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Deformation of Akutan volcano, Alaska, revealed by Satellite Radar Interferometry

Z. Lu, C. Wicks, J. Power and D. Dzurisin

Paper reference: Z. Lu, C. Wicks, J. Power and D. Dzurisin, 2000 in press, Deformation of Akutan volcano, Alaska, revealed by Satellite Radar Interferometry, J. Geophys. Res.

Akutan volcano is one of the most active volcanoes in the Aleutian arc. At least 27 separate eruptive episodes have been noted since 1790, most recently a series of small steam and ash emissions during March-May 1992. In March 1996, an intense swarm of volcano-tectonic earthquakes beneath Akutan (~3000 felt by local residents, depth 0-10 km, Mmax = 5.1) produced extensive ground cracking but no eruptive activity. Radar interferograms that span the time of the earthquake swarm reveal island-wide deformation that we modeled as the emplacement of a shallow, east-west-trending, north-dipping dike plus inflation of a volume source beneath the west flank of the volcano. The magma migrated from two steeply north-dipping dikes, which caused the deflation of the east part of the volcano. This model is generally consistent with the deformation pattern revealed by interferograms, the mapped pattern of ground cracks, and the distribution of earthquake hypocenters. No ground movements greater than one interferometric fringe (2.83 cm) were observed outside the caldera in several interferograms for periods of 4 years before or 2 years after the 1996 earthquake swarm. Inside the caldera, localized subsidence by as much as 10 cm during 1992-1993 and 1996-1998 seems to be associated with a zone of active fumaroles. We conclude that satellite radar interferometry is a useful tool for measuring deformation of Aleutian volcanoes, at least where lava flows predominate and during relatively short Alaskan summers. For the technique to become an effective volcano hazards mitigation tool, however, shorter imaging repeat times (on the order of a few days rather than weeks) are essential. Realization of this potential must await the launch of new satellites with missions dedicated at least partly to radar interferometry.