GoKawiilNorth America wouldn’t look much like it currently does without a tectonic plate that has largely been lost to the Earth’s geological history. The Farallon plate, which has since largely vanished underneath North America, helped build the West Coast by slamming large island chains into the continent as it disappeared. California wouldn’t exist without it, and one of the remaining fragments of the plate presently power the volcanoes of the Cascades.
Now, a new paper suggests that the Farallon plate is still making its presence felt far from the coasts, powering one of North America’s most distinctive phenomena: the Yellowstone hotspot, which has periodically blanketed much of the continent with ash. The new proposal suggests that the plate’s vanishing act has created stresses that have opened paths for molten rock to reach the surface.
Hot spot or not?
Geologic hot spots exist around the globe; they’re areas where deep material from the Earth’s interior finds its way to the surface far from the edges of plates. In many cases, the heat that powers these hot spots is the product of what’s called a mantle plume: a blob of hot molten rock that convection drives to the surface of the mantle. In many cases, the plume appears to stay in place as the plates drift across it, creating a chain of progressively older islands as you move away from the hot spot.
Hotspots are generally associated with islands. The thinner oceanic crust makes it easier for molten material to find a path to the surface than it would if it had to work through the thick continental crust. But there are exceptions, most notably the Yellowstone hot spot. That appears to be behaving a bit like an oceanic hot spot, leaving a trail of massive eruptions across the Snake River Plain that terminates at the immense calderas beneath present-day Yellowstone.