pyroclastic flow

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pyroclastic flow,

turbulent, fluidized mixture of rock, volcanic ash, and hot gas that moves like an avalanche away from a volcanic eruption. A pyroclastic flow may contain a mix of rock fragments ranging up to the size of boulders, with the heavier fragments moving along closer to the ground. The hot, expanding gases suspend ash and smaller rock particles, which can then support larger rock fragments; a lack of friction among the particles enables the mixture to travel great distances.

A flow may result from the collapse of the eruption column of a volcano or the collapse of a lava dome or lava flow. Flows that result from an eruption-column collapse are dominated by pumice and move more rapidly; flows can travel as fast as 100 mph (160 kph), reach temperatures that exceed 900°F; (500°C;), and in some instances climb slopes and cross stretches of open water. The speed at which they move, the heat and toxicity of their gases, and the debris that they carry make pyroclastic flows extremely destructive and deadly. A pyroclastic flow from the 1902 eruption of Mt. Pelée on Martinique killed nearly all of the 28,000 inhabitants of Saint-Pierre.

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pyroclastic flow

[¦pī·rə¦klas·tik ′flō]
Ash flow not involving high-temperature conditions.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
It is classified as a complex stratovolcano because its eruptions consist of explosive eruptions as well as pyroclastic flows.
A pyroclastic flow inundation map can be generated by field surveys from the crater rim to the furthest extent of the pyroclastic flow after a volcanic eruption.
17, 1990, for the first time in around 200 years and caused the massive pyroclastic flow, or a fast-moving current of superheated gas and rock, at 4:08 p.m.
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Technology: The software is being used to simulate ash particles in a pyroclastic flow of a volcanic column of ash and smoke.
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These hazards were pyroclastic flow from dome collapse and column collapse, rock avalanches from the collapse of the crater walls, and explosions with ash and rock fallout (see Figure 4).
Key words: caldera, eruption unit, ignimbrite, domes, magmatic eruption, phreatomagmatic eruption, pyroclastic flow, pyroclastic surge.
A team of scientists said Sunday the latest volcanic activity was ''stable...the likelihood of a pyroclastic flow following an explosive eruption is small for the short term.''
The sky lit up for about 10 minutes immediately after the quake, but no pyroclastic flow was observed, it said.