Lava, molten rock rising to the earth's surface through volcanoes and other fissures, or the same after solidification. Originating as magma deep below the surface, most lavas are basaltic (subsilicic) and flow freely for considerable distances. Lavas of intermediate silica content are called andesite. Silica-rich lavas, such as rhyolite, are much stiffer.
See also: Volcano.