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Community Lecture Series
Community Lecture Series
The Yellowstone Supervolcano: Past, Present and Future
Feb. 19, 2009
Robert B. Smith
Professor of Geophysics,
University of Utah
Yellowstone is rooted in some of Earth’s most violent forces and is the most globally significant continental hotspot. These forces have produced the magnificent scenery of Yellowstone National Park, its world-renowned geysers, the largest volcanic field in North America, and a killer earthquake. The energy responsible for Yellowstone is from hundreds of kilometers deep within the Earth, the power of a magma that rises from a deep mantle plume that tilts west to beneath the Montana-Idaho border and rises to the surface uplifting the Earth into a ~500 m high, 800 km wide topographic swell.
In my lecture I will explain how the 17 My, SW movement of the North American plate that began beneath the Columbia Plateau, Oregon-Washington, has placed Yellowstone National Park over the mantle plume whose “untextbook” like westward tilt is explained by rising magma caught in a mantle “wind” that flows eastward in the opposite direction as the overriding plate. It is the source of three super volcano eruptions at Yellowstone that exploded thousands cubic-kilometers of magma and destroyed mountains and reshaped the topography during its youthful 2 My year history.
New studies of the Yellowstone crustal magma chamber shows that it extends beneath and 20 km north of the caldera, about 20% larger than earlier determined. This magma body continues to fuel Yellowstone’s geysers, it powers a restless living-breathing-shaking caldera; and enhances the interior West’s most seismically hazardous area. Moreover, magma and hydrothermal fluid movement uplifts and drops the ground by meters on decadal scales; and continuously refills the crustal magma reservoir creating an enormous amount of heat flux, >2,000 mWm-2, in excess of 40 times the continental average. Heat flow studies of Yellowstone Lake characterize the thermal energetics of the entire Yellowstone caldera. With the accessibility on Yellowstone Lake by a research vessel outfitted with marine equipment, three “lake bottom “geyser” basins” were discovered with enormously high heat fluxes, the largest exceeding 36,000°C/km at Mary Bay, others are along the east side of Stevenson Island, and in West Thumb. Historically, Yellowstone experiences decades of caldera uplift and subsidence with long term SW extensional opening of ~4 mm/yr pushing the adjacent Snake River Plain region downhill to the southwest away from the high potential energy of the swell and affecting contemporary deformation of much of the western U.S.
I termed the decadal changes in deformation and seismicity of the Yellowstone caldera as a “living, breathing, shaking” caldera. However in 2004 Yellowstone unexpectedly began to experience unprecedented changes in its ground motion and earthquake history. In autumn 2004 the caldera suddenly increased it’s uplift rate from 2-cm/yr uplift to 7 cm/yr, three times larger than its historic rates, and twice as fast as the loading rate on the San Andreas fault. This unprecedented deformation was geographically coincident with the caldera and was modeled as recharging of its crustal magma chamber at 10 km depth. And most recently, in 2008-2009, Yellowstone experienced its second largest historic earthquake swarm located in the Yellowstone Lake area that was well recorded by the real-time seismic network. The sequence consisted of ~1000 earthquakes, 0.5<M<3.9, in a two+ week period, with 20+ felt events of M>3. The earthquake hypocenters define a N-S 12 km-long alignment of earthquakes shallowing from central Yellowstone Lake toward Fishing Bridge. Seismic sources and GPS data reveal the dominance of E-W extensional stresses for the swarm-volume that are interpreted to reflect volcanic dike opening that initiated in the top of the crustal magma chamber allowing upward and outward migration of hydrothermal fluids toward the surface.
I will also note how the ecological extant and interrelationships between Yellowstone’s geologic and biologic features is better termed the “Yellowstone GeoEcosystem”, a term that I first defined in 1985.
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