A debate among scientists about the dynamics of the Cascades subduction system in the western United States has taken a major step toward being resolved, thanks to new evidence provided by a team of international researchers led by University of Rhode Island Professor Christopher Kincaid.

In a letter appearing in Nature Geoscience, Kincaid, GSO alumna Kelsey Druken (PhD 2012),  and researchers from Scripps and Australian National University propose a mechanism that accounts for the apparently contradictory patterns of volcanism: a bifurcating mantle plume.

Using a plate tectonic laboratory model, they showed that volcanism in the Yellowstone area was caused by severely deformed and defunct pieces of a former mantle plume. They further concluded that the plume was affected by circulation currents driven by the movement of tectonic plates at the Cascades subduction zone. By using the model to simulate a mantle plume in the Yellowstone region, the researchers found that it reproduced the characteristically odd patterns in volcanism that are recorded in the rocks of the Pacific Northwest.

Mantle plumes are hot buoyant upwellings of magma inside the Earth. Subduction zones are regions where dense oceanic tectonic plates dive beneath buoyant continental plates. The origins of the Yellowstone supervolcano have been argued for years, with sides disagreeing about the role of mantle plumes.

According to Kincaid, the simple view of mantle plumes is that they have a head and a tail, where the head rises to the surface, producing immense magma structures, and the trailing tail interacts with the drifting surface plates to create a chain of smaller volcanoes of progressively younger age. But Yellowstone doesn’t fit this typical mold. Among its oddities, its eastward trail of smaller volcanoes called the Snake River Plain has a mirror-image volcanic chain, the High Lava Plain, that extends to the west. As a result, detractors say the two opposite trails of volcanoes and the curious north-south offset prove the plume model simply cannot work for this area, and that a plates-only model must be at work.
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Photo of Mt. Hood from Wikipedia