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Rainfall-induced landslides on steep slopes are potential hazards to life and property. The state of Kerala in India is witnessing unprecedented death and damage since last 3 years due to landslides triggered by heavy rainfall. In this paper, we present a cause-impact analysis of landslides that occurred due to the monsoon rainfall in the years 2018, 2019 and 2020. We have created an event-based landslide inventory post-rainfall season for the entire state and then selected six major landslides for detailed analysis. Event-based landslide inventory maps are prepared from Earth observation satellite data such as Resourcesat-2, 2A, Cartosat-2S, WorldView-2, Pleiades-1A and 1B, SPOT-6 and 7 and Sentinel-2 acquired before and after the rainfall events. Then, rainfall data were analysed to find out the role of daily and antecedent rainfalls on landslide trigger. Finally, we have carried out numerical debris flow modeling to characterise landslides and assess the impact. Our results show that landslides are triggered by antecedent rainfall of variable durations and are mostly debris flow type that has followed the channel path. The runout length and lateral spreads are controlled by variable frictional parameters of the slope material. Furthermore, reactivation at the crown region is also noticed in few cases that need to be monitored. [ABSTRACT FROM AUTHOR]

Buildings are the most concerned element in landslide risk assessment. A weak link in landslide risk analysis is the evaluation of building response and vulnerability when impacted by a landslide. In this paper, failure mechanisms and processes of typical reinforced concrete buildings upon landslide impacts are discovered through an explicit time integration analysis in LS-DYNA. The Arbitrary Lagrangian–Eulerian formulation, which allows automatic rezoning, is applied to simulate the landslide flow dynamics and the impact into the building. Three landslide intensity levels are considered. Progressive collapse of the building is observed in the high-impact intensity case. The frontal walls are firstly destroyed due to its low out-of-plane flexural capacity, followed by the progressive failure of columns at the ground floor. The collapse of building occurs when the remaining load-bearing components cannot resist the superstructure loadings. Two plastic hinge failure mechanisms are observed on the damaged columns when the ultimate bending moments of the columns are exceeded at both ends. Finally, a five-class classification system is proposed to evaluate building damage states based on field observations and the numerical simulation results. The analysis helps robust building design and assessment of building vulnerability to landslides. [ABSTRACT FROM AUTHOR]

The term debris flow is associated with a wide variety of phenomena as debris slides, debris torrents, debris floods, mudflows, mudslides, hyper-concentrated flows and lahars (in volcanic slopes). In historical times, they frequently occurred in Campania Region (Southern Italy) producing damage and casualties. In this paper, more than 200 events described as "debris flow" between 1924 and 2020 were collected. They are mainly located in the central sector of the region, which is characterized by pyroclastic deposits resting on steep carbonate and volcanic slopes and highly prone to hydrogeological hazards. Debris flow events registered in the region were classified as "gravity processes" (flow-like landslides, FL) or "fluvial processes" (flash floods, FF). This classification is fundamental for designing effective early warning systems and risk mitigation plans, since the two phenomena are triggered by different types of rainfall events and are responsible for damages of different magnitude. In this study, a large rainfall database was explored to identify the time scales and seasonality of the two classes of rainfall events, respectively triggering the two phenomena. [ABSTRACT FROM AUTHOR]

The Wenchuan earthquake-stricken area is frequently hit by heavy rainfall, which often triggers sediment-related disasters, such as shallow landslides, debris flows, and related natural events, sometimes causing tremendous damage to lives, property, infrastructure, and environment. The assessment of the rainfall thresholds for debris flow occurrence is very important in order to improve forecasting and for risk management. In the context of the Wenchuan earthquake-stricken area, however, the rainfall thresholds for triggering debris flows are not well understood. With the aim of defining the critical rainfall thresholds for this area, a detailed analysis of the main rainstorm events was carried out. This paper presents 11 rainfall events that induced debris flows which occurred between 2008 and 2012 after the Wenchuan earthquake. The rainfall thresholds were defined in terms of mean rainfall intensity I, rainfall duration D, and normalized using the mean annual precipitation (MAP). An ID threshold and a normalized I D threshold graph could be set up for the Wenchuan earthquake-stricken area which forms the lower boundary of the domain with debris flow-triggering rainfall events. The rainfall threshold curves obtained for the study area were compared with the local, regional, and global curves proposed by various authors. The results suggest that debris flow initiation in the study area almost requires a higher amount of rainfall and greater intensity than elsewhere. The comparison of rainfall intensity prior to and after the earthquake clearly indicates that the critical rainfall intensity necessary to trigger debris flows decreased after the earthquake. Rainfall thresholds presented in this paper are generalized, so that they can be used in debris flow warning systems in areas with the same geology as the Wenchuan earthquake-stricken area. [ABSTRACT FROM AUTHOR]

The post-earthquake debris flows in the Wenjia Gully led to the exposure of the shortcomings in the design of the original conventional debris flow mitigation system. A predicament for the Wenjia mitigation system is a large amount of loose material (est. 50 × 10 m) that has been deposited in the gully by the co-seismic landslide, providing abundant source material for debris flows under saturation. A novel design solution for the replacement mitigation system was proposed and constructed, and has exhibited excellent performance and resilience in subsequent debris flows. The design was governed by the three-phase philosophy of controlling water, sediment, and erosion. An Early Warning System (EWS) for debris flow that uses real-time field data was developed; it issues alerts based on the probabilistic and empirical correlations between rainfall and debris flows. This two-fold solution reduces energy of the debris flow by combining different mitigation measures while minimizing the impact through event forecasting and rapid public information sharing. Declines in the number and size of debris flows in the gully, with increased corresponding rainfall thresholds and mean rainfall intensity-duration ( I- D) thresholds, indicate the high efficacy of the new mitigation system and a lowered debris flow susceptibility. This paper reports the design of the mitigation system and analyzes the characteristics of rainfall and debris flow events that occurred before and after implementation of the system; it evaluates the effectiveness of one of the most advanced debris flow mitigation systems in China. [ABSTRACT FROM AUTHOR]

In the last ten thousand years, the explosive activity of some volcanic centers has blanketed with pyroclastic soils the major part of Campania Region, Southern Italy. Experience shows that the sloping deposits may be mobilized by long-lasting precipitations, leading to rapid and sometimes catastrophic flow-type slope movements. This paper summarizes the present knowledge on this subject based on the results of both laboratory tests and experiments and on a review of the main data provided by field surveys. In particular, a careful examination and analysis of the available elements highlight the key role played by lithological and morphological details on failure and post-failure mechanisms, thus affecting landslide hazard. In fact, it is shown that deposition mode and grain size, slope angle, and morphology strongly affect the type of post-failure movement, which may take the features of a debris avalanche, of a debris flow, or of a flowslide and may lead (or not) to soil liquefaction, a mechanism that strongly affects both displacement rate and run-out. [ABSTRACT FROM AUTHOR]

Natural dams formed by landslides may produce disastrous debris flows after dam outburst. However, studies on the critical conditions required for the formation of outburst debris flow resulting from natural dam failure are still at an early stage. In this paper, we present the results of a series of laboratory tests that assessed three different materials, five different flume bed slope angles (2°, 7°, 9°, 10°, and 13°), two in-flow rates, and four types of dam geometric shapes. The results showed that the unit weight of downstream fluid increased with increasing bed channel slope. Additionally, a critical flume bed angle was found for debris flow formation. Furthermore, the combination of lake volume and flume bed angle was found to influence the formation of debris flow. A nonlinear trend was observed between the unit weights of debris flow and the uniformity coefficients of solid material. Based on the theory of stream power, a critical condition for debris flow formation from natural dam failure was established. Based on two case studies, the results indicate that the condition that was established for debris flow formation following natural dam failure agrees well with reality. [ABSTRACT FROM AUTHOR]

Based on former conceptual models of vulnerability, this paper aims to improve the quantitative model for regional vulnerability assessment by analyzing in-depth the relation between vulnerability, exposure, coping capacity, and resilience. Taking the mountain settlements in the upper reaches of Min River, China, as a case study, the method of Contributing Weight Superposition (CWS) is applied in establishing both a model and a system for the vulnerability assessment of elements at risk. The CWS approach consists of 13 index factors including population, economic and road densities, building and farmland coverage, hazard-affected areas, urbanization rate, and GDP per capita. Accordingly, a debris flow hazard vulnerability zoning map was obtained and the assessment results show that the distribution of high and comparatively high vulnerability zones, where economic activities are considerably high, has a close correlation to the topography of the catchment and population characteristics. The results thus may serve as a pertinent guidance for settlement relocation, population distribution readjustment, and management to prevent and reduce hazards in the upper reaches of Min River and beyond. [ABSTRACT FROM AUTHOR]

The present paper aims at characterising Alpine anomalous basin-fan systems, in order to develop a method for hazard assessment for such fans. The review of previous studies revealed that anomalous basin-fan systems are often associated with deep-seated slope failure and present-day hazard is associated to debris flow occurrence. Taking into account these peculiarities, a modelling approach to assess the present day hazard in anomalous fans has been developed and applied to the Sernio fan (Valtellina, northern Italy). Debris flow inundation areas have been simulated by means of a numerical model (RApid Mass MovementS (RAMMS) debris flow), which includes a routine for the sediment entrainment. The range of the model parameters was defined based on previous studies, enabling a sensitivity analysis on the debris flow runout, as well as the flow height and velocity. Numerical results point out the paramount importance of entrainment phenomena on debris flow dynamic in anomalous systems, especially with reference to the bulking factor and debris yield rate that reach very high values, typical of basins with unlimited solid supply. [ABSTRACT FROM AUTHOR]

On 4 July 2013, three catastrophic debris flows occurred in the Hougou, Majingzi, and Xiongjia gullies in Shimian county and produced debris dams and river blockages, resulting in serious casualties and huge economic loss. Though debris flows have been identified prior to the catastrophic events, their magnitudes and destructive power were far beyond early recognition and hazard assessment. Our primary objective for this study was to explore the formation mechanism and typical characteristics and to summarize the lessons learned from these disastrous events in order to avoid the repeat of such disasters in the future. Based on field investigation and imagery interpretation of remote sensing carried out following the catastrophic events, four conclusions were drawn: (1) The catastrophic debris flows were initiated from surface-water runoff, and the triggering factor was attributed to the local intensive rainfall with an hourly intensity of more than 46.7 mm. (2) Entrainment was the most important sediment-supplying method for the debris flow occurrence, and the source materials transported by debris flows from the three gullies were estimated to be about 97 × 10 m in volume altogether. (3) As surface-water runoff eroded and entrained hillslope and channel materials persistently, debris flows were characterized by intensive incision at upper or middle reaches and significant magnification effect in flow discharge and volume downstream. Corresponding peak discharge surveyed at the outlets of the Hougou, Majingzi, and Xiongjia gullies was estimated up to 751.0 m/s, 870.1 m/s, and 758.7 m/s, respectively. (4) Debris flows that occurred from the three gullies all belonged to viscous ones and the bulk densities were calculated more than 1.80 g/cm, indicating a huge carrying capacity and destructive impacting power. In addition, the lessons learned from the catastrophic events were summarized, including recognition and assessment on debris flow hazard and utilization of deposition fan. In this paper, prevention suggestions on debris flow prone valleys with high-vegetation coverage and low occurrence frequency were also put forward. The results of this study contribute to a better understanding on the initiation mechanism, dynamic characteristics, and disaster mitigation of debris flows initiated from intense rainfall and surface-water runoff in mountainous areas. [ABSTRACT FROM AUTHOR]

This paper focuses on characteristics of debris flows from the lower part of the Lotru River basin (South Carpathians, Romania). The damage produced by these debris flows has included burial of agricultural land, roads covered by debris flows, and even the obstruction of the Lotru River. Simple statistical analysis has been used to emphasize the characteristics of the debris flow sites. The collected data show that heavy rainfall is the main triggering mechanism of debris flow events in the Lotru hydrographic basin. The daily rainfall data for this region show that important debris flow events generally occur when rainfall exceeds 40 mm in 24 h, while rainfall levels between 25 and 40 mm in 24 h result in hyperconcentrated flows. For 11 of 14 studied debris flow sites, the fan area is greater than the source area, probably due to the thickness of the regolith, which is up to 5-10 m deep. Both source area and deposition area are very dynamic. The retreat rate calculated for five debris flow sites ranges from 5 to 30 m in 30 years (from 1975 to 2005). Channel cross section measurements on one of the debris flows show that velocity values vary from 1.31 to 2.64 m/s; corresponding discharge values vary from 4 to 10.03 m/s. [ABSTRACT FROM AUTHOR]

On the 26th of November 2022, as a consequence of heavy rainfall, diffuse landslides were triggered in the Northern sector of Ischia. The present study investigated the main features of the debris flow originated in a small catchment basin falling within the Casamicciola Terme Municipality. The debris flow, triggered around 05:00 a.m. from the Northern slope of Mt. Epomeo, travelled about 850 m before impacting a populated area. In detail, it affected about 30 buildings causing 12 casualties and several injured, more than 200 people displaced, and severe damages to the road network, resulting one of the most destructive landslide events occurred on the island. This multidisciplinary work, aimed at a preliminary assessment of the event, considered geological and geomorphological evidence collected during a field investigation, as well as environmental data, to set up numerical models both for landslide triggering and propagation. Along the pre-existing channel, a marked erosional behaviour was observed with a maximum removed thickness of about 5.5 m, whilst the material deposition largely occurred after the impact on buildings. The total volume mobilised by the debris flow was estimated in approximately 40,000 m3. Considering the geological and geomorphological conditions, as well as the high vulnerability and the socio-economic importance of the area, a careful monitoring and risk management activities in the next months will be necessary. [ABSTRACT FROM AUTHOR]

During 11–18 May 2022, the Dima Hasao district of Assam state in India received heavy rainfall. The rainfall triggered floods and landslides across the district, resulting in the death of three people and damage to property (mainly road and rail network) worth few hundred crores of Indian rupees. Platforms of the New Haflong railway station were completely buried by multiple debris flows, and several coaches of a train were overtoppled. We hereby investigate the cause of the landslide disaster by analyzing temporal rainfall data and also assess damages in the region using high-resolution optical satellite imagery from Resourcesat-2A (5.8 m), Sentinel-2 (10 m), and Cartosat-3 (1.1 m) satellites. It is seen from the satellite-based precipitation measurement that the region around Haflong town received maximum 24 h rainfall (156 mm) on 11 May 2022 and the heavy rainfall continued till 18 May 2022. This resulted in the occurrence of 5178 landslides, which are mapped using multi-temporal cloud free optical satellite data. Rainfall data analysis shows that 4 days antecedent rainfall of ~ 200 mm has mainly triggered landslides in this area. The initial heavy rainfall has saturated the soil and increased the pore pressure, which caused slope failure due to subsequent spell of rains. Small-sized landslides are seen to damage buildings in the Haflong town and neighboring villages. Various roads, including the Lumding-Silchar highway, were damaged at multiple places by landslides. Landslides were triggered mainly within Renji and Bokabil Rock Formations on moderate to high slopes. Results are further substantiated by debris flow simulations which showed that ~ 4 m height of debris may have been accumulated in the New Haflong railway station, thus burying the railway track and platforms. [ABSTRACT FROM AUTHOR]

Immersive media technologies, such as virtual and augmented reality, have recently enabled a more holistic way to comprehend natural hazards. In this work, we aim at visualizing the temporal and spatial evolution of a debris flow in a virtual reality environment. We develop a framework to integrate the output results obtained from a debris flow numerical model into virtual reality. To guide the framework, a real debris flow event, which happened in Hunnedalen (Norway) in 2016 and blocked a road network, is considered as a case study. The debris flow is back-calculated using a depth-averaged numerical model and the simulation results are imported into a dedicated game engine to construct a digital model of the debris flow event. The debris flow is visualized using a Head-Mounted Display. We therefore discuss a wide range of potential applications of virtual reality to manage and grasp landslide phenomena: training for rescue operations; improving decision-making; studying early warning systems, and educating communities affected by natural hazards. We finally provide a quantitative evaluation of the hazard perception for a road user. We show that the debris flow movement is perceived at variable delayed times from the triggering of the landslide, depending on the position along the road where the debris flow is observed. Evaluating the realistic perception time of the natural hazard may be fundamental to designing more effective road networks, signs, and mitigation measures. [ABSTRACT FROM AUTHOR]

Debris flow generated by landslides due to intense rainfall can cause extensive damage to residential areas. To predict and prevent the severity of such damage, several numerical models have been developed. However, there are limited studies regarding the entrainment and erosion effect of debris flow. This research aims to analyze several erosion–entrainment models for the selection of erosion–entrainment models in debris-flow analysis. The study focuses on landslides that occurred in the Raemian and Sindonga apartment basins in Mt. Umyeon, Republic of Korea, on July 27, 2011. The impact area, entrainment volume, maximum velocity, inundated depth, and erosion shape resulting from the debris-flow modeling were compared with field data. The simulation results of each erosion–entrainment model were assessed through the receiver operating characteristic method. [ABSTRACT FROM AUTHOR]

Numerical modelling, a physically based method, is adopted to obtain an in-depth understanding of the mechanism of sediment-related hazards such as landslides and debris flows. With its ability to address large deformation problems, the particle flow analysis method (the particle flow code or PFC model) can simulate propagation and runout from landslides to debris flows under complex landslide material compositions with a proper rheological model. Hence, this study aims to analyse the kinematic characteristics of a landslide-generated debris flow event in Shaziba, Enshi City, that occurred on June 8, 2020, with the PFC3D numerical model and linear parallel bonding method. To determine the differences among various processes, field surveys, unmanned aerial vehicle (UAV) photography campaigns, and laboratory direct shear tests were conducted to invert the relevant parameters, such as the digital elevation model (DEM) and shear strength, corresponding to the rheological properties of landslide debris flow materials. In dynamic analysis, the velocity, displacement, and characteristics of landslide deposition were considered. The results indicate that the initial landslide stage started with overall acceleration, and the movement of gravel–silty clay materials lasted approximately 733 s with double-peak velocity curves and nonsynchronous displacement. The maximum velocity of the landslide body was 17.5 m/s, and the maximum displacement exceeded 1000 m. The volume of the landslide body was 9.31 × 105 m3. The simulation results agree with the actual landslide volume (1.5 × 106 m3) and morphology of the landslide dam observed in Qingjiang. The study provides detailed information on the recent Shaziba landslide, thereby providing a useful reference for better understanding the dynamics of gravel–silty clay landslides and preventing the potential hazard for remobilisation of the Shaziba landslide. [ABSTRACT FROM AUTHOR]

In early December 2020, an atmospheric river (AR) and rain-on-snow (ROS) event impacted the Haines, Alaska area, resulting in record-breaking rainfall and snowmelt that caused flooding and dozens of mass movement events. We consider the AR—a one-in-500-year event—as the trigger for the devastating Beach Road Landslide (BRLS), which destroyed or damaged four residences and took the lives of two people. The BRLS started as a debris avalanche and transitioned into a debris flow, with a total approximate landslide volume of 187,100 m3. Geomorphic analysis using lidar data identified evidence of paleo-landslides and displaced masses of rock, one of which served as the source area for the BRLS. Significant structural features in the weak ultramafic bedrock defined the head scarp area and formed the failure plane. This study illustrates the importance of identifying pre-existing landslide features and source areas likely to produce future landslides. As an increase in ROS events is projected for Southeast Alaska with warmer and wetter winters, we recommend the development of an AR scale coupled with geological information for the region, to enhance warnings to residents in landslide-prone areas. [ABSTRACT FROM AUTHOR]

It is widely recognized that post-seismic mass movements amplify and decay. Previous studies have found that most post-seismic mass movement is concentrated in the first few years following an earthquake. A major debris flow occurred in Wenchuan County in 2019, 11 years after the 2008 Wenchuan earthquake, showing that there might be a different temporal evolution pattern. In Wenchuan Country, the area struck by the 2019 disaster was investigated to explore whether a pattern existed. Remote sensing and field surveys investigate the initiation processes, sediment supply, and triggering rainfall. The result shows that most of the active landslides occurred in high-elevation areas where vegetation cover was lacking, and nearly half of them were reactivated landslides. The debris flows were mainly initiated by run-off erosion of debris in steep channels, and more than half of the sediment supply was from deposition along the channels in some catchments. The spatial and temporal evolution of debris flows was analyzed by combining our investigation results with historical events. More debris flows occurred in the northern part of the study area, where the relative annual rainfall and coseismic landslide density were low. The average values of debris-active catchments' size and relief are increasing, while the average values of their coseismic landslide density and the annual rainfall received were decreasing from 2008 to 2019. Larger catchments receiving less annual rainfall tend to have a more prolonged and enhanced mass movement. [ABSTRACT FROM AUTHOR]

The initiation of debris flows is commonly attributed either to fluidization as a result of rainfall-induced landslides or to gully erosion induced by concentrated runoffs. A series of flume tests have been performed to show how the initial soil moisture influences the initiation of debris flows. At the start of each experiment, surface runoff was generated over loose granular deposits, triggering debris flows. These experimental debris flows enacted different scenarios according to the small variations among the initial soil moistures. In the loose granular deposits with initial soil moistures ranging from 1 to 5 %, most runoff water could infiltrate and trigger a landslide, which accelerated within 1 s to speed over 1 ms and then transformed into a debris flow. In the same soil deposits with initial moistures >5 or <1 %, the debris flow was initiated by slow gully erosion with episodic events of damming and breaching due to small-scale landslides occurring on the side-slopes of the erosion valley. The slope failures were not triggered by positive pore pressure but by a decrease in suction due to the wetting of the soil. This suction decrease in initially unsaturated slopes explains why the transformation of these slope failures into debris flows are due not only to an increase of pore pressure leading to soil liquefaction, which is one of the expected triggering mechanisms, but also to a loss of the cohesive strength of the soil. [ABSTRACT FROM AUTHOR]

Climate change and rapid urban expansion can foster landslide disasters and cause severe damage in areas that are traditionally considered relatively safe from such hazards. In this regard, a recent event in Daoshi Town, China, is a good example that showcases the combined effect of extreme rainfall and urbanization in generating a first-time landslide disaster for a developing community. On 10 August 2019, Typhoon Lekima made its landing in Zhejiang Province, China. It generated a rainstorm close to Daoshi Town, inducing severe and unexpected damage from shallow landslides and debris flows (7 deaths, 25,560 affected and a direct economic loss of 1.5 hundred million dollars). In this region, similar rainfall has never been experienced before, and landslides have seldom been reported in the past. Field investigations and measurements were conducted to identify the landslide distributions, size characteristics, and mobility. A landslide inventory map, including 251 shallow landslides and 82 debris flows, was compiled to study the geological and topographical factors related to widespread failure. The results showed that shallow landslides and debris flows mainly occurred in the north-central part of the study area, in which the base was mainly composed of strongly weathered limestone. The elevation, mean slope, and slope aspect also contributed to the occurrence of landslides. In addition, 32.4% of the disasters were located close to buildings and roads, highlighting a relevant predisposing role played by human activity. This typhoon-bound rainstorm gave rise to a higher triggering condition than the normally required rainfall threshold in the study area. Under this circumstance, landslides were easily triggered and were able to transition into debris flows due to liquefaction. Field observations demonstrate that the erosion of slope toes caused by debris flows also facilitated the occurrence of other shallow landslides. A changing climatic setting is a never-before-experienced phenomenon for the study area. This research improves the understanding of landslide development in the area and prepares basic data and information for further studies and mitigation strategies. [ABSTRACT FROM AUTHOR]

Landslides typify one of the most hazardous natural phenomena fostering economic and even human losses worldwide. Several countries like Colombia, in South America, are hotspots for fatal landslides. In this contribution, we thoroughly reviewed four available databases, articles, grey literature and web resources, in order to build up a new catalogue of fatal landslides in Colombia. We gathered a catalogue of 2351 individual fatal landslides which caused about 37,959 deaths. Of these, we found 11 fatal events in historical times (pre-twentieth century). In modern times (1912–2020), we analysed landslides' spatial and temporal distribution, finding that in central-western Colombia, particularly in the departments of Caldas, Risaralda, Quindío and Antioquia, these kinds of events are more frequent. Upward trends in these areas and a nationwide increase in the number of events in the last 20 years suggest that fatal landslides are far from being effectively mitigated. Our findings also show a strong correlation between the climate variability phenomenon known as El Niño Southern Oscillation (ENSO) and fatal landslides, particularly during those years when strong La Niña (cold phase of ENSO) events occur. Despite rainfall being the most common trigger for fatal landslides, we observed an increasing trend in anthropogenically related events in the last decade. Finally, we obtained multiple socio-economic indices and ran a statistical analysis at the departmental level in order to assess whether impoverished and vulnerable people are more affected by fatal landslides. We propose that in most cases, departments with low income, high levels of corruption and inequality are usually more affected. [ABSTRACT FROM AUTHOR]

Some landslides mobilize into flows, while others slide and deposit material immediately down slope. An index based on initial dry density and fine-grained content of soil predicted failure mode of 96 landslide initiation sites in Oregon and Colorado with 79% accuracy. These material properties can be used to identify potential sources for debris flows and for slides. Field data suggest that loose soils can evolve from dense soils that dilate upon shearing. The method presented herein to predict failure mode is most applicable for shallow (depth <5 m), well-graded soils (coefficient of uniformity >8), with few to moderate fines (fine-grained content <18%), and with liquid limits <40. [ABSTRACT FROM AUTHOR]

Submarine landslides are a major geohazard among worldwide continental slopes, posing significant threats to offshore infrastructure, marine animal habitats and coastal urban centres. This study establishes an original numerical package for time-efficient modelling of the entire submarine landslide evolution covering the pre-failure shear band propagation, slab failure and post-failure dynamics. The numerical scheme is based on the conservation of mass and the conservation of momentum and combines the shear band propagation theory and the depth-integrated method, with the consideration of the drag force from the ambient water. Shear band propagation in the weak layer and slab failure in the sliding layer are controlled by the strain softening and rate dependency of the corresponding undrained strength parameters. The post-failure behaviour in the sliding layer, such as retrogression upslope and frontally confined and frontally emergent mechanisms downslope, is also simulated. The numerical results from the proposed method are comparable to the analytical solutions and the large deformation finite element analysis. Application of this method to a back analysis of the St. Niklausen slide in Lake Lucerne reproduced the observed shape of the mass transport deposits, the position of the main scar and the travel distance. Because of its easy implementation and efficiency, the proposed numerical method for modelling of submarine landslides seems promising for practical applications. [ABSTRACT FROM AUTHOR]

In the design of multiple rigid barriers, the height of the first barrier governs the impact dynamics of debris flow on the next barrier in a channel. However, current design approaches neglect the height of the first barrier, and no specific guideline is given on the design of the impact load on the second barrier. In this study, a new impact equation that explicitly considers the effects of the height of the first barrier on the impact dynamics is proposed. This is achieved by adopting the barrier Froude number Frb, which is the ratio of inertia to barrier potential. Thereby, the new impact equation accounts for the static load as a function of the first barrier height. The equation is evaluated using physical experiments carried out in a 5-m-long flume. The experiments modelled dry sand and water flows impacting dual rigid barriers. These two idealised flow types represent extreme cases of frictional and viscous flows, which exhibit entirely different impact mechanisms. A comparison of the experimental results from this study shows that the proposed impact model using the barrier Froude number provides a reasonably conservative estimate for the normalised impact force on the first rigid barrier with overflow. Furthermore, a bilinear design envelop for the impact force exerted on the second barrier is proposed based on the barrier Froude number of the first barrier. [ABSTRACT FROM AUTHOR]

Permafrost and glaciers are being degraded by the warming effects of climate change. The impact that this degradation has on slope stability in mountainous terrain is the subject of ongoing research efforts. The relatively new availability of high-resolution (≤ 10 m) imagery with worldwide coverage and short (≤ 30 days) repeat acquisition times, as well as the emerging field of environmental seismology, presents opportunities for making remote, systematic observations of landslides in cryospheric mountainous terrain. I reviewed the literature and evaluated landslide activity in existing imagery to select five ~ 5000-km2 sites where long-term, systematic observations could take place. The five proposed sites are the northern and eastern flanks of the Northern Patagonia Ice Field, the Western European Alps, the eastern Karakoram Range in the Himalayan Mountains, the Southern Alps of New Zealand, and the Fairweather Range in Southeast Alaska. Systematic observations of landslide occurrence, triggers, size, and travel distance at these sites, especially if coupled with observations from in situ instrumental monitoring, could lead to a better understanding of changes in slope stability induced by climate change. The suggested sites are not meant to be absolute and unalterable. Rather, they are intended as a starting point and discussion starter for new work in this expanding landslide research frontier. [ABSTRACT FROM AUTHOR]

This study derives an empirical equation to determine the rainfall threshold that triggers landslides and subsequent debris flows. In this research, the contribution of different factors, especially various sediment layer thicknesses, was assessed on the landslide leading to debris flows. Bed slope, sediment thickness, sediment mean diameter, sediment layer length, rainfall intensity, and time of landslide occurrence were selected as the effective factors. Rainfall simulator device was used to create rainfall on the sediment sample. The effect of these factors on the landslide which leads to debris flow occurrence was investigated using dimensional analysis of experimental data. Then, linear and power regression models were tested by 30% of the total experimental data to estimate the rainfall-induced landslide. Determination coefficient (R2), mean absolute relative error (MARE), and Akaike information criterion (AIC) were applied to determine the best equation. Results revealed that landslide often occurs at a rapid rate in the thicker deposits than the thinner one. The evaluation of linear and power equations demonstrated that two-variable power model was the best empirical equation for estimation of rainfall threshold in initiation of landslide and debris flows. The evaluation criteria including MARE, R2, and AIC were estimated 0.044, 0.984, and − 25.93, respectively. In this equation, bed slope and the ratio of the time of landslide occurrence to the sediment layer length were used as the effective factors. This study can be used for assessment of the threshold of rainfall-induced landslide which finally leads to debris flow hazard. [ABSTRACT FROM AUTHOR]

Superelevation is an often observed phenomenon in landslide and debris flow down a complex three-dimensional topography. The degree of superelevation is controlled by the geometry of the channel, the material involved and also the flow dynamics. Empirical methods are usually applied to estimate superelevation. However, those models are incomplete and lack important aspects of the channel geometry, material properties and flow dynamics, instigating serious errors in estimating flow velocities that could only be controlled empirically by introducing ad hoc correction factors. Here, we present new and complete analytical models for superelevation and superelevation velocities down a general topography providing a fully dynamical method. New models formally include essential forces that play an important role in the flow dynamics, namely gravitational forces, topographic- and hydraulic-pressure gradients and Coulomb friction. We discuss the importance of geometry in inducing superelevation and that one directional channel without twist cannot produce superelevation. With the new models we can, in principle, exactly obtain the flow velocities of deformable landslide, dynamic impact pressures and the explicit description of deposition. We have formally provided two alternative analytical representations for superelevation: geometrical and dynamical definitions of superelevation, which is a new concept. We proved that for superelevation to take place, the transversal velocity must have a gradient across the channel. We have analytically constructed a new non-dimensional superelevation number. Superelevation velocity appears to be a non-linear function of the superelevation number. We can now explicitly quantify the superelevation intensity in landslide motion. It has several implications. We proved that superelevation is higher for fluid-saturated debris flows than for dry granular flows. New superelevation models have been validated against a laboratory granular flow down a multi-dimensionally curved channel, and a natural debris flow event in Chamoson, Valais, Switzerland. Our theoretical superelevation velocities appear to be very close to the velocity measured in laboratory and in the field, which however, are largely overestimated by the empirical models. We further validated the model by constructing an exact analytical solution and by applying it to describe superelevation-induced propagation and deposition of the natural debris flow event. New simulations produced observed propagating fronts. [ABSTRACT FROM AUTHOR]

Two catastrophic landslides occurred in quick succession on 13 and 16 May 2019, from the north face of Joffre Peak, Cerise Creek, southern Coast Mountains, British Columbia. With headscarps at 2560 m and 2690 m elevation, both began as rock avalanches, rapidly transforming into debris flows along middle Cerise Creek, and finally into debris floods affecting the fan. Beyond the fan margin, a flood surge on Cayoosh Creek reached bankfull and attenuated rapidly downstream; only fine sediment reached Duffey Lake. The toe of the main debris flow deposit reached 4 km from the headscarp, with a travel angle of 0.28, while the debris flood phase reached the fan margin 5.9 km downstream, with a travel angle of 0.22. Photogrammetry indicates the source volume of each event is 2–3 Mm3, with combined volume of 5 Mm3. Lidar differencing, used to assess deposit volume, yielded a similar total result, although error in the depth estimate introduced large volume error masking the expected increase due to dilation and entrainment. The average velocity of the rock avalanche-debris flow phases, from seismic analysis, was ~ 25–30 m/s, and the velocity of the 16 May debris flood on the upper fan, from super-elevation and boulder sizes, was 5–10 m/s. The volume of debris deposited on the fan was ~ 104 m3, 2 orders of magnitude less than the avalanche/debris flow phases. Progressive glacier retreat and permafrost degradation were likely the conditioning factors; precursor rockfall activity was noted at least ~6 months previous; thus, the mountain was primed to fail. The 13 May landslide was apparently triggered by rapid snowmelt, with debuttressing triggering the 16 May event. [ABSTRACT FROM AUTHOR]

An Ms6.9 earthquake in the Yarlung Tsangpo gorge on November 18, 2017 caused more than 700 landslides concentrating along the gorge's great bend, and three dammed lakes. The location and area of the landslides are obtained by interpreting high-resolution satellite images before and after the earthquake. About 31.45 Mm3 of sediment from the landslides are distributed in seven catchments that are highly susceptible to debris flows. In 2018, at least three large-scale glacier-debris flows happened at Sedongpu, one of the seven catchments, and blocked temporarily the main river twice. The subsequent inundation and outburst floods resulted in infrastructure and property losses extensively beyond the high-seismic-intensity zone. Increase in the frequency of debris flows is attributed to the instability of glaciers and sediment supply caused by the earthquake. Glacier-debris flows will remain active for a long period due to massive glacial till, abundant rainfall, and meltwater. Geomorphic hazard chain triggered by such a mid-strong earthquake demonstrates that although coseismic landslides only occur in a limited area, the space and duration of the quake-induced hazards could extend largely under special geographical conditions. [ABSTRACT FROM AUTHOR]

The Clapar landslide induced debris flow consisted of the Clapar landslide occurred on 24 March 2017 and the Clapar debris flow occurred on 29 March 2017. The first investigation of the Clapar landslide induced debris flow was carried out two months after the disaster. It was followed by UAV mapping, extensive interviews, newspaper compilation, visual observation and field measurements, and video analysis in order to understand chronology and triggering mechanism of the landslide induced debris flow in Clapar. The 24 March 2016 landslide occurred after 5 hours of consecutive rainfall (11,2 mm) and was affected by combination of fishponds leak and infiltration of antecedent rain. After five days of the Clapar landslide, landslide partially mobilized to form debris flow where the head scarp of debris flow was located at the foot of the 24 March 2016 landslide. The Clapar debris flow occurred when there was no rainfall. It was not generated by rainstorm or the surface erosion of the river bed, but rather by water infiltration through the crack formed on the toe of the 24 March 2016 landslide. Supply of water to the marine clay deposit might have increased pore water pressure and mobilized the soil layer above. The amount of water accumulated in the temporary pond at the main body of the 24 March 2016 landslide might have also triggered the Clapar debris flow. The area of Clapar landslide still shows the possibility of further retrogression of the landslide body which may induce another debris flow. Understanding precursory factors triggering landslides and debris flows in Banjarnegara based on data from monitoring systems and laboratory experiments is essential to minimize the risk of future landslide. [ABSTRACT FROM AUTHOR]

Rain-induced landslides are recognized as one of the most catastrophic hazards on hilly terrains. To develop strategies for landslide risk assessment and management, it is necessary to estimate not only the rainfall threshold for the initiation of landslides, but also the likely magnitudes of landslides triggered by a storm of a given intensity. In this study, the frequency distributions of both open hillside landslides and channelized debris flows in Hong Kong are established on the basis of the Enhanced Natural Terrain Landslide Inventory (ENTLI) with 19,763 records in Hong Kong up to 2013. The landslide magnitudes are measured in terms of the number, scar area, volume, or density of landslides. The mean values of the scar areas and volumes are 55.2 m2 and 102.0 m3, respectively, for the open hillside landslides and 91.3 m2 and 166.5 m3, respectively, for the channelized debris flows. Empirical correlations between the numbers, scar areas, and volumes of hillside landslides or channelized debris flows and the maximum rolling rainfall intensities of different periods have been derived. The maximum rolling 4- to 24-h rainfall amounts provide better predictions compared with those with the maximum rolling 1-h rainfall. Maximum rolling rainfall intensity-duration thresholds identifying the likely rainfall conditions that yield natural terrain landslides or debris flows of different magnitudes are also proposed. The initiation rainfall thresholds are identified as 75, 90, 100, 120, 150, 180, and 200 mm for the maximum rolling 1-, 2-, 4-, 6-, 8-, 12-, and 24-h rainfall, respectively. [ABSTRACT FROM AUTHOR]

In August 2010, extreme rainfall affected the north of the Czech Republic and caused regional floods and landslides. Three torrential debris flows originated in the Jizerské hory Mts., close to Bílý Potok on the north slope of the Smědavská hora Mt. The rainfall situation which triggered the debris flow was analyzed and compared with the rainfall situation in 1958 when a debris flow occurred in the same area. The rainfall data were obtained from rain gauges of the Czech Hydrometeorological Institute. Four rain gauges were chosen close to the Smědavská hora Mt. with data of daily amounts from 1983 to 2013 and 10-min intensity or hourly amounts from the specific period. The data from 1958 were available from three different rain gauges (only daily amounts). The data series were not complete so linear regression was applied to interpolate them. A number of analyses were carried out including daily rainfall, 2-day/3-day moving values, antecedent precipitation index (API) of 5/10/30 days, 10-min intensity, and hourly amounts, and the trigger factor of the debris flow in the study area was also investigated. It was determined that for the triggering of debris flows, both high API values as well as high-intensity short-duration rainfall is needed. It was documented that in cases of solely high API indices or high-intensity short-duration rainfalls, no debris flows were initiated. [ABSTRACT FROM AUTHOR]

A debris flow is an erosional process that frequently occurs in areas with steep slopes. Although the initiation can be triggered in higher and inhabited altitudes, the propagation and then the deposition can endanger urbanized areas. Frequently, the zones of generation of debris flows are placed in unattainable territories complicating field observations. Moreover, the rapid vegetation's recovery can hide the scars and tracks created by the occurrence of the flow, unlikely to be recognizable in aerial photos. As a consequence, the assessment of debris-flow susceptibility at regional scale is increasing in interest. Two main techniques can be applied for the regional susceptibility assessment: physical models and statistical models. Here, two physical models are introduced simulating the initiation of debris flow by means of shallow landslides: one based on the lateral groundwater flow and the other on vertical groundwater flow. The presented models' algorithms are implemented in a toolbox based on GIS environment and declared as open source code. Being applied in a basin of the Spanish Pyrenees where soil properties and dataset of observations have been gathered, the two models have been evaluated. Successively, they have been compared with a statistical model based on a logistic regression. The results have been aggregated in terrain units, built as fluvio-morphological sub-catchments. Each model has been tested based on the gathered observations. It has been observed that the vertical flow-based model enhances by 18 % the performance of the lateral flow-based model in matching debris-flow susceptible areas. Furthermore, the vertical flow-based model performance is found to be similar to that of the logistic regression, having an averaged quality index of about 70 %. [ABSTRACT FROM AUTHOR]

In order to analyze the changes in the sediment budget after the Wenchuan earthquake and after the heavy rain events in the following years, 12 debris flow gullies in the Longchi Dujiangyan County were selected. A comparison of the TM images taken on 18 September 2007 (before the '5.12' Wenchuan earthquake) with the SPOT5 images taken on 10 February 2009 (after the '5.12' Wenchuan earthquake) indicates that the landslide area in the 12 debris flow watersheds increased from 83.1 × 10 m to 3126.5 × 10 m. Also, the gully length increased by 60.55 %, and the area with deposits in the channel bed increased by 134.80 %. A comparison of the SPOT5 images taken on 10 February 2009 (after the '5.12' Wenchuan earthquake) with the WorldView-2 images taken on 26 April 2011 (after the large rainstorm event in August 2011) showed that the landslide area increased by 24.8 % from 3126.5 × 10 m to 3902.8 × 10 m while the gully length increased by 26 % and the channel deposits by 12 %. A comparison of the WorldView-2 images taken on 26 April 2011 with the WorldView-2 images taken on 14 July 2011 indicated that the landslide area increased in this relatively dry period by only 2.3 %. [ABSTRACT FROM AUTHOR]

In January and February 2013, heavy rainfall during local summer storms triggered a large number of landslides in the Andes Main and Frontal ranges of central Chile and Argentina (32°-34° S). Most of the mass movements classify as debris flows, while rockfalls and debris avalanches also occurred. The major debris flows occurred in the Maipo and Aconcagua valleys (Chile) and along the Mendoza River valley (Argentina). The debris flows caused serious disruption to the international highway connecting both countries and local roads and produced a large impact on the population of major cities downstream, mainly due to potable water supply cutoffs. Debris flow deposits have silt and clay particles usually ranging between 10 and 20 % by weight, which favors the movement of viscous flows in short, steep lateral gullies. Most of the flows tended to channelize, and the materials were deposited in alluvial fans and cones in areas with previous records of such events. This indicates that they constitute a significant hazard that may not have been properly considered in road infrastructure and potable water supply strategies for the region. This potential hazard may become more serious due to climate change in the near future. [ABSTRACT FROM AUTHOR]

The wired and wireless monitoring system installed in the Rebaixader catchment detected six debris flows and 11 debris floods between 2009 and 2012. Apart from results directly related to the processes, many experiences associated with monitoring were collected. Debris flows and debris floods showed clear differences in both the recorded data and field observations. The distinction was especially visible in the stage measurements and the ground vibration registered by the most downstream geophone. At this geophone, a positive relation between the maximum ground vibration and the volume was also observed. The triggering of most events was associated with short, high-intensity rainstorms in summer, but some were also generated in spring, when the melting of snow cover and frozen soil played an additional role. A positive correlation between the volume and both the amount and the intensity of the triggering rainfall was observed. Regarding technical aspects, a switch between a 'no-event' mode with a low sample rate and an 'event' mode with a fast sampling was particularly useful at the station that register the passing of a flow. In addition, the stations, which most recently were installed at Rebaixader, apply wireless devices because wireless techniques include multiple advantages against standard wired systems. Although recorded data or even video images provide detailed information on the debris-flow behavior, we strongly recommend periodic field surveys along the entire torrent to verify and improve the interpretation obtained from the monitoring system. [ABSTRACT FROM AUTHOR]

Rainfall intensity-duration (ID) thresholds are commonly used to predict the temporal occurrence of debris flows and shallow landslides. Typically, thresholds are subjectively defined as the upper limit of peak rainstorm intensities that do not produce debris flows and landslides, or as the lower limit of peak rainstorm intensities that initiate debris flows and landslides. In addition, peak rainstorm intensities are often used to define thresholds, as data regarding the precise timing of debris flows and associated rainfall intensities are usually not available, and rainfall characteristics are often estimated from distant gauging locations. Here, we attempt to improve the performance of existing threshold-based predictions of post-fire debris-flow occurrence by utilizing data on the precise timing of debris flows relative to rainfall intensity, and develop an objective method to define the threshold intensities. We objectively defined the thresholds by maximizing the number of correct predictions of debris flow occurrence while minimizing the rate of both Type I (false positive) and Type II (false negative) errors. We identified that (1) there were statistically significant differences between peak storm and triggering intensities, (2) the objectively defined threshold model presents a better balance between predictive success, false alarms and failed alarms than previous subjectively defined thresholds, (3) thresholds based on measurements of rainfall intensity over shorter duration (≤60 min) are better predictors of post-fire debris-flow initiation than longer duration thresholds, and (4) the objectively defined thresholds were exceeded prior to the recorded time of debris flow at frequencies similar to or better than subjective thresholds. Our findings highlight the need to better constrain the timing and processes of initiation of landslides and debris flows for future threshold studies. In addition, the methods used to define rainfall thresholds in this study represent a computationally simple means of deriving critical values for other studies of nonlinear phenomena characterized by thresholds. [ABSTRACT FROM AUTHOR]

Because of the low-gravity on the Moon and Mars, landslides there have characteristics that are very different from those observed in a conventional gravity environment. These include highly marked dynamic characteristics, evidence of fierce movement at high speed and on a large scale. One of the key problems in extra-planetary exploration is understanding the behavior of granular material flows under the influence of low gravity. A drop-tower testing system situated in Beijing has been developed and used to investigate granular flow in a microgravity environment. A set of granular flow tests was performed in both normal and microgravity environments, during which the configurations of sand flows were captured by the monitoring system. Preliminary results provide fundamental information for the future exploration of planetary landscapes. [ABSTRACT FROM AUTHOR]

A debris flow originating from the Alcamayo River on 10th April 2004 destroyed a part of the town of Aguas Calientes, resulting in 11 victims, and with serious affects to the tourist flow to the Machupicchu inka citadel. On the same day, as well as in January and March 2004, other similar phenomena occurred on the Cedrobamba and Leonchayoq Rivers, affecting the railway and an electrical tower, and disrupting the train service. [ABSTRACT FROM AUTHOR]