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Ioto

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  • Japan
  • Caldera
  • 2022 CE
  •  
  • Country
  • Primary Volcano Type
  • Last Known Eruption
  •  
  • 24.751°N
  • 141.289°E

  • 169 m
    554 ft

  • 284120
  • Latitude
  • Longitude

  • Summit
    Elevation

  • Volcano
    Number
Most Recent Weekly Report: 3 August-9 August 2022 Citation IconCite this Report

JMA reported that minor eruptive activity off the coast at Ioto (Iwo-jima) had been visible daily during 11-31 July. On 14 July pumice pieces from the eruption washed up onto the shore at Onohama and were photographed during a field survey conducted by the National Research Institute for Earth Science and Disaster Prevention. JMA scientist visited the site on 31 July and confirmed the pumice deposits on the beach. They saw eruptive activity every few minutes, and gray, tephra-laden columns of water being ejected 20-30 m above the ocean’s surface. A satellite image on 4 August showed a small rounded gray zone at the water surface and a plume of discolored water drifting NE.

Sources: Japan Meteorological Agency (JMA), Sentinel Hub


Most Recent Bulletin Report: July 2012 (BGVN 37:07) Citation IconCite 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 (see Caption) 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 (see Caption) 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).

Weekly Reports - Index


2022: July | August
2018: September
2012: April
2010: June
2001: September | October


3 August-9 August 2022 Citation IconCite this Report

JMA reported that minor eruptive activity off the coast at Ioto (Iwo-jima) had been visible daily during 11-31 July. On 14 July pumice pieces from the eruption washed up onto the shore at Onohama and were photographed during a field survey conducted by the National Research Institute for Earth Science and Disaster Prevention. JMA scientist visited the site on 31 July and confirmed the pumice deposits on the beach. They saw eruptive activity every few minutes, and gray, tephra-laden columns of water being ejected 20-30 m above the ocean’s surface. A satellite image on 4 August showed a small rounded gray zone at the water surface and a plume of discolored water drifting NE.

Sources: Japan Meteorological Agency (JMA); Sentinel Hub


27 July-2 August 2022 Citation IconCite this Report

Satellite images of Ioto (Iwo-jima) acquired on 15 July showed a darker area in the water along the SE coast, possibly above or near the 2001 vent, and a plume of discolored water drifting NE. Video taken on or around 25 July showed a white plume rising from the same area. Satellite images during 30-31 July showed small rounded gray zones at the water surface.

Sources: Sentinel Hub; Planet Labs


12 September-18 September 2018 Citation IconCite this Report

During an overflight of Ioto (Iwo-jima) on 12 September the Japan Maritime Self Defense Force observed seawater jetting 5-10 m above the sea surface on the S coast, suggestive of a submarine eruption.

Source: Japan Meteorological Agency (JMA)


25 April-1 May 2012 Citation IconCite this Report

According to a JMA report on 2 May, an eruption at Ioto (Iwo-jima) caused water discoloration to the NE. A new fumarole was also confirmed.

Source: Japan Meteorological Agency (JMA)


16 June-22 June 2010 Citation IconCite this Report

Based on a pilot observation, the Tokyo VAAC reported that an ash plume from Ioto (Iwo-jima) drifted more than 35 km N.

Source: Tokyo Volcanic Ash Advisory Center (VAAC)


17 October-23 October 2001 Citation IconCite this Report

On the morning of 19 October a small phreatic eruption was observed at Idogahama, a beach on the NW coast of Iwo-jima. 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. A similar plume was observed for 10 minutes starting at 0806. Observations during 1602-1715 revealed the crater that formed during the eruption was 10 m long and 2-15 m deep. Water inside the crater was dark colored, contained debris, and gushed approximately every 10 minutes. In addition, a steam plume rose up to 600 m above the surface.

Sources: Japan Meteorological Agency (JMA); Volcano Research Center-Earthquake Research Institute (University of Tokyo)


3 October-9 October 2001 Citation IconCite this Report

No volcanic activity was observed at Iwo-jima after 22 September, but discolored seawater was occasionally visible along the SE coast until at least 10 October. The area of discolored water was smaller than when the submarine eruption began on 21 September. During 20 to about 28 September many earthquakes and tremor were detected. Floating pumice collected along Iwo-jima's coast after the eruption is being analyzed to determine if the eruption was magmatic or hydrothermal.

Sources: National Research Institute for Earth Science and Disaster Prevention; Japan Meteorological Agency (JMA)


19 September-25 September 2001 Citation IconCite this Report

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 1,300 km S of Tokyo. The eruption was preceded by isolated and continuous tremor beginning on the evening of 20 September. Visible evidence of the eruption consisted of seawater gushing several meters above sea level near the island's coast and 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 1200-1500. At about 1300 water gushed several ten's of meters above sea level and steam rose to 100-300 m above the sea. JMA personnel observed seawater rising intermittently during 1515-1715 at two points 50 m apart and 150-200 m from the island's SE coast. The temperatures at these points were 33-34 ºC and 50 ºC, while the surrounding water was at 27 ºC. By 1500 ten earthquakes were recorded per hour. During 1600-1700 three eruption sites were visible; at one a pyroclastic cone was slightly above the sea surface. JMA reported that by the next day volcanic and seismic activity returned to usual levels, with zero to four earthquakes occurring per hour and no tremor events.

Sources: Japan Meteorological Agency (JMA); Volcano Research Center-Earthquake Research Institute (University of Tokyo); Reuters


Bulletin Reports - Index

Reports are organized chronologically and indexed below by Month/Year (Publication Volume:Number), and include a one-line summary. Click on the index link or scroll down to read the reports.

01/1977 (NSEB 02:01) Possible submarine eruption 26 km NW of the island in January 1974

09/1982 (SEAN 07:09) Small phreatic explosions on NW flank

04/1983 (SEAN 08:04) Earthquake swarm, two weak steam explosions

09/2001 (BGVN 26:09) In September, a submarine eruption; in October, a phreatic eruption pierces beach

07/2012 (BGVN 37:07) Mud ejections and small phreatic eruptions during early 2012




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


January 1977 (NSEB 02:01) Citation IconCite 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) Citation IconCite 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) Citation IconCite 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) Citation IconCite 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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) Citation IconCite 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 (see Caption) 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 (see Caption) 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).

This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.

Eruptive History

There is data available for 20 confirmed Holocene eruptive periods.

2022 Jul 11 - 2022 Aug 6 ± 2 days Confirmed Eruption  

Episode 1 | Eruption Episode
2022 Jul 11 - 2022 Aug 6 ± 2 days Evidence from Observations: Reported

2012 Feb 10 - 2012 May 2 Confirmed Eruption Max VEI: 1

Episode 1 | Eruption Episode Asodai
2012 Feb 10 - 2012 Apr 6 Evidence from Observations: Reported

List of 8 Events for Episode 1 at Asodai

Start Date End Date Event Type Event Remarks
2012 Feb 1
(in or after)
2012 Feb 14
(in or before)
Phreatic activity 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.
2012 Feb 10    - - - - Mud JMSDF reported a mud ejection at an old crater along the Asodai fault.
2012 Mar 7 2012 Mar 9 Phreatic activity 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.
2012 Mar 7    - - - - Ash Plume 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.
2012 Mar 7 2012 Mar 9 Mud A mud ejection occurred in the same area as previously, and mud was ejected up to 60 m WNW. During a field survey from 7 to 9 March 2012, additional mud ejections were noted from the same area as the previous events on the island's W side.
2012 Mar 7    - - - - VEI (Explosivity Index) VEI 1
2012 Apr 5 2012 Apr 6 Phreatic activity Volcanic tremor and intermittent earthquakes were recorded, and two apparently very small phreatic eruptions were reported.
2012 Apr 5 2012 Apr 6 Seismicity (volcanic) Volcanic tremor and intermittent earthquakes were recorded, and two apparently very small phreatic eruptions were reported.
Episode 2 | Eruption Episode Submarine NE flank
2012 Apr 29 - 2012 May 2 Evidence from Observations: Reported

List of 2 Events for Episode 2 at Submarine NE flank

Start Date End Date Event Type Event Remarks
2012 Apr 29 2012 Apr 30 Phreatic activity The ocean NE of the island was discolored, suggesting an offshore underwater eruption.
2012 Apr 29    - - - - VEI (Explosivity Index) VEI 1

[ 2010 Jun 19 - 2010 Jun 19 ] Uncertain Eruption

[ 2004 Jun 6 - 2004 Jun 8 ] Uncertain Eruption

2001 Sep 21 - 2001 Oct 23 Confirmed Eruption Max VEI: 1

Episode 1 | Eruption Episode Off SE coast and Idogahama (NW coast)
2001 Sep 21 - 2001 Oct 23 Evidence from Observations: Reported

List of 8 Events for Episode 1 at Off SE coast and Idogahama (NW coast)

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Phreatic activity
   - - - -    - - - - Island ephemeral
   - - - -    - - - - Pumice
   - - - -    - - - - Earthquakes (undefined)
   - - - -    - - - - Volcanic tremor Before eruption.
   - - - -    - - - - Volcanic tremor
2001 Sep 21    - - - - VEI (Explosivity Index)

1999 Sep 10 - 1999 Sep 10 Confirmed Eruption Max VEI: 1

Episode 1 | Eruption Episode Asodai area
1999 Sep 10 - 1999 Sep 10 Evidence from Observations: Reported

List of 2 Events for Episode 1 at Asodai area

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Phreatic activity weak or small
1999 Sep 10    - - - - VEI (Explosivity Index)

1994 Aug 22 - 1994 Aug 22 Confirmed Eruption Max VEI: 1

Episode 1 | Eruption Episode NE side
1994 Aug 22 - 1994 Aug 22 Evidence from Observations: Reported

List of 2 Events for Episode 1 at NE side

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Phreatic activity weak or small
1994 Aug 22    - - - - VEI (Explosivity Index)

[ 1993 Oct 27 (?) - 1993 Nov 16 (?) ] Uncertain Eruption

1982 Nov 28 - 1982 Dec 16 (?) ± 15 days Confirmed Eruption Max VEI: 1

Episode 1 | Eruption Episode West side (Asodai)
1982 Nov 28 - 1982 Dec 16 (?) ± 15 days Evidence from Observations: Reported

List of 4 Events for Episode 1 at West side (Asodai)

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Phreatic activity weak or small
   - - - -    - - - - Earthquakes (undefined) Before.
   - - - -    - - - - Earthquakes (undefined)
1982 Nov 28    - - - - VEI (Explosivity Index)

1982 Mar 9 - 1982 Mar 10 Confirmed Eruption Max VEI: 1

Episode 1 | Eruption Episode NW side (Idogahama beach)
1982 Mar 9 - 1982 Mar 10 Evidence from Observations: Reported

List of 3 Events for Episode 1 at NW side (Idogahama beach)

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Phreatic activity weak or small
   - - - -    - - - - Blocks
1982 Mar 9    - - - - VEI (Explosivity Index)

1980 Mar 13 - 1980 Mar 13 Confirmed Eruption Max VEI: 1

Episode 1 | Eruption Episode Kitanohara
1980 Mar 13 - 1980 Mar 13 Evidence from Observations: Reported

List of 2 Events for Episode 1 at Kitanohara

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Phreatic activity weak or small
1980 Mar 13    - - - - VEI (Explosivity Index)

1978 Dec 11 - 1978 Dec 11 Confirmed Eruption Max VEI: 1

Episode 1 | Eruption Episode West side (Asodai)
1978 Dec 11 - 1978 Dec 11 Evidence from Observations: Reported

List of 3 Events for Episode 1 at West side (Asodai)

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Phreatic activity weak or small
   - - - -    - - - - Earthquakes (undefined)
1978 Dec 11    - - - - VEI (Explosivity Index)

1976 Jan 16 ± 15 days Confirmed Eruption Max VEI: 1

Episode 1 | Eruption Episode West side (Asodai)
1976 Jan 16 ± 15 days - Unknown Evidence from Observations: Reported

List of 2 Events for Episode 1 at West side (Asodai)

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Phreatic activity weak or small
1976 Jan    - - - - VEI (Explosivity Index)

[ 1974 Jan 16 ± 15 days - 1974 Feb 2 ] Uncertain Eruption

1969 Dec 1 ± 30 days - 1969 Dec 1 ± 30 days Confirmed Eruption Max VEI: 1

Episode 1 | Eruption Episode
1969 Dec 1 ± 30 days - 1969 Dec 1 ± 30 days Evidence from Observations: Reported

List of 2 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Phreatic activity weak or small
1969 Dec 1 ± 30 days    - - - - VEI (Explosivity Index)

1969 Jan 12 (?) - 1969 Jan 21 (?) Confirmed Eruption Max VEI: 1

Episode 1 | Eruption Episode West side (Asodai)
1969 Jan 12 (?) - 1969 Jan 21 (?) Evidence from Observations: Reported

List of 2 Events for Episode 1 at West side (Asodai)

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Phreatic activity
1969 Jan 12
(?)
   - - - - VEI (Explosivity Index)

1967 Dec 23 - 1967 Dec 23 Confirmed Eruption Max VEI: 1

Episode 1 | Eruption Episode West side (Asodai)
1967 Dec 23 - 1967 Dec 23 Evidence from Observations: Reported

List of 2 Events for Episode 1 at West side (Asodai)

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Phreatic activity
1967 Dec 23    - - - - VEI (Explosivity Index)

1957 Mar 28 - 1957 Mar 28 Confirmed Eruption Max VEI: 1

Episode 1 | Eruption Episode Chidoriga-hara
1957 Mar 28 - 1957 Mar 28 Evidence from Observations: Reported

List of 3 Events for Episode 1 at Chidoriga-hara

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Phreatic activity
   - - - -    - - - - Ash
1957 Mar 28    - - - - VEI (Explosivity Index)

1944 Dec Confirmed Eruption Max VEI: 1

Episode 1 | Eruption Episode North and west sides near the coast
1944 Dec - Unknown Evidence from Observations: Reported

List of 2 Events for Episode 1 at North and west sides near the coast

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Phreatic activity
1944 Dec    - - - - VEI (Explosivity Index)

1935 Confirmed Eruption Max VEI: 1

Episode 1 | Eruption Episode SW side at Chidoriga-hara
1935 - Unknown Evidence from Observations: Reported

List of 2 Events for Episode 1 at SW side at Chidoriga-hara

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Phreatic activity
1935    - - - - VEI (Explosivity Index)

1930 (?) Confirmed Eruption Max VEI: 1

Episode 1 | Eruption Episode NW side near the coast
1930 (?) - Unknown Evidence from Observations: Reported

List of 2 Events for Episode 1 at NW side near the coast

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Phreatic activity
1930
(?)
   - - - - VEI (Explosivity Index)

1922 Jul Confirmed Eruption Max VEI: 1

Episode 1 | Eruption Episode West side (Asodai)
1922 Jul - Unknown Evidence from Observations: Reported

List of 2 Events for Episode 1 at West side (Asodai)

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Phreatic activity
1922 Jul    - - - - VEI (Explosivity Index)

1889 Dec 31 ± 365 days Confirmed Eruption Max VEI: 1

Episode 1 | Eruption Episode Chidoriga-ana
1889 Dec 31 ± 365 days - Unknown Evidence from Observations: Reported

List of 3 Events for Episode 1 at Chidoriga-ana

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Phreatic activity
   - - - -    - - - - Crater Summit.
1889 Dec 31 ± 365 days    - - - - VEI (Explosivity Index)

0850 BCE ± 50 years Confirmed Eruption  

Episode 1 | Eruption Episode Motoyama
0850 BCE ± 50 years - Unknown Evidence from Isotopic: 14C (calibrated)

List of 3 Events for Episode 1 at Motoyama

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Lava flow
   - - - -    - - - - Pumice
Deformation History

There is data available for 6 deformation periods. Expand each entry for additional details.


Deformation during 1993 Jun 28 - 1995 Jul 16 [Subsidence; Observed by InSAR]

Start Date: 1993 Jun 28 Stop Date: 1995 Jul 16 Direction: Subsidence Method: InSAR
Magnitude: 62.000 cm Spatial Extent: Unknown Latitude: Unknown Longitude: Unknown

Reference List: Ohkura et al. 1998.

Full References:

Ohkura, H., 1998. Application of SAR data to monitoring earth surface changes and displacement. Advances in Space Research, 21(3), 485-492.

Deformation during 1977 - 1995 [Subsidence; Observed by Leveling, Trilateration]

Start Date: 1977 Stop Date: 1995 Direction: Subsidence Method: Leveling, Trilateration
Magnitude: 54.000 cm Spatial Extent: Unknown Latitude: Unknown Longitude: Unknown

Remarks: Concentric subsidence around Motoyama at the center of the Iwo-jima caldera is surrounded by a region of uplift.


Reference List: Ukawa et al. 2005.

Full References:

Ukawa, M., E. Fujita, H. Ueda, T. Kumagai, H. Nakajima, and H. Morita, 2005. Long-term geodetic measurements of large scale deformation at Iwo-jima caldera, Japan. J. Volcanol. Geotherm. Res., 150: 98-118.

Deformation during 1977 - 1995 [Uplift; Observed by Leveling, Trilateration]

Start Date: 1977 Stop Date: 1995 Direction: Uplift Method: Leveling, Trilateration
Magnitude: 300.000 cm Spatial Extent: Unknown Latitude: Unknown Longitude: Unknown

Remarks: Concentric subsidence around Motoyama at the center of the Iwo-jima caldera is surrounded by a region of uplift.


Reference List: Ukawa et al. 2005.

Full References:

Ukawa, M., E. Fujita, H. Ueda, T. Kumagai, H. Nakajima, and H. Morita, 2005. Long-term geodetic measurements of large scale deformation at Iwo-jima caldera, Japan. J. Volcanol. Geotherm. Res., 150: 98-118.

Deformation during 1968 - 1979 [Uplift; Observed by InSAR]

Start Date: 1968 Stop Date: 1979 Direction: Uplift Method: InSAR
Magnitude: 305.000 cm Spatial Extent: Unknown Latitude: Unknown Longitude: Unknown

Reference List: Ukawa et al. 2005.

Full References:

Ukawa, M., E. Fujita, H. Ueda, T. Kumagai, H. Nakajima, and H. Morita, 2005. Long-term geodetic measurements of large scale deformation at Iwo-jima caldera, Japan. J. Volcanol. Geotherm. Res., 150: 98-118.

Deformation during 1952 - 1968 [Uplift; Observed by InSAR]

Start Date: 1952 Stop Date: 1968 Direction: Uplift Method: InSAR
Magnitude: 570.000 cm Spatial Extent: Unknown Latitude: Unknown Longitude: Unknown

Reference List: Ukawa et al. 2005.

Full References:

Ukawa, M., E. Fujita, H. Ueda, T. Kumagai, H. Nakajima, and H. Morita, 2005. Long-term geodetic measurements of large scale deformation at Iwo-jima caldera, Japan. J. Volcanol. Geotherm. Res., 150: 98-118.

Deformation during 1911 - 1979 [Uplift; Observed by InSAR]

Start Date: 1911 Stop Date: 1979 Direction: Uplift Method: InSAR
Magnitude: 400.000 cm Spatial Extent: Unknown Latitude: Unknown Longitude: Unknown

Reference List: Ukawa et al. 2005.

Full References:

Ukawa, M., E. Fujita, H. Ueda, T. Kumagai, H. Nakajima, and H. Morita, 2005. Long-term geodetic measurements of large scale deformation at Iwo-jima caldera, Japan. J. Volcanol. Geotherm. Res., 150: 98-118.

Emission History

There is no Emissions History data available for Ioto.

GVP Map Holdings

The maps shown below have been scanned from the GVP map archives and include the volcano on this page. Clicking on the small images will load the full 300 dpi map. Very small-scale maps (such as world maps) are not included. The maps database originated over 30 years ago, but was only recently updated and connected to our main database. We welcome users to tell us if they see incorrect information or other problems with the maps; please use the Contact GVP link at the bottom of the page to send us email.


Title: Geological Map of Japan
Publisher: Geological Survey of Japan
Country: Japan
Year: 1978
Map Type: Geology
Scale: 1:1,000,000
Map of Geological Map of Japan

Title: Ogasawara-Gunto
Publisher: US Army Map Service
Country: Japan
Year: 1944
Series: AMS
Map Type: Topographic
Scale: 1:1,000,000
Map of Ogasawara-Gunto
Smithsonian Sample Collections Database

There are no samples for Ioto in the Smithsonian's NMNH Department of Mineral Sciences Rock and Ore collection.

External Sites