Renewed uplift at the Yellowstone Caldera measured by leveling surveys andsatellite radar interferometry

A first-order leveling survey across the northeast part of the Yellowstone caldera in September 1998 showed that the central caldera floor near Le Har dy Rapids rose 24+/-5 mm relative to the caldera rim at Lake Butte since th e previous survey in September 1995. Annual surveys along the same traverse from 1985 to 1995 tracked progressive subsidence near Le Hardy Rapids at a n average rate of -19+/-1 mm/year. Earlier, less frequent surveys measured net uplift in the same area during 1923-1976 (14+/-1 mm/year) and 1976-1984 (22+/-1 mm/year). The resumption of uplift following a decade of subsidenc e was first detected by satellite synthetic aperture radar interferometry, which revealed approximately 15 mm of uplift in the vicinity of Le Hardy Ra pids from July 1995 to June 1997. Radar interferograms show that the center of subsidence shifted from the Sour Creek resurgent dome in the northeast part of the caldera during August 1992 to June 1993 to the Mallard Lake res urgent dome in the southwest part during June 1993 to August 1995. Uplift b egan at the Sour Creek dome during August 1945 to September 1996 and spread to the Mallard Lake dome by June 1997. The rapidity of these changes and t he spatial pattern of surface deformation suggest that ground movements are caused at least in part by accumulation and migration of fluids in two sil l-like bodies at 5-10 km depth, near the interface between Yellowstone's ma gmatic and deep hydrothermal systems.