From: Andy Soos, ENN
Published October 8, 2010 03:19 PM

Ring of Fire Cause

The Pacific Ring of Fire is an area where large numbers of earthquakes and volcanic eruptions occur in the basin of the Pacific Ocean. In a 25,000 mile horseshoe shape, it is associated with a nearly continuous series of oceanic trenches, volcanic arcs, and volcanic belts and/or plate movements. The Ring of Fire has 452 volcanoes and is home to over 75% of the world's active and dormant volcanoes. Oxford University scientists have potentially discovered the explanation for why the world’s explosive volcanoes are confined to bands only a few tens of miles wide. Most of the molten rock that comes out of these volcanoes is rich in water, but the Oxford team has shown that the volcanoes are aligned above narrow regions in the mantle where water-free melting can take place.

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About 90% of the world's earthquakes and 80% of the world's largest earthquakes occur along the Ring of Fire. The next most seismic region (5—6% of earthquakes and 17% of the world's largest earthquakes) is the Alpide belt, which extends from Java to Sumatra through the Himalayas, the Mediterranean, and out into the Atlantic. The Mid-Atlantic Ridge is the third most prominent earthquake belt.

"It has been recognized for almost 50 years that the volcanic arcs form where one oceanic plate sinks beneath another,’ said Professor Philip England of Oxford University’s Department of Earth Sciences, an author of the report, ”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."

The Ring of Fire is a direct result of plate tectonics and the movement and collisions of crustal plates. The eastern section of the ring is the result of the Nazca Plate and the Cocos Plate being subducted beneath the westward moving South American Plate. The Cocos Plate is being subducted beneath the Caribbean Plate, in Central America. A portion of the Pacific Plate along with the small Juan de Fuca Plate are being subducted beneath the North American Plate. Along the northern portion the northwestward moving Pacific plate is being subducted beneath the Aleutian Islands arc. Further west the Pacific plate is being subducted along the Kamchatka Peninsula arcs on south past Japan. The southern portion is more complex with a number of smaller tectonic plates in collision with the Pacific plate from the Mariana Islands, the Philippines, Bougainville, Tonga, and New Zealand. Indonesia lies between the Ring of Fire along the northeastern islands adjacent to and including New Guinea and the Alpide belt along the south and west from Sumatra, Java, Bali, Flores, and Timor.

The eruptions of volcanoes in the Ring of Fire are typically extremely violent (in contrast with the relatively gentle eruption in Iceland that paralyzed European air travel in April 2010 for example) because the molten rock contains a high proportion of water which, as superheated gas or steam, provides the power for the explosive eruptions. This water is liberated from the tectonic 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," said Dr Richard Katz of Oxford University’s Department of Earth Sciences, an author of the report. The difficulty with such explanations is that wet melting occurs over very broad regions of the mantle, inconsistent with the narrowness of the volcanic chains. "However, we noticed that there is a very simple geometrical pattern in the distribution of the volcanoes which provides a powerful clue as to what is going on," added Dr Katz.

Using a mathematical model of heat transport in the regions where two plates collide, the Oxford team showed that the observed geometrical pattern can only be explained if the volcanoes are localized above the narrow regions in which mantle melts in the absence of water. 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.

In addition to hosting devastating eruptions, the volcanic chains hold valuable clues to the evolution of the earth, because they are the surface expressions of a gigantic chemical factory in which molten rock separates from the mantle to solidify as the crust we live on, and from which significant volumes of gas are emitted into the atmosphere. The team now intends to investigate the implications of their results for the chemical processes happening deep beneath the volcanic chains.

For further information: http://www.ox.ac.uk/media/news_stories/2010/100610_1.html

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