Opening Session

Earth's violent forces have produced the renowned scenery and the world's largest display of geysers at Yellowstone National Park. The energy responsible for these features is the Yellowstone hotspot, a coupled crust-mantle magmatic system that has had a profound influence on a much larger area of the western US; the Yellowstone-Snake River Plain-Newberry volcanic field (YSRPN). This intraplate system is reflected by a 16 Ma NE track of time-progressive silicic-basaltic volcanism of the Snake River Plain now active at Yellowstone and a mirror image of NW-trending magmatism across the High Lava Plains to the Newberry caldera, Ore. The origin of this magmatic-tectono system has been variously ascribed to plume-plate interaction, lithosphere extension, return mantle flow, decompression melting, etc. Integrated interpretation and modeling of the data from a proto-type EarthScope experiment in 1999-2002 we present results of crust-mantle tomography, kinematics from GPS, and dynamic models of the Yellowstone hotspot. Geodetic data show high secular rates of deformation of the Yellowstone Plateau, up to ~1 m from 1923 to 1975 and followed by decadal-scale uplift and subsidence at cm/yr. These data also show sustained ~4mm yr. of SW extension from the +500 m high Yellowstone Plateau, decreasing across the SRP and merging into E-W to NW extension of up to 1 cm/yr across the western U.S. interior. We believe this reflects "downhill flow" by inherent potential energy high of the topographically high Yellowstone swell and positive geoid anomaly. Seismic tomography reveals a pronounced mid-crustal P- and S-wave low velocity body of > 8% melt extending from ~6 km to 15 km beneath the caldera. This system is in turn fed by an upper-mantle low velocity plume-like body of up to 1-2% melt that extends to depths of ~250 km beneath. However this body notably tilts west and extends to ~650 km depth up to ~150 km west of Yellowstone. The bottom of the anomaly is at the bottom of the mantle transition zone. Thermal and mantle flow models are consistent with excess temperatures of +170°K for this body that is tilted upward in eastward motion of upper mantle flow. Using the inclined plume-geometry and the 650-km depth source depth we extrapolate the mantle source southwestward as a plume-head in oceanic lithosphere that occurred beneath the Columbia Plateau basalt field at 16 Ma. Ascent of mantle magma from this source was terminated by SW motion of the thicker continental lithosphere around ~12 Ma, resulting in a less energetic plume-tail along the YSRP, but continuing mantle return flow above the subducting Juan de Fuca plate fueling magmatism of the High Lava Plains and Newberry system. Dynamic models of the Yellowstone system in a western US framework are constrained by rates of deformation from GPS, L. Quat. fault-slip, and seismicity and by mantle flow and rheology deduced from the tomographic models. The importance of the Yellowstone hotspot in a global tectonic framework and as a natural geologic laboratory provides an opportunity to promote earth science literacy through collaborative education and outreach efforts focused on Yellowstone with university, NPS, and K-12 science education involvement.