Rapid Inflation Caused by Shallow Magmatic Activities at Okmok Volcano, Alaska, Detected by GPS Campaigns 2000-2003
Abstract
Okmok volcano is located on Umnak Island in the Aleutian Arc, Alaska. This volcano consists of a large caldera, and there are several post-caldera cones within the caldera. It has erupted more than 10 times during the last century, with the latest eruption occurring in February 1997. Annual GPS campaigns during 2000-2003 have revealed a rapid inflation at Okmok volcano. Surface deformation indicates that Okmok volcano has been inflating during 2000-2003 at a variable inflation rate. Total displacements over three years are as large as 15 cm of maximum radial displacement and more than 35 cm of maximum uplift. Simple inflation pattern after 2001, showing radial outward displacements from the caldera center and significant uplifts, are modeled by a Mogi inflation source, which is located at the depth of about 3.1 km beneath the geometric center of the caldera, and we interpreted the source as a shallow magma chamber. The results from our GPS measurements correspond approximately to the results from InSAR measurement for almost same periods, except for an underestimate of the volume change rate of the source deduced by InSAR data for the period 2002-2003. Taking into consideration the results from InSAR measurements, the amount of volume increase in the source is estimated to be about 0.028 km3 during 1997-2003. This means that 20-54 percent of the volume erupted in the 1997 eruption has been already replenished in the shallow magma chamber. An eruption recurrence time is estimated from the volume change rate of the source to be about 15-30 years for 1997-sized eruptions, which is consistent with about 25 years average time interval between major eruptions at Okmok volcano. An additional modeling using a rectangular tensile source combined to the main spherical source suggests a possibility of other magma storage located between the main source and the active vent, which is associated with lateral magma transportation between them. The combined model improved residuals compared to those from single-source model, and provided significantly better fitting to the deformation data inside the caldera.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.G53A0865M
- Keywords:
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- 1207 Transient deformation (6924;
- 7230;
- 7240);
- 1211 Non-tectonic deformation;
- 1243 Space geodetic surveys