SURFACE DEFORMATION, LAKE LEVEL VARIATION, AND SHORELINE CHANGE AT YELLOWSTONE LAKE, YELLOWSTONE NATIONAL PARK, USA: AN UPDATE ON MODELING RESULTS

The Yellowstone caldera has at least two major centers of deformation, called resurgent domes, and vertical deformation resulting from volcanic activity beneath these resurgent domes and potentially other dynamics of the caldera are temporally and spatially complex. The purpose of this study is to examine and model the response of the Yellowstone Lake shore to caldera deformation and lake level oscillations empirically. Prior studies by other investigators indicated the direction and magnitude of caldera deformation using releveling surveys (1923 through the 1980s), satellite radar observations (late 1980s to the present), and GPS geodesy (mid-1990s to the present). While some studies indicated unidirectional deformation within the caldera (all areas of the caldera either inflating or deflating), other studies indicated shifting centers of deformation between resurgent domes on variable time scales. It was hypothesized that the rate and magnitude of shoreline recession or advance on Yellowstone Lake was controlled primarily by three factors: caldera inflation and deflation, lake level, and sediment redistribution. A model testing the interaction of two of these parameters (vertical deformation and lake level) on shore position was evaluated for the West Thumb arm of Yellowstone Lake. The model combined high-resolution bathymetry (near-shore to several kilometers offshore) with publicly-available 10-meter digital elevation models (DEMs) of the lake and surrounding areas. Deformation of the DEM was achieved using simple tilting surfaces based on available deformation data. Shore position was determined in the model by applying corrected lake level to the deformed DEM. Modeled shorelines were compared to shorelines delineated on 1994 and 2002 digital orthophoto quarter quadrangles in an attempt to replicate observed shoreline change over this 8-year interval. Results indicated a model of simple tilting combined with corrected lake level that was sufficient to replicate observed patterns of shore recession and advance whereas simple tilting alone or corrected lake level alone could not. The preferred model result is reasonable given constraints on spatial and temporal resolution of surface deformation measurements acquired from GPS geodesy and INSAR.