Molten rock welling up from hundreds of miles deep in the Earth has
been detected in two hot superplumes of magma that spread horizontally beneath
the crust south of Hawaii and on the other side of the globe beneath Africa,
Berkeley scientists report.
The plumes may play a major role in the rise of volcanoes around the globe
and the slow movement of vast slabs of the crust, and they could have been
rising from near the Earth's core for millions of years, the researchers say.
Barbara Romanowicz, director of the University of California's Berkeley
Seismological Laboratory, and Yuancheng Gung, a graduate student at the lab,
describe their insights into the planet's dynamic interior in a report
published today in the journal Science.
Using instruments to measure the size of seismic waves that course through
the Earth as the superplumes move upward and spread, the scientists estimate
that the molten material of the plumes is hundreds of degrees hotter than the
5,000-degree temperature of the viscous rock, called the mantle, that lies
between the core and the base of the crust. The mantle itself is believed to
be some 1,750 miles thick.
The Hawaiian superplume, Romanowicz said in an interview yesterday,
originates some 1,250 miles south of the island chain and may well be
responsible for the "hot spot" that has created the series of volcanoes that
make the islands of unique interest to geologists.
As that plume spreads horizontally beneath the rigid crust, its molten
material could be "lubricating" the vast crustal slab known as the Pacific
Plate to create the rift zones of the eastern Pacific where undersea volcanoes
erupt from plate boundaries, she said.
The superplume beneath the African continent could have been an important
influence in the ancient volcanism that has created mountains in southern
Africa, as well as the extinct volcanoes of the great Rift Valley that
stretches for 4,000 miles on the continent's eastern side.
The concept of superplumes has intrigued geologists in recent years, but
the phenomenon is still largely a mystery. The Berkeley researchers have
provided the first estimates of their temperature as well as some theories
about their relation to the "hot spots" that have created many island
volcanoes.
Space scientists studying images of Mars have even proposed that
superplumes may be a major factor in thrusting up at least one thousand-mile
highland region on Mars known as Tharsis, where three huge volcanoes tower
more than 15 miles high -- almost three times higher than Mount Everest.
E-mail David Perlman at dperlman@sfchronicle.com.
