Abstract:

The “20110606” rainstorm(105.9 mm/h)triggered many debris flows in Wangmo County, Guizhou Province. During the hazards, thirtyseven people were killed and fifteen people were lost，and many houses were seriously destroyed. In order to improve the result accuracy of the forecasting and early warning system, based on field investigation and analysis, this paper analysis formation and mechanism of debris flows. The results reveal the following aspects: (1)the tense outbreak of debris flow is an inevitable coupling result of topography, material sources and rainstorms， and the rainfall breaking the 50year record is the main factor for the outbreak of those debris flows, but the steep terrain and soft rock layers, such as sandstones and shales etc., are the important causes;(2) the formation mechanism of debris flows, including bedfailuretriggered debris flow, outbursttriggered debris flow and landslidetriggered debris flow were main types in this area, and the initiation of bedfailuretriggered debris flow was surface flow→erosion gradually→transformed into debris flow, and the initiation of outbursttriggered debris flow was collapse→block→burst→transformed into debris flow, the initiation of landslidetriggered debris flow was rainwater infiltration→failure→fluidization→transformed into debris flow.

Key words: debris flow, formation mechanism, Wangmo, Guizhou