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Rapid flow-like landslides, particularly debris flows and debris avalanches, cause significant economic damage and many victims worldwide every year. They are usually extremely fast with the capability of travelling long distances in short times, sweeping away everything in their path. The principal objective of this paper is to test the ability of the 'GeoFlow-SPH' two-phase model developed by the authors, to reproduce the complex behaviour of natural debris avalanches where pore-water pressure evolution plays a key role. To reach this goal, the model is applied to reproduce the complex dynamic behaviour observed in Johnsons Landing debris avalanche including the observed bifurcation caused by the flowing out of part of the moving mass from the mid-channel. Initial thickness deposit trim-line, distribution of deposit volume, and the average velocities were provided for this real case, making it an appropriate case to validate the developed model. The paper also contributes to evaluate the SPH-FD model's potentialities to simulate the structural countermeasure, like bottom drainage screens, used to reduce the impact of debris flows. The analysis of the results shows the adequacy of the proposed model to solve this complicated geophysical problem. [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]

The paper deals with the effects of artificial barriers on the dynamic features of unconfined flows such as debris avalanches in coarse-grained materials. These phenomena are often responsible for damage to structures and risk to human life. Artificial barriers could mitigate those threats by reducing the flow velocity and the runout distance as well as diverting the flow towards lateral zones constrained by the barriers. A quasi-3D SPH hydro-mechanically coupled model was used to simulate the propagation heights and velocities, the evolution of pore water pressures inside the flow and the entrainment of additional material from the ground surface during the propagation stage. The numerical simulations referred to (i) simple topography resembling typical in situ conditions and (ii) the case history of Nocera Inferiore (Southern Italy) where a destructive debris avalanche occurred in 2005. Different scenarios were analysed relative to the number, type and location of the artificial barriers. The numerical results highlight the variations in propagation pattern, velocity and deposition thickness of the flows, which may occur in presence of artificial barriers. Indications on favourable type and location of barriers are provided both for the simple topography and for the specific case study. [ABSTRACT FROM AUTHOR]

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

On 22 March 2014, a massive, catastrophic landslide occurred near Oso, Washington, USA, sweeping more than 1 km across the adjacent valley flats and killing 43 people. For the following 5 weeks, hundreds of workers engaged in an exhaustive search, rescue, and recovery effort directly in the landslide runout path. These workers could not avoid the risks posed by additional large-scale slope collapses. In an effort to ensure worker safety, multiple agencies cooperated to swiftly deploy a monitoring and alerting system consisting of sensors, automated data processing and web-based display, along with defined communication protocols and clear calls to action for emergency management and search personnel. Guided by the principle that an accelerating landslide poses a greater threat than a steadily moving or stationary mass, the system was designed to detect ground motion and vibration using complementary monitoring techniques. Near real-time information was provided by continuous GPS, seismometers/geophones, and extensometers. This information was augmented by repeat-assessment techniques such as terrestrial and aerial laser scanning and time-lapse photography. Fortunately, no major additional landsliding occurred. However, we did detect small headscarp failures as well as slow movement of the remaining landslide mass with the monitoring system. This was an exceptional response situation and the lessons learned are applicable to other landslide disaster crises. They underscore the need for cogent landslide expertise and ready-to-deploy monitoring equipment, the value of using redundant monitoring techniques with distinct goals, the benefit of clearly defined communication protocols, and the importance of continued research into forecasting landslide behavior to allow timely warning. [ABSTRACT FROM AUTHOR]

Debris avalanches have complex structures due to the internal discreteness of fragmentation events. From a meso perspective, a debris avalanche is essentially a collection of debris particles of various sizes. Friction and collision events are directly influenced by the gradation of debris particles, restricting the movement process of debris avalanches. Accordingly, a series of numerical simulations have been conducted to research the influence of motion behavior based on experimental tests. The results indicate that the inhomogeneous character of a debris avalanche creates a conducive particle structure for the movement of the debris avalanche, in which the fine particles can play a role in the conversion of sliding to rolling at the bottom, causing the reduction of friction dissipation and the differentiation of particle friction resistance along the vertical direction, which continues until deposition. Sudden decreases in friction resistance occurring on high-speed, fluid-like debris avalanches are primarily correlated to the particular particle structure due to the significant inhomogeneity of particle gradation. [ABSTRACT FROM AUTHOR]

On July 23, 2019, a catastrophic high-elevation and long-runout landslide occurred in Shuicheng County, Guizhou Province, the karst mountainous area of southwestern China, causing the death of 51 people and the destruction and burial of 21 houses. The landslide movement consisted of a three-stage chain disaster that included landslide instability, impact and scraping, and debris flow deposit. A field investigation, unmanned aerial vehicle(UAV) image analysis, and dynamic analysis determined that this landslide had the following main characteristics: (1) initiated at high elevation, the elevation difference between the landslide front and the toe of surface of rupture was 340 m, and the horizontal sliding distance was 1360 m, categorizing this landslide as a high elevation and long runout; (2) induced by heavy rainfall, there was no notable sign of pre-landslide deformation but catastrophic events occurred, suggesting heavy rainfall as the main inducing factor for landslide failure; (3) significant entrainment effect, the volume of the sliding body was 70 × 104 m3, and the deposit volume reached 200 × 104 m3, and the impact and scraping characteristics were remarkable, enlarging the scale of the landslide disaster and increasing the difficulty of the rescue effort; and (4) extremely high fluidity, the basalt fragments and quaternary clay were fully and evenly mixed, reflecting the turbulent characteristics and super high mobility of the sliding body during the movement. To date, multiple high-elevation and long-runout landslides of Emeishan basalt have been recorded in the southwestern mountainous area of China, causing enormous casualties. Research establishing early identification and risk zoning methods for high-elevation landslides in the Emeishan basalt mountainous area should take into account the effects of landslide impact, scraping, and the disintegration effect during collision, and further research should be conducted into the post-failure dynamics of high-elevation and long-runout landslides. [ABSTRACT FROM AUTHOR]

Flexible barriers are an effective type of mitigation measure against debris avalanches in valleys and can affect the kinetic energy and mass of debris avalanches. To investigate the complex dynamic interaction between a debris avalanche and a flexible barrier, a modeling framework was developed based on coupled discrete element method (DEM) and finite element method (FEM). The debris avalanche was modeled as an assembly of discrete particles accounting for collision–friction effect, and the flexible barrier was modeled by applying the FEM accounting for connections and contact in a realistic manner. The coupled numerical model was well validated by comparing the numerical results with experimental data reported in the literature. This model was employed to examine the dynamics of debris avalanche–barrier interaction, such as the interaction process, impact force, energy dissipation mechanism, and evolution of the internal forces of the components, as well as the influences of the bulk density and impact height of the debris avalanche and the slope angle of the channel on the coupled impact force. Based on the numerical results, three interaction stages were identified, namely, frontal impact, run-up, and pile-up. During the interaction process, the effects of run-up and dead zone formation need to be accounted to avoid conservative estimates of the impact force. The analyses of the energy transformation showed that 76.2% of the initial total energy was dissipated by interaction friction, and the flexible barriers may mainly focus on the frontal impact energy of the debris avalanche by using an energy design approach. The sensitivities of the bulk density, impact height, and slope angle on the maximum impact force are 1, 0.186, and 2.084, respectively. The parameters with high sensitivity are the main influencing parameters and should be given priority in the design of flexible barriers. [ABSTRACT FROM AUTHOR]

Under the WCoE/IPL project, Landsat Enhanced Thematic Mapper plus (ETM+) and ASTER GDEM data were used to analyze factors associated with frequent debris flow and rock-debris avalanche on the Nigeria-Cameroon mountain range. Detailed processing of the ETM+ imageries of the vulnerable portions on the western part of Adamawa plateau was carried out to identify structural trends relatable to the slope failures. The processing identified the structural characteristics of the study area and clearly distinguished the lineaments associated with the debris flow and rock-debris avalanches. The strongly weathered and fragmented gneissic rocks, shallow groundwater table, as well as the distribution of faults and joint sets were significant factors predisposing the slopes to rapid movements. Recent landslides occurred at the locations with high lineament density and in areas close to major faults and long lineaments. The interaction among the moving mass, slope geometry, local geology, topography, and drainage then resulted in a long runout and a high degree of spreading. Analysis of the ASTER-GDEM delineated landforms, slope morphology, and drainage patterns, which was not possible with conventional mapping techniques. Integration of these results yielded reasonable interpretation of the predisposing factors for the long runout failures and provided logical basis for future landslide susceptibility analysis in the area. Accurate investigation of the predisposing factors and characteristics of landslides in environments that have experienced past failures is therefore important in understanding areas that may be susceptible to landsliding in future. [ABSTRACT FROM AUTHOR]