2:15 PM - 2:30 PM
[MIS20-02] Bathymetric change at the shallow methane hydrate bearing mound during 2013 and 2024, Umitaka Spur, off Joetsu, Japan
Keywords:Off Joetsu, Umitaka Spur, Shallow Methane Hydrate, Bathymetric change, Pockmark, AUV
Summary
Shallow methane hydrate (MH) are exits below two mounds adjust to a pockmark, on the central part of Umitaka Spur in off-joetsu area, Japan. Acoustic investigations using an autonomous underwater vehicle (AUV) (2013 and 2024) and a high-resolution 3D image mapping system named “SeaXerocks1” via an unmanned remotely operated robot (ROV) (2021) were conducted on the mounds and obtained detailed bathymetric data. The Umitaka Spur is a rise that extends northward from the NE Japan into the Sea of Japan. At a depth of 900 m near the western slope of the central part of the spur, there is a nearly circular shaped pockmark and two mounds on the edge of the pockmark. We reported bathymetric change of the two mounds indicated by comparison of bathymetric data obtained in 2013 and 2021, in the last JpGU2024. Here we present a comparison of bathymetric data between 2013, 2021, and newly acquired in August 2024. The detailed bathymetric data acquired in 2024, meaning after the large Noto Peninsula Earthquake on January 1, 2024, indicated that there were no clear differences between the bathymetric data in 2021.
Data acquisition
Acoustic mapping using AUV Deep1 (Fukada Salvage Co., Ltd.) was conducted in 2013 and 2025 with a multi-beam echo sounder and a side-scan sonar and sub-bottom profiler system at ~25 m above the seafloor with ~3 knots of cruising speed. The 3D photographic observation system named “SeaXerocks1” was mounted on an ROV Kaiyo3000 (KAIYO ENGINEERING CO., LTD.) in 2021 and operated at an altitude of 4–5 m with ~0.4 knots, obtaining still images and bathymetric information with laser scanning.
Observations
The pockmark shows nearly circle shape with approximately 500 m in diameter and about 20 m deep. Immediately north of the pockmark, there is a drop-shaped north mound with a major and minor diameter of 200~250 m. Another mound exists at the northwest side of the pockmark, which is an elliptical mound with a major and minor diameter of 250~300 m. Tow mounds stand up from 5~15 m from the surrounding seafloor. The seafloor of the mounds shows rough surface with little variation in height. The bathymetric data obtained by SeaXerocks1 indicated at least four distinct bathymetric changes between 2013 and 2021. However, much little bathymetric change was suggested between 2021and 2024. It indicates that that the effect of the Noto Peninsula Earthquake occurred on January 1, 2024 was not significant on the change of bathymetric pattern (i.e., collapse of seafloor and/or large release of massive shallow MHs on seafloor into seawater) at the surface of mounds. On the other hand, the bathymetry of the north mound showed a shallowing of less than 1 m, and that of the pockmarked bottom showed deepening of less than 1 m, while the west mound and surrounding seafloor did not show any bathymetric change. We further need to be carefully examined in accuracy of the vertical resolution of the MBES in order to verify such minute differences in bathymetry data.
Acknowledgments
This study was conducted as part of a national gas hydrate research project in the Sea of Japan funded by the Ministry of Economy, Trade, and Industry (METI), Japan.
Shallow methane hydrate (MH) are exits below two mounds adjust to a pockmark, on the central part of Umitaka Spur in off-joetsu area, Japan. Acoustic investigations using an autonomous underwater vehicle (AUV) (2013 and 2024) and a high-resolution 3D image mapping system named “SeaXerocks1” via an unmanned remotely operated robot (ROV) (2021) were conducted on the mounds and obtained detailed bathymetric data. The Umitaka Spur is a rise that extends northward from the NE Japan into the Sea of Japan. At a depth of 900 m near the western slope of the central part of the spur, there is a nearly circular shaped pockmark and two mounds on the edge of the pockmark. We reported bathymetric change of the two mounds indicated by comparison of bathymetric data obtained in 2013 and 2021, in the last JpGU2024. Here we present a comparison of bathymetric data between 2013, 2021, and newly acquired in August 2024. The detailed bathymetric data acquired in 2024, meaning after the large Noto Peninsula Earthquake on January 1, 2024, indicated that there were no clear differences between the bathymetric data in 2021.
Data acquisition
Acoustic mapping using AUV Deep1 (Fukada Salvage Co., Ltd.) was conducted in 2013 and 2025 with a multi-beam echo sounder and a side-scan sonar and sub-bottom profiler system at ~25 m above the seafloor with ~3 knots of cruising speed. The 3D photographic observation system named “SeaXerocks1” was mounted on an ROV Kaiyo3000 (KAIYO ENGINEERING CO., LTD.) in 2021 and operated at an altitude of 4–5 m with ~0.4 knots, obtaining still images and bathymetric information with laser scanning.
Observations
The pockmark shows nearly circle shape with approximately 500 m in diameter and about 20 m deep. Immediately north of the pockmark, there is a drop-shaped north mound with a major and minor diameter of 200~250 m. Another mound exists at the northwest side of the pockmark, which is an elliptical mound with a major and minor diameter of 250~300 m. Tow mounds stand up from 5~15 m from the surrounding seafloor. The seafloor of the mounds shows rough surface with little variation in height. The bathymetric data obtained by SeaXerocks1 indicated at least four distinct bathymetric changes between 2013 and 2021. However, much little bathymetric change was suggested between 2021and 2024. It indicates that that the effect of the Noto Peninsula Earthquake occurred on January 1, 2024 was not significant on the change of bathymetric pattern (i.e., collapse of seafloor and/or large release of massive shallow MHs on seafloor into seawater) at the surface of mounds. On the other hand, the bathymetry of the north mound showed a shallowing of less than 1 m, and that of the pockmarked bottom showed deepening of less than 1 m, while the west mound and surrounding seafloor did not show any bathymetric change. We further need to be carefully examined in accuracy of the vertical resolution of the MBES in order to verify such minute differences in bathymetry data.
Acknowledgments
This study was conducted as part of a national gas hydrate research project in the Sea of Japan funded by the Ministry of Economy, Trade, and Industry (METI), Japan.