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A large catastrophic rock avalanche with a total volume of ~18.0 × 106 m3 occurred at 5:38 am, 24th June 2017, at Xinmo Village, Maoxian, Sichuan, China, resulting in 102 casualties (10 deaths, 3 injuries, and 89 missing). We have been conducting a geological and geomorphological investigation in and around the Xinmo landslide site since 2015, and we present our results here, including data obtained before and after the landslide event. The landslide, which had an initial volume of 4.46 × 106 m3 of its source area, was induced by rainfall on a previous landslide scar near the ridge top. This initial landslide then struck and remobilized older landslide deposits in the middle and lower parts of the slope, which subsequently buried Xinmo Village at the landslide toe. The landslide occurred on a dip slope of Triassic calcareous psammitic and pelitic schists. The bedding plane, which dips downslope to the south with an orientation of N80°W/48°S, and high-angle NE–SW striking joints bounded the landslide source area at its base and sides, respectively. Satellite image analysis and field observations of the slope of the landslide scar before and after the landslide strongly suggest that the beds in the source area had already begun gravitationally deforming (e.g., buckling) prior to the 2017 landslide. Moreover, pits on the slip surface were likely the result of the dissolution of calcareous material. Dissolution probably reduced the rock strength along the bedding plane. A rainfall event from the 16th to 24th of June 2017 probably dominated the groundwater drainage, and finally triggered the catastrophic rock avalanche. In addition to the 2017 landslide, the hillslope just to the east of the Xinmo landslide exhibits pronounced gravitational slope deformation, including “A-tent”-like structures and warps induced by buckling. This suggests that this slope could also fail like the Xinmo rock avalanche during a future rainfall or earthquake event.

A dip slope contains weak planes in the same dip direction along the slope face. In this study, a discrete element simulation was implemented to investigate the behavior of a dip slope under shaking table tests. The simulated dip slope model was first verified by testing under different horizontal excitations. Then, the influence of the slope angle and dynamic force on the deformation characteristics of the dip slopes was explored. The simulations provide detailed descriptions of the deformation processes and potential sliding mechanisms associated with the dip slopes. The results of this study are summarized as follows: (1) Two types of slope sliding, namely differential and complete, were recognized. The model with a dip angle lower than 20° was more stable, and differential sliding developed gradually during external excitation. In the model with a dip angle higher than 20°, the external excitation easily triggered complete sliding. (2) For threshold slope angles higher than 20°, the behavior of the dip slope model changed from deformation to sliding, and the displacement within the models increased with increasing slope angle. (3) An increase in frequency led to a decrease in the trigger time for slope sliding. In addition, the slope angle was negatively correlated with the triggering time for sliding. (4) The amplification factor of peak ground displacement (PGD) increased as the slope angle increased. The amplification factors corresponding to low excitation frequencies were considerably lower than those for high excitation frequencies. In contrast to the trends for PGD, the amplification factor of peak ground acceleration (PGA) decreased as the slope angle increased.

The Cotswold Hills, southwest UK, are properly described as a cuesta, with a steep, west-facing scarp slope and a plateau-like dip slope. Drainage reflects this surface morphology, with most rivers flowing southeast along topographic and stratigraphic dip. Here, we compare two superficially highly similar rivers – the Frome and Churn – whose sources are nearly coincident, but whose behaviour dramatically diverges thereafter. We examine longitudinal profiles, channel steepness, predicted discharge, and valley shapes, using digital topographic data. River discharge and water hardness/temperature values were obtained at seven sites on the Churn and nine on the Frome over a two-year sampling campaign, delineated into summer and winter phases. Nearly 100 borehole records were interrogated from the two catchments in order to assess groundwater level variations. The Frome, flowing west against regional dips, develops a steep course and has carved a deep and wide valley that exposes the full sequence of Cotswold Jurassic stratigraphy. On the other hand, discharge and channel gradients are lower for the dip-slope Churn, whose valley exposes less stratigraphy and fewer springs. Our measurements of river water hardness and temperature suggest that a greater proportion of groundwater flows into the Frome, regulating discharge and maintaining baseflow over summer. We suggest that flank uplift of the Cotswolds is at least part of the reason for the higher incision rates of the River Frome, leading to its intersecting a greater number of highly transmissive fractures that contribute to its discharge. In turn, the increased discharge could positively impact local incision rates.

Dip-slope mapping is a fundamental task for landslide investigation and mitigation. However, most dip-slope mapping methods involve visual interpretations and manual processes that are inevitably subjective and time consuming. The advent of high-resolution digital elevation models (DEM) and increases in computing power have provided opportunities to improve the dip-slope mapping process. This study proposes a polygon auto-tracing method for generating dip-slope maps based on airborne Light Detection and Ranging (LiDAR) data and a customized spatial analysis toolset developed in Python. This method requires the input of strata boundaries produced for sedimentary terrain based on 2 m resolution LiDAR DEMs. The method begins by deriving the raster layer of the dip direction of the bedding, and it then executes a series of raster calculations among the three raster layers slope, aspect, and dip direction to extract the dip-slope raster cells. Using the clustering pattern of the dip-slope raster cells, we implement the Point-Density analysis tool to determine the dip-slope areas. The ArcGIS ModelBuilder platform is used to lay out an automated workflow for the proposed polygon auto-tracing method using the customized toolset. For demonstration purposes, we successfully mapped 298 dip slopes in the study area, which frequently experiences dip-slope landslides and is located in the sedimentary terrain of northern Taiwan. The dip-slope mapping results were compared and validated against two government-funded visually interpreted dip-slope maps. Our dip-slope mapping results were also used in a daylight analysis along major freeways to identify potential locations of daylighted dip slopes.

Existing fan-delta depositional models for lacustrine basins do not adequately address significant wave- and storm-related processes. However, in many lakes, such high-energy processes can be effectively driven by winds. As such, the prevailing wind direction determines the propagation direction of wind-induced waves. Observations from modern examples show that wave-dominated deposits commonly exist on one side of the lake, and their sedimentary processes are completely distinct from those on the opposite side. However, equivalent deposits have seldom been identified from subsurface data. We present an ancient example from the Upper Tongbomiao Formation in the Tanan Depression (Tamtsag Basin, Mongolia), which was previously interpreted as a fan-delta depositional system. Based on extensive core investigations, eighteen lithofacies, six lithofacies associations and two genetic deposition systems are identified, and a new sedimentological interpretation is proposed comprising a wave-dominated clastic littoral system in the western half-graben dip slope and a fluvial-dominated fan-delta system in the eastern half-graben. Sediments within the eastern half-graben unit include braidplain, fan-delta front and prodelta environments, while those within the western half-graben dip slope unit comprise dominantly alluvial fan, wave-reworked beach, storm-affected shoreface and offshore sediments. The strikes of the sediments in the western half-graben dip slope unit are parallel to the westward shoreline trend, while the progradation direction of sediments in the eastern half-graben unit is perpendicular to the eastern shoreline. This indicates approximately northwestward-propagating waves that were possibly driven by southeasterly winds, which has implications for understanding the prevailing wind direction in Northeast Asia during the depositional period. Other factors contributing to the preservation of these two distinct sedimentary systems are the paleotopography and subsequent climate shift towards more humid climatic conditions which intensified sediment supply and hydrodynamic conditions that were able to rework the sediments.

Natural soils often exhibit rotated transverse anisotropy due to various geological processes (e.g., tectonic movement, filling and soil deposition), and the trend of soil strength usually changes with depth. This study combines rotated transverse anisotropy with non-stationary random field (RF) to investigate the reliability and failure mechanism of a slope under undrained conditions. Two scenarios of non-stationary RF are considered: (a) the trend of soil strength increases along depth; (b) the trend increases along the direction perpendicular to bedding. It is found that the expected performance levels of slope reliability would be significantly different under different directions of the trend. When the undrained shear strength increases along the direction perpendicular to bedding, the changes of slope reliability and sliding consequence would be sensitive to the dip angle of strata. Besides, the failure mechanism can be affected by the direction of the trend and strata orientation. Generally, shallow failure is more likely to occur on the dip slope when soil strength increases along the direction perpendicular to bedding, while for reverse slope with soil strength increasing perpendicularly to the bedding, deep failure mechanism is significantly dominant.

A natural hillslope developing into a landslide shows ground cracks and topographic deformation. Geomorphological and subsurface investigations using appropriate methodology are essential to understand the failure mechanisms and stability of a hillslope. Huafan University campus located on a dip slope in northern Taiwan is facing a potential landslide hazard. Slope movement was detected through the development of ground cracks and persistent deformation of campus buildings and facilities. To monitor the sliding behavior of the dip slope, a nail network consisting of 144 ground monitoring points was set in 2001, and its coordinates were measured using conventional traverse surveying twice a year until 2017. The 17-year surficial surveying results were presented as a time series of displacements with constraints of geometry and distribution of ground cracks and underground observations. The long-term surveying results reveal multiple potential sliding blocks within the Huafan University campus. A model of landslide movement with a listric sliding surface is proposed. Additionally, from the velocity field derived from the monitoring points, the horizontal strain rates of the slope are estimated. The pattern of strain rates indicates that a plausible fault passing through the campus may have affected the movement of the dip slope. The long-term surface monitoring of a potential landslide slope in this study provides a reliable and economical way to understand the mechanism of movement behavior of the slope and evaluate slope stability.

Large rock avalanches often result in loss of life and catastrophic damage to infrastructure far from their initial failure positions, predominantly due to their tremendous volumes, high velocities and long runouts. Studies of the surface morphologies and internal structures of rock avalanche deposits can reveal evidence of their movement and deposition mechanisms. Through field survey, satellite image interpretation and particle-size distribution analysis, we studied the ancient, long-runout Linka rock avalanche, which is next to the Nujiang River, southeast Tibetan Plateau. The Linka rock avalanche, with a source volume of ~310 Mm3 originated from a high, steep dip slope and then transformed into a channelized rock avalanche, showing high mobility with a superelevation back-calculated maximal velocity of 42 m/s, a travel distance of ~6200 m and a Fahrboschung of 0.24. The slope failure sequence consisted of an initial failure of an outer limestone slab and a second failure of an inner sandstone slab. The limestone avalanche had 2 or 3 surges, while the sandstone avalanche probably had only one surge. The high mobility of the Linka rock avalanche predominantly resulted from a buckling failure occurred on a high relief source, low-energy dissipation during the channelized flow, intensive rock fragmentation in the basal facies and possible water lubrication when propagating bi-directionally along the Waqu River. Our findings for the Linka rock avalanche support previous knowledge that multiple mechanisms have different roles at different stages in a long runout rock avalanche.

Geometry of planner geological structures can interact with topographic slope and cause different types of slope failure (e.g. wedge failure, dip slope failure, and toppling etc.). This study focus on how the tectonic foliation influences the landslide pattern in the southern Central Range of Taiwan. The tectonic foliations in this area range from pencil cleavage to schistosity depending on the increasing of metamorphic grade, and different foliations have different influences on the landslide behaviors. To describe the relation between foliation and topographic slope, we create the θ D value as the angle between the foliation dip direction azimuth and the topographic downslope direction azimuth at a given location. The location of landslides in the area with pencil cleavage has no preferential θ D value, and it suggests the landslide distribution has no correlation with foliation. The location of landslides in the area with well-developed slaty cleavage is mostly in the lower θ D value, which suggests the landslides are more likely located in the area where the foliation dip direction is parallel to the topographic downslope direction. The location of landslide in the area with schistosity is mostly in the high θ D value area, which suggests the landslides are more likely located in the area where the foliation dip direction is opposite to the topographic downslope direction.

Due to the great difficulty of monitoring surface and underground runoff and sediment yield directly, the surface and underground hydrological processes associated with soil leakage loss in karst trough valleys remain unknown. The objective of this study was to analyse the role of the rock dip angle in the water and soil leakage loss processes, to assess the characteristics of surface and underground runoff and soil erosion and to investigate their conversion relationships using rainfall experiments. The results showed the following. i) At a steep rock dip angle (60°), the underground runoff yield had a shorter stabilization time than the surface runoff yield and that the underground runoff coefficient of the dip slope exceeded 0.5. ii) The surface sediment yield could be divided into the suspended load and the bed load and the underground sediment yield included only the suspended load. On the anti-dip slope, the surface erosion modulus was 0.83–2.50 times the underground erosion modulus. iii) The surface and underground cumulative runoff was linearly correlated with the cumulative sediment yield. The rock dip angle had a significant quadratic relationship with the surface and underground runoff and sediment yield. These results improve the understanding of the surface-underground runoff and soil erosion processes and have significance for preventing water and soil leakage loss on the slopes of karst trough valleys.

Rock dip angle plays a significant role in surface hydraulic characteristics and leads to different spatial distribution of water and soil loss in Karst Trough Valleys. In this study, the rock dip angle effect on the hydraulic characteristics and soil detachment rate on dip/anti-dip slopes was explored via rainfall simulations and a steel experimental flume. The rainfall intensities ranged from 30 to 90 mm·h−1, and the rock dip angles varied from 10° to 60°. The results revealed that i) surface runoff on the dip slope was higher than that on the anti-dip slope, whereas underground runoff presented opposite results. The 30° rock dip angle presented the critical flow velocity for the anti-dip slope, and the flow velocity reduced as the rock dip angle of the dip slope increased. ii) Laminar water flow occurred on the dip/anti-dip slope (Re was

Toppling failure of rock slopes is a complicated mode due to a combination of both continuous and discontinuous deformation, especially in dealing with anti-dip rock slopes. In this paper, a novel continuum-based discrete element method (CDEM), which is useful in modeling the entire progressive process from continuous to discontinuous deformation, is proposed to analyze the deformation characteristics, the failure mechanism and the evolution process of a large-scale open pit slope with a typical anti-dip structure. To simulate the slope deformation, the shear strength reduction method (SSR) is adopted to represent the strength degradation of rock mass in the deterioration process. The simulated results are validated using data obtained from a field investigation and continuous monitoring by employing an advanced remote sensing technique called ground-based interferometric synthetic aperture radar (GB-InSAR). To analyze the evolution trend of the anti-dip slope, the subsequent toppling failure mode is predicted using the validated CDEM models. Based on a case study of a slope at the Fushun open pit mine (in Fushun, China), the unique geological structure with various joints and discontinuities, ground-water, intense rainfall, and mining activities are identified as the main triggers for different failure stages. The comparison between the field data and the simulation shows that CDEM accurately depicts the rock deformation and the failure pattern of the studied slope. The proposed numerical modeling techniques can be used for predicting failures of other similar excavated rock slopes. The simulated evolution process and the recorded deformation patterns help engineers to gain a better understanding of rock mass movement of anti-dip slopes, and the presented methodology could be utilized for similar studies and engineering designs. (C) 2015 Elsevier B.V. All rights reserved.

Characteristic landscapes (e.g., cuesta, cliff and overhang of caprock, or stepped terrain) formed by differential erosion can be found in areas composed of variable geology exhibiting different resistances to weathering. Parallel retreat of slopes, defined as recession of slopes without changes in their topography, is sometimes observed on slopes composed of multiple strata. However, the conditions needed for such parallel retreat have not yet been sufficiently clarified. In this study, we elucidated the conditions for parallel retreat of rock slopes composed of alternating layers using a geometric method. In addition, to evaluate whether various rock slopes fulfilled the conditions for parallel retreat, we analyzed topographic data obtained from periodic measurement of rock slopes in the Aka-kuzure landslide, central Japan. Our geometric analysis of the two-dimensional slopes indicates that dip angle, slope gradient, and erosion rate are the factors that determine parallel retreat conditions. However, dip angle does not significantly affect parallel retreat conditions in the case of steep back slopes (slope gradient > 40°). In contrast, dip angle is an important factor when we consider the parallel retreat conditions in dip slopes and gentler back slopes (slope gradient

The relationship between large deep-seated landslides and geologic structures characteristic of accretionary complexes were examined in the Chichibu belt on the eastern part of the Kii Peninsula, central Japan. In the Chichibu belt, bedrock consists of Jurassic accretionary complexes composed of basalt, limestone, chert, Permian–Triassic boundary siliceous shale (PTBS), mudstone, sandstone, and melanges with sheared shale matrices. The landslides treated in this paper include prehistoric examples involving volumes greater than one million cubic meters (located in the Karako, Sono, Kasagi, and Aso areas), and the modern Kasugadani landslide that was triggered by the Typhoon Meari on 29–30 September 2004. The age of the landslide in the Sono area was estimated at 20,440 ± 70 BP and 20,820 ± 70 BP based on AMS-14C ages of wood fragments embedded in the dammed lake sediments, while ages of the other prehistoric slides are not known. All of the landslides occurred on dip slopes. The bedding, foliation, and fault planes of the rocks in the area generally trend E–W and dip to the north, although those in the Kasugadani area dip to the south as a result of local folding. The landslides selectively slid along the planes of (1) PTBS horizons that were less strong than those of underlying chert, (2) lithologic boundaries with physical contrasts, or (3) boundary faults between melange units. These geologic structures, including the north-dipping bedding/cleavage/fault planes, were formed during Jurassic subduction–accretion and later uplift processes. The movement directions estimated for the 269 landslides and unstable slopes in this region are also N–NNE, and their slip planes are subparallel to the general bedding/cleavage planes in this area. Thus, future slides are also likely to occur on north-facing slopes.

Based on numerical simulation, this study investigates the triggering factors and evolution of deep-seated gravitational deformation in a dip-slope consisting of a shale-dominated sequence of sediments. Results from continuum-based (finite difference) numerical modeling demonstrate that long-term strength degradation of a rock mass is a prerequisite for the development of gravitational slope deformation, and that river incision, resulting in change of slope geometry and corresponding stress concentration and redistribution, is a major driving mechanism for the progressive evolution of deep-seated gravitational slope deformation (DSGSD). Numerical simulation considering the influence of weak planes indicates that the bedding planes control the strength of rock mass and form a structural constraint on the development of gravitational slope deformation. A satisfactory correlation between the distribution of numerically simulated plastic shear bands and weak zones in drill cores demonstrates that the weak zones within the slope are formed due to gravitational slope deformation. Furthermore, numerical simulation shows a link between geomorphological development and internal deformation of the slope, which aids in the understanding of relationships between interior deformation of the slope, the exterior geomorphology and related effect factors including river incision and strength degradation.

This study proposed an in-depth multiscale analysis procedure to identify the dip slope area and assess dip slope stability and influencing area. The proposed analysis procedure comprised five stages: (1) identifying the potential area of a dip slope, (2) analyzing the possible failure types of the dip slope, (3) evaluating slope activity, (4) analyzing dip slope stability under the influence of possible triggering factors, and (5) assessment of the deformation and deposition area. To validate the proposed procedure, the Chaochouhu region of Taiwan was analyzed as a dip slope case. In stages (1) to (3), the scale of the utilized map and the precision of associated data were evaluated to identify the potential area of a dip slope, the possible failure types, and the activity of each slope unit. In stages (4) and (5), the processes of deformation and sliding in a high-activity slope unit were simulated using the discrete element method. The numerical model was first verified using in-situ monitoring data obtained from inclinometers. Subsequently, the model was used to predict the slope behavior under conditions of wetting deterioration of geomaterial. The multiscale analysis revealed comprehensive information regarding the dip slope. The application of the proposed approach would be useful to civil engineers for evaluating dip slope stability as well as to relevant authorities for planning hazard mitigation strategies.

Due to various geological processes, rotation of anisotropic soil fabric is commonly observed in nature. This paper investigates the effect of rotated anisotropy on slope reliability evaluation that considers conditional random field. In this investigation, slopes under undrained and drained conditions are studied under two kinds of sampling patterns. It is observed that the rotated anisotropy is a significant factor that influence the conditional simulation. For the conditional simulation, the uncertainty of the factor of safety (FS) and failure scale is generally the highest when the sampling points are distributed along the fabric orientation, and under such circumstance, the corresponding probability of failure Pf is observed to be the highest. Besides, a given sampling pattern leading to the uncertainty reduction relative to the unconditional simulation under the commonly investigated horizontal fabric pattern may not guarantee the uncertainty reduction under other fabric patterns for anisotropically deposited soils. Also, it is interesting to observe that due to the controlling to uncertainty by the conditional simulation, under rotated anisotropy a dip slope may be estimated to be safer than a reverse slope, and for a given fabric orientation, different sampling patterns may lead to significantly different probabilities of failure.

Rockslides commonly form a shear zone to accommodate their displacements. As such, the landslide history and mechanism must be recorded in the structural features of the shear zone. We investigated the basal shear zone of a 60-m-thick rockslide body with a lateral displacement of 200 m on a dip slope and found the evolutionary mechanisms of a basal shear zone of a rockslide. A basal shear zone on a dip slope is initiated along a lithologic boundary that is characterized by a high competency contrast, such as pelitic rock and greenstone or chert, and develops in the weaker rock, which was pelitic rock in the present study. The basal shear zone first develops with fracture of the rock mass, followed by intragranular fracturing of rock fragments. Shear strain by landslide gradually localizes to a narrow zone in the fractured zone to form a clayey layer by cataclasis of rock fragments. The rock fragments in the clayey layer become rounded by attrition, and the clayey layer finally obtains shear surfaces with slickensides.

We analyzed high-quality drill cores with 100% recovery drilled into a gravitationally deformed dip-slope of a shale-dominated sequence of sediments in Japan. The slope had undulating surfaces but no well-defined landslide scarps, suggesting that parts of the slope had undergone gravitational deformation but had not completely separated from the surrounding bedrock. The gravitational deformation of shale and sandstone is characterized by disintegration and brecciation of sediments and the formation of pulverized zones with poorly developed planar structures, jigsaw-like structures, and fracture openings. Shear zones are distributed intermittently within the slope but have not merged discernably into a through-going master sliding surface. Incipient landslide shear zones form openings within coherent rock by shearing along bedding, with these shear zones potentially developing downward in a stepwise manner, which may be related to stress redistribution induced by river incision.

In this paper, the authors present a probabilistic back-analysis of a recent slope failure at a site on Freeway No. 3 in northern Taiwan. Post-event investigations of this failure found uncertain strength parameters and deteriorating anchor systems as the most likely causes for failure. Field measurement after the event indicated an average slip surface of inclination 15°. To account for the uncertainties in input parameters, the probabilistic back analysis approach was adopted. First, the Markov Chain Monte Carlo (MCMC) simulation was used to back-calculate the geotechnical strength parameters and the anchor force. These inverse analysis results, which agreed closely with the findings of the post-event investigations, were then used to validate the maximum likelihood (ML) method, a computationally more efficient back-analysis approach. The improved knowledge of the geotechnical strength parameters and the anchor force gained through the probabilistic inverse analysis better elucidated the slope failure mechanism, which provides a basis for a more rational selection of remedial measures.

The Zenzano Fault scarp has been developed on the top of a 475 m-high erosional escarpment underlain by an upper brittle sequence and a lower halite-bearing evaporitic formation. The 1850 m-long fault, with a maximum displacement of 45 m and parallel to the escarpment, has offset the back of a dip slope, generating an antislope scarp with prominent triangular facets up to 38 m high and obstructing consequent transverse drainages (defeated streams). Both gravitational and tectonic interpretations were previously proposed for this active surface rupture. The fault scarp has been investigated by detailed geological and geomorphological mapping, geophysical surveys (GPR and ERT) and two trenches excavated across the fault in disrupted drainages. The geophysical profiles clearly imaged the fault, helping to site the trenches and roughly estimate the thickness of the deposits accumulated in the downthrown block. Although the maximum displacement to length ratio (Dmax/L) of the fault fall within the range of tectonic faults of similar length, according to the world database, the geological and geomorphological context, together with several parameters reveal that this structure corresponds to a gravitational failure: (1) anomalously high vertical displacement per event (> 1.4 m); (2) high apparent vertical slip rate (~ 0.6 mm/year); and (3) short recurrence interval of faulting events. The negligible horizontal displacement component on the dip-slip fault, as well as the presence of very large caprock collapse sinkholes and saline springs, strongly suggest that interstratal karstification of the halite-bearing evaporites has played a primary role in the development of the gravitational failure. The formation of this morphostructure has been favoured by pre-existing tectonic faults, erosional unloading related to the removal of an overburden ca. 800 m thick, and enhanced groundwater recharge due to the blockage of the drainage. This work illustrates that the proposed multidisciplinary approach allows the identification of features and calculation of parameters that may help to elucidate whether an active failure has a gravitational or a tectonic origin.

The late Wisconsin (c. 18,000 ybp) Saginaw–Huron Ice Stream (SHIS) of the Laurentide Ice Sheet was as much as 800 km long and 250 km wide in the Great Lakes basin of mid-continent North America. In its onset zone in the upper Lake Huron basin of Ontario, Canada it flowed south from the high standing Canadian Shield to move over gently dipping Ordovician and Silurian dolostones devoid of glacial sediment cover. The onset zone is recorded by a distinct ‘hard bed landform assemblage’ across ∼3000 km2 of north-facing escarpments (Niagara, Fossil Hill, and Kagawong) and dip slope pavements on the Bruce Peninsula and Manitoulin Island, and the adjacent floor of Lake Huron. A wide range of glacially-streamlined rock landforms were carved into dolostones below fast flowing ice. The largest are 30 km-wide bullet-shaped escarpment ‘promontories’ that face upglacier. Superposed on these are swarms of rock drumlins up to 5 km wide with downglacier lengths of as much as 10 km. Promontories and drumlins record streaming of dirty basal ice around escarpment highs and create a distinct ‘zig-zag’ planform to the escarpments. In turn, down-dip, trailing-edge dolostone pavements are corrugated by kilometre-long megagrooves and megaflutes cut by basal ice flowing around resistant high-standing bioherm mounds on dolostone bedding planes. The geomorphology of the Niagara Escarpment does not primarily reflect a lengthy history of preglacial Cenozoic fluvial erosion as classically argued, but geologically-brief episodes of accelerated abrasion and quarrying below ice streams within successive Pleistocene ice sheets.

This paper presents a numerical procedure to explore how hydraulic conductivity anisotropy and strength anisotropy affect the stability of stratified, poorly cemented rock slopes. The results provide information about the anisotropic characteristics of the medium, including the orientation of bedding planes, the anisotropic ratios of the hydraulic conductivity and the geological significance of the hydraulic conductivity anisotropy on the pore water pressure (PWP) estimation of finite slopes. Neglecting the hydraulic conductivity anisotropy of a slope with horizontal layers leads to a 40% overestimation of the safety factor. For a dip slope with inclined layers with θ = 30°, including the strength anisotropy caused a 25% reduction of the safety factor compared to the cases which isotropic strength is assumed. This paper highlights the importance of the hydraulic-conductivity anisotropy and the strength anisotropy on the stability of stratified, poorly cemented rock slopes.

Among the extensive failed slopes in the 2004 Niigata-ken Chuetsu Earthquake, Japan, a dip slope at Yokowatashi, Ojiya, was investigated intensively. The sliding plane was along a weak thin tuff sandy layer which had been deeply weathered. Triaxial compression tests and plane strain compression tests were performed on undisturbed specimens obtained by block sampling and boring sampling to evaluate the strength that was mobilized on the sliding plane. Stability analysis based on the test results reveals that, at normal time, without earthquake and without an extremely high groundwater level, the slope is stable. Furthermore, the calculation of earthquake-induced displacement provides a reasonable simulation of the failure of this slope.

An extensive number of slopes failed in the 2004 Niigata-ken Chuetsu Earthquake. Among them, a dip slope containing a weak layer in Yamakoshi Village (currently Nagaoka City) was investigated intensively. Regarding its morphological characteristics, it is argued that the earthquake reactivated a pre-existing failure plane which then formed most of the present sliding plane. In order to reveal the strength properties of the weak layer that formed the sliding plane, including the behavior against cyclic loading, a series of triaxial compression tests and simple shear tests was performed on undisturbed specimens that were retrieved by block sampling from the site. Based on the test results, a stability analysis and the calculation of the earthquake-induced displacement were performed. By extending Newmark's sliding block analysis, while considering the effects of the irregular geometry of the sliding plane and its strain-softening properties, a reasonable simulation of the process of this slope failure could be provided.

In a case history of dip slope failure caused by the 2004 Niigata-ken Chuetsu Earthquake, it has been reported that the slope contained a thin sandy soil layer. The layer may have liquefied if it had been saturated at the time of the earthquake. Undrained cyclic triaxial tests comprise one of the available experimental approaches for evaluating the liquefaction behavior of such thin sandy soil layers. In this study, a series of undrained cyclic triaxial tests was performed on specimens containing an artificial sand layer in order to investigate the effects of system compliance that are possibly induced by partial drainage caused by the changes in volume of the filter paper used to saturate the sand layer and the local drainage at the interface among the specimen, the top cap and pedestal, and the rubber membrane. The observed liquefaction behavior depended on the thickness of the sand layer under otherwise similar conditions, suggesting the significant effect of system compliance. By conducting special tests, while correcting the partial drainage, it was possible to reduce its effect on the liquefaction behavior. Cylindrical specimens with a top cap and pedestal, all having the same diameter, exhibited a smaller effect from partial drainage than prismatic specimens with an oversized top cap and pedestal.

Typhoon Morakot induced the catastrophic and deadly Shiaolin landslide in southern Taiwan on 9 August 2009, resulting in more than 400 casualties. We undertook a geological and geomorphological investigation with the aim of reconstructing the events leading up to this landslide and to clarify factors that contributed to its development. Cumulative rainfall reached up to 1676.5 mm in about three days under the influence of the typhoon, and the Shiaolin landslide, with a volume of 25 × 106 m3, occurred one day after the peak in rainfall intensity. The landslide occurred on a dip slope overlying late Miocene to early Pliocene sedimentary rocks consisting of silty shale, massive mudstone, and sandstone. It started as a rockslide in the upper third of the landslide area and transformed into a rock avalanche that crossed a series of terraces and displaced or buried the village below. It buried the riverbed of the Chishan River and ran up the opposite slope, creating a landslide dam 60 m high, which was breached about 1 h and 24 min later, flooding the village. The velocity of the landslide is estimated to have been 20.4 to 33.7 m s− 1 and its apparent friction angle was 14°, which indicates its high mobility. The detachments in the source area consist of combinations of bedding planes and joints or faults. The landslide was preceded by gravitational deformation, which appeared as hummocky landforms before the landslide and as buckle folds exposed after the event. The landslide deposits consist of fragments of mudstone, shale, and sandstone, as well as clayey material at its base. This clayey material, consisting of illite, chlorite, quartz, feldspar, and calcite, is assumed to have strongly influenced the long, rapid runout.

The damage caused by an earthquake-induced landslide can generally be classified as either a limited deformation or a catastrophic failure. From an engineering point of view, the latter can be much more dangerous because the sliding mass may continue moving until it collides with another object. If a catastrophic failure occurs near a river, the debris may block the river, causing serious damage to the adjacent area. Therefore, examination of the mechanism of such catastrophic slope failures is important with respect to the mitigation of earthquake disasters in mountainous districts, although numerical modeling of such phenomena is rather difficult. In the present study, a new numerical model is developed to simulate an earthquake-induced catastrophic landslide that occured at a typical dip slope, namely, the Yokowatashi Landslide in Japan. In this case, the upper part of the bedrock on the planer tectonic dip surface slid more than 70 m. Only shear-strength degradation at the bedding plane could cause such a long-distance traveling failure. To investigate the strain-softening characteristics of the materials that filled the bedding plane, a series of laboratory tests involving undisturbed block samples was performed. The measured stress-displacement relationships under cyclic loading were numerically modeled as a newly proposed elasto-plastic constitutive model to be used in numerical simulations of landslide, based on the dynamic finite element method. The observed phenomena were appropriately simulated by the proposed method. The mechanism of catastrophic failure is discussed in detail in this paper in order to clarify the relationships between the strain-softening characteristics and the global slope stability. Our newly proposed method to evaluate the possibility of a catastrophic failure was applied to the landslide, and the moment when the slope becomes unstable was able to be predicted. The results confirm that the proposed method can predict the catastrophic failure of a slope.

On the basis of the status quo of Jinyang Grand Buddha in Taiyuan, some factors such as topography, geological structures, climate, hydrology, and engineering geology that influence the stability of the Buddha slope are considered, and several working situations of the slope that possibly suffered are presented in this article. The Buddha slope stands upright and the rock masses are composed of thick Permian sandstone, which dips slightly inward to the slope. Affected by both the incision of regional joints and the load relief to the free surface, the rock mass of the Buddha slope has turned into loosened blocks. Numerical stability analysis by FLAC-2D on the basis of the strength reduction method reveals that the localized deformation of the rock masses near the vertical surface of the slope may trigger reversing of rock beddings making the back dip slope convert into a dip slope with the possibility of plane sliding failure. Furthermore, the pseudostatic method for the dynamic process and limit equilibrium method for the static process are applied to different working situations of the Buddha slope. The analytical results illustrate that plane sliding failure will not occur when the slope is affected only by seism. However, water filling in the cracks of the loosened rock mass may greatly contribute to the potential plane sliding failure. When horizontal seism-force and hydrostatic pressure are coupled, the Buddha slope can hardly keep stable. Additionally, the loosened rock masses are prone to block toppling failure when influenced by the seism force.

Numerous natural or artificially embanked slope failures were caused by the 2004 Niigata-ken Chuetsu Earthquake. Characteristics of large scale natural slope failures that occurred at folding hills, river terraces, etc, were classified from a geometric structural view point. It was noted that surface failures occurred at steep cliffs and landslides occurred at gently slanting dip slopes. The cause of a landslide in a dip slope at Yokowatashi, Ojiya city was analytically investigated based on cyclic shear test results of the laminar sand at the bedding plane. This study revealed that the safety factor of the slope stability became momentarily smaller than 1.0 several times during the earthquake due to the small undrained shear strength of the tuff sand seam and the landslide behavior was simulated by an elasto-plastic dynamic finite element analysis where the strength decrease of the sand seam with increasing number of cycles was taken into consideration. The cause of destructive damage of a school building at Nagaoka National College of Technology (NNCT) was next examined by another elasto-plastic dynamic FEM. From the analysis results, it was confirmed that the building was pulled and twisted by the landslide of the bank shotcrete accompanied with pile fracture.

An array of meander scroll sets (point bar complexes) is exposed over a land surface eroded across the dip slope of sandstones of the Nubia Group, Taref Formation (Turonian) around the southern fringe of Dakhla Oasis, Egypt (25.5°N, 29°E). These sandstones are thus interpreted as fluvially deposited. Using published equations, bankfull channel width, depth, as well as sinuosity are estimated from radii of meander curvature. With a reasonable assumption of velocity, bankfull discharge is then estimated. This is found to be comparable with bankfull discharge values estimated from published plots of hydraulic geometry (width and depth) against discharge. Both approaches result in mean bankfull discharge estimates of 4.4–7.0×103 m3s−1. Using mean radius of meander curvature, sinuosity is estimated at 1.66. In this hyperarid climatic region aeolian erosion has carved yardangs into the Taref sandstone, the flanks of which expose uniform, tabular cross-beds of coarse, clean quartz sand. From the palaeofluvial estimates, from other features of the exhumed meander scrolls, and from the character of the sandstone, channels in which the Taref sands were deposited are inferred to have been wide and shallow, of low sinuosity, rapidly migrating laterally, with minimal overbank deposition of muds, and rapid vertical accretion. Published indications of a tropical monsoon climate over Egypt in the Turonian are harmonized with the absence of fossil flora from the Taref with reference to indications of a rapidly changing fluvial landscape.

Special features were correlated to the geological causes of the Chiu-fen-erh-shan landslide, a gigantic rockslide on a dip slope, induced by the Chi-chi earthquake (ML=7.3) in central Taiwan in 1999. An aerial photo interpretation and the succeeding geological mapping of the failure were employed in this study. A linear depression, a steep step, and a low drainage density in the landslide area were detected from the aerial photos taken in 1998. The gravitational creep was believed to result in the features of the linear depression and the low drainage density. The steep step represented a buckling feature found in the field. The landslide area is composed of stratified sandstone and shale, with dip angles ranging 20–36°. The slip surface developed along a pre-existing bedding fault that resulted from flexural slip folding. Before the Chi-chi earthquake, the rock on the upslope side buckled and was retained by a thick-bedded sandstone downslope. The earthquake shock seriously damaged the sandstone support and led to the catastrophic landslide. This type of landslide is likely to occur on the moderately dipping slope of stratified rocks that were previously deformed by flexural slip folding.

A disastrous earthquake rocked Taiwan on September 21, 1999, with magnitude M L =7.3 and an epicenter near the small town of Chi-Chi in central Taiwan. The Chi-Chi earthquake triggered landslide on the dip slope at the Chiufengershan. In this study, a review of the topography and geology of this area was followed by field investigations. Laboratory testing was applied to understand the geomaterial composing the slope. Then, based on a series of limit equilibrium analyses, the failure mechanism of this landslide and the risk of the residual slope were studied. According to the stability analyses, the pre-quake slope is quite stable, with factor of safety of 1.77 (dry) to 1.35 (full groundwater level); explaining why there is no written record of a landslide here for the past 100 years. In contrast, a back analysis shows that the Chi-Chi earthquake-induced dynamic loading is far more than the dip slope can sustain, due in part to the short distance to the epicenter. A Monte Carlo type probability analysis suggests that the residual slope is more dangerous than the pre-quake slope and needs more attention.

The Tsaoling landslide, one of the largest landslide areas in Taiwan, has been affected by catastrophic events triggered by rain or earthquakes six times since 1862. These landslides, including that caused by the 1999 earthquake, have essentially not been reactivated old slides, but were sequential new ones that developed upslope, retrogressively. The landslide area is underlain by Pliocene sandstone and shale to form a dip slope with a bedding plane, dipping uniformly at 14°. The slip surface of the 1999 landslide was smooth and planar, parallel to the bedding plane with a slightly stepped profile; it formed within thinly alternated beds of fine sandstone and shale with ripple lamination or in a shale bed. The shale is weathered by slaking and probably by sulfuric acid, which is inferred to be one of the major causes of the intermittent retrogressive development of the landslides. The weathering was likely accelerated by the removal of overlying beds during earlier landslides in 1941 and 1942. The top margin of the 1999 landslide, in plan view, coincided with a V-shaped scarplet, which can be clearly recognized on aerial photographs taken before the landslide. This geomorphological feature indicates that this landslide had already moved slightly before its 1999 occurrence, providing precursory evidences.

Different mountain shapes in sedimentary sequences in the Canadian Rockies were enhanced by glacial erosion and have been modified post-glacially by gravity-driven slope processes. Slope modification by both glacial erosion and post-glaciation landslides is related to slope geometry and rock structure, particularly bedding dip. Five mountain peak shapes in monoclinal sequences each fall into different ranges of bedding dips. (1) Castellate and (2) matterhorn mountains occur in sub-horizontal beds and their slopes are generally 35–65° and oblique to both bedding and joints. (3) Cuestas develop in gently to moderately dipping beds. Dip slopes and steeper, normal escarpments form their cataclinal and anaclinal sides, respectively, with the dihedral angle between them about 90°. (4) Hogbacks in moderately to steeply dipping beds have similar slope angles on both cataclinal and anaclinal slopes. Cataclinal slopes are either dip slopes or underdip slopes but anaclinal slopes are often steepened escarpments, the dihedral angle between the slopes is usually Slope gradients on a sample of 34 peaks are closely related to landslides, particularly rock slides and rock topples. These landslide modes are controlled by bedding dips.

Subsurface rocks beneath slopes are deformed to various degrees in various ways by mass rock creep (MRC), when they are subjected to a gravitationally unstable state for a long period. MRC forms folds, faults and numerous kinds of fractures; such deformation is one of the main factors for deteriorating rock masses on slopes and also precursors of many landslides. MRC deformations, which have often been ascribed to tectonic origins, can be distinguished from tectonic ones by their deformational features, landforms and relationships between slope morphology and subsurface structures. MRC folds are flexural-slip folds that have the following mesoscopic to microscopic characteristics: their axial surfaces are not smooth but are jagged and many visible openings or open fractures develop in association with the folds. The jagged axial surfaces become smoother at depth and openings decrease in width with increasing overburden at the deformation site. Macroscopic types of MRC folds change according to the relationship between foliations and slopes; buckling folds form in consequent slopes, drag folds form in a deeper part of obsequent slopes and bending folds form in slopes with steep-dipping foliations (consequent or obsequent) by downslope bowing of foliations. Shear fractures and tension fractures are the main deformational structures formed by MRC in massive rocks. Among shear fractures, those of listric origin are remarkable. Tension fractures, in general, occur either in networks, dividing rocks into fragments that slip and rotate irregularly in relation to each other, or in parallel arrays of steeply dipping fractures. An MRC fault has a shear zone consisting of a pulverized zone with gouge and a phyllitic or brecciated zone. In a densely foliated rock, the phyllitic zone is formed by microscopic slip along foliations; in a sparsely foliated rock, the brecciated zone is formed by random crushing except for the faults made through the shear fractures in massive rocks. Landforms due to MRC are gentle slopes bounded by horseshoe knicklines upslope, convex slopes, ridge-top depressions, multiple ridges, uphill-facing scarps and ridge-crossing depressions.

Summary Although much is already known of the denudation chronology of the South Downs, detailed surveying of the dip-slope reveals the existence of a number of closely-spaced marine platforms, which are intermediate in age between the early Pliocene bench (650–550 feet O.D.) and the Goodwood raised beach (130–80 feet O.D.). A careful examination of the distribution of the platform fragments shows that in certain situations they must be of sub-aerial origin and related to the development of streams in the area. Thus, the river Adur is shown to have migrated eastwards since the early Pliocene, and it is suggested from certain evidence that the Ouse once reached the sea via the mouth of the Cuckmere, its present outlet being of comparatively recent origin. The major longitudinal valleys of the South Downs, i.e., the upper Lavant and the Lewes Winterbourne were clearly in existence by the 475-foot stage, which is the first clearly-defined stillstand in the regression of the sea from the early Pliocene level. The discontinuous secondary escarpment is examined in some detail and it is suggested that it was originally formed by the action of scarp-foot subsequent streams, which were later disrupted. Certain convergent dry valley patterns can be demonstrated to coincide in position with embayments of the shorelines discussed and are thus readily explicable. Finally the debated question of the origin of dry valleys is reviewed and it is concluded that there are no real objections to the hypothesis that they are former river valleys, which have been abandoned as the level of the water-table in the Chalk fell. A detailed summary of the evidence for each platform is included as an appendix.

The structures associated with the steep, northward inclined Portland and Purbeck Beds, and the nearly vertical or overturned Wealden Beds and Chalk, exposed on the Dorset coast between White Nothe and Mupe Bay, form the subject of an important paper by W. J. Arkell (1938) . Arkell thought that the structures occurred on the steep north limb of a major monocline which was formed by lateral pressures from the south. In the present paper the minor structures in the Purbeck Beds are described in detail and it is shown that they can be related to the development of a fold formed by the increasing northward dip of the underlying massive Portland Beds. The direction of overturning of the minor folds indicates movement of the beds down the dip slope and not upward drag as postulated by Arkell. The formation of the sets of shear planes and faults recognised by Arkell in the Chalk is considered, and it is suggested that they can be divided into two genetic groups. The first group of structures formed during the closing of the syncline, while the second group brought about its modification by thrust displacements on southward inclined thrust planes and late faults. Arkell's conclusions concerning the causes of the reduction in the thickness of the incompetent Wealden Beds are summarised briefly, but by the construction of cross-sections of the main structure, it is demonstrated that the missing portions of the Purbeck and Wealden successions could have been displaced only by thrust movements on southward inclined major faults. A stage-by-stage synthesis of the development of the structures is presented and it is suggested that they were formed as the result of the accommodation of the blanket of largely unconsolidated sedimentary beds above a major thrust fault in the basement. At first a broad flexure developed and this became most pronounced in the highest division, the Chalk, because of the buckling and northward sliding of these beds off the rising land to the south. As the magnitude of the fault increased, successively higher beds fractured and eventually the fault extended to the surface and brought about the displacement and modification of the structures formed during the earlier phase of folding.