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.

pyroclastic flow

[¦pī·rə¦klas·tik ′flō]
(geology)
Ash flow not involving high-temperature conditions.
References in periodicals archive ?
A pyroclastic flow is a mix of hot ash, lava fragments and gases
Mount Shindake erupted last summer and the area where that pyroclastic flow occurred has been off limits since then, with the peak under a warning level of 3 on the Japanese scale of 1 to 5.
The volcanic material to the north of the villa, beneath the modern town, also accumulated over the parts pushed over the cliff by the force of the pyroclastic flows.
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.
Another person was also killed by the pyroclastic flow from Fugen Peak on June 23, 1993.
Bits of superheated ash, cinders, bombs, and gas hurl into the atmosphere, and then cascade down the volcano's sides in what's called a pyroclastic flow.
The mountain is very a dangerous volcano because the eruptions are followed by pyroclastic flow that can reach speeds of up to 1,300 kilometres per hour," he said.
Topics include a new geological map of Stromboli volcano in Italy's Tyrrhenian Sea based on application of a lithostratigraphic and unconformity-bounded stratigraphic (UBS) units, a revised volcanostratigraphy of the Upper Miocene to Lower Pliocene Urgup formation in the central Anatolian volcanic province of Turkey, ignimbrite stratigraphy and chronology on Tercerira Island in the Azores, geologic mapping of Mexico's Colima volcanic complex and implications for hazard assessment, and probabilistic digital hazard maps for avalanches and massive pyroclastic flow using TITAN2D computational model.
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).
Pyroclastic flow deposits from boiling-over eruptions are commonly less depleted in fine material, reflecting the reduced interaction with water during flow movement (McPhie et al.
But there is also something called pyroclastic flow, an avalanche of hot ash, gas and rock that sweeps down the hillside at speeds of 60mph or more, destroying everything in its path.
the likelihood of a pyroclastic flow following an explosive eruption is small for the short term.