Flood basalt
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A flood basalt or trapp basalts is a giant volcanic eruption that coats large stretches of land or the ocean floor with basalt lava. Flood basalts have occurred on continental scales in prehistory, creating great plateaus and mountain ranges.
The Deccan Traps of central India, the Siberian Traps and the Columbia River Plateau of the western United States are three regions covered by prehistoric flood basalts. The two largest flood basalt events in historic time have been at Eldgjá and Lakagigar, both in Iceland. The maria on the Moon are another, even more extensive, example of a flood basalt. Flood basalts on the ocean floor produce the oceanic plateaus.
One explanation for flood basalts is that they are caused by the combination of continental rifting and its associated decompression melting in conjunction with a mantle plume also undergoing decompression melting producing vast quantities of a basaltic magma. These lavas have a very low viscosity, which is why they 'flood' rather than forming taller volcanoes.
Partial decompression melting of the ultra-mafic mantle (peridotite) produces mafic (basalt) lava flows.
Flood basalts have erupted at random intervals throughout history and are clear evidence that the Earth undergoes periods of enhanced activity rather than being in a uniform steady state.
Flood basalt volcanism has been implicated (along with the impact of large asteroids and/or comets, as well as disease and long-term climate changes) in major mass extinction events in the past.
