Researchers from the Institute of Geology and Geophysics of the Chinese Academy of Sciences (IGGCAS) have now developed a detailed three-dimensional model of western North America that simulates the present-day behavior of both the lithosphere and the flowing mantle beneath it. Their work reveals a new explanation for how magma is generated beneath supervolcanoes.

The findings were published in Science.

Rethinking How Supervolcanoes Store Magma

For many years, scientists believed that supervolcanoes contained large, long-lived chambers filled primarily with liquid magma. In this traditional view, low-density magma gradually accumulates within the crust, increasing pressure until the surrounding rock fractures, collapses, and ultimately erupts.

However, growing evidence suggests that active supervolcanoes do not contain these persistent liquid reservoirs. Instead, magma appears to be distributed across extensive regions of partially molten rock known as "magma mush" systems. These mush zones can extend through much of the Earth's outer shell (the lithosphere), creating a very different underground structure than previously envisioned.

The lithosphere is the cold, rigid outer layer of Earth and includes both the crust and the uppermost mantle. Beneath it lies the asthenosphere, a hotter and more ductile layer that slowly flows over geologic time.

Recent studies indicate that the magma feeding supervolcanoes originates within the upper asthenosphere (the shallow mantle just beneath the lithosphere). Yet exactly how this material melts has remained uncertain. As molten rock rises into the lithosphere, it mixes with surrounding solid rock and forms a highly viscous magma mush. These mush systems are much thicker and less mobile than liquid magma, making it difficult to explain how they could generate supereruptions through simple buoyancy alone.

Unlike the concentrated magma chambers proposed in older models, these mush systems are spread broadly throughout the lithosphere.

Yellowstone as a Natural Laboratory

The Yellowstone caldera in the western United States is one of the world's best-known supervolcanoes. Over the past 2.1 million years, it has experienced two supereruptions, making it an important site for studying the behavior of giant volcanic systems.

Previous research has shown that Yellowstone contains a large, long-lived magma mush system extending through the lithosphere and dipping toward the southwest. Studies also suggest that a shallower, liquid-rich magma body, similar to the classic concept of a magma chamber, may form only briefly before an eruption occurs.

Although scientists have learned much about Yellowstone's internal structure, the deeper forces responsible for creating and maintaining this system have remained unclear.

A "Mantle Wind" Beneath North America

Using their new geodynamic model, the researchers found that Yellowstone's magma is supplied by the shallow asthenosphere rather than by a deep mantle plume rising from Earth's interior.

According to the model, an eastward-moving "mantle wind" transports hot asthenospheric material toward Yellowstone. This mantle wind is generated by the long-term subduction of the Farallon Plate, remnants of which remain deep beneath central and eastern North America.

Unlike winds in the atmosphere, this mantle wind consists of a broad horizontal movement of hot, slowly flowing rock within Earth's mantle.

As this buoyant material moves beneath the continent, it is drawn downward under the thick lithosphere. The resulting stretching creates conditions that promote decompression melting, producing magma. This finding challenges the long-standing idea that Yellowstone sits above a deep mantle plume rising from the core-mantle boundary.

How Deep Forces Shape Yellowstone's Magma System

The study also shows that the mantle wind helps determine the shape and evolution of Yellowstone's vast magmatic system.

Eastward mantle flow pushes against the thick lithospheric root located east of Yellowstone. At the same time, buoyant lithosphere to the west generates an opposing force. Together, these competing forces effectively "tear" the continental 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 a major role in controlling the structure and long-term development of Yellowstone's magmatic system.

The model's results closely match independent geophysical and geochemical observations collected from the region.

New Insights Into Supervolcano Formation

The researchers say their study provides the most complete explanation to date for how large magmatic systems form beneath supervolcanoes. The model links magma generation in the asthenosphere with its accumulation throughout the lithosphere, connecting processes that were previously difficult to explain within a single framework.

The work also identifies a physical mechanism capable of sustaining large, long-lived magma mush systems, a characteristic shared by many supervolcanoes around the world.