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 ?
P tephrostratigraphy related to the main explosive activity; 2) different pyroclastic density current deposits; 3) typical horseshoe-shaped amphitheatres and their associated debris avalanche deposits, and; 4) lava domes and lava flows.
As of January 30, 2018, about 119 volcanic earthquakes, 68 rockfall events, nine tremor events, two lava fountaining, and two episodes of thick pyroclastic density current (PDC) generation from lava collapse have been recorded and released by PHIVOLCS.
The Philippine Institute of Seismology and Volcanology (Phivolcs) recorded on Thursday afternoon a pyroclastic density current (PDC) caused by lava collapse at the Mayon volcano's summit.
At least 11 episodes of lava collapse pyroclastic density current events were observed between 8:51 a.
The Phivolcs did not record any episodes of lava fountaining and pyroclastic density current during the three eruptions.
No episodes of lava fountaining and pyroclastic density current were recorded during the eruption but a booming sound was heard at Lignon Hill, located 11 km southeast of the volcano.
The pyroclastic density current fell in Basud channel in Sto.
Phivolcs also observed a pyroclastic density current (PDC) heading towards Mi-isi and Bonga Gullies located one kilometer away from the summit.
The public is strongly advised to be vigilant and desist from entering the eight kilometer-radius danger zone, and to be additionally vigilant against pyroclastic density current, lahars, and sediment-laden stream flows along channels draining the edifice,' the Phivolcs said.
There was also one episode of pyroclastic density current generation from lava collapse and numerous rockfall events,Phivolcs said.
According to their latest bulletin, Phivolcs has recorded 21 tremors, 10 volcanic quakes, 21 rock fall events and one pyroclastic density current over Mayon Volcano, which is still under Alert Level 4 during the past 24 hours.
bulletin, the Phivolcs specifically recorded a total of 15 volcanic earthquakes, 19 tremor events - seven of which correspond to the lava fountaining events, one episode of pyroclastic density current (PDC) generation from lava collapse, and numerous rock fall events around Mt.