Lavatubes are natural conduits through whichlavatravels beneath the surface of alava flow. Tubes form by the crusting over of lava channels andpahoehoeflows
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}