Cheng Zunlan

The two main mechanisms of Glacier Lake Outburst Flood in Tibet, China

With the global warming, the disasters of Glacier Lake Outburst Flood (GLOF) have taken place frequently in Tibet in recent years and attracted more and more attention. A systematic survey was conducted on the 19 GLOFs in Tibet to study their two main mechanisms. Investigations indicated that all the events occurred in end-moraine lakes, and the outburst occurred partially and instantly. And the breach had the shape of an arc or a trapezoid in overflow outburst and its top width was 3–5 times more than the height. The two main mechanisms of GLOFs in Tibetan end-moraine Lake were overflow and piping, and the overflow mechanism caused by iceberg collapse was dominated in most cases. A formula was proposed to calculate the critical thickness of iceberg tongue that determines the collapse. Granular analysis of the moraine materials revealed that seepage deformation is crucial in the outburst process. Finally, we conducted a case study of the Guangxiecuo Lake to show its possible process of outburst and estimated the peak discharge of the resulted flood.

Debris Flow Dam Formation in Southeast Tibet

Glaciers with their deposits abound in the alpine areas of Southeast Tibet. Large debris flows occur frequently from these deposits and form dams that block streams. In this paper, 3 events of large debris flows reported in Peilong Valley located in Southeast Tibet, and which resulted 2 blocking dams resulted, are discussed in details, focusing on the major factors controlling dam formation. The results shows that the first surge group caused by snow and ice avalanches, ice-lake breaks, and large-scale landslides, with a high peak discharge and high velocity, and an abundance of boulders, are most likely to form blocking dams.Glaciers with their deposits abound in the alpine areas of Southeast Tibet. Large debris flows occur frequently from these deposits and form dams that block streams. In this paper, 3 events of large debris flows reported in Peilong Valley located in Southeast Tibet, and which resulted 2 blocking dams resulted, are discussed in details, focusing on the major factors controlling dam formation. The results shows that the first surge group caused by snow and ice avalanches, ice-lake breaks, and large-scale landslides, with a high peak discharge and high velocity, and an abundance of boulders, are most likely to form blocking dams.

Notice of Retraction Prevention measures of debris flows along the zhamu-motuo highway, Tibet

Motou in Tibet is still the only county site inaccessible by road. A highway to joint Motuo and Zhamu is under constructing and this paper studies the field surveys on debris flow along the road. Because of the deep gorges and steep slopes, the intensive earthquakes and geotectonic movements, as well as the abundant precipitation and loose materials, debris flows are widely distributed along the highway. This paper puts forward some countermeasures to prevent the potential hazard of debris flow.

ANNUAL TEMPERATURE IMPACT ON MORAINE LAKE OUTBURSTS IN TIBET, CHINA

Glacier-lake outburst is common in Tibet. Global warming is expected to increase the frequency of out- burst. This paper attempts to find out the relationship between the outburst and annual temperature varia- tion based on analysis of 16 outburst events in Tibet. Multiyear climate data from meteorological stations in the study area are used. We find that the outbursts are sensitive to acute change in annual temperature. Specifically, the outburst probability increases when average annual temperature rises by more than 0.5°C. Finally, we put forwards an evaluation of the increas- ing risk of potential outburst of glacier lake in Tibet.

Debris Flow Triggered by Ice-Lake Break in Tibet

Debris flow triggered by break of ice -lake is one of special occurrences in frigid alpine areas. In 1981, there was such a debris flow occurring in the Zizangbu Gully on the south slope of the Himalayas, of return period more than 100 years. Through analysis of this very occurrence, the present paper discusses in details its forming condition, initiation mechanism, developing trend, and hazards.