Ancient eruptions created "extensive hard bottoms" for sea life to colonize.
Ker Than for
National Geographic NewsPublished April 26, 2010
Strange undersea domes spotted off the California coast are extinct "asphalt volcanoes" made from a mixture of hardened crude oil and marine fossils, according to a new study.
First discovered in 2007, the seven mounds sit about 700 feet (213 meters) beneath the ocean, roughly 10 miles (16 kilometers) offshore from Santa Barbara (see map).
Recent explorations using a submarine robot named Alvin have revealed that the largest dome is about as wide as two football fields laid side by side and is as tall as a six-story building. (Related: "Iceland Volcano Creates 27-Story 'Mountain.'")
The domes are made mostly of petroleum, or crude oil—essentially the same stuff used to pave highways and parking lots and the raw material for gasoline.
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The team thinks the Santa Barbara asphalt volcanoes could account for a mysterious spike in ocean methane known to have occurred around 35,000 years ago.
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