Superplumes

Studies Find That Magma Superplumes Are Rising From Base of Earth's Mantle
Associated Press, Apr 18, 2002

Two superplumes of molten rock appear to be powering through the boundary between the Earth's upper and lower mantle, perhaps feeding volcanoes and affecting movement of the planet's crust. New evidence of the superplumes - located beneath the south central Pacific Ocean and southern Africa - comes from studies of seismic waves conducted by scientists at the University of California at Berkeley and reported in Friday's issue of the journal Science. Smaller regions of magma rising to the Earth's crust power volcanoes and other hot spots. But the superplumes come from far deeper, crossing the boundary between the upper and lower mantle about 400 miles deep, an area that had been thought by some scientists to impede the flow of material. "Emphasis so far has been on the cold down-moving subducted plates and their critical role in mantle dynamics. We think the superplumes play an important role as well," researcher Barbara Romanowicz said.

When two of the planet's large surface plates collide, one slips beneath the other in a process called subduction. This can generate earthquakes and volcanoes along the boundary. The study seeks to focus attention on the hot material rising upward from the base of the mantle - the partially molten region that extends about 1,740 miles from the Earth's core to its crust, or lithosphere. "The hot material brought under the lithosphere by the superplumes then spreads out horizontally toward mid-ocean ridges," Romanowicz explained. The ridges are often active volcanic areas. The material heats up the region under the plates that cover the Earth's surface and thus may be an active contributor to their movement. ...

Regions above the superplumes tend to bulge upward. The plateaus of southern and eastern Africa are about 1,600 feet higher than most old continental areas in the world, she pointed out. This is referred to as the "African superswell." Also, she said, heat flow from the Earth's interior measured in a wide area of southern Africa is higher than expected, indicating that an unusually large supply of heat must be coming from underneath. There are volcanoes in Africa and in the southern Atlantic Ocean that could be related to the superplume in the same way as Hawaii and other hotspot volcanoes in the southern Pacific may be related to the Pacific superswell, she said.