for National Geographic News
A new type of volcano may be heating up the floor of the western Pacific Ocean.
Scientists suspect the new volcanoes occur at a crack in tectonic plates caused by stress as the plates slide past each other.
The group of small volcanoes, called petit spot volcanoes, was discovered far from the tectonic-plate boundaries (such as mid-oceanic ridges) that often spawn volcanoes, earthquakes, and other geologic activity.
Until now, scientists explained volcanoes located outside tectonic boundaries using mantle-plume theory. According to the theory, molten rock from deep within the Earth rises to the surface to produce these volcanoes.
But geoscientist Naoto Hirano's team suggests that the petit spot volcanoes are instead fueled by partially melted rock from much closer to the Earth's surface.
The team will report its findings in tomorrow's edition of the journal Science.
Mantle-plume theory suggests that "plumes" of molten rock originate deep within the planet and rise to the surface to produce "hot spot" volcanoes like those in the Hawaiian Islands.
It has been the dominant theory for nearly 30 years. (Related story: "Deep Sea Volcano Erupts on FilmA First" [May 24, 2006].)
But Hirano's team reports that petit spot volcanoes yield no evidence of a liquid rock source from deep within the Earth.
They believe the source of these volcanoes is melted rock from the upper mantle, much closer to the surface, which has been squeezed through cracks in the tectonic plate above.
When one tectonic plate slides beneath another in a process known as subduction, the forces flex and bend the plates. This may be responsible for creating such cracks.
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