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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]

A consequent slope, comprising weak planes in the same dip direction along the slope face, is the most dangerous type of rock slope. Herein, a consequent landslide that occurred on May 5, 2018, in Mabian County, Southwest China, was investigated. This landslide occurred in a region with a complex geological background and strong geological activity and is considered a typical consequent landslide. Field investigations and aerial photographic interpretations revealed that the rock mass slipped along the contact surface of the strongly and moderately weathered rock mass, triggered by continuous rainfall. A depth-integrated continuum method was used to study the dynamic process of the landslide. The applicability of the depth-integrated method was verified by comparing the moving boundary of the landslide extracted from a video with the simulation results. The results show that the velocity of the landslide first increased and then decreased from the top to the bottom of the landslide and reached a maximum of 21 m/s in the middle of the landslide. Based on this method, we predicted the potential danger zones and velocity distribution of unstable masses next to the Mabian landslide. On comparing the calculated results of a depth-integrated continuum method with the Scheidegger method, in the case of the Mabian landslide, a reduction factor λ was added to the Scheidegger formula to achieve a modified formula that determines the velocity of such consequent landslides relatively accurately. This work could provide reference for the study of landslide velocity and disaster prevention. [ABSTRACT FROM AUTHOR]

Jiuzhaigou County in Sichuan, China is renowned for its beautiful natural scenery, recognized as a World Heritage Site and World Biosphere Reserve by the UNESCO. On August 8, 2017, a M s 7.0 (M w 6.5) earthquake struck the region, causing severe damage and casualties. The earthquake triggered thousands of landslides and the collapse of the natural travertine dam impounding Huohua Lake, an important tourist attraction in the reserve. In this study, the dam failure process was investigated through field surveys and remote sensing observations. The propagation of the flood surge was analyzed by Massflow, a depth-integrated continuum model based on the MacCormack-TVD finite difference algorithm. The model results were validated against vegetation maps evaluated from satellite multispectral data recorded before and after the event. The relation between changes in vegetation coverage and computed flooded areas, flow depth, and velocities was elucidated. This study is preliminary in nature, yet the proposed approach could be used, after further validation, in flood hazard and vegetation damage assessments, which may be especially valuable in nature reserves. • A travertine dam collapsed during an earthquake in Jiuzhaigou's natural reserve. • A deep-integrated model was used to simulate the propagation of the flood surge. • A method was proposed to estimate flooded areas based on vegetation damage. [ABSTRACT FROM AUTHOR]