Debris avalanche

A very rapid downslope movement of fragmented rock and soil, often involving large volumes and traveling far beyond the source slope.

Landslide: The downslope movement of rock, soil, or debris under gravity. Debris avalanches are a rapid, highly fragmented type of landslide.
Volcanic flank collapse: The sudden gravitational failure of part of a volcano’s side. Volcanic flank collapse can generate exceptionally large debris avalanches.
Mount St. Helens: An active volcano in Washington State that underwent a major lateral eruption in 1980. Its 1980 north-flank collapse produced a vast debris avalanche.
Debris-avalanche deposit: A chaotic accumulation of rock and soil left by a debris avalanche. Its hummocky terrain and mixed blocks can preserve evidence of the event.
Slope failure: The loss of stability that causes a slope to move downslope. A debris avalanche begins when a slope or volcanic flank loses stability.
Earthquake: The sudden release of energy in Earth’s crust that produces seismic waves. Strong shaking can trigger slope failures that become debris avalanches.
1980 Mount St. Helens eruption: A major volcanic eruption on May 18, 1980, following collapse of Mount St. Helens’ north flank. The eruption began with a debris avalanche that exposed pressurized magma.
Lahar: A rapidly moving mixture of volcanic debris and water flowing down a volcano. Debris avalanches can transform into lahars when they mix with water.
Rock fragmentation: The breaking of rock into smaller pieces through physical processes. Fragmentation helps turn a coherent slide into a mobile avalanche.
Volcanic eruption: The release of magma, gas, and other material from a volcano. Eruptive activity can weaken volcanic slopes before catastrophic collapse.

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