Translational Rockslides Research Articles

Influence of Rock Slide Geometry on Stability Behavior during Reservoir Impounding

Assessing the stability behavior of deep-seated rock slides in the surroundings of large dam reservoirs requires an understanding of the geometry, the kinematics, the groundwater situation, and the rock mass and shear zone properties. This study focuses on the influence of rock slide geometry on stability evolution during initial reservoir impounding. Therefore, nine different rock slide models, mainly taken from published case studies with a well-explored geometry, were analyzed. Based on the assumption that the rock slides are close to limit equilibrium in a no-reservoir scenario, reservoir impounding causes a reduction in the factor of safety (FoS). The results show a large impact of the water level for rotational slides where the majority of the rock mass is located at the lower part of the slope. This results in a maximum reduction in the FoS of up to 12%. In contrast to this, translational rock slides are less affected by reservoir impounding. The stability analysis shows that the change in FoS is strongly controlled by the kinematics of the rock slide and the geometry near the foot of the slope. Consequently, a comprehensive in situ investigation of the geometry and kinematics is necessary in order to reliably assess the influence of initial reservoir impounding.

Force and energy equilibrium-based analytical method for progressive failure analysis of translational rockslides: formulation and comparative study

Force and energy equilibrium-based analytical method for progressive failure analysis of translational rockslides: formulation and comparative study

Mechanisms of rock slope failures triggered by the 2016 Mw 7.8 Kaikōura earthquake and implications for landslide susceptibility

Landslide failure mechanisms are influenced by topography, lithology, structure and rock mass damage – factors that also control landslide susceptibility. Failure mechanisms, however, are rarely considered in regional-scale coseismic landslide susceptibility analyses. In this study, we use 3D pixel tracking in pre- and post-earthquake aerial imagery, geomorphic mapping, rock mass characterisation, and geophysical ground investigations to develop conceptual models for three earthquake-induced landslides triggered by the 2016 Mw 7.8 Kaikōura earthquake on New Zealand's South Island. Analysis of two incipient landslides in Cretaceous greywacke illustrates the failure stages of a rock mass comprising multiple sets of closely-spaced and low persistence discontinuities. Conversely, analysis of a landslide in Neogene massive siltstones illustrates the role of high-persistence bedding planes in generating large translational rockslides. These two distinct mechanisms typify failures in highly deformed basement and overlying massive sedimentary rocks respectively, and highlight the link between rock mass damage, failure mechanism, and initiation. In greywacke failures, the rupture plane initiated close to the ridgetop and propagated as a joint-step-path failure along pre-existing, but low-persistence joints whereas the landslide in Neogene siltstone initiated by sliding along weak, high persistence, bedding planes near the base of the slope where topographic stresses are highest. Analysis of landslide displacements furthermore points out that the evolution of landslides is closely related to rock mass characteristics. In highly jointed Cretaceous greywacke, relatively little displacement is needed for rock mass disintegration and avalanching to occur whereas in Neogene siltstone, the landslide displaces as a coherent body - even at large displacements.Our results suggest that (1) failure mechanisms and, as a result, coseismic landslide susceptibility factors, may vary fundamentally in different geological settings; (2) characteristic spatial landslide displacement patterns may be used to remotely identify relevant failure mechanisms; and (3) the amount of displacement that can be accommodated before a failure transitions from sliding to avalanching, is highly dependent on material characteristics and topographic constraints.

A LiDAR-based landslide inventory and associated map portal (story map) for Grand Teton National Park

Funding has enabled the design and implementation of a preliminary landslide inventory including roughly 500 deposits throughout GTNP. The three most common mass movement deposits were related to debris flows, translational earth slides and translational rock slides. More than 10% of the features were field-verified during campaigns mapping along the Teton Fault and in areas across varying lithology and relief including Steamboat Mountain, Paintbrush Canyon, Cascade Canyon, Two Ocean Lake, Open Canyon and lower Granite Canyon. Features were mapped according to protocols established by the Oregon Department of Geology and Mineral Industries (DOGAMI) and supported by the USGS. The Story Map remains under development, awaiting revised mapping and feedback from GTNP staff.
 
 Featured photo taken from the AMK Ranch photo collection. https://flic.kr/p/RdWTqz

Tree ring evidence of slope movements preceding catastrophic landslides

Catastrophic landslides represent one of the most dangerous natural hazards. Detailed knowledge about the pre-landslide behaviour of the affected slope is crucial for effective modelling of the landslide origin in the future or even for creating an early warning system. As precise retrospective reconstruction of slope movements in the pre-landslide period is very limited, dendrogeomorphic methods can be effective tools for these purposes due to the high sensitivity of trees to slope movements and the spatial aspects of data provided by the position of affected trees. This study presents the results of tree ring-based analysis of slope movements preceding three selected catastrophic landslides of different types in the Outer Western Carpathians (Girova 2010—translational rockslide; Brodska 1997—earthflow; Hluboce 2006—rotational rockslide). Three aspects of pre-landslide slope movements were analysed in detail (frequency, intensity, spatial distribution). In total, 300 tree ring series from 150 trees disturbed by pre-landslide movements were used for these purposes. The Girova landslide was preceded by an increasing frequency and intensity of movements but without any spatial pattern. The Brodska landslide was preceded by a low frequency of low-intensity movements without any temporal trends but with significant clustering several years before the landslide. The Hluboce landslide was preceded by a decreasing frequency of movements with increasing intensity and concentration in the source zone. The character of pre-landslide movements is probably influenced by the presence of old landslide structures on the affected slope and by the mechanism of the movements themselves.

Giant landslides in the foreland of the Patagonian Ice Sheet

Quaternary glaciations have repeatedly shaped large tracts of the Andean foreland. Its spectacular large glacial lakes, staircases of moraine ridges, and extensive outwash plains have inspired generations of scientists to reconstruct the processes, magnitude, and timing of ice build-up and decay at the mountain front. Surprisingly few of these studies noticed many dozens of giant (≥108 m3) mass-wasting deposits in the foreland. We report some of the world's largest terrestrial landslides in the eastern piedmont of the Patagonian Ice Sheet (PIS) along the traces of the former Lago Buenos Aires and Lago Puyerredón glacier lobes and lakes. More than 283 large rotational slides and lateral spreads followed by debris slides, earthflows, rotational and translational rockslides, complex slides and few large rock avalanches detached some 164 ± 56 km3 of material from the slopes of volcanic mesetas, lake-bounding moraines, and river-gorge walls. Many of these landslide deposits intersect with well-dated moraine ridges or former glacial-lake shorelines, and offer opportunities for relative dating of slope failure. We estimate that >60% of the landslide volume (∼96 km3) detached after the Last Glacial Maximum (LGM). Giant slope failures cross-cutting shorelines of a large Late Glacial to Early Holocene lake (“glacial lake PIS”) likely occurred during successive lake-level drop between ∼11.5 and 8 ka, and some of them are the largest hitherto documented landslides in moraines. We conclude that 1) large portions of terminal moraines can fail catastrophically several thousand years after emplacement; 2) slopes formed by weak bedrock or unconsolidated glacial deposits bordering glacial lakes can release extremely large landslides; and 3) landslides still occur in the piedmont, particularly along postglacial gorges cut in response to falling lake levels.

Landslides types controlled by tectonics-induced evolution of valley slopes (Northern Apennines, Italy)

This paper investigates the role played by geomorphological and tectonic processes affecting a portion of an active mountain belt in causing the occurrence of different types of landslides developed in flysch bedrock. The adopted multidisciplinary approach (geomorphology, geology and geophysics) allowed to recognize in a portion of the Northern Apennines of Italy different types of landslides that developed in response to slope dynamics, in turn dependent on broader regional-scale tectonic processes. Sedimentary bed attitude, local tectonic discontinuities and lithology only partially influenced the type of landslides, which have been deeply affected by the activity of regional-scale antiform that controlled the hillslope geomorphic evolution in different ways. The growth of this structure and the tilting of its forelimb produced gently dipping slopes that approached the threshold angle that can cause the occurrence of (mainly) translational rockslides. Conversely, high-angle normal faulting parallel to the antiform axis (related to a later stage of activity of the antiform itself) strongly controlled the stream network evolution and caused the watercourses to deeply incise portions of their valleys. This incision produced younger steep valley slopes and caused the development of complex landslides (roto-translational slides-earth/debris flow). The results of the integrated study presented in this paper allowed to distinguish two main types of landslides whose development reflects the events that led to the geomorphological and geological evolution of the area. In this perspective, within the study area, landslides can be regarded and used as indicators of broader-scale recent tectonic processes.

Tectonic constraints on a deep-seated rock slide in weathered crystalline rocks

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 (~7ha) and (ii) a more recent and active body (~13ha) 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 (1.6m/year during paroxysmal stages) to extremely slow (<16mm/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 6Mm3) slid at one time on a failure surface that dipped<27°, and the maximum depth, as determined by inclinometer measurements, was approximately 58m. 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.

Characterization and analysis of a translational rockslide on a stepped-planar slip surface

In 2014 a small stepped-planar rockslide blocked a road near the town of San Germano Chisone in northwest Italy. Photographs of the rock cut that failed above the road were taken before and after the rockslide occurred. Some photos were acquired with the assistance of a UAV. These photos were used to conduct a forensic analysis of the rockslide. With the aid of photogrammetry software, it was possible to characterize the slope geometry and the larger geological structures that influenced the slope behaviour. A stepped-planar slip surface and the shape of the slabs of rock that failed were defined by discontinuities and these were well documented in the 3D photogrammetry models. The effective dilation angle was estimated from an assessment of the roughness of the discontinuity surfaces forming the slip surface. The stability of the rockslide was analysed as a stepped-translational failure mechanism. A two-block force equilibrium model of the rockslide was developed. With this analytic model, both deterministic and probabilistic methods were used to study the influence of water pressure as well as time-dependent shear strength degradation along the discontinuities and corrosion of rockbolts. The analysis suggests that the rockslide was caused by a combination of inadequate rock support, time-dependent shear strength degradation, and water pressure in the joints resulting from above average rainfall.

The Benner pass rock avalanche cluster suggests a close relation between long-term slope deformation (DSGSDs and translational rock slides) and catastrophic failure

In mountain ranges deep-seated gravitational slope deformations (DSGSDs) and extremely rapid mass wastings of rock >105m3 in volume (catastrophic rock-slope failures, CRF) are present, yet their mutual relation is poorly documented. Near the Brenner Pass (1370m 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 110Mm3 and show fahrboeschung angles of 10–27°. Numerical dating (14C, 234U/230Th) suggests that all catastrophic slope failures of the BPC occurred between ≤13.5 and 6.2ka. Three of the CRF events may have occurred during the Younger Dryas (12.7–11.7ka), whereas two events occurred during the Holocene. Backwater basins dammed up by the CRFs range from 2.5km2 (Ridnaun rock avalanche) to 15.5km2 (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.

Basal sliding and plastic deformation of a slow, reactivated landslide in New Zealand

The Taihape landslide is a large, deep-seated, translational rockslide in central North Island of New Zealand, one of over 7000 large landslides mapped in the late Neogene deposits of this area. This study examined its patterns of movement using high temporal resolution, high-precision monitoring and explored the relationships between the movement and triggering mechanisms. During the 30-year monitoring period, movement was always extremely slow, but included periods of faster and slower motion due to a combination of simultaneous basal sliding, internal plastic deformation and seasonal soil shrinkage and swelling. The data suggested that movement rate was not controlled by pore-water pressure or any other monitored parameter. Intervals of more rapid movement appear to follow toe erosion that debuttress the landslide mass, an example of which occurred following a flood in February 2004 that had a return period of about 100years.The high-temporal and spatial frequency of the monitoring and the measurement precision of the instruments have allowed new insights into the complex movement patterns of deep-seated, slow moving rockslides. The patterns of movement observed here, and the techniques described to collect and analyse the data, are applicable to many slowly moving landslides in New Zealand, and to those occurring in similar environments worldwide.

Integrated geophysical and morphostratigraphic approach to investigate a coseismic (?) translational slide responsible for the destruction of the Montclús village (Spanish Pyrenees)

A 12 million of m3 translational rockslide developed on a dip slope underlain by limestone with interlayered marls, and responsible for the destruction of the Montclus village in the fourteenth century, has been investigated by means of geomorphological and geophysical surveys. The combination of historical-geoarcheological, geomorphological, seismic refraction and electrical resistivity imaging datasets allowed the (1) reconstruction of the late Quaternary episodic evolution of the landslide, (2) characterization of the geometry and internal structure of the slid mass and (3) identification of preferential groundwater flow paths that favoured slope instability. The development of the landslide involved at least two different displacement episodes controlled by sliding surfaces at successively deeper stratigraphic positions. The first landsliding event, recorded by highly weathered landslide deposits situated above a perched failure plane, occurred approximately during the global Last Glacial Maximum (23–19 ka BP). The most recent event, which destroyed the Montclus village built on already slid rocks, is placed in the fourteenth century. Most probably, this reactivation event was triggered by the 1373 Ribagorza earthquake, with an estimated moment magnitude of M w 6.2. This work illustrates the benefits of combining geomorphological data with complementary geophysical technics in landslide investigation.

Patterns of movement in reactivated landslides

The primary aim of this research was to study the relationship between landslide motion and its causes, with reference to large, slow moving, reactivated translational rock slides. Surface displacements of the 22×106m3 Utiku landslide, in central North Island, New Zealand were measured using continuous GPS (cGPS), for three years. The nature of the movement of such slides has often been difficult to determine because of poor temporal and spatial monitoring resolutions. After removal of tectonic plate motion, the temporal pattern of the landslide's surface motion could be understood to arise from irregular episodes of faster (up-to-21mm/day) and slower (up to 26mm/yr) post-failure landslide displacement, and seasonal cyclic displacements of about 20mm/yr–10mm per half year in alternating directions. Intervals of faster motion gave rise to displacements of between 10 and 120mm per event. Faster displacement was associated mostly with basal sliding (mechanism 1), involving deformation within a thin clay seam as recorded by borehole inclinometer surveys. Slower surface displacement involved permanent internal deformation of the larger landslide mass, consisting of plastic deformation within the landslide body and/or slip along existing internal planes of weakness, and slip on the slide base (mechanism 2); it accounted for up to 26mm/yr of displacement at a mean angle of about 49° from the horizontal, indicating that the slide mass was thinning as it moved down slope. Seasonal cyclic displacements were synchronous with changes in pore pressure, suggesting that it is a shrink/swell process (mechanism 3) associated with wetting and recharge of groundwater during the wetter winter months, leading to a downslope movement, and soil shrinkage leading to upslope rebounds during the dryer summer months. The brief periods of faster displacement were triggered by seasonal peaks in pore pressure, linked to long periods (12 to 20weeks) of increased precipitation and lowered evapotranspiration. Faster displacement, however, was not arrested by lowering pore pressure or by any other monitored factor. Similarly, periods of slower displacement did not correlate with pore pressure changes, or with any other monitored factor. This study has shown that the annual movement pattern of a reactivated landslide is a combination of these processes that generate a complex overall movement record. The field measurements showed real variability arising from variations in rainfall and pore pressure, which were overprinted with measurement noise that may mask some other processes.

An extended Nishihara model for the description of three stages of sandstone creep

SUMMARY ManygentlydippingtranslationalrockslideshavetakenplaceinredJurassicstratainWanzhou which is located in the middle bank area of the Three Gorges Reservoir, China. In order to study the mechanism of these translational rock slides, conventional triaxial tests and creep tests on sandstone specimens from red Jurassic strata in Wanzhou are performed, and the rheological properties of the sandstone at accelerating creep stage are discussed. The quasistatic Nishihara model for transient and steady-state creep is modified by adding a straintriggered inertial element in series, resulting in a phase of quadratic accelerating creep. The model fits the experimental data at all stages of creep, allowing its parameters to be inferred from the data. Finally, a sensitivity study for the analytical solution of the proposed model is carried out, showing the effects of the inertial element and stress level on the creep strain of sandstone.

The Todagin Creek landslide of October 3, 2006, Northwest British Columbia, Canada

The Todagin Creek landslide is located at 57.61° N 129.98° W in Northwest British Columbia. A seismic station 90 km north of the landslide recorded the event at 1643 hours coordinated universal time (UTC; 0943 hours Pacific daylight time (PDT)) on October 3, 2006. The signal verifies the discovery and relative time bounds provided by a hunting party in the valley. The landslide initiated as a translational rock slide on sedimentary rock dipping down slope at 34° and striking parallel to the valley. The landslide transformed into a debris avalanche and had a total volume estimated at 4 Mm3. An elevation drop of 771 m along a planar length of 1,885 m resulted in a travel angle (fahrboschung) of 21.3°. The narrowest part of the landslide through the transport zone is 345 m. The widest part of the divergent toe of the landslide reaches a width of 1,010 m. Landslide debris impounded a lake of approximately 32 ha and destroyed an additional 67 ha of forest. The impoundment took 7 to 10 days to fill, with muddied waters observed downstream on October 13. No clear linkage exists with precipitation and temperature records preceding the landslide, but strong diurnal temperature cycles occurred in the days prior to the event. The Todagin Creek area appears to have an affinity for large landslides with the deposits of three other landslides >5 Mm3 observed in the valley.

Rock slope instability assessment using spatially distributed structural orientation data in Darjeeling Himalaya (India)

AbstractWe discuss a geographic information system (GIS)‐based methodology for rock slope instability assessment based on geometrical relationships between topographic slopes and structural discontinuities in rocks. The methodology involves (a) regionalization of point observations of orientations (azimuth and dip) of structural discontinuities in rocks in order to generate a digital structural model (DStM), (b) testing the kinematical possibility of specific modes of rock slope failures by integrating DStMs and digital elevation model (DEM)‐derived slope and aspect data and (c) computation of stability scenarios with respect to identified rock slope failure modes. We tested the methodology in an area of 90 km2 in Darjeeling Himalaya (India) and in a small portion (9 km2) within this area with higher density of field structural orientation data. The results of the study show better classification of rock slope instability in the smaller area with respect to known occurrences of deep‐seated rockslides than with respect to shallow translational rockslides, implying that structural control is more important for deep‐seated rockslides than for shallow translational rockslides. Results of scenario‐based analysis show that, in rock slopes classified to be unstable, stress‐induced rock slope instability tends to increase with increasing level of water saturation. The study demonstrates the usefulness of spatially distributed data of orientations of structural discontinuities in rocks for medium‐ to small‐scale classification of rock slope instability in mountainous terrains. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Spatial analysis of mutual fault/fracture and slope controls on rocksliding in Darjeeling Himalaya, India

In this paper, the Fry analysis was applied to study the spatial patterns (in terms of trends) of rockslides; proportion analysis was applied to study the spatial associations between rockslides and slope aspects; and distance distribution analysis was applied to study the spatial associations of rockslides with different sets of faults/fractures based on trends. In a study area in the Darjeeling district (India), the results of applications of these spatial analytical techniques support a proposition of mutual fault/fracture and slope controls on rocksliding. In different parts of the study area, deep-seated rockslides are associated with (a) NE-trending faults/fractures and SSE-facing slopes, (b) NW-trending faults/fractures and ENE-facing slopes, and (c) NNE-trending faults/fractures and SE- or ENE-facing slopes; whereas shallow translational rockslides are associated with (a) NNE-trending faults/fractures and SE-, NW-, WNW- or WSW-facing slopes, (b) WNW-trending faults/fractures and SW-facing slopes, (c) NNW-trending faults/fractures and ESE- or SW-facing slopes, and (d) NW-trending faults/fractures with SW-facing slopes. Creating and integrating spatial evidence layers representing mutual fault/fracture and slope controls on rocksliding can be achieved satisfactorily via application of evidential belief functions. A predictive map of rockslide susceptibility derived by using slope aspects, slope inclinations and proximity to the faults/fractures that are spatially associated with rockslides is superior to that derives by using slope aspects, slope inclinations and proximity to all faults/fractures. The proposed analytical methods are suitable for first-pass regional-scale assessment of rockslide susceptibility.

Mechanism of the Anlesi landslide in the Three Gorges Reservoir, China

Many gentle dip translational rock slides have taken place in the Three Gorges Reservoir, China. In order to study the mechanism of these translational rock slides, the authors use the Anlesi landslide as a typical case study to investigate in detail. Field investigations show that the slip zones of the Anlesi landslide were formed from a white mudstone in Jurassic red strata. X-ray diffraction and infrared ray analysis showed that the main mineral components of the slip zones are montmorillonite, illite, feldspar and quartz. Laboratory tests indicate that the slip zone soils are silty clay, of medium-swelling potential, the shear strength decreasing significantly as the slip zone attracts water and saturates. The main factors contributing to the Anlesi landslide are recent tectonic activity, incompetent beds, and intensive rainfall. Recent tectonic activity had caused shear failure along the incompetent beds, and joints within the sandstone. With the effect of intensive rainfall, water percolates to the incompetent beds along tectonic fissures, resulting in swelling of the soil material and high groundwater pressures within fissures in the strata. As a consequence, the Anlesi slope is prone to slide along these incompetent beds. Flac3D software was used to simulate the mechanism of the Anlesi landslide considering the rheological properties of soil and rock. The simulation results demonstrate that the stress, displacement and failure area changes with simulated creep time. The maximum displacement in the X direction reaches 7.59 m after 200-year simulated creep. Therefore, the mechanism of the Anlesi landslide can be illustrated considering the rheological properties of Jurassic red strata.

Geotechnical characteristics of large slow, very slow, and extremely slow landslides

Based on a study of 45 large slow-moving landslides, it is apparent that for a landslide to travel slowly after failure, the sliding is most likely to be active or reactivated, on a basal rupture surface at or close to residual strength. The likelihood of slow movement after failure is also increased when the inclination of the basal rupture surface is less than the residual friction angle. The slow-moving landslides are all of low rock-mass strength with varying degrees of disaggregation, or they possess soil strength. The influence of lateral margins on landslide restraint is generally small, with landslide movement typically controlled by fluctuations in piezometric pressure. The most commonly observed slow large landslides are mudslides and translational debris–rock slides, followed by particular forms of translational rock slides and internally sheared compound slides. Some mudslides display evidence of short periods of up to moderate velocities.

Predesign, failure and displacement mechanisms of large rockslides in the Annapurna Himalayas, Nepal

The paper analyses and compares four major mass movements (rockslides and rock avalanches) with volumes of 1 to 5 km 3 around the Annapurna Himalayan region from engineering, geological, quaternary geological, and geomorphological viewpoints. It shows how paleotectonic and neotectonic predesign, as well as morphological overprint caused by glacial activities, are the main preparatory causal factors for the sliding events. That is why giant failures of mountain crests have mainly occurred in areas of tectonic activity. The mechanism of failure, and displacement of the resulting large mass movements also strongly depends on this litho-tectonic predesign and continues in giant translational rockslides in which the primary rock structure or fabric is preserved, but shattered by mechanical stress during the sliding event.