Dynamic Characteristics of the Long Runout Rock-ice Avalanche at High Altitude——A Case from the Zelongnong Basin,Eastern Himalayan Syntaxis,China

Rock-ice avalanches have frequently occurred in the Eastern Himalayan Syntaxis region due to climate change and active tectonic movements.These events commonly trigger catastrophic geohazard chains,including debris flows,river blockages,and floods.This study focuses on the Zelongnong Basin,analyzing the geomorphic and dynamic characteristics of high-altitude disasters.The basin exhibits typical vertical zonation,with disaster sources initiating at elevations exceeding 4000 m and runout distances reaching up to 10 km.The disaster chain movement involves complex dynamic effects,including impact disintegration,soil-rock mixture arching,dynamic erosion,and debris deposition,enhancing understanding of the flow behavior and dynamic characteristics of rock-ice avalanches.The presence of ice significantly increases mobility due to lubrication and frictional melting.In the disaster event of September 10,2020,the maximum flow velocity and thickness reached 40 m/s and 43 m,respectively.Furthermore,continuous deformation of the Zelongnong glacier moraine was observed,with maximum cumulative deformations of 44.68 m in the distance direction and 25.96 m in the azimuth direction from March 25,2022,to August 25,2022.In the future,the risk of rock-ice avalanches in the Eastern Himalayan Syntaxis region will remain extremely high,necessitating a focus on early warning and risk mitigation strategies for such basin disasters.

Evidence of ancient rock-ice avalanches along the China-Bhutan Chomolhari Range,and their implications for demise of the summit

Large-scale rock-ice avalanches resulting from the interaction of tectonics and climate are characterized with high mobility,huge volumes of sediment,and rapid denudation,being a major agent of landscape evolution in high altitude mountainous regions.Specifically,the extreme glaciated slope failures often transform into extraordinarily large and mobile debris flows,resulting in disastrous consequences such as sedimentation and desertification.Due to a dearth of on-site observation data and experimental data collection,our comprehension of the geomorphic and kinematic characteristics of rock-ice avalanches remains poor.Here we report a cluster of ancient rock-ice avalanches spreading along the Chomolhari range of the China-Bhutan Himalayas.By integrating remote sensing image interpretation with detailed field investigations,we demonstrate the geomorphic and sedimentary characteristics of four events among the avalanches.The estimated volumes of the four are 23.73 Mm³,39.69 Mm³,38.43 Mm³,and 38.25 Mm³,respectively.The presence of pre-existing moraines or alluvial fans constrained their movement,resulting in deposition features such as marginal digitated lobes at higher elevations and large depressed areas in the interior.Applying the Savage-Hutter theory,we calculate the basal friction angle and travel angle of these ancient rock-ice avalanches that are both less than 10°,affirming the similarity of these avalanches in the study area to those occurring in other regions.Our study significantly contributes to understanding the geomorphic and kinematic characteristics of rock-ice avalanches in high-altitude mountainous regions,providing valuable insights into their response to the disproportionate growth of Himalayan peaks.

丽江干河坝冰-岩碎屑流地貌、沉积特征与成因机制分析

2004年3月12日,云南省丽江市玉龙雪山南坡发生了较大规模的冰-岩碎屑流型高速远程滑坡。位于斜坡顶部(高程为4337~5350 m)的岩体和冰川块体沿着高陡岩壁向下滑动,在峡谷地形控制下于干河坝内形成体积约11.2×10^(6) m^(3)的滑坡堆积体。本文通过遥感影像分析和现场调查,对干河坝冰-岩碎屑流的地貌与堆积特征进行了详细研究,初步阐释了干河坝冰-岩碎屑流发生的成因机制和运动过程。研究结果表明,节理裂隙发育、源区冻融作用加剧和历史地震效应是此次地震的诱发因素。地形的坡度变化特征、滑体表面“乘船石”结构及内部岩屑的定向排列表明滑坡的运动过程可分为碰撞破碎阶段和扩散堆积阶段。滑坡堆积区广泛分布的“冰川乳坑”和冰水沉积物暗示堆积体底部松散沉积物减阻或是干河坝冰-岩碎屑流具有远程效应的有利因素。深入理解干河坝冰-岩碎屑流的地貌特征及运动学过程,对揭示高速远程滑坡的超强运动机理具有重要的理论意义,同时对我国西部高寒山区大型滑坡灾害的预测预警亦具有现实意义。

The joint driving effects of climate and weather changes caused the Chamoli glacier-rock avalanche in the high altitudes of the India Himalaya

Ice avalanches are one of the most devastating mountain hazards,and can pose a great risk to the security of the surrounding area.Although ice avalanches have been widely observed in mountainous regions around the world,only a few ice avalanche events have been studied comprehensively,due to the lack of available data.In this study,in response to the recent catastrophic rock-ice avalanche(7 February 2021)at Chamoli in the India Himalaya,we used high-resolution satellite images and found that this event was actually a glacier-rock landslide,where the collapse of the rock-ice body was caused by the sliding of the bedrock beneath the glacier,for which the source area and volume loss were about 2.89×10^(5) m^(2) and 2.46×10^(7) m^(3),respectively,corresponding to an average elevation change of about−85 m.Furthermore,visual analysis of the dense time-series satellite images shows that the overall downward sliding of the collapsed rock-ice body initiated around the summer of 2017,and thereafter exhibited clear seasonality(mainly in summer).Meteorological analysis reveals a strong rainfall anomaly in the initiation period of the sliding and a remarkable winter warming anomaly in the 40 days before the collapse.Comparisons of multi-temporal digital elevation models(DEMs)further suggest that the glacier geometry in the collapsed areas was likely changing(i.e.,accelerated surface thinning in the lower part of the glaciers and insignificant change in the upper part),which is consistent with the region-wide climate warming.Finally,by combining the above findings and a geomorphic analysis,we conclude that the rock-ice avalanche event was mainly caused by the joint effects of climate and weather changes acting on a steeply sloping and fracture-prone geological condition.The findings of this study provide new and valuable evidence for the study of slope/glacier instability at high altitudes.This study also highlights that,for the Himalaya and other high mountain ranges,there is an urgent need to identify the glaciers that have a high risk of ice avalanches.