2:45 PM - 3:00 PM
[MIS26-04] High-resolution seafloor observation of a shallow methane hydrate area off Sakata, eastern margin of the Sea of Japan, using a three-dimensional pictorial mapping system
Keywords:shallow methane hydrate, acoustic mapping, 3D pictorial mapping system
Shallow methane hydrate (MH) has been reported from the top of the Sakata knoll (tentative name) along a reverse fault at the foot of the southwest side of the knoll off Sakata, along the eastern margin of the Sea of Japan (Temma and Goto, 2018). Previous observation cruises conducted in this area acquired results from acoustic mapping using research vessels and autonomous underwater vehicles, optical observations using remotely operated vehicles (ROVs), logging-while-drilling measurements, and sediment sampling (Morita, 2015; Temma and Goto, 2018; Yokota, 2020). These results reveal a depression bordered by steep slopes at the top of the knoll (~1 km×~300–400 m in diameter, ~12-m deep), two terraces on its northern and southern sides, a single hill near its center, and swells around the depression at the top of the knoll (~15 km×~5–10 km in diameter, ~120-m relative height from the southwestern foot of the knoll). The distribution of backscatter strength is largest on the steep slopes and relatively large on the terraces within the depression and the surrounding swells continuing southwestward along the knoll.
To examine the possibility of production and to assess the environmental impact, cruise 1K20 used Kaiyomaru no.1 (Kaiyo Engineering Co., Ltd.) and the ROV-Kaiyo3000 equipped with the SeaXerocks 1 mapping system (Kaiyo Engineering Co., Ltd.) to acquire high-resolution 3D images on the Sakata knoll. SeaXerocks 1 was maintained at an altitude of ~4 m above the seafloor and at a speed of ~1.5 knots. Still images and topographical data by laser scanning were acquired. The resolution of the resulting 3D images was 2 mm (in the direction orthogonal to the track) × several centimeters (along the track), which provides a detailed distribution of the chemosynthetic animals and rocks on the seafloor. SeaXerocks 1 does not have a function that merges overlapped images on different tracks and, thus, only displays independent images along the tracks. SeaXerocks 1 observations were conducted in and around the depression. We observed no MH on the seafloor. Seawater tends to be turbid, and relatively large animals (e.g., of squid and starfish) are abundant in the depression. A portion of the steep slope and the hill in the center of the depression has relatively rich biological heat and rock. Sediments are present at the base of depression. The two terraces on the northern and southern sides of the depression and the swells are extensively covered with sediments; however, rock outcrops and small biological mats are rarely observed. These observations suggest that fluid seepage is limited to the steep slope around the depression and a few parts of the swells and is less active in the present stage.
This study was conducted as part of the methane hydrate research project funded by the Ministry of Economy, Trade and Industry (METI).
References:
Temma and Goto (2018) 33rd investigative commission for methane hydrate development, METI (in Japanese)
Morita (2015) FY2014 AUV survey in shallow methane hydrate fields in Japan Sea, Japan Geoscience Union meeting 2015, MIS24-02, abstract (May 27, Chiba)
Yokota (2020) Results of high-resolution 3D seismic reflection survey, Research and development of shallow methane hydrate, FY2020 Achievements Report Meeting, Research and development project for shallow methane hydrate, AIST (in Japanese)
To examine the possibility of production and to assess the environmental impact, cruise 1K20 used Kaiyomaru no.1 (Kaiyo Engineering Co., Ltd.) and the ROV-Kaiyo3000 equipped with the SeaXerocks 1 mapping system (Kaiyo Engineering Co., Ltd.) to acquire high-resolution 3D images on the Sakata knoll. SeaXerocks 1 was maintained at an altitude of ~4 m above the seafloor and at a speed of ~1.5 knots. Still images and topographical data by laser scanning were acquired. The resolution of the resulting 3D images was 2 mm (in the direction orthogonal to the track) × several centimeters (along the track), which provides a detailed distribution of the chemosynthetic animals and rocks on the seafloor. SeaXerocks 1 does not have a function that merges overlapped images on different tracks and, thus, only displays independent images along the tracks. SeaXerocks 1 observations were conducted in and around the depression. We observed no MH on the seafloor. Seawater tends to be turbid, and relatively large animals (e.g., of squid and starfish) are abundant in the depression. A portion of the steep slope and the hill in the center of the depression has relatively rich biological heat and rock. Sediments are present at the base of depression. The two terraces on the northern and southern sides of the depression and the swells are extensively covered with sediments; however, rock outcrops and small biological mats are rarely observed. These observations suggest that fluid seepage is limited to the steep slope around the depression and a few parts of the swells and is less active in the present stage.
This study was conducted as part of the methane hydrate research project funded by the Ministry of Economy, Trade and Industry (METI).
References:
Temma and Goto (2018) 33rd investigative commission for methane hydrate development, METI (in Japanese)
Morita (2015) FY2014 AUV survey in shallow methane hydrate fields in Japan Sea, Japan Geoscience Union meeting 2015, MIS24-02, abstract (May 27, Chiba)
Yokota (2020) Results of high-resolution 3D seismic reflection survey, Research and development of shallow methane hydrate, FY2020 Achievements Report Meeting, Research and development project for shallow methane hydrate, AIST (in Japanese)