CoachA flank collapse is the failure of a large part of the flank of a volcano, which slides away under its own weight. When the moving mass breaks up and runs out fast, as a flow of blocks and rubble that can travel far beyond the foot of the volcano, it is a debris avalanche. When it moves slowly, as large blocks rotating on faults rooted in a deep décollement and staying near the volcano, it is a slump.
