11:45 AM - 12:00 PM
[STT39-05] Monitoring of landslide displacements in Owakudani, Hakone volcano, Japan using SAR interferometry
Keywords:InSAR, landslide, Hakone volcano, Owakudani
The area around Hakone volcano, which is located western part of Kanagawa Prefecture, is one of the heaviest rainfall areas in Japan. In recent years, landslide disasters have frequently occurred due to heavy rainfall. Owakudani (Owakuzawa Valley), the largest fumarole area in the volcano, is a sightseeing spot that approximately 3 million people visit per year and a major hot spring water production site. On the other hand, Owakudani is a place where volcanic disasters occur all the time, such as the mudslide disaster that killed six people in 1910 and the phreatic eruption in 2015. Since the 2015 eruption, many visible cracks have appeared on the erosion control weir at the uppermost part of the Owakuzawa Valley. Therefore, it is important to monitor surface displacements that may lead to slope failure to protect life and property.
This study estimated 1) 3-D displacement around Owakudani by multi-looking InSAR analysis results and 2) time series slope displacements by SBAS-InSAR analysis. The results of this study are as follow;
1) 3-D displacement around Owakudani
3-D displacement around Owakudani was estimated using multi-looking InSAR analysis results between 2017 and 2020. Analyzed datasets are Path119 (ascending left-looking), Path126 (ascending, right-looking), Paths18 and 19 (descending, right-looking). The result shows ca. 17 cm of displacement in the NNW direction at the right bank of the Owakuzawa Valley for three years (after this referred to as Location A). Moreover, ca. 6 cm of displacement in the SE direction was observed at the left bank of the valley for three years (after this referred to as Location B). Both locations show displacement toward inclination directions of slopes. Moreover, the displacement of Location B agrees with the displacement direction observed by GNSS, which was installed by the Hot Springs Research Institute of Kanagawa Prefecture.
2) Result of InSAR time series analysis
Doke et al. (2021) performed the InSAR time series analysis of ALOS-2/PALSAR-2 data (Paths 126 and 18) after the 2015 phreatic eruption by using the SBAS method. Moreover, quasi-EW and quasi-UD components were estimated by 2.5-D analysis. Based on this result, both Locations A and B show the same tendency of the displacement toward inclination directions of slopes mentioned above. The displacement at Location A was particularly significant, showing a displacement away from the satellite of ca. 26 cm during the analysis period for Path 18, which is descending orbit and right-looking. Assuming that the displacement is in the inclination direction of slope, the velocity is estimated to be ca. 5.2 cm/year. The displacement time series at Location A tends to accelerate from autumn to winter, suggesting that landslide displacement may have accelerated during heavy rainfall (such as typhoon) seasons.
On July 3, 2021, a collapse occurred downstream of location A, damaging some of the hot spring supply facilities. There are no ground-based observation sites around this location; therefore, continuous SAR observations are important for monitoring the displacement.
Acknowledgment
ALOS-2/PALSAR-2 data were provided by JAXA via the Coordinating Committee for the Prediction of Volcanic Eruption as part of the project, “ALOS Domestic Demonstration on Disaster Management Application,” of the Volcano Working Group. The ALOS-2/PALSAR-2 data belong to JAXA.
Reference
Doke, R., Mannen, K., & Itadera, K. (2021). Observing Posteruptive Deflation of Hydrothermal System Using InSAR Time Series Analysis: An Application of ALOS-2/PALSAR-2 Data on the 2015 Phreatic Eruption of Hakone Volcano, Japan. Geophysical Research Letters, 48, e2021GL094880. https://doi.org/10.1029/2021gl094880
This study estimated 1) 3-D displacement around Owakudani by multi-looking InSAR analysis results and 2) time series slope displacements by SBAS-InSAR analysis. The results of this study are as follow;
1) 3-D displacement around Owakudani
3-D displacement around Owakudani was estimated using multi-looking InSAR analysis results between 2017 and 2020. Analyzed datasets are Path119 (ascending left-looking), Path126 (ascending, right-looking), Paths18 and 19 (descending, right-looking). The result shows ca. 17 cm of displacement in the NNW direction at the right bank of the Owakuzawa Valley for three years (after this referred to as Location A). Moreover, ca. 6 cm of displacement in the SE direction was observed at the left bank of the valley for three years (after this referred to as Location B). Both locations show displacement toward inclination directions of slopes. Moreover, the displacement of Location B agrees with the displacement direction observed by GNSS, which was installed by the Hot Springs Research Institute of Kanagawa Prefecture.
2) Result of InSAR time series analysis
Doke et al. (2021) performed the InSAR time series analysis of ALOS-2/PALSAR-2 data (Paths 126 and 18) after the 2015 phreatic eruption by using the SBAS method. Moreover, quasi-EW and quasi-UD components were estimated by 2.5-D analysis. Based on this result, both Locations A and B show the same tendency of the displacement toward inclination directions of slopes mentioned above. The displacement at Location A was particularly significant, showing a displacement away from the satellite of ca. 26 cm during the analysis period for Path 18, which is descending orbit and right-looking. Assuming that the displacement is in the inclination direction of slope, the velocity is estimated to be ca. 5.2 cm/year. The displacement time series at Location A tends to accelerate from autumn to winter, suggesting that landslide displacement may have accelerated during heavy rainfall (such as typhoon) seasons.
On July 3, 2021, a collapse occurred downstream of location A, damaging some of the hot spring supply facilities. There are no ground-based observation sites around this location; therefore, continuous SAR observations are important for monitoring the displacement.
Acknowledgment
ALOS-2/PALSAR-2 data were provided by JAXA via the Coordinating Committee for the Prediction of Volcanic Eruption as part of the project, “ALOS Domestic Demonstration on Disaster Management Application,” of the Volcano Working Group. The ALOS-2/PALSAR-2 data belong to JAXA.
Reference
Doke, R., Mannen, K., & Itadera, K. (2021). Observing Posteruptive Deflation of Hydrothermal System Using InSAR Time Series Analysis: An Application of ALOS-2/PALSAR-2 Data on the 2015 Phreatic Eruption of Hakone Volcano, Japan. Geophysical Research Letters, 48, e2021GL094880. https://doi.org/10.1029/2021gl094880