Flood basalt

A flood basalt or trap basalt is the result of a giant volcanic eruption or series of eruptions that coats large stretches of land or the ocean floor with basalt lava.

Flood basalts have covered areas as large as a continent in prehistory, creating great plateaus and mountain ranges. Flood basalts have erupted at various times throughout Earth history. They are clear evidence that the Earth has periods of higher activity rather than being in a uniform steady state.^[1]

One explanation for flood basalts is that they are caused by the combination of continental rifting and its associated melting. Then a mantle plume produces vast quantities of a basaltic magma. These have a low viscosity, which is why they 'flood' rather than form taller volcanoes.

Flood basalts start at between 100 and 400 km depth, in the asthenosphere. To get a partial melting as large as that of the traps, expelling huge quantities of lava, it is necessary to have a large heat input. Such melting can take place near a hotspot, resulting in a mixture of magma from the depths of the hotspot with superficial magma produced by a mantle plume.

1. ↑ Mahoney J.J. & Coffin M.F. Large igneous provinces: continental, oceanic, and planetary flood volcanism. Geophysical Monograph 100. Washington, DC: American Geophysical Union. [1]