Lava is magma once it has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or undersea, usually at temperatures from 800 to 1,200 °C (1,470 to 2,190 °F). The volcanic rock resulting from subsequent cooling is also often called lava. A lava flow is an outpouring of lava during an effusive eruption. On the other hand, an explosive eruption produces a mixture of volcanic ash and other fragments called tephra, rather than lava flows. Although most molten lava is about 10,000 to 100,000 times more viscous than water, with a viscosity roughly similar to ketchup, lava can flow great distances before cooling and solidifying because lava exposed to air quickly develops a solid crust that insulates the remaining liquid lava, helping keep it hot and inviscid enough to continue flowing. The word lava comes from Italian and is probably derived from the Latin word labes, which means a fall or slide.Its first known use in connection with extrusion of magma from below the surface was in a short account of the 1737 eruption of Vesuvius written by Francesco Serao.[4] Serao described "a flow of fiery lava" as an analogy to the flow of water and mud down the flanks of the volcano (a lahar) following heavy rain.


My type of lava is felsic. Felsic lavas have a silica content greater than 63%. They include rhyolite and dacite lavas. With such a high silica content, these lavas are extremely viscous, ranging from 108 cP (105 Pa⋅s) for hot rhyolite lava at 1,200 °C (2,190 °F) to 1011 cP (108 Pa⋅s) for cool rhyolite lava at 800 °C (1,470 °F). For comparison, water has a viscosity of about 1 cP (0.001 Pa⋅s). Because of this very high viscosity, felsic lavas usually erupt explosively to produce pyroclastic (fragmental) deposits. However, rhyolite lavas occasionally erupt effusively to form lava spines, lava domes or "coulees" (which are thick, short lava flows).The lavas typically fragment as they extrude, producing block lava flows. These often contain obsidian.