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Active fault zones are areas impacted by intense tectonic activity, where geohazards such as landslides occur and their distribution characteristics vary across segments. Using the Litang fault zone in the eastern Tibetan Plateau as an example, this study cataloged landslides within a 10 km range on both sides of the fault zone. The Litang fault zone was divided into four sections based on landform characteristics and the spatial distribution of active faults. A comprehensive analysis was conducted on the relationship between landslide distribution and topography, lithology, and active faults in different sections. Additionally, the study employed a random forest model to compare landslide susceptibility between the whole-region and its sub-regions. The results show that lithology and topography significantly influence the distribution of landslide types. The Upper Triassic sandstone, Slate exhibit more debris flows in areas with slopes ranging from 5° to 35°, while slopes >35° in the Upper Triassic sandstone, Slate are prone to unstable slopes. Rock avalanche occur in Upper Triassic sandstone, Slate, and Quaternary sand and gravel. Active faults play a key role in control ling landslides distribution through distance, hanging wall, locked segment, and direction effects. The number of landslides is positively correlated with the activity of faults. Additionally, the dip angle and motion characteristics of faults have significant influence on the distribution of landslides. The results of landslide susceptibility evaluation show that sub-region models have higher accuracy than the whole-region model. This study provides a new method for exploring the spatial distribution of landslides and can provide scientific reference for reducing landslide disasters in active fault zones. • Landslides is significantly influenced by distance, hanging wall, locked section, and directionality of the active fault • Fault activity is positively correlated with landslide numbers, while the dip angle and motion affect distribution pattern • Sub-regional model can effectively reveal the spatial differences in landslide susceptibility along the active fault zone [ABSTRACT FROM AUTHOR]

Intensive fragmentation is a pervasive process during rock avalanche propagation, with a series of typical shearing characteristics being generated, indicating the occurrence of differential shear-induced comminution of clasts. However, much less is known about how shearing evolves within a rock avalanche over long runout. In the Iymek rock avalanche (IRA), pervasive shear zones characterized by multistoried, multiscale, and multistyle shear structures are well developed along the travel path of the IRA, providing an invaluable opportunity to decipher the evolution of shear-induced fragmentation occurred in rock avalanches. In these shear zones, a series of indicative structures, including preserved stratigraphic sequences, jigsaw structures, Riedel shear arrays, sigmoidal shear planes, asymmetrical folds, bookshelf and boudin-like structures, and anastomosing shear networks, are identified. These structures indicate that a laminar-like flow regime characterized by low disturbance but intensive shearing should dominate the emplacement of the IRA, contributing to the formation of these pervasive shear structures and material facies. As indicated by the progressive evolution of these pervasive shear structures, three facies are determined from the transition zone to the accumulation zone, i.e., low-fragmented facies, ductile-dominated facies and brittle-dominated facies. The low-fragmented facies is mainly distributed in the transition zone, similar to a semisolid phase rather than the solid phase of the bedrock in the source area. Conversely, the brittle-dominated facies features a high fragmentation degree and is predominant in the accumulation zone, which mainly consists of a semifluid to fluid phase. This indicates that the rock avalanche mass should evolve from a solid phase to a fully fluid phase during propagation, which involves clast fracturing and comminuting, frictional sliding and rotation. Therefore, we propose that the rock avalanche is a classical cataclastic flow driven by progressive and differential shearing comminution during its laminar-like propagation instead of a granular flow. These results provide a significant basis for interpreting similar structures in other rock avalanche deposits and yield new insights for understanding the emplacement mechanisms of rock avalanches. [Display omitted] • The multistoried, multiscale and multistyle shear zones are identified in the IRA deposit. • Three fragmented facies featured by brittle to ductile deformations are generalized. • Phase transition from a solid to a fluid phase due to progressive fragmentation occurred. • The IRA is a cataclastic flow driven by progressive and differential shear-induced comminution. [ABSTRACT FROM AUTHOR]

Rock avalanche-induced air blasts are widespread, damaging, and deadly. They can add to the destructive potential of avalanches far beyond the avalanche zone, but no landslide risk assessment in practice to date has accounted for the potential air blast danger. Here, field investigations and numerical studies were employed to quantitively analyze the initiation and propagation mechanism of air blasts triggered by the 2008 Wenjia Valley rock avalanche in Sichuan, China. Our findings indicate that the most significant air blast triggered by the Wenjia Valley avalanche was near bends in the valley, with a maximum pressure of over 25 kPa and a maximum velocity of 73 m/s. The avalanche violently collided with the valley wall at bends, generating multiple destructive air blasts and avalanche deflection. Subsequently, the separated air blast propagated as inertia flows and caused huge forest destruction. A systematic parametric study combined with case studies was further performed to investigate the possible contribution of topography and sliding mass properties to the air blast power. Large avalanche volume and high velocity both appear to be necessary conditions to generate a destructive air blast, while the sudden topography change is also greatly influential. Our work provides new insights into the initiation and propagation of rock avalanche-induced air blasts, compelling to consider this sort of cascading effect during landslide risk assessment in mountainous regions. • Rock avalanche-induced air blasts can cause damage far beyond the sliding mass. • Large avalanche volume and high velocity are necessary conditions to generate powerful air blasts. • Geomorphology is influential in both air blast initiation and propagation. [ABSTRACT FROM AUTHOR]

Within mountainous landscapes neighboring glaciers, slope instabilities and consequent catastrophic mass flows are vital processes on Earth's surface, which have been of increasing interest for decades. These events commonly exhibit large volume, high velocity, and high mobility. Recently, a catastrophic debris flow occurred in India on 7 February 2021, which unfortunately claimed 70 lives and left 134 people missing. The failed mass comprises 80 % rock debris and 20 % glacier ice. Our remote sedimentological investigation of remnant deposition shows clear evidence of wet granular flow in upper Ronti Gad valley, which doesn't support the previous interpretation of immediate melting of the failed 20 % ice mass during the falling and impacting process. We further utilized the superelevation phenomenon to back-calculate the velocity downstream of the impact zone, and estimated the peak discharge, which is verified by field-documented data. Our results revealed an initial waning trend of rock and ice mass flow. As it entered the narrow valley of the lower Ronti Gad River, the extensive material erosion resulted in three-fold flow enlargement, which gave rise to a maximal peak discharge of up to 48–54 × 104 m3/s. The transition from granular flow to debris flow occurred in the 2-km-long channel downstream of the Ronti Gad-Rishigangga confluence. The sediment deposition of 4.8 × 104 m3 and the incorporation of stream water in this zone have dominated the rheologic transition. We inferred that the intense erosion of erodible sediment due to topographic constraint plays an essential role in maintaining the mobility of the flow. Therefore, the effect of glacier ice meltwater on high mobility may be overestimated. As long as the granular flow can access the stream water in major rivers, flow transformation can easily happen because of sufficient water supply in the channel. The valley morphology in the proglacial region is commonly featured by the shift from an upstream U-shaped valley carved by glacier erosion into a downstream fluvial-erosion-dominated V-shaped valley. This geomorphic setting of glaciated tributary favors the long-distance run-out of rock and ice avalanche. • Material erosion due to valley confinement enlarged Chamoli mass flow • The effect of glacier ice meltwater on high mobility may be overestimated. • The proglacial geomorphic setting favors high mobility of rock-ice avalanche. [ABSTRACT FROM AUTHOR]

A number of large landslides, which have strongly affected fluvial processes in the upstream catchment of the Minjiang River along the eastern margin of the Tibetan Plateau, Sichuan, were investigated with regard to both geological structure and topographic development. Topographic analysis suggested that there is a major knickpoint that formed not as a result of landslides but via tectonic activity and that the knickpoint propagated upstream, forming an inner gorge and undercutting and destabilizing nearby slopes. The effects of the knickpoint propagation and inner gorge formation on slope stability are dependent on the geometrical relationships between the river and geological structures. When the geological trend is normal or highly oblique to the river axis, landslides generally do not occur, but gigantic rockslides have occurred on one side of the Minjiang valley, which can be attributed to a wedge structure consisting of bedding planes and joints with intersections dipping valleyward and tight folds with hinges plunging valleyward. When the beds are planar, moderately dipping, and strike nearly parallel to the river, buckling deformation commonly occurs on cataclinal slopes, often transforming into catastrophic failure. Landslide dams form another type of knickpoint on the river channel that gradually disappear from the downstream to upstream as a result of river erosion. Our findings strongly suggest that the study of slope development by river incision must consider geological structures and that an understanding of geological structures and river incision history can provide a conceptual model for the prediction and mitigation of geohazards in tectonically active drainage basins. [ABSTRACT FROM AUTHOR]

The Ötz Valley and adjacent regions in Tyrol (Austria) have been repeatedly affected by large rockslope failures following deglaciation. Six rockslides, each over 10 7  m 3 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. [ABSTRACT FROM AUTHOR]

In this study a combination of different topographic data from historic topographic maps and remote sensing is used to reconstruct and monitor the behaviour of the high alpine ice contact rockslide system Marzell and its response to glacial debuttressing in the Eastern Alps. Topographic data from archives (historical topographic maps, national glacier inventories, aerial images, orthoimages and ALS data) and data from monitoring campaigns (geodetic measurements, terrestrial laser scanning and UAV imaging campaigns) are processed to georeferenced images and/or elevation data, respectively. The data from different data sources is compiled and analysed with the aim to i) reconstruct the extent, thickness and volume changes of the glacier since 1893 and ii) to analyse the rockslide deformation evolution by extracting information about the displacement direction, dip angle, velocity and partial failure of rockslide slabs since 1951. The rockslide is compound of different rockslide slabs which move downwards as rigid blocks along basal shear zones. The analyses and interpretation of the data suggest a rotational type of rockslide failure mechanisms. The rockslide activity correlates with the ice volume loss at the adjacent part of the glacier. In the period between 1971 and 1997 the annual average rockslide activity was about 0.05 m/a and the annual average ice thickness loss was 0.1 m/a. Since the end of the last century the annual average ice thickness loss increased dramatically to 5 m/a. In that period the rockslide activity accelerated. The highest rockslide activity (up to 1.5 m/a) was observed in the 2000s when half of the slope toe was exposed because of glacier retreat. Since 2010 a deceleration of the rockslide can be observed. In the vicinity of the rockslide the glacier almost disappeared and lost 99.88% of its ice volume between 1893 and 2014. The geomorphological and geological information gathered about the rockslide evolution and the glacier retreat form the base for further rockslide analyses and allow to study and model the influence from glacial debuttressing. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Deep-seated rock slides (DSRSs), recognised as one of the most important mass wasting processes worldwide, involve large areas and cause several consequences in terms of environmental and economic damage; they result from a complex of controlling features and processes. DSRSs are common in Calabria (southern Italy) where the complex geo-structural setting plays a key role in controlling the geometry of the failure surface and its development. This paper describes an integrated multi-disciplinary approach to investigate a DSRS in Palaeozoic high-grade metamorphic rocks of the Sila Massif; it focuses on the definition of the internal structure and the predisposing factors of the Serra di Buda landslide near the town of Acri, which is a paradigm for numerous landslides in this area. An integrated interdisciplinary study based on geological, structural, and geomorphological investigations—including field observations of weathering grade of rocks, minero-petrographic characterisations, geotechnical investigations and, in particular, fifteen years of displacement monitoring—is presented. Stereoscopic analysis of aerial photographs and field observations indicate that the Serra di Buda landslide consists of two distinct compounded bodies: (i) an older and dormant body (~ 7 ha) and (ii) a more recent and active body (~ 13 ha) that overlies the previous one. The active landslide shows movement linked to a deep-seated translational rock slide (block slide); the velocity scale ranges from slow (1.6 m/year during paroxysmal stages) to extremely slow (< 16 mm/year during stable creep stages). The geological structures and rock weathering have played a key role in the landslide's initiation and further development. Steep slope angles, rugged topography, river deepening and erosion at the toe of the slope are also responsible for the formation of this landslide. In particular, the landslide shows a strongly tectonic constraint: the flanks are bounded by high-angle faults, and the main basal failure surface developed inside an E–W southward-dipping thrust fault zone. The entire active rock mass (total volume of approximately 6 Mm 3 ) slid at one time on a failure surface that dipped < 27°, and the maximum depth, as determined by inclinometer measurements, was approximately 58 m. Petrographic and mineralogical analyses suggest that the rocks in the thrust zones, where the failure surfaces develop, are highly affected by weathering processes that significantly reduce the rock strength and facilitate the extensive failure of the Serra di Buda landslide. Finally, the landslide's internal structure, according to geotechnical investigations and displacement monitoring, is proposed. The proposed approach and the obtained results can be generalised to typify other deep landslides in similar geological settings. [ABSTRACT FROM AUTHOR]

Ground-Based Interferometric Synthetic Aperture Radar (GB-InSAR) campaigns were performed in summer 2011 and 2012 in the Romsdalen valley (Møre & Romsdal county, western Norway) in order to assess displacements on Mannen/Børa rock slope. Located 1 km northwest, a second GB-InSAR system continuously monitors the large Mannen rockslide. The availability of two GB-InSAR positions creates a wide coverage of the rock slope, including a slight dataset overlap valuable for validation. A phenomenon of rock slope breathing is detected in a remote and hard-to-access area in mid-slope. Millimetric upward displacements are recorded in August 2011. Analysis of 2012 GB-InSAR campaign, combined with the large dataset from the continuous station, shows that the slope is affected by inflation/deflation phenomenon between 5 and 10 mm along the line-of-sight. The pattern is not homogenous in time and inversions of movement have a seasonal recurrence. These seasonal changes are confirmed by satellite InSAR observations and can possibly be caused by hydrogeological variations. In addition, combination of GB-InSAR results, in situ measurements and satellite InSAR analyses contributes to a better overview of movement distribution over the whole area. [ABSTRACT FROM AUTHOR]

In mountain ranges deep-seated gravitational slope deformations (DSGSDs) and extremely rapid mass wastings of rock > 10 5 m 3 in volume (catastrophic rock-slope failures, CRF) are present, yet their mutual relation is poorly documented. Near the Brenner Pass (1370 m asl) in the eastern Alps, five catastrophic rock-slope failures of medium- to high-grade metamorphites are clustered (‘Brenner Pass Cluster’; BPC), and three of them are related to DSGSDs. The catastrophic rock-slope failures involved volumes from 12 to 110 Mm 3 and show fahrboeschung angles of 10–27°. Numerical dating ( 14 C, 234 U/ 230 Th) suggests that all catastrophic slope failures of the BPC occurred between ≤ 13.5 and 6.2 ka. Three of the CRF events may have occurred during the Younger Dryas (12.7–11.7 ka), whereas two events occurred during the Holocene. Backwater basins dammed up by the CRFs range from 2.5 km 2 (Ridnaun rock avalanche) to 15.5 km 2 (Stilfes rock avalanche). Three of the catastrophic rock-slope failures are associated with and developed as a partial failure of a DSGSD. This suggests that progressively slow deformation of slopes ultimately exceeded a stability threshold, resulting in catastrophic rock-slope failures. The initial kinematic mechanisms of failure vary between large-scale toppling, wedge sliding, and planar sliding and are strongly controlled by the structural setting of the slopes. A direct connection of catastrophic mass wasting with specific palaeoclimatic conditions (e.g., phases of enhanced precipitation) is not indicated; however, this does not exclude specific meteorological situations (e.g., occurrence of short-term heavy rainfall) that may have expedited slope instability and perhaps even triggered catastrophic events. Attempts to correlate catastrophic rock-slope failures with specific palaeoclimatic regimes are still encumbered by substantial methodical uncertainties and imprecisions as well as the scarcity of dated CRF events. The mapped distribution of CRFs unequivocally indicates that structural predisposition is the most significant long-term control in forming CRF clusters. [ABSTRACT FROM AUTHOR]

On 22 February 1756 the largest historically recorded rockslide in Norway took place at Tjelle in the Langfjord (Western Norway). The rockslide created three displacement waves of up to 50 m in height that caused 32 casualties and destroyed most houses and boats along the shores of the Langfjord. The trigger and contributing factors leading to the Tjellefonna rockslide are largely unknown and even seismic triggering has previously been suggested. This study provides a thorough back-analysis of the Tjellefonna rockslide using detailed geomorphological, engineering geological and tectonic field mapping in combination with topographic reconstructions, bathymetry analysis, volume estimations and numerical slope stability analysis. The back-scarp and eastern flank of the Tjellefonna scar form several tens of meter high rock walls, while the basal failure surface and other parts of the scar are covered by rock avalanche debris that extend from the back-scarp down to the bottom of the Langfjord. The rockslide occurred in granodioritic gneisses with variably developed metamorphic foliation that is folded and strike parallel to the fjord. Two prominent fault zones are present in close proximity to the Tjellefonna scar; one is steeply SE-dipping (Tjelle fault), while the other one is sub-horizontal to shallow SE-dipping (Ritlehamran fault). Both fault zones are linked to the Møre-Trøndelag Fault Complex, with one of its branches forming the Langfjord lineament and probably also the faults at Tjellefonna. Additionally, there are four persistent joint sets that together with the metamorphic foliation and the Tjelle fault define the back-scarp of the rockslide and give a fracturing of the rock mass corresponding to a Geological Strength Index (GSI) of 45–55. The GSI decreases significantly to 10–20 in the fault zones, which form distinct weakness zones in the rock slope. Volume estimates based on a reconstruction of the ante-rockslide topography range from 9.3 to 10.4 million m 3 , which is lower than previous volume estimates (12–15 million m 3 ). Large portions of the failed rock mass remained on land and only approximately 3.9 million m 3 entered the fjord. The observed discontinuities in the rock mass at Tjellefonna do not allow for a simple kinematic failure mechanism due to the lack of moderately SE-dipping structures. The basal failure surface was most likely not composed of a single structure, but of a complex interplay of fault zones, metamorphic foliation, joints and broken rock bridges. Numerical slope stability modelling highlights that weak fault zones are essential for the development of the failure surface over a long time. This progressive failure was likely aided by low- to medium-magnitude earthquakes that are frequent in the region. Numerical slope stability modelling and historical accounts suggest, however, that heavy, long-lasting rainfall was the triggering factor for the 1756 Tjellefonna rockslide rather than an earthquake. [ABSTRACT FROM AUTHOR]

Rockfalls and rockslides are significant geomorphic processes on high alpine proglacial rock slopes. In this study, we quantitatively evaluate sediment transport on a recently deglaciated rock slope that is directly connected to the shrinking Gepatschferner glacier, by multi-temporal terrestrial and airborne LiDAR observations. According to the LiDAR measurements, sediment transport by gravitational mass movements on this single proglacial rock slope (0.2 km 2 ) yielded 159 GJ/a geomorphic work. The most significant part (141 GJ/a) was released by rockfall while 18 GJ/a were performed by the sliding activity of a 1,250,000 m 3 large unstable rock mass. The results indicate that slope development and talus formation in proglacial environments may be a rapid process despite of being caused by continuous rockfall activity over several millennia. [ABSTRACT FROM AUTHOR]

In the Indian Himalayan region (IHR), landslide-driven hazards have intensified over the past several decades primarily caused by the occurrence of heavy and extreme rainfall. However, little attention has been given to determining the cause of events triggered during pre- and post-Indian Summer Monsoon (ISM) seasons. In the present research, detailed geological, meteorological, and remote sensing investigations have been carried out on an extreme rainfall landslide event that occurred in Sadal village, Udhampur district, Jammu and Kashmir Himalaya, during September 2014. Toward the receding phase of the ISM (i.e., in the month of September 2014), an unusual rainfall event of ~ 488.2 mm rainfall in 24 h took place in Jammu and Kashmir Himalaya in contrast to the normal rainfall occurrence. Geological investigations suggest that a planar weakness in the affected region is caused by bedding planes that consist of an alternate sequence of hard, compact sandstone and weak claystone. During this extreme rainfall event, the Sadal village was completely buried under the rock slides, as failure occurred along the planar weakness that dips toward the valley slope. Rainfall data analysis from the Tropical Rainfall Measuring Mission (TRMM) for the preceding years homogeneous time series (July-September) indicates that the years 2005, 2009, 2011, 2012, and 2014 (i.e., closely spaced and clustering heavy rainfall events) received heavy rainfalls during the withdrawal of the ISM; whereas the heaviest rainfall was received in the years 2003 and 2013 at the onset of the ISM in the study region. This suggests that no characteristic cyclicity exists for extreme rainfall events. However, we observe that either toward the onset of the ISM or its retreat, the extreme rainfall facilitates landslides, rockfall, and slope failures in northwestern Himalaya. The spatiotemporal distribution of landslides caused by extreme rainfall events suggests its confinement toward the windward side of the Himalayan front. [ABSTRACT FROM AUTHOR]

In order to increase the understanding of deep-seated rock slides in terms of formation processes, kinematics, and the impact of geometrical factors on slope stability and deformation behaviour, a 300 m thick active rock slide located in Austria was investigated. Results of geological and geodetic field surveys, geophysical in-situ investigations and numerical modelling are presented and analysed. Particular focus is given on the geomechanical characterisation of the rock slide mass, progressive topographical slope changes due to initial rock slide formation processes, internal rock mass deformation processes and back-calculated strength properties of the basal shear zone. Back calculations considering the actual rock slide geometry yields a friction angle of the basal shear zone of about 24°. Rock slide volume balance analyses are performed in order to determine mass loss due to secondary slides and river erosion. In relation to the pre-failure topography, the middle to upper part of the rock slide has lost (zone of depletion) and the foot of the slope has accumulated rock mass material (zone of accumulation). GIS-based estimations show an enormous volume imbalance between the depletion and accumulation zones. Given that the volume accumulation at the foot of the slope is nearly three times smaller than the volume depletion at higher elevations, considerable erosion of the toe by the river has occurred. The complex geological interaction of the rock slide with the alluvium at the toe of the slope was a key question of this study, and thus the geomechanical impact of the alluvium on slope deformation and stability behaviour was studied by applying 2D discrete element modelling methods. Results show that the alluvium at the foot of the slope has a positive effect on the slope stability and the sensitivity of the stability behaviour. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The long-lasting earthquake sequence of Central Italy in 2016 triggered around 1370 landslides, most of which were observed close to ridge areas. The area of San Pellegrino di Norcia (PG) was badly affected by the 6.5 Mw Norcia earthquake that triggered 95 rock falls and slides with volumes ranging from 0.5 m3 to 380 m3 over an area of 0.6 km2. The presence of such a large number of coseismic landslides in a small area provided a suitable case study for investigating triggering mechanisms related to slope morphology and the subsequent propagation dynamics of rockfalls. To this aim, detailed field data collection and up-to-date terrain modelling based on Unmanned Aerial Vehicle (UAV) imagery were carried out. They permitted to perform morphometric analyses oriented at defining: (a) the frequency of occurrence of rockfall with reference to the energy relief, (b) the relationships between extensions of source and propagation areas and (c) the change in the shape of the propagation area as a function of the different terrains crossed by rockfalls. The results of the morphometric study were compared with dynamic analyses of rock-slides onset and simulations of rockfall propagation. They highlighted that, disregarding the presence of steep rock faces, the failures were located close to ridge and slope edges, thus pointing out the role of topography on triggering of landslides. Moreover, it was possible to observe that even small-sized rockfalls had a widening effect in the foothill characterized by longer runouts compared to rockfall simulations. This issue was due to the mobilization of the talus debris covering the limestone bedrock. This study investigates an area where a significant increase in rockfall hazard can be expected due to the coupled effect of topographic amplification and debris remobilization. • A slope highly affected by coseismic rockfalls is studied with integrated approaches. • Rockfalls were triggered close to ridges regardless of rock mass features. • Topographic amplification of the PGA is quantitatively evidenced. • Small rockfalls remobilized slope debris, causing large propagation areas. • Slopes in seismic areas covered by debris can suffer increased rockfall hazard. [ABSTRACT FROM AUTHOR]

Zhao et al. (2019) examine gigantic landslides in the Diexi area along the eastern margin of the Tibetan Plateau and propose their successive failure based on a knickpoint migration conceptual model. They postulate that a major river knickpoint (KpMJ) identified by them in the middle reaches of the Minjiang River (Sichuan, China) was initiated at the Longmenshan Fault and subsequently propagated ~ 85 km to its present position upstream of the Diexi lake. They then argue that this retreating knickpoint left in its wake an inner gorge that undercut and destabilized hillslopes, triggering a series of large landslides in the Diexi area. We question this interpretation based on our high-resolution landslide mapping, an analysis of knickpoints (i.e., profile convexities >30 m high) in the Minjiang channel network, and field observations of lacustrine sediments and epigenetic gorges associated with the Diexi landslides. We confront the model proposed by Zhao et al. (2019) with three key arguments: 1) Major profile convexities in the Diexi area, including KpMJ, are associated with landslide or debris flow deposits and there is no basis for connecting explicitly any of these to long-distance knickpoint retreat; 2) the giant Diexi paleolandslide predates the debris avalanches at KpMJ, therefore the latter cannot have been the trigger for landsliding in this area; and 3) the spatial distribution of 666 mapped knickpoints in the Minjiang River mainstem and tributaries is not consistent with simple long-distance propagation of an 'incisional wave' initiated at the Longmenshan Fault. [ABSTRACT FROM AUTHOR]

Uplifting mountains are denudated by gravitational deformation, landslides, and glacial or fluvial erosion. We investigated the response of valley slopes to glacial and fluvial erosion along the Kali Gandaki (KG) River, one of the largest rivers that flows through the High Himalaya southward from Tibet to India and diagonally cuts the strikes of gneiss and slate foliations. Satellite images with 2.5 m resolution and 5-m Digital Elevation Models (DEMs) were used for the investigation. Within a 20-km reach of the KG River, we found a series of 11 landslides, which vary from a total area of 0.58 to 12 million m2 each. The foliations generally strike NW–SE and dip at 30° to 50° to the NE, so the left bank slopes are anaclinal and the right bank slopes are cataclinal. On the cataclinal slopes, buckling of beds occurs, and gradual deformation proceeds in slate and two-mica gneiss, while in the more competent calc gneiss, buckling deformation develops into a rock avalanche. Such rock avalanches are represented by the largest Dhampu-Chhoya landslide, which once blocked the KG River and drastically changed the river morphology. Anaclinal slopes of two-mica gneiss were toppled and transformed into rock avalanches on three slopes. The KG River has a prominent fluvial knickpoint, which is currently at an elevation of 1800 m, and it has slope breaks on the left bank that are 200–400 m above the riverbed downstream of the knickpoint. Toppling was observed on slopes higher than slope breaks, which suggests that toppling began before the formation of slope breaks by fluvial incision and that the lower slopes did not adapt to the younger fluvial incision. In contrast, slope breaks are scarcely found on the right bank, probably because slow-moving DGSDs, which followed the river incision, erased them. • The Himalayan mountains respond to erosion based on geological structures. • Buckling and gradual deformation proceed on dip slopes of incompetent rock. • Buckling of competent rock develops into catastrophic failure. • On anaclinal slopes, toppling and catastrophic failure occur. • Upstream migration of a fluvial knickpoint induced a series of mass movements. • Glacial erosion and deglaciation destabilized the feet of dip slopes, inducing buckling deformation. [ABSTRACT FROM AUTHOR]

Based on a morphostructural analysis of a cliff coast segment of Forkastningsfjellet, back analysis of the August 12th, 2016 rock slide situated at 78°19′10"N/15°39′52″E was carried out. This rock slide comprises a volume of 175,000 m3, and indicates a partial reactivation at the front of the ~100 million m3 large postglacial Forkastningsfjellet rock slide. We studied the controlling and triggering factors of the reactivation using a 2-D limit-equilibrium calculations and a 3-D simulation with Scoops3D. Slope instability initiated along a pre-existing listric block fault that was inherited from the postglacial Forkastningsfjellet rock slide. The cause of the failure is attributed to a strength decrease and additional water pressures along the pre-existing sliding plane, possibly in combination with a degradation of the affected weak shales of the Rurikfjellet Formation, which build up a major part of the steep slope. Although the analysis suggests a structural control on the type and mechanism of slope failure, a significant impact of climate-related factors is inferred. Increasing temperatures and changing precipitation trends are reported from Svalbard. These are interpreted to foster permafrost degradation and reduce bonding forces in the thawing ice-filled fractures at the site. In addition, progressive weakening by more frequent frost and thaw cycles of the slaking shales and the introduction of additional water pressures to the rock mass are considered to contribute to the instability. The final trigger of the 2016 failure is attributed to a two-day rainfall that had preceded the event. The application of the Scoops3D software tool showed that it is capable of predicting the locations and affected volumes of landslides with reasonable accuracy, when the geological and structural setting is well established. Under such premises the tool can be used to support preliminary susceptibility assessments in study areas with comparable geological and morphostructural settings. • Active rock slide along the Isfjorden coast of Svalbard • Rock slope failure along reactivated pre-existing faults • Back calculation of a rock slide in weak intensely fractured rock mass • Rock slide suggests influence of climate warming. • Rock slide susceptibility modelling with Scoops 3D [ABSTRACT FROM AUTHOR]

In rapidly uplifting regions, deep seated landslides are a prominent natural hazard that influence landscape evolution and are an important source of sediment. They pose a threat to infrastructure, and their failure can deliver sediment that overwhelms or blocks river channels. Consequently, a better understanding of why and where deep-seated landslides occur would help us reduce hillslope erosion, improve water quality, and allow us to better understand how landscapes evolve. Although the slope threshold model provides a framework for understanding how these landslides form, it has several shortcomings. Specifically, it fails to predict the spatial organization of landslides within a region, and it does not explain why landslide-prone portions of a region can exhibit relatively low slopes. To explore these issues, we have used a landslide susceptibility analysis within the Whanganui Basin of the North Island of New Zealand to explore the role that multiple susceptibility factors play in the occurrence of both translational and rotational deep-seated rock slides. Our findings contribute to a growing view of the relative importance of fluvial incision and the more subordinate role that earthquakes play in the development of large, deep-seated landslides. Additionally, our analyses identify the potential influence that widespread deforestation may have had on promoting instability, despite the deep-seated nature of the landslides studied. Most importantly however, we find that where slopes and weak geological structures align, a universal threshold slope does not exist, and many landslides develop on hillsides with below-average slope angles. This suggests that the presence of structural controls on landslide occurrence create a more complex landscape, where hillsides structurally predisposed to landslide occurrence have a much lower threshold slope angle. • We implement a deep-seated landslide susceptibility model within New Zealand. • Seismic factors were not predictive of deep-seated landslide occurrence. • Slope and bedding alignment was predictive of deep-seated landslide occurrence. • Slope and bedding alignment resulted in deviations from a universal slope threshold model. • Reducing river incision may be an effective way to prevent future failures. [ABSTRACT FROM AUTHOR]

Rockfalls and rockslides are often dominant geomorphic processes in steep bedrock landscapes, but documenting their occurrence can be challenging, requiring frequent monitoring and well resolved spatial data. Repeat application of remote sensing methods such as Terrestrial Laser Scanning (TLS) and Structure-from-Motion (SfM) photogrammetry can detect even very small rockfalls, but typically these acquisitions span only years and may not record rockfall activity representative of longer-term rates of cliff erosion. Inventory databases can extend rockfall records, but are commonly incomplete and prone to observation bias. We employed TLS and SfM on two adjacent cliffs (El Capitan and Middle Brother) in Yosemite Valley, integrating semi-annual data collections from 2010 to 2017 with "historical" (archival) SfM models derived from oblique photographs taken in 1976. Comparing the 1976 SfM models against more recent data allows for more accurate and precise rockfall detection and volume measurement over a 40-year period. Change detection indicates that 235 rockfalls occurred from the two cliffs, more than twice as many events as are recorded in Yosemite's inventory database. Although individual rockfall volumes reported in the inventory database vary from those measured by SfM-TLS, reported cumulative volumes are similar to measured volumes, likely because the large-volume events that account for most of the cumulative volume tend to be widely observed and well-documented. Volume-frequency relationships indicate that the cliffs erode predominantly by less frequent, larger-volume rockfalls, at rates of 0.9 to 1.7 mm/yr. Our study demonstrates how integrated SfM and TLS measurements, especially utilizing SfM models derived from historical imagery, allow detection and quantification of rockfalls spanning several decades, complementing and improving inventory databases, informing rockfall hazard assessment, and providing longer-term rates of cliff erosion. • 1976's photographs yielded high-resolution models of two cliffs in Yosemite Valley. • "Historical" models were compared to terrestrial lidar data acquired in 2010/2016. • 235 rockfalls were detected from the two monitored cliffs over a 40-year period. • Both cliffs experienced twice as many rockfalls as are recorded in the database. • Rockfall volume-frequency relationships indicate erosion rates of 0.9 to 1.7 mm/yr. [ABSTRACT FROM AUTHOR]

Moderate-relief landscapes, such as the Czech Flysch Outer Western Carpathians (COWC), in comparison with alpine regions are rarely subject to extensive landslide inventory mapping. An understanding of landslides in such a landscape is needed, because densely populated hilly landscapes in temperate zones are usually of major socio-economic importance. In this study, we performed the first LiDAR-based landslide mapping for the entire COWC area (~7539 km2), one of the most landslide-prone regions in Europe. By calculating various landscape and landslide metrics, we infer the distribution, frequency-area relationships, kinematics and controls of mass movements with special attention on large landslides (≥0.1 km2) and deep-seated gravitational slope deformations (DSGSDs). We mapped a total of 13,611 landslides, of which 1357 failures are large landslides and DSGSDs. Whereas the lower and more subdued areas in the southern part of COWC are hotspots in terms of the total number of landslides, the higher and more topographically pronounced areas in the northeast are affected predominantly by large landslides and DSGSDs. However, landslides with ≥0.1 km2 are widespread throughout the whole territory of COWC. A discrepancy also exists in the spatial distribution of different types of landslides. Rock slides and DSGSDs are dominant in the north-east, while flow-type landslides are dominant in the southern lower topographic relief with claystone-dominated flysch. We conclude that 1) distinct geological units (nappes) produce landslide populations with different frequency-area distributions; 2) stratigraphic composition alongside the tectonic style of flysch formations control the type of landslides; 3) DSGSDs affect mainly slopes formed by rigid rocks sitting atop soft formations; and 4) geological conditions, rather than topography, control distribution of large landslides and DSGSDs in COWC. Unlabelled Image • New LiDAR-based inventory of landslides in the Czech Outer Western Carpathians (COWC) • More than 13,600 landslides are mapped, of which 1357 slope failures are large landslides (≥0.1 km2) and DSGSDs. • Large landslides and DSGSDs are widespread throughout the whole territory of COWC. • Geology rather than topography controls the distribution of large landslides and DSGSDs in the COWC. [ABSTRACT FROM AUTHOR]