Lava

 

Molten rock (magma) that has been ejected from the interior of a terrestrial planet (such as Earth) or a moon is referred to as lava. Magma is created by the planet's or moon's internal heat, and it erupts as lava at volcanoes or through cracks in the crust at temperatures ranging from 800 to 1,200 °C (1,470 to 2,190 °F). Lava is the term used to describe the volcanic rock that forms after cooling.

A lava flow is a lava outpouring caused by an effusive eruption. Rather than lava flows, explosive eruptions produce tephra, a mixture of volcanic ash and other debris. Despite the fact that lava is 100,000 times more viscous than water, it can flow for long distances before cooling and hardening because lava exposed to air forms a thick crust quickly. This helps to keep the leftover liquid lava hot and inviscid by insulating it.

Lava is an Italian word that is most likely derived from the Latin word labes, which meaning "to fall or slide." The term was first used in relation to ejected magma (molten rock beneath the Earth's surface) in a short description published by Francesco Serao about Vesuvius' eruption in 1737. Serao compared the rush of water and dirt down the volcano's sides following heavy rain as "a flood of molten lava."