Subsidence at lava dome of Tarumae volcano as revealed by ALOS-2/PALSAR-2 InSAR(2015-2019)

We applied interferometry analysis to the L-band SAR (Synthetic Aperture Radar) images acquired by ALOS-2 satellite for the Tarumae Volcano from 2015 to 2019 and detected ground deformation at lava dome and eastern mountain flank. As a result, the observed distance length change in line-of-sight increased up to 4 cm at lava dome and eastern flank for 4 years. By the multiple images from two different track directions, quasi east-west and vertical ground deformation was also estimated. Each displacement at the lava dome and eastern flank were < 5 cm of east-west intension and < 5 cm subsidence, and 5 cm of eastward displacement and 7 cm subsidence, respectively. Source modeling to explain the displacement at the lava dome, shows 104 m3 order of deflation at the depth of 200～500 m below the lava dome. A previous study supposed that the observed GNSS baseline length change in the same period is caused by depressurization and cooling at shallow hydrothermal reservoir. Our result also supports this suggestion. Several previous studies suggested that a shallow hydrothermal reservoir at around the same depth has been inflated for 1999～2000. Therefore, it is assumed that this reservoir is contracting during our observation period. On the other hand, it is thought that the eastward and subsidence displacement at the eastern flank might be not caused by volcanic activity for the present. more detailed SAR data analysis, and its temporal accumulation monitoring will give us further constrains on the on-going process at the shallow hydrothermal system of the Tarumae Volcano