Hydrothermal Explosion : Explosion that can occur when hot water within a volcano's hydrothermal (hot water) system flashes to steam, breaking rocks and throwing them into the air
U.S. Geological Survey, U.S. Department of the Interior, Volcano Hazards Program, Glossary, Washington, DC, USA 2011. http://volcanoes.usgs.gov/vsc/glossary/alluvium.ht ml, (ND/ Volc Emr - Amer) {795}