Synthetic aperture radar interferometry of Okmok volcano, Alaska: Radar observations

Abstract

Abstract. ERS-1/ERS-2 synthetic aperture radar interferometry was used to study the 1997 eruption of Okmok volcano in Alaska. First, we derived an accurate digital elevation model (DEM) using a tandem ERS-1/ERS-2 image pair and the preexisting DEM. Second, by studying changes in interferometric coherence we found that the newly erupted lava lost radar coherence for 5-17 months after the eruption. This suggests changes in the surface backscattering characteristics and was probably related to cooling and compaction processes. Third, the atmospheric delay anomalies in the deformation interferograms were quantitatively assessed. Atmospheric delay anomalies in some of the interferograms were significant and consistently smaller than one to two fringes in magnitude. For this reason, repeat observations are important to confidently interpret small geophysical signals related to volcanic activities. Finally, using two-pass differential interferometry, we analyzed the preeruptive inflation, coeruptive deflation, and posteruptive inflation and confirmed the observations using independent image pairs. We observed more than 140 cm of subsidence associated with the 1997 eruption. This subsidence occurred between 16 months before the eruption and 5 months after the eruption, was preceded by-•18 cm of uplift between 1992 and 1995 centered in the same location, and was followed by •10 cm of uplift between September 1997 and 1998. The best fitting model suggests the magma reservoir resided at 2.7 km depth beneath the center of the caldera, which was -5 km from the eruptive vent. We estimated the volume of the erupted material to be 0.055 km 3 and the average thickness of the erupted lava to be---7.4 m.

InSAR analysis of natural recharge to define structure of a ground‐water basin, San Bernardino, California

“…In this preliminary analysis, we used a total of 13 SAR images for the period April 24, 1992, to December 2, 1995, obtained from the Western North America InSAR Consortium (WInSAR) archive. We used a 2-pass InSAR method [Massonnet and Feigl, 1998] to produce the land-surface deformation map. The digital elevation model (DEM) used in the processing is from the U.S. Geological Survey (USGS) 7.5-minute map data, which has a horizontal resolution of 30 m and a specified vertical accuracy of 7 m RMS.…”

“…Almost all permanent subsidence occurs due to the irreversible (inelastic) compression or consolidation of aquitards. Recoverable (elastic) subsidence can occur in both aquifers and aquitards [Tolman and Poland, 19401. Traditional hydrogeologic investigations have relied on expensive, ground-based data collection to define important InSAR utilizes two or more coherent phase signals acquired at different times for the same land area to map changes in range (satellite to earth distance) at a spatial resolution of tens of meters and a vertical accuracy of centimeters [Massonnet and Feigl, 1998]. InSAR analysis of an aquifer system involves mapping and analyzing the surface deformation caused by hydrogeologic processes [e.g., …”

Physical volcanology of the 2,050 bp caldera-forming eruption of Okmok volcano, Alaska

“…Intracaldera activity following the younger Okmok II caldera event formed numerous basaltic cones and lava flows. Ongoing deformation of the caldera floor has been recognized by SAR interferometry (Lu et al 2000), and the most recent eruption was in 1997. Although numerous geologic (Byers, 1959) and geochemical observations (Byers, 1961) have been collected at Okmok, most were aimed at the questions of arc petrogenesis (e.g., Kay and Kay 1994) and physical processes of specific volcanic events to date have not been explored systematically.…”

Post-Eruptive Inflation of Okmok Volcano, Alaska, from InSAR, 2008–2014

“…Deformation at the volcano has been thoroughly examined with InSAR and GPS, while field and remote sensing investigations have characterized both historic and prehistoric eruptive activities e.g., [1,[9][10][11][12][13][14][15][16][18][19][20][28][29][30][31]. Although the general geometry of deformation is relatively constant over time, suggesting a persistent source, deformation rates varied greatly in time, which suggests changes in magma supply of the volcano's shallow reservoir system [1,11,20].…”

“…The 1997 and 2008 eruptions are extremely well-documented thanks, in part, to the advent of space-based observations-especially the Synthetic Aperture Radar (SAR) interferometry (InSAR) technique. The 1997 eruption, which began in early February 1997 and ended in late April 1997, was preceded by several years of inflationary deformation amounting to tens of centimeters, accompanied by over a meter of subsidence, and followed by tens of cm of re-inflation [1,6,[12][13][14][15]. Based on these InSAR-derived displacement patterns, Lu et al [16] modeled the deformation as due to a point source or spherical magma reservoir located beneath the center of the caldera at a depth of 2.6-3.2 km below sea level [17].…”