Great Volcano Eruptions in Earth History

Great Eruptions in Earth History

The great continental flood-basalt eruptions of the geological past are the largest eruptions of lava on Earth, with known volumes of individual lava flows exceeding 2000 cubic kilometres. For comparison, the ongoing eruption of Kilauea volcano on Hawaii has produced just 1.5 cubic kilometres in 16 years! A series of these huge eruptions builds up a thick stack of basalt lava flows as shown in the photograph below.

Extending over areas of more than a million square kilometres. Flood basalts are one type of large igneous province (LIP) that characterise the Earth's surface and have been formed at various times in the geological past - some in a submarine environment and some on land. Notable examples are the Siberian Traps and the Deccan Traps (trap is a Sanskrit word meaning 'step', referring to the step-like topography produced by the stacked layers of lava). The Columbia River province featured in the above photograph is minute in comparision to the size of these enormous outpourings of lava.

Mantle Plumes

Thor Thordarsson Flood Basalts: Columbia River basalt lava flows in the canyon of the Grande Ronde River, Washington State. Each flow is 15-20m thick.

Large igneous provinces are thought to be caused by the arrival of a mantle plume in the Earth's outermost layer, the lithosphere. The plumes are proposed to be richer in lighter elements and hotter than the surrounding mantle. As they rise, magma (liquid rock) is generated by partial melting of the plume material. The magma is injected into the lithosphere and erupted onto the Earth's surface to form huge basalt lava flows. The first few million years of a newly arrived mantle plume seem to be the most fertile in terms of magma production and flood basalts are therefore formed in a very short period of geological time.

USGS/Hawaiian Volcano Observatory Basalt lava cascading over the rim of a crater