The crust appears to be two separate branches originating from the same common location at the mantle boundary. One branch descends to the northeast to feed the Yellowstone caldera, and the second extends into the Snake River plain. The branches split so that a volcanic-free zone results between the two features.
The researchers reasoned that the pathways to the surface could be made possible by stresses in the Earth’s crust, regardless of anything else that would provide the molten material. And it will depend both on the existing properties of the earth’s crust (mainly obtained through seismic data) and on the larger-scale processes taking place in the mantle below. Thus, the model contained both basic geological details, known physical processes, and some history in the sense of what we know about how that part of the Earth’s crust formed.
And we return to the Farallon plate. Its remnants are dragged under the North American plate and continue to sink and move along the mantle. According to the researchers, this causes a general eastward flow of material through the viscous mantle. Just east of Yellowstone, this stream flows into the old boundary of the North American plate, where the crust is thicker and denser than the continental portion deposited by the Farallon plate.
New ways
This thick crust causes the mantle to flow downward. And this change in flow causes a number of stresses in the Earth’s crust, especially compression between the old and new parts of the North American plate, as well as downward drag on the old part. In addition to local stresses, the fact that all the material that erupted to form the Snake River Plain is denser than most of the surrounding rocks puts stress on nearby rocks as they try to sink.
