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The road that crosses the Haibat Sultan Mountain in the northern part of Iraq; is one of the dangerous roads in this region. To perform a slope stability analysis for the dangerous parts of the road, we have used Bejerman’s Method. We have reviewed satellite images of the road and all those potential areas were checked in the field; accordingly, eleven stations were recognized. Landslide Possibility Index was determined at the studied stations following Bejerman’s field method. The road climbs the southern face (dip slope) of the mountain through very hard carbonate rocks of the Pila Spi Formation, where the bedding planes daylight in the slope face near the road cuts. This produced many large landslides. Along the northern face of the mountain, the road runs through soft clastic rocks where joint planes in the rock mass intersect and daylight in the slope face near the road cut. In order to prevent future wedge failures, a 30 m offset was created from the toe of the slope to the road. In almost all cases, the Landslide Possibility Index indicated a moderate to very high likelihood for failure along all road cuts.

Landslide dams can be very dangerous, with inundation occurring via rising waters upstream, and flooding downstream via dam breaching. Here, we report on a landslide that dammed the Mangapoike River in eastern North Island, New Zealand. The landslide is a low-angle wedge failure in the Miocene weak rock sandstones and mudstones of the Tolaga Group, forming a landslide dam (volume c. 8 million m3) and a lake 50 m deep with a surface area of 0.35 km2, before explosives were used to form a dam spillway to decrease lake level. The landslide formed along an escarpment in northwest-dipping sandstones, and is characterised by a linear lateral scarp, a headscarp, and a bedding-plane rupture surface, which controlled the landslide block geometry. The headscarp and lateral scarp have developed along propagating vertical fractures. The slide surface is a smoothed, northwest-dipping bedding plane, and intersects the vertical fractures in the lateral scarp, forming a wedge. While the principal failure mechanism was sliding involving a single large wedge-shaped block, the rapid movement led to disintegration of most of the block. Part of the detached slide block remained intact, but most of the displaced mass forming the landslide dam is disaggregated blocks in a sandy-silty matrix. Rainfall and meteoric groundwater probably did not initiate failure. Instead, river incision of the dip slope toe, and overpressurisation of fluids that are known to accumulate in sandstones overlain by impermeable mudstones in the region, probably decreased the effective stress along the existing bedding plane, initiating failure.

On May 12, 2019, a landslide occurred near a construction site of a reservoir dam along the left bank of the Wulong River, Qinghai Province, China. Video footage showed that the entire failure process of the landslide lasted for 15 min. Although an excavator that parked on the foundation pit was buried and the Wulong River was blocked, this landslide did not cause any casualties. Based on field investigations, 3D laser scanning, unmanned aerial vehicle observations, and borehole surveys, this study aims to reveal the cause and initiation mechanisms of the landslide. The landslide developed on a typical dip slope with thick-bedded conglomerates intercalated with a few mudstone layers. The slide mass mainly consisted of conglomerates with a dip angle varying from 20 to 40°, failing along bedding plane contacts with the underlying muddy intercalation. Numerous tension cracks had developed in the upper part of the slope due to stress relaxation during the process of bank slope evolution associated with rapid river incision. These cracks damaged the integrity of the rock mass and promoted rapid rainfall infiltration. The water infiltrated into the slope and deteriorated the mechanical properties of the rock mass, which resulted in long-term deterioration of the slope stability conditions. In addition, the temperature of Tongren County was below zero for 5 months in a year, hence the freeze–thaw cycle of the water filled in the cracks would have reduced the shear strength further. There were 10 days of continuous rainfall before the landslide occurred, and the cumulative precipitation in 2018 and 2019 was also significantly more than that of previous years. Three primary factors are involved in the landslide event: (1) thick-bedded conglomerates intercalated with a few mudstone layers with contrasts in strength, (2) development of numerous relaxation cracks, and (3) long-term rainfall accumulation.

The major regions of Taiwan consist of high-relief terrain exposed to frequent typhoons and earthquakes. Recently, thousands of potential large-scale landslides have been delineated via remote sensing analysis and field surveys. However, little attention has been paid to the stability of colluvium, which is a potential hazard. This study investigated a paleo-rockslide site in detail and proposes a geological model to explain the failure mechanism. The studied area is in Jiasian, Southern Taiwan, and the site is a dip slope consisting of Miocene sedimentary rocks. Detailed topographic features, including residual slip surfaces, platforms, scarps, and colluviums, are identified using the slope map of a 1- m airborne remotely sensed digital elevation model. Platforms beneath the residual slip surfaces represent the topographic features of the paleo-rockslide, an interpretation validated by field works and core analysis. The platforms consist of a displaced rock mass (DRM) with a gentle bedding dip angle and interbedded structure that has been preserved. A geological model is established according to the data compiled; outcrops of DRM and colluviums on bedrock were delineated in the geological map and profiles. Outcrops of shear off, buckling, and compressive ridges within the alternating sandstone and shale are distributed at the toe of the residual slip surfaces. A geological model with identified topographic features is adopted to establish the geomorphological evolution of the site. A buckling-induced rockslide model in the dip slope of the interbedded layers is proposed, and potential future slope failure scenarios can be evaluated using the geomorphological evolution model.

A slow-moving landslide on the Huafan University campus, which is located on a dip slope in northern Taiwan, has been observed since 1990. However, reliable monitoring data are difficult to acquire after 2018 due to the lack of continuous maintenance of the field measurement equipment. In this study, the multitemporal interferometry (MTI) technique is applied with Sentinel-1 SAR images to monitor the slow-moving landslide from 2014–2019. The slow-moving areas detected by persistent scatterer (PS) pixels are consistent with the range of previous studies, which are based on in situ monitoring data and field surveys. According to the time series of the PS pixels, a long period gravity-induced deformation of the slow-moving landslide can be clearly observed. Moreover, a short period seasonal surface fluctuation of the slow-moving landslide, which has seldom been discussed before, can also be detected in this study. The seasonal surface fluctuation is in-phase with precipitation, which is inferred to be related to the geological and hydrological conditions of the study area. The MTI technique can compensate for the lack of surface displacement data, in this case, the Huafan University campus, and provide information for evaluating and monitoring slow-moving landslides for possible landslide early warning in the future.

Geological structures precondition hillslope stability as well as the processes and landslide mechanisms which develop in response to deglaciation. In areas experiencing glacier retreat and debuttressing, identifying landslide preconditions is fundamental for anticipating landslide development. Herein, the ~ 150 M m3 Mueller Rockslide in Aoraki/Mount Cook National Park, New Zealand, is described; and we document how preconditions have controlled its morphology and development in response to thinning of the adjacent Mueller Glacier. A combination of geomorphological and geotechnical mapping—based on field, geophysical and remote sensing data—was used to characterise the rock mass and morphology of the rockslide and surrounding hillslope. Mueller Rockslide is identified as a rock compound slide, undergoing dominantly translational failure on a dip slope. The crown of the rockslide is bounded by several discontinuous, stepped scarps whose orientation is controlled by joint sets; these scarps form a zone of toppling that is delivering rock debris to the main rockslide body. Surface and subsurface discontinuity mapping above the crown identified numerous joints, fractures and several scarps that may facilitate continued retrogressive enlargement of the rockslide. The presence of lateral release structures, debuttressing of the rockslide toe and steeply dipping bedding suggest that the rockslide may be capable of evolving to a rapid failure.

To clarify the scale effect of slope deformation, this study investigates the behaviors of dip slopes with various heights and geological properties using centrifuge and numerical modeling. Three types of physical and numerical models with different rock layer thicknesses and weak plane angles were constructed for analysis and validation. The models were subject to toe submersion to simulate the wetting deterioration condition. Based on the analysis results, the deformation, sliding, and debris accumulation of small slopes (a few meters high) may be insignificant. However, the deformation behaviors of higher slopes with the same angle (with a height of tens to a hundred meters) can be more severe and affect the whole slope, especially if the slope has a high weak plane angle with alternating thin rock layers. Some early warning signs, such as bulging-induced tension cracks close to the toe or the relative sliding of layers at the slope surface or crest, can produce more massive landslides or debris accumulation of the dip slopes, especially for high slopes.

Anti-dip slope that fails in the form of flexural toppling is commonly encountered in rock engineering. This paper presents an approach to calculate the local failure probability of the anti-dip slope susceptible to flexural toppling. The realization of this approach consists of four major steps: (1) establishing geo-mechanical model of the slope and generating physical parameters randomly using Monte Carlo simulation, (2) determining the demarcation of the toppling and sliding failure zones, (3) evaluating the stability state of each single column, and (4) deriving the local failure probability by an iterative calculation. A case study of the Mari landslide is analyzed by employing the proposed approach, and the Maxwell model is applied to reduce physical parameters with time. The results show that the instability grade increases gradually throughout the whole evolution process of the slope. In the incipient stage, particular attention should be paid to the middle–upper columns, which have the highest failure probabilities. However, as the slope deformation increases, all the columns should be taken into account since they have approximately the equal possibility of failure. A simplified slope model is employed to perform a parametric analysis. The results show that (1) the local failure probability of the slope tends to decrease with increases in the rock friction angle, rock tensile strength or interface friction angle, while increasing the rock unit weight leads to a higher probability of local failure; (2) the computation results are more sensitive to the uncertainty in the interface friction angle than that in the other three above-mentioned parameters; and (3) the maximum failure probability depends on the geometric parameters, including the column interface angle, slope angle, crest angle, slope height and column thickness.

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.

At 5 am 24th June 2017, a catastrophic landslide hit Xinmo Village, Maoxian County, Sichuan Province, China. The slide mass rushed down from an altitude of 3400m and traveled 2700 m in a high velocity. The 13 million m3 deposition buried the whole village and caused about 100 deaths. The source area of the landslide is located in a high steep slope, average slope angle is 40o and maximal angle is 65o. The strata are interbedded Triassic Zagunao Formation metamorphic sandstone and slate with the dip slope angle of 45°. Based on high-resolution satellite remote sensing image, UAV image, DEM data, and field investigation, failure mechanism, travel features, and deposit characteristics were analyzed. The results showed that this landslide was influenced by Songpinggou Fault zone. According to the topography before the failure, the landslide is located in the back scarp of an antecedent landslide induced by Diexi Earthquake in 1933. The bedding slope provided potential rupture surface. Historical seismic activities and long-term gravitational deformation caused rock mass accumulated damages. Weathering and precipitation weakened the rock mass and finally induced shearing and tension failure. A huge block detached from the top rock slope, pushed the past landslide deposits in the middle part, rushed out of the slope bottom in a high velocity and buried the Xinmo Village. The rapid movement entrained and brought the soil into the Songping Gully which recoiled with and bounced back from the opposite mountain.

This study investigated the effect of internal discontinuity on the dynamic response of a dip slope and evaluated the performance of Newmark’s theory on the sliding of a dip slope with multi-slip planes. A series of shaking table tests were performed under various geometric conditions to explore the dynamic behavior of a dip slope under different external excitations. The test results, including for deformation processes and critical accelerations, under various slope angles, slope sizes, and seismic intensities were examined and further compared with Newmark’s theory. The results of this study are summarized as follows: (1) two types of slope sliding (differential and complete) were determined. (2) Increasing the slope angle and the height of sliding mass tended to shorten the duration of slope deformation. (3) Critical acceleration of the slope increased gradually with increasing peak ground accelerations of input excitations; when the slope height and dip angle increased, the critical acceleration decreased. (4) The triggering time became earlier as the frequency of input excitation increased; the magnitude of sliding mass greatly depended on the amplitude of the input excitation. (5) By comparing critical acceleration between the experimental and theoretical results, Newmark’s theory was determined to overestimate critical acceleration during seismic-induced dip slope failure. This may cause unsafe evaluations, and sliding along existing discontinuities develops more easily in reality.

On June 24, 2017, a catastrophic landslide (Xinmo landslide) occurred on the left bank of Songping river in Diexi town, Sichuan Province, China. Based on field investigations, this paper tries to reveal the cause and mechanism of the initiation and development of the Xinmo landslide. Xinmo landslide is located in the so called “Minshan block.” This tectonic block is very active and generates many earthquakes. Among them, the 1933 Diexi Ms 7.5 earthquake which had an indispensable effect on the occurrence of the Xinmo landslide, whose distance to the recent Xinmo landslide is only 8.7 km. The 1933 earthquake triggered the collapse of the Qianxin gully, which damaged the rock mass forming the source of the Xinmo landslide and creating a free prominent ridge. The later 1976 Songpan Ms 7.2 earthquake and the 2008 Wenchuan Ms 8.0 earthquake further damaged the integrity of the rock mass in the source area of the 2017 Xinmo landslide. The Xinmo landslide developed on a typical bedding dip slope with metasandstone intercalated with a few thin bedded slate layers. The slate intercalation gives the slope a very low shear strength in the dip direction and the long term rainfall may have softened the slip zone and the locked section. These two aspects have promoted the occurrence of Xinmo landslide.

Slope failure is a widely observed phenomenon in the mountainous areas in Taiwan due to rainy climatic and fragile geological conditions. Landslides easily occur after intense rainfall, especially from typhoons, and, accordingly, cause a great loss of human life and property. At the northern end of the Western Foothill belt in northern Taiwan, Huafan University is founded on a dip-slope about 20° toward the southwest composed of early Miocene alternations of sandstone and shale. Data from continuous monitoring using inclinometers and groundwater gauges reveal that 6–10 mm/month of slope creeping occurs, and a potential sliding surface is then detected about 10–40 m beneath the slope surface. To understand the potential runout process of the dip-slope failure at the campus, particle flow code 3D models based on a discrete element method are applied in this study. Results of the simulation reveal a critical value of the friction coefficient to be 0.13 and that more than 90% of the campus buildings will slide down in 100 s when the friction coefficient is reduced to half the critical value. The weakening of the shear zone due to the rise of groundwater during rainstorms is assumed to be the main factor. Some suggestions for preventing landslide disasters are to construct catchpits to drain runoff and lower the groundwater table and to install a sufficient number of ground anchors and retaining walls to stabilize the slope.

Several related pre-event environment indices coupled with a 200-year event of Typhoon Morakot were used in this study to analyse landslide risk/scale for mapping and verifying the danger grade of watershed landslides. Risk analysis was modelled using maximum daily rainfall of the tested event as the hazard factor, and a complex indicator derived from indices of return period, road development and green deterioration as the vulnerability factor. The vulnerability factor was then modified using the slope to adjust the weight for excluding the flat areas and increasing impact of steep areas. A comprehensive indicator integrated from indices of river concave, headward erosion and dip slope was provided as the hotspot of potential large-scale landslides which were modified by vegetation index to correct sediment yield due to antecedent effects. Finally, sites with high potential large-scale landslide could be interpreted by the danger grade calculated from collapse risk/scale analysis. The results show that the higher the danger grade, the greater the collapse ratio; and the coefficient of determination for the relationship is greater than 0.9. The model developed in this study for accurately estimating the risk/scale of rainfall-induced landslide can be fulfilled.

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.

The 17 June 2017 rock avalanche in the Karrat Fjord, West Greenland, caused a tsunami that flooded the nearby village of Nuugaatsiaq and killed four people. The disaster was entirely unexpected since no previous records of large rock slope failures were known in the region, and it highlighted the need for better knowledge of potentially hazardous rock slopes in remote Arctic regions. The aim of the paper is to explore our ability to detect and locate unstable rock slopes in remote Arctic regions with difficult access. We test this by examining the case of the 17 June 2017 Karrat rock avalanche. The workflow we apply is based on a multidisciplinary analysis of freely available data comprising seismological records, Sentinel-1 spaceborne synthetic-aperture radar (SAR) data, and Landsat and Sentinel-2 optical satellite imagery, ground-truthed with limited fieldwork. Using this workflow enables us to reconstruct a timeline of rock slope failures on the coastal slope here collectively termed the Karrat Landslide Complex. Our analyses show that at least three recent rock avalanches occurred in the Karrat Landslide Complex: Karrat 2009, Karrat 2016, and Karrat 2017. The latter is the source of the abovementioned tsunami, whereas the first two are described here in detail for the first time. All three are interpreted as having initiated as dip-slope failures. In addition to the recent rock avalanches, older rock avalanche deposits are observed, demonstrating older (Holocene) periods of activity. Furthermore, three larger unstable rock slopes that may pose a future hazard are described. A number of non-tectonic seismic events confined to the area are interpreted as recording rock slope failures. The structural setting of the Karrat Landslide Complex, namely dip slope, is probably the main conditioning factor for the past and present activity, and, based on the temporal distribution of events in the area, we speculate that the possible trigger for rock slope failures is permafrost degradation caused by climate warming. The results of the present work highlight the benefits of a multidisciplinary approach, based on freely available data, to studying unstable rock slopes in remote Arctic areas under difficult logistical field conditions and demonstrate the importance of identifying minor precursor events to identify areas of future hazard.

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.

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.

A consequent slope comprises weak planes in the same dip direction along a slope face. This study investigated scale effects on the gravitational deformation of consequent slopes. A series of centrifuge model tests under simplified environmental conditions were performed. Particle image velocimetry (PIV) was then adopted to evaluate the displacement distribution from the centrifuge model test results. On the basis of the PIV results, the relationship between slope deformation and surface settlement was investigated. Subsequently, the discrete element method (DEM) was used to execute simulations to provide detailed descriptions of the crack development and failure mechanisms associated with consequent slopes at different scales. The results of this study are summarized as follows. (1) The slopes exhibited similar deformation patterns in the centrifuge model tests. As the gravitational force increased, the magnitude of slope deformation increased significantly. (2) A modified dimensional relationship of material parameters was proposed for DEM simulation. According to this relationship, the simulated deformation patterns were in strong agreement with the actual deformations at various slope scales. (3) According to the DEM simulations, for the slopes with the same slope and weak plane angles, more cracks and displacements were generated in the higher slopes, leading to a greater sliding volume.

The first area is rock instability in conglomerates walls, and the second area is soil instability in a slope composed of sand gravel and shale in the south of the study area. In the first area, rock slopes were studied by fractures condition, slope morphology, measured engineering features of rocks, and then interpreted by Dips software to define the fracture types for analysis of block toppling. The rock slope of the area was modeled by Rock plan by adding water penetration and earthquake. The results showed that in dry condition these slopes were stable, but by penetrating water and saturation of the open spaces of the fractures, the block toppling will occur. Also, seismic activities in the area caused the instability of the slopes, and landslide will happen. In the second area, landslides were spoon-shaped type. To investigate the soil slope stability, the condition of slope was modeled by using soil engineering properties and measuring the morphological condition of the slope such as slope dip, layers thickness, layers dip and slope elevation. It was shown instability of the soil slopes. To stabilize the sliding areas, the dip changing method and formation of stepped-style slope were done. However, the new condition changed the formation of sliding areas in the upper most part of the stairs. The retaining walls formed from the local materials were applied to the slope to provide the desire stability.

We explore the controls of the litho-tectonic architecture on the erosional flux in the 370-km2 Glogn basin (European Alps). In this basin, the bedding and schistosity of the bedrock dip parallel to the topographic slope on the NW valley flank, leading to a non-dip slope situation on the opposite SE valley side. While the dip slope condition has promoted the occurrence of landslides (e.g. the c. 30-km2 deep-seated Lumnezia landslide), the opposite non-dip slope side of the valley hosts >100-m-deeply incised tributary streams. 10Be concentrations of stream sediments yield catchment-averaged denudation rates that vary between 0.27 ± 0.03 and 2.19 ± 0.37 mm a−1, while the spatially averaged denudation rate of the entire basin is 1.99 ± 0.34 mm a−1. Our 10Be-based approach reveals that the Lumnezia landslide front contributes c. 30–65% of the entire sediment budget, although it covers

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.

The paper discusses structural considerations relating to landform development on Mt. Babia Góra (1,725 m a.s.l.), the highest massif in the flysch section of the Western Carpathian Mountains. The Babia Góra massif consists of folded Palaeogene-age sediments, including resistant Magura sandstone and less resistant sub-Magura layers, with numerous tectonic faults. The area has inverse-type geomorphology. The monoclinal ridge of the massif itself consists of the resistant Magura sandstone dipping southwards. Since the Miocene, the development of the massif’s relief has involved a number of processes, including: tectonic uplifting, removal of a thick layer of rocks, exposure of sub-Magura layers over a large area, the staged development of valleys dissecting the pediments surrounding the ever higher ridge, and slope retreat due to deep landsliding. Axes of linear terrain forms, escarpments of landslide scars and of headwater areas follow two main intersecting fracture lines present within the massif. Large quantities of colluvial material are transported away from the massif along these lines. The development of the land relief has led to the elongation of slopes as local elevation differences increased. Landsliding has developed in an uphill direction, which means that the youngest relief is observed on the highest sections of steep slopes. The development of the massif’s northern slope, which has formed a high and precipitous cuesta, began to accelerate only after a nearly complete exposure of the sub-Magura layers at its foot. Following this exposure the profile of the massif’s N-S cross-section has begun to become asymmetrical. With time, the degree of general remodelling of the massif has tended to decrease. As a result, the geomorphological contrast between the northern and southern sides of the massif has become well established. The description of the probable development of the Babia Góra relief is based on the author’s fieldwork, an analysis of geological maps and aerial photos, and on literature.

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.

The Seymareh rock avalanche, first described by J. V. Harrison and N. L. Falcon in the 1930s, is the largest known subaerial non-volcanic landslide on Earth. The volume of its debris (44 Gm 3 ) is approximately equal to that of the largest known subaerial landslide of any kind, the 100 ka collapse of Mount Shasta volcano (45 Gm 3 ) and approaches those of gigantic landslides on Mars. Using satellite imagery, SRTM-3 data, and detailed field investigations, we gain a new understanding of the gigantic rock avalanche. The initial failure (38 Gm 3 ), involving a dip slope consisting of a relatively weak interbedded limestone–mudrock sequence capped by resistant Asmari Limestone, had an average thickness of 410 m along a 15.5 km width of the Kabir Kuh anticline. The rockslide transformed into a rock avalanche that travelled 19.0 km with a fahrboschung (the angle between the highest point of the pre-landslide source area topography and the distal limit of the debris) of only 3.6°. Initial failure involved complex planar sliding dictated by four structural elements: (1) bedding-parallel shears and (2) across-bedding break-throughs combined to produce a low-angle (11°) overall sliding surface that (3) broke out through the Asmari carapace at the toe of the failed slope while (4) tectonically weakened bedding-normal joints provided lateral release surfaces. Nine discrete bedding-parallel basal sliding surfaces divided the detached mass into nine stacked plates. The upper plate (23 Gm 3 ) included 20.7 Gm 3 of Asmari Limestone. Analysis of accelerator mass spectrometry radiocarbon dates from this study and by others indicates that the rock avalanche occurred between c . 8710 and 9800 14 C years BP. Supplementary material: A summary of the tectonics, stratigraphy and physiography of the Zagros Fold–Thrust belt together with a description of surficial gravity collapse structures in the region (Harrison & Falcon 1934, 1936) is available at www.geolsoc.org.uk/SUP18612.

This study investigated the creep deformation of a gentle dip slope induced by river erosion. In the Ai Liao River (Southern Taiwan), more than 20 rainfall events have induced massive landslides in the dip slope terrain as a result of lateral erosion of the river channel. Numerical simulations revealed that when the riverbank cutting angle is less than 30°, only circular slip and creep folds occur in the slope, with multiple small folds occurring from the toe to the top of riverbank (but no rapid damage occurs). When the river cutting angle is between 30° and 45°, drag bending folds are likely to occur on the contact surface between the surface and bottom layer, and a sliding surface appears along the contact surface. Finally, when the river cutting angle is more than 45°, slope movements occur, leading to significant, rapid block damage.

This study examined differences in landslide sediment production and sediment transportation abilities of reservoir watersheds in different geological environments after extreme rainfall. The watershed in this study covered an area of 109 km2; the upstream river banks of the reservoir contained interbedded shale and faulted shale and had a sandstone dip slope. This paper uses a LiDAR-derived DTM taken in 2005 and 2010 to investigate the landslide sediment production and riverbed erosion and deposition in the watershed. This study also applied the conservation of mass concept to analyze the sediment outflux in the subwatersheds. The research results indicated that although the right bank, which had interbedded shale and a sandstone dip slope, had a substantially greater number of landslides, the sediment production of it was less than that of the left bank, which had numerous deep-seated landslides caused by fault zones. However, affected by the higher sediment production of the left bank and under the same stream power, the left bank subwatersheds also had higher sediment outflux.

On September 15, 2012, torrential rains carried by the peripheral circulation of Typhoon Sanba and the northeast monsoon induced a translational landslide near Pingguang Road in Xindian District of New Taipei City, Taiwan. The total volume of the landslide was ~162,000 m3. The sliding mass destroyed two houses across the stream and formed a landslide dam at the toe of the slope, constricting the stream. For the purpose of reducing sediment-relative hazard around mountainous area, the paper attempts to explore the dynamics and phenomenon of the landslide on dip slope. This study interpreted remote sensing images and terrestrial LiDAR scanning, conducted onsite surveys to obtain material parameters, and performed simulations using the discrete element method to reconstruction the post-event, in order to elucidate the mechanisms involved in the landslide process. Survey results revealed complex geological conditions with tension cracks spreading in all directions at source area. This facilitated the infiltration of surface runoff into weak surfaces and raised groundwater levels. Slope failure may occur along the stratum boundary once the intrinsic shear strength of regolith drops below a critical value. The results of numerical simulation reveal that at 80 s after the Pingguang stream landslide began, a maximum deposition depth of 20 m had been reached. The sliding mass cut off the stream and pushed the stream flow roughly 35 m to the southeast. Because the slope materials surrounding the study area and the landslide-inducing mechanisms are similar, the top of the slopes to the northwest of the study area requires close monitoring. Finally, a detailed potential landslide mapping and interpretation from the high-resolution digital elevation model also present to prevent further landslides. The investigation indicates that the occurrence of landslide is highly related to seepage effect of accumulated rainfall, toe erosion by surface runoff, and local unstable geological structure.

A catastrophic dip slope failure occurred suddenly at an anchored cut slope of Freeway No. 3 in 2010 after 13 years in service. Among the factors contributing to this landslide, serious corrosion on tieback anchors was the most obvious factor in addition to the groundwater hydrology inside the slope. In the past, most of the ground anchors in Taiwan were constructed with limited or no corrosion protection. So, it is likely that the tieback anchors on slopes are suffering similar corrosion problem under the humid weather condition. So, the Ministry of Transportation and Communication (MOTC) of Taiwan government launched an extensive island-wide investigation program to check the status quo of existing anchored slopes along the highways, railways, and public roads. Not surprisingly, corrosion is found to be a common problem for the existing ground anchors. A national overhaul program for the anchored slopes along the highways and railways has been launched. This paper covers the findings from the anchored slopes inspection and the measures taken to improve the corrosion protection of the existing anchors. In addition, some minor modification on anchor tendon assembly and cement grouting process has been suggested to upgrade the corrosion protection of the new anchors.

The Italian cultural heritage is one of the most noticeable in the world; an important part of it is subjected to natural hazard and risk conditions. Religious buildings, due to their location on impervious sites are particularly exposed to landslides. In this paper we study the hermitage of Cerbaiolo (Tuscany, central Italy). The hermitage, founded in the 8th century as a Benedictine monastery is now a Franciscan Women Institute seat. The buildings are on the edges of a limestone plate overlapped to a clayey formation. Falls, toppling and slides are present along the limits of the plate due to the geomechanics properties of the rock and to the contrast between the two lithological complexes. In order to identify the main joint sets affecting the rock mass a structural-geological survey was carried out and four sets are identified. The rock plate was classified according to Bieniawski, Barton and Geological Strength Index approaches. The outcomes confirm the predisposing factors to mass movements, corresponding to the intensity and characteristics of fracturing of the rock mass. With regard to the slope stability analysis, a failure mechanism involving sliding along a single plane (plane failure) was assumed on the first approximation. The analyses take into account the presence of tension cracks as an indicator factor for the instability phenomenon. The results of stability analyses, performed in static and seismic conditions, indicate a widespread instability condition. The dip slope direction, the properties and type of discontinuities and the local variation of composition influence the hazard assessment.

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 Shanshucao landslide is a recent landslide that occurred in the China Three Gorges Reservoir area. It is next to the Daling Hydropower Station landslide, one of the geological hazard professional monitoring points in the China Three Gorges Reservoir. The Shanshucao landslide had not shown a significant deformation during recent decades until September 2nd, 2014. On that day, the Shanshucao landslide abruptly started to move at around 9 a.m. local time, stopped at 13:19 p.m., and caused a 43.2 × 104m3 landslide mass which slipped into the Luogudong River, the secondary branch of Yangtze River. Fortunately, the local government gave an efficient early warning and organized a successful emergency evacuation. Nobody was injured or killed in this landslide failure event. The Daling Hydropower Station and its attached buildings were eradicated by the landslide. Posterior to the failure, a newborn free surface occurred on the dip slope. The remaining body of the landslide poses a great threat to the safety of both the village and the Three Gorges Reservoir operation. Subsequently, an emergency monitoring system has been placed on the slope to observe any subsequent deformation. By applying the kinematic model, this article will give a general outlook on the failure event and investigate the geological features which caused the slope instability. Also, the two inclined blocks models are introduced in the back analysis and show a good comparison to the site observation results. This article will provide guidance and suggestion for the stability analysis of similar highly weathered bedded landslides in the China Three Gorges Reservoir area.

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.

The 12 March 2001 landslide at a slate quarry in Okayama, Japan killed three workers. Composite studies based on field surveys of the landslide slope, interviews with local residents and quarry workers, and inspections of hydrological and seismological data have been used to clarify the causes of this slide and its movements. The results indicate that the landslide was enabled firstly by the steepness of the slope, which had been undercut by river; secondly, the structure was that of a dip-slope that was prone to deep-seated slides along bedding planes; thirdly, numerous joints and faults were present. Surprisingly, rainfall, earthquakes, and explosions do not appear to have played any role in the triggering of this slide. The interviews demonstrated that the frequency of precursory failures increased over a period of several hours before the 12 March 2001 landslide. Inspection of the seismograph records and the eyewitness evidence both indicate that the main part of the landslide consisted of two phases of slope failure within 23 s. After the slide, the frequency of the failures gradually decreased with time over a period of several days. Three new terms are proposed for landslides: foreslide, mainslide, and afterslide, following the terms foreshock, main shock, and aftershock used in seismology.

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.

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.

It is found by engineering geological exploration that No.5 slope in Wutai-Yuxian expressway is typical dip slope forming in ancient gneiss terrain. We conclude that slope deformation and failure mainly result from the gneiss and mica schist constituting the slope and the heavy precipitation in construction period. Besides, the insufficiency of geological exploration in revealing the complex geology and the deficiency of designation and constructing in preventing and controlling geohazards are the engineering factors causing landslide in No.5 slope. Slope cutting and reinforcement, draining and cutting off the surface water, and enhancing the displacement monitoring for potential sliding surface may serve as a reference for construction and supporting designation of deep cutting slope in this area as well as for constructing slope engineering in the areas sharing similar geology with this area.

Owing to tectonic collision, about 70% of Taiwan’s land are mountains and foothills. With several unfavourable conditions such as typhoons, strong rainfalls, and earthquakes, the landslide hazard is a critical issue in Taiwan. This issue is increasingly important because the use of hillsides for residence are growing in recent years. To address the issue and to protect its citizens, Taipei City Government initiated a pilot project to monitor landslide displacements in 2010. The project involves a selected hillside community with dip slope in Taipei City. The community had a major landslide in 1983.The monthly monitoring with non-automated devices is not helpful for residence to react to landslides. To help improve the situation, we use motion sensors to develop fully automated devices to infer displacements. We also used numerical analyses to help determine the best locations to install these devices. They were mounted to the ground surface to sense the tilt. The tilt converts to displacements by assuming slip surfaces. Small displacements were detected during a typhoon event in July of 2013.With the developed monitoring device, standard operation procedures were developed accordingly. Community residents has been educated how to react to unfavourable conditions. These conditions are defined by displacements exceeding certain thresholds.

Tsaoling is an important area for landslide studies in Taiwan because of its repetitive occurrences of landslides. In 1999, the Chi-Chi earthquake triggered a dip slope failure and the landslide mass deposit in the channel and opposite bank of the Chinshui River. Long-term (3 decades) as well as the rapid landscape evolution after the Chi-Chi earthquake is inspected in the present study, by using a total number of ten high-resolution digital terrain models (DTMs). These DTMs were constructed by using aerial orthophotos dated between 1979 and 2009 and they were calibrated against the 2009 DTM, with the root mean square error controlled to be less than 1 m. The focus is on the surface elevation changes of two representative cross-sections and recession of the Chunqui Cliff in the landslide scarp zone. Because the Chinshui River cuts through the loose deposit, significant incision was found and the incision undergoes a common exponential natural process. The half-life time is estimated about 3.2–4.3 years. On the other hand, cliff recession is associated with the extreme climate events and the recession rate is found to increase after 2003.

Large rock and soil landslides are an important part of the geodiversity in Nahanni National Park in Canada’s Northwest Territories. Here we describe five notable events, including two in soil, two in rock, and one involving rock and soil. Three of the events resulted in landslide dams. The Ram Plateau flowslide involved a collapse of a scree slope and fine textured soil over massive ground ice. This complex landslide continues to move in response to permafrost thaw and seasonal moisture. The Wrigley landslide is a large debris slide, involving thick till that dammed Wrigley Creek. The Cathedral Creek rock slide is a dip slope failure which dammed two large creeks. Cliff collapse of limestone on the Ram Plateau transformed into a rock avalanche, which dammed a stream. The Grizzly landslide involved both rock and soil. It is a large rock slide—earth flow in which, we suspect, undrained loading played an important role.

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.

Owing to plate collision effect, there is about 70% area of Taiwan covered with mountain. Thus landslide hazard is an important issue because typhoon and earthquake attacks Taiwan every year. Development of slope land in recent years is rapid thus slope land community is more common than before. Landslide hazard in community scale is challenge task since more and more people live in this slope land area. A community with dip slope was selected in this project to perform landslide displacement monitoring. Numerical analysis for sensor alignment location was executed to help decision. Two triaxial acceleration sensors were mounted to the ground surface to calculate tilt of ground surface. Thus the displacement can be derived base on slip surface assumption. Small displacement was found during a typhoon event in July, 2013.

This study uses three periods of airborne laser scanning (ALS) digital elevation model (DEM) data to analyze the short-term erosional features of the Tsaoling landslide triggered by the 1999 Chi-Chi earthquake in Taiwan. Two methods for calculating the bedrock incision rate, the equal-interval cross section selection method and the continuous swath profiles selection method, were used in the study after nearly ten years of gully incision following the earthquake-triggered dip-slope landslide. Multi-temporal gully incision rates were obtained using the continuous swath profiles selection method, which is considered a practical and convenient approach in terrain change studies. After error estimation and comparison of the multi-period ALS DEMs, the terrain change in different periods can be directly calculated, reducing time-consuming fieldwork such as installation of erosion pins and measurement of topographic cross sections on site. The gully bedrock incision rate calculated by the three periods of ALS DEMs on the surface of the Tsaoling landslide ranged from 0.23 m/year to 3.98 m/year. The local gully incision rate in the lower part of the landslide surface was found to be remarkably faster than that of the other regions, suggesting that the fast incision of the toe area possibly contributes to the occurrence of repeated landslides in the Tsaoling area.

As a result of the 2011 Great Earthquake off the Pacific coast of Tohoku, four large landslides occurred in northern Ibaraki Prefecture and caused damage that closed roads. These landslides were characterized by the following geological and geographic features: 1, each slide occurred near the tip of a ridge; 2, each ridgeline was almost perpendicular to a line drawn from the landslide to the epicenter; and 3, geologically, each slope was a dip slope of soft Neogene sandstones and/or siltstones. In an earthquake, the ground motion of the upper part of the slope is bigger than that of the lower part of the slope. We can infer that if the tip of the ridge is equivalent to the upper part of the slope, then a large amount of ground motion likely occurred there in the 2011 Great Earthquake; this might have placed fracture stress along the bedding planes of the dip slope, thus triggering a landslide. In future disaster management, we need to be aware of slopes that have the geographic and geological features mentioned above.