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The Snake River Plain As A Divergent Boundary. Yellowstone Caldera.
Let's take a look at The Snake River Plain satellite photo at: OSU, "The Snake River Plain and the Yellowstone Hot Spot" ( http://volcano.oregonstate.edu/vwdocs/volc_images/north_america/yellowstone.html ) [Accessed Jun-18, 2011]
Let's consider Eastern part of the plain (the one that is closer to Yellowstone). Interestingly, for this part of the plain, its North-West border would fit exactly South-East border if the plain between borders gets cut off the image. And, as the ridges are very diverse in their shape on a distance even much less than width of the plain, the only explanation of it, I can think of, can be the divergent boundary formed perpendicular to the ridges. Assuming the divergent process is 1sm/year, it would take approx 10 million years to spread the plain. The divergent process may have stopped long ago for most of The Snake River Plain, but apparently not for its North-Eastern tip.
It woud be very interesting to compare the plain's crust and relief to some oceanic (Pacific) divergent boundary's crust and relief. I've looked through approx a couple of dozens .gov and .edu sites on The Snake River Plain, - none of the sites mentioned that the borders of the East of The Snake River Plain would fit each other. Am I missing something?
The possible scenario for Yellowstone Caldera can be that the divergent boundary had been developing pressure and trying to build its "Bridge Over Troubled Magma." (see http://divergent-boundaries.blogspot.com/2011/05/ridge-push-or-bridge-over-troubled.html and http://divergent-boundaries.blogspot.com/2011/06/tectonics-types-of-heat-transport-to.html ). As the process is relatively local (in comparison to oceanic divergent boundaries), it can't develop the force to break the plate and move its parts apart. Instead, the process would be pumping the top layer of the plate up. If the magma finds its way to escape the chamber, the volcano won't erupt.
(edited Jun-20, 2011)
reposted from http://sukhotinsky.blogspot.com/