Ash Cloud : The fine material that is generated by a pyroclastic flow and rises above it. (Gardner, et.al., 1995) Cloud of ash formed by volcanic explosions or derived from a pyroclastic flow. (Miller, 1989)
U.S. Department of the Interior, U.S. Geological Survey, US Geological Society (USGS), Glossary of Volcano and Related Terminology, USGS/Cascades Volcano Observatory, Vancouver, Washington, USA 2006. http://vulcan.wr.usgs.gov/Glossary/volcano_termino logy.html, (ND/ Volc Sci - Amer) {493}