Volcano number:311340
Country:United States
Geodetic measurements?Yes
Deformation observation?Yes
Measurement method(s):InSAR, GPS - campaign
Duration of observation:1991 - 2000, 2003 - 2010
Inferred cause of deformation:Magmatic
Characteristics of deformation:

During the 1991 – 1992 eruption of Westdahl, interferograms spanning 21 – 30 November 1991 indicate ~6 cm of subsidence attributed to magma withdrawl from a shallow reservoir. This is modelled as a point source with volume decrease of 0.03 ± 0.01 km³ at 5 – 7 km depth beneath the summit area.

Between 1992 – 2000 and 2003 – 2010, interferograms show inflation of the volcano at a decreasing rate, with maximum displacements of ~3 cm/yr. The source of deformation is thought to be the same as coeruptive subsidence in 1991 and is modelled as a point source at 6 km depth. In total 0.06 km³ of magma is thought to have accumulated between 1992 – 2010. The magma flow rate is though to be governed by the pressure gradient between a deeper source region and the reservoir.

Reference:Lu, Zhong, Wicks, Charles, Dzurisin, Daniel, Thatcher, Wayne, Freymueller, J. T., McNutt, S. R., and Mann, Dorte, 2000, Aseismic inflation of Westdahl volcano, Alaska, revealed by satellite radar interferometry: Geophysical Research Letters, v. 27, n. 11, p. 1567-1570.
Reference:Lu, Z., Masterlark, T., Dzurisin, D., Rykhus, R., & Wicks, C. 2003, Magma supply dynamics at Westdahl volcano, Alaska, modeled from satellite radar interferometry. Journal of Geophysical Research: Solid Earth (1978–2012), 108(B7).
Reference:Mann, Dorte, and Freymueller, J., 2003, Volcanic and tectonic deformation on Unimak Island in the Aleutian Arc, Alaska: Journal of Geophysical Research, v. 108, n. 2, p. 1-12.
Reference:U.S. Geological Survey Alaska Volcano Observatory (AVO) website
Reference:Lu, Z., and Dzurisin, D., 2014, InSAR imaging of Aleutian volcanoes: Chichester, UK, Springer-Praxis, 390 p.
Location:-164.65, 54.518

Summit of Westdahl. Source C. Read, U.S. Geological Survey AVO website