Navy Detects Underwater Volcano

April 9 -- A network of underwater microphones, originally planted to detect enemy submarines, has picked up what scientists believe is an erupting underwater volcano 130 miles off the Oregon shore.

"It's very active," says Chris Fox, geophysicist with the National Oceanic and Atmospheric Administration. "It's setting off earthquakes every four to five minutes."

Fox and his team, who monitor readings from the U.S. Navy's Cold War-era sound system known as SOund SUrveillance System, or SOSUS, began sensing unusual activity from the region about six days ago. Since the first tremors, the system has picked up the rumblings of more than 2,500 earthquakes, peaking with a 4.5 magnitude shake last Thursday.

The location of the active volcano appears to be in the Gorda tectonic ridge, about 2 miles below the ocean's surface. The ridge is part of a seafloor spreading system that wraps around the world's ocean floors for about 46,000 miles.

Like 'Squeezed Toothpaste'

The hot spots are formed where lava bubbles up from an underwater crack in the ocean floor and then spreads and extends the surface of the oceanic plate. The eruptions cause the Pacific Ocean floor to spread about 5.5 centimeters each year and are considered the "engine" of plate tectonics, which control nearly all geologic activity on the planet.

"[Underwater volcanoes] are usually not explosive like many above-ground volcanoes," explains Fox. "It looks like toothpaste squeezing out of the ground and forming pillow-shaped layers of lava on the ocean floor."

While most underwater volcanoes might not be as violent as ones above ground, they are more common. Fox says more than 90 percent of the Earth's volcanic activity is underwater and geologists estimate there are thousands of volcanoes on the ocean floor.

Occasionally, underwater volcanic activity can be violent. One well-known example of an explosive underwater eruption is Surtsey, a volcano off the south shore of Iceland. When the volcano erupted it punched through the sea and, by 1967, became an island.