pyroclastic flow

Volcanology
Fluid avalanche of turbulently mixed ash, lava and or rock fragments, and air, that flows down the flanks of a volcano, driven by gravity. Pyroclastic flows are usually very hot and highly destructive.

Pyroclastic flow travelling down the Krasak ravine at Merapi volcano on 27 May 2006.

Pyroclastic flow travelling down the Krasak ravine at Merapi volcano on 27 May 2006.
The billowing ash could of the advancing pyroclastic flow.

The billowing ash could of the advancing pyroclastic flow.
Merapi seen from the area of Kaliadem with the fresh deposits of a pyroclastic flow (June 06) in the foreground. This flow killed two people trapped inside a bunker that became buried under the hot deposit.

Merapi seen from the area of Kaliadem with the fresh deposits of a pyroclastic flow (June 06) in the foreground. This flow killed two people trapped inside a bunker that became buried under the hot deposit.
A pyroclastic flow is a ground-hugging avalanche of hot ash, pumice, rock fragments, and volcanic gas that rushes down the side of a volcano as fast as 100 km/hour or more. The temperature within a pyroclastic flow may be greater than 500°C, sufficient to burn wood. Once deposited, the ash, pumice, and rock fragments may deform (flatten) and weld together because of the intense heat and the weight of the overlying material.

Facts and figures:
On 8. May 1902 a pyroclastic flow from Montagne Pelée, Martinique, caused the worst volcanic disaster of the 20th century. 28'000 people perished in the city of St. Pierre, located 7 km from the volcano's summit

Related keywords (4):

ash - base surge - debris avalanche - explosive
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