CONSTRAINING VOLCANIC INFLATION AT THREE SISTERS VOLCANIC FIELD THROUGH MICROGRAVITY AND DEFORMATION MODELING

Recent volcanic unrest at Three Sisters volcanic field, Oregon, started early in 1998 and provides a unique opportunity to study intrusive processes via integrated geodetic (gravity and deformation) techniques. Microgravity surveys completed between August 2002 and October 2008 provide a time series to constrain the deformation event currently taking place at Three Sisters Volcanic Field. 35 individual surveys have been completed to facilitate modeling of the rate, mass flux, and density of the intrusion. Studies of spring geochemistry in Separation creek at the center of the deforming area confirm that there is a magmatic component to the spring water. However, current activity does not appear to have affected the local hydrothermal system. A combination of leveling, InSAR, and GPS studies suggest the intrusion of a prolate spheroid at ~5 km depth with a volume of 37 x 10⁶ to 42 x 10⁶ m³. Preliminary forward modeling of gravity data suggests that the inflationary signal is significant and should be visible above background noise. Further modeling of the integrated geodetic data will be used to test whether the deformation is due to a visco-elastic response to a nearly instantaneous pressurization of the crust, hydraulic response of continual injection of material, over-pressurization of the hydrothermal system, or a combination of the above. The combination of geodetic and geochemical data with advanced modeling is fundamental to advancing our understanding of physicochemical processes responsible for changes in volcanic activity. Original funding supported by NSF Award 0439812