冰湖溃决泥石流的形成、演化与减灾对策

THE INITIATION,MOTION AND MITIGATION OF DEBRIS FLOW CAUSED BY GLACIAL LAKE OUTBURST

本文分析了主要由冰滑坡和冰崩入湖导致的冰湖溃决的机理和条件。进而 ,从气候条件、水文条件、终碛堤、冰湖规模、冰滑坡、沟床特征和固体物质补给等方面分析了冰湖溃决泥石流的形成条件和特点 ,归纳出冰湖溃决泥石流沿程演化的 6种模式 :溃决洪水 -稀性泥石流、溃决洪水 -黏性泥石流、溃决洪水 -稀性泥石流 -黏性泥石流、溃决洪水 -黏性泥石流 -稀性泥石流、溃决洪水 -稀性泥石流 -黏性泥石流 -稀性泥石流和溃决洪水 -黏性泥石流 -稀性泥石流 -洪水。针对冰湖溃决泥石流突发性强、频度低、洪峰高、流量大、流量过程暴涨暴落、破坏力强和灾害波及范围广等特点 ,提出了 7点减灾对策。

This paper discusses conditions and motion changes of debris flow caused by glacial lake outburst flood (GLOF), and also puts forward measures for mitigation of the hazard. Debris flows caused by glacial lake outburst are distributed in mountains like Alps, Andes, Tianshan, Himalaya and mountains in the Qinghai-Xizang Plateau. The GLOF is precondition of generation of GLOF caused debris flow. Weather changes and the consequent accumulation, ablation, advance and retreat of glacier are close to the formation of such debris flow. Normally, the GLOF happens in warm seasen. Outbursts are mainly caused by under-cutting and erosion of over flow induced by glacier slides and avalanches, and waves striking and abrupt elevation of water level. Some events are generated by melting of buried ice and pipe infiltration. Outburst is determined by hydrologic conditions that can be expressed as: H _1> H _0, outburst; H _1< H _0 and ( H _1+ H _2 )> H _0, possible outburst; ( H _1+ H _2)< H _0, no outburst. The major influencing factors involve terminal moraine, marine lake glacier, slides and channel slope. It is revealed that the slope of channel is very important in debris flow initiation and motion processes. Statistics show that the bed in 30‰～ 50‰ satisfies the sub-viscous debris flow initiation and large then 50‰ with plentiful loose earth satisfies the viscous debris flow initiation. The loose earth on both sides and bed are crucial to the formation and feature of debris flow. The changing models of GLOF to debris flow and features of debris flow can be concluded into 6 patterns. Some mitigation measures are proposed in the end, such as evaluating stability of moraine dams and analyzing risk of glacial lakes outburst, forecasting and warning of the debris flows, remote sensing monitoring on potentially dangerous glacial lakes, artificial lowing lake level and stabilizing dangerous moraine dams, dangerous degree zoning of glacial lake outburst regions, post disaster rescuing program, setting up disaster reduction decision system and management system for organizing disaster mitigation.