Monitoring of landslide displacements in Owakudani, Hakone volcano, Japan, using SAR interferometry

Owakudani (Owakuzawa Valley), the largest fumarole area in Hakone volcano, Japan, is a place where volcanic disasters occur frequently, such as the mudslide disaster that killed six people in 1910 and the phreatic eruption that destroyed hot spring supply facilities in 2015. Therefore, monitoring surface displacements that may lead to slope failure is important for protecting life and property. In this study, we estimated three-dimensional displacements from interferometric synthetic aperture radar (InSAR) analysis from the ALOS-2/PALSAR-2 satellite data and detected landslide displacement around Owakudani. Moreover, the temporal variation of the landslide displacement was clarified from the InSAR time series analysis results. The landslide displacement detected in this study corresponds to a pre-existing collapsed landform whose underground structure was unknown. Additionally, the results of finite element analysis clarified the subsurface deformation concentration zone, suggesting the displacement on the pre-existing sliding surface. The landslide displacement started after the 2015 phreatic eruption. Therefore, fluid injection during the eruption might be one of the triggers of the displacement. Moreover, the annual displacement variation corresponds to changes in precipitation, suggesting that underground pore pressure changes have accelerated the displacement. These results demonstrate that the series of our approach can contribute to understanding the causes and mechanisms of landslides for which underground geological surveys are inadequate.