Supereruptions are one of the most powerful volcanic phenomena on Earth. These large eruptions can release more than 1,000 cubic kilometers of magma, rock, and ash, with dramatic impacts on climate, ecosystems, and human societies. Because of their impact, scientists are working to better understand the underground processes that create and sustain these giant volcanoes.
Researchers at the Institute of Geology and Geophysics, Chinese Academy of Sciences (IGGCAS) have recently developed a detailed three-dimensional model of western North America that simulates the current behavior of the lithosphere and underlying mantle. Their research revealed a new explanation for how magma is generated beneath supervolcanoes.
The survey results are science.
Rethinking how supervolcanoes store magma
Scientists have long believed that supervolcanoes contain large, long-lived chambers filled primarily with liquid magma. In this traditional view, low-density magma gradually builds up within the Earth’s crust, increasing pressure until the surrounding rock cracks, collapses, and eventually erupts.
However, increasing evidence suggests that active supervolcanoes do not have such permanent liquid reservoirs. Instead, the magma appears to be distributed in widespread regions of partially molten rock known as “magma mash” systems. These muddy zones could extend through much of the Earth’s outer shell (the lithosphere), creating subsurface structures quite unlike anything previously imagined.
The lithosphere is the cold, hard outer layer of the Earth, including both the crust and the uppermost mantle. Beneath it lies the asthenosphere, a hotter, more ductile layer that flows more slowly over geological time.
Recent studies have shown that the magma that feeds supervolcanoes originates within the upper asthenosphere (the shallow mantle directly beneath the lithosphere). But exactly how this material dissolves remains unclear. As the molten rock rises into the lithosphere, it mixes with the surrounding solid rock, forming highly viscous magma mush. These mushy systems are much thicker and less mobile than liquid magma, making it difficult to explain how simple buoyancy alone could cause a supereruption.
Unlike the concentrated magma chambers proposed in older models, these muddy systems are widely spread throughout the lithosphere.
Yellowstone as a natural laboratory
The Yellowstone caldera in the western United States is one of the world’s most famous supervolcanoes. It has experienced two supereruptions in the past 2.1 million years, making it an important site for studying the behavior of large volcanic systems.
Previous studies have shown that Yellowstone contains a large, long-lived magmatic mash system that dips southwestward through the lithosphere. The study also suggests that shallower, liquid-rich magma bodies, similar to the classic magma chamber concept, may only form for a short period of time before an eruption occurs.
Scientists have learned a lot about Yellowstone’s internal structure, but the deep forces involved in building and maintaining this system remain unknown.
“Mantle wind” beneath North America
Using a new geodynamic model, researchers found that Yellowstone’s magma is fed by a shallow asthenosphere, rather than a deep mantle plume rising from the Earth’s interior.
According to this model, eastward-moving “mantle winds” carry hot asthenosphere material toward Yellowstone. This mantle wind is generated by the long-term subduction of the Farallon Plate, which remains deep underground in central-eastern North America.
Unlike atmospheric winds, these mantle winds consist of wide horizontal movements of hot, slow-flowing rocks within the Earth’s mantle.
As this buoyant material moves beneath the continent, it is pulled downward beneath the thick lithosphere. The resulting elongation creates conditions that promote vacuum melting, producing magma. The discovery challenges the long-held idea that Yellowstone rests on a deep mantle plume that rises from the core-mantle interface.
How deep forces shape Yellowstone’s magma system
The study also shows that mantle winds help determine the shape and evolution of Yellowstone’s vast magmatic system.
Eastward mantle flow pushes the roots of the thick lithosphere east of Yellowstone. At the same time, the buoyant lithosphere in the west generates an opposing force. Together, these competing forces effectively “rip apart” the continent’s lithosphere, creating a southwest-dipping channel beneath Yellowstone.
This channel serves as an efficient pathway for magma to rise, move, and evolve within the lithosphere. As a result, it plays an important role in controlling the structure and long-term evolution of Yellowstone’s magmatic system.
The model results are in general agreement with independent geophysical and geochemical observations collected in the region.
New insights into the formation of supervolcanoes
The researchers say their study provides the most complete explanation to date of how large magma systems form beneath supervolcanoes. This model links magma production in the asthenosphere and magma accumulation throughout the lithosphere, connecting processes that have previously been difficult to explain within a single framework.
The study also identified a physical mechanism that can maintain large, long-lived magma mush systems, a common feature of many supervolcanoes around the world.
