[1] A group of satellite radar interferograms that span the time period from 1991 to 2000 shows that Westdahl volcano, Alaska, deflated during its 1991-1992 eruption and is reinflating at a rate that could produce another eruption within the next several years. The rates of inflation and deflation are approximated by exponential decay functions having time constants of about 6 years and a few days, respectively. This behavior is consistent with a deep, constant-pressure magma source connected to a shallow reservoir by a magma-filled conduit. An elastic deformation model indicates that the reservoir is located about 6 km below sea level and beneath Westdahl Peak. We propose that the magma flow rate through the conduit is governed by the pressure gradient between the deep source and the reservoir. The pressure gradient, and hence the flow rate, are greatest immediately after eruptions. Pressurization of the reservoir decreases both the pressure gradient and the flow rate, but eventually the reservoir ruptures and an eruption or intrusion ensues. The eruption rate is controlled partly by the pressure gradient between the reservoir and surface, and therefore it, too, decreases with time. When the supply of eruptible magma is exhausted, the eruption stops, the reservoir begins to repressurize at a high rate, and the cycle repeats. This model might also be appropriate for other frequently active volcanoes with stable magma sources and relatively simple magma storage systems.

Interferometric synthetic aperture radar (InSAR) is capable of measuring groundsurface deformation with centimeter-to-subcentimeter precision at a spatial resolution of tens of meters over a large region. With its global coverage and all-weather imaging capability, InSAR has become an increasingly important measurement technique for constraining magma dynamics of volcanoes over remote regions such as the Aleutian Islands. The spatial distribution of surface deformation data derived from InSAR images enables the construction of detailed mechanical models to enhance the study of magmatic processes. This paper summarizes the diverse deformation patterns of the Aleutian volcanoes observed with InSAR. These include the following: 1) inflation of Mount Peulik Volcano preceding a seismic swarm at nearby Becharof Lake in 1998; 2) persistent volcano-wide subsidence at Aniakchak and Fisher Volcanoes; 3) magmatic intrusion and associated tectonic stress release at Akutan Volcano; 4) magmatic intrusion at Makushin Volcano associated with a small eruption in 1995; 5) complex patterns of transient deformation during and after the 1992-93 eruption at Seguam Volcano; 6) subsidence caused by a decrease in pore fluid pressure in an active hydrothermal system beneath Kiska Volcano; and 7) lack of expected deformation associated with recent eruptions at Shishaldin, Pavlof, Cleveland, and Korovin Volcanoes. We also present preliminary InSAR results for the Katmai Volcano group, and Chiginagak and Dutton Volcanoes. These studies demonstrate that deformation patterns and associated magma supply mechanisms in the Aleutians are diverse and vary between volcanoes. These findings provide an improved understanding of magmatic plumbing systems in the Aleutians.

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ERS-1 and ERS-2 SAR data were collected in tandem over a four-month period and used to generate interferometric coherence, phase, and intensity products that we compared to a classified land cover coastal map of Big Bend, Florida. Forests displayed the highest intensity, and marshes the lowest. The intensity for fresh marsh and forests progressively shifted while saline marsh intensity variance distribution changed with the season. Intensity variability suggested instability between temporal comparisons. Forests, especially hardwoods, displayed lower coherences and marshes higher. Only marshes retained coherence after 70 days. Coherence was more responsive to land cover class than intensity and provided discrimination in winter. Phase distributions helped reveal variation in vegetation structure, identify broad land cover classes and unique within-class variations, and estimate water-level changes.