Temporal gravity and height changes of the Yellowstone caldera, 1977-1994

This paper describes the longest record of gravity measurements in the area of the Yellowstone caldera, Wyoming. The temporal gravity changes, at the +/-12 mu Gal (10(-8) ms(-2)) precision level, are compared with changes in heights from leveling and GPS. The gravity field decreased across the caldera from 1977 to 1983 during the uplift and attained a maximum decrease of up to -60 +/- 12 mu Gal along the Caldera axis, The gravity field then reversed polarity to increasing values, of up to 60 +/- 12 mu Gal between 1986 and 1993. The ratio between height and gravity changes varied during the entire time, but converged over the latter period following the free-air gravity gradient. General ground deformation deduced from leveling showed caldera-wide uplift of similar to 15 mm/a during the period of gravity decrease, then from leveling and GPS, subsidence of similar to 25 mm/a during the gravity increase.