Model points to mantle flow as Yellowstone magma driver
A new study says broad mantle movement, rather than a deep plume, may help generate and sustain Yellowstone’s underground magma system.
By Lucas Ferreira · Science & Environment Writer
3 min read
A new geodynamic model suggests Yellowstone’s volcanic system may be powered by broad sideways flow in Earth’s mantle rather than a narrow plume rising from deep inside the planet. The finding matters because it offers a different explanation for how supervolcanoes can maintain large magma systems over long periods, according to researchers from the Institute of Geology and Geophysics of the Chinese Academy of Sciences.
The study, published in Science, used a three-dimensional model of western North America to simulate the present behavior of the lithosphere and the mantle beneath it, the Chinese Academy of Sciences said. The team reported that hot material in the shallow asthenosphere, the ductile layer beneath the rigid outer shell of Earth, can feed magma beneath Yellowstone.
Supereruptions release more than 1,000 cubic kilometers of magma, rock and ash, according to the academy. Because eruptions on that scale can affect climate, ecosystems and human societies, researchers have tried to identify the processes that build and preserve the volcanic systems capable of producing them.
A different picture of magma storage
Older models treated supervolcanoes as systems with large, long-lived chambers holding mostly liquid magma, the academy said. In that view, buoyant magma collects in the crust until pressure fractures surrounding rock and contributes to eruption.
Recent evidence points to a less fluid structure, according to the researchers. Active supervolcanoes appear to hold magma across broad zones of partly molten rock known as magma mush, which can extend through much of the lithosphere.
The academy said those mush systems are thicker and less mobile than liquid-filled chambers, making buoyancy alone a poor explanation for how supereruptions develop. Studies cited by the researchers indicate that magma feeding supervolcanoes begins in the upper asthenosphere, but the melting process has been hard to pin down.
Yellowstone’s mantle wind
Yellowstone, in the western United States, is one of the best studied supervolcanoes. The academy said the caldera has produced two supereruptions over the past 2.1 million years and contains a long-lived magma mush system that extends through the lithosphere and dips toward the southwest.
The new model identifies an eastward-moving “mantle wind” as a driver of that system, according to the study by Zebin Cao, Lijun Liu, Bo Wan, Ling Chen and Craig Lundstrom. The researchers linked that flow to the long history of subduction of the Farallon Plate, remnants of which remain deep beneath central and eastern North America.
In the model, hot asthenospheric rock moves horizontally beneath the continent and is pulled downward under thicker lithosphere, the academy said. That stretching promotes decompression melting, which can generate magma closer to the surface than a plume rising from the core-mantle boundary would imply.
The researchers also reported that mantle flow helps shape Yellowstone’s magma pathways. Eastward mantle movement pushes against a thick lithospheric root east of Yellowstone, while buoyant lithosphere to the west exerts an opposing force, producing a southwest-dipping channel that can carry magma through the lithosphere, according to the academy.
The academy said the model matches independent geophysical and geochemical observations from the region. The researchers said the work links magma generation in the asthenosphere with accumulation in the lithosphere, offering a single mechanism for sustaining large magma mush systems beneath Yellowstone and other supervolcanoes.
This story draws on original reporting from ScienceDaily.