Geologists have figured out the details of the inner structure of the Yellowstone supervolcano, including physical conditions, chemical composition and the reasons for the formation of its various layers. The achievement is described in a scientific article published in Geophysical Research Letters by Dylan Colon and Ilya Bindeman of the University of Oregon, and Taras Gerya of the Swiss Higher Technical School of Zurich.
Back in 2014, using seismic waves "scanning", scientists discovered in the depths of Yellowstone a large accumulation of magma (a magmatic body, as experts say).
However, the caldera gives off too much helium and carbon dioxide to be explained only by the found magma body. This prompted scientists to believe that another "bubble" of magma lies at great depths. In 2015, seismological studies confirmed this assumption.
But how much magma is in these two bodies? What physical condition is she in? What is its chemical composition? All these questions remained unanswered.
To find out, Colon's team performed large-scale supercomputer simulations using seismic data and well-known physical laws.
As a result, geologists presented the following picture. At a depth of 5–10 kilometers, the so-called brittle – ductile transition zone is observed. Here the hard brittle rocks of the upper crust give way to plastic and viscous. This is because an increase in temperature increases the plasticity of the substance, while an increase in pressure decreases fragility.
The complex physical conditions prevailing in this zone lead to the formation of a relatively hard, not molten underlying layer, which occupies a depth of 10–20 kilometers. It consists mainly of gabbro, a rock that is solidified magma with a high melting point.
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Below this layer, at depths of 20–40 kilometers, the lower magmatic body is located, and above - the upper one. They differ in chemical composition. In particular, the upper magma consists of rhyolite and is rich in dissolved gases. What these structures have in common is that they consist of a substance with a relatively low melting point. This makes the magma liquid. Most of this material is molten crustal rocks, although the lower magma body is partially fed from the mantle.
The upper “lake” of magma heats up and softens the nearby crustal layers, but the large amount of water prevents it from heating up too much. This water also feeds the famous geysers and hot springs of Yellowstone.
“The simulation results are consistent with observations made by sending seismic waves through this area,” explains Bindeman. "This work seems to confirm the original assumptions and give us more information about the location of magma in Yellowstone."
The researchers also found out the characteristics of the mantle plume lying deep under Yellowstone. It is 175 degrees Celsius hotter than the surrounding rocks, and its upper boundary is located at a depth of 80 kilometers.
“This study also helps explain some of the chemical signatures that are found in erupted materials,” Colon says. "We can also use it to study how hot the mantle plume is by comparing different plume models to the actual situation in Yellowstone."
Unfortunately, to date, the results of the work still do not allow predicting the date of the next supervolcano eruption. Let us recall that such a cataclysm is capable of covering an entire continent with a layer of ash. The last large-scale eruption of Yellowstone occurred about 630 thousand years ago.
By the way, the data obtained are of interest not only for researchers studying Yellowstone. Colon said the resulting picture may be typical of supervolcanoes around the world.
Anatoly Glyantsev