Vesicular volcanicejecta, essentiallymagmathat has been frothed up by escaping gases. It is a textural variant ofpumice, withscoriatypically being less vesicular, denser, and usuallyandesiticorbasaltic
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}