Flume tests to study the initiation of huge debris flows after the Wenchuan earthquake in S-W China

The experimental results showed that the initiation mechanism of debris flows for gentle slopes and steep slopes was different. On steeper slope, incision by run-off water was very rapid initiating directly the start of a debris flow. The debris flow volume increased rapidly by a chain of subsequent cascading processes starting with collapses of the side walls, damming and breaching leading to a rapid widening of the erosion channel. At gentler slopes less intensive run-off incision caused an accumulation of material down slope, which, after saturation, failed as shallow slides transform in a second stage into debris flows. It was demonstrated that the slope was the dominant factor in controlling the scale of the debris flows while the effect of discharge on erosion and the size of the debris flows was less clear.