5:15 PM - 7:15 PM
[SVC32-P07] Crustal deformation associated with the unrest of Iwate Volcano in 2024 detected by InSAR analysis with ALOS-2/4 data
Keywords:Iwate Volcano, ALOS-2, ALOS-4, InSAR time series analysis, volcanic crustal deformation
Iwate Volcano is a composite, basaltic-andesitic stratovolcano located in the northeastern Japan. In recorded history, magmatic eruptions occurred at the East Iwate Volcano in 1686 and 1732, and a phreatic eruption occurred at the West Iwate Volcano in 1919. In 1998, active seismic activity and crustal deformation were observed, although no eruption occurred. After that, the volcanic activity was quiet for more than 20 years. Since April 2024, widespread deformation indicating deep inflation has been observed by GNSS network, and from around May 2024, volcanic earthquakes increased near Kurokura-yama in the West Iwate Volcano (Japan Meteorological Agency (JMA), 2024). In response to this, the Advanced Land Observing Satellite-2 (ALOS-2) has conducted emergency SAR observations since August 2024.
At Geospatial Information Authority of Japan (GSI), we have conducted analysis immediately after the observations by ALOS-2 and have provided the analysis results to the Coordinating Committee for Prediction of Volcanic Eruptions and other relevant organizations for the purpose of monitoring the progress of volcanic activity at Iwate Volcano. The results of InSAR analysis using the ALOS-2 observation data have revealed a displacement toward the satellite around Ojigoku Valley, which is located in the east of Kurokura-yama. This displacement was captured for the first time and was used for deciding to raise Volcanic Alert Level of Iwate Volcano by JMA in October 2024. We also conducted InSAR time series analysis (Kobayashi et al., 2018) using the ALOS-2 data, which was observed continuously thereafter. As a result, not only the displacement around Ojigoku Valley but also a displacement toward the satellite were also detected near Mitsuishi-yama in the west of Iwate Volcano. In addition, we conducted 2.5-dimensional analysis (Fujiwara et al., 2000) using line-of-sight (LOS) displacements from November 2023 to November 2024, which were obtained from the results of InSAR time series analysis of right observations from the descending and ascending orbits. This analysis has revealed an uplift of ~10 cm and a displacement of ~4 cm expanding east and west in an area with a radius of 1 km centered on the vicinity of Ojigoku Valley, and an uplift of ~8 cm was detected in an area with a radius of ~4 km near Mitsuishi-yama. Moreover, InSAR analysis using data of the Advanced Land Observing Satellite-4 (ALOS-4), launched on July 1, 2024, and ALOS-2 also gave results consistent with these deformations.
We estimated a pressure source for the deformation detected around Ojigoku Valley by inversion analysis. In this inversion analysis, we use LOS displacements from November 2023 to November 2024, which are calculated from the results of the InSAR time series analysis. The source geometry was assumed to be two types: sphere and dike. The results indicate that the estimated inflation source, in either geometry, is located at a depth of several hundred meters beneath Ojigoku Valley with a volume change amount of approximately +0.1×106 m3. The source location lies above the dyke estimated for the 1998 magma intrusion (Sato and Hamaguchi, 2006). The inflation source estimated in this study suggests the presence of a magma and/or hydrothermal reservoir beneath Ojigoku Valley.
Acknowledgments: ALOS-2 and ALOS-4 data were provided based on the joint research agreement with Japan Aerospace Exploration Agency (JAXA) and under a cooperative research contract between GSI and JAXA. The ownership of ALOS-2 and ALOS-4 data belongs to JAXA. The numerical weather model was provided from JMA based on the agreement.
At Geospatial Information Authority of Japan (GSI), we have conducted analysis immediately after the observations by ALOS-2 and have provided the analysis results to the Coordinating Committee for Prediction of Volcanic Eruptions and other relevant organizations for the purpose of monitoring the progress of volcanic activity at Iwate Volcano. The results of InSAR analysis using the ALOS-2 observation data have revealed a displacement toward the satellite around Ojigoku Valley, which is located in the east of Kurokura-yama. This displacement was captured for the first time and was used for deciding to raise Volcanic Alert Level of Iwate Volcano by JMA in October 2024. We also conducted InSAR time series analysis (Kobayashi et al., 2018) using the ALOS-2 data, which was observed continuously thereafter. As a result, not only the displacement around Ojigoku Valley but also a displacement toward the satellite were also detected near Mitsuishi-yama in the west of Iwate Volcano. In addition, we conducted 2.5-dimensional analysis (Fujiwara et al., 2000) using line-of-sight (LOS) displacements from November 2023 to November 2024, which were obtained from the results of InSAR time series analysis of right observations from the descending and ascending orbits. This analysis has revealed an uplift of ~10 cm and a displacement of ~4 cm expanding east and west in an area with a radius of 1 km centered on the vicinity of Ojigoku Valley, and an uplift of ~8 cm was detected in an area with a radius of ~4 km near Mitsuishi-yama. Moreover, InSAR analysis using data of the Advanced Land Observing Satellite-4 (ALOS-4), launched on July 1, 2024, and ALOS-2 also gave results consistent with these deformations.
We estimated a pressure source for the deformation detected around Ojigoku Valley by inversion analysis. In this inversion analysis, we use LOS displacements from November 2023 to November 2024, which are calculated from the results of the InSAR time series analysis. The source geometry was assumed to be two types: sphere and dike. The results indicate that the estimated inflation source, in either geometry, is located at a depth of several hundred meters beneath Ojigoku Valley with a volume change amount of approximately +0.1×106 m3. The source location lies above the dyke estimated for the 1998 magma intrusion (Sato and Hamaguchi, 2006). The inflation source estimated in this study suggests the presence of a magma and/or hydrothermal reservoir beneath Ojigoku Valley.
Acknowledgments: ALOS-2 and ALOS-4 data were provided based on the joint research agreement with Japan Aerospace Exploration Agency (JAXA) and under a cooperative research contract between GSI and JAXA. The ownership of ALOS-2 and ALOS-4 data belongs to JAXA. The numerical weather model was provided from JMA based on the agreement.