For a long time, supervolcanoes have been described as immense reservoirs of liquid magma. However, recent research suggests a very different picture. Scientists now speak of networks of partially molten rock, spread over great depths, without a true liquid magma chamber.
The study published in
Science is based on a three-dimensional model of western North America. The researchers simulate interactions between the lithosphere and the mantle. They show that these two layers cooperate closely to organize magma circulation. This approach explains to us in particular the functioning of the famous Yellowstone site.
Comparison between a classical magma chamber and a diffuse magma mush system traversing the lithosphere.
Credit: Image by LIU Lijun's group
At the heart of this new description is the "magma mush". It is a thick mixture, composed of both solid and molten rock. Unlike a fluid liquid, this material circulates with difficulty. Its progression requires significant stress, which explains the slowness of the processes involved.
Scientists place the origin of the magma in the shallow asthenosphere. This ductile layer gradually feeds the upper regions. A slow horizontal current, described as a mantle wind, would transport hot material eastward. This movement plays a decisive role in feeding volcanic systems.
When this flow encounters a thicker lithosphere, it is forced to sink. This compression triggers decompression melting, generating magma. The phenomenon is accompanied by mechanical forces that deform the surrounding rocks. Gradually, inclined pathways form, facilitating the ascent of the magma.
Formation of Yellowstone's underground magmatic system under the influence of mantle movements and lithospheric stresses.
Credit: Image by LIU Lijun's group
This mechanism directly influences the structure of volcanic systems. The combined stresses open pathways through the Earth's crust. Magma therefore does not accumulate immediately into a single chamber. It rather organizes itself into an evolving network, shaped over long periods.
Yellowstone illustrates this model particularly well. The site would harbor a vast zone of magma mush extending through the lithosphere. A more liquid pocket, similar to the old descriptions, would appear only temporarily. It would form shortly before an eruption, then disappear quickly.
This work offers a unified vision of how supervolcanoes function. It links the deep movements of the mantle to phenomena observed at the surface.