What is a pyroclastic flow?
Quick Answer
A pyroclastic flow is a ground-hugging avalanche of hot gas, ash and rock that races down a volcano at extreme speed.
The Full Story
A pyroclastic flow happens when an eruption column collapses or a lava dome crumbles, sending a dense cloud of volcanic material pouring downhill. These flows can reach temperatures of several hundred degrees Celsius, sometimes over 700 °C. They commonly move at more than 100 km/h, far too fast for people to outrun. The eruption of Mount Vesuvius in AD 79 sent pyroclastic surges into Pompeii and Herculaneum, killing residents who had not fled. In 1902 a pyroclastic flow from Mount Pelée destroyed the town of Saint-Pierre on Martinique, killing around 28,000 people.
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"The deadliest thing a volcano can do, explained"