3:30 PM - 3:45 PM
[SVC34-11] Volcanic Activity in the Izu-Ogasawara Arc in 2022 - Fukutoku-Oka-no-Ba Volcano, Kaitoku Volcano, Nishinoshima Volcano, and Myojin-Syo Volcano -
Keywords:sea area volcano, the Izu-Ogasawara Arc, Fukutoku-Oka-no-Ba Volcano, Kaitoku Volcano, Myojin-Syo Volcano, Nishinoshima Volcano
The Japan Coast Guard (JCG) monitors and observes volcanoes in the Izu-Ogasawara Arc and the Ryukyu Arc using aircrafts and survey vessels. The following is a summary of the volcanic activities observed at Fukutoku-Oka-no-Ba Volcano, Kaitoku Volcano, Nishinoshima Volcano, and Myojin-Syo Volcano.
1. Fukutoku-Oka-no-Ba Volcano
The eruption of Fukutoku-Oka-no-Ba Volcano began on August 13, 2021 and plumes and explosions on the sea surface were observed until August 16, 2021. After that, discolored water with high temperature and bubbles and floating pumice were often observed until around August 2022, suggesting that volcanic activity in the submarine crater continued. Since September, the emergence of discolored water has almost ceased, and the crater and lava distributed around it can be seen from the sky.
2. Kaitoku Volcano
Kaitoku Volcano consists of three volcanic units: Nishi-Kaitoku-Ba, Higashi-Kaitoku-Ba, and Kaitoku-Kita-no-Ba. The eruption was reported by the Spanish ship "San Juan" in 1543. And the shoals were discovered by the fishing boat "Kaitoku Maru" in 1926-1927. The first well-observed eruption occurred in March 1984. The phenomena of intense upwelling of discolored water, eruption plumes, hot floating pumices and rock reefs were observed. The ejecta at that time was nonalkaline dacite with a SiO2 content of 62.38% and nonalkaline basalt with a SiO2 content of 47.81% was obtained from the Kaitoku-Kita-no-Ba. Later, in 2001, a fishing boat operating in the vicinity reported bubbles gushing to the sea surface and water temperature 5 degrees higher than the surrounding area, but no discolored water was found. The volcanic activity in 2022 was discovered by the fishing boat as discolored water activity on August 18 and 19. On August 23 and 28, the Japan Coast Guard found light green discolored water and a small amount of floating pumices around the volcano. The activity of the discolored water intensified on October 12 and November 25 and the momentum of discolored water upwelling was so strong that concentric waves were seen rising from the point of discharge on November 25(Fig. 1). However, no pumices or other suspended solids were observed on the surface of the surrounding sea despite the intense activity of the discolored water.
3. Nishinoshima Volcano
Observations by the JMA using the Himawari meteorological satellite indicate that the eruption occurred between October 1 and 12, 2022. The Japan Coast Guard conducted the observation by aircraft on October 12 and could not confirm the eruption, but observed that volcanic ash deposited on the mountainside was being blown away by the strong wind. Later, on January 25, 2023, a large amount of white fumaroles were ejected from the crater at the summit, and explosions that occasionally spewed black pyroclastic materials were observed. These explosions may have been phreatic or phreatomagmatic explosions, because it contained much white fumaroles, did not rise strongly after the explosion, and did not appear to be very hot in the infrared image.
4. Myojin-Syo Volcano
Myojin-Syo Volcano erupted intermittently after the 1952 eruption until 1970. After that, discolored water was seen until 1988, but it disappeared and only recently discolored water was seen in 2017. The latest observation on January 26, 2023, was the first time in six years that discolored water was observed. The diameter was about 100 m, the color was yellowish green, and there were no floating objects in the surrounding area(Fig. 2). Although no significant eruptive activity was observed there, continued observation will be necessary.
1. Fukutoku-Oka-no-Ba Volcano
The eruption of Fukutoku-Oka-no-Ba Volcano began on August 13, 2021 and plumes and explosions on the sea surface were observed until August 16, 2021. After that, discolored water with high temperature and bubbles and floating pumice were often observed until around August 2022, suggesting that volcanic activity in the submarine crater continued. Since September, the emergence of discolored water has almost ceased, and the crater and lava distributed around it can be seen from the sky.
2. Kaitoku Volcano
Kaitoku Volcano consists of three volcanic units: Nishi-Kaitoku-Ba, Higashi-Kaitoku-Ba, and Kaitoku-Kita-no-Ba. The eruption was reported by the Spanish ship "San Juan" in 1543. And the shoals were discovered by the fishing boat "Kaitoku Maru" in 1926-1927. The first well-observed eruption occurred in March 1984. The phenomena of intense upwelling of discolored water, eruption plumes, hot floating pumices and rock reefs were observed. The ejecta at that time was nonalkaline dacite with a SiO2 content of 62.38% and nonalkaline basalt with a SiO2 content of 47.81% was obtained from the Kaitoku-Kita-no-Ba. Later, in 2001, a fishing boat operating in the vicinity reported bubbles gushing to the sea surface and water temperature 5 degrees higher than the surrounding area, but no discolored water was found. The volcanic activity in 2022 was discovered by the fishing boat as discolored water activity on August 18 and 19. On August 23 and 28, the Japan Coast Guard found light green discolored water and a small amount of floating pumices around the volcano. The activity of the discolored water intensified on October 12 and November 25 and the momentum of discolored water upwelling was so strong that concentric waves were seen rising from the point of discharge on November 25(Fig. 1). However, no pumices or other suspended solids were observed on the surface of the surrounding sea despite the intense activity of the discolored water.
3. Nishinoshima Volcano
Observations by the JMA using the Himawari meteorological satellite indicate that the eruption occurred between October 1 and 12, 2022. The Japan Coast Guard conducted the observation by aircraft on October 12 and could not confirm the eruption, but observed that volcanic ash deposited on the mountainside was being blown away by the strong wind. Later, on January 25, 2023, a large amount of white fumaroles were ejected from the crater at the summit, and explosions that occasionally spewed black pyroclastic materials were observed. These explosions may have been phreatic or phreatomagmatic explosions, because it contained much white fumaroles, did not rise strongly after the explosion, and did not appear to be very hot in the infrared image.
4. Myojin-Syo Volcano
Myojin-Syo Volcano erupted intermittently after the 1952 eruption until 1970. After that, discolored water was seen until 1988, but it disappeared and only recently discolored water was seen in 2017. The latest observation on January 26, 2023, was the first time in six years that discolored water was observed. The diameter was about 100 m, the color was yellowish green, and there were no floating objects in the surrounding area(Fig. 2). Although no significant eruptive activity was observed there, continued observation will be necessary.