A pyroclastic flow consists of superheated volcanic gases mixed with volcanic ash and dust. It is one of the most lethal aspects of a volcanic eruption.
Hazards:
(1) high heat (100 to 400°C, theoretically up to 1,00°C), which kills immediately and which can ignite fires
(2) high velocity (from 10 to over 200 meters per second)
(3) large volume of dust and ash, which can bury an area
(4) mixture with water to form a lahar
(5) the material moving at a high velocity can significant pressures
A flow from a large eruption can travel for many miles. The flow can even run over the surface of water for some distance.
A dense flow tends to follow valleys and depressions, but lighter flows can go over obstacles.
It is impossible to outrun a pyroclastic flow on foot. It may take a jet to outpace the fastest flows.
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