Mechanism of ice avalanche in the Sedongpu sag, Yarlung Zangbo River basin-an experimental study

doi:10.13745/j.esf.sf.2023.2.64

Abstract

Abstract:

In recent years ice avalanche disasters occur frequently in the Tibetan Plateau and the mechanism of ice avalanche has attracted much attention. In this paper, the evolutionary process and controlling factors of ice avalanche in the Sedongpu sag were investigated via multi-stage imaging analysis. In the mechanistic study, shear strength tests were carried out at different temperatures on two types of ice materials: crystalline ice and ice-rock mixture. The crystalline ice sample was prepared by pressing crushed ices into a mold, and the ice-rock mixture was prepared by pressing crushed ices and slate. Imaging analysis results showed that glaciers with 30° or steeper terrain slopes were prone to ice avalanche while strong near-field earthquakes aggravated glacier deformation/fracture, and climate warming was the main reason for the frequent occurrence of ice avalanches in the Sedongpu sag. In the shear test, the shear stress-shear displacement curves for both materials revealed brittle deformation type, while for polycrystalline ice a “secondary peak” appeared under low temperature conditions, indicating refreezing phenomenon. With increasing temperature, the cohesive strength and internal friction angle of both materials decreased linearly, even at an accelerated pace; whilst at the same temperature, the cohesive strength was less and the internal friction angle was greater for ice-rock mixture than for polycrystalline ice. Thus the likely genetic mechanism of ice avalanche is that the rise of temperature leads to decrease of shear strength of the ice/rock shear sliding zone thus its anti-sliding force to trigger an ice avalanche.

Key words: ice avalanche, genetic mechanism, evolution characteristics, shear test, interpretation of remote sensing, Sedongpu sag

CLC Number:

P694
P642.2

TANG Minggao, LIU Xinxin, LI Guang, ZHAO Huanle, XU Qiang, ZHU Xing, LI Weile. Mechanism of ice avalanche in the Sedongpu sag, Yarlung Zangbo River basin-an experimental study[J]. Earth Science Frontiers, 2023, 30(4): 405-417.

Figures/Tables 17

Fig.1 Distribution of glaciers and loose accumulation layers in the Sedongpu sag

Fig.2 Vertical division of the Sedongpu sag

Table 1 Basic experimental parameters for satellite remote sensing image collection of debris flow disaster in the Sedongpu sag

事件	影像时间	影像来源	影像精度	云量/可视程度	波段数	备注
	2012-12-16	Google Earth	约1 m	15%/较好	3
2014年碎屑流事件	2014-10-25	Google Earth	约1 m	<5%/好	3
2014年碎屑流事件	2016-12-22	资源三号-02	2.1 m	0%/好	4	立体像对
2017年10月22日碎屑流堵江事件、 2017年11月3日碎屑流事件	2017-12-16	SPOT	1.5 m	0%/好	4	近红外波段
2017年12月21日碎屑流堵江事件	2017-12-28	Planet4	3.8 m	0%/好	4	近红外波段
2018年1月碎屑流堵江事件	2018-01-29	Planet4	3.8 m	10%~15%/较好	4	近红外波段
2018年7月26日碎屑流事件	2018-9-19	Planet4	3.8 m	30%/一般	4	近红外波段
2018年10月17日碎屑流堵江事件、 2018年10月29日碎屑流堵江事件	2018-10-30	Planet4	3.8 m	15%/较好	4	近红外波段
2018年10月17日碎屑流堵江事件、 2018年10月29日碎屑流堵江事件	2018-11-30	资源三号-02	2.1 m	5%/好	4	立体像对

Fig.3 Evolutionary stages (stages A-E) of a typical ice avalanche disaster event in the Sedongpu sag

Fig.4 Sedongpu sag slope zoning statistics

Table 2 Slope parameters of glaciers in the Sedongpu sag

冰川分区	冰川编号	平均坡度	坡度超过30°面积占比
①	SDP1	27.66°	26.05%
②	SDP2-a	57.66°	50.00%
	SDP2-b	43.80°	45.16%
	SDP2-c	37.87°	44.32%
	SDP2-d	31.0°	35.63%
	SDP2-e	20.27°	13.20%
③	SDP3-a	20.02°	19.67%
	SDP3-a残余	34.61°	45.7%
	SDP3-b	39.51°	46.75%
④	SDP4	26.38°	27.14%
⑤	SDP5	18.52°	8.28%
⑥	SDP6	29.08°	30.91%
⑦	SDP7	16.15°	3.64%
⑧	SDP8	27.16°	24.95%
⑨	SDP9	25.41°	17.90%

Fig.5 Annual variation of temperature, rainfall and ice avalanche occurrence at the Nyingchi meteorological station between 2017-2018

Fig.6 Polycrystalline ice (left) and ice-rock mixture (right) samples

Fig.7 Experimental setup for the YDS-2 Portable Multifunctional Tester for Rock and Soil Mechanical Properties

Fig.8 Sample appearance characteristics after shearing

Fig.9 Shear stress-shear displacement curves for polycrystalline ice at different temperatures a-0.5 ℃;b-10 ℃;c-20 ℃;d-30 ℃;e-40 ℃。

Fig.10 Shear stress-shear displacement curves for ice-rock mixture at different temperatures a-0.5 ℃;b-10 ℃;c-20 ℃;d-30 ℃;e-40 ℃。

Fig.11 Shear strength changes in polycrystalline ice and ice-rock mixture at different temperatures

Fig.12 A simplified model of avalanche ice sliding

Fig.13 Deformation-time curves for ice-rock materials during ice avalanche under different sliding forces

Fig.14 Deformation-time curves for ice-rock materials during ice avalanche under different temperatures

Fig.15 Deformation stages of ice material with temperature rise leading to avalanche

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