pyroclastic flow

(redirected from Pyroclastic Eruption)

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]
Ash flow not involving high-temperature conditions.
References in periodicals archive ?
While the mountain has not had a second devastating pyroclastic eruption it has had some eruptions that resulted in the minor rebuilding of the volcano.
Thus, Burnham concludes that the maximum total energy released from water-saturated magma at depth is sufficient to produce an explosive pyroclastic eruption upon decompression and rapid expansion of the gas phase.
To evaluate the conditions necessary for a submarine pyroclastic eruption to occur at depths of greater than 1 km and even those greater than 3.
The second kind of pyroclastic eruption is less familiar to most observers.
This water-infused deposit occurs within the ruined crater between Doppelmayer and Vitello, and to the west along the Rimae Doppelmayer, which was the vent for that part of the pyroclastic eruptions.
It makes geochemical sense that water would be associated with pyroclastic eruptions.
Are pyroclastic eruptions more common than we thought, or is there something special about the conditions along the Gakkel Ridge?
There is a hint, from the relative ages of the volcanoes and the stratigraphic positions of the mechanically weaker layers within them, that pyroclastic eruptions were commoner in the early part of Mars' history.
Based on studies of small pyroclastic eruptions on Earth, and the formation of lines of pit craters in Hawaii, Wilson and his colleagues propose this sequence of events: a 240-meter-wide vertical sheet of magma called a dike moved upward and horizontally from the mantle.
Pyroclastic eruptions often build steep-sided volcanoes such as Mount Fuji in Japan.
However, few observers are aware of another important form of lunar volcanism: explosive pyroclastic eruptions.
A speculative geologic history of the Marius Hills would start with early gas-rich magma rising from the lunar mantle, producing pyroclastic eruptions, which built the steep-sided cones.