5:15 PM - 7:15 PM
[SVC36-P01] Submarine Geology of the Western Offshore Area of Suwanosejima Island: Preliminary Result of 2024 Survey
★Invited Papers
Keywords:Tokara Islands, submarine sediment, submarine topography, Shipboard three components magnetometer
Surface sediments supposed to be event deposits were collected southwest off Suwanosejma Island during marine geological survey cruise GB21-1 conducted by AIST for the purpose of the marine geological mapping around the Tokara Islands (Suzuki et al., 2022). In order to reveal the sedimentary processes in the western Suwanosejima Island area, including the origin of the event deposit, we conducted a marine geological survey in the western area off Suwanosejima Island from July to August 2024. We conducted geomagnetic survey, bathymetry survey, and bottom sediment sampling. This presentation shows a preliminary result of this survey. Due to operational limitations, bottom sediment samples were collected at depths shallower than 300 m.
In the survey area, rocks were exposed at many locations in the waters, and even in areas where sandy or muddy sediments were obtained, sedimentary structures suggesting the influence of bottom currents were observed. Movements of sediment particles at a rate of several tens of centimeters per second were observed in the seafloor images. The sedimentary environment seems to be strongly influenced by the Kuroshio Current, which meanders around the Tokara Islands and passes from the East China Sea to the Pacific Ocean. Therefore, fine-grained materials are considered to move within a very short period of time even if they were supplied from the islands.
Seafloor topographic data was acquired up to 2 km offshore west of Suwanosejima Island. Reflecting the sedimentary environment, seafloor topography showed a relatively wide range of volcanic landforms, including lava features that is supposed to be submarine extensions of Bunka Lava on the 1813 eruption and a rise that appears to be an old volcano with a flat summit. From geomagnetic observations, positive magnetic anomalies were observed offshore of Nabedao volcano, which is a relatively old volcanic body exposed on land, and offshore of Akazumiura, where the lobe topography that reaches the sea is interrupted. Suwanosejima Island is an active volcano that continues to be active today.
Although detailed investigations of the land area have progressed, including the publication of a volcanic geologic map (Shimano et al., 2013), detailed investigations of the submarine area have not been conducted. The data obtained from this survey will contribute to the elucidation of the eruption mechanism of Suwanosejima and the geomorphic processes such as eruption and collapse of the volcano. We aim to conduct a detailed sediment survey regarding the origin of the event sediments, including areas not covered in this study, such as areas deeper than 300 m and the area around Tairajima island in the future.
[Reference]
Suzuki et al. (2022) Submarine sediment distribution and its controlling factors around the Takarajima Island and the Suwanosejima Island. Bulletin of the Geological Survey of Japan, Geological Survey of Japan.
Shimano et al. (2013) Geological Map of Suwanosejima Volcano. Geological Map of Volcano, Geological Survey of Japan.
In the survey area, rocks were exposed at many locations in the waters, and even in areas where sandy or muddy sediments were obtained, sedimentary structures suggesting the influence of bottom currents were observed. Movements of sediment particles at a rate of several tens of centimeters per second were observed in the seafloor images. The sedimentary environment seems to be strongly influenced by the Kuroshio Current, which meanders around the Tokara Islands and passes from the East China Sea to the Pacific Ocean. Therefore, fine-grained materials are considered to move within a very short period of time even if they were supplied from the islands.
Seafloor topographic data was acquired up to 2 km offshore west of Suwanosejima Island. Reflecting the sedimentary environment, seafloor topography showed a relatively wide range of volcanic landforms, including lava features that is supposed to be submarine extensions of Bunka Lava on the 1813 eruption and a rise that appears to be an old volcano with a flat summit. From geomagnetic observations, positive magnetic anomalies were observed offshore of Nabedao volcano, which is a relatively old volcanic body exposed on land, and offshore of Akazumiura, where the lobe topography that reaches the sea is interrupted. Suwanosejima Island is an active volcano that continues to be active today.
Although detailed investigations of the land area have progressed, including the publication of a volcanic geologic map (Shimano et al., 2013), detailed investigations of the submarine area have not been conducted. The data obtained from this survey will contribute to the elucidation of the eruption mechanism of Suwanosejima and the geomorphic processes such as eruption and collapse of the volcano. We aim to conduct a detailed sediment survey regarding the origin of the event sediments, including areas not covered in this study, such as areas deeper than 300 m and the area around Tairajima island in the future.
[Reference]
Suzuki et al. (2022) Submarine sediment distribution and its controlling factors around the Takarajima Island and the Suwanosejima Island. Bulletin of the Geological Survey of Japan, Geological Survey of Japan.
Shimano et al. (2013) Geological Map of Suwanosejima Volcano. Geological Map of Volcano, Geological Survey of Japan.