Two distinct arms seem to begin from roughly the same spot at the crust-mantle boundary. One arm angles northeastward toward the Yellowstone caldera, while the other extends toward the Snake River Plain. The split between them produces the volcano-free zone lying between those two features.
The researchers concluded that, regardless of other factors supplying molten material, the routes to the surface were likely controlled by stresses in the crust. Those stresses depend on both the crust’s existing structures (mapped largely via seismic data) and broader processes occurring in the underlying mantle. Consequently, the model incorporated basic geological details, established physical processes, and some historical context about how that section of crust developed.
This brings the Farallon plate back into the picture. Its remnants, pushed beneath the North American plate, continue to sink and move through the mantle. The researchers infer that this motion drives a general eastward flow of material through the viscous mantle. Just east of Yellowstone, however, that flow encounters the older margin of the North American plate, where the crust is thicker and denser than the portion of the continent laid down by the Farallon plate.
New pathways
That thicker crust forces the mantle flow to bend downward. The change in flow generates a range of stresses in the crust, most notably compression between the older and newer sections of the North American plate and a downward drag on the older block. Local stresses are further increased because the material that erupted to form the Snake River Plain is denser than much of the surrounding rock, producing strain on nearby rocks as it attempts to sink.
