A fast-moving current of hot gas, ash and volcanic rock that races down a volcano's slopes during an explosive eruption or the collapse of a lava dome, capable of traveling at speeds exceeding one hundred kilometers per hour at temperatures hot enough to incinerate everything in its path. Because a pyroclastic flow moves too fast to outrun and destroys through both heat and impact, it is one of the deadliest volcanic hazards, responsible for the destruction of Pompeii and Herculaneum in the 79 CE eruption of Mount Vesuvius.
Facts
Identification
Distinguishing AppearanceA pyroclastic flow is a dense, fast moving flow of solidified lava pieces, volcanic ash and hot gases, with a thick cloud of ash forming above the flow itself. 1 ScaleA pyroclastic flow can move at speeds as high as 200 meters (656 feet) per second. 1 Connections
Associated With
Lahar, Natural Phenomena Loose pyroclastic-flow deposits on a volcano's flanks are readily remobilized by rainfall into lahars long after the flow itself has stopped, a documented secondary hazard of pyroclastic deposition.
Pyroclastic flows are a direct, fast-moving product of certain explosive volcanic eruptions, formed when an eruption column collapses or a lava dome fragments, sending superheated gas and volcanic matter down the slope.
Sources
1. National Geographic Education: Pyroclastic Flow
Speed paragraph
It may move at speeds as high as 200 meters (656 feet) per second.
Composition and appearance paragraph
A dense, fast-moving flow of solidified lava pieces, volcanic ash, and hot gases.
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