Surface Deformation Caused by a Shallow Magmatic Source at Okmok Volcano, Aleutian Arc
Abstract
Okmok Volcano, located on Umnak Island in the eastern Aleutian arc, last erupted in 1997. Okmok consists of a 10 km wide caldera with several cones located inside. Significant surface deformation before, during and after the eruption has been measured using InSAR. However, the area of coherent data has been limited to the northern part of the caldera, with some additional coherent areas along the outer flanks of the volcano. With support from NASDA (National Space Development Agency of Japan) and the International Arctic Research Center, we carried out GPS campaigns in 2000 and 2001 to supplement the InSAR data with 3D measurements of deformation at well-distributed points. We surveyed 24 sites on and around Okmok in 2000, and 31 sites in 2001. As of this date, no SAR data from suitable passes has been acquired in the summer of 2001; if any are acquired, we will also analyze this data. InSAR data for the period 1997-2000 show what appears to be a radially-symmetric pattern of displacements, consistent with the inflation of a shallow (3-4 km) pressure (Mogi) source located beneath the geoemtric center of the caldera. A deflation source at the same location and depth was inferred from an interferogram spanning the eruption. The 2000-2001 GPS data, on the other hand, show evidence for rapid horizontal extension between sites in center of the caldera. This signal cannot be explained by a Mogi source, and may represent the intrusion of a shallow dike. In addition to this probable dike source, it appears that overall inflation of the volcano continues. The proposed dike extends from roughly the center of the caldera toward the 1997 eruptive vent. In May 2001, a swarm of micro-earthquakes occurred somewhere close to Okmok Volcano (location errors are very large as the closest permanent seismic site is ~100 km from Okmok). It is possible that this small earthquake swarm could have been associated with the intrusion of the shallow dike.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFM.G31C0163M
- Keywords:
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- 1206 Crustal movements: interplate (8155);
- 8419 Eruption monitoring (7280)