Landslide or Debris Avalanche
A debris avalanche is the sudden catastrophic collapse (landslide) from an unstable side of a volcano.
Many volcanic cones are steep sided and unstable due to rapid growth of the cone. Rising magma, earthquakes, weakening due to hydrothermal alteration and heavy rain can trigger a debris avalanche of this unstable material. Avalanched material follows valleys as it moves down the side of the volcano under the force of gravity. Debris avalanches can be wet, dry or both, and if wet, an avalanche may evolve and continue to flow further down slope as a lahar.