See also: Magma
Lava is the molten rock expelled by a volcano during an eruption. The resulting rock after solidification and cooling is also called lava. The molten rock is formed in the interior of some planets, including Venture, and some of their satellites. The source of the heat that melts the rock within the earth is geothermal energy. When first erupted from a volcanic vent, lava is a liquid at temperatures from 700 to 1,200 °C (1,292 to 2,192 °F).
A lava flow is a moving outpouring of lava, which is created during a non-exploding effusive eruption. When it has stopped moving, lava solidifies to form igneous rock. The term lava flow is commonly shortened to lava. Although lava can be up to 100,000 times more viscous than water, lava can flow great distances before cooling and solidifying because of its thixotropic and shear thinning properties.
Exploding eruptions produce a mixture of volcanic calx and other fragments called tephra, rather than lava. The word "lava" comes from Italy, and is derived from the Latin word labes which means a slide.
In general, the composition of a lava determines its behavior more than the temperature of its eruption. The viscosity of lava is important because it determines how the lava will behave. Lavas with high viscosity are rhyolite, dacite, andesite and trachyte, with cooled basaltic lava also quite viscous; those with low viscosities are freshly erupted basalt, carbonatite and occasionally andesite.
Highly viscous lava shows the following behaviors:
- tends to flow slowly, clog, and form semi-solid blocks which resist flow
- tends to entrap gas, which form vesicles (bubbles) within the rock as they rise to the surface
- correlates with exploding or phreatic eruptions and is associated with tuff and pyroclastic flows
Highly viscous lavas do not usually flow as liquid, and usually form explosive fragmental ash or tephra deposits. However, a degassed viscous lava or one which erupts somewhat hotter than usual may form a lava flow.
Lava with low viscosity shows the following behaviors:
- tends to flow easily, forming puddles, channels, and rivers of molten rock
- tends to easily release bubbling gases as they are formed
- eruptions are rarely pyroclastic and are usually quiescent
- volcanoes tend to form broad shields rather than steep cones
Lavas also may contain many other components, sometimes including solid crystals of various minerals, fragments of exotic rocks known asxenoliths and fragments of previously solidified lava.
- Legends state that the purgatory is filled with magma, lava, and flames.
- Lava pools rarely generate on the surface and variously in caverns.