Guide to Geologic Hazards in Alaska - Glossary

Pyroclastic density current
A gravity-controlled, laterally moving mixture of pyroclasts and gas. It is a more general term that includes pyroclastic flow and pyroclastic surge (Neuendorf, K.K.E. and others, 2005)
Pyroclastic flows (incandescent flows of ash, gas, and coarse volcanic debris) and surges (hurricane-force blasts of turbulent hot gas and ash clouds) can race down slopes at speeds as great as 100 meters per second, travel 10 to 30 kilometers from the vent, and overtop hills and other topographic obstacles. (RI 2004-3)