An assemblage of crustal rocks that represents a section of the Earth's oceanic crust and upper mantle that has been uplifted and exposed above sea level
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}