DETAILED GRAVITY STUDIES OF GEYSER BASINS IN WESTERN YELLOWSTONE NATIONAL PARK, WYOMING, USA

The Yellowstone volcanic complex (YVC) has been associated with a stationary plume source and this plume system has provided the heat for the world famous geothermal features within the Yellowstone caldera. Gravity studies have long been used to understand the crustal and lithospheric structure of YVC but detailed gravity surveys of the geothermal areas have been lacking. Since 2016, I have been collecting detailed gravity data in the western portions of the YVC within the Upper, Midway and Lower geyser basins. The data were collected using differential GPS methods in order to obtain centimeter level elevation data. To data over 500 stations have been collected in these basins and have processed into complete Bouguer gravity anomalies using 10 m and 2 m DEM models. The resultant data were analyzed using wavelength filtering and derivative methods in order to better define the density structure of the basins. More regional anomaly maps indicate that the Mallard Lake Dome, the Lone Star Geyser region and the northern section of the Lower Geyser Basin are associated with gravity minima that may be related to more hydrothermally altered volcanic rocks. Detailed data collected surrounding the Old Faithful geyser indicates that there exists a gravity minimum to the west of the geyser agreeing the surface wave models of the area which indicates a velocity minimum in the region. This minimum has been explained to be caused by hot water filled fractures that might be the source of water in Old Faithful. However, the highest amplitude minimum is to the northwest of these minimum, just west of the Yellowstone lodge in an area with active, small scale geothermal features. This region might contain an additional reservoir of water or be a region of altered volcanic material. New data collected in the summer of 2019 will further define this anomaly.