Submarine eruption with discolored water, pumice, and gas emissions during July-December 2022

Ioto (Iwo-jima), located about 1,200 km S of Tokyo, lies within a 9-km-wide submarine caldera along the Izu-Bonin-Mariana volcanic arc. Previous eruptions date back to 1889 and have consisted of dominantly phreatic explosions, pumice deposits during 2001, and discolored water (figure 7). An eruption during February-May 2012 included small phreatic eruptions, mud ejections, tremor events, discolored water, and some gas-and-steam and ash emissions (BGVN 37:07). This report updates information since May 2012, covering multiple small events on the island and offshore, through the July-December 2022 submarine eruption that included pumice, black ejecta, and discolored water. Information primarily comes from the Japan Meteorological Association (JMA), the Japan Coast Guard (JCG), and satellite data.

Figure 7. Map of Ioto showing the locations of recorded eruptions from 1889 through December 2022. The most recent eruption in 2022 is highlighted in red just off the SE coast of the island and E of the 2001 eruption site. From Ukawa et al. (2002), modified by JMA.

Activity during June-December 2012. Activity was relatively quiet after May 2012, with occasional white fumaroles seen by the Japan Coast Guard (JCG). Intermittent volcanic earthquakes and tremors also occurred. On 9 July 2012 the Japan Maritime Self Defense Force (JMSDF) reported that a white volcanic plume rose 15 m high around 1215 on the W side of the island. At 1330 mud was ejected tens of meters high; JMA noted that this activity occurred due to a small phreatic explosion, and no associated earthquakes, shock waves, or volcanic tremors were recorded.

On 1 December 2012 JMSDF reported that there were traces of mud ejections in the same location as the July 2012 activity on the W side of the island, with deposits scattered about 10 m from the vent. JMA compared this event to activity during February-April 2012 and reported that it was also possibly a small phreatic explosion.

Activity during 2013. Reports from JMSDF noted that on 18 February 2013 mud had erupted around the former crater known as “Million Dollar Hole” (a depression along the Asodai fault) and included rocks with diameters up to 40 cm. The deposits were mainly scattered about 150 m W. JMSDF identified this event as a small phreatic explosion, similar but larger than those that occurred in 2012.

On 6 March an overflight by JMA allowed observations of a new depression in the Million Dollar Hole that measured about 15 m in diameter. Though no new deposits were visible around the depression, and the exact date and time of the event were unknown, larger volcanic earthquakes from 1800 on 5 March to 0600 on 6 March indicated a small phreatic explosion.

A black plume was visible rising about 400 m above Million Dollar Hole on the W side of the island at 1600 on 11 April, according to a report from JMSDF (figure 8). Volcanic material was also deposited, and volcanic tremor lasted about eight minutes and 50 seconds starting around 1559. These events indicated that a small phreatic explosion had occurred.

Figure 8. Photos of an eruption plume rising 400 m above Million Dollar Hole on the W side of Ioto on 11 April 2013. Around 1600 a small phreatic explosion occurred. Courtesy of JMSDF via JMA.

Off the NE coast of the island near Kitanohana, aerial observations showed white discolored water on 21 August 2013. Further NW from this point, about 150 m off the coast and 300 m N of Kitanohana, on 28 and 30 August more discolored water was confirmed (figure 9).

Figure 9. Photos of blue-yellow discolored water off the NE coast of Ioto near Kitanohana on 28 (left) and 30 (right) August 2013. Photo on the right has been color corrected. Courtesy of JMSDF via JMA.

Activity during 2014-2019. Activity was relatively low during 2014-2019 with occasional seismicity, fumarolic activity, and small eruptions. On 22 May, 24 May, and 20 June 2015 gas-and-steam emissions rose 100-200 m high near the Idogahama Beach on the NW side of the island. Some fumarolic activity was also recorded up to 10 m at the Asodai Sinkhole. A small eruption was recorded near Kitanohana Beach on the N part of the island on 7 August 2015. Mud and rocks were scattered within about 27 m around the eruption vent.

Eruptive activity was reported by JMA during 31 August to 1 September 2016; the National Research Institute for Earth Science and Disaster Prevention confirmed that new volcanic blocks had been ejected about 50 m from the Asodai Sinkhole, accompanied by fumarolic activity. Intermittent fumarolic activity continued through December 2017.

JMA reported that during 8-14 September 2018 the number of volcanic earthquakes increased, and for the first time since April 2012 the daily number of earthquakes exceeded 600. The number of earthquakes decreased slightly after 8 September but remained high through the 14th. During a JMSDF overflight on 12 September 2018 seawater jetting was observed 5-10 m above the ocean surface on the S coast, which JMSDF suggested may have been a submarine eruption. In addition, discolored water was also visible.

Activity during 2020-June 2022. During 2020-2021, activity remained relatively low. An aerial observation conducted by JCG on 4 February 2020 reported that there was discolored water off the W (Chidorigahama) and SE (Okinahama) coasts of the island (figure 10). A small eruption occurred at the Asodai Sinkhole at 1948 on 28 December 2020, which generated a plume that rose 400 m high (figure 11). Volcanic tremors were detected around this time as well. A field survey conducted by JMSDF that night and the morning of 29 December identified volcanic blocks with diameters of 20 cm that had been ejected 50-100 m from the sinkhole; mud deposits were also noted.

Figure 10. Photo of yellow discolored water off the SE coast of Ioto on 4 February 2020. Photo has been color corrected. Courtesy of JCG via JMA.

Figure 11. Webcam image showing an eruption plume rising 400 m above the Asodai Sinkhole on the NW side of Ioto at 1951 on 28 December 2020. Courtesy of JMA.

A surveillance camera, located approximately 900 m ENE of the Asodai Sinkhole on the W side of the island, showed a fumarolic plume rising less than 200 m high on 6 January 2021. Then, on 1 February 2021 a gray eruption plume was detected rising 20 m high at 0905. Mud eruptions around this time were also confirmed at the Asodai Sinkhole. During March 2021 yellowish discolored water was observed near the SE coast. Based on information from JMSDF, a helicopter overflight on 5 April reported that there were dried traces of mud eruptions in the Million Dollar Hole. JMA suggested that several days had passed since the mud eruption occurred. Discolored water was observed during an overflight on 12 July 2021 off the northern NW (Tamehachi) coast.

Off the SE coast (Okinahama), columns of water were reported by JMSDF to be rising from several to tens of meters high during 12 August, 23-26 August, 2-3 September, and 17 September 2021. The JCG reported bluish-white discolored water, gray particles, and bubbles seen during an overflight on 26 August and 12 September off the SE coast (figure 12). On 24 November JMSDF reported that a white volcanic plume rose 60 m high around 0540 from the NW side of the island; occasional gray ejecta rose 20-30 m high that same day NE from the site of the white plume. This activity was accompanied by an increase in volcanic earthquakes and tremor during 23-26 November.

Figure 12. Photo of gray particles and discolored water observed off the SE (Okinahama) coast of Ioto on 26 August 2021. Courtesy of JMA.

Activity during July-August 2022. JMA reported that minor eruptive activity, such as fumaroles, ejecta, and discolored plumes were observed off the SE coast of Ioto each day during 11-31 July 2022. JCG observed brown discolored water beginning on 11 July off the SE coast (figure 13). A column of water containing black ejecta rose meters to tens of meters at intervals of several minutes. On 14 July pumice clasts from the eruption washed onto shore at Okinahama and were photographed by the National Research Institute for Earth Science and Disaster Prevention during a field survey (figure 14). Aerial observations conducted by JCG on 15 July revealed bubbles near the eruptive vent. Additionally, a Sentinel-2 satellite image showed that on 15 July a dark spot off the SE coast near the 2001 vent location was the source of a green-yellow plume of discolored water that drifted NE (figure 15).

Figure 13. Photo showing brown discolored water first appearing off the SE (Okinahama) coast of Ioto on 11 July 2022. Photo has been color corrected. The scale of the affected area was not recorded. Courtesy of Japan Coast Guard.

Figure 14. Photo of rocks on Okinahama (SE coast beach) thought to have originated from a submarine eruption of Ioto. Photo was taken on 14 July 2022 by the National Research Institute for Earth Science and Disaster Resilience. Courtesy of JMA.

Figure 15. Sentinel-2 satellite image showing a dark spot of water off the SE coast of Ioto with a discolored plume drifting NE on 15 July 2022. The location of this activity was near the 2001 vent. Image with “Natural color” rendering (bands 4, 3, 2). Courtesy of Sentinel Hub Playground.

Video taken around 25 July showed a white plume rising from the same location. Satellite images during 30-31 July showed small, rounded gray zones on the surface of the water (figure 16). JMA scientists visited the site on 31 July and confirmed pumice deposits on the beach (figure 17) and noted offshore eruptive activity every few minutes consisting of gray, tephra-laden columns of water rising 20-30 m above the ocean surface (figure 18). On 1 August a photo showed white gas-and-steam emissions rising above the submarine vent, accompanied by floating pumice deposits (figure 19). Another small, rounded gray zone in the water was also captured in a 4 August satellite image (figure 16); an associated discolored plume of water was visible drifting NE. Activity remained relatively low after 9 August, according to JMA, though disturbed water and a green-blue discolored plume in the same area was seen by the JCG on 23 August (figure 20).

Figure 16. Sentinel-2 satellite image showing a small, rounded, gray zone at the surface of the water off the SE coast of Ioto on 30 July 2022 (left) and 4 August 2022 (right). A yellow-green discolored plume was visible on 4 August drifting NE. Image with “Natural color” rendering (bands 4, 3, 2). Image on the left has been color corrected due to cloud cover. Courtesy of Sentinel Hub Playground.

Figure 17. Photos showing pumice deposited on Okinahama (SE coast beach) from the Ioto submarine eruption on 31 July 2022. The size of the clast shown here on the right is 90 cm in length. Courtesy of JMA.

Figure 18. Photos showing the submarine eruption at Ioto taken from the SE coast of the island around 1427 on 31 July 2022. The dark water column was ejected 20-30 m high. Courtesy of JMA.

Figure 19. Photo of white gas-and-steam emissions on 1 August 2022 rising above the submarine eruptive vent off the SE coast of Ioto, accompanied by floating pumice deposits. Photo has been color corrected. Courtesy of JMA.

Figure 20. Photo of a blue-green discolored water plume off the SE (Okinahama) coast of Ioto on 23 August 2022. Photo has been color corrected. The scale of the affected area was not recorded. Courtesy of Japan Coast Guard.

Activity during September-December 2022. JMSDF reported that discolored water on the evening of 4 October was visible off the SE coast, in the same location as the activity during July-August, which was followed by an eruption during 5-8 October. A column of water containing black ejecta rose meters to several tens of meters above the ocean surface at several minute intervals. An overflight on 12 October confirmed a discolored water plume off the SE coast (figure 21) that drifted NE from the same source as the July-August activity.

Figure 21. Photos of a strong discolored water plume off the coast of Ioto near Okinahama taken on 12 October 2022. Photo on the left has been color corrected. Courtesy of JCG (left) and JMA (right).

According to JMSDF an eruption during 7-11 December 2022 included black ejecta rising to tens of meters above the ocean surface in about ten-minute intervals. On 9 December pumice clasts may have been spotted floating on the water. Discolored water was visible on 13 December near the same eruptive vent active during July-August and October.

References. Ukawa, M., Fujita, E., Kobayashi, T., 2002, Recent volcanic activity of Iwo Jima and the 2001 eruption, Monthly Chikyu, Extra No. 39, 157-164.

Information Contacts: Japan Meteorological Agency (JMA), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); 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/kaiyo22-2.htm); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Information is preliminary and subject to change. All times are local (unless otherwise noted)

January 1977 (NSEB 02:01) Cite this Report

Possible submarine eruption 26 km NW of the island in January 1974

[A table of possible submarine eruptions based on aerial observations of water discoloration by the Japanese Maritime Safety Agency included an entry for 24.88°N, 141.17°E, in January 1974. This location is ~26 km NW of Iwo-jima.]

Information Contacts: AFP; U.S. Defense Mapping Agency.

September 1982 (SEAN 07:09) Cite this Report

Small phreatic explosions on NW flank

Five small phreatic explosions without detonations or recorded seismic events were reported by the Japanese National Research Center for Disaster Prevention. They occurred 9-10 March on the NW shore of the island, producing a new crater N of Asodai Crater (which erupted in 1967, 1969, 1976 and 1978) and "Million Dollar Hole." The three craters lie on the Asodai fault. The ejecta were no larger than 25 cm in diameter and were scattered within 300 m of the new crater. No juvenile material was found, only fragmented older rock.

Information Contacts: JMA.

April 1983 (SEAN 08:04) Cite this Report

Earthquake swarm, two weak steam explosions

The National Research Center for Disaster Prevention reported that two weak steam explosions from Asodai Crater 28-29 November 1982 were associated with an earthquake swarm 25-30 November. Among the 1,492 recorded seismic events were 13 felt shocks. Before the swarm, the maximum number of recorded seismic events for a 5-day period had been 104. The earthquakes cracked roads in some places.

Information Contacts: JMA.

September 2001 (BGVN 26:09) Cite this Report

In September, a submarine eruption; in October, a phreatic eruption pierces beach

A submarine eruption at Iwo-jima, off of the island's SE coast, on 21 September was the first reported volcanic activity since November 1982 when an earthquake swarm and weak steam explosions occurred at Asodai Crater (SEAN 08:04). Approximately 1 month after the submarine eruption on the SE side of the island, a small phreatic eruption occurred at Idogahama, a beach on the NW coast of the island.

At 1015 on 21 September a submarine eruption began off of the SE coast of Iwo-jima, an island inhabited by U.S. and Japanese military personnel approximately 1,250 km S of Tokyo. The Japan Maritime Self Defense Force stationed on Iwo-jima observed the eruption, which was preceded by isolated and continuous tremor beginning on 20 September at 2000. Visible evidence of the eruption consisted of seawater gushing several meters above sea level near the island's SE coast. In addition, the eruption was accompanied by an area of discolored seawater extending 300-400 m in length. During 1000-1100 approximately 30 earthquakes occurred in the active area; the typical rate is one or two earthquakes per hour.

The climax of the eruption occurred during 1300-1500. At about 1300 water gushed ~40 m above sea level and accompanying steam rose to 100-300 m. During 1515-1715, Japan Meteorological Agency (JMA) personnel observed seawater rising intermittently in two small dark-gray colored areas 50 m apart and 150-200 m from the island's SE coast (Okinahama beach). The two areas were surrounded by zones of bubbling, white-colored water. The water outside the bubbling zone was emerald green in color. A plume of water rose every few to ten minutes in the western-most area. Measurements with an infrared thermometer revealed that the temperatures in these two areas were 33-34°C and 50°C, while the surrounding water was at 27°C. An approximately 8-km-long and 500-m-wide area of discolored water stretched away from the two areas. By 1500 the number of earthquakes decreased from 30 per hour to about ten. During 1600-1700 three eruption sites were visible; at one a pyroclastic cone was slightly above the sea surface (figures 1 and 2).

Figure 1. Photograph showing three activity sites off the SE coast of Iwo-jima on 21 September 2001 during 1600-1700. Water depth in this area is less than 10 m. A pyroclastic cone that rose above the sea surface is visible at the site furthest to the right; at sea level the diameter of the cone was ~10 m. The coast (Okinahama beach) is approximately 150-200 m to the W (right on the photo). Photo courtesy of Mr. Odai, JMA.

Figure 2. Submarine eruption off the SE coast of Iwo-jima on 21 September 2001 during 1600-1700. The arrow indicates the location of the bubbling water shown in figure 1. The photo was taken facing towards the SW coast of the island. Okinahama beach is visible to the right. Photo courtesy of Mr. Odai, JMA.

JMA reported that the day after the eruption, 22 September, volcanic and seismic activity returned to usual levels, with no water plumes observed and 0-4 earthquakes per hour. In addition, the isolated and continuous tremor events that were recorded during the night of 20 September to the morning of 22 September temporarily ceased. After 21 September areas of discolored water were still visible (figure 3). Until about 28 September many earthquakes and tremor were detected. Results are pending from the analysis of floating pumice that was collected along Iwo-jima's coast after the eruption. Until at least 10 October areas of discolored water were occasionally seen; these were smaller than when the submarine eruption began on 21 September.

Figure 3. View of the SE side of Iwo-jima on 22 September during 1300-1400, about 27 hours after the start of a submarine eruption. The arrow indicates the location of bubbling water seen the day before. An area of green and tan discolored water (light water near the coast on the photo) is visible extending an unstated distance along and beyond the SE coast. Photo courtesy of Mr. Nakahori, JMA.

After 21 September there was no volcanic activity at Iwo-jima until 19 October. On the morning of 19 October a small phreatic eruption was observed at Idogahama, a beach on the NW coast of the island. The last reported volcanic activity at Idogahama occurred in March 1982 and consisted of a small phreatic eruptions (SEAN 07:09). The Japan Maritime Self Defense Force observed a grayish-white colored plume rising to 200-300 m above the beach surface for 2-3 minutes starting at about 0725. Another similarly sized plume was observed for 10 minutes starting at 0806. JMA, with support from the Japan Maritime Self Defense Force and the Japan Air Self Defense Force, observed the eruption from a helicopter soon after it began.

JMA personnel observed the eruption during 1602-1715 and measured the temperature of the eruption site with an infrared camera. They estimated that the main crater formed during the eruption was about 10 m long and 2-3 m deep. Inside the crater, every 10 minutes intermittent gushing of black water and entrained debris was observed (figure 4). An accompanying white steam plume reached a maximum height of 600 m above the beach during the observations. The temperature inside the crater was 56°C.

Figure 4. Small phreatic eruption at Idogahama, a beach on the NW coast of Iwo-jima, at 1703 (top) and 1704 (bottom) on 19 October 2001. The crater is about 10 m long and 2-3 m deep. The steam cloud rose to a maximum height of 600 m above the beach. Photo courtesy of Mr. Odai and Mr. Nakahori, JMA.

Information Contacts: Setsuya Nakada, Volcano Research Center, Earthquake Research Institute, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-0032, Japan (URL: http://www.eri.u-tokyo.ac.jp/VRC/index_E.html); Mr. Odai, Mr. Nakahori, and Tomoyuki Kanno, Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan (URL: http://www.jma.go.jp/).

July 2012 (BGVN 37:07) Cite this Report

Mud ejections and small phreatic eruptions during early 2012

This report first briefly notes an article discussing deformation at Ioto (also called Iwo-jima), an island located within a submerged caldera ~1,200 km S of Tokyo. Ozawa and others (2007) discuss both complex deformation measured during 2006-2007 and the extremely high rate of uplift during the last few hundred years. The rest of this report is devoted to observations by the Japan Meteorological Association (JMA) and other agencies at Ioto during October 2010 to May 2012, including more deformation, small emissions of hot mud and steam, and discolored seawater that suggested a NE flank submarine eruption.

Our previous report on Ioto (Iwo-jima), discussed a submarine eruption off the SE coast that occurred in September 2001, and a small phreatic eruption at Idogahama, a beach on the NW coast of the island, in October 2001 (BGVN 26:09). Ioto is mildly seismically active with many fumaroles and occasional phreatic explosions, but the volcano has not experienced a magmatic eruption in 400 years (Newhall and Dzurisin, 1988; Lowenstern and others, 2006; Yokoyama and Nazzaro, 2002; and Ukawa and others, 2006).

The locations of the major volcanoes of Japan, including the island of Ioto, are shown in figure 5. Figure 6 is a map of Ioto, summarizing its topography and past eruption sites.

Figure 5. A map of the major volcanoes of Japan. Ioto (Iwo-jima) is shown in the lower right. Ioto is about 1,200 km SSE of Tokyo, in the Volcano Islands of the W Pacific Ocean. Courtesy of the U.S. Geological Survey.

Figure 6. Map of Ioto showing topography, major features (including the Asodai fault), and past eruption sites. From Ukawa and others (2006).

Deformation. Ozawa and others (2007) noted that the overall pattern of deformation seen in the last several hundred years averaged to ~0.25 m of uplift per year, but often exceeded uplift rates of 1 m per year. They plotted uplift and subsidence during January 2006-late 2007 from satellite radar interferometry. Concluding that the deformation pattern is very complicated both spatially and temporally, the authors noted that "In August of 2006, subsidence which had continued from 2003 rapidly changed to uplift, and an increase of seismicity was also observed simultaneously." They divided the uplift during August 2006-late 2007 into 3 stages. The authors used gravity and magnetic data to constrain the shape of the shallow intruding magma under the island's main edifice (Motoyama, also spelled Moto-yama) centered in the bulbous NE portion of the island (figure 6). They described the intruding magma body as having a funnel shape, narrowing towards the bottom and centered about the main topographic high. The authors' modeling suggested that the block of material trapped within the funnel was variously displaced during each of the deformation stages, shifting the block depending on where the magma pooled.

JMA reports. The following material summarizes activity from October 2010 to May 2012, based on monthly volcanic activity reports from JMA. JMA reports on Ioto between November 2001 and September 2010 are not available in English; translations into English resumed in October 2010.

In October 2010, Japan's National Research Institute for Earth Science and Disaster Prevention (NIED) reported that seismicity remained at a low level. GPS observations by the Geospatial Information Authority of Japan (GSI) indicated that an episode of uplift that had ceased around October 2009 resumed in May 2010. N-S baseline displacement (extension) accelerated during late September-early October 2010, accompanied by an eastward deformation in the central part of the island. The uplift slowed after mid-November 2010. This upheaval followed one that occurred during August 2006-October 2009.

During 29-30 January 2011, aerial observations were conducted in cooperation with the Japan Maritime Self-Defense Force (JMSDF). No change in the distribution of thermal anomalies or emissions was detected since the last observation in July 2010.

According to NIED and GSI, both shallow seismicity and the rate of uplift at Ioto increased in February 2011 and continued through at least January 2012. GPS measurements showed a rapid southward displacement at the S part of island. Moreover, between 26 August and 2 September 2011, a local westward displacement was observed SW and SE of Motoyama.

A field survey during 16-18 November 2011 revealed that the water level in Asodai crater (along the fault of the same name, figure 6) had risen compared with the last observation during 29-30 January 2011. The temperature of the muddy water at the bottom of the pit was estimated to be ~100°C, the same as that observed in January 2011. Associated discharges reached a maximum height of 20 m above the crater. No change in the distribution of thermal anomalies or emissions was detected since the last observation in January 2011.

On 10 February 2012, JMSDF reported a mud ejection at an old crater (another depression along the Asodai fault, a spot sometimes called "Million Dollar Hole"). According to field surveys on 14 and 15 February, three major ejection sites were aligned in the N-S direction, the deepest being about 13 m. Mud was ejected to distances of up to 100 m NE of the main vent. No seismicity was observed to be associated with this event, but JMA believed a very small phreatic explosion probably occurred during early February. The maximum temperature of the mud was 96.6°C. Another mud ejection occurred on 7 March in the same area, and mud was ejected up to 60 m WNW. Ash emissions also rose from Asodai, but not from Idogahama.

During another field survey from 7 to 9 March 2012, further mud ejections were noted from the same area as the previous events on the island's W side. In addition, a very small phreatic eruption was noted, with tremor (90-minute duration) and intermittent ejections of steam plumes, mud, and small rocks. Emissions rose 20 m above the crater, and small amounts of ash rose more than 10 m and scattered within 20 m in every direction. During that time, the water level in Asodai crater was higher than that observed during the 16-18 November observation.

During 5-6 April 2012, volcanic tremor and intermittent earthquakes were recorded, and two apparently very small phreatic eruptions were reported. This was accompanied by intermittent noises and emissions at the old crater to the W of the island. According to GSI, ground deformation and seismic activity were greater than usual during 27-28 April, but both subsided after 4 May.

During 29-30 April, the ocean NE of the island was discolored, suggesting an offshore underwater eruption. An aerial observation conducted by the Japan Coast Guard (JCG) on 16 May revealed that discoloration persisted, but in smaller areas. On the N part of the island, steam plumes rose to heights of up to 10 m on 30 April.

During May 2012, ground deformation was almost static. Seismic activity diminished, and no volcanic tremors were observed. Based on camera monitoring, emissions from Asodai crater were low, and no emissions were noted in Idogahama.

References. Lowenstern, J.B., Smith, R.B., and Hill, D.P., 2006, Monitoring super-volcanoes: geophysical and geochemical signals at Yellowstone and other large caldera systems, Phil. Trans. R. Soc. A 364, p. 2055-2072.

Yokoyama, I., and Nazzaro, A., 2002, Anomalous crustal movements with low seismic efficiency-Campi Flegrei, Italy and some examples in Japan, Annals of Geophysics, v. 45, no. 6, p. 709-722.

Newhall, C.G., and Dzurisin, D., 1988, Historical unrest at large calderas of the world, U.S. Geological Survey Bulletin 1855: 1108 p, 2 vol, pgs. 509-520.

Ukawa, M., Fujita, E., Ueda, H., Kumagai, T., Nakajima, H., and Morita, H., 2006, Long-term geodetic measurements of large scale deformation at Iwo-jima caldera, Japan, J. of Volcanology and Geothermal Research, v. 150, p. 98-118.

Ozawa, T., Ueda, H., Ukawa, M., and Miyazaki, S., 2007, Temporal change in crustal deformation related to volcanic activity of Iwo-jima observed by PALSAR/InSAR, Proceedings of the First Joint PI Symposium of ALOS, Data Nodes for ALOS Science Program (DIS 10).

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/); Japan’s National Research Institute for Earth Science and Disaster Prevention (NIED), 3-1, Tennodai, Tsukuba, Ibaraki, 305-0006, Japan (URL: http://www.bosai.go.jp/e/); Geospatial Information Authority of Japan (GSI) (URL: http://www.gsi.go.jp/ENGLISH/); Japan Maritime Self-Defense Force (JMSDF) (URL: http://www.mod.go.jp/msdf/formal/english/index.html); Japan Coast Guard (JCG) (URL: http://www.kaiho.mlit.go.jp/e/index_e.htm).

January 2023 (BGVN 48:01) Cite this Report

Submarine eruption with discolored water, pumice, and gas emissions during July-December 2022

Ioto (Iwo-jima), located about 1,200 km S of Tokyo, lies within a 9-km-wide submarine caldera along the Izu-Bonin-Mariana volcanic arc. Previous eruptions date back to 1889 and have consisted of dominantly phreatic explosions, pumice deposits during 2001, and discolored water (figure 7). An eruption during February-May 2012 included small phreatic eruptions, mud ejections, tremor events, discolored water, and some gas-and-steam and ash emissions (BGVN 37:07). This report updates information since May 2012, covering multiple small events on the island and offshore, through the July-December 2022 submarine eruption that included pumice, black ejecta, and discolored water. Information primarily comes from the Japan Meteorological Association (JMA), the Japan Coast Guard (JCG), and satellite data.

Figure 7. Map of Ioto showing the locations of recorded eruptions from 1889 through December 2022. The most recent eruption in 2022 is highlighted in red just off the SE coast of the island and E of the 2001 eruption site. From Ukawa et al. (2002), modified by JMA.

Activity during June-December 2012. Activity was relatively quiet after May 2012, with occasional white fumaroles seen by the Japan Coast Guard (JCG). Intermittent volcanic earthquakes and tremors also occurred. On 9 July 2012 the Japan Maritime Self Defense Force (JMSDF) reported that a white volcanic plume rose 15 m high around 1215 on the W side of the island. At 1330 mud was ejected tens of meters high; JMA noted that this activity occurred due to a small phreatic explosion, and no associated earthquakes, shock waves, or volcanic tremors were recorded.

On 1 December 2012 JMSDF reported that there were traces of mud ejections in the same location as the July 2012 activity on the W side of the island, with deposits scattered about 10 m from the vent. JMA compared this event to activity during February-April 2012 and reported that it was also possibly a small phreatic explosion.

Activity during 2013. Reports from JMSDF noted that on 18 February 2013 mud had erupted around the former crater known as “Million Dollar Hole” (a depression along the Asodai fault) and included rocks with diameters up to 40 cm. The deposits were mainly scattered about 150 m W. JMSDF identified this event as a small phreatic explosion, similar but larger than those that occurred in 2012.

On 6 March an overflight by JMA allowed observations of a new depression in the Million Dollar Hole that measured about 15 m in diameter. Though no new deposits were visible around the depression, and the exact date and time of the event were unknown, larger volcanic earthquakes from 1800 on 5 March to 0600 on 6 March indicated a small phreatic explosion.

A black plume was visible rising about 400 m above Million Dollar Hole on the W side of the island at 1600 on 11 April, according to a report from JMSDF (figure 8). Volcanic material was also deposited, and volcanic tremor lasted about eight minutes and 50 seconds starting around 1559. These events indicated that a small phreatic explosion had occurred.

Figure 8. Photos of an eruption plume rising 400 m above Million Dollar Hole on the W side of Ioto on 11 April 2013. Around 1600 a small phreatic explosion occurred. Courtesy of JMSDF via JMA.

Off the NE coast of the island near Kitanohana, aerial observations showed white discolored water on 21 August 2013. Further NW from this point, about 150 m off the coast and 300 m N of Kitanohana, on 28 and 30 August more discolored water was confirmed (figure 9).

Figure 9. Photos of blue-yellow discolored water off the NE coast of Ioto near Kitanohana on 28 (left) and 30 (right) August 2013. Photo on the right has been color corrected. Courtesy of JMSDF via JMA.

Activity during 2014-2019. Activity was relatively low during 2014-2019 with occasional seismicity, fumarolic activity, and small eruptions. On 22 May, 24 May, and 20 June 2015 gas-and-steam emissions rose 100-200 m high near the Idogahama Beach on the NW side of the island. Some fumarolic activity was also recorded up to 10 m at the Asodai Sinkhole. A small eruption was recorded near Kitanohana Beach on the N part of the island on 7 August 2015. Mud and rocks were scattered within about 27 m around the eruption vent.

Eruptive activity was reported by JMA during 31 August to 1 September 2016; the National Research Institute for Earth Science and Disaster Prevention confirmed that new volcanic blocks had been ejected about 50 m from the Asodai Sinkhole, accompanied by fumarolic activity. Intermittent fumarolic activity continued through December 2017.

JMA reported that during 8-14 September 2018 the number of volcanic earthquakes increased, and for the first time since April 2012 the daily number of earthquakes exceeded 600. The number of earthquakes decreased slightly after 8 September but remained high through the 14th. During a JMSDF overflight on 12 September 2018 seawater jetting was observed 5-10 m above the ocean surface on the S coast, which JMSDF suggested may have been a submarine eruption. In addition, discolored water was also visible.

Activity during 2020-June 2022. During 2020-2021, activity remained relatively low. An aerial observation conducted by JCG on 4 February 2020 reported that there was discolored water off the W (Chidorigahama) and SE (Okinahama) coasts of the island (figure 10). A small eruption occurred at the Asodai Sinkhole at 1948 on 28 December 2020, which generated a plume that rose 400 m high (figure 11). Volcanic tremors were detected around this time as well. A field survey conducted by JMSDF that night and the morning of 29 December identified volcanic blocks with diameters of 20 cm that had been ejected 50-100 m from the sinkhole; mud deposits were also noted.

Figure 10. Photo of yellow discolored water off the SE coast of Ioto on 4 February 2020. Photo has been color corrected. Courtesy of JCG via JMA.

Figure 11. Webcam image showing an eruption plume rising 400 m above the Asodai Sinkhole on the NW side of Ioto at 1951 on 28 December 2020. Courtesy of JMA.

A surveillance camera, located approximately 900 m ENE of the Asodai Sinkhole on the W side of the island, showed a fumarolic plume rising less than 200 m high on 6 January 2021. Then, on 1 February 2021 a gray eruption plume was detected rising 20 m high at 0905. Mud eruptions around this time were also confirmed at the Asodai Sinkhole. During March 2021 yellowish discolored water was observed near the SE coast. Based on information from JMSDF, a helicopter overflight on 5 April reported that there were dried traces of mud eruptions in the Million Dollar Hole. JMA suggested that several days had passed since the mud eruption occurred. Discolored water was observed during an overflight on 12 July 2021 off the northern NW (Tamehachi) coast.

Off the SE coast (Okinahama), columns of water were reported by JMSDF to be rising from several to tens of meters high during 12 August, 23-26 August, 2-3 September, and 17 September 2021. The JCG reported bluish-white discolored water, gray particles, and bubbles seen during an overflight on 26 August and 12 September off the SE coast (figure 12). On 24 November JMSDF reported that a white volcanic plume rose 60 m high around 0540 from the NW side of the island; occasional gray ejecta rose 20-30 m high that same day NE from the site of the white plume. This activity was accompanied by an increase in volcanic earthquakes and tremor during 23-26 November.

Figure 12. Photo of gray particles and discolored water observed off the SE (Okinahama) coast of Ioto on 26 August 2021. Courtesy of JMA.

Activity during July-August 2022. JMA reported that minor eruptive activity, such as fumaroles, ejecta, and discolored plumes were observed off the SE coast of Ioto each day during 11-31 July 2022. JCG observed brown discolored water beginning on 11 July off the SE coast (figure 13). A column of water containing black ejecta rose meters to tens of meters at intervals of several minutes. On 14 July pumice clasts from the eruption washed onto shore at Okinahama and were photographed by the National Research Institute for Earth Science and Disaster Prevention during a field survey (figure 14). Aerial observations conducted by JCG on 15 July revealed bubbles near the eruptive vent. Additionally, a Sentinel-2 satellite image showed that on 15 July a dark spot off the SE coast near the 2001 vent location was the source of a green-yellow plume of discolored water that drifted NE (figure 15).

Figure 13. Photo showing brown discolored water first appearing off the SE (Okinahama) coast of Ioto on 11 July 2022. Photo has been color corrected. The scale of the affected area was not recorded. Courtesy of Japan Coast Guard.

Figure 14. Photo of rocks on Okinahama (SE coast beach) thought to have originated from a submarine eruption of Ioto. Photo was taken on 14 July 2022 by the National Research Institute for Earth Science and Disaster Resilience. Courtesy of JMA.

Figure 15. Sentinel-2 satellite image showing a dark spot of water off the SE coast of Ioto with a discolored plume drifting NE on 15 July 2022. The location of this activity was near the 2001 vent. Image with “Natural color” rendering (bands 4, 3, 2). Courtesy of Sentinel Hub Playground.

Video taken around 25 July showed a white plume rising from the same location. Satellite images during 30-31 July showed small, rounded gray zones on the surface of the water (figure 16). JMA scientists visited the site on 31 July and confirmed pumice deposits on the beach (figure 17) and noted offshore eruptive activity every few minutes consisting of gray, tephra-laden columns of water rising 20-30 m above the ocean surface (figure 18). On 1 August a photo showed white gas-and-steam emissions rising above the submarine vent, accompanied by floating pumice deposits (figure 19). Another small, rounded gray zone in the water was also captured in a 4 August satellite image (figure 16); an associated discolored plume of water was visible drifting NE. Activity remained relatively low after 9 August, according to JMA, though disturbed water and a green-blue discolored plume in the same area was seen by the JCG on 23 August (figure 20).

Figure 16. Sentinel-2 satellite image showing a small, rounded, gray zone at the surface of the water off the SE coast of Ioto on 30 July 2022 (left) and 4 August 2022 (right). A yellow-green discolored plume was visible on 4 August drifting NE. Image with “Natural color” rendering (bands 4, 3, 2). Image on the left has been color corrected due to cloud cover. Courtesy of Sentinel Hub Playground.

Figure 17. Photos showing pumice deposited on Okinahama (SE coast beach) from the Ioto submarine eruption on 31 July 2022. The size of the clast shown here on the right is 90 cm in length. Courtesy of JMA.

Figure 18. Photos showing the submarine eruption at Ioto taken from the SE coast of the island around 1427 on 31 July 2022. The dark water column was ejected 20-30 m high. Courtesy of JMA.

Figure 19. Photo of white gas-and-steam emissions on 1 August 2022 rising above the submarine eruptive vent off the SE coast of Ioto, accompanied by floating pumice deposits. Photo has been color corrected. Courtesy of JMA.

Figure 20. Photo of a blue-green discolored water plume off the SE (Okinahama) coast of Ioto on 23 August 2022. Photo has been color corrected. The scale of the affected area was not recorded. Courtesy of Japan Coast Guard.

Activity during September-December 2022. JMSDF reported that discolored water on the evening of 4 October was visible off the SE coast, in the same location as the activity during July-August, which was followed by an eruption during 5-8 October. A column of water containing black ejecta rose meters to several tens of meters above the ocean surface at several minute intervals. An overflight on 12 October confirmed a discolored water plume off the SE coast (figure 21) that drifted NE from the same source as the July-August activity.

Figure 21. Photos of a strong discolored water plume off the coast of Ioto near Okinahama taken on 12 October 2022. Photo on the left has been color corrected. Courtesy of JCG (left) and JMA (right).

According to JMSDF an eruption during 7-11 December 2022 included black ejecta rising to tens of meters above the ocean surface in about ten-minute intervals. On 9 December pumice clasts may have been spotted floating on the water. Discolored water was visible on 13 December near the same eruptive vent active during July-August and October.

References. Ukawa, M., Fujita, E., Kobayashi, T., 2002, Recent volcanic activity of Iwo Jima and the 2001 eruption, Monthly Chikyu, Extra No. 39, 157-164.

Information Contacts: Japan Meteorological Agency (JMA), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); 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/kaiyo22-2.htm); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).