10:45 AM - 11:00 AM
[SCG52-11] Topography and crustal structure of Kaikata Seamount in the southern Izu-Ogasawara arc
Keywords:Izu-Ogasawara Arc, submarine volcano, Kaikata Seamount, caldera, gravity anomaly, crustal structure
Kaikata Seamount is a submarine volcano located around 26°40' N on the Shichito-Ioto Ridge, a volcanic front in the Izu-Ogasawara arc south of 30° N. The seamount consists of four peaks (KN, KM, and KS peaks on the west part, and KC peak on the east part). KC peak has a presumed caldera and a horseshoe-shaped collapsed landform. Volcanic activities have been observed at seamounts and the island around Kaikata Seamount in recent years. The volcanic eruption at the Nishinoshima Island is still continuing since 2013. The eruption of Fukutoku-Okanoba in 2021 erupted the large amount of pumice. Discolored seawater has been observed around the Kaitoku Seamount from August 2022.
Most of geophysical studies in the Izu-Ogasawara arc have been concentrated north of 30° N, although several studies about Nishinoshima or Fukutoku-Okanoba have been recently conducted (e.g. Tada et al., 2021; Onodera et al., 2003). One of the reasons is that there are less volcanic islands south of 30° N than north of 30° N. Therefore, it is important to study the south part of the Izu-Ogasawara arc to understand the present volcanic activities in this area. Kaikata Seamount is in the southern arc. Hydrographic and Oceanographic Department, the Japan Coast Guard (JHOD) reported the results of the bathymetric, gravity, and geomagnetic surveys (Japan Coast Guard, 2011; 2014). Hydrothermal activity at the Kaikata Seamount was reported by Yuasa (1986) and Tsuchida et al. (2001). The detailed studies about topography and crustal structure of the seamount are still obscured.
The purpose of this study is to expose topographic features and crustal structure of the Kaikata Seamount by multibeam bathymetric and gravity data. The data of this study were obtained from JHOD, Japan Agency for Marine-Earth Science and Technology, and National Centers for Environmental Information/National Oceanic and Atmospheric Administration. We made bathymetric and gravity grid files at a 100 m and a 500 m spacing, respectively. The areas without multibeam data were filled by GEBCO One Minute Grid (General Bathymetric Chart of the Oceans, 2008). We calculated the Bouguer gravity anomaly assuming the densities of seawater and crust was 1035 kg/m3 and 2050 kg/m3, respectively, using the method of Kuo and Forsyth (1988). In order to remove the long wavelength components of the Bouguer anomaly, we calculated upward continuation based on the spectral analysis.
The results suggest that the density structure of the seamount is inhomogeneous. The anomaly high is situated at KC peak and the low is at KM peak. This suggests the presence of denser materials at KC peak and lower density materials at KM peak in shallow areas. We also found the anomaly highs over the presumed caldera and the horseshoe-shaped collapsed landform at KC peak similar in morphology. This implies that the horseshoe-shaped landform originated from the collapse of a caldera like the proposal by Tsuchida et al. (2001).
Most of geophysical studies in the Izu-Ogasawara arc have been concentrated north of 30° N, although several studies about Nishinoshima or Fukutoku-Okanoba have been recently conducted (e.g. Tada et al., 2021; Onodera et al., 2003). One of the reasons is that there are less volcanic islands south of 30° N than north of 30° N. Therefore, it is important to study the south part of the Izu-Ogasawara arc to understand the present volcanic activities in this area. Kaikata Seamount is in the southern arc. Hydrographic and Oceanographic Department, the Japan Coast Guard (JHOD) reported the results of the bathymetric, gravity, and geomagnetic surveys (Japan Coast Guard, 2011; 2014). Hydrothermal activity at the Kaikata Seamount was reported by Yuasa (1986) and Tsuchida et al. (2001). The detailed studies about topography and crustal structure of the seamount are still obscured.
The purpose of this study is to expose topographic features and crustal structure of the Kaikata Seamount by multibeam bathymetric and gravity data. The data of this study were obtained from JHOD, Japan Agency for Marine-Earth Science and Technology, and National Centers for Environmental Information/National Oceanic and Atmospheric Administration. We made bathymetric and gravity grid files at a 100 m and a 500 m spacing, respectively. The areas without multibeam data were filled by GEBCO One Minute Grid (General Bathymetric Chart of the Oceans, 2008). We calculated the Bouguer gravity anomaly assuming the densities of seawater and crust was 1035 kg/m3 and 2050 kg/m3, respectively, using the method of Kuo and Forsyth (1988). In order to remove the long wavelength components of the Bouguer anomaly, we calculated upward continuation based on the spectral analysis.
The results suggest that the density structure of the seamount is inhomogeneous. The anomaly high is situated at KC peak and the low is at KM peak. This suggests the presence of denser materials at KC peak and lower density materials at KM peak in shallow areas. We also found the anomaly highs over the presumed caldera and the horseshoe-shaped collapsed landform at KC peak similar in morphology. This implies that the horseshoe-shaped landform originated from the collapse of a caldera like the proposal by Tsuchida et al. (2001).