On the absence of InSAR-detected volcano deformation spanning the 1995–1996 and 1999 eruptions of Shishaldin Volcano, Alaska S.C. Moran a, * , O. Kwoun b,1 , T. Masterlark c,2 , Z. Lu b,3 a U.S. Geological Survey, Cascades Volcano Observatory, 1300 SE Cardinal Ct., Bldg. 10, Vancouver, WA 98683, United States b U.S. Geological Survey, EROS Data Center, SAIC, 47914 252nd Street, Sioux Falls, SD 57198, United States c Department of Geological Sciences, University of Alabama, Tuscaloosa, AL 35487, United States Received 1 June 2004; received in revised form 10 September 2004 Available online 8 September 2005 Abstract Shishaldin Volcano, a large, frequently active basaltic-andesite volcano located on Unimak Island in the Aleutian Arc of Alaska, had a minor eruption in 1995–1996 and a VEI 3 sub-Plinian basaltic eruption in 1999. We used 21 synthetic aperture radar images acquired by ERS-1, ERS-2, JERS-1, and RADARSAT-1 satellites to construct 12 coherent interferograms that span most of the 1993–2003 time interval. All interferograms lack coherence within ~5 km of the summit, primarily due to persistent snow and ice cover on the edifice. Remarkably, in the 5–15 km distance range where interferograms are coherent, the InSAR images show no intrusion- or withdrawal-related deformation at Shishaldin during this entire time period. However, several InSAR images do show deformation associated with a shallow M L 5.2 earthquake located ~14 km west of Shishaldin that occurred 6 weeks before the 1999 eruption. We use a theoretical model to predict deformation magnitudes due to a volumetric expansion source having a volume equivalent to the 1999 erupted volume, and find that deformation magnitudes for sources shallower than 10 km are within the expected detection capabilities for interferograms generated from C-band ERS 1/2 and RADARSAT-1 synthetic aperture radar images. We also find that InSAR images cannot resolve relatively shallow deformation sources (1–2 km below sea level) due to spatial gaps in the InSAR images caused by lost coherence. The lack of any deformation, particularly for the 1999 eruption, leads us to speculate that magma feeding eruptions at the summit moves rapidly (at least 80m/day) from N 10 km depth, and that the intrusion–eruption cycle at Shishaldin does not produce significant permanent deformation at the surface. Published by Elsevier B.V. Keywords: satellite interferometry; volcano deformation; deformation modeling; magma ascent rates; Shishaldin Volcano; Aleutian Islands 0377-0273/$ - see front matter. Published by Elsevier B.V. doi:10.1016/j.jvolgeores.2005.07.013 * Corresponding author. Tel.: +1 360 993 8934; fax: +1 360 993 8980. E-mail addresses: smoran@usgs.gov (S.C. Moran), okwoun@usgs.gov (O. Kwoun), masterlark@geo.ua.edu (T. Masterlark), lu@usgs.gov (Z. Lu). 1 Tel.: +1 605 594 6153. 2 Tel.: +1 205 348 5095. 3 Tel.: +1 605 594 6063. Journal of Volcanology and Geothermal Research 150 (2006) 119– 131 www.elsevier.com/locate/jvolgeores