A series of mysterious eruptions in the western Pacific could be caused by a new type of volcano, a new study suggests.

Three processes are responsible for the formation of volcanoes on Earth, according to theories:

Divergent faults: The planet's tectonic plates, which move around something like broken eggshells on water, can move away from each other, allowing magma to seep up. Iceland, which sits atop the Mid-Atlantic Ridge where the North American and Eurasian plates diverge, is a result of such volcanic activity.

Convergent faults: The plates can also move towards each other, forcing eruptions. Recent volcanic eruptions and earthquakes in Indonesia are the result of the Australian plate colliding with the Eurasian plate.

Hot spots: Plumes of magma at fixed locations well up from deep inside the Earth. The Hawaiian island chain was formed by consecutive volcanoes as the Pacific plate passed over a hot spot over tens of millions of years.

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In the July 28 issue of the journal Science, researchers report the discovery of tiny active volcanoes on the Pacific plate that aren't caused by any of these mechanisms.

These small volcanoes may be widespread on ocean floors where the mantle just under the crust is squeezed out by tectonic forces when one plate moves under another, the researchers explained.

"The possibility of this type of volcanism had been proposed in the past, but had never been adequately documented," said study co-author Naoto Hirano of the Scripps Institution of Oceanography at the University of California, San Diego. "We believe that these volcanoes should be classified as a fourth type of volcanism."

Dubbed "petit spots," these new types of volcanoes are difficult to spot using satellite technology.

Specific geophysical and sampling expeditions would have to be carried out in order to locate them, Hirano explained.

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