Previous models relating the Snake River plain and Columbia River Basalt (northwest United States) to the Yellowstone plume have not taken into account the effects of the subducted Farallon and Juan de Fuca plates. Not only did subduction shield the surface from mantle plume activity, but it deflected the plume in the direction of plate motion. A variety of geophysical and geologic evidence suggests that the plume penetrated the subducted slab at ∼17.5 Ma, causing eruption of the Columbia River Basalt. The plate boundary then migrated over the plume, and the Yellowstone plume has recovered to a more nearly vertical conduit, forming the Snake River plain and Yellowstone plateau.

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