CT scan of earth shows volcanic hot spots

Scientists at the University of California, Berkeley, have produced the first-ever computer simulation that shows plumes of hot rock rising through Earth’s interior to feed volcanoes like those in Hawaii, Samoa and Iceland.

The picture was generated at the National Energy Research Scientific Computing Center at the Lawrence Berkeley National Laboratory.

In a news release Wednesday, the scientists compared the video to a computed tomography or CT scan of Earth’s interior.

While medical CTs use X-rays to probe the body, the scientists mapped mantle plumes by analyzing the paths of seismic waves in Earth’s interior from 273 strong earthquakes over the past 20 years that rang Earth like a bell.

Previous attempts to image mantle plumes have detected pockets of hot rock rising, but it was unclear whether they were connected to volcanic hot spots at the surface or deeper — specifically, at the roots of the plumes at the core-mantle boundary, 1,800 miles below the surface.

The new, high-resolution map of the mantle — the hot rock below Earth’s crust but above the planet’s iron core — shows connections to Hawaii’s hot spot and others.

“No one has seen before these stark columnar objects that are contiguous all the way from the bottom of the mantle to the upper part of the mantle,” said Scott French, a computational scientist at the computing center and lead author of the study, which appeared Thursday in the British journal Nature.

Barbara Romanowicz, a UC-Berkeley professor of earth and planetary science, said that the connections between the lower-mantle plumes and the volcanic hot spots are not direct because the tops of the plumes spread out like a river delta as they merge with the less viscous upper-mantle rock.

“These columns are clearly separated in the lower mantle, and they go all the way up to about 1,000 kilometers below the surface, but then they start to thin out in the upper part of the mantle, and they meander and deflect,” she said. “So while the tops of the plumes are associated with hot-spot volcanoes, they are not always vertically under them.”

Seismologists proposed some 30 years ago that stationary plumes of hot rock in the mantle occasionally punched through the crust to produce volcanoes, which, as the crust moved, generated island chains such as Hawaii and the Galapagos.

Evidence for the plume and hot-spot theory had been circumstantial until now, and some seismologists argued instead that hot spots are very shallow pools of hot rock feeding magma chambers under volcanoes.

The supercomputer analysis did not detect plumes under all hot-spot volcanoes, such as those in Yellowstone National Park. The plumes that feed them may be too thin to be detected given the computational limits of the global modeling technique, French said.

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