Pyroclastic Flow

High Quality Content by WIKIPEDIA articles! A pyroclastic flow (also known scientifically as a pyroclastic density current is a common and devastating result of certain explosive volcanic eruptions. The flows are fast-moving currents of hot gas and rock (collectively known as tephra), which travel away from the volcano at speeds generally as great as 700 km/h (450 mi/h). The gas can reach temperatures of about 1,000 C (1,830 F). The flows normally hug the ground and travel downhill, or spread laterally under gravity. Their speed depends upon the density of the current, the volcanic output rate, and the gradient of the slope.