered zones allow to impact upon the planning processes in these areas. This calls for the ability to make Type A predictions, according to Lambe (1973), which are done before an event. But Type A predictions are only possible if sufficient understanding of the mechanisms involved in a process is available. The motivation of the doctoral thesis research project presented is therefore to reveal the mechanics of sturzstroms in more detail in order to contribute to the development of a Type A run out prediction model. It is obvious that a sturzstrom represents a highly dynamic collisional granular regime. Thus particles do not only collide but will eventually crush each other. Erismann and Abele (2001) describe this process as dynamic disintegration, where kinetic energy is the main driver for fragmenting the rock mass. In this case an approach combining the type features long run out and fragmentation within a single hypothesis is represented by the dynamic fragmentation-spreading model (Davies and McSaveney, 2009; McSaveney and Davies, 2009). Unfortunately, sturzstroms, and fragmentation within sturzstroms, can not be observed directly in a real event because of their long "reoccurrence time" and the obvious difficulties in placing measuring devices within such a rock flow. Therefore, rigorous modelling is required in particular of the transition from static to dynamic behaviour to achieve better knowledge of the mechanics of sturzstroms, and to provide empirical evidence to confirm the dynamic fragmentation-spreading model. Within this study fragmentation and their effects on the mobility of sturzstroms have been made observable and reproducible within a physical and a distinct element numerical modelling environment (DEM). As link between field evidence gained from the deposits of natural sturzstroms, the physical model within the ETH Geotechnical Drum Centrifuge (Springman et al., 2001) and the numerical model PFC-3D (Cundall and Strack, 1979; Itasca, 2005), serves a deterministic fractal analytical comminution model (Sammis et al., 1987; Steacy and Sammis, 1991). This approach allowed studying the effects of dynamic fragmentation within sturzstroms at true (macro) scale within the distinct element model, by allowing for a micro-mechanical, distinct particle based, and cyclic description of fragmentation at the same time, without losing significant computational efficiency. Theses experiments indicate rock mass and boundary conditions, which allow an alternating fragmenting and dilating dispersive regime to evolve and to be sustained long enough to replicate the spreading and run out of sturzstroms. The fragmenting spreading model supported here is able to explain the run out of a dry granular flow, beyond the travel distance predicted by a Coulomb frictional sliding model, without resorting to explanations by mechanics that can only be valid for certain, specific of the boundary conditions. The implications derived suggest that a sturzstrom, because of its strong relation to internal fractal fragmentation and other inertial effects, constitutes a landslide category of its own. Its mechanics differ significantly from all other gravity driven mass flows. This proposition does not exclude the possible appearance of frictionites, Toma hills or suspension flows etc., but it considers them as secondary features. The application of a fractal comminution model to describe natural and experimental sturzstrom deposits turned out to be a useful tool for sturzstrom research. Implemented within the DEM, it allows simulating the key features of sturzstrom successfully and consistent, based on standardised rock and rock mass properties. It also allows revealing the micro mechanical and energetically aspects of a sturzstrom, which suggests that the DEM, modified and developed in the frame of the research project is a promising tool for further research on sturzstroms. This study provides therefore good empirical evidences both to confirm the dynamic fragmentation-spreading model, and to provide a basis on which a successful Type A run out prediction model of sturzstrom may be developed. Cundall, P.A. and Strack, O.D.L., 1979. A discrete numerical model for granular assemblies. Géotechnique, 29(1): 47-65. Davies, T.R.H. and McSaveney, M.J., 2009. The role of rock fragmentation in the motion of large landslides. Engineering Geology, 109(1-2): 67-79. Erismann, T.H. and Abele, G., 2001. Dynamics of rockslides and rockfalls. Springer, Berlin, Heidelberg, Germany, 316 pp. Itasca, 2005. Particle Flow Code in 3 Dimensions. Itasca Consulting Group, Inc., Minneapolis, Minnesota. Lambe, T.W., 1973. The 13th Rankine Lecture, 1973: Predictions in soil engineering. Géotechnique, 23(2): 149-202. McSaveney, M.J. and Davies, T.R.H., 2009. Surface energy is not one of the energy losses in rock comminution. Engineering Geology, 109(1-2): 109-113. Sammis, C., King, G. and Biegel, R., 1987. The kinematics of gouge deformation. Pure and Applied Geophysics, 125(5): 777-812. Springman, S., Laue, J., Boyle, R., White, J. and Zweidler, A., 2001. The ETH Zurich Geotechnical Drum Centrifuge. International Journal of Physical Modelling in Geotechnics, 1(1): 59-70. Steacy, S.J. and Sammis, C.G., 1991. An automaton for fractal patterns of fragmentation. Nature, 353(6341): 250-252.

The Alaska earthquake, March 27, 1964: lessons and conclusions

USGS Publications Warehouse

Eckel, Edwin B.

1970-01-01

One of the greatest earthquakes of all time struck south-central Alaska on March 27, 1964. Strong motion lasted longer than for most recorded earthquakes, and more land surface was dislocated, vertically and horizontally, than by any known previous temblor. Never before were so many effects on earth processes and on the works of man available for study by scientists and engineers over so great an area. The seismic vibrations, which directly or indirectly caused most of the damage, were but surface manifestations of a great geologic event-the dislocation of a huge segment of the crust along a deeply buried fault whose nature and even exact location are still subjects for speculation. Not only was the land surface tilted by the great tectonic event beneath it, with resultant seismic sea waves that traversed the entire Pacific, but an enormous mass of land and sea floor moved several tens of feet horizontally toward the Gulf of Alaska. Downslope mass movements of rock, earth, and snow were initiated. Subaqueous slides along lake shores and seacoasts, near-horizontal movements of mobilized soil (“landspreading”), and giant translatory slides in sensitive clay did the most damage and provided the most new knowledge as to the origin, mechanics, and possible means of control or avoidance of such movements. The slopes of most of the deltas that slid in 1964, and that produced destructive local waves, are still as steep or steeper than they were before the earthquake and hence would be unstable or metastable in the event of another great earthquake. Rockslide avalanches provided new evidence that such masses may travel on cushions of compressed air, but a widely held theory that glaciers surge after an earthquake has not been substantiated. Innumerable ground fissures, many of them marked by copious emissions of water, caused much damage in towns and along transportation routes. Vibration also consolidated loose granular materials. In some coastal areas, local subsidence was superimposed on regional tectonic subsidence to heighten the flooding damage. Ground and surface waters were measurably affected by the earthquake, not only in Alaska but throughout the world. Expectably, local geologic conditions largely controlled the extent of structural damage, whether caused directly by seismic vibrations or by secondary effects such as those just described. Intensity was greatest in areas underlain by thick saturated unconsolidated deposits, least on indurated bedrock or permanently frozen ground, and intermediate on coarse well-drained gravel, on morainal deposits, or on moderately indurated sedimentary rocks. Local and even regional geology also controlled the distribution and extent of the earthquake's effects on hydrologic systems. In the conterminous United States, for example, seiches in wells and bodies of surface water were controlled by geologic structures of regional dimension. Devastating as the earthquake was, it had many long-term beneficial effects. Many of these were socioeconomic or engineering in nature; others were of scientific value. Much new and corroborative basic geologic and hydrologic information was accumulated in the course of the earthquake studies, and many new or improved investigative techniques were developed. Chief among these, perhaps, were the recognition that lakes can be used as giant tiltmeters, the refinement of methods for measuring land-level changes by observing displacements of barnacles and other sessile organisms, and the relating of hydrology to seismology by worldwide study of hydroseisms in surface-water bodies and in wells. The geologic and hydrologic lessons learned from studies of the Alaska earthquake also lead directly to better definition of the research needed to further our understanding of earthquakes and of how to avoid or lessen the effects of future ones. Research is needed on the origins and mechanisms of earthquakes, on crustal structure, and on the generation of tsunamis and local waves. Better earthquake-hazard maps, based on improved knowledge of regional geology, fault behavior, and earthquake mechanisms, are needed for the entire country. Their preparation will require the close collaboration of engineers, seismologists, and geologists. Geologic maps of all inhabited places in earthquake-prone parts of the country are also needed by city planners and others, because the direct relationship between local geology and potential earthquake damage is now well understood. Improved and enlarged nets of earthquake-sensing instruments, sited in relation to known geology, are needed, as are many more geodetic and hydrographic measurements. Every large earthquake, wherever located, should be regarded as a full-scale laboratory experiment whose study can give scientific and engineering information unobtainable from any other source. Plans must be made before the event to insure staffing, funding, and coordination of effort for the scientific and engineering study of future earthquakes. Advice of earth scientists and engineers should be used in the decision-making processes involved in reconstruction after any future disastrous earthquake, as was done after the Alaska earthquake. The volume closes with a selected bibliography and a comprehensive index to the entire series of U.S. Geological Survey Professional Papers 541-546. This is the last in a series of six reports that the U.S. Geological Survey published on the results of a comprehensive geologic study that began, as a reconnaissance survey, within 24 hours after the March 27, 1964, Magnitude 9.2 Great Alaska Earthquake and extended, as detailed investigations, through several field seasons. The 1964 Great Alaska earthquake was the largest earthquake in the U.S. since 1700. Professional Paper 546, in 1 part, describes Lessons and Conclusions.

Large rock avalanches in southern Perù: the Cerro Caquilluco - Cerrillos Negros rock slide - avalanche (Tacna, Tomasiri, Perù)

NASA Astrophysics Data System (ADS)

Crosta, G.; Hermanns, R. L.; Murillo, P. V.

2012-04-01

The Andean bent which coincides with the Peruvian-Chilean border region is characterised by one of the largest relief contrasts on earth with depth of the subduction trench ranging from 5000 to 6000 m below sea level and mountain tops ranging from 5500 to 6300 m a.s.l.. The western flank of the Andes is subdivided in 4 major geologic zones (i.e. Coastal Cordillera, longitudinal Basin or depression, the Precordillera or western escarpment and western Cordillera). Local relief contrasts are also pronounced due to the incision of deep canyons into several million old uplifted surfaces, preserved because of the extremely dry climate with precipitation averaging a few mm and less per year. The Lluta collapse (minimum age of 2.5 Ma; volume 26 km3) is one of the largest non-volcanic non-marine landslides on Earth and has been mapped in that area (Wörner et al., 2002). Systematic mapping in northern Chile and Southern Peru has revealed that this is not the only gigantic landslide in the area but that further landslides of similar size occurred in the area, located both along the canyon slopes and along the western escarpment of the Cordillera. This suggests that landsliding has been a major factor in controlling erosion. This contribution describes first results on mapping a giant landslide complex in southern Perù called the Cerro Caquilluco - Cerrillos Negros Tomasiri rock slide - avalanche complex. The systematic mapping we have carried out in the area is presented in a further contribution to this conference. The Cerro Caquilluco - Cerrillos Negros Tomasiri rock slide - avalanche complex affected the upper part of a SW dipping paleosurface (8° to 9°) cut by a disconnected and regular primitive drainage network organized in a series of SW trending parallel valleys. This network developed within the lower Miocene pinkish tuffaceous deposits of the Huaylillas formation, whereas the main landslide scarp lies within the conglomerates of the Upper Moquegua formation (lower Oligocene). The same type of landscape is found to the southeast of Tacna and Arica (Huaylillas anticline, Oxaya anticline and Sucuna homocline) The Cerro Caquilluco - Cerrillos Negros Tomasiri rock slide - avalanche complex has a total length of about 43 km, a source area width and length of about 4 km and 5.1 km, respectively. The computed fahrböschung is equal to 4.6° with an H/L ratio of about 0.08 and resulting in an extremely large excessive travel distance. The H/L value is well below the expected value computed according to the classical (H/L) vs volume empirical relationships presented in the literature. Deposition occurred along most of the transportation area and is evidenced by a series of wide lobes (10 to 65 m high) and levees (from a few meters to some tens of meters high) with an average extent of 8 km transversally to the flow direction. Flow structures are visible all over the transportation area and several lobes can be mapped out. Presently, we cannot determine if most of these failures belong to a consequent large retrogressive event or to different events separated in time. The longest lobe has only pristine morphology in the most distal part of the accumulation area. Here the deposit is represented by a unique tongue shaped deposit, 11 km long, 3 km wide and 25 to 60 m thick (rough volume estimate 1.15 km3) ), deposited along the piedmont surface (ave. slope: 2°). This deposit presents a series of features typical of rock avalanches deposited on regular smooth surfaces, like: lateral levees, longitudinal and transversal ridges and furrows. The extreme runout of this failure could be explained assuming a single failure event or the detachment from a part of the slope located well below the present day upper scarp. In the middle part of the deposition/transportation area few lateral levees are preserved and deep valleys have been eroded into the deposit. Considering the relationship with the piedmont deposits and the faults cutting through the area the deposit could be up to 2-2.3 Ma old. The morphology of this lower lobe is contrasting to the upper lobes which smooth out the landscape. The minimum volume involved in the giant rockslide-avalanche complex amounts to about 9 km3. The headscarp area is affected by smaller and likely younger rock avalanche lobes overlying the more massive rock-avalanche lobe complex. These features are well preserved also to the west of the main slide complex, along the E-W trending high scarp cutting the old paleosurface, where more pristine rock avalanche lobes with more blocky surfaces overlie older lobes characterized by a smooth topography cut by high scarps. Conditioning factors of the slope instabilities could have been: the SW dipping of weak formations (tuffs and conglomerates), the presence of ENE trending sinistral faults offsetting the primitive drainage network close to the headscarp, the intense seismicity and/or a wetter climate, the continuous uplift (min. 0.04-0.3 mm/yr). This area is less than 230 km away from the subduction trench and magnitude 7 to 9 earthquakes occur on average every 100 years on the subduction segment. Megathrust earthquakes are quite common in the area on geological time scales and no big landslides of that site has been reported during multiple historic subduction earthquakes in southern Peru and northern Chile. Some results concerning slope stability analyses and runout modelling are presented to support possible failure mechanisms and to understand the exceptional avalanche mobility.

Seismic and tsunami hazard in Puerto Rico and the Virgin Islands

USGS Publications Warehouse

Dillon, William P.; Frankel, Arthur D.; Mueller, Charles S.; Rodriguez, Rafael W.; ten Brink, Uri S.

1999-01-01

Executive SummaryPuerto Rico and the Virgin Islands are located at an active plate boundary between the North American plate and the northeast corner of the Caribbean plate. The region was subject in historical times to large magnitude earthquakes and devastating tsunamis. A major downward tilt of the sea floor north of Puerto Rico and the Virgin Islands, large submarine rockslides, and an unusually large negative gravity anomaly are also indicative of a tectonically active region. Scientists have so far failed to explain the deformation of this region in a coherent and predictable picture, such as in California, and this has hampered their ability to assess seismic and tsunami hazards in the region. The NE corner of the Caribbean is unique among the seismically-active regions of the United States in that it is mostly covered by water. This fact presents an additional challenge for seismic and tsunami hazard assessment and mitigation.The workshop, convened in San Juan on March 23-24, 1999, was "historic" in that it brought together for the first time a broad spectrum of scientists, engineers, and public and private sector officials who deal with such diverse questions as tectonic models, probabilistic assessment of seismic hazard, prediction of tsunami runup, strong ground motion, building codes, stability of man-made structures, and the public’s preparedness for natural disasters. It was an opportunity for all the participants to find out how their own activity fit into the broad picture of science and how it aids society in hazard assessment and mitigation. In addition, the workshop was offered as a continuing education course at the Colegio de Ingenieros y Agrimensores de Puerto Rico, which assured a rapid dissemination of the results to the local community. A news conference which took place during the workshop alerted the public to the efforts of the USGS, other Federal agencies, the Commonwealth of Puerto Rico, universities and the private sector.During the first day of the workshop, participants from universities, federal institutions, and consulting firms in Puerto Rico, the Virgin Islands, the continental U.S., Dominican Republic, and Europe reviewed the present state of knowledge including a review and discussion of present plate models, recent GPS and seismic reflection data, seismicity, paleoseismology, and tsunamis. The state of earthquake/tsunami studies in Puerto Rico was presented by several faculty members from the University of Puerto Rico at Mayaguez. A preliminary seismic hazard map was presented by the USGS and previous hazard maps and economic loss assessments were considered. During the second day, the participants divided into working groups and prepared specific recommendations for future activities in the region along the six following topics below. Highlights of these recommended activities are:Marine geology and geophysics – Acquire deep-penetration seismic reflection and refraction data, deploy temporary ocean bottom seismometer arrays to record earthquakes, collect high-resolution multibeam bathymetry and side scan sonar data of the region, and in particular, the near shore region, and conduct focussed high-resolution seismic studies around faults. Determine slip rates of specific offshore faults. Assemble a GIS database for available marine geological and geophysical data.Paleoseismology and active faults - Field reconnaissance aimed at identifying Quaternary faults and determining their paleoseismic chronology and slip rates, as well as identifying and dating paleoliquefaction features from large earthquakes. Quaternary mapping of marine terraces, fluvial terraces and basins, beach ridges, etc., to establish framework for understanding neotectonic deformation of the island. Interpretation of aerial photography to identify possible Quaternary faults.Earthquake seismology – Determine an empirical seismic attenuation function using observations from local seismic networks and recently-installed broad-band stations. Evaluate existing earthquake catalogs from local networks and regional stations, complete the catalogs. Transcribe the pre-1991 network data from 9-track tape onto more stable archival media. Calibrate instruments of local networks. Use GPS measurement to constrain deformation rates used in seismic-hazard maps.Engineering – Prepare liquefaction susceptibility maps for the urban areas. Update and improve databases for types of site conditions. Collect site effect observations and near-surface geophysical measurements for future local (urban-area) hazard maps. Expand the number of instruments in the strong motion program. Develop fragility curves for Puerto Rico construction types and details, and carry out laboratory testing on selected types of mass-produced construction. Consider tsunami design in shoreline construction projects.Tsunami hazard - Extract tsunami observations from archives and develop a Caribbean historical tsunami database. Analyze prehistoric tsunami deposits. Collect accurate, up-to-date, near-shore topography and bathymetry for accurate inundation models. Prepare tsunami flooding and evacuation maps. Establish a Caribbean Tsunami Warning System for Puerto Rico and the Virgin Islands. Evaluate local, regional, national, and global seismic networks and equipment, and their role in a tsunami warning system.Societal concerns – Prepare warning messages, protocols, and evacuation routes for earthquake, tsunami, and landslide hazards for Puerto Rico and the U.S. Virgin Islands. Advocate enforcement of existing building codes. Prepare non-technical hazard assessment maps for political and educational uses. Raise the awareness of potentially affected populations by presentations at elementary schools, by the production of a tsunami video, and by distribution of earthquake preparedness manuals in newspaper supplements. Promote partnerships at state and federal level for long-term earthquake and tsunami hazard mitigation. This partnership should also include the private sector such as the insurance industry, telecommunication companies, and the engineering community.The following reports of the various working groups are the cumulative recommendations of the community of scientists, engineers, and public officials, who participated in the workshop. The list of participants and the workshop’s agenda are given in the appendix.Marine and Geology and Geophysics Working GroupPaleoseismology and Active Faults Working GroupJoint Working Group for Earthquake Seismology and EngineeringTsunami Working GroupSocietal Concerns Working Group

Monitoring the Dynamic of a Fluvial Channel after Lahar Disturbance: Huiloac Gorge (Popocatepetl Volcano, Mexico)

NASA Astrophysics Data System (ADS)

Andres, N.; Palacios, D.; Zamorano, J. J.; Tanarro, L. M.; Renschler, C.; Sanjosé, J. J.; Atkinson, A.

2009-04-01

Volcanic eruptions generate disturbances that affect hydrological systems (Major, 2003) by depositing large volumes of sediments in watersheds that exceed amounts common to non-volcanic river systems (Montgomery, 2005). If the eruption releases abundant melt water, the river system may respond immediately by forming hazardous flows called lahars. River system recovery following eruptive and laharic impact is an important process, but it has received little attention (Gran and Montgomery, 2005) despite the fact that Major et al. (2000) and Hayes et al. (2002) have shown that these disruptions cause long term instability and their effects persist for decades. Lahar deposits resulting from interaction between volcanic activity and the glacier located above the Huiloac Gorge on the northern slope of Popocatepetl volcano (19°02´ N, 98°62´ W, 5,424 m), have infilled the gorge (Palacios, 1995; Palacios et al., 1998 and 2001; Capra et al., 2004; Muñoz, 2007). All of the major lahars that occurred on the volcano in 1995 (4 km), 1997 (21 km), and 2001 (14 km) have channelled through Huiloac Gorge, and have dramatically altered its morphology and dynamics through erosion and deposition. The present study traces these changes in the aftermath of the laharic events that occurred from 1997-2001. A sector of the channel, located at 3200m-3240m altitude, of 500 m long and 15 to 20 m wide, in the mid-section of the gorge, was chosen as the control site. Precipitation is heaviest there and is most apt to trigger secondary post-eruptive lahars. ArcGis software was used to draw 6 geomorphic maps of the site showing spatial variations in the landforms for the period February 2002 - February 2008. In addition, 29 cross-profiles were made of the gorge for the same time interval, excluding February 2004. The volume of sediment eroded and deposited was calculated for each date by comparing variations in the height of the floor and banks of the gorge depicted in the cross-profile, and estimating the volume of erosion and deposition for a given time interval. Analysis of the geomorphic variations for the period February 2002-February 2008, shows that the banks formed by lahar deposits in 1997 and 2001 at the study site receded from 48.6% to 27.4% in favor of the riverbed, and 31.0% to 52.7%, in favor of the terraces formed by secondary lahars. The time sequence for the cross-profiles depicts a general widening and infilling of the gorge floor, with greater emphasis on erosion from September 2003-February 2008 (1523 m3as compared to 387 m3of accretion). The changes, however, were not homogeneous during the study period, due to varying rainfall patterns that cause fluctuations in runoff. This relationship became evident after comparing geomorphologic and topographic alterations and heavy precipitation (maximum/24 hrs), and variations in monthly precipitation yield and average yield for the period 1971-2000 (data provided by the Mexico's National Meteorological Service). Although both lower slope recession and lahar-induced deposition on the floor of the channel increased during the period February-October 2002, down cutting and evacuation of materials (677 m3) greatly surpassed deposition (145 m3). The predominance of one process in relation to another was much more acute for this period than for any other, even though it occurred during a relatively dry rainy season with below average precipitation. The explanation for this is attributed to the onset of lahar activity in January 2001 and high maximum rainfall late in the rainy season. This was followed by a dry spell and a second very wet rainy season from October 2002 - September 2003. During this time, the slopes continued to recede in favor of the riverbed, where some down cutting and infilling occurred, resulting in a slight net gain in surface area. During the next five months of the dry season, changes in the landforms were proportionally greater, producing a substantial increase in surface area and laharic deposition formations. These features are attributed to an unusually long rainy season with above average values in October, and to atypical precipitation in the normally dry month of January. Modifications in the surface area from February 2004-March 2006 reached 19.2%, a decrease from the previous two-year period (28.1%), which was caused by a slight increase in average precipitation in 2004 and a marked decrease in 2005. Values for erosion (620 m3) and deposition (621 m3) are similar for the period from September 2003 - March 2005, and the slopes receded slowly as new laharic deposits increased the level of the channel floor. The final two-year interval shows an increase in changes (31.1%) where the receding sides of the banks affected the ridges of the levees, and the floor of the channel, marked by areas of deposition and incision, became flatter and wider. The increased activity is associated with the prolonged effect of El Niño (ENSO), more rainfall during the 2006 rainy season, and below reference values for 2007 for the average wet and dry seasons. The volume of material removed and accreted was 1424 m3 and 277 m3, respectively. Changes occurring in the channel to recover equilibrium in the river system included the widening and infilling of the floor, but these alterations were largely conditioned by increased water supply that triggered secondary lahars. The short interval between deposition by the primary lahar and the exceptionally heavy precipitation at the end of the rainy season, contributed to increased erosion of the gorge. The time intervals that registered below average precipitation are characterized by less surface disturbances and greater infilling of the channel floor. The opposite is true for the rainy seasons with above average values when slope erosion caused uneven deposition on the channel floor, or during the dry months that registered the most significant changes in response to episodes of exceptional heavy rainfall. References Capra, L.; Poblete, M.A. and Alvarado, R. 2004. The 1997 and 2001 lahars of Popocatépetl volcano (Central Mexico): textural and sedimentological constraints on their origin and hazards. Journal of Volcanology and Geothermal Research, 131: 351-369. Gran, K. y Montgomery, D., 2005. Spatial and temporal patterns in fluvial recovery following volcanic eruptions: Channel response to basin-wide sediment loading at Mount Pinatubo, Philippines. GSA Bulletin, 117; 1-2: 195-211. Hayes, S.K., Montgomery, D.R. and Newhall, C.G., 2002, Fluvial sediment transport and deposition following the 1991 eruption of Mt. Pinatubo. Geomorphology. Vol. 45: 211-224. Major, J.J., Pierson, T.C., Dinehart, R.L. y Costa, J.E. 2000. Sediment yield following severe volcanic disturbance- A two-decade perspective from Mount St. Helens. Geology, 28, n° 9: 819-822. Major, J.J., 2003. Post-eruption hydrology and sediment transport in volcanic river systems, Water Resources IMPACT, 5(3): 10-15. Muñoz, E. 2007. Los lahares del Popocatépetl: tratamiento de la información para la prevención de catástrofes. (PhD thesis, Universidad Complutense de Madrid.) Palacios, D., 1995. Rockslide processes on the north slope of Popocatépetl Volcano, Mexico, Permafrost and Periglaciar Processes, 6: 345-356. Palacios, D., J.J. Zamorano and G. Parrilla. 1998. Proglacial debris flows in Popocatépetl North Face and their relation to 1995 eruption. Z. Geomorph. N. P., 42(3), 273-295 Palacios, D., J.J. Zamorano and A. Gómez. 2001. The impact of present lahars on the geomorphologic evolution of proglacial gorges: Popocatépetl, Mexico. Geomorphology, 37(1-2), 15-42.

Geologic effects of the March 1964 earthquake and associated seismic sea waves on Kodiak and nearby islands, Alaska: Chapter D in The Alaska earthquake, March 27, 1964: regional effects

USGS Publications Warehouse

Plafker, George; Kachadoorian, Reuben

1966-01-01

Kodiak Island and the nearby islands constitute a mountainous landmass with an aggregate area of 4,900 square miles that lies at the western border of the Gulf of Alaska and from 20 to 40 miles off the Alaskan mainland. Igneous and metamorphic rocks underlie most of the area except for a narrow belt of moderately to poorly indurated rocks bordering the Gulf of Alaska coast and local accumulations of unconsolidated alluvial and marine deposits along the streams and coast. The area is relatively undeveloped and is sparsely inhabited. About 4,800 of the 5,700 permanent residents in the area live in the city of Kodiak or at the Kodiak Naval Station. The great earthquake, which occurred on March 27, 1964, at 5:36 p.m. Alaska standard time (March 28,1964, 0336 Greenwich mean time), and had a Richter magnitude of 8.4-8.5, was the most severe earthquake felt on Kodiak Island and its nearby islands in modern times. Although the epicenter lies in Prince William Sound 250 miles northeast of Kodiak—the principal city of the area—the areal distribution of the thousands of aftershocks that followed it, the local tectonic deformation, and the estimated source area of the subsequent seismic sea wave, all suggest that the Kodiak group of islands lay immediately adjacent to, and northwest of, the focal region from which the elastic seismic energy was radiated. The duration of strong ground motion in the area was estimated at 2½ minutes. Locally, the tremors were preceded by sounds audible to the human ear and were reportedly accompanied in several places by visible ground waves. Intensity and felt duration of the shocks during the main earthquake and aftershock sequence varied markedly within the area and were strongly influenced by the local geologic environment. Estimated Mercalli intensities in most areas underlain by unconsolidated Quaternary deposits ranged from VIII to as high as IX. In contrast, intensities in areas of upper Tertiary rock ranged from VII to VIII, and in areas of relatively well indurated lower Tertiary and Mesozoic rocks, from VI to VII. Local subsidence of as much as 10 feet was widespread in noncohesive granular deposits through compaction, flow, and sliding that resulted from vibratory loading during the earthquake. This phenomenon, which was largely restricted to saturated beach and alluvial deposits or artificial fill, was locally accompanied by extensive cracking of the ground and attendant ejection of water and water-sediment mixtures. Numerous landslides, including a wide variety of rockfalls, rockslides, and flows along steep slopes, were triggered by the long-duration horizontal and vertical accelerations during the earthquake. The landslides are most numerous in a narrow belt along the southeast coast of Kodiak Island and the nearby offshore islands. Their abundance appears to be related to an area underlain predominantly by Tertiary rocks. Temporary and permanent changes of level occurred after the earthquake in some wells, lakes, and streams throughout the area; ice was cracked, and the salinity of a few wells increased. Permanent change of water level at some localities appears to be related to readjustments of fracture porosity by earthquake-induced movements of bedrock blocks. Increased salinity of wells in coastal areas resulted from encroachment of seawater into aquifiers after subsidence during the earthquake, and to flooding of watersheds by seismic sea waves. Vertical displacements, both downward and upward, occurred throughout the area as a result of crustal warping along a northeast-trending axis. Most of Kodiak and all of Afognak, Shuyak, and adjacent islands are within a regional zone of subsidence whose trough plunges gently northeastward and approximately coincides with the mountainous backbone of Kodiak Island. Subsidence in excess of 6 feet occurred throughout the northern part of the zone-a maximum subsidence of 6½ feet having occurred on Marmot and, eastern Afognak Islands. Southeast of the axis of tectonic tilting, uplift of at least 2lh feet occurred in a narrow zone that includes most of the southeasterly capes of Kodiak Island, the southeastern half of Sitkalidak Island, and Sitkinak Island. The uplift is inferred to extend offshore over much or all of the continental shelf adjacent to the Kodiak group of islands. Within the affected area, tectonic subsidence, which was locally augmented by surficial subsidence of unconsolidated. deposits, caused widespread inundation of shorelines and attendant damage to intertidal organisms, nearshore terrestrial vegetation, and salmon-spawning areas. The most devastating effect of the earthquake on Kodiak Island and nearby islands resulted from seismic sea waves that probably originated along a linear zone of differential uplift in the Gulf of Alaska. A train of at least seven seismic sea waves, having initial periods of 50–55 minutes, struck along all the southeast coast of the island group from 38 to 63 minutes after the earthquake. The southeast shores were repeatedly washed by destructive waves having runup heights along exposed coasts of perhaps as much as 40 feet above existing tide level, and of 8–20 feet along protected shores. Runup heights of the waves were much less on the northwest and southwest sides of the islands, and no wave damage was incurred there. Locally, high-velocity currents that accompanied the waves caused intense erosion and redistribution of unconsolidated natural and artificial shore deposits and of shallow sea-floor deposits. The Alaska earthquake was the greatest natural catastrophe to befall the Kodiak Island area in historic time. The combination of seismic shock and the earthquake-related tectonic deformation and seismic sea waves took 18 lives, destroyed property worth about $45 million, and resulted in estimated losses of income to the fishing industry of an additional $5 million. Most of the damage and all of the loss of life were directly attributable to the seismic sea waves that crippled the city of Kodiak, wiped out the village of Kaguyak, and destroyed most of the village of Old Harbor and parts of the villages of Afognak and Uzinki. Bridges and segments of the highways in the vicinity of the city of Kodiak were washed out, and parts of the Kodiak Naval Station were inundated and damaged. Especially serious to all the damaged communities was the loss of fishing boats, seafood processing plants, and other waterfront installations, which had been the mainstay of the economy. Additional heavy losses resulted from the combined regional tectonic and local surficial subsidence that occurred during the earthquake. Widespread shoreline flooding by high tides necessitated raising, protecting, or removing many installations otherwise undamaged by the earthquake or waves. Structural damage attributable to seismic shock during the earthquake was relatively light and was restricted to areas underlain by saturated unconsolidated deposits. The chief structural failure in the area as a result of shaking was the collapse of part of a cannery built on saturated beach deposits that were partially liquefied during the earthquake. Minor structural damage resulted from differential settlement and cracking of the ground on natural granular deposits and artificial fills. The overwhelming majority of structures are constructed on indurated bedrock; none of these sustained damage other than small losses resulting from shifting about and breakage of their contents.