Scientists at Oxford University say most of the molten rock that comes out of the explosive volcanoes is rich in water, but paradoxically they lie in narrow regions in Earth's mantle where water-free melting of rock can take place, ScienceDaily.com reported Thursday.

"It has been recognized for almost 50 years that the volcanic arcs form where one oceanic plate sinks beneath another," Professor Philip England of Oxford University's Department of Earth Sciences said, "but while many models of this process have been put forward, none has been able to explain the location, and narrowness, of the volcanic arcs."

Ring of Fire eruptions are extremely violent because the molten rock contains a high proportion of water, which, as superheated steam, powers for the explosive eruptions.

This water comes from the plates descending beneath the volcanoes and lowers the melting point of rocks in the mantle.

"Most previous explanations for the origins of volcanoes suggested that this kind of 'wet' melting is responsible for getting a volcano started," researchers Richard Katz said.

Wet melting occurs over very broad regions of the mantle, inconsistent with the narrowness of the volcanic chains.

Using a mathematical model of heat movement where two plates collide, the Oxford team found the narrowness of the pattern can only be explained if the volcanoes are above narrow regions in which mantle melts in the absence of water.

Researchers say they believe melt rising from this region blazes a trail for more water-rich magma to follow all the way to the surface where it erupts to form volcanoes.

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