Fragmented rock material formed by a volcanic explosion or ejection from a volcanic vent.

Ash Flow

A turbulent mixture of gas and rock fragments, most of which are ash-sized particles, ejected violently from a crater or fissure. The mass of pyroclastics is normally of very high temperature and moves rapidly down the slopes or even along a level surface.

Pyroclastic Flow

A hot, dry, fast-moving (10-100m/s) and high-density mixture of ash, pumice, rock fragments, and gas formed during explosive eruptions or from the collapse of a lava dome.

Pyroclastic Surge

Turbulent, low-density cloud of hot rock debris and gases that moves over the ground surface at high speed. Lower density than Pyroclastic Flow.

See also: Volcanoes.

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Subjects: Geology