Flood basalt
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A flood basalt 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 that have survived many millions of years.
The Deccan Traps of central India and the Columbia River Plateau of the western United States are two 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 conjuction 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 volcanos.
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) in mass extinction events in the past.
See also
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