Active Mass Movements Research Articles

Geomorphological study of the debris flow events in the Harsovska River (Blagoevgradska Bistritsa catchment), observed within 2019-2023

Debris flow events in the Blagoevgradska Bistritsa catchment (SW Bulgaria) become more frequent in the past few years. To localize the debris source along the tributary system, the Harsovska River is chosen in this study. During the observation period a torrential event was registered in June 2023. The synoptic situation, which caused the flood, is re-analyzed and also geomorphological research is made for depositional landforms in the river channel for the period 2019-2023. In the study, the alluvial sediments are defined by grain size and also by morphoscopic study of pebble-sized grains. During the field research, two critical flood-risk sites are pointed, located in the Harsovo hamlet. The data about past debris flow events are collected from residents of Harsovo with interviews regarding their experience in this issue. In the period of the study, the main part of debris nourishment in Harsovska catchment is provided by the tributary Marulevska River, where active mass movement processes are registered. However, the alluvial profiles of both rivers – Marulevska and Harsovska, showed an alternation of coarser and finer materials, resulting of turbulent and calm discharge. Such periodical change in the sedimentary environment of the two compound rivers demonstrates their unsteady torrential character. Regarding the fortification activities in this area, at the moment some new forestation has been noticed. Still, the species, used to fortify the river banks are not suitable for the climate and hydrological regime of the region. The channel fortifications, built in the middle of the 20th century, currently are not maintained properly, which puts under threat of future debris flow events the settlements and infrastructure along this catchment.

Improvement of Workflow for Topographic Surveys in Long Highwalls of Open Pit Mines with an Unmanned Aerial Vehicle and Structure from Motion

Conducting topographic surveys in active mines is challenging due ongoing operations and hazards, particularly in highwalls subject to constant and active mass movements (rock and earth falls, slides and flows). These vertical and long surfaces are the core of most mines, as the mineral feeding mining production originates there. They often lack easy and safe access paths. This framework highlights the importance of accomplishing non-contact high-accuracy and detailed topographies to detect instabilities prior to their occurrence. We have conducted drone flights in search of the best settings in terms of altitude mode and camera angle, to produce digital representation of topographies using Structure from Motion. Identification of discontinuities was evaluated, as they are a reliable indicator of potential failure areas. Natural shapes were used as control/check points and were surveyed using a robotic total station with a coaxial camera. The study was conducted in an active kaolin mine near the Alto Tajo Natural Park of East-Central Spain. Here the 140 m highwall is formed by layers of limestone, marls and sands. We demonstrate that for this vertical landscape, a facade drone flight mode combined with a nadir camera angle, and automatically programmed with a computer-based mission planning software, provides the most accurate and detailed topographies, in the shortest time and with increased flight safety. Contrary to previous reports, adding oblique images does not improve accuracy for this configuration. Moreover, neither extra sets of images nor an expert pilot are required. These topographies allowed the detection of 93.5% more discontinuities than the Above Mean Sea Level surveys, the common approach used in mining areas. Our findings improve the present SfM-UAV survey workflows in long highwalls. The versatile topographies are useful for the management and stabilization of highwalls during phases of operation, as well closure-reclamation.

Geoengineering properties of the Ertugrul (Cayirkoy) district, Nilufer Province, Bursa-Turkey, by using geophysical methods and borehole data

In this study, soil classification experiments and geophysical studies are carried out for the evaluation of local ground soil conditions by using the data and samples from the boreholes in the Quaternary sediments in the Ertugrul district of Nilufer, Bursa, then the engineering parameters and index classifications are also investigated with the soil mechanics experiments using the disturbed samples from the drill holes.The grade of swelling (bulking) potential in the ground soil is found medium, high and very high in different parts of the study area. The basement units for the constructions bear very low liquefaction risk. The plasticity index varies between 9 and 25, but active mass movements are not expected. However, engineering problems such as swelling (bulking), soil settlements, bearing capacity reduction may be expected under the seismic forces because of the alluvial composition, 0–5 degree soil inclinations and being located in the 1st degree earthquake hazard risk zone. Therefore, the study area may be classified in the ‘precautionary zone’ in the urbanization category in terms of engineering problems.

Geological and geophysical characterization of the Brindisi di Montagna Scalo landslide (Basilicata, Southern Italy)

The Brindisi di Montagna Scalo Landslide in Southern Italy is an active complex mass movement, which affects the left slope of the Basento River. In the last few decades, this landslide has been continuously monitored, as it directly threatened some of the most important communication routes in the Basilicata Region. Nevertheless, little progresses have been made to prevent further landslide advancement, and continuous maintenance is required. With the aims of better understanding, the main factors controlling the evolution of this landslide, and suggesting the most appropriate countermeasures, a multidisciplinary study, based on the integration of direct and indirect techniques, was carried out. Direct techniques included multi-temporal geomorphological analysis of the slope, alongside geological and structural field observations. Indirect techniques consisted of electrical resistivity tomography acquisition. The combined analyses of the geological and geophysical data showed that Quaternary tectonic processes played a fundamental role as a predisposing factor, whereas seasonal rainfall, and the perpetual undercutting by erosional processes caused by the Basento River at the toe of the landslide are the main triggering mechanisms. The Brindisi di Montagna Scalo Landslide represents an outstanding case-study, concerning the interaction between a flow-like complex landslide and essential linear infrastructure, such as motorways and railways.

Hydrogeological investigation of landslides Urbas and Čikla above the settlement of Koroška Bela (NW Slovenia)

The area above the settlement of Koroška Bela is highly prone to slope mass movements and poses a high risk for the safety of the settlement. To get an insight into the hydrogeological conditions and processes which can affect mass movements in this area, hydrogeological investigations, including hydrogeological mapping, discharge measurements of springs, performance of infiltrometer and slug tests were performed. The results of these investigations show complex and heterogeneous hydrogeological conditions, predisposed by geological and tectonic setting and active mass movements which cannot be uniformly described. Observed large fluctuations in the rate of discharge of springs and groundwater level in observation wells are highly dependent on meteorological conditions. Estimated hydraulic conductivity of the soil is relatively high (2×10-4 m/s) and reflects the loose structure and high content of organic matter in the upper part of the forest soil. Hydraulic conductivity of more permeable sections of boreholes is in general higher in the upper parts, in predominantly gravel layers (in range from 2×10-3 to 1×10-5 m/s), than in the deeper clayey gravel parts (3×10-5 to 1×10-7 m/s). In the area of the Čikla landslide the average hydraulic conductivity is estimated at 8.99×10-4 m/s and is higher than in the area of the Urbas landslide (3.05×10-4 m/s).

Landslides susceptibility mapping using GIS and weights of evidence model in Tetouan-Ras-Mazari area (Northern Morocco)

The 590 km2 of the Western Rif (North of Morocco) is well known for active mass movements due to the strong climatic and anthropogenic aggressions in this area, where lithology and topographic relief are likely the phenomena that cause slope instability problems. In this study, we have focused on mass movements that have been occurred in the last two decades, namely landslides, complex slides and block slides. Over the years, this site and its surroundings have experienced repeated landslides. For this reason, landslides susceptibility mapping is mandatory to prevent natural risk and to better manage land-use. The application of weight of evidence method using remote sensing and geographical information systems (GIS) were used to generate a susceptibility map. Six conditioning factors were used in this study: lithology, distance to faults, distance to drainage, slope, aspect and hypsometry. A total of 126 mass movements locations were detected; 63 landslide location (50%) were randomly selected as input data for the entire process using the spatial data model (SDM) and the remaining locations were used for validation purposes. The final map of areas susceptible to mass movements has an accuracy of 95.3% and has been classified into four classes (very high, high, moderate and low).

Geomorphology of the Mount Akdag landslide, Western Taurus range (SW Turkey)

ABSTRACTThis paper presents the results of a geomorphological investigation of Mount Akdag landslide complex, located on the Western Taurus range, SW Turkey. The landslide, resulting in the collapse of a 5 km segment of Mount Akdag, covers an area of 9.8 km2 and has a volume of about 3 × 108 m3. The 1:15,000 scale geomorphological map (Main Map) of the Akdag landslide presented here was produced from a combination of field studies and unmanned aerial vehicle-based DSM, including aerial-photo interpretation and geomorphometric analysis of landforms. The map shows contemporary and past geomorphological hillslope processes and landforms associated with the landslide complex. Our new map suggests that the Akdag landslide was a complex rockslide consisting of multiple landslide types that developed through various movements. We found that 43 highly developed and active mass movements on the main body and side slopes of the landslide made a major contribution to the sediment input. The sediment produced in the upstream severely threatens the touristic site of Saklikent Canyon in the lower catchment via an increasing magnitude of torrents. This map will provide important data for local and national administrators regarding monitoring up-to-date mass-wasting processes, understanding the landslide and its related sedimentary dynamics, and implementing risk assessment and necessary precautions.

Evolution of Mass Movements near Epicentre of Wenchuan Earthquake, the First Eight Years.

It is increasingly clear that landslides represent a major cause of economic costs and deaths in earthquakes in mountains. In the Wenchuan earthquake case, post-seismic cascading landslides continue to represent a major problem eight years on. Failure to anticipate the impact of cascading landslides could lead to unexpected losses of human lives and properties. Previous studies tended to focus on separate landslide processes, with little attention paid to the quantification of long-term evolution of multiple processes or the evolution of mass movements. The very active mass movements near the epicentre of the Wenchuan earthquake provided us a unique opportunity to understand the complex processes of the evolving cascading landslides after a strong earthquake. This study budgets the mass movements on the hillslopes and in the channels in the first eight years since the Wenchuan earthquake and verify a conservation in mass movements. A system illustrating the evolution and interactions of mass movement after a strong earthquake is proposed.

An example of active DSGSD in the Carnian Alps (NE Italy)

In the northern part of Friuli Venezia Giulia Region (Italy), in the Carnic Alps, above the Cercevesa stream, an active mass movement has been recently identified and classified as Deep Seated Gravitational Slope Deformation (DSGSD). The phenomenon covers an area of about 0.5 km2 and involves limestones overlying sandstones and mudstones. The most evident morphological feature of the Cercevesa DSGSD is a double-crested ridge on the top of the slope. The first measurements, recorded since June 2008, show a constant opening rate of about 58 cm/yr, a really rare value for gravitational phenomena in the Alps. To detect the triggering factor, geomorphological data, meteorological time series (rainfall, snowfall and temperature) and seismological data have been analyzed. The comparative analysis highlighted that the persistent rainfall of mid-November 1990 can be identified as the root cause of the phenomenon.

A New Assessment Method for Structural-Control Failure Mechanisms in Rock Slopes — Case Examples

Mass movement processes of bedrock slopes are highly dependent on the orientations of structural discontinuities within the rock mass. The associated hazards are typically defined by the orientation of structures and associated mechanisms of slope failure such as planar sliding, wedge sliding and toppling. A typical rock mass with multiple weak surfaces, or discontinuities, may form a consistent pattern over a range of spatial scale. The type of hazard resulting from the pattern of discontinuities will vary according to the angle and direction of the slope face. Assessing the risk of rock slope instability involves understanding of the complex three-dimensional structural features of the rock mass. Recent developments in stereographic methods show advantages are gained by representing wedges by linking great circles rather than showing the intersection line on the stereograph. We applied these methods to three rock slopes where active mass movement has occurred. The case studies include a large rock slide-debris avalanche in the Philippines, coastal cliffs in Australia and mining excavation slopes in Ghana, West Africa.

A spatial database for landslides in northern Bavaria: A methodological approach

Landslide databases provide essential information for hazard modeling, damages on buildings and infrastructure, mitigation, and research needs. This study presents the development of a landslide database system named WISL (Würzburg Information System on Landslides), currently storing detailed landslide data for northern Bavaria, Germany, in order to enable scientific queries as well as comparisons with other regional landslide inventories. WISL is based on free open source software solutions (PostgreSQL, PostGIS) assuring good correspondence of the various softwares and to enable further extensions with specific adaptions of self-developed software. Apart from that, WISL was designed to be particularly compatible for easy communication with other databases.As a central pre-requisite for standardized, homogeneous data acquisition in the field, a customized data sheet for landslide description was compiled. This sheet also serves as an input mask for all data registration procedures in WISL. A variety of “in-database” solutions for landslide analysis provides the necessary scalability for the database, enabling operations at the local server.In its current state, WISL already enables extensive analysis and queries. This paper presents an example analysis of landslides in Oxfordian Limestones in the northeastern Franconian Alb, northern Bavaria. The results reveal widely differing landslides in terms of geometry and size. Further queries related to landslide activity classifies the majority of the landslides as currently inactive, however, they clearly possess a certain potential for remobilization. Along with some active mass movements, a significant percentage of landslides potentially endangers residential areas or infrastructure.The main aspect of future enhancements of the WISL database is related to data extensions in order to increase research possibilities, as well as to transfer the system to other regions and countries.

Landslide susceptibility modeling assisted by Persistent Scatterers Interferometry (PSI): an example from the northwestern coast of Malta

Persistent Scatterers Interferometry (PSI) techniques are widely employed in geosciences to detect and monitor landslides with high accuracy over large areas, but they also suffer from physical and technological constraints that restrict their field of application. These limitations prevent us from collecting information from several critical areas within the investigated region. In this paper, we present a novel approach that exploits the results of PSI analysis for the implementation of a statistical model for landslide susceptibility. The attempt is to identify active mass movements by means of PSI and to avoid, as input data, time-/cost-consuming and seldom updated landslide inventories. The study has been performed along the northwestern coast of Malta (central Mediterranean Sea), where the peculiar geological and geomorphological settings favor the occurrence of a series of extensive slow-moving landslides. Most of these consist in rock spreads, evolving into block slides, with large limestone blocks characterized by scarce vegetation and proper inclination, which represent suitable natural radar reflectors for applying PSI. Based on geomorphometric analyses and geomorphological investigations, a series of landslide predisposing factors were selected and a susceptibility map created. The result was validated by means of cross-validation technique, field surveys and global navigation satellite system in situ monitoring activities. The final outcome shows a good reliability and could represent an adequate response to the increasing demand for effective and low-cost tools for landslide susceptibility assessment.

Post-earthquake landsliding and long-term impacts in the Wenchuan earthquake area, China

The Ms 8.0 Wenchuan earthquake on May 12, 2008 triggered tens of thousands of landslides and produced large amounts of loose material. The loose material accumulated in gullies or on slopes provides abundant sources for the consequent debris flows, which will endanger resettled residents and destroy urban reconstruction. During the 5years following the Wenchuan earthquake event, heavy rainfalls have already induced a great number of debris flows in the earthquake-damaged area, resulting in serious casualties and property losses. The co-seismic landslides and the debris flows induced by rainfalls in the Mianyuan River basin are analyzed using multi-temporal remote sensing images. More than 2000 landslides were triggered and about 4.0×108m3 of loose material was generated in the Mianyuan River basin, and the volume of erodible material is 6.0×107–1.6×108m3. There were 1.27×107m3 of bed load sediments and 6.3×105m3 suspended load sediments transported into the river system in the past 5years. The active mass movements will last for a long period in the Mianyuan River basin.

Geochemical characteristics and genesis of Mačje Jame and Vranjski Potok As-Cu-bearing iron occurrences west and southwest of the town of Busovača, Mid-Bosnian Schist Mountains

Investigated landslide is the largest active mass movement along the Croatian coast, situated on the north-eastern slope in the central part of the Rjecina Valley (north-eastern coastal part of Adriatic Sea, Croatia). Slopes in this valley are formed in siliciclastic rocks - flysch, while limestone rock mass is visible on the cliffs around the top of the river valley. The slopes are at the limit of a stable equilibrium state, and mass movement phenomena have been recorded since 19th century. Samples for laboratory testing were taken from the flysch bedrock, weathered zone and slope formations, and were recovered to provide specimens for data on their mineralogical, physical and geotechnical properties. Correlation between mineralogical and geotechnical properties and their influence on sliding processes are presented in this paper. Clay fraction in samples ranges from 17 % to 38 %. Clay activity of the tested samples is from 0.45 to 0.89, and the residual friction angle varies from 13.0° to 17.7°. These results correspond to the presence of kaolinite and illite groups of clay mineral. Mineral composition and decrease in strength of fine-grained soil materials, due to the increase of pore water pressures, contributes to the slope movements.

Active sinking at the bottom of the Rincón de Parangueo Maar (Guanajuato, México) and its probable relation with subsidence faults at Salamanca and Celaya

Rincon de Parangueo is a Quaternary maar that had a perennial lake until the 1980s. The lake was gradually desiccated as a consequence of drawdown in the Salamanca-Valle de Santiago regional aquifer and now functions as a playa-lake. In contrast with the features observed in other crater-lakes in the region (La Alberca, Cintora, and San Nicolas), which also dried up at the same time, the bottom of the Rincon crater displays clear evidence of active deformation associated with mass movement of lake sediments towards the depocenter inside the crater. The most conspicuous topographic feature is a 10 – 12 m high scarp parallel to the former lake coast. The scarp is produced by an annular shaped normal fault system, down towards the depocenter. Evidence of active mass movement is observed along the topographic scarp. Rotational slides associated with rollover anticlines and local grabens produced by antithetic faults are common on the eastern and northern parts of the scarp. Planar slides with open folds at their base occur at western part of the lake basin. Evaporites (trona, thermonatrite, eitelite, halite, and silvite) are abundant in the playa-lake sediments. Their presence makes us believe that a mass removal process is acting as a consequence of salt dissolution and infiltration of the brine towards the aquifer. This process, probably in conjunction with lake sediment compaction and/or diatreme subsidence, may explain the significantly higher fault displacement rate observed inside the crater ( ≈ 50 cm/year ) in comparison with active faults elsewhere in the Salamanca-Valle de Santiago aquifer ( ≈ 6 cm/year ).

Persistent Scatterers Interferometry Hotspot and Cluster Analysis (PSI-HCA) for detection of extremely slow-moving landslides

The synthetic aperture radar (SAR) interferometry (InSAR) technique has already shown its importance in landslide mapping and monitoring applications. However, the usefulness of traditional differential InSAR applications is limited by disturbing factors such as temporal decorrelation and atmospheric disturbances. The Persistent Scatterers Interferometry (PSI) technique is a recently developed InSAR approach. It generates stable radar benchmarks (namely persistent scatterers, PSI point targets) using a multi-interferogram analysis of SAR images. The PSI technique has the advantage of reducing temporal decorrelation and atmospheric artefacts. The PSI technique is suitable for the investigation of extremely slow-moving landslides due to its capability to detect ground displacements with millimetre precision. However, the interpretation of PSI outputs is sometimes difficult for the large number of possible persistent scatterers (PSs). A new approach of PSI Hotspot and Cluster Analysis (PSI-HCA) is introduced here in order to develop a procedure for mapping landslides efficiently and automatically. This analysis has been performed on PSs in hilly and mountainous areas within the Arno river basin (Italy). The aim is to use PSs processed from 4 years (2003–2006) of Radarsat images for identifying areas preferentially affected by extremely slow-moving landslides. The Getis–Ord Gi * statistic is applied in the study for the PSI-HCA approach. The velocity of PSs is used as weighting factor and the Gi * index is calculated for each single point target. The results indicate that both high positive and low negative Gi * values imply the clustering of potential mass movements. High positive values suggest the moving direction towards the sensor along the satellite line-of-sight (LOS), whereas low negative values imply the movement away from the sensor. Furthermore, the kernel function is used to estimate PS density based on these derived Gi * values. The output is a hotspot map which highlights active mass movements. This spatial statistic approach of PSI-HCA is considered an effective way to extract useful information from PSs at a regional scale, thus providing an innovative approach for rapid mapping of extremely slow-moving landslides over large areas.

Challenges in Understanding the Hydrologic Controls on the Mobility of Slow‐Moving Landslides

Slow‐moving landslides are a wide‐spread type of active mass movement, can cause severe damages to infrastructure, and may be a precursor of sudden catastrophic slope failures. Pore‐water pressure is commonly regarded as the most important among a number of possible factors controlling landslide velocity. We used high‐resolution monitoring data to explore the relations of landslide mobility and hydrologic processes at the Heumöser landslide in Austria, which is characterized by continuous slow movement along a shear zone. Movement rates showed a seasonality that was associated with elevated pore‐water pressures. Pore pressure monitoring revealed a system of confined and separated aquifers with differing dynamics. Analysis of a simple infinite slope mobility model showed that small variations in parameters, along with measured pore pressure dynamics, provided a perfect match to our observations. Modeling showed a stabilizing effect of snow cover due to the additional load. This finding was supported by a multiple regression model, which further suggested that effective pore pressures at the slip surface were partially differing from the borehole observations and were related to preferential infiltration and subsurface flow in adjacent areas. It appears that in a setting like the Heumöser landslide, hydrologic processes delicately influence slope mobility through their control on pore pressure dynamics and the weight of the landslide body, which challenges observation and modeling. Moreover, it appears that their simplicity, and especially their high sensitivity to parameter variations, limits the conclusions that can be drawn from infinite slope models.

Assessing susceptibility to landslides: Using models to understand observed changes in slopes

A map of landslide susceptibility is a necessary tool for proper planning and selection of sites for agriculture, infrastructure and other human developments. The Paonia–McClure Pass area of Colorado, USA, is well known for active mass movements. Large losses of property and risks to people highlight the need to accurately map susceptibility to shallow landslides and to identify safe locations for infrastructure and residential development. We mapped 735 active mass movements and 17 factors about each one. The weights of evidence, frequency ratio of landslides, and fuzzy-logic method were used to create an optimum map of landslide susceptibility. Weights of the evidence were used to categorize continuous factor data, frequency ratios of shallow landslides were used to assign the membership values for the categories of the factors, and the fuzzy-logic method was used to integrate the membership values. Four models from the fuzzy-inference network of mapping susceptibility to shallow landslides were developed based on the combination of factors using five types of fuzzy operators. The first inference network model was comprised of the combination of factors, which are independent of each other. The second, third and the fourth inference network models were developed such that factors are not necessarily independent of each other. These models combine all dependent and independent factors, based on the expert's knowledge. Intermediate steps in the second, third and fourth models were developed by combining the fuzzy factors in the first step by fuzzy-OR, fuzzy-AND, and fuzzy-OR plus fuzzy-AND operations, respectively. All models predicted similar percentages of observed shallow landslides with the fuzzy-gamma operation. Although the prediction capabilities of all the models are not significantly different, the fourth model is the best because it is the only model that accommodates the under-sampled and missed landslide data and the effect of increasing and decreasing gamma values. The first and third models create a problem if a category of a factor has a 0 membership value because of the absence or under-sampling of shallow landslides. The second model incurs the highest increasing effect of gamma values, and the third model incurs the highest decreasing effect of gamma values. The approaches described in this paper reduce the uncertainties associated with the categorization of continuous data, determination of fuzzy-membership values, and the combination of factors that causes shallow landslides.

Modeling susceptibility to landslides using the weight of evidence approach: Western Colorado, USA

The Paonia–McClure Pass area of Colorado is well known for active mass movements. We examined 735 active shallow movement features, including debris flows, debris slides, rock slides and soil slides, in this area. Identification of the hazardous areas is a fundamental component of disaster management and an important basis for promoting safe human occupation and infrastructure development in landslide prone areas. Bayes' theorem, based on the weight of evidence (WOE), was used to create a map of landslides that could be hazardous. The modeling was accomplished by employing a geographical information system (GIS) and a statistical package. Seventeen factors that cause landslides were measured and weighted using the WOE method to create a map of areas susceptible to landslides. The maps of weighted factors were summed on a pixel-by-pixel basis after performing chi-square tests to determine factors that are conditionally independent of each other. By combining factors that represent topography, hydrology, geology, land cover, and human influences, six models were developed. The performance of each model was evaluated by the distribution of the observed landslides. The validity of the best map was checked against landslides, which were not entered in the analysis. The resulting map of areas susceptible to landslides has a prediction accuracy of 78%.

Mass movement mapping for geomorphological understanding and sustainable development: Tigray, Ethiopia

Mass movement topography characterises the escarpments and piedmont zones of the tabular ridges in the western part of the Mekelle outlier, Tigray, Ethiopia. Several types of mass movements can be distinguished. The first type is rockfall produced by 357 km rocky escarpments and cliffs during the rainy season. In the study area, every current kilometer of Amba Aradam sandstone cliff annually produces 3.7 m 3 of rock fragments. However, this is an under-estimation of the actual cliff and escarpment evolution, which is also characterised by debris slides and small rock slides. In the debris flow class, three dormant flow types are recognised. The first type comprises preferential or undifferentiated mobilisations of the so-called plateau layers, the whitish sandy-clayey lacustrine deposits and the lower and upper basalts, and more especially, the swelling clays, derived from the basalts. These debris flows start on the nearly horizontal Amba Aradam Sandstone tabular extensions, jump over cliff recessions or even spurs, and go very far into the valley. In some instances parts of Amba Aradam sandstone and Antalo limestone cliffs are transported. Secondly, some debris flows take their origin in the Antalo limestone supersequence. It concerns deeply weathered layers resting upon aquicludes/aquitards. Finally, gigantic debris flows and rock slides occur around dolerite dyke ridges. About 20% of the total surface of the study area is occupied by landslide topography. Most of the landslides affect the steep edges of the table mountains or the dykes/sills. Mapping and listing of active and dormant mass movements increases knowledge in three domains which are crucial for sustainable development of the study area. The first one is geomorphological risk assessment. The distribution map of active rockfall and dormant landslides shows the areas where potential risks are located. Land use changes which improve the water infiltration capacity of dormant landslides, should be followed up. Secondly, the impact of global climate change on these risk areas can be assessed. The second domain is the water sector, which needs attention in the study area and in many parts of Africa. Landslides mobilised by hydrostatic pressures are related to the occurrence of aquicludes and aquifers. In the study area, landslide mapping led to the location of three aquitards, not described before. The third domain is the pedological mapping. In the study area, soil distribution is very well explained by the morphology and extension of dormant landslides. Finally, mapping of dormant landslides stimulates the academic debate on the geomorphological significance of mass movements in hillslope retreat in tropical areas.