Leveling surveys were repeated 22 times at and around Asama volcano between 19 (Murase et al. Geodetic measurements of surface deformation at active volcanoes can provide important clues for assessing volcanic activity (Pinel et al. For this reason, monitoring the activity of Asama volcano is essential for mitigating volcanic hazards during future large eruptions. For instance, the 2004 eruption in Asama volcano produced large ash clouds and led to ashfall in the Tokyo metropolitan area (Tsunematsu et al. An eruption at Asama volcano has the potential of posing volcanic hazards to the Tokyo metropolitan area, which is about 160 km southeast of the volcano with a population of more than 20 million. Asama volcano has been active for about 100,000 years and repeatedly erupted every several years in history (Aoki et al. ![]() We highlight that efforts should be taken to monitor the slope instability at Asama volcano in the future.Īsama volcano is an andesitic composite volcano and one of the most active volcanoes in Japan. We interpreted that the subsidence at the NEF of Asama is primarily due to the hydrothermal activity, while the deformation at SEF is plausibly due to flank instability. Comparisons of the vertical subsidence at two continuous GNSS stations near the summit crater with our InSAR observations indicate small discrepancies smaller than 4 mm/year. Decomposition of the LOS displacements reveals nearly pure subsidence at the NEF, while the SEF exhibits a substantial eastward component as well as subsidence. The southeast flank (SEF) shows LOS extensions in the ascending observations and LOS shortening in the descending observations with velocities between − 12 and 9 mm/year. The northeast flank (NEF) exhibits line-of-sight (LOS) extensions in all the three SAR datasets with maximum velocities of − 14, − 10, and − 12 mm/year for the descending ALOS-2, ascending, and descending Sentinel-1 measurements, respectively. Our observations reveal an asymmetric deformation around the volcano with two main deformation regions on the northeast and southeast flanks, respectively. We exploited both persistent and distributed scatterers to overcome decorrelation of SAR signals and applied a three-dimensional unwrapping method to retrieve the displacement time series efficiently. This study presents the first interferometric synthetic aperture radar (InSAR) observation of ground deformation at Asama volcano with 120 Sentinel-1 SAR images from both ascending and descending tracks and 20 descending ALOS-2 images acquired between 20. ![]() Spatially dense surface deformation at Asama volcano has rarely been documented because of its high topography and snow cover around the summit. Asama volcano is one of the most active volcanoes in Japan.
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