In broad outlines, the geological activity that produced Yellowstone is well understood. The North American plate is drifting westward over a hotspot in the mantle, a hotspot that has littered the landscape to the west with volcanic features. Since landing under Yellowstone, it's set off some truly cataclysmic eruptions, one of which is thought to have expelled 2,500 cubic kilometers of material.
Understanding the current state of the plumbing beneath Yellowstone could be key to determining the risk of another event of this magnitude (even a smaller one would be rather significant). And here's where we've got a bit of a gap in our knowledge. While we have good imaging of the mantle plume itself and the area immediately under the caldera, it's not been clear what's between the two. In this week's edition of Science that gap has been closed.
Scientists already knew something was up at the intervening depths. There's a volume of partly molten material between the depths of five and 16km, one that may occupy up to 10,000km3. But Yellowstone emits an estimated 45,000 tons of carbon dioxide daily, and it's impossible to get that much gas out of that volume of molten rock. And the plume of hot mantle material is far too deep at 60km.
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