Giant Undersea Volcano Found Off Iceland

Richard A. Lovett
for National Geographic News

A giant and unusual underwater volcano lies just offshore of Iceland on the Reykjanes Ridge, volcanologists have announced. The Reykjanes formation is a section of the Mid-Atlantic Ridge, which bisects the Atlantic Ocean where the North American and Eurasian tectonic plates are pulling apart.

As magma wells up from the rift between the plates, it cools to form ridges.

But it doesn't generally form giant volcanoes, said Ármann Höskuldsson, a University of Iceland volcanologist who was part of the international team that discovered the volcano last summer.

That's because mid-ocean ridges are constantly pulling apart, making it harder for large volcanoes to form without being torn asunder.

"We were doing a normal oceangoing mission, and we found a big edifice" about 90 miles (150 kilometers) south of Iceland, Höskuldsson said.

The structure turned out to be an active volcano that rises about 3,300 feet (1,000 meters) above the surrounding sections of the ridge, coming within 1,300 feet (400 meters) of the surface.

At its base the volcano is approximately 30 miles (50 kilometers) across. The peak contains a depression known as a caldera that is 6 miles (10 kilometers) wide.

That indicates that the mountain is being fed by its own magma chamber, Höskuldsson said.

"It's a higher magma production that generates the edifice."

Seafloor Mapping

The underwater mountain resembles Krafla, an active aboveground volcano in northeastern Iceland that contains a similar-size caldera, according to Höskuldsson.

Krafla has erupted 29 times in recorded history, most recently in 1984. Nobody knows when the undersea volcano might next erupt, but Höskuldsson thinks it is only a matter of time.

Still, the people of Iceland are in no danger, he said, because the volcano is so deep under water.

"We wouldn't expect much to happen on the surface."

Mostly, the find indicates how little is known about the seafloor, Höskuldsson said.

"We are getting better techniques, but the oceans of the world are huge."

In the United States, for example, ocean scientists studying a swarm of earthquakes off the Oregon coast are having a hard time pinning down the temblors' source, because much of the seabed is poorly mapped.

"There are all kinds of things on the seafloor we don't know about," said Robert Embley, a National Oceanic and Atmospheric Administration scientist involved in the Oregon project.

Embley, who was not part of Höskuldsson's team, noted that satellite maps of Earth's gravitational field can be used to map out undersea structures.

But these maps don't provide the type of detail found by Höskuldsson. "Even though … you can see big features, you can't really tell what they are. All you can say is its a big feature," Embley said.

Höskuldsson will present his results this summer at the annual conference of the International Association of Volcanologists, to be held in Iceland.

Next year, he told the Icelandic press, his team plans to dive to the mountain with a small submarine to gather more clues as to why such a large volcano exists along the ridge.