Huge Underground "Ocean" Found Beneath Asia
Richard A. Lovett
for National Geographic News
|February 27, 2007|
A giant blob of water the size of the Arctic Ocean has been discovered
hundreds of miles beneath eastern Asia, scientists report.
Researchers found the underground "ocean" while scanning seismic waves as they passed through Earth's interior.
But nobody will be exploring this sea by submarine. The water is locked in moisture-containing rocks 400 to 800 miles (700 to 1,400 kilometers) beneath the surface.
"I've gotten all sorts of emails asking if this is the water that burst out in Noah's flood," said the leader of the research team, Michael Wysession of Washington University in St. Louis.
"It isn't an ocean. [The water] is a very low percentage [of the rock], probably less than 0.1 percent."
Given the region's size, however, that's enough to add up to a vast amount of water.
Earthquakes Reveal "Ocean"
Wysession and former graduate student Jesse Lawrence discovered the damp spot by observing how seismic waves from distant earthquakes pass through Earth's mantle.
The wet zone, which runs from Indonesia to the northern tip of Russia, showed up as an area of relatively weak rock, causing the seismic waves to lose strength much more rapidly than elsewhere (see map of Asia.)
The water got there by the process of plate tectonics, in which sections of the Earth's crust shift. This process caused the ocean bottom to be pulled beneath continental plates all around the Pacific Rim.
Normally, Earth's internal heat bakes the water out of the rocks before it gets more than 60 miles (100 kilometers) deep. The water then escapes upward as volcanic gas.
But along the eastern Pacific Rim, conditions allow the rock to be drawn much deeper before the moisture is cooked out.
The find may help scientists better understand the formation of volcanic regions such as those in Iceland, Hawaii, and Yellowstone National Park.
(Read related story: "Supervolcano Raises Yellowstone, Fuels Geysers, Study Says" [March 1, 2006].)
One theory suggests that these areas are volcanic because hot spots deep within the Earth's interior melt the underlying rock like a giant blowtorch, producing large quantities of lava.
Wysession says that the presence of water may allow such hot spots to melt more rock, thereby creating more lava.
"If you add water [to the rock] you can get an increased amount of melting," he said.
"There's a consensus that not all hot spots are equal. Some are hot spots; some are wet spots."
Wysession and Lawrence report their findings in a study published by the American Geophysical Union.
A Look at Earth's Fate
The new study also reveals clues to Earth's long-term fate, says Norman Sleep, a geophysicist at Stanford University who was not involved in the project.
When the planet was young, steam came from the deep interior to the surface as volcanic gas and eventually produced today's oceans. But as Earth's interior ages and cools, it becomes easier for water to return below the surface.
"So, rather than degassing, now [Earth] may be losing water into the mantle," Sleep said.
This gradual suction of water back below the surface may be a good thing for Earth's geological stability, he notes.
Underground water acts as a kind of lubricant that allows plates in Earth's crust to keep shifting at their present rate, Sleep explains.
This helps keep the thickness and elevation of the continents relatively stable.
If things changed, he said, "we'd have Pike's Peak boat tours."
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