Lateral flowage of a turbulent mixture of hot gases and unsorted pyroclastic material (volcanic fragments, crystals, ash, pumice, and glass shards) that can move at speed (50 to 100 miles an hour). The term also can refer to the deposit so formed. (Foxworthy and Hill, 1982)
A hot (300-800 degrees C (570-1470 degrees F)), dry, fast-moving (10 to more than 100 meters per second (20 to more than 200 miles per hour)) and high-density mixture of ash, pumice, rock fragments, and gas formed during explosive eruptions or from the collapse of a lava dome. Moves away from a volcano at high speeds.
Pyroclastic flows are arguably the most dangerous of all volcanic flows, due to their fast speed and destructive power.