The Yellowstone Hotspot: Past, Present and Future

Robert Smith
University of Utah
EarthScope Distinguished Speaker
28 April 2010

The Yellowstone hotspot resulted from interaction of a mantle plume with the overriding North American plate producing a ~800-km wide, ~300-m high topographic swell centered on Yellowstone National Park. It also produced the 800 km-long, 17 million year old Yellowstone-Snake River Plain (YSRP) volcanic field. The Yellowstone Plateau has extensive seismicity including the deadly M7.5 Hebgen Lake Earthquake in 1959. There are also extensive earthquake swarms; the latest in late 2008 and early 2009 produced a thousand events on the caldera edge that migrated at ~1,000 meters per day beginning with an explosive M4 earthquake. Heat flow is extraordinarily high, ~ 2,000 mWm2, indicative of the thermal energetics of this active volcano-tectonic system. Large-scale geophysical experiments have provided seismic and GPS images of the hotspot and data on its kinematic and dynamic properties. Tomography reveals a caldera-wide Yellowstone crustal magma reservoir, that is fed by an upper-mantle plume composed of melt blobs, 80 km to 650 km deep, titled 60 degrees NW. Deformation of Yellowstone is dominated by SW-extension at up to ~0.3 cm/yr, a fourth of the total Basin-Range opening rate, but with superimposed volcanic related uplift and subsidence at decadal scales, averaging ~2 cm/yr. An unprecedented episode of caldera uplift, up to 7 cm/yr from 2004-2008, was modeled as recharge of the crustal magma body at 10-km depth. Upper mantle convection models for Yellowstone are characterized by eastward flow beneath Yellowstone at 5 cm/yr. This suggests that the strong eastward mantle flow that deflects the ascending melt into a tilted configuration, i.e. "bending the plume in the mantle wind." Dynamic models reveal relatively low plume temperatures, up to 150 degrees K excess temperatures, consistent with a weak buoyancy flux of ~0.25 Mg/s, but strong enough to produce the Yellowstone swell. Kinematic and dynamic modeling suggest that the excess gravitational potential of the swell drives the SW motion of the YSRP lithosphere "downhill" where it becomes part of clockwise rotation of western U.S. intraplate blocks. Extrapolating the location of the Yellowstone mantle-source southwestward to an initial position at 17 million years ago beneath eastern Oregon and the southern Columbia Plateau basalt field, suggests a common mantle source for these features. We suggest that the original plume ascended vertically behind the subducting Juan de Fuca plate, becoming entrained in faster mantle flow beneath continental lithosphere and became tilted into its present configuration about 12 million years ago.

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