Determining a volcanic source model for the post eruptive behavior of the 2008 Okmok eruption by combining GPS and InSAR

Okmok volcano is one of the most active volcanoes in the Aleutian Island chain, showing significant non-linear deformation as it progresses through eruption cycles. Okmok most recently erupted in July 2008 creating a new cone (~250m in height) and greatly changing the topography inside the caldera. Okmok's previous 9 eruptions originated from cone A, whereas the 2008 eruption moved spatially approximately 4 km northeast of cone A within the 10km wide caldera. This geographic change in eruption location combined with the post eruptive rapid inflation of the caldera floor create new possibilities for source modeling of this active volcano. This study compiles both GPS and SAR measurements to constrain the post eruptive behavior, and examine the possible changes below the surface. With continuous and campaign GPS stations and L-band radar imagery from the JAXA AOLS PALSAR satellite spanning August 2008 to October 2010, we were able to develop a source model for the post eruptive behavior. Previously, a simple Mogi model was used in describing the behavior seen at Okmok, but due to the spatial variance exhibited in this eruption other possibilities were also explored. The GPS and InSAR data show a distinct change in velocity observed during the 2 year time period studied, suggesting a rapid refilling of the storage area that slowed approximately 14 months after the eruption ended. We evaluate whether this change is due to a change in the magma influx rates, a change in the source geometry, or a combination of the two.