Formation mechanism and disaster characteristics of debris flow in the Tianmo gully in Tibet
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摘要: 西藏林芝市波密县天摩沟于2007年9月、2010年7月、2010年9月和2018年7月分别发生大型和巨型泥石流，4次泥石流活动均不同程度堵塞主河帕隆藏布，淤埋国道318或摧毁桥梁，堰塞湖淹没村道、溃决造成下游塌岸，给当地居民生命财产尤其是交通干道造成极大危害。文章针对以上4次泥石流活动，采用高分辨率遥感影像，对泥石流发生前的孕灾背景进行解译，同时结合无人机航空摄影和地面调查对天摩沟泥石流形成机制和成灾特征进行了对比分析，得到以下结论：（1）天摩沟内冰川发育，年际变化大，目前泥石流形成的主要方式为岩崩和堵溃，其中2018年和2007年为岩崩引发，2010年为堵溃引发，该沟同时具有冰川泥石流和降雨泥石流的特征。（2）经历了2007年和2010年3次大规模泥石流后，天摩沟内斜坡类物源储量增加了19.6%，绝大部分启动的冰碛物和崩滑物源都转化为泥石流沟道堆积物或冲出沟口。（3）天摩沟2018年泥石流容重为2.10 g/cm3，为黏性泥石流，流速快冲击力强，帕隆藏布河道受到挤压多次变道，历史上最大偏移距离为190 m。（4）2018年7月11日泥石流成因为降雨条件下加剧冰川消融引发主沟沟源右侧岩崩，形成多阵次泥石流，主泥石流体积18×104 m3，淤埋G318近220 m。后续依然具有暴发大型泥石流的可能性，建议进行防治降低其危害程度。Abstract: In September of 2007, July of 2010, September of 2010 and July of 2018, four large or giant debris flows took place in the Tianmo gully in Bomi county of Linzhi in Tibet. Four debris flow activities all blocked the Parlung River to varying degrees, buried the 318 national highway and destroyed bridges. Dammed lakes flooded village roads and caused downstream bank collapses. They caused great damage for the local residents’ life and property, especially the traffic trunk roads. Based on the above four debris flow activities, this paper uses high resolution remote sensing images to interpret the disaster-pregnant environment. Formation mechanism and disaster characteristics of different debris flows are analyzed in combination with the UAV aerial photography and ground investigation. The results show that (1) glaciers in the Tianmo gully is rich, and its interannual change is big. Formation of the primary debris flows in the Tianmo gully is rockfall (debris flows in 2007 and 2010) and dam breaking (debris flow in 2010). The Tianmo gully is characterized by glacial debris flow and rainfall debris flow at the same time. (2) After three large-scale debris flows in 2007 and 2010, the slope material source reserve in the Tianmo valley increased by 19.6 %, and most of the activated moraine and landslide material sources were converted into debris deposits in the debris flow gully or out of the gully mouth. (3) In 2018, the mass density of debris flow in the Tianmo gully is 2.10 g/cm3, and it is a viscous debris flow. The debris flow has a strong impact force and squeezes the Parlung river channel for many times. The maximum deviation distance in history is 190 m. (4) The debris flow on July 11 of 2018 is formed by rockfall on the right side of the main gully source caused by intensified glacier melting under the rain-fall condition, which has multiple bands. The volume of the main debris flow is 18×104 m3, and buried the G318 for nearly 220 m. The possibility of large-scale debris flows still exist in the future. It is suggested that prevention and controlling of debris flows are effective ways to reduce damage caused by debris flows.
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Key words:
- Tibet /
- Tianmo gully /
- debris flow /
- geological hazards /
- dammed lake /
- remote sensing /
- UVA
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