Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> On 22 March 2021, an approximately 50 Mm<span class="inline-formula"><sup>3</sup></span> ice-rock avalanche occurred from 6500 m a.s.l. in the Sedongpu basin, southeastern Tibet. The avalanche transformed into a highly mobile mass flow which temporarily blocked the Yarlung Tsangpo river. The avalanche flow lasted <span class="inline-formula">∼</span> 5 min and produced substantial geomorphological reworking. This event, and previous ones from the basin, occurred concurrently with, or shortly after, positive seasonal air temperature anomalies. The occurrence of future large mass flows from the basin cannot be ruled out, and their impacts must be carefully considered given implications for sustainable hydropower and associated socioeconomic development in the region.

Highlights

  • Catastrophic mass flows originating from the mountain cryosphere can cause hazard and risk cascades that result in widespread loss of life, destruction of property, and significant geomorphological reworking (Haeberli et al, 2004; Jacquemart et al, 2020; Kääb et al, 2021; Shugar et al, 2021)

  • Data and Methods The basin’s recent event history led to the installation of time-lapse optical/thermal cameras and an automatic weather station (AWS) at the exit of the basin in September-October 2019 (3 hours interval transmitted by the Inmarsat maritime satellite system) for the purpose of obtaining photographic and meteorological evidence of future mass flows and their timing, and a Campbell CS477 radar-based water level monitoring system at Gyala, which is located on the Yarlung Tsangpo ~6 km 65 upstream of the exit of the Sedongpu basin (Fig. 1b) to provide early warning and a real-time (10 min interval) record of water level and, by implication, flow impedance in the case of future blockages

  • Our data and accompanying analysis provide insight into the source, process, magnitude and impacts of the massive 22 190 March 2021 ice-rock avalanche which originated in the Sedongpu basin and temporarily dammed the Yarlung Tsangpo river

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Summary

Introduction

Catastrophic mass flows originating from the mountain cryosphere can cause hazard and risk cascades that result in widespread loss of life, destruction of property, and significant geomorphological reworking (Haeberli et al, 2004; Jacquemart et al, 2020; Kääb et al, 2021; Shugar et al, 2021). The Sedongpu basin (29.80°N, 94.92°E) in Nyingchi prefecture, PRC, has a history of large avalanches and low-angle glacier detachments which have transformed into powerful debris flows in the southeastern Tibetan Plateau (Tong et al, 2019; Chen et al, 2020; Wang et al, 2020; Kääb et al, 2021). 50 2017 and into 2018, and the detachment of the tongue of Sedongpu Glacier in two separate events with a total of ~130 Mm3 on 17/18 October and 29 October 2018 (Kääb et al, 2021) Both detachments in 2018 transformed into debris flows; the earlier detachment blocked the Yarlung Tsangpo for ~60 hours, and the rapid rise in upstream water level damaged or seriously threatened roads, power lines, hydropower stations, and other riverside infrastructure and prompted relocation of more than. We utilise in-situ field investigations, highresolution satellite imagery and digital elevation models (DEMs) of difference, seismic records, and meteorological data to analyse the evolution of the event and its impact, discuss potential drivers, and briefly reflect on implications for the sustainable development of the region

Data and Methods
Field observations of March 2021 avalanche and river blockage
Possible drivers for the 2021 ice-rock avalanche
Conclusions and Implications
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