pyroclastic flow


pyroclastic flow
   A fast density current of pyroclastic material, usually very hot, composed of a mixture of gasses and a high concentration of pyroclastic particles in a variety of sizes and composition (ash, pumice, scoria, lava fragments, etc.); produced by the explosive disintegration of viscous lava in a volcanic crater, collapse of an eruption column, or by the explosive emission of gas-charged ash from a fissure and which tends to follow topographic lows (e.g., valleys) as it moves; used in a more general sense than ash flow.
   SW, SN, & GG

Glossary of landform and geologic terms. 2013.

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