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Mobility of long-runout catastrophic landslides (debris flows, debris and rock avalanches) can be characterized by several parameters. Those, allowing predicting exposure of elements at risk that might be threatened by such hazardous natural phenomena if they will occur—the affected area and runout, are most important for risk assessment. They can be estimated using two general approaches—one based on the numerical modeling and another one based on the empirical relationships between runout and affected area on the one hand and parameters characterizing the potential source zone on the other hand. The latter are volume of the anticipated rock slope failure and height of the unstable slope. Both can be assessed prior to failure with certain accuracy by contrast with the height drop defined as the elevation difference between headscarp crown and the deposit tip. The optimal input parameter is the product of the unstable slope height and possible failure volume that is, in general, proportional to the potential energy of the unstable rock massif. According to the analysis of the Central Asian rockslides/rock avalanches database that includes quantitative parameters of 515 case studies with defined confinement, the relationships of such product with runout and affected area have high correlation coefficients regardless of the confinement conditions and, therefore, allow prediction of the parameters in question with sufficient reliability. It is pointed out that requirements to the accuracy of slope height and failure volume assessment depend on a large extent on the variability range of these parameters within the inventories used to derive the empirical relationships. [ABSTRACT FROM AUTHOR]

Rock avalanches typically entail the flow-like motion of angular rock blocks and fragments of diverse size. Numerical simulations are instrumental in understanding their dynamic process, supporting hazard and risk assessments. Simplified failure criteria, such as the Mohr-Coulomb or Drucker-Prager, are commonly adopted in landslide models relying on the material point method (MPM). However, these criteria cannot capture the transitions between solid-like, liquid-like, and gas-like behaviors exhibited by granular materials. Here, we relied on the moving least-squares MPM, which offers high computing efficiency and stability, and adopted a nonlocal μ(I) rheology model implemented by Haeri and Skonieczny (Comput Methods Appl Mech Eng, 2022). This approach can account for the rate-dependent, pressure-dependent, and size-dependent characteristics of friction in granular materials. By simulating a small-scale flume experiment as well as a large-scale event (the Nayong rock avalanche in Guizhou, China), we verified that the nonlocal μ(I) rheology model can capture the motion and deposition processes in rock avalanches effectively. This feature can be advantageous in physically based hazard assessments of such events. [ABSTRACT FROM AUTHOR]

Herein, fast fracture initiation in glacier ice is modeled using a Material Point Method and a simplified constitutive law describing tensile strain softening. Relying on a simple configuration where ice flows over a vertical step, crevasse patterns emerge and are consistent with previous observations reported in the literature. The model's few parameters allows identification of a single dimensionless number controlling fracture spacing and depth. This scaling law delineates two regimes. In the first one, ice thickness does not play a role and only ice tensile strength controls the spacing, giving rise to numerous surface crevasses, as observed in crevasse fields. In this regime, scaling can recover classical values for ice tensile strength from macroscopic field observations. The second regime, governed by ice bending, produces large‐scale, deep fractures resembling serac falls or calving events. Plain Language Summary: In ice sheets and alpine glaciers, fast‐flowing sections are often characterized by crevasse fields that play a significant role in the cryo‐hydrologic system by facilitating meltwater flow, enhancing basal sliding, weakening the ice, and impacting glacier thermodynamics. Modeling these fractures at the glacier scale remains challenging and often necessitates integrating diverse models which hinders the straightforward consideration of physical issues associated with crevasse fields on a large scale. Here, a new numerical framework allows us to conduct field‐scale experiments and paves the way for a scaling law to elucidate the macroscopic factors influencing fracture fields and to easily incorporate crevasse depth and spacing into large‐scale models. A newly discovered scaling law highlights the transition between a mechanical behavior where the regular crevasse spacing is unaffected by geometry to a regime where geometry plays a significant role, particularly in large‐scale fracture processes like glacier calving. While the numerical experiments in this paper focus on glaciers, the model and conceptual framework is versatile and can address the mechanical behavior of fractures in broader geophysical contexts such as snow, rock or ice avalanches, tectonics and landslides. Key Points: Fractures in glacier flow are modeled using material point method with elastoplasticity and tensile strain softeningA dimensional analysis reveals a key dimensionless number characterizing two different regimes of fast fractureOne regime predicts acknowledged ice tensile strength from field observations and characterizes the regular crevasse spacing [ABSTRACT FROM AUTHOR]

As a result of climate change, rockfalls and rock avalanches as well as landslides lead to an increasing hazard for settlement areas and infrastructures. The hazards of such mass movements mean that numerous protective structures must be planned and built. In addition to building such constructions, the refurbishment of existing protective structures is also playing an increasingly important role. Some of these protective structures are rigid structures consisting of concrete and/or steel elements. Due to the difficult accessibility, flexible net constructions are often considered. Embankment constructions are normally erected to protect against large mass movements. The choice of the right type of construction is based not only on geotechnical and geographical conditions, but also on the occurring energies and the impact of rockslides on the protective structure. In this study, small-scale laboratory experiments with different protective structures are presented. Rigid and flexible structures as well as reinforced embankments are investigated. Based on the results of the experiments, the impacts and deformations are recalculated numerically using the discrete element method (DEM). From the small-scale laboratory experiments and numerical simulations, the differences regarding the construction type of the protective structure can be investigated. An essential main point concerns the relationship between the flexibility of the barrier and the total impact load. The presented work is limited to the investigation of strongly fragmented gravitational mass movements such as rock avalanches. Highlights: The results from model experiments are shown and analyzed to investigate the impacts on protective structures due to highly fragmented granular mass movements (rock avalanches). The behavior of protective structures, such as rigid barriers, flexible barriers, and embankments, is investigated. Numerical simulations based on the discrete element method (DEM) are used to calculate the flow characteristics of the granular mass, the force–time behavior of the impact on the different types of barriers, and the deformations of the flexible barriers. Based on the model experiments and DEM simulations, a limit value is determined depending on the deformation, at which an increased load on flexible protective structures should be taken into account. [ABSTRACT FROM AUTHOR]

Rock fragmentation plays a critical role in rock avalanches, yet conventional approaches such as classical granular flow models or the bonded particle model have limitations in accurately characterizing the progressive disintegration and kinematics of multi-deformable rock blocks during rockslides. The present study proposes a discrete-continuous numerical model, based on a cohesive zone model, to explicitly incorporate the progressive fragmentation and intricate interparticle interactions inherent in rockslides. Breakable rock granular assemblies are released along an inclined plane and flow onto a horizontal plane. The numerical scenarios are established to incorporate variations in slope angle, initial height, friction coefficient, and particle number. The evolutions of fragmentation, kinematic, runout and depositional characteristics are quantitatively analyzed and compared with experimental and field data. A positive linear relationship between the equivalent friction coefficient and the apparent friction coefficient is identified. In general, the granular mass predominantly exhibits characteristics of a dense granular flow, with the Savage number exhibiting a decreasing trend as the volume of mass increases. The process of particle breakage gradually occurs in a bottom-up manner, leading to a significant increase in the angular velocities of the rock blocks with increasing depth. The simulation results reproduce the field observations of inverse grading and source stratigraphy preservation in the deposit. We propose a disintegration index that incorporates factors such as drop height, rock mass volume, and rock strength. Our findings demonstrate a consistent linear relationship between this index and the fragmentation degree in all tested scenarios. [ABSTRACT FROM AUTHOR]

Rock avalanches are generally difficult to prevent and control due to their high velocities and the extensive destruction they cause. However, barrier structures constructed along the path of a rock avalanche can partially mitigate the magnitudes and consequences of such catastrophic events. We selected a rock avalanche in Nayong County, Guizhou Province, China as a case to study the effect of the location and height of a retaining wall on the dynamic characteristics of rock avalanche by using both actual terrain-based laboratory-model tests and coupled PFC3D–FLAC3D numerical simulations. Our findings demonstrate that a retaining wall can largely block a rock avalanche and its protective efficacy is significantly influenced by the integrity of the retaining wall. Coupled numerical simulation can serve as a powerful tool for analyzing the interaction between a rock avalanche and a retaining wall, facilitating precise observations of its deformation and destruction. The impact-curve characteristics of the retaining wall depend upon whether or not the rock avalanche-induced destruction is taken into account. The location of the retaining wall exerts a greater influence on the outcome compared to the height and materials of the retaining wall, while implementing a stepped retaining-wall pattern in accordance with the terrain demonstrates optimal efficacy in controlling rock avalanche. [ABSTRACT FROM AUTHOR]

An editorial focuses on the potential for increased catastrophic flow events in alpine glacier zones due to climate change, using the Chamoli rock-ice avalanche as a case study. It highlights the severe instability of alpine slopes as a consequence of glacial retreat and warming temperatures, suggesting that such events are likely to become more frequent and severe. It emphasizes the need for ongoing monitoring and assessment of these high-risk areas to mitigate future disasters.

The dynamic fragmentation characteristics of a heavily jointed rock avalanche have been analyzed collaboratively via the discrete element method (DEM) and the rock avalanche-induced field seismic signal. First, the DEM results indicate that the jointed source rock mass produces basal crushing damage due to the self-weight, leading to a toppling collapse pattern. Then, we noticed that the velocity, relative breakage ratio, fracture evolution, and the bond breakage energy dissipation of the avalanching mass all show positive performance during the initial stage, consistent with the intensity distribution of the Hilbert spectrum transformed by seismic signal. Meanwhile, the fractal dimension D and the shape parameter β of the rock fragments increased rapidly at this stage as well. These findings indicate that the principal dynamic fragmentation process of this heavily jointed rock avalanche occurs in its initial stage, owing to there are two key processes involved, the overall collapse of the jointed rock mass due to crushing damage of the bottom layer, and the violent collision of the rock avalanching mass with the basement, as the Hilbert spectrum revealed. Finally, we suggest that the dynamic fragmentation of the rock avalanches is closely related to the topography and the motion behaviors of the avalanching mass. [ABSTRACT FROM AUTHOR]

It has been proposed that most cirques are source‐area depressions of large, deep‐seated rock‐slope failures. Yet the close relation between cirques and climate is convincing evidence of the dominance of glacial erosion, rather than rock‐slope failure, in mountain cirque development and distribution. Cirque floor altitudes have a lower limit that varies with snowfall by 1000 m or more between windward and leeward sides of mountain systems. Glaciation levels and equilibrium line altitudes implied by cirques vary in parallel with those for modern glaciers. Cirques are often found mainly on the poleward or leeward slopes of individual mountain ranges, as are modern small glaciers (because of solar radiation and wind effects on ablation and accumulation). Most rock‐slope failures (RSFs: rock slides, rock avalanches and gravitational deformations) do not involve the deep‐seated rotational movement that would produce a cirque form. Although some deep‐seated RSFs with arcuate head scars may be confused with cirques, identification as a glacial cirque is more confident as the floor is longer, wider and more gently sloping. Some scars from major RSFs may resemble poor or moderately developed cirques, but tend to have steeper floors, to be more scattered and closely related to geology, whereas glacial cirques develop on all rock types. Deep‐seated RSFs high on slopes can be associated with seismic shaking, but cirques develop without relation to seismicity. Degree of cirque development can be related to duration of exposure to glaciation. Often RSFs are found adjacent to cirques, or in glacial transfluences; only a proportion are well situated to develop into glacial cirques. Valley‐head cirques are continued down‐valley by glacial troughs. The 'overdeepening' (rock basins with reversed slopes) found in a large minority of cirques is not due to rock avalanching, fluvial or periglacial erosion. The RSF proposal should therefore be rejected in favour of the traditional glacial explanation, without any nivation stage being necessary. Rock‐slope failure is one of several possible ways of initiating hollows for glacier accumulation, as well as an ancillary process of cirque extension or widening through collapse of glacially oversteepened slopes. Headward extension of adjacent cirques on a ridge leads to displacement of the divide, sometimes by 2 km or more, lowering ridge and summit altitudes and producing the 'glacial buzzsaw' effect. Where a relatively lower snowline has led to cirque erosion on all sides of a mountain, cirque intersection lowers summits further. The buzzsaw hypothesis is not applicable, however, where remnants of a preglacial summit surface survive. © 2020 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Rockfalls and rockslides often occur in mountainous areas, and they may develop into rock avalanches because of fragmentation. A series of laboratory experiments were conducted to study the contributions of rock mass structure to the emplacement of fragmenting rockfalls and rockslides. In these experiments, we considered the process of breakable analog blocks with different structures sliding along an inclined plane, impacting at the kink point with a horizontal plane where deposition occurs. The results show that the initial geometrical subdivision (i.e., the rock mass structure) of the source rock can greatly influence the impact of the fragmentation process and total runout, while the degree of fragmentation controls the travel distance of the center of mass. The occurrence of transversal discontinuities enhances the momentum transfer efficiency from the rear to the front part of the rock mass. A negative correlation between the apparent friction coefficient (linked to the total runout) and equivalent friction coefficient (linked to the center of mass runout) was found, which appears to be induced by fragmentation. We proposed a new fragmentation‐spreading model to describe this negative correlation. This simple physical model supports the importance of fragmentation in rock fragment trajectories and the runout of rockfalls and rockslides. Fragmentation is an energy‐sinking process that will shorten the runout of the center of mass. Thus, we suggest that impact fragmentation does not fully account for the long runout of large rockfalls and rockslides. Key Points: Structural features influence the fragmentation and runout, while the degree of fragmentation influences the runout of the center of massA negative correlation between the total runout and the runout of the center of mass appears to be induced by fragmentationImpact fragmentation is an energy‐sinking process that will shorten the runout of the center of the sliding mass [ABSTRACT FROM AUTHOR]

Rock slides quite commonly transform into flow-like landslides along their runout paths. At three initial rock slides in northern British Columbia, which occurred between 2002 and 2005, around 50–70% of the entire runout distance is composed of debris avalanche and debris flow deposits, which is comparable to other composite landslides around the world. Saturated ground conditions at the time of rock sliding make entrainment or undrained loading as agents of flow transformation from initially dry rock slides to partially saturated debris avalanches, respectively, fully saturated debris flows likely. Hummocks occur as clusters within the rock slide parts, whereas the flow-like depositions have more subdued morphologies. We show that late- or post-emplacement motion of individual hummocks is possible and can even divert in direction from the dominant landslide trajectory by responding to the underlying topographic gradient. Analyses of the well-preserved deposits suggest hummock formation above a basal sliding plane (low-angle normal fault) and along subordinate shear zones (high-angle normal faults) within a largely translational mass movement, thereby supporting the hypothesis of hummock formation proposed by Paguican et al. (2014). Pebbles on top of rock slide-debris avalanche boulders and on top of snapped-off trees record much higher dynamic debris flow heights. These and other features are not recorded on ancient landslides due to rapid erosion. [ABSTRACT FROM AUTHOR]

The identification of hazardous slopes with degrading permafrost is a key task in the mountain periglacial environment. If rockslides have previously been preconditioned by rock wall permafrost, similar events may be triggered from present unstable rock walls. An inventory of rockslides and rock avalanches in the austral part of the Santa Cruz river basin (31°40′–31°50′S, 70°30′–70°10'W), San Juan, Argentina, was made. The study area comprises a surface of approximately 432 km2 (50% above 3,500 m asl); 15 rockslides, 12 complex rockslides evolving to rock avalanches and 19 rock avalanches were identified. The deposits were analyzed with remote sensory imagery and during fieldwork in order to study processes under permafrost degradation caused by global warming. Rock sampling procedures and laboratory rock‐resistivity testing were also carried out. We characterized the detachment scars and deposits for two rockslides. Two different mechanisms were identified. In one rockslide, shallow active layer detachment was favored by shear‐displacement along pre‐existing joints, as a result of short‐term periods of climate warming. In the other, long‐term permafrost degradation favored a deeper failure process. The studied landslide processes could not be explained by permafrost degradation alone. Faults, the geometric arrangement of their structural elements and seismic activity may contribute to trigger these phenomena. It is expected that the magnitude and frequency of rockslide hazards will increase during the 21st century. [ABSTRACT FROM AUTHOR]

Landslide dam resulted from the natural blockages of river channels caused by rockslide-derived debris is easy to burst, which usually leads to a catastrophic damage. In this work, the physical model tests were carried out to investigate the movement process and accumulation characteristics of rock fragments on sliding surfaces with different characteristics, mainly taking into consideration of the influence of the initiated angle, sliding region angle and sliding bed roughness. The results show that after particle separation and collision during the movement process of rock fragments, large particles were widely distributed on the surface of the final deposit while small particles were deposited at the bottom. The sliding region angle and the roughness of the sliding surface had a great influence on the front inclination angle of the deposit dam. The sliding region angle also had a significant influence on the accumulation area and dam morphology in the rough group, while only a little effect was observed on the dam morphology in the smooth group. The distribution of the particles in the deposit dam was affected mainly by the roughness of the sliding surface. • The movement process and accumulation characteristics of rock fragments on sliding surfaces with different characteristics were investigated. • Large particles were widely distributed on the surface of the final deposit. • The sliding region angle and the roughness had a great influence on the front inclination angle. [ABSTRACT FROM AUTHOR]

The goal of this paper is to evaluate the post-failure behavior of the Hsien-du-shan rock avalanche, which was triggered by Typhoon Morakot in 2009, using a three-dimensional (3D) discrete element program, namely, 3DEC. The 3D slope topography and local joint sets are explicitly considered in the calculations, and the joint sets cut the sliding rock mass into blocks with arbitrary shapes. The modeled blocks exhibit the elastic behavior of the local rocks. The analysis successfully simulates the wedge failure at the initiation of the landslide. Additionally, the 3DEC results clarify the local rock sliding phenomena at the boundaries of the source area. The simulated depositional area correlates well with the actual area affected by the Hsien-du-shan rock avalanche. In addition, the erosion of a ridge by the sliding rock near the southwestern margin of the area at an elevation of 590 m has a significant influence on the shape and size of the impacted area. The interlocking effect between blocks is also considered. [ABSTRACT FROM AUTHOR]

This study investigates the predisposing geological and anthropogenic factors and indicative precursors preceding the fatal 5 June 2009 Jiweishan rock avalanche. It began as a rockslide and transformed into a rock avalanche that killed 74 people and caused major property loss due to misdiagnosis of the failure mode, and underestimation of volume and travel distance. Besides topography, structure and stratigraphy that favoured failure, mining below the failed rock mass had changed the state of stress and altered groundwater flow. The anthropogenic factors caused deformation and accelerated failure of the slope, and therefore were important contributions. Cracks and a karstic zone had developed along regional joints and defined several boundaries of the failed rock mass. Furthermore, a 2-m-wide crack developed since 1958 revealed a potential basal failure surface at the contact between karstic limestone and an underlying pre-sheared thin shale aquiclude. Increasing magnitude and frequency of rockfalls and tension cracks at the front end of the sliding block appeared three days before the event and implied the likely movement direction of the sliding rock mass. These could have warned of a developing giant failure. Topography included a large elevation difference between the toe of the failure surface and the cliff base, a narrow valley to channel debris, and the steep gradient of the downstream Tiekuang Creek, could have suggested that failure might lead to a rapid and long-runout rock avalanche. However, access to the densely vegetated source area before the failure was difficult, and local investigators did not have all of the evidence that might have led them to recognize that potential danger was more than continuing rockfalls. [ABSTRACT FROM AUTHOR]

Rock glaciers are distinct landforms in high mountain environments indicating present or past permafrost conditions. Active rock glaciers contain permafrost and creep slowly downslope often forming typical flow structures with ridges and furrows related to compressional forces. Rock glaciers are widespread landforms in the Austrian Alps (c. 4600). Despite the high number of rock glaciers in Austria, only few of them have been studied in detail in the past. One of the best studied ones is the 950 m long Dösen Rock Glacier located in the Hohe Tauern Range. This rock glacier has been investigated since 1993 using a whole suite of fieldbased and remote sensing-based methods. Research focused on permafrost conditions and distribution, surface kinematics, internal structure and possible age of the landform. Results indicate significant ground surface warming of the rock glacier body during the period 2007-2015 accompanied by a general acceleration of the rock glacier surface flow velocity (max. 0.66 m/a) over the last two decades. This speed-up is possibly related to higher ice temperature and water content. As judged from various geophysical measurements, the maximum thickness of the rock glacier is about 30-40 m with an active layer of several meters depending on the location. The permafrost thickness beneath the active layer was quantified to be between 10 m (at the margins) and 40 m (at the central and upper parts). Massive sedimentary ice has not been observed or detected by geophysics so far at the central and lower part but might exist to in the rooting zone of the rock glacier as indicated from field evidences. The Dösen Rock Glacier is primarily a talus-derived rock glacier although a small glacier might have existed some times in the past in the eastern part of the rooting zone. Age estimations of the rock glacier by using the Schmidt-hammer exposure-age dating method indicate a formation period of several thousand years with alternating periods of faster and slower evolution. Research findings at this typical alpine rock glacier in the Austrian Alps clearly point out that the morphogenesis, the internal structure as well as the climaterock glacier relationship is complex but typical for such peculiar alpine landforms. [ABSTRACT FROM AUTHOR]

Large landslides in fjord environments have the potential to cause catastrophic damage and trigger secondary submarine landslides and tsunamis. Of the 14 largest tsunamis on record, 10 were triggered by subaerial landslides, often rock avalanches, into fjords or lakes in high relief glaciated terrane. These complex hazards are well documented in the fjords of Greenland, Norway, and Alaska, with several resulting in fatalities and permanent damage to coastal settlements. However, despite the recognized hazard potential, few rock avalanches have been reported on Baffin Island where the extensive coastline is deeply incised by fjord systems. Are rock avalanches going unnoticed in this isolated region? Or are these events comparatively less common on Baffin Island despite high relief, rapid deglaciation, thawing permafrost, and regions of active seismicity? Here we develop the first systematic inventory of onshore rock avalanche deposits in this area, mapped using high-resolution optical imagery and digital elevation models, to answer these questions and evaluate the prevalence and distribution of rock avalanches in NE Baffin Island. In a study area that encompasses ~60 000 km2 of fjord terrane between the hamlets of Clyde River and Pond Inlet, on the NE coast of Baffin Island, we find only 6 preserved onshore rock avalanche deposits within the study area. Of these, only 2 deposits are dated, using historical imagery, to the last century while 4 deposits can only be inferred as post-glacial, without a more precise age limit. Why are comparatively few rock avalanche deposits observed in NE Baffin Island? We hypothesize that (1) persistent permafrost in the region continues to act as a stabilizing factor, (2) overall rock mass competence is high in areas of most extreme relief contrast, and (3) some deposits remain masked underwater in deep and steep-walled fjords where bathymetric data is either lacking or too sparse for systematic mapping. [ABSTRACT FROM AUTHOR]

Large, rapid rockslope failures generate deposits with complex morphologies due to a number of causal and influencing factors. To investigate these, we conducted a detailed case study at the carbonate Tschirgant deposit (Tyrol, Austria). It preserved evidence of simultaneous rock sliding (very large, coherent hummocks) and rock avalanche spreading (smaller, more scattered hummocks and ridges). Motion indicators, such as longitudinal ridges furthermore pinpoint the transition between linear sliding and radial spreading. The lithological distribution in the Tschirgant deposit shows that it retained source stratigraphy despite being split into two accumulation lobes by a high bedrock ridge. Furthermore, lithology had a very strong control on the final deposit morphology in that the different lithologic units form individual deposit surfaces. River erosion has created fortuitous outcrops that reveal the basal rock avalanche contact. The underlying valley-fill sediments (substrates) have been intricately involved in shaping the rock avalanche morphology and, where entrained, highlight internal rock avalanche deformation features. This study shows that intrinsic dynamic properties of granular media (e.g. tendency for longitudinal alignments), emplacement mode, lithology (and source predisposition), runout path topography, and substrates form the quintet of causal factors that shape rock avalanche morphology. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This Hans Cloos lecture paper develops general reflections inspired by Ian McHarg's () book, 'Design with Nature' and concerning engineering geology. Three case studies are illustrated: landslides in reservoirs, gallery excavation in a shield volcano, large rockslides and rock avalanches. For these three case studies, the potential and limits of conceptual and numerical models are discussed. [ABSTRACT FROM AUTHOR]

Rapid sliding in a rock avalanche may occur from strain- and strain-rate- weakening of the rupture-surface strength. However, existing research on rock-avalanche dynamics pays little attention to rupture-surface weakening. In this paper, we used high-speed-friction tests on limestone and shale of the Qixia Formation to determine strain- and strain-rate- weakening of the rupture surface of the Jiweishan rock avalanche. The strain- and strain-rate- weakening model inferred that the friction coefficient of the rupture surface decreased rapidly to a residual value of <0.1 within a short interval after rock-avalanche failure, which was collectively determined by shear rate and shear displacement. We used this rate-weakening in a numerical model to investigate the dynamics of the rock avalanche, and compared it with another model that used a constant value of friction. Our model results suggested that rupture-surface weakening could cause the disintegration of the sliding body and influence the post-failure motion of the Jiweishan rock avalanche. With strain- and strain-rate- weakening, a larger sliding-out velocity (~ 13–27 m/s) of the rock mass was modelled due to reduction of frictional energy consumption causing by rupture-surface weakening. Hence a strain and strain-rate- weakened rock mass could both fly farther in the air and strike the ground at a lower angle maintaining more kinetic energy. The transport distance of such a sliding rock mass would have been ~50–500 m longer than in a model without weakening. Our study suggested that strain- and strain-rate- weakening behavior of a rupture surface would significantly increase the rock-avalanche transport distance. Use of such a model might provide more accurate prediction of the disaster reach of rock avalanches. • Rupture-surface strength decreases rapidly after rock-avalanche initiation. • Rupture-surface strength is quantitatively studied by numerical modeling. • Rupture-surface strength weakening promotes the disintegration of a rock avalanche. [ABSTRACT FROM AUTHOR]

Rock avalanches are the largest granular flows on Earth. In contrast to artificial, small-scale granular avalanches, they exhibit a large degree of fragmentation with reduction of average grain volume by a factor of up to 10-10. Even though fragmentation likely affects the whole dynamics of the rock avalanche, as yet the basic mechanics of the process is poorly known. In this work, a simple model is presented for the fragmentation of rock avalanches, assuming that most of the fragmentation occurs along force chains in the granular medium. The landslide motion is simulated along a curved bumpy profile path. The predicted grain spectra are found to agree reasonably with field data. [ABSTRACT FROM AUTHOR]

Abstract: Many formerly-glaciated mountains exhibit a high density of postglacial rock-slope failures (RSFs) in the form of rockslides, rock avalanches or deep-seated gravitational slope deformations. Such RSFs are often termed ‘paraglacial’ as they reflect pre-conditioning by glaciation and deglaciation. The temporal pattern of paraglacial RSFs is unknown. We employ 47 cosmogenic isotope exposure ages obtained for 17 catastrophic RSFs in the Scottish Highlands to test models of changes in RSF frequency since deglaciation. Our results show that RSF activity spans almost the entire postglacial period from ~17ka until ~1.5ka, and that the periodicity of sampled postglacial RSFs is statistically indistinguishable from a pattern of uniform periodicity (~1ka−1). Our data do not conform to proposed models of declining RSF frequency with time elapsed since deglaciation, but suggest that the temporal distribution of postglacial RSFs is best described by a combination of rapid response (enhanced RSF frequency during or immediately after deglaciation) followed by approximately constant periodicity. Our findings are consistent with near-surface fracturing of rock when glacially-induced confining stresses are removed, causing some failures during or immediately after deglaciation and reducing other slopes to critical conditional stability so that failure is triggered by progressive rock-mass weakening or by transient triggering mechanisms. Neither permafrost degradation (thaw of ice in joints) nor seismic activity offers a general explanation for triggering Scottish RSFs, but could be contributory in some cases. The quasi-constant periodicity inferred for Holocene RSFs implies that the probability of RSFs in this seismically-quiescent intraplate area has not changed in the past ~10ka, and that further (though infrequent) catastrophic RSFs are likely to occur in the future. [Copyright &y& Elsevier]

Abstract: Around 11.5∗106 m3 of rock detached from the eastern slope of the Santa Cruz valley (San Juan province, Argentina) in the first fortnight of January 2005. The rockslide–debris avalanche blocked the course, resulting in the development of a lake with maximum length of around 3.5km. The increase in the inflow rate from 47,000–74,000m3/d between April and October to 304,000m3/d between late October and the first fortnight of November, accelerated the growing rate of the lake. On 12 November 2005 the dam failed, releasing 24.6∗106 m3 of water. The resulting outburst flood caused damages mainly on infrastructure, and affected the facilities of a hydropower dam which was under construction 250km downstream from the source area. In this work we describe causes and consequences of the natural dam formation and failure, and we dynamically model the 2005 rockslide–debris avalanche with DAN3D. Additionally, as a volume ~24∗106 m3of rocks still remain unstable in the slope, we use the results of the back analysis to forecast the formation of a future natural dam. We analyzed two potential scenarios: a partial slope failure of 6.5∗106 m3 and a worst case where all the unstable volume remaining in the slope fails. The spreading of those potential events shows that a new blockage of the Santa Cruz River is likely to occur. According to their modeled morphometry and the contributing watershed upstream the blockage area, as the one of 2005, the dams would also be unstable. This study shows the importance of back and forward analysis that can be carried out to obtain critical information for land use planning, hazards mitigation, and emergency management. [Copyright &y& Elsevier]

Absolute dating of mass movements is crucial for disentangling possible release factors and determining the frequency of events. Here, we present an overview of a recent approach to dendrochronological dating of rockfalls, flows, landslides and avalanches. The results, based on 69 casestudies, show that methodological approaches to sampling and material processing differ considerably for different types of mass movements. Landslides are usually detected through abrupt growth changes and changes in stem eccentricity, whereas high-energy events as avalanches and flows are mostly identified by the formation of traumatic resin ducts, reaction wood, growth injuries and eccentricity changes. Cross-dating of dead wood is applicable as well. The dating of most mass movements except landslides is common, even with sub-annual resolution. In comparison to other methods of absolute dating, the main benefit of dendrochronology still lies in the high temporal resolution of the results. If living material is accessible, on-going research progress makes absolute dating of most mass-wasting events possible with sub-annual precision. [ABSTRACT FROM AUTHOR]

Abstract: A specific contact model was used in a code (discrete element method) to explain the mechanisms of energy dissipation by collision and friction during the propagation of a granular mass on a slope. The numerical model focused on both realistic block shapes and the relevance of the single-collision law that make physical parameters easily assessable. Identification of the contact parameters was carried out by means of the digital image analysis of two-body collisions. To this purpose, the dropping of single blocks on a flat surface was filmed from two angles with high speed cameras. The digital images acquired during the rebound were then analyzed to extract accurately the block kinematics (3D trajectory and velocities). The contact parameters were optimized by minimizing an error function obtained by comparison between the numerical predictions and the experimental results. Once the parameters were set, a simulation of the collective behavior of the release of piled and randomly poured bricks under the same conditions as those released experimentally as described in the literature, was carried out. The satisfactory match between the experiments and the numerical predictions showed that (i) the proposed collision laws are sufficient to describe with accuracy the energy dissipation that occurs during binary collision or during mass propagation, (ii) the optimization procedure enables correct identification of the parameters, and (iii) the initial layout of the blocks is of primary importance in this process. [Copyright &y& Elsevier]

Abstract: This paper reports a detailed rock slope hazard investigation of the Portillo Rock Avalanche site located in the rugged mountains of the Andean Cordillera of central Chile. The site is important as it lies along the International Santiago–Mendoza Highway Corridor connecting Chile and Argentina, and a major ski resort is located on its deposits. A number of large lobate-shaped diamicton deposits were mapped and dated by cosmogenic nuclides (36Cl), with the results showing that they correspond to two significant prehistoric rockslide events. An integrated field mapping and numerical modelling investigation was subsequently carried out to assess the threat posed to the area by further rocksliding activity. Distinct-element modelling was used to back analyze the failure mechanism and identify the geological model that best reproduced the Portillo Rock Avalanche failure surface. Results show that a stress-controlled failure at the toe of the slope followed by sliding along volcaniclastic bedding was the likely failure mechanism. A 3-D dynamic runout analysis was carried out to back analyze which combinations of rheologies, material properties and rockslide sequencing were best able to reproduce the current distribution of rockslide deposits. Results indicate that two separate sliding events originating from different sources had occurred, with each involving different combinations of frictional and Voellmy rheologies depending on the level of entrainment that occurred along each travel path. Insights gained from the back analysis were then used to carry out a forward analysis to assess the potential for a recurring major rockslide under several different triggering scenarios. Results suggest that a low probability M 7.8 earthquake would be required to trigger another rockslide from the original source area. The rock slope was otherwise found to be stable, even following high precipitation events. Nevertheless, runout simulations for the estimated large-magnitude earthquake-triggered rockslide volume showed that for both a highly frictional and non-saturated path (i.e. dry season) and a snow covered path (winter), the leading edge of the flow would override part of the International Santiago–Mendoza Corridor with the debris coming to rest in a flat-lying area in the upper part of the valley. Overall, the results from this integrated hazard assessment suggest that the hazard level is low. [Copyright &y& Elsevier]

Dormant volcanoes are typically thought of as relatively safe environments to live around. However, under certain geological conditions, such volcanoes can be prone to collapse and may generate massive rockslide avalanches reaching tens of kilometres from the volcano. [ABSTRACT FROM AUTHOR]

We present a structural analysis of subaerial natural and analogue rockslide avalanches. Such deposits often have well- developed faults, folds, and hummocks. These structures can be used to determine the kinematics and dynamics of emplacement. Large-scale terrestrial rockslide avalanches show large runout distances compared to their fall height. Most attempts to explain this phenomenon invoke fluidizing mechanisms or lubricating agents to reduce forces opposed to momentum, especially at the base. However, the properties and mechanics of low friction are still poorly understood. Any model for motion and emplacement must integrate geometric, morphologic, and structural features, all crucial in constraining kinematics and dynamics. Here we fi rst examine the morphological and structural features displayed by 13 natural rockslide avalanche deposits; we then use simple and well-constrained analogue models involving the slide of stratified granular material down smooth, curved ramps. These differ from previous analogue models in that we concentrate on observing the structures produced by brittle deformation and use a low-friction sliding surface. Models show that variations in the sliding surface curvature, lateral profile, roughness, and modifications in material cohesion can successfully reproduce the majority of rockslide-avalanche deposit features. After discussing the geometrical and dynamic similarity between experiments and natural examples, we propose a model for structure formation and a fourfold classification based on model and natural deposit morphology and dynamics: hummocky, nonhummocky, dominantly extensional, and dominantly compressional rockslide avalanches. The models require a brittle core and surface that spreads and contracts by adjustment on large numbers of faults that bottom into a low-friction décollement layer. Spreading is accommodated by normal and strike-slip faults, while on deceleration, thrust faulting generates thickening. To be realistic, any physical predictive model must take into account these fundamental kinematic and structural aspects. [ABSTRACT FROM AUTHOR]

The paper examines the role of rockslide–rock avalanches in mountain landscapes, and the landforms associated with them. While the landslides are extremely short-lived events, rock wall detachment scars and rock avalanche deposits can persist for long periods as influences on landscape development. Especially significant are rock avalanches with complex runout and emplacement related to interactions with rugged terrain or deformable substrates. Their characteristics greatly increase the scope of landscape disturbance. Hundreds of rock avalanches are now known, worldwide, that have formed crossvalley barriers interrupting mountain drainage systems. Many have done so for millennia or tens of millennia. They give rise to distinctive sediment assemblages, constructional and erosion landforms generated by other processes responding to the landslides and constrained by them. A landslide interruption epicycle of five phases is described, and related sediment assemblages. These provide the basis for defining a landslide interrupted valley landsystem. Its full significance is seen in mountain drainage basins affected by multiple landslide interruptions. These create naturally fragmented fluvial systems, in which a disturbance regime geomorphology is identified. Stream profiles, sediment delivery, and related landforms are kept in a chronic state of disequilibrium with respect to climatic and geotectonic controls, and drainage organization. The transHimalayan Upper Indus Basin provides an example, a large high mountain drainage system fragmented by more than 170 late Quaternary rock avalanches. In this case, as elsewhere, misidentification of rock avalanches led to neglect of their role in Quaternary histories. The nature and limitations of disturbance regime geomorphology are discussed, and broader implications for mountain landscapes. [ABSTRACT FROM AUTHOR]

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Many rock avalanches entrain and liquefy saturated soil from their paths. Evidence for this includes mud displaced from the margins of rock avalanche deposits, substrate material smeared along the base of deposits, extrusion of liquefied soil upward through the deposits, and increases of volume. A hypothesis first suggested in 1881 and since reinforced by several authors suggests that entrainment of substrate material increases mobility. Although the process has been discussed in the literature for more than 100 years, few detailed and quantitative descriptions exist. The main purpose of this paper is to describe two recent cases from British Columbia, Canada, where rockslides entrained substrate on a very large scale, influencing the character of the events. Estimated volume balance curves, based on detailed field mapping, are provided for both cases. Dynamic analyses are carried out using a numerical model and using the same set of rheological parameters. The mechanism of material entrainment and displacement is discussed. The data suggest that rapid rock failures entraining very large quantities of saturated substrate material represent a special type of landslide, transitional between rock avalanche and debris avalanche. Many rock avalanches can thus be seen as end members of a continuum of phenomena involving rock failure followed by interaction with saturated substrate. [ABSTRACT FROM AUTHOR]

A sturzstrom is a large-scale landslide that evolves during transport into a rapid granular flow (rock avalanche) by a dynamic disintegration process. Numerous theoretical hypotheses have been proposed to explain the excessive mobility of these catastrophic mass movements, but the role of disintegration processes remains poorly understood. Exceptional outcrop conditions at the giant (12 km3) Flims sturzstrom (Swiss Alps) permit the analysis of disintegration processes that result from shearing during transport. In confined zones of the rock mass, shearing is concentrated along preferred surfaces (originating as bedding planes), which evolve into shear band layers. Differential velocities of slabs separated by these shear layers induce oblique fractures in the slabs by accommodation. Contacts between grains are maintained in the shear layers. In unconfined zones near the top and the lateral margins, shearing generates dilatancy. The rock mass is affected by anisotropic dispersion without mixing, and disintegrated material is preferentially produced to the top due to inflation. The rock slide then evolves to a granular flow. The consequence of these processes is the formation of two distinct depositional facies in the sturzstrom. The structured facies exhibits a stratified aspect close to the base, reflecting confined slab-on-slab shearing motion. Towards the top and distally, it evolves into a chaotic facies with some isolated pockets of the structured facies. Reduction of confining forces on the moving sturzstrom allows transformation of the structured facies into the chaotic facies. This characteristic transition, observable in many sturzstrom deposits, seems to be necessary for the rock avalanche process to occur, and offers insights into the long-runout characteristics of these catastrophic mass movements. [Copyright &y& Elsevier]

A reliable forecast of the failure stage of large rockslides is difficult, because of non-linear time dependency of displacements and seasonal effects. Aim of this paper is to suggest a practical method to prepare alert thresholds for large rockslides, assessing critical values of velocity for carrying out civil protection actions using monitoring data. Adopted data concern the 20 Mm3 Ruinon rockslide (Valfurva, Central Alps, Italy), still evolving and suitable to originate a fast moving rock avalanche. Multitemporal analysis of aerial photos, LIDAR-ALTM laser topography, field survey and geomechanical analyses allowed to infer the rockslide kinematics and better understand data provided by a monitoring network including distometers, extensometers, GPS benchmarks and inclinometers. The analysis of displacement and rainfall data over five years (1997–2001) allowed to recognise three different evolutionary patterns of displacements, showing a continuously increasing rate since 1997. Data representing large-scale behaviour of the rock mass were fitted by power-law curves, according to the “accelerating creep” model by Voight, in order to evaluate a suitable failure time. This was hampered by the large seasonal deviations, which can significantly delay the occurrence of failure. Data were fitted using the Voight’s equation, expressed in terms of displacement, through non-linear estimation techniques, in order to find values of the controlling parameters (A, α and tf) suitable to represent the mechanical behaviour of the rock mass approaching the failure. This allowed to compute velocity–time theoretical curves and to define different velocity threshold values (pre-alert, alert and emergency) to be used for emergency management. [Copyright &y& Elsevier]

• The DDA simulates the mining-induced rock avalanche. • The failure process of the landslide was numerically identified. • The simulated failure process correlates well with the expert image and the local landform. This study numerically simulated the failure process of a mining-induced landslide at Nattai North, Australia. Results obtained using Discontinuous Deformation Analysis (DDA) matched the conceptual failure process suggested by local geologists and the observed maximum run-out distance. The maximum velocity of the sliding rocks exceeded 40 m/s. Computational results showed that the slope with inward sub-horizontal bedding planes and sub-vertical discontinuities remained stable if the mining-induced high principle stresses did not fracture the rocks near the slope toe. Failure of the rocks near the toe of the slope was a key causal factor in the subsequent landslide. This paper presents the first numerical simulation of the post-failure behavior of the mining-induced landslide at the Nattai North site. It also represents the first DDA simulation to clarify the chain reaction of a mining-induced landslide and demonstrate its applicability in such investigations. [ABSTRACT FROM AUTHOR]

Rockfall and snow avalanche events often cause injury to European larch (Larix decidua Mill.) trees, giving rise to the formation of callus tissue and tangential rows of traumatic resin ducts (TRDs). We analyzed and quantified anatomical reactions of juvenile trees injured before the start of the growing season by snow avalanches (15 trees, 324 cross sections) or rockfalls (18 trees, 270 cross sections). Traumatic resin ducts were observed in the growth ring formed following injury in 94.3% of the rockfall samples and 87.3% of the snow avalanche samples. Traumatic resin ducts were formed at the beginning of the new annual ring around wounds caused by rockfalls. In contrast, in trees injured by snow avalanches, TRDs were not formed until after the formation of several rows of early earlywood (EE) tracheids (mean ± SD = 4.19 ± 2.56 rows). The dimensions of the EE tracheids observed in the snow avalanche samples were greatly reduced in the tissues bordering the wound, with radial width reaching an average of only 50% and lumen cross-sectional area an average of only 46% of pre-event values. It is therefore possible to differentiate injuries due to past snow avalanches from injuries due to rockfall based on anatomical growth reactions in the tissues bordering scars. [ABSTRACT FROM AUTHOR]