A general term for all rocks originating in molten streams from volcanoes, includes traps, basalts, pumice, and others; the surface of a lava stream cools and hardens quickly, presenting a cellulose structure, while below the heat is retained much longer and the rock when cooled is compact and columnar or crystalline; the largest recorded lava flow was from Skaptar Jökull, Iceland, in 1783.