13:45 〜 15:15
[SVC34-P08] Detailed seafloor morphology and bubble plumes around Ioto in the Izu-Bonin Arc
キーワード：海底地形、熱水、カルデラ、溶岩流、硫黄島、伊豆-小笠原弧
Background
Ioto is located in the Izu-Bonin Arc where the Pacific plate subducts beneath the Philippine Sea plate. Ioto is an active volcanic massif whose basal diameter is 40-50 km and rises 1000-2000 m from the surrounding seafloor. Submarine part of the edifice is poorly understood due to lack of geophysical and geological surveys. The seafloor around Ioto was mapped by JCG in 1981 (Kato and Ikeda, 1984) and 1991 (Watanabe, 1994), but their sparse soundings prevent us to understand detailed volcanic features.
Method
Multibeam bathymetry and backscatter intensity data were acquired during JCG several cruises in 2021 (S/V Heiyo, MD50), 2013 (S/V Shoyo, EM710 & 122), 2003, 2002 (S/V Shoyo, SeaBeam2112). Raw files (*.s7k, *.all, *.mb41) were imported in CARIS HIPS software and processed. The processed soundings were gridded with a cell size of 30 m using the swath-angle weighting algorithm. Water column data were recorded only in 2021. The occurrence of bubble plumes was checked visually using swath-angle editor tool.
Result & Discussion
(caldera) Detailed bathymetry revealed fines-scale morphology of the poorly-known caldera structure around the main island. The caldera rim consists of several discontinuous submarine and subaerial edifices. The northern caldera rim consists of flat-topped submarine edifices whose flat parts are surrounded by 200-m-depth contour and have shallowest depth of ~80 m. The ring faults well develop between the flat-topped submarine edifices and main island. The caldera rims and ring faults north of the island appear to be traced to the east and west of the island, but its continuities are unknown due to incomplete mapping coverage. (plume) The intense bubble plumes rising from the seafloor were imaged in the water column. Most plumes are spatially confined within the possible caldera structure except for one plume southeast off Suribatiyama. (lava flows) Previously unmapped lava flows with high backscatter intensity were mapped outside the caldera structure, on the submarine flanks of Ioto Island, showing the relatively young eruptions. (depth change) The bathymetric comparison between the 2013 survey and 2021 survey revealed that significant depth change occurred. Overall uplifts were identified inside the northern caldera. A collapse scar was newly formed along the ring fault.
These volcanic features suggest that volcanic activities occur underwater as well as on the island and provide new insights into understanding how Ioto Island evolves.
Ioto is located in the Izu-Bonin Arc where the Pacific plate subducts beneath the Philippine Sea plate. Ioto is an active volcanic massif whose basal diameter is 40-50 km and rises 1000-2000 m from the surrounding seafloor. Submarine part of the edifice is poorly understood due to lack of geophysical and geological surveys. The seafloor around Ioto was mapped by JCG in 1981 (Kato and Ikeda, 1984) and 1991 (Watanabe, 1994), but their sparse soundings prevent us to understand detailed volcanic features.
Method
Multibeam bathymetry and backscatter intensity data were acquired during JCG several cruises in 2021 (S/V Heiyo, MD50), 2013 (S/V Shoyo, EM710 & 122), 2003, 2002 (S/V Shoyo, SeaBeam2112). Raw files (*.s7k, *.all, *.mb41) were imported in CARIS HIPS software and processed. The processed soundings were gridded with a cell size of 30 m using the swath-angle weighting algorithm. Water column data were recorded only in 2021. The occurrence of bubble plumes was checked visually using swath-angle editor tool.
Result & Discussion
(caldera) Detailed bathymetry revealed fines-scale morphology of the poorly-known caldera structure around the main island. The caldera rim consists of several discontinuous submarine and subaerial edifices. The northern caldera rim consists of flat-topped submarine edifices whose flat parts are surrounded by 200-m-depth contour and have shallowest depth of ~80 m. The ring faults well develop between the flat-topped submarine edifices and main island. The caldera rims and ring faults north of the island appear to be traced to the east and west of the island, but its continuities are unknown due to incomplete mapping coverage. (plume) The intense bubble plumes rising from the seafloor were imaged in the water column. Most plumes are spatially confined within the possible caldera structure except for one plume southeast off Suribatiyama. (lava flows) Previously unmapped lava flows with high backscatter intensity were mapped outside the caldera structure, on the submarine flanks of Ioto Island, showing the relatively young eruptions. (depth change) The bathymetric comparison between the 2013 survey and 2021 survey revealed that significant depth change occurred. Overall uplifts were identified inside the northern caldera. A collapse scar was newly formed along the ring fault.
These volcanic features suggest that volcanic activities occur underwater as well as on the island and provide new insights into understanding how Ioto Island evolves.