Temporal gravity and mass changes accompanying the 2004-2008 unprecedented uplift of the Yellowstone caldera

Beginning in late 2004, GPS and InSAR data revealed the beginning of an unprecedented episode of uplift in the 0.64 Ma Yellowstone caldera at rates up to 7 cm/yr. The caldera tumescence has been modeled as an expanding volcanic sill of ~1200 square kilometers at 10 km depth beneath the caldera, coincident with the top of the seismically imaged crustal magma chamber. The modeled rate of source volume increase of 0.1 cubic kilometers per year is evidence of an influx of molten material to the system as the main mechanism for the uplift and is consistent with the 2,000 mW/m2 total heat flux. To evaluate the mass rate change of the volcanic source of the accelerated uplift, temporal variations in gravity were measured from 2007-2008 at the precision Yellowstone gravity network established in 1975. We compare the changes in gravity and equivalent mass changes to infer whether the uplift is due to the influx of magma or a change in the orthometric height alone.