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Outburst floods generated by dam breaches associated with debris flow may have long-lasting effects on the formation and development landscape and the safety of human beings, increasing the difficulty of disaster prevention and mitigation. However, little was considered about channel aggradation contributing downstream damage of outburst flood. Therefore, we investigated a debris flow dam's breaching and flooding process triggered by a 50-year heavy rainfall occurring on 17th June 2020 in Danba, China. The 6-m dam and a concomitant 1.04 × 106 m3 barrier lake were formed by a tributary debris flow blocking the Xiaojin river. We used the dam breach overtopping and two-dimensional hydrodynamic models to simulate the whole process. The dam breach event persisted for 4.5 h with an outburst flood peak discharge of 823.5 m3/s, equal to a 20-year flood. It was noted that numerous sediments of approximately 5 × 106 m3 were transported to the downstream channel, elevating the main channel bed and the terrace by 10–15 m and 2–5 m, respectively. Averaged transportation efficiency of an outburst flood is 1269.73 times greater than a 20-year seasonal flood. We simulated representative seasonal floods and outburst floods based on the pre-beach river geometry, which shows that previous channel capacity is sufficient to convey seasonal floods and the outburst flood. However, the outburst flood could easily submerge terraces and living land using after-breach geometry. Due to river aggradation lifting river elevation, deposited riverbed promotes sediment and flood evolute to living land, resulting in amplified damage. Additionally, we collected 59 dam breaches and demonstrated that local riverbed slopes could increase more than 100 times. During dam breaches, the sharp slope plays a key role in high sediment transportation efficiency. This study can promote understanding the formation and development of channel aggradation triggered by outburst flood and provide more reasonable considerations for disaster prevention and mitigation triggered by outburst flood hazard chain. [ABSTRACT FROM AUTHOR]

On the night of October 3, 2023, the moraine-dammed South Lhonak Lake in Sikkim suddenly discharged a substantial volume of water, resulting in a glacial lake outburst flood (GLOF) that caused 178 fatalities and the destruction of three downstream hydropower projects, making it one of the most devastating GLOF events in the Himalayas. Leveraging satellite imagery and numerical modeling, this study analyzed the long-term evolution and outburst mechanisms of South Lhonak Lake, as well as the propagation of the GLOF, to provide valuable insight for regional GLOF risk assessment and management. The South Lhonak GLOF was triggered by the collapse of a massive lateral moraine, with an estimated collapse material volume of 16.75 × 106 m3. Following the outburst flood, the lake area decreased by 15.38%, from 1.69 ± 0.03 to 1.46 ± 0.03 km2. The impact of the GLOF extended to 169 km downstream, corresponding to a total inundation area of 32.04 ± 1.91 km2. A multi-phase r.avaflow model was employed to simulate the mass flow and cascading process. An impulse wave displacement speed of approximately 26 m·s−1 was observed after the collapse of the lateral moraine, and the overtopping height on the moraine dam reached 16.11 m. The hydrograph at the dam breach site revealed that approximately 38.49 × 106 m3 of water was released during the drainage process and that the peak discharge of 3.02 × 105 m3·s−1 occurred 140 s after the dam breach. Upon entering the downstream channel, the peak discharge was attenuated, and its duration was prolonged because of the influence of the valley terrain. Given the current challenges in accurately identifying potential avalanche zones, we identified a discrepancy between GLOF triggers and modeling scenarios. A novel framework for GLOF hazard assessment involves driving collapses of varying magnitudes to strike the lake and subsequently simulating GLOF initiation and downstream propagation for the most plausible outburst scenario. This conceptual approach can be used to design artificial drainage and determine dam immobilization engineering criteria and to evaluate the resistance performance of remedial measures under specific striking probabilities. [ABSTRACT FROM AUTHOR]

Flash flood after the breaching of South Lhonak Lake (glacier lake outburst flood (GLOF)) along with prolonged rainfall event in the first week of October 2023 significantly triggered numerous landslides along the side of the river, roads, and vulnerable slopes within the upper catchment of Teesta basin, Sikkim. In this paper, we present documentation on the occurrences of series of landslides just after the flood and heavy rainfall event in upper Teesta basin and try to find out the relevant causes. Primarily, flash flood due to glacial lake outburst and extensive rainfall accelerated series of landslides; however, the landslides are controlled by some other secondary factors including soil and slope condition, lithological diversity, geological discontinuities, and anthropogenic influences. The InSAR coherence analysis significantly shows the lowering of coherence value (decorrelation) in the moraine dam area within pre and post GLOF event which indicates breaching of the dam. The result of the slope stability assessment showed that majority slopes along the river Teesta are highly vulnerable with less safety factor and low cohesiveness of soil materials. Furthermore, the northern part of the MCT (Main Central Thrust) is composed by high-grade metamorphic rocks with exposed structures (high lineament density) that provoke landslides. Consequently, the result also highlighted that most of the slides along the side of Teesta occurred due to high water discharge and elevated gauge height after the GLOF event. Here, NH-10 (National Highway 10) runs on the high grade vulnerable litho-units and in between Dikchu and Chungthang, NH-10 is passing at the close proximity of river Teesta. So, different pockets of North Sikkim along the NH-10 were engulfed by high river discharge and gauge height due to large scale destruction of Chungthang Hydroelectric Power Plant constructed across the river Teesta. [ABSTRACT FROM AUTHOR]

Under the climate warming, the ice avalanches (IAs) and glacier lake outburst floods (GLOFs) will continue or even intensify in the future. In order to find out the number, spatial distribution, and characteristics of hidden dangers of IA and GLOF-prone lakes on the Tibetan Plateau (TP), the first inventory is presented. (1) The study has identified and analyzed 581 IAs and 369 GLOFs on the TP. IAs and GLOFs are widely distributed in the Tibet Autonomous Region (TAR), concentrating in the Yarlung Zangbo River basin and the Nyainqntanglha and Himalaya Mountain range. (2) Most of the IAs have an area of 0.1 ~ 1 km2. The IAs occur on vulnerable slopes ranging from 35 to 45°, with an elevation between 4500 and 5500 m and a north-friendly aspect. (3) Most of the GLOFs with a lake area of 0.1 ~ 0.3 km2 and a north-facing outburst direction are developed in an elevation range from 4500 to 5500 m. There are about half of the GLOF-prone lakes to be close to the front edge of the mother glaciers. (4) The front elevation of IAs changes regularly with the eastern Himalayan syntaxis region as the boundary. It generally increased from west to east on the west side, while a "V-shaped" trend first decreased and then increased, and decreased from south to north on the east side. (5) The IAs and GLOFs are mainly distributed in the southern and northwestern TP with "clustering" characters due to the topographical and climatic settings. [ABSTRACT FROM AUTHOR]

On June 25, 2020, Jinweng Co in Yiga, Tibet, experienced an outburst flood that resulted in catastrophic damage to farmland and roads. The complex causal factors for glacial lake outburst flooding (GLOF) are not fully understood. This paper provides a systematic analysis of the contributing factors leading to the GLOF disaster in terms of meteorological triggering, glacial activity, lake expansion, landslide, and glacial collapse. The analysis is based on multi-source remote sensing approaches. Pixel offset tracking of Sentinel-1 images shows changes in the glacier flow velocity from 2017 to 2020. Sentinel-2 and Landsat-8 images and inventory data have revealed the expansion of the lake since 1998. The satellite precipitation measurements revealed that the highest daily rainfall in recent years occurred approximately 4 days before the GLOF. Time series synthetic aperture radar (SAR) backscattering images and interferograms suggest that a landslide had occurred from the western lateral moraine into the lake. Additionally, SAR images suggest possible ice collapse from the glacier tongue into the lake. The causal mechanism for the June 2020 GLOF event was likely the dam failure triggered by heavy rainfall and combined with landslides and ice collapses. Our research can provide a reference to identify and mitigate glacial lake outburst disasters in mountainous regions based on satellite optical and radar images. [ABSTRACT FROM AUTHOR]

A large paleolandslide occurred opposite the Gangda village in the upper Jinsha River, SE Tibetan Plateau. Field geological investigations and remote sensing indicated that the Gangda paleolandslide once blocked the Jinsha River. Evidence of river blocking, including landslide dam relics, upstream lacustrine sediments, and downstream outburst sediments, has been well preserved. To understand the river-blocking event including landslide, dam breach, and associated outburst flooding, optically stimulated luminescence (OSL) dating and numerical simulations were performed in this study. OSL dating results showed that the paleolandslide dam was formed at 5.4 ± 0.5 ka BP and breached at 3.4 ± 0.3 ka BP, indicating that the dam lasted approximately 2000 years. The discrete element method was used to simulate the dynamics of the Gangda rock landslide based on the restored topography, while a fluid–solid coupling model was performed to simulate the landslide dam breaching and flooding. The fluid–solid coupling model can simultaneously reflect the process of landslide-dam collapse and the propagation of outburst flood. The simulated results indicate that the whole landslide process lasted about 60 s with a peak velocity of 38 m/s. It is significant that the simulated morphology of the residual landslide dam and downstream outburst sediments is consistent with the field observations. The combined numerical investigation in this paper provided new insights into the research of landscape evolution and helped to understand the chain disaster of landslide, dam breach, and flooding. [ABSTRACT FROM AUTHOR]

A landslide dam in most cases fails due to overtopping within a year of its formation, triggering a massive outburst flood. Although landslide dam material has a wide grain size distribution, the effects of coarse particles, which are immovable under normal river flow, on dam erosion processes and outflow discharge remain unknown. In this study, flume experiments on landslide dam failure caused by overtopping were conducted to reveal the effects of coarse particles on dam erosion processes and outflow discharge. In addition, this study developed a two-dimensional shallow water hydrodynamic model for predicting outflow discharge of a landslide dam with coarse particles. Our experiments demonstrated that an increase in the coarse particle fraction of dam material can increase the peak outflow discharge. This is because it can cause more rapid lowering of the maximum dam height due to the changes in erosion patterns. The numerical model proposed in this study successfully reproduced the experimental results showing temporal changes in outflow discharge of a landslide dam with and without coarse particles. Such a numerical model that can explain the transport of the non-uniform sediment particles could be an effective tool for predicting outburst floods of a landslide dam with a wide grain size distribution. [ABSTRACT FROM AUTHOR]

Barrier dams formed by the large-scale debris flow that blocks the river often are subjected to a high risk of break. The catastrophic flood arising from dam break has been confirmed as the most serious hazard-causing body of the debris flow dams. A novel method is proposed in this study to regulate the discharge of the debris flow dam break based on a flexible protective net (FPN). Next, 17 sets of flume experiments were performed to investigate the effects of different inflow discharges, dam grain size distribution, and downstream boundary locations of the FPN on discharge regulating effectiveness, such that the flow regulating mechanism of the FPN was revealed. As indicated by the results, (1) a significant traceability scarp was formed in the debris flow dam-break process. The whole dam-break process fell into three stages, i.e., traceability scarp formation, traceability scarp erosion, and traceability scarp decline. (2) When the downstream boundary of the FPN was located close to the downstream dam toe of the debris flow dam, regardless of the inflow discharge and the grain size distribution of the dam, the FPN laid on the surface of the debris flow dam took on critical effect in regulating the outburst discharge. (3) The inhibitory effect of the FPN on the particle initiation and the interception effect on particle transport, as well as the energy dissipation effect of the FPN and coarsening layer on outburst flood, fundamentally accounted for the good flow regulating effect of the above-described method. The method proposed in this study is capable of achieving an ideal outburst flood regulating effect by ensuring construction safety. [ABSTRACT FROM AUTHOR]

The Teesta basin within the Sikkim Himalaya encapsulates a number of glacial lakes, prominently featuring the expansive and swiftly evolving South Lhonak Lake. The recent South Lhonak Lake Glacial Lake Outburst Flood (GLOF) in Sikkim has triggered a major flash flood in the river. Satellite imagery acquired by the National Remote Sensing Centre revealed that a massive landslide caused a sudden surge in the water levels of the glacial lake, eventually leading to the breach of the moraine dam. The catastrophic GLOF event led to the collapse of the Chungthang Dam, located 65.92 km downstream of the glacier lake, resulting in widespread human casualties and substantial infrastructural devastation. This paper presents a comprehensive analysis, simulation, and reconstruction of the entire GLOF process chain. A key innovation of this study is the consideration of cascading failure effects, including the landslide, South Lhonak Lake breach, and subsequent Chungthang Dam breach. Additionally, this study introduces the application of photogrammetric techniques for the first time to accurately calculate the landslide volume and the corresponding volume of displaced water. The GLOF process chain encompasses the volume of debris falling into the lake, impulse-wave initiation, moraine dam overtopping, moraine dam breaching, and flood propagation. Photogrammetric techniques are applied using pre- and post-event high-resolution stereo-satellite images for estimating the landslide volume and the volume of water displaced due to the reduction in water level. Numerical simulations from the study show the generation of a significant impulse wave, leading to the overtopping of the moraine dam with an exceptionally high overtopping discharge of 15,850 m3/s. The estimated peak discharge due to the moraine dam breach is 12,564 m3/s. The findings indicate that the collapse of the Chungthang Dam generated two distinct peak discharges of 14,673 m3/s and 10,282 m3/s, respectively. The results are illustrated across different sites and validated by comparison with high-resolution satellite imagery and field data. The study demonstrates an integrative scientific methodology that includes photogrammetric techniques, sophisticated numerical modeling, and dam break analysis in simulating the landslide-induced GLOF. [ABSTRACT FROM AUTHOR]

On August 7, 2021, a disastrous rainfall-induced landslide occurred at Mt. Silabaku in the Yusui Stream source area, Taiwan. The huge deposits from the Silabaku landslide severely damaged the Minbaklu Bridge, and minor collapses in the Yusui Stream disrupted the only major road, Expressway No. 20. More than 400 residents from the three adjacent villages were stranded for 19 days in the mountainous area. The analysis of rainfall data, seismic records, topographic and geologic data, and historical orthoimages of the slope conditions, landform evolution, and current status of the Silabaku landslide revealed that the landslide resulted from slate avalanche induced by heavy rains, with local failures during Typhoon Morakot in 2009. Based on the high-resolution topographic data of light detection and ranging and an unmanned aerial vehicle, the debris deposits accumulated along the Yusui Stream were estimated to be above 8 million m3. In addition, a fan volume of 2 million m3 changed the flow line of the Laonong River, and the thick deposits pose a considerable threat to the safety of the nearby villages and infrastructures. [ABSTRACT FROM AUTHOR]

Affected by earthquakes and heavy rainfall, multiple landslide dams often cluster closely together along river reaches or gullies. Compared with a single landslide dam, the burst flood produced by the cascading failure of multiple landslide dams can be enhanced, seriously threatening life and property downstream. Here, we conduct a series of experiments in a 42 m flume to investigate the failure mechanisms of single and paired dams with fine-grained, well-graded, and coarse-grained debris; analyze the effects of dam geometry and initial water level of a downstream dam on the cascading breach; and quantitatively evaluate the amplification effect of cascading breach discharge. Single dams fail by overtopping along with seepage instability for a fine-grained dam, headcutting for a well-graded dam, and overtopping for a coarse-grained dam, respectively. The type of failure which occurs for a single dam is influenced by the shear strength of the dam material and seepage. However, the downstream dams in cascading tests fail by overtopping irrespective of dam material due to the large outburst floods from the upstream dams. A general flat slope angle is maintained during breaching for the fine-grained and coarse-grained dams, while a step-pool structure is developed for the well-graded dams because the finer grains are easier to wash away than coarse grains. The peak breach discharge for a downstream dam is 1.4–1.9 times the value for an upstream dam in the experimental runs, indicating the amplification effect of breach discharge. The amplification effect has a negative linear correlation with the time interval between the peak breach discharges of the two dams because the overlap of breach processes of upstream and downstream dams is gradually reduced as the time interval increases. [ABSTRACT FROM AUTHOR]

Forests, serving as natural barriers in mountainous regions, can reduce surface erosion, enhance water flow resistance and facilitate sedimentation. While extensive research has been conducted for forests and their capacity to withstand debris flows, there has been relatively little investigation into the interactions between riparian forests and debris flows. In this paper, a field investigation of Keze gully was conducted through section surveys, quadrat surveys and unmanned aerial vehicle field investigations. Based on the flow calculation results, analysis of sediment characteristics, gully morphology change and analysis of stand characteristics, the interaction model between the riparian forest and debris flow in the complex channel was discussed. The results further emphasise the role of forests in mitigating debris flows. Furthermore, the results show that the identified critical slope for the study area provides a threshold to explain two different flow interaction dynamics with riparian forests. Above the critical slope, debris flows predominantly follow the main channel, where the root-soil complex of riparian forests reduces channel bank erosion. However, this erosion can also lead to the uprooting and destruction of trees. Below the critical slope, floodplains are vital in accommodating overflow. Debris flows interact not only with the roots of trees near the riverbank but also with the trunks of trees on floodplains. Trees with a diameter less than 30 cm may also suffer damage due to broken stems. [ABSTRACT FROM AUTHOR]

Glacier lake outburst floods (GLOFs) initiate with the rapid outburst of a glacier lake, endangering downstream populations, land, and infrastructure. The flow initiates as a mud flow; however, with the entrainment of additional solid material, the flood will often transform into a debris flow. As the run-out slope flattens, the coarse solid material deposits and the flow de-waters. The flow transforms back into a muddy, hyperconcentrated flow of fine sediments in suspension. These flow transitions change the flow composition dramatically and influence both the overall mass balance and flow rheology of the event. In this paper, we apply a two-phase/layer model to simulate flow transitions, solid–fluid phase separations, entrainment, and run-out distances of glacier lake outburst floods. A key feature of the model is the calculation of dilatant actions in the solid–fluid mixture which control flow transitions and phase separations. Given their high initial amount of fluid within the flow, GLOFs are sensitive to slope changes inducing flow transitions, which also implies changes in the flow rheology. The changes in the rheology are computed as a function of the flow composition and do not need any adaptation by ad-hoc selection of friction coefficients. This procedure allows the application of constant rheological input parameters from initiation to run-out. Our goal is to increase the prediction reliability of debris flow modeling. We highlight the problems associated with initial and boundary (entrainment) conditions. We test the new model against the well-known Lake 513 (Peru, 2010), Lake Palcacocha (Peru, 1941), and Lake Uchitel in the Aksay Valley (Kyrgyzstan) GLOF events. We show that flow transition modeling is essential when studying areas that have significant variations in slope. [ABSTRACT FROM AUTHOR]

Secondary sediment disasters caused by the failure of landslide-dammed lakes are often more severe than the primary landslide events, resulting in catastrophic damage to surrounding infrastructure and the environment. The lifespan of landslide-dammed lakes is a crucial factor in determining the success of disaster prevention and response measures. However, the locations of landslide-dammed lakes are often inaccessible due to disrupted transportation or damaged access roads, making it difficult to obtain real-time information. Being able to estimate the time of dam failure is essential for assessing disaster response and making informed decisions. In this study, we analyzed 30 cases of landslide-dammed lakes in Taiwan, classifying them based on the actual time of dam failure and extracting geomorphic factors from the dam's catchment area. Using discriminant analysis, we quantitatively described the lifespan of the lakes. The results indicate that geomorphic factors in the dam's catchment area can effectively predict the lifespan of landslide-dammed lakes, with a classification accuracy of 93.3%. Through this research model, it is possible to predict the time of dam failure for landslide-dammed lakes, serving as a reference for establishing disaster warning, landslide-dammed lake monitoring, and disaster prevention notification systems. [ABSTRACT FROM AUTHOR]

The Xiaomojiu landslide is a typical high-elevation, long-runout landslide located in the Jinsha River Corridor. In this study, sequential InSAR time-series estimation was used to calculate the line of sight (LOS) surface displacements with descending and ascending Sentinel-1 images, and it turned out that the cumulative LOS surface displacement of the landslide was up to −78.4 mm during the period from October 2017 to April 2021 with the maximum LOS surface displacement rate of −38.5 mm/year. The landslide body could be divided into five zones (A, B1, B2, B3, and C) according to its topographical characteristics together with the LOS surface displacement time series. Combining engineering geological characteristics, LOS cumulative surface displacements with site investigation suggest that the Xiaomojiu landslide is likely to be a precipitation-triggered ancient traction rock landslide at the accelerated deformation stage. A dynamic simulation of the Xiaomojiu landslide with the PFC3D software shows that it could take approximately 65 s for the Xiaomojiu landslide from start-up to acceleration to deceleration to build-up of a barrier lake, followed by a simulation from the barrier lake to outburst floods with the HEC-RAS software indicating that the maximum depth of the outburst floods could be 13.5 m (15%), 24.6 m (25%), 42.1 m (50%), and 50.3 m (75%) along Qinghai-Tibet Plateau Transportation Corridor (QTPTC). It is believed that the results of this study provide a reference for landslide prevention along the QTPTC and the Jinsha River. [ABSTRACT FROM AUTHOR]

During the dry season of December 2020, two sliding subzones of the Qingliu landslide in southwest China slid out of stability, severely damaging the buildings on the slope. To investigate the mechanism and movement of landslides in the dry season, we employed high-resolution unmanned aerial vehicle mapping, electrical resistivity tomography, on-site union boreholes, groundwater detection, deep displacement monitoring, and numerical simulation to analyze the deep geotechnical structural characteristics, groundwater runoff paths, and destabilization range and movement processes at different times. Preliminary analysis showed that the slow infiltration of rainwater during the rainy season and infiltration of snow melt in winter, topography, and loess clay layers of the slide zone type are related to the triggers of landslide instability. Four layers of rock-soil stratification interfaces with different resistivity values, revealed by electrical resistivity tomography, comprising loess-like pulverized clay, gravelly pulverized clay, and bedrock, existed at different burial depths in the longitudinal section. Borehole and displacement monitoring revealed the existence of a primary slip surface and several secondary slip surfaces, with an average thickness of 16–22 m and a maximum daily displacement at the slip surface of approximately 2.29 mm. The deepest groundwater level of the water-bearing section in the borehole was 25.8 m, and it percolates and drains through fractures in the loess-like layer. Startup acceleration, deceleration pileup, front-edge pileup stopping, and middle- to rear-edge pileup stopping are the four primary discrete element simulation movement phases. The findings help deepen the understanding of similar dry-season landslides and their disaster-causing effects. [ABSTRACT FROM AUTHOR]

Landslide damming is a widespread phenomenon worldwide and significantly affects the evolution of fluvial landscapes. However, it is rarely witnessed from an antiquities perspective, and the case for observing their internal structure is challenging. We attempt to visualize the subsurface structure and understand the likely breaching mechanism of the late Pleistocene Diexi gigantic landslide dam (longevity of ~ 10 ka), using electrical resistivity tomography (ERT) method. Eight ERT measurements on the Diexi dam body revealed high resistivity zones near the periphery and lower resistivity zones in the middle portion of the profiles. Geomorphological mapping based on the LiDAR data determined the boundary of the landslide. Field investigation found that zones of low resistivity were connected to a ditched gully. Because breaching such an enormous lake with a total area of 21.4 km2 dammed by a gigantic landslide body with intact rocks was not likely by overtopping alone. The authors postulate that differential seepage of water from the gullies through the landslide debris could have accelerated the undercutting erosion of the otherwise stable Diexi dam. Utilizing geophysical techniques, along with field geomorphology works, can provide valuable information on the evolution of a gigantic paleo-landslide dam, which has real implications for the stability evaluation and forecast of future landslide dams. [ABSTRACT FROM AUTHOR]

Owing to the superelevation in the bend, debris flow rushed out of the channel and destroyed the engineering facilities near the bend, which brings challenges to the design of disaster prevention and mitigation projects. Under the assumption of a continuous homogeneous medium and rectangular channel section, the debris flow velocity in the bend is decomposed into a tangential velocity that causes superelevation and a normal velocity that generates runup. The calculation equations of superelevation, runup, and total superelevation of debris flow in the bend are derived based on the gravity center offset of the flow section in the debris flow movement. The proposed equation can determine and depict the evolution of total superelevation value along the bend, which is useful for engineers to carry out the targeted design in debris flow prevention and control engineering. Meanwhile, using the equation in this paper and two other representative equations, the total superelevation, superelevation, and runup height of debris flow in 37 groups of test data and bends in the case study are computed to compare with the test and measured results. The test findings showed that the runup height accounts for about 40% of the total superelevation, and the runup height of the five bend points in the case accounts for 43–48%, indicating that the runup is an essential part of the total superelevation and needs to be calculated in the design of the bend of the debris flow prevention and control project. [ABSTRACT FROM AUTHOR]

On April 9, 2018, a massive rock avalanche hit the area of Karimabad, Hunza. Approximately 2Mm3 of rock mass detached from the source area and traveled a total of 4.88 km. The rock mass deposited along 2000 m length and destroyed the Ultar meadows. The avalanche killed three tourists and resulted in a vast dust cloud that engulfed the entire town of Karimabad in a few seconds. In this paper, we have analyzed the dynamic characteristics of the Ultar rock avalanche and subsequent airblast using a coupled three-dimensional discrete element modeling and computational fluid dynamics approach. Two-way coupling was carried out using an application programming interface that transferred the data between models to simulate the avalanche movement and induced airblast. We have also analyzed the formation and propagation of induced dust clouds based on field investigation, captured video, and climatic conditions. The study concludes that the Ultar rock avalanche's movement lasted 148 s. The average velocity of sliding material was found to be 26.35 m/s. The dynamics of induced airblast were studied along the entire runout path. The maximum velocity of generated airblast along different sections of the runout path was found to be 40 m/s and 35 m/s, respectively, whereas the relative pressure of the blast wave was found to be 0.6 kPa. Furthermore, the results revealed that a low-pressure dust cloud traveled a long distance due to the continuous fragmentation of the sliding material along a steep runout path. The induced dust cloud engulfed the entire town of Karimabad, Hunza, for several hours. This study is expected to help scientists further explore the dynamics of the airblast. It will also help understand the formation and propagation of dust clouds induced by rock avalanches involving excessive fragmentation. [ABSTRACT FROM AUTHOR]

In the Eastern Himalayas syntaxes (Tibet Plateau, China), increasing periglacial debris flows have been documented in recent decades, but minimal research has focused on the material properties and the topography of initiation areas. In this work, we applied a series of satellite images from 2000 to 2021 to examine the hanging glacier status and debris-flow initiation conditions in Sanggu watershed. Five large-scale debris flow events in 2003, 2015, 2018, 2020, and 2021 were interpreted. Visual interpretation, together with pixel dichotomy model and the COSI-Corr method, demonstrated that debris flows mainly initiated from the periglacial environment of catchments I and II. Since 2000, the glacier has exhibited general shrinkage, punctuated by occasional advance. The failure potential, expressed as the product of changed glacier area and topographic slope, positively relates to the inundation area of debris flows. This result implies that either abrupt glacier advancement or retreat may result in large debris flows, and glacier terminus position may serve as the main driving factor for debris flow initiation. Importantly, a lower limited area-slope initiation condition was developed in this work, which may provide a reference point for identifying possible failure areas of periglacial debris. The results of this work contribute to knowledge about the material properties and magnitude prediction of periglacial debris flows in alpine watersheds. [ABSTRACT FROM AUTHOR]

In this paper, a depth-averaged numerical model is proposed to simulate the propagation of debris flows. To understand the dynamical features of debris flows, the granular-liquid mixture model is employed, where the resistance of liquid constituent consisting of water and fine particles is described by Herschel-Bulkley rheology, and the resistance of granular constituent involving the coarse particles is formulated by the Voellmy model. An Eulerian leapfrog finite difference scheme is employed to numerically solve the governing equations of debris flows. Several idealized dam break problems are numerically implemented to test the accuracy and stability of the numerical scheme, and good agreement with the analytical solutions is found. Furthermore, the experiment carried out by Iverson (2010) is numerically implemented in this study to validate the proposed model, and the results are in good agreement. Then, a typical debris flow in Tianmo gully in Tibet, China, is numerically analyzed based on the proposed model. The results show that several details of the motion of debris flows over a real terrain can be accurately predicted by the proposed model. The comparisons between the basal Coulomb friction model and the Voellmy model show that the mobility of debris flows can be overestimated when only the Coulomb friction model is employed. An analysis based on the unsteady motion of a uniform mass indicates that Voellmy resistance can rescue the issue in regard to the absence of resistance of the granular component due to fully liquefied states. Finally, the influence of the rheology of liquid slurry on the motion of debris flows is analyzed, and the results demonstrate that the basal resistances caused by the liquid slurry were very small relative to the basal resistances caused by granular constituent. [ABSTRACT FROM AUTHOR]

Massive slope failures often occur along the Himalayan orogenic belt, where the Indian plate subducts beneath the Eurasian plate. On March 22, 2021, a slope failure hazard occurred at the Grand Canyon section of the Yarlung Tsangpo River, eastern Himalayan syntaxis, and blocked the river leading to a water level rise of over 10 m. We conducted an analysis of the seismic waveforms recorded by broadband seismic stations which we deployed around the Grand Canyon. These seismograms showed emergent onsets with a total duration of approximately 300 s and corroborated their origination as a glacier collapse along the remote Sedongpu basin. Based on direct measurements of seismic energy and an empirical distance attenuation function, we estimated the volume to be approximately 50 × 106 m3. The source process was interpreted as a single force with three possible stages: progressive coherent block fracturing, mass flow through the Sedongpu basin with downslope acceleration-deceleration-stable motions, and continuous flow along the river after the formation of a temporary dam at the outlet basin. [ABSTRACT FROM AUTHOR]

Glacial detachment is a newly emerged glacial hazard type, and more than 20 cases have been identified worldwide. The Xiao Ma Glacier in the Amney Machen Mountains, northeastern Tibetan Plateau, experienced an intensive detachment of the terminal low-slope glacier in 2004, forming a large dammed lake downstream and burying 2.27 km2 of grassland. An advanced multi-phase r.avaflow model was used to simulate this glacier detachment event to reconstruct its slide mechanism and dynamic process. In total, 9.77 × 106 m3 mass detached were categorized into three different phases according to their properties: the old ice remaining in the middle layer following the 1988–1997 glacier surge (47% of total volume), new ice in the upper layer originating from the 2003–2004 surge, which directly caused the 2004 detachment (48%), and subglacial water trapped in the bedrock (5%). The modeling results showed that the glacier detachment–induced debris flow reached a peak discharge of 0.25 × 106 m3/s at 40 s at the mouth of the Xiao Ma Valley, and the entire propagation process was completed within 140 s. The initially trapped meltwater dominated the debris flow state, with a maximum velocity of 103 m/s. The underlying old glacial ice was pushed and deposited to the front of the fan, and the new ice in the upper layer was primarily deposited over the middle fan. Additionally, several important parameters in the r.avaflow model were recommended for the optimal interval of values via optimality analysis, and the potential of the model to be extensively applied for large-scale risk assessment was discussed under relatively simple settings. The modeling of the 2004 Amney Machen glacier detachment has resulted in a comprehensive understanding of the dynamic processes of such events, which is significant for future glacier disaster simulation and assessment thereby improving regional strategies in hazard early warning, prevention, and mitigation. [ABSTRACT FROM AUTHOR]

Rock avalanches can be a significant hazard to communities located in mountainous areas. Probabilistic predictions of the 3D impact area of these events are crucial for assessing rock avalanche risk. Semi-empirical, calibration-based numerical runout models are one tool that can be used to make these predictions. When doing so, uncertainties resulting from both noisy calibration data and uncertain governing movement mechanism(s) must be accounted for. In this paper, a back-analysis of a database of 31 rock avalanche case histories is used to assess both of these sources of uncertainty. It is found that forecasting results are dominated by uncertainties associated with the bulk basal resistance of the path material. A method to account for both calibration and mechanistic uncertainty is provided, and this method is evaluated using pseudo-forecasts of two case histories. These pseudo-forecasts show that inclusion of expert judgement when assessing the bulk basal resistance along the path can reduce mechanistic uncertainty and result in more precise predictions of rock avalanche runout. [ABSTRACT FROM AUTHOR]

In Tibet Plateau, China, debris flows have been commonly documented in the marine monsoon climate region, yet few cases were recorded in continental climate regions, such as the mountain belt of Kallash and Back-Himalayas. In July 2021, prolonged low-intensity rain in Angla Mountain, another short-duration intensive rain in Purang County, initiated runoff-triggered debris flows. In this work, we are mainly concerned with the differences in the triggering rainfall condition and local landscape dissection with respect to the freeze–thaw state. The results reveal that the low triggering rainfall of debris flows at Angla Mountain may attribute to the long freeze–thaw duration. The high triggering rainfall of debris flows in Purang County may attribute to the high saturated hydraulic conductivity and short freeze–thaw duration. Nevertheless, freeze–thaw duration, together with the low saturated hydraulic conductivity, may result in heavy landscape dissection of Angla Mountain. The Melton's ruggedness number of catchments in the two areas is greater than some suggested criteria, indicating they are susceptible to debris flows. Debris flow deposits have low proportions of grain size fractions < 0.1 mm and higher fractions of 1–10 mm in size. Field measurement of a slope debris flow found that the mean diameter decreases as the slope gradient decreases and channel geometry widens. Such changes in gradient and channel geometry may lead to a volumetric concentration decrease, and the deposits become finer. This work preliminarily contributes to know about the effect of a freeze–thaw state on the triggering rainfall of debris flows and local landscape dissection in the continental climate region, Tibet Plateau, China. [ABSTRACT FROM AUTHOR]

The geometries and material properties of a landslide dam depend on the dam formation process and affect the breaching process. A comprehensive understanding of the entire process of dam formation and breach is necessary for a more accurate analysis of the dam stability and failure characteristics, but little research has been done in this area. In this study, the effects of debris composition, sliding width, and valley shape on dam breaching by considering dam formation features were experimentally investigated. Results reveal that the stability and failure modes of landslide dams are predominantly governed by the debris composition. The dam stability increases with mean grain size, especially the grain size at the overflow location. Dam height and width are largely influenced by debris composition and sliding width, and the lake volume is highly dependent on the valley shape. The arrival time of peak discharge for balance-grained dams is more related to the dam height than the lake volume, while fine-grained dams are the opposite. The peak discharge is significantly influenced by the lake volume and released water volume, while the effects of dam height, downstream slope, and lake shape coefficient are negligible. Balance-grained dams exhibit two longitudinal evolution models in different shaped valleys. The evolution model of fine-grained dams is different from that of balance-grained dams and is independent of valley shape. This study improves our current understanding of the whole process of landslide dams from formation to failure and the effects of dam formation features on dam breaching. [ABSTRACT FROM AUTHOR]

Flexible barriers may be installed upstream in debris flow channels to reduce entrainment of bed material. Simulating both the entrainment and the impact on a barrier by the same numerical tool remains challenging. For this purpose, a three-dimensional one-phase material point method (MPM) software is used herein to back-calculate two large-scale flume experiments. These experiments were conducted to measure the entrainment of an erodible bed and the impact on a flexible barrier. To simulate the entrainment of the wet bed, a Mohr–Coulomb softening model is introduced. In the model, the apparent friction angle of the bed material decreases as a function of the distortional strain, effectively reproducing the pore pressure increase observed in the experiments. From the tests and the numerical simulations, we identify two main mechanisms leading to entrainment: (i) the direct rubbing and colliding effect of the flow on to the bed and (ii) a significant bed shear strength reduction. Concerning the first mechanism, existing models only consider the rubbing of the bed surface by a shear stress parallel to the slope. However, we observe that a ploughing-type erosion occurs due to normal stresses acting on the bed in the flow direction. The additional ploughing explains why beds which are mechanically stronger than the flow can also be partly entrained. Larger entrainment volumes are found when the bed material loses shear strength due to pore pressure buildup that eventually leads to a self-propelled entrainment where the bed no longer has frictional strength to carry its own weight. [ABSTRACT FROM AUTHOR]

The existing empirical models do not consider the influence of material composition of landslide deposits on the peak breach flow due to the uncertainty in the material composition and the randomness of its distribution. In this study, based on the statistical analyses and case comparison, the factors influencing the peak breach flow were comprehensively investigated. The highlight is the material composition-based classification of landslide deposits of 86 landslide cases with detailed grain-size distribution information. In order to consider the geometric morphology of landslide dams and the potential energy of dammed lakes, as well as the material composition of landslide deposits in an empirical model, a multiple regression method was applied on a database, which comprises of 44 documented landslide dam breach cases. A new empirical model for predicting the peak breach flow of landslide dams was developed. Furthermore, for the same 44 documented landslide dam failures, the predicted peak breach flow obtained by using the existing empirical models for embankment and landslide dams and that obtained by using the newly developed model were compared. The comparison of the root mean square error (Erms) and the multiple coefficient of determination (R2) for each empirical model verifies the accuracy and rationality of the new empirical model. Furthermore, for fair validation, several landslide dam breach cases that occurred in recent years in China and have reliable measured data were also used in another comparison. The results show that the new empirical model can reasonably predict the peak breach flow, and exhibits the best performance among all the existing empirical models for embankment and landslide dam breaching. [ABSTRACT FROM AUTHOR]

This paper presents a study on an ancient river-damming landslide in the SE Tibet Plateau, China, with a focus on time-dependent gravitational creep leading to slope failure associated with progressive fragmentation during motion. Field investigation shows that the landslide, with an estimated volume of 4.9 × 107 m3, is a translational toe buckling slide. Outcrops of landslide deposits, buckling, toe shear, residual landslide dam, and lacustrine sediments are distributed at the slope base. The landslide deposits formed a landslide dam over 60 m high and at one time blocked the Jinsha River. Optically stimulated luminescence dating for the lacustrine sediments indicates that the landslide occurred at least 2,600 years ago. To investigate the progressive evolution and failure behavior of the landslide, numerical simulations using the distinct element method are conducted. The results show that the evolution of the landslide could be divided into three stages: a time-dependent gravitational creep process, rapid failure, and granular flow deposition. It probably began as a long-term gravitationally induced buckling of amphibolite rock slabs along a weak interlayer composed of mica schist which was followed by progressive fragmentation during flow-like motion, evolving into a flow-like movement, which deposited sediments in the river valley. According to numerical modeling results, the rapid failure stage lasted 35 s from the onset of sudden failure to final deposition, with an estimated maximum movement rate of 26.8 m/s. The simulated topography is close to the post-landslide topography. Based on field investigation and numerical simulation, it can be found that the mica schist interlayer and bedding planes are responsible for the slope instability, while strong toe erosion caused by the Jinsha River caused the layered rock mass to buckle intensively. Rainfall or an earthquake cannot be ruled out as a potential trigger of the landslide, considering the climate condition and the seismic activity on centennial to millennial timescales in the study area. [ABSTRACT FROM AUTHOR]

The evaluation of landslide runout behavior plays a vital role in the risk assessment of landslides. In this study, the runout behavior of a landslide that occurred on December 10, 2019, in the Three Gorges Reservoir region, China, known as the Kamenziwan landslide, is studied with the discrete element method. A field survey is first conducted to study the geological characteristics and failure mechanism of this landslide. The survey results indicate that this landslide is possibly caused by the long-term fluctuation of the reservoir water level. Then, a three-dimensional (3-D) numerical model of this landslide is constructed on the basis of the terrain data obtained before and after the landslide occurrence. The critical input parameters to the numerical model, in terms of the contact micro-parameters among particles, are calibrated with the machine learning method and uniaxial compression tests. To depict the effectiveness of the built numerical model, the simulation results are compared with the video snapshots taken by a local resident. Finally, the runout behavior and the energy transformation of the landslide are analyzed based on the validated numerical model. [ABSTRACT FROM AUTHOR]

Determining the premonitory and dynamic characteristics of landslide dam failures can provide an early warning as well the identification of the evolution of the failure process, and it is therefore extremely important in the risk management of chain disasters. We conducted 12 dam failure tests to analyze the process of landslide dam failure—from seepage deformation to breaching and outburst floods—with synchronous measurements of the flow dynamics and the resulting seismic signal. The Hilbert-Huang transform (HHT) was used to evaluate the time–frequency spectrum and amplitudes of the seismic signals. The results showed that dam failure or settlement deformation was affected by internal structural rearrangements driven by seepage and internal erosion, which could be detected by microseismicity (MS) monitoring. During the breaching process, the spectral magnitude of microseismicity at high frequency was well correlated with the discharge, reflecting energy variations during the breaching and flooding process, which will help to identify and invert the dynamic process of landslide dam failure. The following stages were identified: Stage I, initial breach development; Stage II, head cutting; Stage III, intense erosion; and Stage IV, attenuation and re-equilibration. The process of breaching was rapid, and the peak value of the outflow discharge, flood velocity, and impact force downstream increased due to the reduction in the shear strength of the dam caused by seepage. In addition, we attempted to establish correlations between discharge, flow velocity, and Arias intensity. Our application of MS to the process of landslide dam failure has improved our understanding of the precursory characteristics of failure and variations in the energy of outflow discharge along the channel, and the results provide a future reference for early warning monitoring and the emergency treatment of landslide dams. [ABSTRACT FROM AUTHOR]

Increasingly frequent glacier-rock avalanches (GRAs) – events triggered by the detachment of both glacier and rock materials – have occurred in recent years in the Sedongpu gully in the eastern Himalayan syntaxis, blocking the course of the Yarlung Zangbo River repeatedly. To identify spatio-temporal patterns and influencing factors of these GRAs, we analyzed remote sensing images and produced high-resolution digital surface models. At least eight GRAs, originating from the same source areas, have occurred in the past decades: one in 1974, one in 2014, and six between 2017 and 2018. The GRAs that occurred since 2014 were responsible for the loss of > 70 Mm3 of glacier and rock and > 150 Mm3 of moraine deposits and increased the elevation of the basin outlet by 60–120 m. Climate change-induced glacier retreat, steep topography, and a recent strong earthquake were found to be related to the occurrence of the recent GRAs, which resulted in the formation of a knickpoint in the Yarlung Zangbo River. [ABSTRACT FROM AUTHOR]

The Sichuan-Tibet railway goes across the Upper Jinsha River, along which a large number of large historical landslides have occurred and dammed the river. Therefore, it is of great significance to investigate large potential landslides along the Jinsha River. In this paper, we inspect the deformation characteristics of a rapid landsliding area along the Jinsha River by using multi-temporal remote sensing, and analyzed its future development and risk to the Sichuan-Tibet railway. Surface deformations and damage features between January 2016 and October 2020 were obtained using multi-temporal InSAR and multi-temporal correlations of optical images, respectively. Deformation and failure signs obtained from the field investigation were highly consistent. Results showed that cumulative deformation of the landsliding area is more than 50 cm, and the landsliding area is undergoing an accelerated deformation stage. The external rainfall condition, water level, and water flow rate are important factors controlling the deformation. The increase of rainfall, the rise of water level, and faster flow rate will accelerate the deformation of slope. The geological conditions of the slope itself affect the deformation of landslide. Due to the enrichment of gently dipping gneiss and groundwater, the slope is more likely to slide along the slope. The Jinsha River continuously scours the concave bank of the slope, causing local collapses and forming local free surfaces. Numerical simulation results show that once the landsliding area fails, the landslide body may form a 4-km-long dammed lake, and the water level could rise about 200 m; the historic data shows that landslide dam may burst in 2–8 days after sliding. Therefore, strategies of landslide hazard mitigation in the study area should be particularly made for the coming rainy seasons to mitigate risks from the landsliding area. [ABSTRACT FROM AUTHOR]

On July 5, 2021, a catastrophic rock avalanche hit an area in the upper Naltar valley, located in northwestern Gilgit, Pakistan. The 14 Mm3 rock mass flowed down the hillslope and traveled a distance of approximately 5 km. The avalanche killed four people and damaged more than 150 livestock. Based on a field investigation, the event is classified as a dual-phase avalanche comprising glacial ice and rock mass mixtures. In this study, the runout behavior and characteristics of the upper Naltar rock avalanche are analyzed using DAN3D. The simulation results indicate that the propagation process lasted for 140 s, with an average maximum velocity of 32 m/s. The frictional-Voellmy model for the materials in the source and erosion areas produced the best results for DAN3D. Parameter calibration, model performance, and verification were performed numerically and based on field observations. It is hoped that the selected model and parameters will help the relevant agencies understand the propagation process of similar kinds of rock avalanches in the area surrounding the current avalanche, thus improving the hazard zonation in this region. [ABSTRACT FROM AUTHOR]

In the plenary and parallel session of WLF5 held on 3-6 November 2021, a total of 492 speeches were orally presented in one of three modes (onsite, online-virtual or pre-recorded mode) at the Kyoto International Conference Center, Kyoto Japan. Director, International Research Institute of Disaster Science (IRIDeS) at Tohoku University, Japan) B Commentators: b Rick Bailey (Head of Secretariat, IOC-UNESCO Indian Ocean Tsunami Warning and Mitigation System), Shinji Sassa (Chair of the World Tsunami Awareness Day Special Event, National Institute of Maritime, Port and Aviation Technology, Japan), Julian Kwan (Geotechnical Engineering Office, Civil Engineering and Development Department, Hong Kong, China) and others. [Extracted from the article]