Understanding and Reducing Landslide Disaster Risk

Rock avalanches represent the specific type of flow-like landslides—dry granular flows—that pose major threat to population in mountainous regions and in the adjacent plains. Being extremely mobile, they can affect areas up to dozens of square kilometers, extending sometimes for more than 10 km from the feet of the collapsing slopes. The internal structure of their deposits is characterized by intensive fragmentation of inner parts overlain by much coarser carapace. Such internal structure is typical of the vast majority of large-scale rock slope failures, both long runout and forming compact blockages in narrow river valleys. Therefore, all of them should be classified as rock avalanches, rather than as rock slides. Three additional classification criteria closely related to rock avalanche mobility and allowing more strict definition of a particular rock avalanche are discussed, i.e. the confinement conditions, debris distribution along the rock avalanche path, and directivity of debris motion. Besides providing information on debris motion mechanism(s), these characteristics predetermine the assessment of the exposure of elements at risk that might be affected by rock avalanche. It is demonstrated that transformation from the block slide to granular flow depends somehow on the morphology of the transition-deposition zone and on the mechanical properties of the basal surface, but is independent from the type and mechanical properties of the host rocks.

Liquefaction Induced Mass Landslide in Palu Donggala Earthquake on 28 September 2018 was one of the rare and biggest event on these types of landslides in the world. The phenomena was the most complete occurence since all mechanism of liquefaction and liquefaction induced landslides were represented. On these particular event, the author has conducted study on the liquefaction mechanism based on field observation including running drone in several areas, conducting soil investigations, work on analysis and collect as much as data from local people. This paper discusses Liquefaction Mechanism in these unique and spectacular sites (mainly in four areas: Balaroa, Petobo, Jono Oge and Sibalaya) because the earthquake seems to trigger liquefaction by multidirectional vibration and of particular interest is because the earthquake are near faults with shallow earthquake focus of about 10 km below the city. The extraordinary distance of liquefaction flow and lateral spreading is one of unique phenomena which is believed to be caused by the existence of initial artesian pressure and significant vertical acceleration causing the soil loosing contact stress. Layers of sands and clays or silts might have caused significant force to the liquefied sands and flow laterally. Instead of surface phenomena, the main objectives of this paper is also to discuss the results of CPTu tests conducted for analysis and fact findings on liquefaction phenomena. Each data of CPTu yields liquefaction potential index which is used to characterize the severity of ground damage and discuss mitigation and risk reduction in the future.

This article describes large landslide on the left-bank slope of the Kuban River Valley, Northern Caucasus, Russia. Its evolution along with the conditions of its triggering and activation are described. Landslide that took place in 2016 was just is a partial reactivation of a much larger ancient landslide. While modern landslide was triggered by the climatic factors, slope stability assessment allows assumption that formation of the ancient landslide could be induced by seismic activity.

Earthquake-induced landslide mass mobility is a topic of particular relevance for the analysis of earthquake-induced ground effects scenarios. The landslide masses already existing on the slopes interact with the seismic waves that propagate from the bedrock, giving rise to effects of amplification of the seismic motion at specific frequencies connected to their geometry and their dynamic properties. The quantification of the earthquake-induced displacements expected in landslide masses through numerical models under dynamic conditions highlights how, especially for medium-low energy levels of the seismic input, the displacements thus obtained are generally higher than those computed by conventional approaches (e.g. Newmark method applied to the hypothesis of rigid or deformable block and related semiempirical relations). A series of case studies has also proved that the geometry of significantly dislodged landslide masses (i.e. segmented into kinematically distinct portions, namely “blocks”) due to their geomorphological evolution over time, significantly controls the seismic-induced displacements obtained by numerical models. In particular, the results highlight that the maximum displacements computed through the numerical models do not correspond to seismic inputs whose characteristic periods coincide to those of the resonance or of the length of the landslide mass but are more directly connected to the smaller dimensions of the individual blocks in which the landslide mass is segmented.

Although there is no commonly accepted methodology for evaluation of deep-seated landslide susceptibility, the progress on remote sensing technology such as aerial photos, satellite images, precise DEM and InSAR data have made it easier to detect ground movement at time interval and cost-effective. Combining these techniques and ground truth, the authors attempt to understand the nature of Jure landslide in Nepal that occurred due to heavy rain in August 2014. They have also studied the effect of Nepal Gorkha earthquake on the Jure landslide. Gravitational deformation, so-called “rock creep” has proceeded for long time forming thick weathering layer at the Jure landslide site. Small and shallow deformations have occurred in and around the site since a decade or before. However, significant enlargement of the landslide due to the earthquake in 2015 was not detected by InSAR because the quake occurred at the end of dry season.

Coseismic landslide inventorying is of great significance for understanding the occurrence, distribution, and risk assessment of earthquake-triggered landslides. Based on manual visual interpretation of high-resolution satellite images acquired before and after the event and field survey verification, this work prepared an inventory map of the landslides triggered by the 2012 Ms6.6 Heijing, Xinjiang, China earthquake. Results show that this earthquake triggered at least 453 landslides with a total area of 0.664 km2 in the areas of VII and VIII seismic intensity. The area density of the landslides is 0.01% and the landslide point density is 0.07 km−2. A north-east extending river valley west of the epicenter registered the highest landslide density. The reason of this is considered to be the strongest ground motion during the earthquake, the steep topographic relief, the large slope gradient, and accumulated loose materials at this site, which means the area is prone to landsliding. This study provides a typical case with weak landslide triggering capability which was associated with special local conditions.

The 2018 Hokkaido Eastern Iburi Earthquake triggered numerous shallow landslides on slopes covered with thick pyroclastic fall deposits. These shallow landslides tended to occur on concave rather than convex slopes and their slip surfaces were very wet, indicating that water played an important role in landslide initiation. As a first step toward clarifying the role of water in these landslides, we used tensiometers to monitor pressure head dynamics on a natural hillside covered with thick pyroclastic deposits that remained in place throughout the earthquake. We found that on concave slopes, the lower part of the pyroclastic fall deposits throughout the weathered basement complex (sedimentary rock) were always wet. Notably, the interface between the pyroclastic fall deposits and weathered basement complex, which forms a potential slip surface for earthquake-induced landslides, was always at or near saturation. On convex slopes, the weathered basement complex was never saturated and showed greater pressure head fluctuation. We infer that the pyroclastic fall deposits over the basement complex tend to weather more easily and are more susceptible to intense ground motion on concave than on convex slopes and the landslide slip surface was saturated at the timing of the earthquake on concave slopes. We conclude that these factors contributed to the larger number of shallow landslides initiated on concave slopes.

A strong earthquake could trigger a large number of co-seismic landslides and induce large amount of loose materials on steep slopes and in the gullies. Under strong rainfall conditions, these loose materials could induce devastating debris flows, which will endanger the resettled population and destroy the re-built infrastructures. From 19 to 20 August 2019, fourteen debris flows were triggered by extreme rainstorms near the epicentre of the Wenchuan Earthquake. Among the fourteen incidents, three of them produced debris flow dams, which changed the course of the Minjiang River and resulted in flooding at different parts of the reconstructed Miansi town. In addition, sixteen casualties, twenty two missing persons, and destruction of four main roads were reported. In this paper, one typical catchment, named as “Dengxi gully”, near the epicentre of the Wenchuan earthquake (Sichuan Province, China) was chosen as a case study for remote sensing analysis, field investigation of landslide evolution and debris flow development before and after the catastrophic events. The debris flow in the study area was initiated in four stages: (a) generation of a large amount of loose materials from the Wenchuan Earthquake; (b) run-off erosion from co-seismic landslide material on hilly slopes and repeated mobilizations in steep channels over the years; (c) development of high intensity localised rainfall events; (d) wash out of accumulated materials in gully by the flood. The study of “8.20 debris flows” can provide a benchmark for analysis of long-term evolution of debris flows in order to identify potential continuing hazards in the earthquake-affected areas and make proper engineering decisions.

This paper presents an inventory of lakes in the Central Andes region (31°–36° S) of Argentina by using high resolution satellite images. Lakes were classified according to the damming processes or associated landforms. Statistical analysis of main lakes attributes was carried out showing that larger lakes are associated with volcanic and karstic landforms, while smaller ones correspond to thermokarst supraglacial lakes. Lake distribution is forced by the regional topography being mainly located in the periglacial and glacial environment (above the 3730 m a.s.l.). Moreover, latitudinal distribution of different types of lakes differs. Larger water bodies in the Argentinean Central Andes are landslides dammed except to the 34°–35° S volcanic region. These findings set the first step in hazard analysis and highlight the need for carrying out further research to assess outburst flood hazard in the Arid Central Andes of Argentina.

The current global climate change is accelerating many natural processes that can lead to the rupture of dams of glacial lakes. One of these lakes is Lake Imja in the Khumbu area of Nepal. Three factors that influence the stability of the moraine dam were selected for analysis in this work—rockfalls/rockslides, growth of the lake area and melting of dead ice in the frontal moraine. The results of this study show that there is currently no risk of rockslide into the lake, which, however, may change due to the accelerating growth of the lake in the near future. The development of temperatures is also observed, where the increase in the last two decades is particularly striking. Crucial for the stability of the moraine dam is now the melting of dead ice at its core, as new thermokarst lakes are forming on the moraine surface, and a leak through the moraine in its southwestern part has also been discovered.

The Bureya landslide was formed on December 11, 2018 in the Bureya River valley in the Far East of Russia. It affected metamorphic rocks of the Upper Proterozoic age. The peculiarity of this rock slope failure was that it occurred in winter when air temperature dropped from ca. −3 °C to −37 °C. Landslide had complex structure and was formed in several stages with variable displacement mechanism. The first stage of main displacement can be classified as wedge failure transformed into rock avalanche more than 700 m long (measured from the slope foot) that moved with velocity up to 25–26 m/s. Landslide collapsed into reservoir and formed the splash wave up to 60 m high that washed out the taiga forest on the opposite slope of the valley. During the second stage that followed the first one in few seconds, large block of rock (260 × 280 m) slid down from the eastern part of the headscarp and formed rock avalanche up to 860 m long. The mean velocity of its motion was ~23–25 m/s, while the maximal one in its front could reach ~60 m/s. During the last stage several smaller secondary slides occurred on the slopes of the main landslide body and within the main headscarp. The total volume of the affected rocks can be estimated as 25 million m3, up to 12 million m3 of which were displaced during the first stage, up to 11.8 million m3—during the second stage and up to 1.2 million m3—during the secondary landslides formation. The Bureya landslide formed the natural dam more than 70 m high and up to 550 m wide that split the reservoir into two parts, so that special measures had to be undertaken to restore normal water flow.

In the last few decades, >200 new natural (mainly landslide) dams have formed in New Zealand. Several of these dams, such as the: 1996/97 Mount Ruapehu tephra dam (formed by volcanic eruption); 2007 Young River landslide dam; largest ten landslide dams associated with the 2016 Kaikōura Earthquake; and 2019 Kaiwhata landslide dam, have been studied in detail to better understand their: (a) formation mechanisms; (b) material properties; (c) failure modes; and (d) downstream impacts. This paper outlines a method to assess the longevity and downstream impacts of landslide dams, post-formation, by adopting a combination of field techniques, forecast models and expert judgement based on the performance of past landslide dams, immediately post-event. To do this we use the following steps: (1) carry out initial breach and inundation modelling using existing information—done prior to visiting the site; (2) detailed, high-resolution topographic surveys of the dam and downstream area; (3) site-specific investigations to measure key parameters such as the volume and geometry of the dam and lake, and the particle size distribution of the dam materials; (4) dam breach modelling using empirical methods to identify dam failure scenarios; (5) numerical flood/debris inundation modelling to determine area of impact; and (6) overlaying dam failure and debris inundation scenario models on asset maps to identify people, buildings and other infrastructure that are potentially at risk. This study summarises the method for assessing the likelihood of dam failure and the potential downstream consequences, using the Hapuku River and Kaiwhata dams as case studies.

Detailed information on the internal structure and sedimentological characteristics of landslide dams is important for natural dam hazard assessment studies. The materials composing landslide dams play a significant role in determining their overall longevity and stability. This, on the other hand, is linked to their source stratigraphy and the degree of fragmentation and pulverization undergone by the materials during their transport and emplacement history. Overall, the time of failure of landslide dams and the magnitude of the outburst flood depend on the internal characteristics of the impoundment, such as the grain size distribution, grain shape, degree of consolidation, presence of subsurface discontinuities, erodibility, and clay percentage. The evolution of internal erosion and piping in landslide dams has been ascribed to the relationship between the internal structure of the dam and the discharge rate through the impoundment. This paper presents a systematic review of the influence of the internal structure and sedimentological characteristics of landslide dams on the piping failure of natural river blockages. The paper highlights the processes of emplacement of landslide dams, the internal modification of the sediment during transport, the different facies assemblages and their role in the evolution of internal erosion and piping. Results obtained from the microtremor (MTM) chain array survey gave a better understanding of the evolutionary history of landslide dams. Furthermore, preliminary results obtained from laboratory experiments gave credence to the notion that the longevity and stability of landslide dams formed by translational mass movements are higher than those formed by rock avalanche processes.

The results are summarised of the correlation between long-term geotechnical monitoring, geological and geophysical surveys, finite element method modelling and their geomorphological interpretation in the area of North Bohemia affected by coal mining for more than 100 years. An underground mining-induced catastrophic landslide occurred in 1952 and had direct impacts on the local municipality, this still active and complex landslide has been well described since a detailed monitoring network was installed in the 1980s. Unique deep rock-mass monitoring is based on precise geodetical measurement in an exploration gallery from 1980. Several different types of deep-seated and near-surface landslide processes with different dynamics were identified during four decades of interdisciplinary monitoring, FEM modelling, ERT profiling and numerous other surveys. Landslide processes are influenced by anthropogenic activities in varying degrees, but climate factors have played the main triggering role in the recent past.

Mount Meager, a glacier-clad volcanic complex in British Columbia, Canada, is known for its large landslides, as well as a major eruption about 2360 years ago. In 2010, after decades of glacier retreat, the south flank of Mount Meager collapsed, generating a huge (53 Mm3) landslide. In 2016, fumaroles formed ice caves in one of the glaciers on the complex. This glacier is bordered by a large unstable slope presently moving about 3.5 cm per month. If this slope were to fail, a long-runout debris avalanche would reach the floor of the Lillooet River valley, with possible destructive effects on downstream infrastructure. The unloading of the volcanic edifice from an abrupt failure would also have unknown effects on the magmatic plumbing system. From geochemical, geophysical, and petrological data, we infer the presence of a magmatic chamber at 3–16 km depth. Based on numerical model simulations carried out to constrain the stress change, the failure would affect the stress field to depths of up to ~6 km, with changes in effective stress of up to ~4 MPa. The change in effective stress following such a landslide might destabilize the magmatic chamber and trigger an eruption. This result also suggests that a previously documented major flank collapse may have had a role in the 2360 cal yr BP eruption.

Large-scale slope instability is a very characteristic geological hazard in the entire Western Caucasus., Rock avalanches with volume up to 60 million m3 and a displacement distance of more than 2–3 km are widely developed in this region, especially in the upper reaches of the Mzymta River basin. Such rock avalanches are dangerous for densely populated and developed areas, such as the Krasnaya Polyana village. This article describes a typical prehistoric rock avalanche in this region. The conditions of its formation and characteristic features of the structure are presented, based on interpretation of aerial photographs, field observations, digital geological models, as well as physical-mechanical testing of soil samples.

The stability of rock slopes is often guided by the structural geology of the rocks composing the slope. In this work, we analyse the influence of structural characteristics, and of their seismic response, on large and deep-seated rock slope failure development. The study is focused on the Tamins and Fernpass rockslides in the Alps and on the Balta and Eagles Lake rockslides in the southeastern Carpathians. These case studies are compared with catastrophic rock slope failures with ascertained or very likely seismic origin in the Tien Shan Mountains. The main goal is to identify features allowing to identify seismically induced deformation modes based on the source zone rock structures. We will present examples of classical anti-dip slope and along-strike rock structures that hint at a possible/partial seismic origin, but we will also consider a series of mixed structural types, which are more difficult to be interpreted. This morpho-structural study is supported by distinct element numerical modelling results showing that seismic shaking typically induces deeper seated deformation in initially ‘stable’ rock slopes. In addition, for failures partially triggered by dynamic shaking, these studies can help identify the contribution of the seismic factor to slope movements. The identification of the partial seismic origin on the basis of the dynamic response of rock structures can be particularly interesting for case histories in less seismically active mountain regions (in comparison with the Andes, Tien Shan, Pamirs), such as in the Alps and the Carpathian Mountains.

A Deep-Seated Gravitational Slope Deformation (DSGSD) affects the SE slope of the Siah-kuh anticline in its SE periclinal tip in the Ilam region (Zagros Mts., Iran), almost 30 km south of the Seymareh Landslide, which represents the largest landslide on Earth surface. The DSGDS is driven by a Mass Rock Creep (MRC) process and involves an area of about 8 km2. The evolution of such a gravity-induced process is strictly related to the evolution of the of Dowairij River drainage system. River incision originated a stress release at the bottom of the slope which likely caused the initiation of the deformational process. The present study is part of a broader International Programme on Landslide project (Project IPL-237) focused on the role of time-dependent rock mass deformations and landscape evolution rates as predisposing factors for massive rock slope failures. In this regard, the preliminary results of an ongoing research are here presented focusing on the assessment of the present-day landscaping processes. Specifically, a geomorphological survey was carried out in this area firstly through the analysis and interpretation of remote data (Google Earth satellite optical images), which led to the first detection of possible gravity-induced landforms, such as evidence of bulging and lateral release within the deforming slope of the Siah-kuh fold-related ridge. To confirm and quantify the existence of ground displacement due to a MRC process, InSAR techniques were performed for the Siah-kuh slope and surrounding areas by processing 279 satellite Sentinel-1 (A and B) radar images of the ascending and descending orbit spanning from 06 October 2014 to 31 March 2019. Moreover, a quantitative morphometric evaluation was also performed through a morphometric index suitable for predicting the catchment-scale suspended sediment yield on the deformation area produced by the Dowairij River system. We derived the erosion rate of the drainage network responsible for the valley engraving which allows to estimate a starting time for MRC in the order of 101 ka. The comparison between the valley erosion rate and the slope strain rate reveals a difference of almost one order of magnitude allowing to assume that the gravity induced process, identified from remote and field geomorphological survey, evolves faster and originates landforms which can be preserved by the drainage system of the Dowairij River.

Catastrophic landslides are reported to be related to large amounts of unstable rocks preceded by deep-seated gravitational slope deformation (DGSD), where the slopes are underlain by Eocene to Miocene slate in the Central Range of Taiwan. To understand basic geological causes of the slope processes, the study was conducted in the Cifeng, Lixing, and Maliguan areas along the Lixing Industrial Road where many DGSDs threat important infrastructures and villages directly. Geological survey suggests that the beds beneath the slopes are mainly slate interlayered with thin metamorphosed sandstone. The slate along the river beds displays a distinct slaty cleavage which strikes NE–SW and dips 60–80° to the SE, but was observed to have gravitationally deformed to form buckling and toppling folds. DGSDs on overdip cataclinal and anaclinal slopes are subjected to buckling and toppling, respectively. Some of DGSDs of both types have led to deep-seated rockslides. Besides, sites with potential of future catastrophic landslides may be geomorphically identified at undercut slopes that have small head scarps upslope.

This paper considers the formation of submarine landslides on the Jan Mayen Ridge. A large submarine landslide, about 50 km wide, 40 km long and 500 m deep, has developed into an amphitheatre-shaped depression with subsequent retrogressive sliding along bedding planes to form secondary and tertiary landslide scars. This retrogressive process proceeded via small slope failures that generated erosive, confined turbidity currents. Consequently, long channels developed downslope of the secondary and tertiary landslide scars. Other small landslides are located on the deep-sea terraces at the foot of the southeast ridge. Internal normal faults on the terrace have generated an irregular bathymetry with many superimposed landslides. These small landslides formed on areas of relatively steep seafloor and are triggered by normal faulting.

The coastal ridge of Forkastningsfjellet comprises a ~100 million m3 rock rotational slide, which occurred in the hangingwall of a listric, northwest-dipping slide surface, probably in postglacial times. Active mass wasting and seacliff erosion, mainly controlled by the inherent discontinuities of the fractured and tilted rock masses, currently take place along the steep slopes of the coastal tilt blocks. A catastrophic reactivation of such slide blocks as very rapid rock slide could have severe consequences for the surrounding coastal regions and for Longyearbyen, the capital of Spitsbergen, which is situated nearby. This paper introduces the present knowledge about the rock slide and describes the current multidisciplinary investigation program that is conducted to better understand the nature and state of activity of the rock slide. The investigation is necessary to improve the hazard assessment of Forkastningsfjellet rock slide, which also serves as a showcase for the impact of climate change on landslide activity in the Longyearbyen region.

The Himalayan geo-environment has been experiencing slope instability hazards of catastrophic dimensions in historical past. Large rocks and debris avalanche have been recognized largely in higher domains in easternmost extremity covering Sikkim and Arunachal and Northwest Himalaya encompassing Kumaun, Garhwal, Himachal, Jammu and Kashmir and Ladakh Himalayas. These domains have witnessed societal and morphological impacts due to such extreme events. The catastrophic landslides are mainly triggered by earthquakes and climate change related intense rainfall, cloudbursts, Glacial Lake outburst Floods (GLOF) etc. in different sectors of Himalaya. These cataclysmic events are caused by various proportions of geological, geomorphologic and geotechnical characteristics of slopes, relief and tectonic conditions including anthropogenic activities. Each of the recorded landslides differs greatly in their causes, triggering agents, run-out distances and impacts. A case study of recent catastrophic landslide in Garhwal Himalaya has been presented. The paper highlights importance of the historical records of catastrophic landslides and attendant changes in terrain morphology to plan for strategy for sustainable regional development.

Over the past 40 years, a comprehensive slope safety system has been developed and implemented by the Geotechnical Engineering Office (GEO) to manage the landslide risk in Hong Kong to a reasonably low level. However, extreme rainfall events due to the effect of climate change could bring about widespread and large-scale landslides. Therefore, the GEO has made concerted efforts to enhance our preparedness for extreme landslide events. This paper highlights the holistic, multi-pronged approach adopted to manage the landslide risk associated with climate change.

Over the past 100 years, the process of global climate change has accelerated, and the air temperature has also appeared an increasing trend in the high latitude permafrost area of northeast of China, the permafrost degradation which dramatically changed the environmental geological conditions,resulting in the change of landform and the increase of geological disasters.However, there are few research results about this area. In this paper, we take the road area of Bei'an-Heihe highway crossing the Lesser Khingan Mountain as the study area. Using a total of 18 ALOS/PALSARSAR images, through the SBAS-InSAR technique to draw the surface deformation map of the study area from July 2007 to December 2010, combined with the local meteorological data and the permafrost distribution map in the study area obtained by our research group, the relationship between distribution characteristics of permafrost, permafrost degradation, and surface deformation were analyzed. The results show that the annual average deformation rate of surface in the study area is ± 70 mm/year, the surface deformation is closely related to the permafrost distribution, and the distribution law is consistent.Climate warming is the main factor leading to the permafrost degradation. In the context of continued warming and accelerating degradation of permafrost, we will face landslides, ground surface subsidence or more ecological and engineering problems, threaten the safety of local engineering structures. The results reveal the law of the permafrost degradation process under the background of climate warming, and provide a reference for future research.

Climate change is expected to affect the elements of the hydrological cycle, which are also related to the landslides and debris flows triggering mechanics. In the scope of this contribution, we evaluated climate change impact on the water balance components in the hinterland of the Koroška Bela (NW Slovenia), which is one of the endangered settlements in Slovenia. For this purpose, we focused on the representative concentration pathway (RCP) RCP4.5 scenario, which can be described as a midway scenario. Lumped conceptual hydrological model was used in order to model the relationship between the hydrological cycle elements. Moreover, climate change impact on the intensity-duration-frequency (IDF) curves was also estimated. The results indicate that total rainfall as well as effective rainfall could increase in the future. Mainly due to air temperature increase, we could see an evapotranspiration increase in the future. Moreover, hydrological model results indicate a possible surface runoff increase from the Bela stream catchment. However, these changes are mostly in the range of the 5% with the exception of the air temperature data where difference between future and past is larger. Furthermore, subsurface water storage included in the model indicates that only slight changes in the wetness of the catchment might be expected. Additionally, climate change could also affect the extreme rainfall characteristics, which can be seen as a change in the IDF curves. However, these changes are relatively small.

Signals of global climate change are increasingly evident in the Alps where, in recent years, a growing number of landslides occurred in glacial and periglacial areas. In order to document such a case, a landslide is described and analysed, which affected the SE side of a rocky ridge and the Trajo Glacier below in the Gran Paradiso Massif (NW Italy) during the warm summer of 2017. It was a multiple rockfall of about ½ million m2, with vertical drop of ≈300 m, a runout distance of ≈900 m, and 17° of travel angle. Prompt field surveys, interpretation of Sentinel-2 satellite images, and an analysis of data from several weather stations, are used to reconstruct the phenomenon and its causes. This study highlights the geological structure of the area (which reflects the morphology and geo-mechanical characteristics of the slope) and the meteorological conditions during the months before the main failure. Moreover it reveals that the landslide was not a single event but developed over time through at least five failures. According to available information, several predisposing factors seem to have played an important such as the degradation of permafrost (probably affecting rock masses at depth), the alternation of freeze-thaw cycles, and the availability of a considerable amount of water from rainfall and snowmelt, infiltrating the rock mass.

A rainfall-induced debris flow disaster occurred in Shelong Gully on the 22th June, 2019. More than 26,300 m2 of farmland and 14 houses were buried and transportation and power supply broke down in the worst catastrophe in the history of Shelong area. To investigate this disaster, a detailed interpretation was carried out using (Unmanned Aerial Vehicle) UAV-based images. Analysis of disaster characteristics based on images and field survey revealed that the disaster could be identified as a consequence of compound mountain hazards including mass movements and mountain torrent in Shelong Gully. Moreover, the dynamic process of debris flow was analysed by using the finite difference method. Its dynamic characteristics indicated that the structure of debris materials changed during the movement process of debris flow. The results reveal that the loose materials, steep terrain condition and abundant rainfall are the main causal factors of this disaster event. This research on the analysis of hazard formation conditions and dynamic process for debris flows is of guiding significance to the formulation of disaster risk assessment and disaster mitigation plans.

The paper discusses the topic of dynamic impact of fast-moving flow-like landslides against structures such as masonry walls and buildings. A set of numerical simulations is developed through the Material Point Method (MPM) to investigate the landslide-structure interaction. First, some experimental results available in the literature for masonry walls made of clay bricks and mortar joints are simulated in 2D and 3D conditions appropriately reproducing the overall stiffness, resistance and displacement of the wall in out-of-plane loading, until plastic hinges are formed and complete collapse occurs. In these cases, a known external pressure is applied to the wall. Then, realistic flow-like landslide scenarios are considered for analysing the impact on reinforced concrete buildings with unreinforced masonry infilled walls. Particularly, the impacting mass is modelled as a frictional material composed of a solid skeleton saturated with water. MPM simulations are developed in 2D conditions, focusing the attention on the failure of non-structural elements and damage to the different floors. MPM simulations are varied again over a range of properties to assess the role of key parameters, among impact velocity, volume, and soil properties such as unit weight and internal friction angle. The potential of a unitary approach for simulating the fast propagation of a saturated soil and the stress-strain response of a structural element is discussed.

In summer 2018, in an area above lake Oeschinen in Kandersteg (Bernese Alps, Switzerland), significant terrain changes with indication of fast ground movements were observed. The NW dipping rock and debris slope named “Bim Spitze Stei” had been known to be under constant movement before. However, the rapid acceleration from a maximum volume prone to failure of about 20 mm3 prompted the authorities to undertake a thorough analysis of the situation and analyse primary (rock avalanche) and secondary (floods and debris-flows out of the rock avalanche debris) hazard processes and the risk they pose to the nearby Village of Kandersteg. A first assessment of the most recent Sentinel-1 satellite InSAR data confirmed rapid ground movement in the order of several mm/d up to cm/d and a rapid acceleration of the west-flank of “Bim Spitze Stei” landslide from initially 7 mm/d to few cm/d within 2 weeks in July 2018. In addition, different sectors with different kinematics could be identified by interpretation of single interferograms. In a second step, an archive analysis of historical InSAR data reaching back to 1991 clearly showed that an acceleration trend from initially sub-stable conditions up to several m/a. Finally, based on the findings from the satellite InSAR analysis, a survey campaign with a terrestrial radar interferometer was performed in order to define the current state and location of the potentially outcropping glide plane in the west-flank. The successful campaign led to the observation of the presence of two active glide planes with the lowermost encompassing the maximum estimated volume of the mass in movement thus helping for the definition of potential failure scenarios thus helping in the selection of enhanced monitoring systems and increasing the preparedness for the runout-areas.

With the development of global warming, the permafrost in Northeast China, which is located in the south margin of permafrost area in Eurasia, has gradually degenerated, resulting in an increased incidence of landslides. At present, research on the occurrence mechanism, movement process characteristics and evolution trend of landslides in permafrost area, is limited and lacking in detail. It is difficult to identify landslides that have cured within the last hundred years as movements have been relatively small during this time period. In addition, the lack of written records, the unusual geological environment and landforms and the surface coverage, as well as the landslide mechanisms mean that accurate identification is difficult using existing technology. In this paper, Beian-Heihe expressway, which is located in the permafrost degradation area of Northeast China, is selected as the research area. Field investigation, 3D modeling of UAV image, high-density electrical survey, geological drilling and other methods are used to study the distribution of new and old landslides in the area. The study found that the distribution of tree populations at the boundary of the old landslide and some parts on the landslide body was significantly different from the distribution of tree populations outside the landslide body. In combination with tree core sampling, with the help of the relevant theories and methods of dendrochronology, Statistical analysis of tree species distribution and tree ring differences was used to estimate the occurrence time of old landslides. Combined with the previous research results, the relationship between the movement process of landslides and the degradation of permafrost in the study area is analyzed. This method can effectively realize the positioning and model reconstruction of old landslides in a short time scale, which will have important theoretical and practical significance for the early warning and treatment of landslides in permafrost degradation area.

On February 2 2015, a quick clay landslide occurred adjacent to Mofjellbekken's two parallel bridges (referred to as the Skjeggestad landslide) on the E18 motorway from Oslo to the southeastern coast of Norway. The landslide damaged one bridge foundation which led to partial collapse of the southbound bridge. The damaged bridge had to be demolished and rebuilt. NVE, the Norwegian Water Resources and Energy Directorate, established an independent investigation commission to study the cause and the failure mechanism of the landslide. The Commission examined evidence from the soil investigation, available topographic data, observations in situ, eye witness statements and photographs taken by drones. These evidences were used to reconstruct the most probable sequence of events during the landslide. Both natural causes (erosion, rainfall, snow/ice melting) and man-made causes (vibration, fill construction or other disturbance) were investigated using the available data and stability analyses. The Commission concluded that fill placement on top of the slope in the period 1998–2006 reduced the safety margin considerably. The last fill placed shortly before the landslide occurred in 2015 was the trigger of the landslide which had by then a marginal factor of safety. This paper presents the forensic investigative process by the NVE investigation commission.

Unmanned Aerial Vehicle (UAV) has been widely used for slope stability analysis. The objective of this research is to test the digital surface model (DSM) results generated from UAV images with the data acquired from total station for a deformed slope. A slope along the Pan Borneo Highway was selected for the study. The UAV survey was undertaken by utilizing DJI Inspire 1 with Zenmuse X3 Gimbal. A total of 10 ground control points (GCPs) were marked during the surveying for validation purposes. Structure from motion (SfM) technique adopted Pix4D enterprise version 4.3.33 to stitch the images for the production of orthophotos and DSM. The root mean square error (RMSE) of the GCPs were checked, where the horizontal RMSE in x direction and y direction are 1.4 cm and 1.8 cm respectively while RMSE in z direction is 2.6 cm. The total station surveying was taken at various locations of slope, which include slope surface with slight to moderate deformation, slope surface with severe deformation, surface channel and at the edge of surface channel. The elevations of DSM results were tested with those surveying data acquired from site. The results show that for slope with slight to moderate deformation, the accuracy of the RMSE in elevation of 4.2 cm can be achieved. Similar RSME accuracy can be attained for surface channel which is 5 cm. However, the RMSE for slope portion with severe deformation is 10.6 cm. From this research, it is found that the UAV-based DSM lower accuracy will be attained for locations of sharp changes in elevation.

As in the case throughout the world, landslides in Turkey have accounted for significant amount of economic losses and caused damage to properties as well as the environment and inhabitants. For example, considering the last 70 years’ landslide records in Turkey, it was revealed that more than 60,000 people were affected due to landslides. Thus, in order to minimize the undesired landslide consequences, some measures and initiatives had to be taken. Particularly in the last 10 years, many projects have been initiated by the governmental agencies in Turkey. Of these, a web-based landslide susceptibility and hazard mapping system project, namely Disaster and Risk Reduction System (ARAS), has been initiated in 2016. The most important objective of ARAS is to establish a spatial decision support and analysis system to reduce the mass movement risk for mitigation efforts using today’s technologies and data processing techniques. In this study, it was aimed at introducing ARAS and its applications on producing landslide susceptibility and hazard maps in a web-based platform. For this purpose, whole stages of ARAS in its current version were explained and landslide susceptibility and hazard maps of Kastamonu city, located in Middle Black Sea region of Turkey, were produced for this study. In ARAS, risk assessment stage is an ongoing process at the moment, and will be completed in a few years. When completed, decision-makers, planners and local authorities will benefit from the advantages of ARAS, which will provide significant gains for sustainable risk management in Turkey.

The Quaternary geology of western Norway’s landscape is the result of glacial and post-glacial sedimentation and erosional processes, a significant sea-level drop and high rock-slope failure activity. All these processes are represented within a small valley section below the Mannen rock-slope instability in Romsdal valley, western Norway. Here, exposure ages, Quaternary geological mapping and geophysical investigations permit the development of a paraglacial landscape evolution model. The model contextualises at least six catastrophic rock-slope failure events within the overall sequence of fjord-valley infilling following deglaciation. A transition from a wide basin-like valley into a strongly confined valley section led to the build-up of more than 40 m thick stratified drift, which was at least partly deposited within a marine environment. The morphology of these sediments features two distinct erosional levels, which are interpreted to be connected to tidal currents during post-glacial sea-level drop. The landform evolution model illustrates the importance of catastrophic rock-slope failures and the impact of strong tidal currents on the typical sediment fill in narrow, high-relief fjord valleys.

A multimethodological method based on environmental, stress–strain, microseismic, and ambient seismic noise monitoring is here presented, with a view to identifying non-linearity of thermally-induced deformation of jointed rock masses at different dimensional scales. Rock masses experience non-negligible deformation cycles due to the continuous fluctuations of their surficial temperatures. However, the interpretation of such strain effects, in terms of the ratio between elastic and inelastic percentages, is still debated. In particular, the relation between microseismic emissions, considered as primary indicators of crack-growth related energy release, and resonant frequencies fluctuations of rock structures, witnesses of the thermally-induced effect at the macro- or structure-scale, have not been yet studied within a coupled framework. The combination of different approaches able to investigate the behavior of rock masses from micro- to macro-scale, then from fracture-scale to joint-isolated rock blocks up to rock structures, could provide new insights and perspectives on the effects related to shallow thermal stresses fluctuations. This paper presents the preliminary outcomes from two case studies, the Acuto experimental test-site (Italy) and the Wied Il-Mielaħ sea arch (Malta), where multiparametric monitoring surveys were conducted and are still ongoing, aiming at the assessment of the cause-to-effect relation between near-surface thermal stresses and induced strains. Data analysis was carried out following different approaches, with a particular emphasis on the Acuto test-site dataset recorded so far, allowing to establish a well-constrained correlation among temperature fluctuations and rock mass deformation both at the daily and seasonal scale.

The purpose of this study is to evaluate Autoencoder-based landslide susceptibility areas triggered by extreme rainfall in Shimane Prefecture, Japan. Deep learning methods can take advantage of the high-level representation and reconstruction of information from landslide-affecting factors. In this paper, a novel deep learning-based algorithm that combine classifiers of both deep learning and machine learning is proposed for landslide susceptibility assessment. A stacked autoencoder (StAE) and a sparse autoencoder (SpAE) both consist of an input layer for raw data, hidden layer for feature extraction, and output layer for classification and prediction. As a study case, Oda City and Gotsu City in Shimane Prefecture, southwestern Japan, were used for susceptibility assessment and prediction of landslides triggered by extreme rainfall. The prediction performance was compared by analyzing real landslide and non-landslide data. The prediction performance of random forest (RF) was evaluated as better than that of a support vector machine (SVM) in traditional machine learning, so RF was combined with both StAE and SpAE. The results show that the prediction ratio of the combined classifiers was 93.2% for StAE combined with RF model and 92.5% for SpAE combined with RF model, which were higher than those of the SVM (87.4%), RF (89.7%), StAE (84.2%), and SpAE (88.2%). This study provides an example of combined classifiers giving a better predictive ratio than a single classifier. The asymmetric and unsupervised autoencoder combined with RF can exploit optimal non-linear features from landslide-affecting factors successfully, outperforms some conventional machine learning methods, and is promising for landslide susceptibility assessment.

As a tropical country which faces two monsoons with heavy precipitation, rainfall is identified as the major triggering factor for landslides in Sri Lanka. Reactivation of ancient landslides is a major challenge faced by the engineers in infrastructure development in the hilly terrain of the country. An ancient landslide at Bridge No. 48/2 in Avissawella—Hatton—Nuwaraeliya road was reactivated by excavation at the toe for the proposed widening of the bridge. This propagated further by the extensive rainfall that occurred subsequently. The site is a sloping ground with undulating topography towards upper slope in the form of a valley formed by an ancient landslide. Mitigation of the landslide was done to accommodate the widening of the bridge and to minimize the risk of further activation by rainfall. Mitigation measures adopted were drainage improvement, slope modification and soil reinforcement. Soil nailing was used as the reinforcement technique. Surface and subsurface drainage improvement was used for economizing the nailing design. This study presents how the nailing design was optimized by using different drainage arrangements. GeoStudio SEEP/W and SLOPE/W software were used for seepage and slope stability analyses, respectively.

Flow-like landslides, such as debris avalanches, are often dangerous for both structures and human life due to the high velocities and large runout distances. Artificial barriers are proposed to mitigate the landslide threats by reducing the flow velocity and the runout distance as well as diverting the flow towards lateral zones constrained by the barriers. A procedure is here proposed based on multiple steps. The first step focuses on the propagation of debris avalanche along a real topography through the meshless GeoFlow_SPH model in presence of one or more barriers. The second step deals with the behaviour of Deformable Geosynthetics Reinforced Barriers (DGRBs) under horizontal pressures, calculated with reference to literature formulations which include a dynamic component (dependent on landslide velocity at the impact stage), and a static component (height dependent). The time trend of impact pressure is computed from landslide volume and impulse theorem. The third step concerns the evaluation of the performances of the barrier under the impact. The main goal is to present such procedure and to evaluate the performances of DGRBs in: changing the area affected by landslide and dissipating impact energy through deformation and displacement mechanisms.

In the last years, the use of Unmanned Aerial Vehicles (UAVs) has developed rapidly across several field of earth sciences application, including landslides characterisation and monitoring, therefore providing a strong support for hazard and risk management activities especially with the introduction and advances in the miniaturization of traditional and new generation sensors. The flexibility, low cost, easy operability, and rapidness of intervention in emergency situation gives to these instruments, a strong potential in opening up a vast new area of opportunities in remote sensing for observation, measuring, mapping, monitoring, and management in various landslide environment. Unless initially only air photography was the main application for UAVs, recently new sensors, both passive and active, are being increasingly used. This paper, through some case studies on landslide investigations, aims at giving an overview on several sensors and techniques using UAVs platform addressed to landslide detection, characterization and monitoring.

High-mountain environments in an active tectonic setting are prone to landsliding. The triggering mechanisms can vary, as these areas are influenced by several pre-conditioning factors coupled with active seismicity and climatic forcings. Understanding the intrinsic and external mechanisms by which these events are influenced would help to establish better constraints onto their timing and periodicity and, eventually, hazard assessment and prediction. Glacially eroded valleys are especially prone as they deeply incise mountain ranges leaving unstable slopes once they retreat. Establishing the timing of such events enables better understanding of the triggering and pre-conditioning factors of landslides. To this aim, 10Be and 26Al cosmogenic age determinations were performed in three landslide deposits in a poorly studied area of San Juan province, all of which are novel to the area. Coupled with remote sensing techniques, field observations and detailed stratigraphic and sedimentological studies, these new large landslides represent a first approach to understand this dynamic environment. The three landslides were categorized as rock avalanches found in the middle and lower reaches of the Blanco River, sourced from the Choiyoi Group with evidence of hydrothermal alteration and including/deforming moraine deposits during their fall. Ages are 20.9 ± 1.4, 10.8 ± 0.7 and 12.8 ± 0.9 ka from the lowermost deposit to the highest, respectively. Even though one sample per deposit is not enough to have statistically significant exposure ages, these values, along with the established chronostratigraphy, allow first order interpretations regarding the links between deglaciation processes and readjustment of the slopes via large landslide events.

In mountainous terrains, landslides and their deposits form a major natural hazard for human settlements and economic activities. The characterization and analysis of landslide volumes is important to understanding their behaviors and the effects of their potential propagation distances. The Washington Geological Survey (WGS) created a new protocol to map landslides with consistent data in Washington State using Light Detection and Ranging (LiDAR). The protocol uses the surface area and the average depth of landslides to estimate their initial volumes. The aim of this paper is to present the ongoing research project from the Institute of Geography at the National Autonomous University of Mexico (UNAM) and WGS to estimate sediment production and distribution by taking full advantage of LiDAR and standardized landslide volume calculation in a Geographic Information System (GIS). We develop two landslide volume models by using Python scripts. These models are a systematic methodology for modeling volume of shallow and deep-seated landslides. The methodology and its implementation in the GIS-based technology is presented and discussed.

Understanding long-term hillslope and fluvial processes in tropical mountainous settings is key for improving models of local landscape evolution and natural hazard assessment, particularly in relation to mass-wasting and torrential events. Cosmic Ray Exposure (CRE) dating is a powerful tool to constraining timing and rates of geomorphic processes at the Earth’s surface. In this study, we calculate the ages of torrential alluvial deposits of the Farallones River located on the eastern slopes of the Western Cordillera of Colombia; a region characterized by high local relief (>3800 m), steep slopes, and relatively high mean annual precipitation (>2000 mm). Ages of alluvial deposits were calculated using a CRE approach based on in-situ produced 10Be concentrations from boulder samples and varying erosion rates between 0 and 1 mm/y. Rock boulder ages range slightly between 6.1 ± 0.5 to 7.9 ± 0.8 ky, despite assuming contrasting erosion rates, and between 6.1 ± 0.5 to 8.5 ± 0.9 ky with erosion rates of 0.01 mm/y. These results indicate that the torrential alluvial deposits of the Farallon River were exposed to cosmic radiation during the middle Holocene, and probably after the after the 8.2 ky event. Moreover, modern catchment morphology and precipitation patterns records are consistent with the long-term geomorphic control on mass movement and torrential behaviour of this mountainous river. The integration of these first CRE ages with quantitative geomorphology analysis allows us to delimit the nature and the chronology of major torrential and landslide events in the tropics, and specifically in the Northern Andes where planning approaches to reduce natural hazards are in strong need of accurate quantitative data.

Understanding of landslide mechanisms is necessary for hazard and risk assessments and designing proper protection measures, including monitoring. It is the key to the sustainable development of urban and mining areas with existing landslide hazards. The mechanisms and main features of deep-seated block landslides of compression-uplifting type are considered in this paper. The scientific methodology for the design of effective reinforcement and planning for sustainable development of landscapes with deep block-slides is provided. The suggested protection strategy is based on earlier received theoretical solutions concerning the reasons of landslide occurrence (the genesis of considered landslide type), on taking into account the mechanism features of deep block-slides, and also on our experience of investigation such landslides in different engineering geological conditions. New protection technologies for areas with deep-seated landslides of compression-uplifting type are discussed in the article.

The high-altitude Kumtor Goldmine is located in the Tien Shan nival-glacial belt at the altitudes of 3,900–4,400 m above sea level. Harsh climatic conditions of the region, active glaciers and permafrost, complicated geological and tectonic structure of the deposit combined with high seismic and geodynamic activity of the region cause instability of the huge dumps of waste stored on the glaciers and landslides’ activity. In recent years, the systematic and safe mining at Kumtor has been seriously complicated by deformations of waste and ice dumps and their sliding down the glacier valleys towards the Kumtor river bed. The first gigantic landslide of more than 200 million m3 in volume at the Kumtor mine dumps with huge economic damage was recorded in spring 2013, in the Davydov glacier valley. In December 2019, collapse and sliding of the rock-ice mass of more than 30 million m3 in the Lysyi glacier valley killed two people. This paper describes the structure and features of the Kumtor mountainous dumps deformation and the main causes of the December 1, 2019 landslide.

The paper presents successful experiences using geosynthetic reinforced soil structures for slope stabilization and landslide rehabilitation in Myanmar, Indonesia, and Japan. In all the presented cases, reinforced soil structures, combining high strength uniaxial geogrids and metallic gabion units provided with integrated reinforcing tails, were built. The first project highlights the challenges faced in the design and construction of a reinforced soil structure built to rehabilitate the collapsed portion of a national road in Myanmar. The second case study focuses on the application of reinforced soil structures for the reconstruction of road slope failures in Indonesia. The last case study describes the technical solution selected to stabilize a 14 m high slope for the Harima Expressway embankment located in Hyogo prefecture, Japan.

The International Consortium on Landslides (ICL) and The Global Promotion Committee of the International Programme on Landslides (GPC/IPL) have been responsible for organizing the World Landslide Forums (WLFs) every three years since 2008.