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This subsidence of the crust produced a large, slightly depressed lava plain now known as the Columbia Basin or Columbia River Plateau.
The northwesterly advancing lava forced the ancient Columbia River into its present course.
Using tomographic images based on seismic waves, relatively narrow, deeply seated, active convective plumes have been detected under Yellowstone and several other hot spots.
These plumes are much more focused than the upwelling observed with large-scale plate-tectonics circulation.
states of Washington, Oregon, Idaho, Nevada, and California.
Further, the Yellowstone images show necking of the plume at 650 km (400 mi) and 400 km (250 mi), which may correspond to phase changes or may reflect still-to-be-understood viscosity effects.
Additional data collection and further modeling will be required to achieve a consensus on the actual mechanism.
An abrupt transition to shield volcanic flooding took place in the mid-Miocene.
The flows can be divided into four major categories: The Steens Basalt, Grande Ronde Basalt, the Wanapum Basalt, and the Saddle Mountains Basalt.