Monday, 9 September 2013

IMMENSE SHIELD VOLCANO DISCOVERED





A volcano the size of New Mexico or the British Isles has been identified under the Pacific Ocean, about 1,000 miles (1,600 kilometers) east of Japan, making it the biggest volcano on Earth and one of the biggest in the solar system. The structure topples the previous largest on Earth, Mauna Loa in Hawaii.

Tamu Massif is a rounded dome that measures about 280 by 400 miles (450 by 650 kilometers), or more than 100,000 square miles. Its top lies about 6,500 feet (about 2,000 meters) below the ocean surface, while the base extends down to about 4 miles (6.4 kilometers) deep. Tamu Massif dwarfs the largest active volcano on Earth, Mauna Loa in Hawaii, which measures about 2,000 square miles (5,200 square kilometers).

Made of basalt, Tamu Massif is the oldest and largest feature of an oceanic plateau called the Shatsky Rise in the northwestern Pacific Ocean. The total area of the rise is similar to Japan or California.

The researchers doubted the submerged volcano's peak ever rose above sea level during its lifetime and say it is unlikely to erupt again.

"The bottom line is that we think that Tamu Massif was built in a short (geologically speaking) time of one to several million years and it has been extinct since," co-author William Sager, from the University of Houston, US, told the AFP news agency.
"One interesting angle is that there were lots of oceanic plateaus (that) erupted during the Cretaceous Period (145-65 million years ago) but we don't see them since. Scientists would like to know why."

Prof Sager began studying the structure two decades ago, but it had been unclear whether the massif was one single volcano or many - a kind that exists in dozens of locations around the planet.




While Olympus Mons on Mars has relatively shallow roots, the Tamu Massif extends some 30 km (18 miles) into the Earth's crust. And other volcanic behemoths could be lurking among the dozen or so large oceanic plateaux around the world, he thought.

"We don't have the data to see inside them and know their structure, but it would not surprise me to find out that there are more like Tamu out there," said Dr Sager. "Indeed, the biggest oceanic plateau is Ontong Java plateau, near the equator in the Pacific, east of the Solomon Islands. It is much bigger than Tamu - it's the size of France."

The name Tamu comes from Texas A&M University, where Prof Sager previously taught before moving to the University of Houston.

Sager said scientists are still trying to work out the details of how Tamu Massif formed. He said it seems likely that the spot on the seafloor had the right mix of elements, including a boundary of three tectonic plates, thin crust, and a source of hot magma below that was able to bubble up to the surface. The molten rock poured out, and then built up a wide, gradual rise as it cooled.

Precisely how the magma made it to the surface is an open question. Perhaps a blob of the rock got superheated, and then rose to the surface due to buoyancy. Or, cracks in the overlying crust could have opened, allowing molten rock to spill out.

The next step will be more work to figure out what the source of the magma was, said Sager. He would like to go back and measure the magnetic properties of the rock, using a ship that is equipped with GPS. The data will give him a better idea how the lava spread out, he said.

— Source: Nature GeoScience, National Geographic, BBC Science.



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