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Wednesday, November 18, 1998 Published at 19:41 GMT


Deep heat under Hawaii

The fiery fountains of Hawaii

Earth scientists believe they have found the source of the spectacular "fountains of fire" seen on the volcanic islands of Hawaii.

A large mass of hot rock rising through the Earth and erupting through the ocean floor has been building islands in the central Pacific for at least 80 million years.

Now a team from the University of California, Santa Cruz (UCSC) believes this plume of rock extends about 2,890km beneath the surface of the Earth.

This is right on the edge of Earth's metallic core. If the research published in Nature is correct, it will settle one of the biggest arguments in Earth science.

Seismic waves

The Santa Cruz team was able to picture the interior of the earth by studying the energy released by earthquakes.

[ image: Lava flows away from fissures in the rock]
Lava flows away from fissures in the rock
Sudden movements in the Earth's crust send shock waves in all directions. The speed and other properties of these seismic waves are affected by the type of rock they encounter.

By following the paths they take, scientists get clues as to the internal structure of the planet.

Research shows that hot material is flowing horizontally in the boundary layer between the Earth's core and the mantle - the layer of rock that makes up the greater part of the Earth - before rising vertically to form the Hawaiian islands.

The Hawaiian hotspot, as it is known, is one of the most productive in the world, says Thorne Lay, professor of Earth Sciences at UCSC. Its volcanic eruptions built underwater mountains that eventually emerged from the sea as islands.

Mauna Loa, for example, is the mountain with the largest mass on Earth, occupying 10,000 cubic miles and rising 20,000 feet from the sea floor.

[ image: Thorne Lay: Provocative paper]
Thorne Lay: Provocative paper
The movement of the Pacific plate has resulted in a series of volcanoes on the sea floor and a line of mountains extending north-west of Hawaii.

Just how deep the Hawaiian plume extends has long been a subject of debate among scientists. Many think the origin for such features has to be closer to the surface.

"This will certainly be a provocative paper and if it turns out to be right it will be a landmark," said Prof Lay.

[ image: Seismic waves change speed and direction as they go through the Earth]
Seismic waves change speed and direction as they go through the Earth
Separate research conducted in Iceland, also published in the scientific journal Nature, appears to support the idea that hot plumes can come up from the core-mantle boundary.

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