Magazine article Science News

Breaking Crust: Sonar Finds New Kind of Deep-Sea Volcano

Magazine article Science News

Breaking Crust: Sonar Finds New Kind of Deep-Sea Volcano

Article excerpt

Explorations east of Japan have revealed a previously unknown type of volcano.

Volcanoes typically emerge in one of three geological settings, explains Stephanie P. Ingle, a geochemist at the University of Hawaii in Honolulu. Some crop up along mid-ocean ridges, where Earth's tectonic plates spread apart. Others, such as those on land along the western coast of North America, form where one plate is being sub-ducted, or forced beneath, another plate. And volcanoes far from plate boundaries, such as those in Hawaii, appear where hotter-than-normal plumes of Earth's mantle well up (SN: 7/9/05, p. 24).

Ingle and her colleagues, however, have found inactive volcanic features in a completely new setting under the sea about 600 kilometers from Japan. "Finding these peaks was serendipitous luck" Ingle notes.

Analyses of ocean floor nearer Japan had hinted at the presence of undersea volcanoes. So, Ingle's team used sonar to scan the ocean bottom farther offshore. In a 6-km-deep location in the Pacific, the team spotted peaks about 1 km across and 50 meters high. Lava samples were then dredged from the exposed portions of those mostly buried volcanoes.

The thickness of mineral layers that had formed on the surfaces of lava chunks suggests that the undersea volcanoes were last active 50,000 to 1 million years ago, the researchers report in an upcoming Science. The scientists also describe the peaks they had found nearer Japan. Those erupted between 8 million and 4 million years ago.

Chemical analyses of crystals embedded in the lava hint that the material originated about 14 km below the ocean floor. …

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