Kita-Ioto (also known as “Kita-Iwo Jima”) is located about 1,100 km S of Tokyo, Japan. It is a highly eroded stratovolcano with a steep-sided cone that rises about 800 m above the ocean surface. Eruptions from the Funka Asane submarine vent, 4-5 km NW of the main cone (figure 1), have been recorded since 1780, characterized by submarine eruptions during 1780, 1880, and 1930-1945, discolored seawater, and some degassing. This report summarizes previous events of discolored water and degassing, and includes a more recent events consisting of an eruption plume and discolored water during March-April 2022. Information for this report comes primarily from the Japan Coast Guard (JCG), the Japan Meteorological Agency (JMA), the Tokyo Volcanic Ash Advisory Center (VAAC), and satellite data.

Figure 1. Bathymetric and topographic map showing the island of Kita-Ioto on the right and the submarine Funka Asane cone to the NW. Courtesy of JCG.

Summary of activity. Visual observations of discolored water, and later, occasional degassing bubbles have been made at Funka Asane since May 1953 (table 1). Discolored water typically originates from a point source and appears pale green, yellow-green, blue-white, or milky white; on 5 November 2003, for example, discolored bluish-white water was visible from a single point (figure 2). Some of the discolored areas extended in different directions for 10-200 m, the latter of which occurred on 26 January 2000 and 10 March 2003. On 25 January 2000 three points of bluish-white discolored water appeared at 1410-1425. Pumice-like material was observed floating to the NE of the discolored water with a width of over 500 m and a length of 1.5 km. By the 26th during 0925-0930, the three points decreased to two points and the thin, milky white discolored water extended 200 m NNW, and no floating material was observed. On 16 March 2006 bubbles were first observed during 0942-0949. This type of event occurred intermittently through 9 March 2012. During 1330-1334 on 5 August 2021 light blue-white discolored water was reported by JCG to the S of Kita-Ioto. JCG also made observation flights over the area where they noted no activity. These flights were made on 14 June 2005, 26 February 2009, 30 June 2013, 17 August 2015, 24 December 2016, 24 March 2017, 11 December 2017, 18 July 2018, 29 January 2019, 19 November 2019, 8 June 2021, 9 July 2021, 11 November 2021, 27 December 2021, 15 March 2022, and 29 March 2022.

Table 1. Summary of observations made at Funka Asane between May 1953 and August 2021 by Japanese authorities. The Japan Coast Guard visited the site intermittently, noting occasional water discoloration, degassing bubbles, and one observation of floating material. Data from JMA (Japan Meteorological Agency) and JCG (Japan Coast Guard).

Figure 2. Photo of blue-white discolored water originating from a single point at the Funka Asane submarine vent of Kita-Ioto on 5 November 2003 (black arrow). Courtesy of JCG.

Activity during March-April 2022. A submarine eruption at Funka Asane was reported by JMA based on satellite images at 1800 on 27 March 2022. An eruption plume rose to 5.5 km altitude at 2100 and may have contained some ash (figure 3). By 2330 and through at least 0300 on 28 March, the plume had risen to 7 km altitude, according to HIMAWARI satellite images (figure 3). The altitude of the plume had dropped to 3.6 km at 0820 on 28 March, and by 1420 it was no longer visible. Aerial observations by JCG on 29 March did not detect discolored water or floating objects surrounding Funka Asane.

Figure 3. HIMAWARI meteorological satellite images showing eruption plumes rising from Funka Asane on 27 March (left) and 28 March 2022 (right). The image on the left was taken around 2100 and the plume rose to 5.5 km altitude and drifted NE. By 2330 that same day, the plume was confirmed to have risen to 7 km altitude. The white arrow points to Kita-Ioto in relationship to the point of origin for the eruption plume. The image on the right taken at 0000 on 28 March 2022 shows the plume continuing to drift NE (blue dotted circle). Courtesy of HIMAWARI via JMA (volcanic activity bulletin at Asane, March 28, 2020 01:50).

A small amount of brown floating material was observed during 1329-1400 on 18 April, originating from the N crater, about 5 km SE from Funka Asane, according to observations made by JCG. Some light brown and yellow-green discolored water were seen off the N coast to the W coast of the volcano (figure 4).

Figure 4. Aerial images showing the north side (left) and west side (right) of Kita-Ioto on 18 April 2022. Light brown and yellow-green discolored water were observed from the N coast to the W coast of the island. Courtesy of JCG.

Geological Summary. No historical eruptions have occurred from the deeply eroded Kita-Ioto stratovolcano, which forms a steep-sided basaltic cone rising about 800 m above the sea. However, eruptions have been recorded since the 18th century from Funka Asane, a submarine vent 4-5 km NW of the island. Kita-Ioto is the northernmost of the Kazan Retto (Volcano Islands), located in the middle of the Izu-Marianas arc.

Information Contacts: Japan Coast Guard (JCG) Volcano Database, Hydrographic and Oceanographic Department, 3-1-1, Kasumigaseki, Chiyoda-ku, Tokyo 100-8932, Japan (URL: https://www1.kaiho.mlit.go.jp/GIJUTSUKOKUSAI/kaiikiDB/kaiyo18-e1.htm); Japan Meteorological Agency (JMA), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/).