Grandaddy Magma Plume Found

By Aries Keck,
Discovery.com News

June 21, 2000 — Scientists believe they've located the largest river of
superhot rock that may connect the center of the Earth with Hawaii.
Cutting like a laser beam through the Earth's mantle, this plume breaks
through the Earth's surface and releases tons of magma under the Pacific
Ocean. As the magma cools into rock, it creates massive underwater volcanoes,
the tips of which are the Hawaiian Islands.

Scientists have believed that geologic "hot spots" — areas of long-term
volcanism fueled by magma plumes — like this one run so deep into the mantle
that the plume essentially stays still as the massive tectonic plate of the
Earth's crust glides overhead. The plate drags the top layers of the cooled
rock with it, dotting oceans with strings of islands.


Plumes of the World


 But, until now, it's always been a theory.

A team lead by Rainer Kind, a geophysicist from the Geo-Research Institute in
Potsdam, Germany, reports in the journal Nature that it found the magma plume
86 miles right below the main island of Hawaii by measuring the echoes of
earthquakes.

Large earthquakes give off vibrations that can travel through or bounce off
layers of rock deep in the Earth. By knowing exactly when an earthquake
happens, and comparing it to the time it takes to "hear" the earthquake
somewhere else, scientists can measure the depth and size of these rock
layers.

The seismic echoes indicate an area with a density consistent with magma
directly under Hawaii.

Because they've found it near an area of the Earth thought to be one of the
Earth's hot spots, the researchers believe this mantle plume originates deep
inside the Earth, at the edge of the Earth's molten core. Others aren't
entirely convinced.

"They're making this connection that requires a little bit of a leap of
faith," said Yang Shen, a geophysicist at the University of Rhode Island.
Shen says their data doesn't clearly show that the plume continues down into
the lower mantle.

Shen himself found the first evidence connecting a known hot spot in Iceland
to a magma plume deep in the lower mantle.

"(They have) a very significant finding," Shen said, adding that what's
needed is more data clearly showing the origin and dimensions of the plume.

Kind's team is taking more seismic readings from the ocean floor near Hawaii.
But his team says that the heat levels already support a deep mantle plume.

Measurements indicate the plume is 1,650 degrees Celsius. "This is about 300
degrees Celsius hotter than normal mantle at this depth and at least 100
degrees hotter than the Iceland plume," said co-author Stephan Sobolev of the
Geo-Research Institute.

"(This) confirms expectations of scientists that the Granddaddy plume, the
nickname of the Hawaiian plume, is really the hottest plume in the world,"
said Sobolev.




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