Geologist, Jonny Wu from the University of Houston, USA, has discovered a 50 million years ago a chain of volcanoes that lasted for 10 million years between Northeast Asia and Russia were forced into a period of dormancy.
10 million years later when the volcano revived the radiogenic isotopes within the magma were noticeably different. Wu said the productivity of magma within the once-violent chain of volcanoes was only one-third its previous level.
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. - Jonny Wu.
In the journal Geology, Wu stated that due to the mysterious changes of the largest Earth's tectonic plate it is believed to be the reason the dormancy of a volcanic area stretching 900 miles, between Japan and the Sikhote-Alin mountain range in Russia.
Generally, volcanic activity above subduction zones is driven by water that is brought deep within the Earth by the diving subducting plate. After the water reaches deep around 65 miles, it causes the solid mantle to melt and produce magma that may rise and feed volcanoes. But this was not the case for East Asian volcanoes, as "subduction of the immense seafloor crack interrupted its water-laden conveyor belt into the deep Earth. As a result, the volcanoes turned off," noted Wu.
Wu along with UH doctoral student Jeremy Tsung-Jui Wu have also found that the crack in the Pacific Plate was much shorter than it was originally believed.