Post-2008 Inflation of Okmok Volcano, Alaska, from InSAR

Okmok Volcano, a dominantly basaltic volcanic complex that occupies most of the northeastern end of Umnak Island, is among the most active volcanoes in the Aleutian arc (Lu and Dzurisin, 2014). Minor ash eruptions were reported a dozen times since the 1930s. Blocky basalt flows were extruded during dominantly effusive eruptions in 1945, 1958, and 1997, together with minor amounts of ash. From the 1930s to 1997, all of Okmok’s eruptions originated from Cone A within the summit caldera. The most recent eruption at Okmok during July-August 2008 was by far the largest and most explosive eruption since at least the early 19th century. The eruption issued from a new vent in the northeast part of the caldera near Cone D, about 5 km northeast of Cone A. The eruption was strongly hydrovolcanic in nature and produced a new tuff cone roughly 240 m high, dramatically altering the landscape inside the caldera.

Interferometric synthetic aperture radar (InSAR) observations suggest that a magma reservoir, probably an interconnected network of magma bodies of varying sizes located beneath the caldera and centered ~3 km BSL, was responsible for volcano-wide deformation during 1992-2008, including the 1997 and 2008 eruptions (Lu and Dzurisin, 2014). The reservoir inflated at a variable rate before the 1997 and 2008 eruptions, and withdrawal of magma during both eruptions depressurized the reservoir, causing rapid volcano-wide subsidence. In this study, we report re-inflation of the Okmok reservoir from 2008 to 2014. InSAR imagery from X-band TerraSAR-X, C-band Envisat and L-band ALOS PALSAR satellites indicate that Okmok started inflating soon after the end of 2008 eruption at a rate of 5-10 cm/year, which is confirmed by GPS measurements. Deformation modeling suggests the inflation source is located beneath the center of Okmok caldera at ~3 km BSL, which is essentially the same location responsible for uplift and subsidence during 1992-2008.

Lu, Z., and Dzurisin, D., 2014. “InSAR Imaging of Aleutian Volcanoes: Monitoring a Volcanic Arc from Space”, Springer Praxis Books, Geophysical Sciences, ISBN 978-3-642-00347-9, 390 pp.