Avalanche Source Research Articles

Uncovering avalanche sources via acceleration measurements

Avalanche sources describe rapid and local events that govern deformation processes in various materials. The fundamental differences between an avalanche source and its associated measured acoustic emission (AE) signal are encoded in the acoustic transfer function, which undesirably modifies the properties of the source. Consequently, information about the physical characteristics of avalanche sources is scarce and its exposure poses a great challenge. We introduce a novel experimental method based on acceleration measurements, which eliminates the effect of the transfer function and distills the avalanche source. Applying this method to deformation twinning in magnesium shows that the amplitudes and characteristic times of avalanche sources are unrelated by a clear physical law. Conversely, the amplitudes and durations of AE signals are related by a power law, which is attributed to the transfer function. Using our method, we identify and compute a new feature of avalanche sources, which is directly linked to the growth rate of the twinned volume. This feature displays a power-law distribution, implying an unpredicted behavior at dynamic criticality. Simultaneously, the characteristic times of avalanche sources possess an intrinsic upper bound, indicating a predicted limit that relates to the underlying physical process of twinning.

Wall heating by subcritical energetic electrons generated by the runaway electron avalanche source *

Subcritical energetic electrons (SEEs) produced by the runaway electron (RE) avalanche source at energies below the runaway threshold are found to be the primary contributor to surface heating of plasma-facing components (PFCs) during final loss events. This finding is supported by theoretical analysis, computational modeling with the Kinetic Orbit Runaway electrons Code (KORC), and qualitative agreement with DIII-D experimental observations. The avalanche source generates significantly more secondary electrons below the runaway threshold, which thermalize rapidly when well-confined. However, during a final loss event, the RE beam impacts the first wall, and SEEs are deconfined before they can thermalize. Additionally, because the energy deposition length decreases faster than energy, the deposited energy density, and thus the maximum PFC surface temperature change, is larger for SEEs than REs. KORC simulations employ an analytic first wall to model particle deconfinement onto a non-axisymmetric wall composed of individual tiles. PFC surface heating is calculated using a 1D model extended to include an energy-dependent deposition length scale. Simulations of DIII-D qualitatively agree with infrared (IR) imaging only when SEEs from the avalanche source are included. These results demonstrate that SEEs are the dominant contributor to PFC surface heating and indicate that the avalanche source plays a critical role in the PFC damage caused during final loss events. The prominence of SEEs also has important implications for interpreting IR imaging, one of the primary diagnostics for RE-wall interaction diagnosis, despite REs dominating the energy and current density. This result improves predictions of wall damage due to post-disruption REs to estimate material lifetime and design RE mitigation systems for ITER and future reactors.

Modeling Potential Glacial Lake Outburst Flood Process Chains and Effects From Artificial Lake‐Level Lowering at Gepang Gath Lake, Indian Himalaya

AbstractGlacial lake outburst floods (GLOFs) are a severe threat to communities in the Himalayas; however, GLOF mitigation strategies have been implemented for only a few lakes, and future changes in hazard are rarely considered. Here, we present a comprehensive assessment of current and future GLOF hazard for Gepang Gath Lake, Western Himalaya, considering rock and/or ice avalanches cascading into the lake. We consider ground surface temperature and topography to define avalanche source zones located in areas of potentially degrading permafrost. GLOF process chains in current and future scenarios, also considering engineered lake lowering of 10 and 30 m, were evaluated. Here, varied avalanche impact waves, erosion patterns, debris flow hydraulics, and GLOF impacts at Sissu village, under 18 different scenarios were assessed. Authors demonstrated that a larger future lake does not necessarily produce larger GLOF events in Sissu, depending, among other factors, on the location from where the triggering avalanche initiates and strikes the lake. For the largest scenarios, 10 m of lowering reduces the high‐intensity zone by 54% and 63% for the current and future scenarios, respectively, but has little effect on the medium‐intensity flood zone. Even with 30 m of lake lowering, the Sissu helipad falls in the high‐intensity zone under all moderate‐to‐large scenarios, with severe implications for evacuations and other emergency response actions. The approach can be extended to other glacial lakes to demonstrate the efficiency of lake lowering as an option for GLOF mitigation and enable a robust GLOF hazard and risk assessment.

Cosmogenic age constraints on rock avalanches in the Qinling Range associated with paleoearthquake activity, central China

Although it is generally assumed that understanding the trigger factor leading to the transition from a progressive rock failure toward sudden and rapid events is better to risk management, the ability to identify triggering factors responsible for prehistoric catastrophic rock avalanches is still debated. Here we describe two rock avalanches (Ganqiu and Shuiqiu) in the Cuihua Mountain area of the Qinling Range, China, providing new mapping of rock avalanche source areas and deposits and absolute age constraint from cosmogenic 10Be surface exposure dating. Results reveal that the Ganqiu rock avalanche is controlled by three sets of joints, causing the 380 m high ridge to collapse. Debris filled roughly the entire V-shaped valley and has a width ranging from 250 to 470 m, extending ~1260 m from the base of the cliff. The Shuiqiu rock avalanche was sourced near the summit of Cuihua Mountain from a cliff above 60° that is mainly controlled by inherited fault and joints. The rock mass fell ~250 m as a giant blocky stream across the width of the valley floor, with the deposit extending ~300 m from the base of the cliff. Both events caused the large-scale collapse of ridge crests and developed into high-mobility rock avalanches with long runout. Cosmogenic 10Be surface exposure dating from seven different parts of the deposits revealed nearly coincident ages for both rock avalanches, 10.0 ± 0.9 ka for the Ganqiu rock avalanche and 9.5 ± 1.2 ka for the Shuiqiu rock avalanche. Because this region was not affected by valley glaciation, rock avalanches triggering by paraglacial stress release can be excluded. Moreover, without clear evidence for specific climatic conditions in the Qinling area circa 9–10 ka, a climatic trigger for the Cuihua Mountain rock avalanches is equivocal. Instead, we find coincidence between the concurrent exposure ages and paleoseismic records from the nearby Qinling North Piedmont fault (QNF). This coincidence of ages, combined with the fact that the Mw 8.0 1556 CE Huaxian earthquake triggered numerous large rock falls in the Huashan Mountains at the eastern end of the Qinling Range, suggest that a large-magnitude earthquake centered in the middle-east section of QNF at ca. 8–11 ka may have triggered the Ganqiu and Shuiqiu rock avalanches.

New Insights into Ice Avalanche-Induced Debris Flows in Southeastern Tibet Using SAR Technology

Drastic climate change has led to glacier retreat in southeastern Tibet, and the increased frequency and magnitude of heavy rainfall and intense snow melting have intensified the risk of ice avalanche-induced debris flows in this region. To prevent and mitigate such hazards, it is important to derive the pre-disaster evolutionary characteristics of glacial debris flows and understand their triggering mechanisms. However, ice avalanche-induced debris flows mostly occur in remote alpine mountainous areas that are hard for humans to reach, which makes it extremely difficult to conduct continuous ground surveys and optical remote sensing monitoring. To this end, synthetic aperture radar (SAR) images were used in this study to detect and analyze the pre-disaster deformation characteristics and spatial evolution in the Sedongpu Basin and to detect changes in the snowmelt in the basin in order to improve our understanding of the triggering mechanism of the ice avalanche-induced debris flows in this region. The results revealed that the maximum average deformation rate in the basin reached 57.3 mm/year during the monitoring period from January 2016 to October 2018. The deformation displacement in the gully where the ice avalanche source area was located was intimately correlated with the summer snowmelt and rainfall and was characterized by seasonal accumulation. Clear acceleration of the deformation was detected after both the most recent earthquake and the strong rainfall and snowmelt processes in the summer of 2018. This suggests that earthquakes, snowmelt, and rainfall were significant triggers of the Sedongpu ice avalanche-induced debris flows. The results of this study provide new insights into the genesis of the Sedongpu ice avalanche-induced debris flows, which could assist in disaster warning and prevention in alpine mountain regions.

Evolution and temporal constraints of a multiphase postglacial rock slope failure

Large rock slope failures are temporal processes which act to modify the landscape after glacial retreat. The slope failure process often shows a lag time of thousands of years after deglaciation, with multiple failure events possible. While global datasets constrain this lag time from extensive mapping and dating of paraglacial rock avalanches, the timeline is poorly refined in northern Norway. We present a case study of multiphase failure at Skredkallen on Vanna, one of a group of coastal islands in Troms, northern Norway. The site contains an actively deforming rock slope above a large rock avalanche deposit. The rock slope deformation (RSD) is a system of fractured and dislocated blocks up to 3 Mm3, and is moving slowly ~5 mm/yr downslope to the north-east. The metasedimentary rock mass contains four pervasive joint sets and a foliation, contributing to a compound structure failure mechanism. The rock mass is further weakened by foliation-parallel sheared mylonite, and the presence of a brittle fault in the immediate area, with evidence of hydrothermal fluid flow though the RSD.The rock avalanche deposit below the slope deformation is calculated to be 3 Mm3, and extends >1 km from the source area, displaying typical mobility for north Norwegian rock avalanches onto undrained sediments. The deposits showcase exceptional lobate morphology with elongated ridge-and-furrow features. Raised shorelines predating and postdating the deposit provide temporal constraints on the deposit and an opportunity to reconstruct a relative timeline for the slope evolution. The postglacial marine limit (>14 cal. ka BP) is obscured by the deposit, while shorelines corresponding to the early Younger Dryas (12.2 cal. ka BP) and the subsequent Tapes transgression maximum (7.6–7.2 cal. ka BP) are prominent across the deposits, implying that the avalanche was emplaced between 15 and 12.2 cal. ka BP. Failure occurred during a time of immense climate instability at the boundary to the early Holocene, consistent with global reports of mountain slope failure following glacial retreat. The avalanche was emplaced into what would have been the marine environment. The anomaly between the rock avalanche source area volume (35 Mm3), and the rock avalanche deposit implies previous failure events, the deposits of which were either removed due to failure of the underlying marine sediments into the fjord, by retreating glacial ice or scour. The initiation of movement at the RSD may be attributed to periods of local climate changes, such as the Holocene Thermal Maximum. Cosmogenic nuclide dating is suggested as the next step to fill gaps in the slope evolution story through the mid to late Holocene.

Registration of avalanches in the Khibiny Mountains by the geophysical methods

In the winter months of 2018-2020 the Kola Branch of the Unified Geophysical Service RAS conducted experiments on the joint registration of avalanches in the Khibiny mountain range using seismic and infrasonic sensors during work on the forced descent of the snow mass. The aim of the experiments is to assess the possibility of avalanche detection using the geophysical methods. The lack of representative statistics on the frequency and regularity of avalanches is the reason for the relevance of developing methods of their remote registration. The difficulty of registering avalanches is due to their occurrence often in hard-to-reach areas and in poor visibility conditions. To record signals generated by avalanches, different configurations of infrasound panels consisting of three spatially separated sensors (MPA 201 or Hyperion IFS-4000 microbarographs) and a portable seismic station Guralp CMG-6TD were used. As a result of the experiments, infrasound recordings were obtained at different distances from the avalanche source. The infrasound group recordings collected from the experiments were processed using an automatic detector implementing amplitude and cross-correlation signal detection methods. The spectral composition of the recordings and their characteristic appearance were analyzed. Avalanche-induced signals are characterized by long duration and changes in azimuth to the source. The dominant frequencies of the signal lie in the region of 1-10 Hz. Conclusions are made about the insufficient sensitivity of the seismic method when the seismometer is located at a distance of the first kilometers from the avalanche source, as well as the high applicability of the infrasound method for recording the facts of avalanches. The results obtained will make it possible to develop a methodology for automatic detection of signals generated by avalanches using the data of infrasound registration. This is the necessary basis for building a system for continuous monitoring of avalanche activity.

Snow Avalanche Detection and Source Constraints Made Using a Networked Array of Infrasound Sensors

AbstractWe studied a triggered snow avalanche (∼60 s in duration and with ∼1,100 m run‐out) using a network of infrasound arrays and time‐synced video, with the objective of understanding the relationship between infrasound generation and flow dynamics. Using standard array processing techniques, we compared the infrasound source back azimuths with the avalanche flow path identified by frame‐differenced, geo‐referenced video. Results show that infrasound records begin with direct arrivals followed by echoes from the avalanche‐triggering explosions and these decay within 35 s of the detonations. Subsequent infrasound, which lasts 20–30 s, could then be attributed exclusively to the avalanche. These infrasound detections, and their triangulated source locations, progress downhill over time and the most intense infrasound appears to originate from a steep, mid‐path cliff band, where the avalanche reached speeds in excess of 30 m/s and accelerations of more than 5 m/s2. The recorded infrasound was compared to two candidate source models extracted from video: total flow motion and advancing flow motion. Advancing source locations were compared to acoustic intensity time series using a nonnegative least squares inversion to solve for, and to quantify, time‐varying infrasound source intensity. We observed that certain portions of the flow, most notably the early stages and the end stages (when the powder cloud was expanding and settling) were infrasonically quiet.

A 60-GHz SiGe Radiometer Calibration Switch Utilizing a Coupled Avalanche Noise Source

This letter presents a novel implementation of a ${V}$ -band single-pole double-throw switch that facilitates the internal calibration of radiometers by integrating an ambient noise source and an avalanche noise source. The switch is implemented in a 0.13- $\mu \text{m}$ SiGe bipolar-CMOS (BiCMOS) process and uses a shunt topology with $\lambda $ /4 directional couplers that inject noise from the avalanche source. The avalanche source is implemented using the collector-base junction of a SiGe heterojunction bipolar transistor (HBT) and attains a measured excess noise ratio of 18.7 dB at 60 GHz. The switch achieves a midband insertion loss of 2.0 dB and an isolation of 22 dB at 60 GHz. An excess input-referred noise temperature of 620 K is added with the noise source ON. To the best of our knowledge, this is the first avalanche noise source using a diode-configured SiGe HBT and the first monolithic two-reference switch for calibrating millimeter-wave radiometers.

A new approach to mapping landslide hazards: a probabilistic integration of empirical and physically based models in the North Cascades of Washington, USA

Abstract. We developed a new approach for mapping landslide hazards by combining probabilities of landslide impacts derived from a data-driven statistical approach and a physically based model of shallow landsliding. Our statistical approach integrates the influence of seven site attributes (SAs) on observed landslides using a frequency ratio (FR) method. Influential attributes and resulting susceptibility maps depend on the observations of landslides considered: all types of landslides, debris avalanches only, or source areas of debris avalanches. These observational datasets reflect the detection of different landslide processes or components, which relate to different landslide-inducing factors. For each landslide dataset, a stability index (SI) is calculated as a multiplicative result of the frequency ratios for all attributes and is mapped across our study domain in the North Cascades National Park Complex (NOCA), Washington, USA. A continuous function is developed to relate local SI values to landslide probability based on a ratio of landslide and non-landslide grid cells. The empirical model probability derived from the debris avalanche source area dataset is combined probabilistically with a previously developed physically based probabilistic model. A two-dimensional binning method employs empirical and physically based probabilities as indices and calculates a joint probability of landsliding at the intersections of probability bins. A ratio of the joint probability and the physically based model bin probability is used as a weight to adjust the original physically based probability at each grid cell given empirical evidence. The resulting integrated probability of landslide initiation hazard includes mechanisms not captured by the infinite-slope stability model alone. Improvements in distinguishing potentially unstable areas with the proposed integrated model are statistically quantified. We provide multiple landslide hazard maps that land managers can use for planning and decision-making, as well as for educating the public about hazards from landslides in this remote high-relief terrain.

Globally scalable alpine snow metrics

Horizontal and altitudinal redistribution of snow by wind transport and avalanches can be important controls on small- and large-scale snow accumulation patterns that control meltwater supply in alpine environments. Redistribution processes control the spatial variability of snow accumulation, which not only controls meltwater supply, but also regulates snowmelt timing, duration, and rates, as well as snow-covered area depletion and the variable contributing area for meltwater runoff generation. However, most hydrological models and land surface schemes do not consider snow redistribution processes, and those that do are difficult to verify without spatially distributed snow depth measurements. These are rarely available in both high resolution and covering large scales. As an increased number of hydrological models include snow redistribution processes there is a need for additional snowcover metrics to verify snow redistribution schemes over large areas using readily available data.This study develops novel high-resolution (20 m), snowcover indices from remotely sensed imagery (Landsat-8 and Sentinel-2) to evaluate snow redistribution models over alpine areas without in-situ or airborne snow observations. A snowcover absence (SA) index, calculated from snow-free areas during the winter, identifies areas of wind erosion or avalanche source areas. A snowcover persistence (SP) index, calculated from snow-covered areas during the summer, identifies snow deposition in drifts and avalanche deposits.The snowcover indices captured the relative differences in surface observations of snow presence and absence between exposed and sheltered sites on an intensely instrumented ridge in the Canadian Rockies Hydrological Observatory. Within the Tuolumne River Basin in central California (1100 km2), the SP index captured roughly half of the spatial variability (R2 = 0.49 to 0.56) in peak SWE as estimated from airborne LiDAR-derived snow depths. At the individual mountain ridge scale (~800 m), variability in both ablation and snow redistribution controlled the SP patterns over 7979 ridges. Differences in shortwave irradiance explained 76% of the SP variance across ridges, but could not explain smaller-scale (~100 m) SP peaks that are associated with snowdrifts and avalanche deposits. The snowcover indices can be used to evaluate snow redistribution models of the finer scale impacts of snow redistribution by wind and gravity as long as the larger scale influences of spatially variable solar irradiance effects are also simulated.

Multiple remote-sensing assessment of the catastrophic collapse in Langtang Valley induced by the 2015 Gorkha earthquake

Abstract. The main shock of the 2015 Gorkha Earthquake in Nepal induced numerous avalanches, rockfalls, and landslides in Himalayan mountain regions. A major village in the Langtang Valley was destroyed and numerous people were victims of a catastrophic avalanche event, which consisted of snow, ice, rock, and blast wind. Understanding the hazard process mainly depends on limited witness accounts, interviews, and an in situ survey after a monsoon season. To record the immediate situation and to understand the deposition process, we performed an assessment by means of satellite-based observations carried out no later than 2 weeks after the event. The avalanche-induced sediment deposition was delineated with the calculation of decreasing coherence and visual interpretation of amplitude images acquired from the Phased Array-type L-band Synthetic Aperture Radar-2 (PALSAR-2). These outline areas are highly consistent with that delineated from a high-resolution optical image of WorldView-3 (WV-3). The delineated sediment areas were estimated as 0.63 km2 (PALSAR-2 coherence calculation), 0.73 km2 (PALSAR-2 visual interpretation), and 0.88 km2 (WV-3). In the WV-3 image, surface features were classified into 10 groups. Our analysis suggests that the avalanche event contained a sequence of (1) a fast splashing body with an air blast, (2) a huge, flowing muddy mass, (3) less mass flowing from another source, (4) a smaller amount of splashing and flowing mass, and (5) splashing mass without flowing on the east and west sides. By means of satellite-derived pre- and post-event digital surface models, differences in the surface altitudes of the collapse events estimated the total volume of the sediments as 5.51 ± 0.09 × 106 m3, the largest mass of which are distributed along the river floor and a tributary water stream. These findings contribute to detailed numerical simulation of the avalanche sequences and source identification; furthermore, altitude measurements after ice and snow melting would reveal a contained volume of melting ice and snow.

Snow avalanche hazard of the Krkonoše National Park, Czech Republic

ABSTRACTThis paper presents a snow avalanche hazard map of the most avalanche-prone mountain range in the Czech Republic, the Krkonoše Mountains. The map was prepared using historical records of 1132 avalanches which occurred over the last 54 years and state-of-the-art modelling of avalanche propagation and the spatial distribution of potential avalanche source areas. The map provides not only reliable and easy to understand information for the Mountain Rescue Service of the Czech Republic and mountain tourists, but also for land use managers to identify areas where new avalanche paths may develop under favourable conditions, including the total removal of forest cover.

Two early Holocene rock avalanches in the Bernese Alps (Rinderhorn, Switzerland)

Large rock avalanches constitute a critical process modulating the evolution of alpine landscapes; however, the relatively infrequent occurrence of these high-magnitude events makes identifying underlying process controls challenging. Here we describe two rock avalanches in the Rinderhorn area of the Bernese Alps, Switzerland, providing new mapping of rock avalanche source areas and deposits, refined volume estimates for each event, runout modeling back-analyses, and absolute age constraint from cosmogenic 36Cl surface exposure dating. Results reveal that the Daubensee rock avalanche released ~4millionm3 of limestone sliding from the western crest of the Rinderhorn. Debris ran out across a Lateglacial moraine before reaching the valley bottom and spreading, leaving thin (on average 7m) deposits across a broad area. The runout resulted in a Fahrböschung angle of 21°. Part of the deposit now lies beneath Lake Daubensee. The Klein Rinderhorn rock avalanche released ~37millionm3 of limestone along a dip-slope sliding plane, with a maximum runout distance of 4.3km and estimated Fahrböschung angle of 14°. Deposits bulked to ~47millionm3 running up the opposing slope, with distinct hummocky morphology in the proximal area and a distal longitudinal flow ridge. These deposits were later modified and partly obscured by ice avalanches from the nearby Altels peak. Cosmogenic 36Cl surface exposure dating revealed nearly coincident ages for both rock avalanches of 9.8±0.5ka. The large lag time between local deglaciation and failure suggests that the events were not directly triggered by deglaciation. Rather, the concurrent exposure ages, also coinciding with the nearby Kander valley rock avalanche as well as paleoseismic records from nearby lakes, strongly suggest seismic triggering.

Sediment Transport and Bedrock Erosion by Wet Snow Avalanches in the Guggigraben, Matter Valley, Switzerland

Wet snow avalanches breaking through to the base of the snowpack or overriding snowfree surfaces can entrain basal material and act as important agents of sediment transport in steep alpine catchments. Here we present results from 4 years of measurements at the Guggigraben catchment (Matter Valley, Canton Valais), quantifying the volume of sediment transported by avalanches each winter season. Sediment load was estimated by measuring the debris content within representative areas and then extrapolating the cumulative volume. Results reveal a total transported sediment volume of 70 m3 in 2009, 23 m3 in 2010, 15 m3 in 2011, and 35 m3 in 2012, which correspond to catchment-wide erosion rates of approximately 0.05, 0.02, 0.01, and 0.03 mm/a, respectively. Sediment appears to be sourced predominantly from within the main channel or one its tributaries, originating first from rockfall or landslides. Avalanches thus play an important role at the Guggigraben in transporting loose sediment from temporary storage sites to the fan and main river system. Within the bedrock gully and in the avalanche source region above, signs of abrasive wear were evident on exposed bedrock surfaces. These included rounded and scoured bedrock, fresh boulder impacts, and scratch marks on the gully walls.

A modified analytical hierarchy process (M-AHP) approach for decision support systems in natural hazard assessments

The Analytical Hierarchy Process (AHP) is a classic and powerful decision support tool. However, the conventional AHP has some disadvantages originating in the expert decision-making process. To minimize the disadvantages of the conventional AHP, a modified analytical hierarchy process (M-AHP), is suggested in this study. This study is conducted in three stages: (i) the theoretical background for the conventional AHP is introduced, (ii) essentials for the proposed M-AHP technique are given with an example solution for the evaluation of snow avalanche source susceptibility, and (iii) a computer code named M-AHP is presented. By applying the methodology suggested in this study, the consistency ratio value for the comparison matrix and the weight vector never exceeds 0.10. The M-AHP program is a complementary tool for natural hazard, natural resource, or nature preservation researchers who apply the M-AHP technique to their decision support problem.

Catastrophic rock avalanche 3600 years BP from El Capitan, Yosemite Valley, California

AbstractLarge rock slope failures from near‐vertical cliffs are an important geomorphic process driving the evolution of mountainous landscapes, particularly glacially steepened cliffs. The morphology and age of a 2·19 × 106 m3 rock avalanche deposit beneath El Capitan in Yosemite Valley indicates a massive prehistoric failure of a large expanse of the southeast face. Geologic mapping of the deposit and the cliff face constrains the rock avalanche source to an area near the summit of ∼8·5 × 104 m2. The rock mass free fell ∼650 m, reaching a maximum velocity of 100 m s−1, impacted the talus slope and spread across the valley floor, extending 670 m from the base of the cliff. Cosmogenic beryllium‐10 exposure ages from boulders in the deposit yield a mean age of 3·6 ± 0·2 ka. The ∼13 kyr time lag between deglaciation and failure suggests that the rock avalanche did not occur as a direct result of glacial debuttressing. The ∼3·6 ka age for the rock avalanche does coincide with estimated late Holocene rupture of the Owens Valley fault and/or White Mountain fault between 3·3 and 3·8 ka. The coincidence of ages, combined with the fact that the most recent (AD 1872) Owens Valley fault rupture triggered numerous large rock falls in Yosemite Valley, suggest that a large magnitude earthquake (≥M7.0) centered in the south‐eastern Sierra Nevada may have triggered the rock avalanche. If correct, the extreme hazard posed by rock avalanches in Yosemite Valley remains present and depends on local earthquake recurrence intervals. Published in 2010 by John Wiley & Sons, Ltd.

The Hattian Bala rock avalanche and associated landslides triggered by the Kashmir Earthquake of 8 October 2005

The Kashmir Earthquake of the 8 October killed an estimated 87 350 people, 25 500 through co-seismic landslides. The largest landslide associated with the earthquake was the 68 × 10 6 m 3 Hattian Bala rock avalanche that destroyed a village and killed around 1000 people. The deposit blocks the valley to a depth of 130 m impounding a lake that reached the dam-crest in April 2007. An outburst flood now threatens a major settlement 3 km downstream. A series of space images reveals landslide clusters in the rock avalanche source area prior to the earthquake. The images also reveal a large slow-moving landslide with its toe in the lake, failure of this landslide may induce dam failure through overtopping and scour. Eighty five landslides in the Hattian Bala catchment predate the shaking of 8 October 2005, a further 73 are co-seismic with the main shock, and 21 postdate it in the period up to October 2006. Landslide magnitude–frequency distribution plots derived from satellite images allow an assessment of the contribution of seismically triggered events as compared to background rates of activity.

Rock Mass Strength Assessment and Significance to Edifice Stability, Mount Rainier and Mount Hood, Cascade Range Volcanoes

—Catastrophic edifice and sector failure occur commonly on stratovolcanoes worldwide and in some cases leave telltale horseshoe-shaped calderas. Many of these failures are now recognised as having resulted from large-scale landsliding. These slides often transform into debris avalanches and lahars that can devastate populations downstream of the volcano. Research on these phenomena has been directed mainly at understanding avalanche mechanics and travel distances and related socioeconomic impacts. Few investigations have examined volcanic avalanche source characteristics. The focus of this paper is to 1) describe a methodology for obtaining rock strengths that control initial failure and 2) report results of rock mass strength testing from Mount Rainier and Mount Hood. Rock mass and shear strength for fresh and hydrothermally altered rocks were obtained by 1) utilizing rock strength and structural information obtained from field studies and 2) applying rock mechanics techniques common in mining and civil engineering to the edifice region. Rock mass and intact rock strength differences greatly in excess of one order of magnitude were obtained when comparing strength behavior of fresh and completely altered volcanic rock. The recognition and determination of marked strength differences existing on the volcano edifice and flank, when combined with detailed geologic mapping, can be used to quantify volcano stability assessment and improve hazard mitigation efforts.

Computer simulations of pyroclastic flows from dome collapse

We present a method of simulating both the avalanche and surge components of pyroclastic flows generated by lava collapsing from a growing Pelean dome. This is used to successfully model the pyroclastic flows generated on 12 May 1996 by the Soufriere Hills volcano, Montserrat. In simulating the avalanche component we use a simple 3‐fold parameterisation of flow acceleration for which we choose values using an inverse method. The surge component is simulated by a 1D hydraulic balance of sedimentation of clasts and entrainment of air away from the avalanche source. We show how multiple simulations based on uncertainty of the starting conditions and parameters, specifically location and size (mass flux), could be used to map hazard zones.