Why did the 900-mile-long volcanic chain go dormant?

Map of tectonic plates
iStock/Naeblys

Jonny Wu, from the University of Houston, USA, has discovered a chain of volcanoes stretching between Northern Asia and Russian. Research conducted by Wu suggests that the chain of volcanoes was forced into dormancy by a tectonic shift in the Pacific Ocean.

Shortly after the end of the dinosaurs, at the end of the Cretaceous Period, the largest of the Earth’s tectonic plate changed direction which is believed to be the reason behind the prominent bend in the Hawaiian Island chain. Another result of this shift is believed to be the dormancy of a volcanic area stretching 900 miles, between Japan and the Sikhote-Alin mountain rang in Russia.

“Around the time of the volcano dormancy, a crack in the Pacific Ocean Plate subducted, or went below, the volcanic margin. The thin, jagged crack in the seafloor was formed by plates moving in opposing directions and when they subduct, they tend to affect volcanic chains,” reports Jonny Wu.

“The productivity of magma within the once-violent chain of volcanoes was only one-third its previous level.” Wu has since linked the phenomenon to the subduction of the Pacific-Izangi mid-ocean ridge, an underwater mountain.

It is a long-understood fact that volcanic activity above subduction zones, where one tectonic plate converges towards and dives beneath another, is driven by water brought deep within the earth by the dividing subducting plate. Once the water reaches depth of around 65 miles, it causes the solid mantle to partially melt and produce magma which could subsequently feed volcanoes.

“However, in the case of the East Asian volcanoes, subduction of the immense seafloor crack interrupted its water-laden conveyor belt into the deep Earth. As a result, the volcanoes turned off,” said Wu.

Further research conducted by Jeremy Tsung-Jui Wu discovered the dormancy after researching a catalogue of 900 igneous rock radio-isotopic values spanning from the Cretaceous to Miocene eras. After said research, Wu also discovered evidence that the crack in the Pacific Plate was around 50% shorter than originally believed.

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