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]
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 extreme degree of supersaturation produced upon decompression drives the entire system to sustain a pyroclastic eruption until the pressure in the magma chamber is returned from supralithostatic to sublithostatic.
At exit velocities below sonic conditions one would predict a boiling over, directed pyroclastic eruption (Fig.
This interpretation assumes that pyroclastic eruptions cannot occur below the critical point of seawater (31.
Results of the CONFLOW modelling support our hypothesis that magmatic volatile phase expansion is alone capable of providing enough energy and high enough melt/gas ratio, to initiate submarine pyroclastic eruptions in silicic magmas to the water depths typically associated with VMS genesis, i.
Burnham (1983) then modelled the kinetics of deep submarine pyroclastic eruptions for rhyolitic tuff and tuff breccia that underlie the Kuroko ores; it was postulated that these were erupted onto the sea floor at depths as great as 3500 m (Guber and Merrill, 1983).
The main focus is on CONFLOW (Mastin and Ghiorso, 2000) modelling, which is used to investigate the depth limits of pyroclastic eruptions in a subaqueous environment.
A full treatment of the deposits generated by pyroclastic eruptions in the deep sub-aqueous environment is beyond the scope of this paper.
For pyroclastic eruptions of magmatic or phreatomagmatic origin, the high heat capacity and thermal conductivity of water leads to rapid heat transfer and potentially to another phase of fragmentation (Gudmundsson, 2003).
Are pyroclastic eruptions more common than we thought, or is there something special about the conditions along the Gakkel Ridge?