5:15 PM - 7:15 PM
[STT39-P02] Shallow thermal activity of Tokachidake Volcano explored by repeated drone aeromagnetic surveys
Keywords:Aeromagnetic survey, Drone, Tokachidake
In recent years, new geothermal anomalies are observed in regions slightly away from the 62-II crater of Tokachidake Volcano in Hokkaido, Japan. These surface manifestations suggest that new pathways for hydrothermal fluids and volcanic gases are forming in the shallow subsurface, leading to temperature rises and hydrothermal alteration along these paths. Since hydrothermal alteration can weaken subsurface rocks and contribute to edifice collapse (Roverato et al., 2021), making it crucial to understand the distribution of alteration zones and associated temperature variations to predict potential collapse sites. This study aims to visualize thermal activity in the shallow subsurface of Tokachidake using aeromagnetic surveys.
Magnetic surveys provide insights into subsurface temperature changes and the progression of alteration. Aeromagnetic surveys, in particular, enable efficient investigation of shallow volcanic thermal activity without terrain-related access limitations. Recently, low-cost drone aeromagnetic surveys have become practical, making repeated observations more flexible. In this study, we collected aeromagnetic data around the geothermal anomaly area at a constant clearance above the ground using a drone in 2023 and 2024. From these datasets, we retrieved magnetic anomalies originating from volcanic edifice and their temporal changes, and applying inversion analysis to reveal the three-dimensional distribution of magnetization intensity and changes in the shallow subsurface.
For the analysis, we used the three-dimensional magnetic inversion method developed by Koyama et al. (2021). Our 3D magnetization model identified a columnar low-magnetization zone beneath the 62-II crater, likely representing high-temperature regions and hydrothermal alteration surrounding the fumarolic conduit. Additionally, the spatial distribution of magnetization intensity in the shallow subsurface correlated well with the crater morphology and geological structures, suggesting the presence of thermal fluid flow pathways confined by these boundaries.
Meanwhile, our magnetization change model revealed remagnetization beneath the 62-II crater and demagnetization in the geothermal anomalies This likely reflects changes in heat supply within the shallow subsurface due to the formation of new fluid pathways toward the geothermal anomalies. Furthermore, the shape of the demagnetized area suggests the progression of hydrothermal alteration surrounding the slope, implying a decreasing trend in slope stability at Tokachidake.
Moving forward, it is necessary to use slope stability analysis (e.g., Scoops3D, Reid et al., 2015) to quantify the volume of unstable slopes that may be prone to collapse. This will be crucial for developing effective disaster mitigations strategies against potential volcanic edifice failure.
This study was supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan, under its Earthquake and Volcano Hazards Observation and Research Program.
Magnetic surveys provide insights into subsurface temperature changes and the progression of alteration. Aeromagnetic surveys, in particular, enable efficient investigation of shallow volcanic thermal activity without terrain-related access limitations. Recently, low-cost drone aeromagnetic surveys have become practical, making repeated observations more flexible. In this study, we collected aeromagnetic data around the geothermal anomaly area at a constant clearance above the ground using a drone in 2023 and 2024. From these datasets, we retrieved magnetic anomalies originating from volcanic edifice and their temporal changes, and applying inversion analysis to reveal the three-dimensional distribution of magnetization intensity and changes in the shallow subsurface.
For the analysis, we used the three-dimensional magnetic inversion method developed by Koyama et al. (2021). Our 3D magnetization model identified a columnar low-magnetization zone beneath the 62-II crater, likely representing high-temperature regions and hydrothermal alteration surrounding the fumarolic conduit. Additionally, the spatial distribution of magnetization intensity in the shallow subsurface correlated well with the crater morphology and geological structures, suggesting the presence of thermal fluid flow pathways confined by these boundaries.
Meanwhile, our magnetization change model revealed remagnetization beneath the 62-II crater and demagnetization in the geothermal anomalies This likely reflects changes in heat supply within the shallow subsurface due to the formation of new fluid pathways toward the geothermal anomalies. Furthermore, the shape of the demagnetized area suggests the progression of hydrothermal alteration surrounding the slope, implying a decreasing trend in slope stability at Tokachidake.
Moving forward, it is necessary to use slope stability analysis (e.g., Scoops3D, Reid et al., 2015) to quantify the volume of unstable slopes that may be prone to collapse. This will be crucial for developing effective disaster mitigations strategies against potential volcanic edifice failure.
This study was supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan, under its Earthquake and Volcano Hazards Observation and Research Program.