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The 2018, Mw 6.6 Hokkaido Eastern Iburi earthquake in Japan triggered over 10,000 landsliding in an area spanning about 500 km2, altering the local topography and leading to the accumulation of loose deposits on hillslopes and in valleys. However, a comprehensive post-seismic landslide inventory and an assessment of topographic changes are lacking, hindering a quantitative hazard assessment. Additionally, the extent of vegetation recovery in areas affected by coseismic landslides, a key indicator of post-seismic debris flow hazard, has not been evaluated. Here, we utilize high-resolution digital elevation models and multi-temporal satellite imagery to analyze topographic changes and vegetation dynamics in the earthquake's epicentral area (seismic intensity >5.5). We observe that the event roughened the overall gentle topography of the region and made the slopes steeper. Owing to the absence of significant rainstorms and snowmelt post 2018, only a few debris remobilizations (60) and new landslides (80) have occurred in the affected region. Moreover, we noticed a slow vegetation recovery in the post-seismic phase, suggesting that the likelihood of debris flows and gully erosion remains elevated, highlighting the need for continued monitoring and assessment. [ABSTRACT FROM AUTHOR]

Rock avalanches typically entail the flow-like motion of angular rock blocks and fragments of diverse size. Numerical simulations are instrumental in understanding their dynamic process, supporting hazard and risk assessments. Simplified failure criteria, such as the Mohr-Coulomb or Drucker-Prager, are commonly adopted in landslide models relying on the material point method (MPM). However, these criteria cannot capture the transitions between solid-like, liquid-like, and gas-like behaviors exhibited by granular materials. Here, we relied on the moving least-squares MPM, which offers high computing efficiency and stability, and adopted a nonlocal μ(I) rheology model implemented by Haeri and Skonieczny (Comput Methods Appl Mech Eng, 2022). This approach can account for the rate-dependent, pressure-dependent, and size-dependent characteristics of friction in granular materials. By simulating a small-scale flume experiment as well as a large-scale event (the Nayong rock avalanche in Guizhou, China), we verified that the nonlocal μ(I) rheology model can capture the motion and deposition processes in rock avalanches effectively. This feature can be advantageous in physically based hazard assessments of such events. [ABSTRACT FROM AUTHOR]

This article discusses a landslide that occurred on the G213 National Highway in Songpan County, Sichuan, China. The landslide, which was triggered by heavy rainfall, led to the closure of the highway for almost 50 days and caused damage to infrastructure. The article provides a detailed analysis of the landslide, including information about the geological setting, climate conditions, and morphology. The study emphasizes the importance of long-term monitoring and disaster prevention measures in landslide-prone areas and provides data that can be used for further research and awareness. [Extracted from the article]

Thermochemical pressurization is a possible weakening mechanism that could explain the hypermobility of large landslides in carbonate rock. However, the factors controlling the efficiency of this mechanism in generating hypermobility have not been elucidated. Here, we use mass and energy conservation equations—accounting for the thermal decomposition of carbonate and a thermoporoelastic mechanism—to evaluate the efficiency of thermochemical pressurization in the 2009 Jiweishan rockslide event in China. We consider distinct permeability functions for the shear zone and the rock wall, controlled by distinct mechanical processes, and explore the sensitivity of the model to changes in the values of the key parameters. We evaluate that a combination of pore pressure increase and the endothermic nature of the chemical reaction may effectively limit frictional heating. We observe that the increase in pore pressure is controlled by the permeability of the rock wall rather than by that of the shear zone and its thickness. We also find that the permeability of the damaged rock wall is the key factor controlling the energy ratio—a measure of efficiency. We conclude that the comparatively low velocity and small thickness of the sliding body, and the relatively high permeability of the formation in which the Jiweishan landslide developed may have limited the effect of thermal decomposition. Highlights: Shear-zone and wall rock permeabilities evolve differently during a landslide event in carbonate rock. Wall rock permeability controls pore pressure evolution and the efficiency of thermal decomposition. Thermal decomposition in the Jiweishan rockslide was limited but not negligible. [ABSTRACT FROM AUTHOR]

To understand the factors that make certain areas especially prone to landslides, statistical approaches are typically used. The interpretation of statistical results in areas characterised by complex geological and geomorphological patterns can be challenging, and this makes the understanding of the causes of landslides more difficult. In some cases, landslide inventories report information on the state of activity of landslides, adding a temporal dimension that can be beneficial in the analysis. Here, we used an inventory covering a portion of Northwestern Turkey to demonstrate that active and relict landslides (that is, landslides that occurred in the past and are now stabilised) could be related to different triggers. To do so, we built two landslide susceptibility models and observed that the spatial patterns of susceptibility were completely distinct. We found that these patterns were correlated with specific controlling factors, suggesting that active landslides are regulated by current rainfalls while relict landslides may represent a signature of past earthquakes on the landscape. The importance of this result resides in that we obtained it with a purely data-driven approach, and this was possible because the active/relict landslide classification in the inventory was accurate. [ABSTRACT FROM AUTHOR]

In tectonically active steep mountain belts, such as those in west Sichuan in China, frequent landslide disasters can occur during the rainy season. High-locality landslides often initiate with the failure of fractured rock masses or regolith near the ridge of a high and steep slope. Often, these events occur suddenly in the sense that people downslope are caught by surprise. High-locality landslides can be destructive owing to the large momentum and entrainment potential of the moving mass. Increasing attention has been given to these events since the 2008 Wenchuan earthquake. Indeed, slope ridges are particularly susceptible of topographic amplification of the seismic shaking, resulting in mechanical weakening that predisposes them to enhanced weathering and rain-triggered failures years or decades after the mainshock. Risk reduction in such cases must begin with a systematic surveying of the ridges to identify criticalities. Then, quantitative (numerical) approaches must be used to evaluate volumes and describe the movement. Risk assessments can then be produced, and mitigations suggested. Here, we describe the Tonghua landslide in Li County, which is currently in a creeping stage but threatens critical infrastructures and dwellings. We monitored the site for 3 years and identified additional potentially unstable areas before performing physically based modeling and hazard zonation. Our results could be useful in decision-making for risk reduction. [ABSTRACT FROM AUTHOR]

The patterns and controls of the transient enhanced landsliding that follows strong earthquakes remain elusive. Geostatistical models can provide clues on the underlying processes by identifying relationships with a number of physical variables. These models do not typically consider thermal information, even though temperature is known to affect the hydro-mechanical behavior of geomaterials, which, in turn, controls slope stability. Here, we develop a slope unit-based multitemporal susceptibility model for the epicentral region of the 2008 Wenchuan earthquake to explore how land surface temperature (LST) relates to landslide patterns over time. We find that LST can explain post-earthquake landsliding while it has no visible effect on the coseismic scene, which is dominated by the strong shaking. Specifically, as the landscape progressively recovers and landslide rates decay to pre-earthquake levels, a positive relationship between LST and landslide persistence emerges. This seems consistent with the action of healing processes, capable of restoring the thermal sensitivity of the slope material after the seismic disturbance. Although analyses in other contexts (not necessarily seismic) are warranted, we advocate for the inclusion of thermal information in geostatistical modeling as it can help form a more physically consistent picture of slope stability controls. [ABSTRACT FROM AUTHOR]

Major earthquakes in steep orogens can trigger extensive landsliding. Most of the landslide bodies come to rest high on the slopes, but subsequent rainfalls can easily remobilize them. Sharp peaks in landslide rates are systematically observed after major earthquakes, followed by rapid decays to background levels in just several years. Yet, the migration of coseismic debris into tributary channels and rivers remains poorly understood. We collected 12 years of observations of the 2008 Wenchuan earthquake's epicentral region in China and evaluated that debris flows and fluvial transport could only evacuate a small portion of coseismic debris, while over 70% of it had stabilized on the hillslopes. Coseismic debris may remain in the orogen for a long time, but estimates based on initial landslide abundance and sediment export are hampered by uncertainties in the debris fate throughout the earthquake cycle. Plain Language Summary: Strong earthquakes leave a trail of destruction that lasts much longer than the dramatic minutes of strong ground motion. Earthquakes shake the mountains, causing extensive landsliding that delivers huge amounts of debris along the slopes and in drainage channels. This debris is loose and unconsolidated, prone to generating subsequent landslides and debris flows. We have monitored the epicentral area of the magnitude 7.9 Wenchuan Earthquake (2008, China) for 12 years to study the evolution of landslide activity in space, time, and characteristics, and track the fate of the debris from the slopes into channels and rivers. We found that the landslide rates have decreased rapidly. After 10 years, they were already comparable to the pre‐earthquake levels. Most of the debris remained on the slopes, though: it stabilized and never moved again. At current rates, the removal of the earthquake‐generated debris from the landscape through landsliding may take a long time. Key Points: Despite large amounts of erodible coseismic debris, post‐seismic landslide rates decayed to pre‐earthquake levels in less than a decadeOnly a small proportion of debris has left the orogen so far: over 70% of it has stabilized in place, along the hillslopesWith erosion proceeding at this pace, a residence time of several centuries for the debris can be expected [ABSTRACT FROM AUTHOR]

Strong earthquakes, especially on mountain slopes, can generate large amounts of unconsolidated deposits, prone to remobilization by aftershocks and rainstorms. Assessing the hazard they pose and what drives their movement in the years following the mainshock has not yet been attempted, primarily because multitemporal landslide inventories are lacking. By exploiting a multitemporal inventory (2005–2018) covering the epicentral region of the 2008 Wenchuan Earthquake and a set of conditioning factors (seismic, topographic, and hydrological), we perform statistical tests to understand the temporal evolution of these factors affecting debris remobilizations. Our analyses, supported by a random‐forest susceptibility assessment model, reveal a prediction capability of seismic‐related variables declining with time, as opposed to hydro‐topographic parameters gaining importance and becoming predominant within a decade. These results may have important implications on the way conventional susceptibility/hazard assessment models should be employed in areas where coseismic landslides are the main sediment production mechanism on slopes. Plain Language Summary: Strong earthquakes in mountain regions can trigger thousands of landslides, forming deposits of rock and soil debris along steep slopes. Months to years later, rainstorms may generate debris flows—destructive water‐debris mixtures that rush downslope and flood valleys. Scientists use models to estimate the hazard of landslides and debris flows, which are based on accurate maps of the slopes, the type of rock or soil, inventories of known landslides, rainfall trends, and more. Susceptibility and hazard maps are the main product of these models. They are used to predict the probability of a hazardous event occurring at a given location in a given time span. These maps are usually "static," in the sense that they are thought to remain valid for a long time because the data they are based upon (such as the shape of slopes) do not vary much. However, postearthquake landscapes are very dynamic: debris moves downslope, carried by rain or shaken by aftershocks; meanwhile, new landslides occur on some slopes, while others revegetate and stabilize. The overall picture is complex as many variables are involved. We use machine learning to demonstrate that static hazard maps become unable to predict landslides after just a few years, and advocate for the use of frequently updated maps linked to fresh inputs, tracking the location and activity of debris deposits, and old and new landslides. Key Points: We explored the rapidly evolving controls of postseismic debris remobilizationThe increasing importance of hydrological factors and a large amount of channel deposits cause persisting postseismic debris flow occurrencesHazard models need to be frequently updated by timely inventories in order to assess the hazard evolution of postseismic landslides [ABSTRACT FROM AUTHOR]

Frictional shearing along the basal slip surface is the main energy dissipation mechanism in coherent landslides, which undergo little internal deformation during runout. Most landslide bodies, however, deform and break down more or less extensively; thus, only a portion of their potential energy is dissipated through basal shearing. The mineral components of rocks and soils have individual melting temperatures. Therefore, as temperature increases, selective melting will occur in a defined sequence. The product of such melting is termed frictionite. Here, we exploited a sliding block model to investigate the role of selective melting in the evolution of the frictional resistance (and hence mobility) of partially coherent landslides. We recognized three frictional stages, characterized by weakening, strengthening, and melt lubrication. As melting proceeds, a gradual transition from solid friction to viscous flow occurs, which can be modeled in terms of the molten mineral fraction. The chemical composition also evolves and so does its viscosity. Rocks with different mineral proportions (e.g., mafic vs. felsic rocks) will exhibit different frictional evolutions. Our model results are consistent with the recognized role of landslide thickness in defining its mobility. Moreover, the frictional strengthening stage is shown to become irrelevant under high confinement, thereby facilitating higher mobility, or sometimes shifting slip surface if weak layer exists. We also discussed the relevance of some strengthening‐upon‐melting behavior observed at the experimental scale, pointing out the role of the energy conversion coefficient, which is a proxy for landslide coherence. Key Points: Selective melting may occur in rock minerals on the slip surface upon shearing under sufficient stress and shear rateA molten fraction with variable composition defines the solid and molten rock friction as well as the molten rock viscosityLandslide and shear‐zone thicknesses and the energy conversion coefficient control the mobility of partially coherent landslides [ABSTRACT FROM AUTHOR]

Individual, large thrusting earthquakes can cause hundreds to thousands of years of exhumation in a geologically instantaneous moment through landslide generation. The bedrock landslides generated are important weathering agents through the conversion of bedrock into mobile regolith. Despite this, orogen-scale records of surface uplift and exhumation, whether sedimentary or geochemical, contain little to no evidence of individual large earthquakes. We examine how earthquakes and landslides influence exhumation and surface uplift rates with a zero-dimensional numerical model, supported by observations from the 2008 Mw7.9 Wenchuan earthquake. We also simulate the concentration of cosmogenic radionuclides within the model domain, so we can examine the timescales over which earthquake-driven changes in exhumation can be measured. Our model uses empirically constrained relationships between seismic energy release, weathering, and landsliding volumes to show that large earthquakes generate the most surface uplift, despite causing lowering of the bedrock surface. Our model suggests that when earthquakes are the dominant rock uplift process in an orogen, rapid surface uplift can occur when regolith, which limits bedrock weathering, is preserved on the mountain range. After a large earthquake, there is a lowering in concentrations of 10Be in regolith leaving the orogen, but the concentrations return to the long-term average within 10 3 years. The timescale of the seismically induced cosmogenic nuclide concentration signal is shorter than the averaging time of most thermochronometers (>103 years). However, our model suggests that the short-term stochastic feedbacks between weathering and exhumation produce measurable increases in cosmogenically measured exhumation rates which can be linked to earthquakes. [ABSTRACT FROM AUTHOR]

The evolution of the shear resistance at the base of a coherent landslide body can effectively control its dynamic behavior. High‐velocity rotary shear experiments have allowed scientists to explore stress‐strain conditions close to those found in large landslides and faults. These experiments have led to two alternative models being proposed, which describe the evolution of the shear resistance through friction laws that depend either on normal stress or on velocity. Here, we discuss an integrated approach, first proposed to study seismic fault behavior, that reconciles these two models under a single parameter—the power density—which we utilize for the first time to investigate landslide dynamics. Using thermodynamic and process‐based considerations, different soil and rock types can be related to different weakening mechanisms, which in turn can determine different landslide behaviors. Plain Language Summary: In coherent landslides, the shape and structure of the unstable soil or rock mass remains intact while it slides down. Large coherent landslides are relatively uncommon, yet they are of great concern because of their destructive power. The friction at the base of the unstable mass is a fundamental parameter that controls the movement of landslides. It can be estimated through laboratory experiments and is often assumed as a constant value. However, this assumption does not always hold, especially for large and fast‐moving landslides, where friction changes through time, or according to the velocity and thickness of the sliding mass. The dynamic stresses in large coherent landslides and seismic faults are somewhat similar. Geophysicists have proposed the concept of power density to explain the behavior of faults. Here, for the first time, we apply this concept to landslides. We analyze data from 280 published experiments on soils and rocks, showing how the power density correlates with friction for various minerals. By discussing the mechanical and thermodynamic processes that are involved, we provide a framework to link the behavior of coherent landslides to physicochemical parameters using the power density concept. Key Points: A power density‐dependent friction law can be used to describe the runout of coherent landslidesDifferent minerals are associated with different frictional weakening mechanisms, likely determining different landslide dynamicsThe rate of frictional weakening seems sample size dependent: Much faster weakening may occur in landslides than in the laboratory [ABSTRACT FROM AUTHOR]

Critical and residual states are key soil conditions relevant to slope stability. Evaluating the available shear strength in relation to these conditions is crucial for reliable stability analyses. However, limited availability of direct measurements in the usual engineering practice makes such evaluation seldomly straightforward. The issue is sometimes alleviated by utilising empirical correlations with soil index properties, more easily determinable, yet much care is needed in applying generic correlations to specific materials, as the related uncertainties might override their predictive capability. By analysing soil samples from the Dobkovičky landslide in Czech Republic, we discuss the extent to which some established correlations can be misleading, but also that relationships calibrated on site-specific data are not necessarily performing better. We then demonstrate that empirical models may fail to capture correlations if the sample set is rather homogeneous and noise from reasonable experimental uncertainties is introduced. Finally, we provide some guidelines on the use of different soil strength parameters, laboratory tests, and empirical relationships for slope stability analyses in engineering practice. [ABSTRACT FROM AUTHOR]

The 2008 Wenchuan earthquake (China, Mw 7.9) highlighted the importance of assessing and mitigating the hazards from co-seismic landslides and landslide dams. The seismic shaking triggered hundreds of thousands of landslides, about 800 of which dammed the course of rivers. To understand whether distinctive factors concurred with the river-damming events, we analyzed the spatial patterns of the river-damming landslides and the non-damming landslides separately, with reference to a number of possible controlling factors. Then, we quantified the significance of these factors using the weight of evidence method, and we used the results to perform a susceptibility assessment in a portion of the earthquake-affected region to verify the effectiveness of the method. We find that the distance to the fault surface rupture, peak ground acceleration (PGA) and lithology play a controlling role for co-seismic landslides of any type. The occurrence of river-damming landslides, rather than by a specific lithology or topography, is more related to hydrological factors, while topographic controls (slope, internal relief and terrain roughness) are more significant for the non-damming landslides. [ABSTRACT FROM AUTHOR]

Large earthquakes initiate chains of surface processes that last much longer than the brief moments of strong shaking. Most moderate‐ and large‐magnitude earthquakes trigger landslides, ranging from small failures in the soil cover to massive, devastating rock avalanches. Some landslides dam rivers and impound lakes, which can collapse days to centuries later, and flood mountain valleys for hundreds of kilometers downstream. Landslide deposits on slopes can remobilize during heavy rainfall and evolve into debris flows. Cracks and fractures can form and widen on mountain crests and flanks, promoting increased frequency of landslides that lasts for decades. More gradual impacts involve the flushing of excess debris downstream by rivers, which can generate bank erosion and floodplain accretion as well as channel avulsions that affect flooding frequency, settlements, ecosystems, and infrastructure. Ultimately, earthquake sequences and their geomorphic consequences alter mountain landscapes over both human and geologic time scales. Two recent events have attracted intense research into earthquake‐induced landslides and their consequences: the magnitude M 7.6 Chi‐Chi, Taiwan earthquake of 1999, and the M 7.9 Wenchuan, China earthquake of 2008. Using data and insights from these and several other earthquakes, we analyze how such events initiate processes that change mountain landscapes, highlight research gaps, and suggest pathways toward a more complete understanding of the seismic effects on the Earth's surface. Plain Language Summary: Strong earthquakes in mountainous regions trigger chains of events that modify mountain landscapes over days, years, and millennia. Earthquake shaking can cause many tens of thousands of landslides on steep mountain slopes. Some of these sudden slope failures can block rivers and form temporary lakes that can later collapse and cause huge floods. Other landslides move more slowly, in some cases in a stop‐start fashion during heavy rains or earthquake aftershocks. Debris from these landslides can clog channels, and during heavy rainfall, the debris can be transported downstream for many kilometers with catastrophic consequences. New landslides tend to happen more frequently than usual for months to years following an earthquake because the strong ground shaking has fractured and weakened the slopes. Other effects of large earthquakes can last, in various forms, over geologic time scales. Over the past two decades, our understanding of these issues has advanced because of the detailed study of the 1999 Chi‐Chi earthquake in Taiwan and the 2008 Wenchuan earthquake in China. We compile and discuss the results of research on these and other earthquakes and explain what we have learned, what we still need to know, and where we should direct future studies. Key Points: Coupled surface processes initiated by strong seismic shaking are important hazards in mountain landscapesEarthquake‐induced landslides pose challenges to hazard and risk assessment, management, and mitigationMultidisciplinary approaches further the understanding of the earthquake hazard cascade, yet challenges remain [ABSTRACT FROM AUTHOR]

We release two datasets that track the enhanced landsliding induced by the 2008 Mw 7.9 Wenchuan earthquake over a portion of the Longmen Mountains, at the eastern margin of the Tibetan Plateau (Sichuan, China). The first dataset is a geo-referenced multi-temporal polygon-based inventory of pre- and coseismic landslides, post-seismic remobilisations of coseismic landslide debris and post-seismic landslides (new failures). It covers 471 km 2 in the earthquake's epicentral area, from 2005 to 2018. The second dataset records the debris flows that occurred from 2008 to 2017 in a larger area (∼17000 km 2), together with information on their triggering rainfall as recorded by a network of rain gauges. For some well-monitored events, we provide more detailed data on rainfall, discharge, flow depth and density. The datasets can be used to analyse, on various scales, the patterns of landsliding caused by the earthquake. They can be compared to inventories of landslides triggered by past or new earthquakes or by other triggers to reveal common or distinctive controlling factors. To our knowledge, no other inventories that track the temporal evolution of earthquake-induced mass wasting have been made freely available thus far. Our datasets can be accessed from https://doi.org/10.5281/zenodo.1405489. We also encourage other researchers to share their datasets to facilitate research on post-seismic geological hazards. [ABSTRACT FROM AUTHOR]

On August 28, 2017, a large rock avalanche occurred in Pusa, a village in the County of Nayong (Guizhou Province, China). About 500,000 m3 of rock detached from a mountain ridge, slid over debris from earlier landslides and buried several buildings. The rock mass, heavily fragmented, eventually formed a deposit of 800,000 m3, up to 4 m thick. Twenty-six fatalities and 9 people missing were reported. Based on site investigation, live footage, UAV photography, GBSAR monitoring, historical records and remote sensing imagery, we describe characteristics of failure and runout of the avalanche. Extensive coal mining under the slope had probably weakened and fractured the rock mass, enhancing climate-induced weathering. Failure was anticipated by cracks opening and minor rockfalls in the past decade, which intensified in the last rainy season. [ABSTRACT FROM AUTHOR]

Strong earthquakes in mountainous areas can trigger a large number of landslides that generate deposits of loose and unconsolidated debris across the landscape. These deposits can be easily remobilised by rainfalls, with their movement frequently evolving into catastrophic debris flows and avalanches. This has been the fate of many of the 200,000 co-seismic deposits generated by the 2008 Mw 7.9 Wenchuan earthquake in Sichuan, China. Here we present one of the first studies on the post-seismic patterns of landsliding through a detailed multi-temporal inventory that covers a large portion of the epicentral area (462.5 km2). We quantify changes of size-frequency distribution, active volumes and type of movement. We analyse the possible factors controlling landslide activity and we discuss the significance of mapping uncertainties. We observe that the total number of active landslides decreased with time significantly (from 9189 in 2008 to 221 in 2015), and that post-seismic remobilisations soon after the earthquake (2008-2011) occurred stochastically with respect to the size of the co-seismic deposits. Subsequently (2013-2015), landslide rates remained higher in larger deposits than in smaller ones, particularly in proximity to the drainage network, with channelised flows becoming comparatively more frequent than hillslope slides. However, most of the co-seismic debris remained along the hillslopes and are largely stabilised, urging to rethink the way we believe that seismic activity affects the erosion patterns in mountain ranges. [ABSTRACT FROM AUTHOR]

We release two datasets that track the enhanced landsliding induced by the Mw 7.9 2008 Wenchuan earthquake over a portion of the Longmen mountains, at the eastern margin of the Tibetan plateau (Sichuan, China). The first dataset is a geo-referenced multi-temporal polygon-based inventory of pre- and coseismic landslides, post-seismic remobilisations of coseismic landslide debris, and post-seismic landslides (new failures). The inventory covers 462.5 km² in the earthquake's epicentral area, from 2005 to 2015. The second dataset records the debris flows that occurred from 2008 to 2017 in a larger area (~ 17,000 km²), together with information on their triggering rainfalls recorded by a network of rain gauges. For some well-monitored event, we provide detailed information on rainfall, discharge, flow depth and density. The datasets can be used to analyse, at various scales, the patterns of enhanced landsliding caused by the earthquake. They can be compared to inventories relative to past or new earthquakes or other triggers to reveal common or distinctive controlling factors. To our knowledge, no other inventories that track the temporal evolution of earthquake-induced mass wasting have been made freely available thus far. Our datasets are available at https://doi.org/10.5281/zenodo.1405490. We also encourage other researchers to share their datasets to facilitate research on post-seismic geological hazards. [ABSTRACT FROM AUTHOR]

Rock avalanches represent a serious risk for human lives, properties, and infrastructures. On June 24, 2017, a catastrophic landslide destroyed the village of Xinmo (Maoxian County, Sichuan, China) causing a large number of fatalities. Adjacent to the landslide source area, further potentially unstable masses were identified. Among them, a 4.5-million m3 body, displaced during the landslide event by about 40 m, raised serious concerns. Field monitoring and a reliable secondary risk assessment are fundamental to protect the infrastructure and the population still living in the valley. In this framework, the use of distinct element methods and continuum model methods to simulate the avalanche process was discussed. Various models (PFC, MatDEM, MassMov2D, Massflow) were used with the aim of reproducing the Xinmo landslide and, as predictive tools, simulating the kinematics and runout of the potentially unstable mass, which could cause a new catastrophic event. The models were all able to reproduce the first-order characteristics of the landslide kinematics and the morphology of the deposit, but with computational times differing by several orders of magnitude. More variability of the results was obtained from the simulations of the potential secondary failure. However, all models agreed that the new landslide could invest several still-inhabited buildings and block the course of the river again. Comparison and discussion of the performances and usability of the models could prove useful towards the enforcement of physically based (and multi-model) risk assessments and mitigation countermeasures. [ABSTRACT FROM AUTHOR]

On 8th August 2017, a magnitude Ms 7.0 earthquake struck the County of Jiuzhaigou, in Sichuan Province, China. It was the third Ms ≥ 7.0 earthquake in the Longmenshan area in the last decade, after the 2008 Ms 8.0 Wenchuan earthquake and the 2013 Ms 7.0 Lushan earthquake. The event did not produce any evident surface rupture but triggered significant mass wasting. Based on a large set of pre- and post-earthquake high-resolution satellite images (SPOT-5, Gaofen-1 and Gaofen-2) as well as on 0.2-m-resolution UAV photographs, a polygon-based interpretation of the coseismic landslides was carried out. In total, 1883 landslides were identified, covering an area of 8.11 km2, with an estimated total volume in the order of 25-30 × 106 m3. The total landslide area was lower than that produced by other earthquakes of similar magnitude with strike-slip motion, possibly because of the limited surface rupture. The spatial distribution of the landslides was correlated statistically to a number of seismic, terrain and geological factors, to evaluate the landslide susceptibility at regional scale and to identify the most typical characteristics of the coseismic failures. The landslides, mainly small-scale rockfalls and rock/debris slides, occurred mostly along two NE-SW-oriented valleys near the epicentre. Comparatively, high landslide density was found at locations where the landform evolves from upper, broad valleys to lower, deep-cut gorges. The spatial distribution of the coseismic landslides did not seem correlated to the location of any known active faults. On the contrary, it revealed that a previously-unknown blind fault segment—which is possibly the north-western extension of the Huya fault—is the plausible seismogenic fault. This finding is consistent with what hypothesised on the basis of field observations and ground displacements. [ABSTRACT FROM AUTHOR]

Bedding-controlled landslides in alternated mudstone and sandstone beds in cataclinal slopes are common in the Sichuan basin and in the Three Gorges area in China. They are characterised by very gentle dip angles of the beds (<10°), and usually exhibit slow creep movements throughout the year. However, during the rainy season, they can have sudden accelerations and undergo large displacements. In this work, the influence of saturation degree, displacement rate and stress state on the shear strength of the shear-zone soil was investigated. The results of the displacement-controlled ring-shear tests show a rate-weakening behaviour even at low rates of displacement. Dually, the shear-controlled tests show that the displacement rate can increase dramatically in response to a slight increase of the shear stress. The threshold stress that triggers large displacement is equal to the rate-dependent residual shear strength of the soil. [ABSTRACT FROM AUTHOR]

Landslides of the flow type are among the most destructive mass movements due to their potential high mobility, long runout distance and capacity of entraining further material during movement. Generation of positive pore pressure excess is considered to be a fundamental triggering mechanism which, in some cases, can produce stress state instability and fluidization of both fine-grained and granular deposits, resulting in extremely fast and catastrophic events. Several experimental works and theoretical studies have been carried out so far to investigate the initiation mechanism and runout of flowslides. However, efforts are still needed to improve the understanding, for instance, of the role of the soil grading on the initiation and evolution of the movement. To this aim, a series of flume tests has been carried out using granular mixtures of coarse and small particles. High temporal resolution data acquisition has been used to investigate the onset of failure in terms of pore pressures, surface and internal displacements and vibration signals. By means of shear-controlled triaxial tests and permeability tests, the hydraulic conductivity has been found to be a controlling factor in the landslide initiation, whereas the uniqueness of the instability line – the lower bound of potentially unstable stress states – regardless of the soil grading, suggests that pore pressure measurement in the field can serve as a reliable indicator in early-warning systems. [ABSTRACT FROM AUTHOR]

At 5:38 am on the 24th June, 2017, a catastrophic rock avalanche destroyed the whole village of Xinmo, in Maoxian County, Sichuan Province, China. About 4.3 million m of rock detached from the crest of the mountain, gained momentum along a steep hillslope, entrained a large amount of pre-existing deposits, and hit the village at a velocity of 250 km/h. The impact produced a seismic shaking of ML = 2.3 magnitude. The sliding mass dammed the Songping gully with an accumulation body of 13 million m. The avalanche buried 64 houses; 10 people were killed and 73 were reported missing. The event raised great concerns both in China and worldwide. Extensive field investigation, satellite remote sensing, UAV aerial photography, and seismic analysis allowed to identify the main kinematic features, the dynamic process, and the triggering mechanism of the event. With the aid of ground-based synthetic aperture radar monitoring, the hazard deriving from potential further instabilities in the source area has been assessed. The preliminary results suggest that the landslide was triggered by the failure of a rock mass, which had been already weakened by the M 7.5 Diexi earthquake in 1933. Several major earthquakes since then, and the long-term effect of gravity and rainfall, contributed to the mass failure. The high elevation, slope angle, and vegetation cover in the source area hinder geological field investigation and make hazard assessment difficult. Nonetheless, monitoring and prevention of similar collapses in mountainous areas must be carried out to protect human lives and infrastructures. To this aim, the integrated use of modern high-precision observation technologies is strongly encouraged. [ABSTRACT FROM AUTHOR]

The rock avalanche that destroyed the village of Xinmo in Sichuan, China, on June 24th, 2017, brought the issue of landslide risk and disaster chain management in highly seismic regions back into the spotlight. The long-term post-seismic behaviour of mountain slopes is complex and hardly predictable. Nevertheless, the integrated use of field monitoring, remote sensing and real-time predictive modelling can help to set-up effective early warning systems, provide timely alarms, optimize rescue operations and perform secondary hazard assessments. We believe that a comprehensive discussion on post-seismic slope stability and on its implications for policy makers can no longer be postponed. [ABSTRACT FROM AUTHOR]

Landslide initiation and dynamics are approached with different methods according to the scale of investigation. Individual landslides are typically described mechanistically, relying on the known coupling between the hydrological input – via atmosphere-soil interaction – and the mechanical response. As the scale increases, fully-coupled hydro-mechanical approaches gradually give way to simpler sequential couplings of hydrological and infinite slope or rigid block models, and finally to geostatistical models. At any scale, while the role of temperature in controlling evapotranspiration and thus the hydrological balance is well recognised, direct thermo-mechanical couplings are systematically neglected unless changes in water phase are involved. This contrasts with abundant experimental evidence of a fully-coupled thermo-hydro-mechanical behaviour of most geomaterials, even in ranges of temperature naturally experienced at the ground surface or in the near subsurface. Here, we review temperature-dependent processes that are potentially relevant to slope stability, focusing in particular on clayey slopes in temperate and warm regions. Our thought-provoking hypothesis is that temperature fluctuations and trends induced by climate change may exert, in short to long terms, a hydro-mechanical forcing on slopes (by altering permeability, water retention capacity, compressibility, shear strength). Together with other known effects (such as altered precipitation patterns and changes in land use), they could affect landslide activity and the distribution and frequency of slope failures. To verify this hypothesis across the scales, systematic field monitoring of temperature-related variables is necessary, together with geostatistical analyses entailing thermal remote sensing products. At the same time, fully-coupled approaches need to be upscaled to permit physically-based catchment- or regional-scale studies accounting for appropriate temperature-related variables and the inherent heterogeneity in materials and boundary conditions. [ABSTRACT FROM AUTHOR]

Coastal retreat is a non-recoverable phenomenon that—together with a relevant proneness to landslides—has economic, social and environmental impacts. Quantitative data on geological and geomorphologic features of such areas can help to predict and quantify the phenomena and to propose mitigation measures to reduce their impact. Coastal areas are often inaccessible for sampling and in situ surveys, in particular where steeply sloping cliffs are present. Uses and capability of infrared thermography (IRT) were reviewed, highlighting its suitability in geological and landslides hazard applications. Thanks to the high resolution of the cameras on the market, unmanned aerial vehicle-based IRT allows to acquire large amounts of data from inaccessible steep cliffs. Coupled structure-from-motion photogrammetry and coregistration of data can improve accuracy of IRT data. According to the strengths recognized in the reviewed literature, a three-step methodological approach to produce IRTs was proposed. [ABSTRACT FROM AUTHOR]

Rain‐triggered landslides in loosely packed granular deposits are highly hazardous because of their sudden failure, flow‐like motion, and high mobility. Predicting their initiation and establishing monitoring and early‐warning strategies based on the actual mechanisms of failure, rather than on statistical‐empirical relations, can be challenging. Experiments on artificial granular slopes revealed a systematic instability‐triggering process entailing the internal erosion and seepage‐driven transport of small grains. This rearrangement of matter generates acoustic signals and microseismicity detectable prior to any pore water pressures spikes or macroscopic deformations, which are common proxies for slope stability monitoring. Acoustic emissions are more pronounced in loose assemblies, while they are much weaker in densely packed mixtures, which will not exhibit fluid‐like motion. Acoustic sensors and accelerometers in support to monitoring networks for flow‐like landslides can improve our early warning capabilities, as long as their good performance is confirmed in real‐scale applications. Plain Language Summary: Some landslides initiated by rainfalls and evolving into very fast and destructive fluid‐like movements are hardly predictable because they happen suddenly, with little warning. Traditional monitoring systems might fail to capture precursory signals, and thus, timely alarms cannot always be released. These systems mostly rely on known correlations between the amount and intensity of rainfall and the occurrence of landslides in the past or on the detection of water level and pressure changes by instruments installed within the slopes. However, these changes are often detected late, when the movement is already accelerating dramatically. In our experiments, we found that one of the processes that trigger flow‐like landslides in granular soils is the internal erosion of small soil particles transported by water flowing within the slopes. This produces measurable vibrations (microseismicity) and sounds (acoustic emissions) well before water pressure changes and deformation trends can be identified. The performance of real‐scale acoustic and seismic monitoring systems is still being verified, but we believe that complementing slopes monitoring with acoustic and seismic sensors can be the winning strategy to provide more timely alarms to evacuate people along the landslide paths and save more lives. Key Points: Seismic and acoustic emissions from granular slopes are detected prior to rain‐triggered failure and fluidizationSeismic and acoustic emissions anticipate pore water pressure spikes and macroscopic deformationsMonitoring through seismic and acoustic sensors may improve early warning capabilities for flow‐like landslides in granular slopes [ABSTRACT FROM AUTHOR]

Thick loess deposits are considered problematic soils due to their susceptibility to collapse suddenly and in large volumes upon increase of water content. In the past decades, a large number of landslides occurred in the Loess Plateau in Gansu Province, north-western China, triggered by the extensive irrigation. The increase of water content has been identified as a key factor controlling the loess strength. However, the role of long-term saturation and pore fluid chemistry changes has not been investigated systematically. This paper reports on an experimental study on loess samples from Heitai loess terrace (Yongjing, Gansu) carried out through chemical analyses, oedometer and ring shear tests. The natural pore fluid was found to be a concentrated saline solution in unsaturated soil condition. Upon saturation, the pore ion concentration drop can contribute to shear strength loss in the clay component and volume decrease. A prolonged exposure to the irrigation water might facilitate cement dissolution, which could result in further weakening. [ABSTRACT FROM AUTHOR]

The 2008 M w 7.9 Wenchuan Earthquake (Sichuan, China) was possibly the largest and most destructive recent earthquake as far as the geo-hazards are concerned. Of the nearly 200,000 landslides triggered originally, many remobilized within a few years after the initial event by rainfall, which often caused catastrophic debris flows. The cascades of geo-hazards related to the Wenchuan Earthquake motivated research worldwide to investigate the triggering and mechanisms of co-seismic landslides, their rainfall-induced remobilization, the generation of debris flows, the evolution of their controlling factors, and the long-term role of earthquakes in shaping the topography. On the eve of the 10th anniversary of the 2008 Wenchuan Earthquake, we present a short review of the recent advances in these topics, discuss the challenges faced in the earthquake-related geo-hazards mitigation practice, and suggest priorities and guidelines for future research. [ABSTRACT FROM AUTHOR]

Earthquakes alter the topography of mountain ranges by shortening and thickening the crust, while also causing erosion via co-seismic landsliding. For single large (>Mw7) earthquakes, co-seismic landslide volumes can exceed the volume of rock uplifted by the earthquake. Hence, large earthquakes are hypothesised to generate rock uplift, but minimal (or no) surface uplift. Surface uplift of mountains is affected by existing regolith limiting the amount of bedrock erosion by landslides, rock uplift by small earthquakes (that do not produce landslides), inter-seismic erosion, and a-seismic rock uplift, hence the role of earthquakes in generating surface uplift of mountains is poorly constrained. Observations of a post seismic multi-temporal landslide inventory of the 2008 Wenchuan earthquake demonstrate that landslide deposits are likely to remain within the Longmen Shan for longer than previously assumed. We demonstrate the importance of persistent regolith and aseismic uplift to surface uplift by using a dimensionless seismic volume balance model. Regolith generated by large earthquakes limits exhumation rates over 102-103 years because smaller landslides remobilise existing regolith rather than eroding bedrock, creating a depth-dependent co-seismic landslide regolith production function (CLRPF). Applying this model to the Longmen Shan in China reveals that 42% of the regolith generation is by co-seismic landsliding. We varied the proportion of rock uplift by earthquakes to a-seismic processes, demonstrating that stochastic rock uplift and CLRPF leads to statistically significant differences in the variability of exhumation rates measured across cosmogenic timescales. To test this model result, we analysed a global database of detrital cosmogenic nuclides from a range of tectonic settings, demonstrating that seismically active compressional landscapes have significantly higher variance and skew. The results demonstrate that the influence of earthquakes on the exhumation of mountains extends beyond the timescale of most dating methods (including cosmogenic radionuclide dating) and that average erosion rates calculated by these methods may significantly underestimate erosion rates. [ABSTRACT FROM AUTHOR]