Scientists have long wondered why the world’s most volcanic regions are thousands of kilometres long, but only a few tens of kilometres wide. One of the most obvious examples is the Ring of Fire, a ring of volcanoes that stretches from southernmost Chile, via Alaska and Japan, to New Zealand.
Oxford University scientists have finally discovered an explanation for the narrowness of these explosive tracts of fire, published in a report in the latest edition of the journal Nature.
“It has been recognised 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 explosive power of the volcanoes found in locations such as the Ring of Fire can be explained by the high concentrations of water intermixed with the magma that spews up through the volcano. The water, when superheated into gas, provides the power necessary to create the famous explosions volcanoes are known for.
However such high concentrations of water do not make sense in volcanoes that are so narrow. Wet melting – where the water trapped beneath the plate lowers the melting point of rocks in the mantle – occurs over a much broader region of the mantle than is consistent with the creation of narrow volcano chains such as the Ring of Fire.
The Oxford scientists used a mathematical model for heat transport focused on the region where two tectonic plates collide and create a subduction zone – where one plate collapses underneath the other – and found that the narrow chain of volcanoes can only be explained if they are located above a region in which the mantle melts in the absence of water.
Water will later mix with the magma in such a location and provide the necessary power for the explosions, but in the beginning, a waterless-melt takes place.
The Ring of Fire rings the basin of the Pacific Ocean in a 40,000 kilometre horseshoe shape, contains 452 volcanoes and is home to over 75% of the world’s active and dormant volcanoes.