地質学：イエローストーンの火山活動は北東方向に移動しているかもしれない

Magma beneath the Yellowstone Caldera may be shifting to the northeast, according to new research on the properties of the crust beneath the area published in Nature.

The Yellowstone Caldera is one of the largest volcanic systems on Earth. The system has gone through three major caldera-forming eruptions in the past 2.1 million years, which are each characterized by the eruption of up to thousands of cubic kilometres of lava and ash. Previous attempts to paint a picture of the magma distribution beneath the Yellowstone Caldera have been limited by methodologies that are also affected by variations in other properties of the crust, such as temperature, in addition to melt.

Ninfa Bennington and colleagues modelled the distribution of magma beneath Yellowstone using an electromagnetic geophysical method that relies on variations in the Earth’s magnetic field to infer the conductivity structure of the crust. The researchers identified at least seven regions of relatively high magma content, some of which feed into each other, at various depths from 4 to 47 kilometres (where the crust and mantle meet). Bennington and colleagues also deduced that the volcanic activity in the west part of Yellowstone could be waning, while magma reservoirs in the northeast are likely to host future rhyolitic eruptions (a distinct form of lava). They estimate that there is a maximum melt volume of about 440 cubic kilometres beneath northeastern Yellowstone, similar in volume to the Mesa Falls caldera-forming eruption that occurred at Yellowstone some 1.3 million years ago.

The researchers note that while large-scale eruptions have occurred previously in the Yellowstone Caldera, estimates on when this northeastern magma reservoir could erupt require further research.