Abstract
The Nyexon Rock Avalanches in the southern Qinghai-Tibet Plateau is a huge scale earthquake-induced slope disaster in the Holocene, the accumulation area has distinct sedimentological characteristics, which is of great significance for studying the intrusion and restraint mechanism during long-distance transportation of large rock avalanches or debris avalanche. This long-distance transportation induced a series of landform types, such as ridges, hills, and ravines; they are widely distributed in all areas and extensively developed shear zones, jigsaw cracks, and other structures within the sedimentary structure. With the analysis of DEM data and geological survey, two main types of basement structures and their transition relationships are distinguished; they play an essential role in the restraining bottom during rock avalanches. In the sedimentary structure, the block facies and mixing facies occupy the main body of the deposition from the center to the distal area. Under the basement restriction, mixing facies are formed between the bottom of the sedimentary layer and the basement sedimentary structure; the shear band is mainly developed along with the mixing facies and basement facies, which is accompanied by basement liquefaction and rheology. A sedimentary facies model is established based on the sedimentary structure sequence of the Nyexon Rock Avalanches transportation. After analyzing the failure mechanism of the rock avalanches, it is believed that in the initial stage of failure, the rock avalanches is transformed into a particle flow that is similar to the debris avalanche, which is restrained by the basement structure and lateral bound; then, an accumulated obstacle highland is formed in the central area after deceleration, making the transportation of the main fluid to deflect quickly.
Highlights
Since the Holocene age, many giant rock slides and rock avalanches have been active in the QinghaiTibet Plateau and the surrounding areas (Hewitt, 1999; Strom and Korup, 2006; Qi et al, 2011; Xu et al, 2012; Wang et al, 2017; Wang et al, 2018; Zeng el al., 2020)
The debris formed after rock avalanche damage is transported from the gentle slope belt in front of the mountain to the flat and open lower reaches of the Angang River valley, during which the transport direction of the rock avalanche abnormally changes; this makes the Nyexon avalanche be a specific case of studying the failure mechanism and intrusion constraints of large rock avalanches
1) The collapse and failure mode of the Nyexon rock avalanche the foundation failure after the earthquake stress is superimposed on the weak foundation that is formed under the control of the fracture in the bottom area of the slope under the action of strong earthquakes, and after its strong collision with the bottom surface and caused rapid fragmentation, the rock mass in the scar area is broken and decomposed to form the initial condition for rockfall debris to be transported by particle flow
Summary
Since the Holocene age, many giant rock slides and rock avalanches have been active in the QinghaiTibet Plateau and the surrounding areas (Hewitt, 1999; Strom and Korup, 2006; Qi et al, 2011; Xu et al, 2012; Wang et al, 2017; Wang et al, 2018; Zeng el al., 2020). During the risk assessment of natural disasters in plateau areas, the kinematic study of large-scale rock slides and rock avalanches with exceptional mobility has received particular attention. The complete intrusion process of large rock avalanches or debris avalanches is rarely recorded. There have been many discussions about the transportation and emplacement of rock avalanches or debris avalanches (Anma et al, 1989; Vallance and Scott, 1997; Takarada et al, 1999; Capra and Macias, 2000; Bernard et al, 2009; Hu et al, 2009; Roverato et al, 2015). There is still no universal mechanism or theory to explain all these types and phenomena (Orwin et al, 2004; Devies et al, 2011)
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