Iwatesan

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  • Last Known Eruption
  • 39.853°N
  • 141.001°E

  • 2038 m
    6685 ft

  • 283240
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Most Recent Bulletin Report: February 2000 (BGVN 25:02)


Tremor event and earthquake swarm on 12 November 1999

At 1800 on 18 October 1999, the National Coordination Committee for Prediction of Volcanic Eruptions reported that the volcano's fumarolic area had expanded and the amount of steam had increased in the western part of Iwate volcano. New fumaroles have been observed since May on the N slopes of Mts. Ubakura-yama and Kurokura-yama and in the western stream of Ojigokudani (inside the erosion caldera). This fumarolic activity has intermittently increased since July, and ground temperatures between Mts. Kurokura-yama and Ubakura-yama also increased with time. Analyses of fumarolic gas collected between Ojigokudani and Mt. Ubakura-yama in August and October revealed a magmatic component. Although GPS measurements showed the end of the elongation trend observed since July, relatively large volcanic earthquakes occurred during May and June. Deep-seated (~30 km depth) low-frequency earthquakes, relatively deep-seated (6-13 km depth) low-frequency earthquakes, and shallow high-frequency earthquakes occurred under the eastern cone of Iwate. However, the overall level of seismicity has decreased compared to 1998 (figure 5).

Figure 5. Daily numbers of earthquakes at Iwate (recorded at the Matsukawa station) during 1 January 1998-13 November 1999. Courtesy of JMA.

On the evening of 12 November JMA issued a Volcano Advisory on Iwate after a 4-minute volcanic tremor (M 2.1) saturated local instruments starting at 2054. The event hypocenter was located 2-3 km below the Ubakura-yama and Kurokura-yama areas of western Iwate (figure 6). An earthquake swarm continued for 2 hours after the tremor event at a rate of 16-20 events/hour. Inspection from the air the following day did not show any major change in fumarolic activity or any deposition of new volcanic ash.

Figure 6. Hypocenters of earthquakes under the western section of Iwate during 11-12 November 1999. Courtesy of JMA.

On the evening of 16 November, the extended National Coordination Committee for Prediction of Volcanic Eruptions met in the city of Morioka, Iwate Prefecture, to review the events that occurred on the 12th. They noted that the tremor was similar in shape, amplitude, and duration to one (M 2.4) that occurred on 10 July 1999; hence it was considered likely that the two events occurred in the same place. Changes detected in tilt- and strain-meters located on the flank during the tremor were probably caused by subsurface ground faulting or fluid movement. After the tremor, however, no subsequent changes were observed. Neither the GPS-based, N-S traverse distance across the volcano nor the fumarole temperatures in the Ubakura-yama to Kurokura-yama region changed before or after the event. Fumarolic activity in western Iwate had increased since May as had the number of shallow earthquakes in the Ojigokudani area (erosion caldera). The tremor event on 12 November suggested a continuing possibility of a phreatic explosions in western Iwate.

Information Contacts: Kazuo Sekine, Sendai District Meteorological Observatory, Japan Meteorological Agency, 1-3-15 Gorin, Miyagino-ku, Sendai 983, Japan (Email: kazuo.sekine@met.kishou.go.jp); Hiroyuki Hamaguchi, Faculty of Science, Tohoku University, Sendai 980-8578 Japan (Email: hama@aob.geophys.tohoku.ac.jp, URL: http://www.sci.tohoku.ac.jp/); Setsuya Nakada, Volcano Research Center, ERI, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113, Japan (Email: nakada@eri.u-tokyo.ac.jp, URL: http://hakone.eri.u-tokyo.ac.jp/ vrc/VRC.html); Jun-ichi Hirabayashi, Kusatsu-Shirane Volcano Observatory, Tokyo Institute of Technology, Kusatsu, Agatsuma-gun, Gunma 377-17 Japan (Email: jhirabay@ksvo.titech.ac.jp, URL: http://131.112.25.6/).

The Global Volcanism Program has no Weekly Reports available for Iwatesan.

Index of Bulletin Reports


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.

09/1995 (BGVN 20:09) Tremor and low-frequency earthquakes

10/1995 (BGVN 20:10) Short tremor episode

02/1996 (BGVN 21:02) Small-amplitude tremor

03/1996 (BGVN 21:03) Volcanic tremor registered again on 4 March

05/1996 (BGVN 21:05) Small-amplitude volcanic tremor

07/1996 (BGVN 21:07) Volcanic tremor

08/1996 (BGVN 21:08) A M 1.9 earthquake at 3 km depth

11/1996 (BGVN 21:11) Microearthquakes and tremor

04/1998 (BGVN 23:04) Rising earthquake counts during January-May

07/1998 (BGVN 23:07) Monthly seismicity increases; volcanic history

09/1998 (BGVN 23:09) Nearby M 6.2 earthquake on 3 September, but volcano still slumbering

10/1998 (BGVN 23:10) Seismic crisis ends on 3 November

05/1999 (BGVN 24:05) A M 3.6 tectonic earthquake in September preceded ongoing seismic swarms

02/2000 (BGVN 25:02) Tremor event and earthquake swarm on 12 November 1999




Bulletin Reports

All information contained in these reports is preliminary and subject to change.


09/1995 (BGVN 20:09) Tremor and low-frequency earthquakes

Between 0019 and 0105 on 15 September, Tohoku University seismometers near Iwate volcano registered intermittent small-amplitude volcanic tremors and low-frequency earthquakes. Four low-frequency earthquakes had epicenters 2 km E of the summit at ~8 km depths.

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.
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10/1995 (BGVN 20:10) Short tremor episode

Tohoku University seismometers near Iwate volcano continued to register tremor (BGVN 20:09). Beginning at 0009 on 20th October, the tremor lasted ~25 minutes.

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.
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02/1996 (BGVN 21:02) Small-amplitude tremor

On 13, 24, and 29 January small-amplitude volcanic tremors occurred. Such tremors were previously observed on 20 October 1995.

Information Contacts: Japan Meteorological Agency (JMA), Volcanological Division, Seismological and Volcanological Department, 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan.
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03/1996 (BGVN 21:03) Volcanic tremor registered again on 4 March

Small-amplitude volcanic tremor was detected on 4 March. Tremor was last registered on three days in January 1996 (BGVN 21:02) and once in October 1995.

Information Contacts: Japan Meteorological Agency (JMA), Volcanological Division, Seismological and Volcanological Department, 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan.
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05/1996 (BGVN 21:05) Small-amplitude volcanic tremor

Small-amplitude volcanic tremor was detected on 12 May. Tremor was last reported on 4 March (BGVN 21:03), and previously in January and October 1995.

Information Contacts: Japan Meteorological Agency (JMA), Volcanological Division, Seismological and Volcanological Department, 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan.
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07/1996 (BGVN 21:07) Volcanic tremor

On 10, 11, 12, and 17 June, small-amplitude volcanic tremors were detected. According to reports from the Observation Center for Prediction of Earthquakes and Volcanic Eruptions, Tohoku University, there were also shallow volcanic microearthquakes beneath Iwate on 7 and 27 June, and on 2 and 6 July. Tremor was previously reported on 4 March and 12 May 1996 (BGVN 21:03 and 21:05), and in September and October 1995 (BGVN 20:09 and 20:10).

Information Contacts: Volcanological Division, Japan Meteorological Agency, 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan
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08/1996 (BGVN 21:08) A M 1.9 earthquake at 3 km depth

On 25 August a M 1.9 earthquake was recorded 3 km beneath the top of Iwate. This was considered a remarkable event in this region.

Information Contacts: Volcanological Division, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan.
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11/1996 (BGVN 21:11) Microearthquakes and tremor

On 11 September, 2 October, and 24 and 25 November, shallow volcanic microearthquakes were recorded below Iwate. On 12 September and 11 October small-amplitude volcanic tremors were observed.

Information Contacts: Volcanological Division, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan.
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04/1998 (BGVN 23:04) Rising earthquake counts during January-May

According to the Japan Meteorological Agency (JMA), high seismicity (figure 1) and strong deformation began at Iwate in March and remained high in early May. In the first week of May, 30-80 volcanic earthquakes registered per day at the Matsukawa observation site (5 km NW of the summit). Rising monthly earthquake totals during January-May are listed in table 1. On 29 April, 285 earthquakes occurred; the strongest recorded was M 2.7. Tiltmeter and volumetric strain meters disclosed large changes at around 1500. On 7 May, a M 3.3 earthquake occurred at 0300.

Figure 1. Map view of volcanic earthquake locations at Iwate during 27 March-29 April (top) and a W-E cross-section showing earthquake depths (bottom). Tohoku University's instrument observation sites (crosses) are projected onto the line of cross section, explaining why some appear to lie in the subsurface. Courtesy of Tohoku University.

Table 1. Monthly earthquake counts at Iwate during January-May 1998. Courtesy of JMA.

    1998                       Earthquakes
    January                        22
    February                       68
    March                         424
    April                         764
    May (as of 1600 on 7 May)     364

A GPS survey revealed N-S extension of the volcanic cone during February-May. The 29-km line between two observation sites N and S of the summit began to extend in February; the rate of movement accelerated in late April. By early May, the extension totaled 2 cm. A 1 May air survey revealed no anomalies on or around the summit area.

Information Contacts: Volcanological Division, Seismological and Volcanological Department, 1-3-4 Ote-machi, Japan Meteorological Agency (JMA), Chiyoda-ku, Tokyo 100, Japan; Volcano Research Center, Earthquake Research Institute (ERI), University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113, Japan (Email: nakada@eri.u-tokyo.ac.jp); Noritake Nishide, Sendai District Meteorological Observatory, Japan Meteorological Agency, 1-3-15 Gorin, Miyagino-ku, Sendai 983, Japan (Email: nnishide@redc-sn.eqvol.kishou.go.jp); Hiroyuki Hamaguchi, Faculty of Science, Tohuku University, Sendai 980-77, Japan (Email: hama@aob.geophys.tohoku.ac.jp);Takashi Tada, Geographical Survey Institute, Tsukuba-shi, Ibaraki, Japan (Email: t-tada@gsi-mc.go.jp).
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07/1998 (BGVN 23:07) Monthly seismicity increases; volcanic history

A pattern of high seismicity but low deformation that began at Iwate in March (BGVN 23:04) continued through June and July. The following also discusses Iwate's history (as reported to JMA and Tohoku University), and details of recent hazards.

Seismicity. According to reports issued by the Japan Meteorological Agency (JMA), monthly totals of volcanic earthquake events recorded at the Matsukawa observation site of Tohoku University increased progressively: 424 in March, 764 in April, 1,283 in May, and 1,806 in June. Seismicity during 1-17 July totalled 1,116 events (figure 2).

Figure 2. Numbers of earthquakes and tremors at Iwate recorded at the Matsukawa observation site at Tohoku University, 1-17 July 1998. Data courtesy of JMA.

Low-frequency earthquakes occurred at 2124 on 23 June, and 0915 and 1037 on 24 June. A few minutes of volcanic tremor was observed at 0519 and 0701 on 24 June, and at 0754 on 25 June. Earthquake swarms below Nishi-Iwate continued to increase. (The place names Nishi- and Higashi-Iwate refer to West- and East-Iwate, respectively.) Further tremor took place at 1005 and 1642 on 27 June, and 1741 and 1759 on 28 June. Sixteen low-frequency earthquakes took place between the latter two events. Researchers at Tohoku University located these earthquakes at ~2 km SE of the summit of Higashi-Iwate at a depth of 8 km below sea level. This was close to where GPS surveys found a pressure source for crustal deformation. A swarm of low-frequency earthquake and tremor events occurred here in 1995, and it is just S of the craters of the 1732 (Yakebashiri) lava flow. Epicenters of high-frequency earthquakes were also located beneath Nishi-Iwate.

On the morning of 10 July, felt earthquakes occurred W of Iwate Volcano. Four minutes of large-amplitude tremor began at 0829 followed by a volcanic earthquake of M 2.5 at 0831. No surface phenomena were reported. Epicenters for seven earthquakes that morning were located at 3-5 km depth about 5 km west of Nishi-Iwate.

Epicenters of volcanic earthquake swarms under Nishi-Iwate migrated gradually to the W during May-June. New events occurred to the W of the swarms in July. Recent GPS measurements indicated that the source of deformation was located W of Iwate, in an area where no activity had occurred during the past 30,000 years. Although the degree of movement at stations remote from the volcano had become smaller since May, movement at stations closer to the volcano continued. Researchers believe that the source of deformation approached the surface, but they did not determine its depth.

Deformation surveys. Strain and tiltmeters at observation sites recorded little change since March. According to a field survey during 16-18 June, a fumarolic area in Nishi-Iwate seems to have been more active recently, since the fumarole temperature had increased. GPS surveys showed a steady and continuous lengthening between S and N sites of the volcano: a baseline of 9 km underwent a 5-cm extension in the last 5 months. Based on these results, volcanologists suspected a W-E dike intrusion at around 10 km below the summit of Higashi-Iwate, as opposed to just below Nishi-Iwate as indicated by earthquake swarms.

A geodetic measurement team from five Japanese national universities started a leveling survey at the E and S bases of Iwate Volcano on 17 July. The survey lines cover 19 km N-S and 15 km E-W.

History. Based on his recent field survey, Nobuo Doi, a geologist with Geothermal Engineering Co. Ltd., summarized Iwate's eruptive history. He concluded that Iwate began ~700,000 years ago. After the formation of a large cone (Nishi-Iwate), the eruption center migrated eastwards to Higashi-Iwate. Iwate collapsed to form debris avalanches seven times in the past 230,000 years; the most recent collapse took place sometime during the interval 915-1686 AD.

During a large collapse ~6,000 years ago, a mass of debris rushed NE but subsequent topographic constraints redirected debris SSE. The debris followed the Kitakami River reaching the present site of Morioka City (population 235,000). The episode left a large scar open to the NE on Higashi-Iwate's summit.

The present peak of Higashi-Iwate grew within this scar but it left part of the scar visible on its W side. During the last 6,000 years, magmatic eruptions occurred frequently; scoria eruptions have occurred more than 11 times. Lavas and pyroclastics younger than 6,000 years occur in the NE sector of Higashi-Iwate.

The 1686-87 AD eruption started with a pyroclastic surge; this was followed by scoria emission, a mudflow, a second pyroclastic surge, and it ended with a phreatic phase. In 1732, basaltic andesite lava flowed 2.5 km. Small explosions took place during 1934-35.

At Nishi-Iwate more than four phreatic eruptions have occurred in the past 7,500 years. The latest eruption here was phreatic and took place at O-Jigokudani ("large valley of hell") in 1919; an associated mudflow descended NNW.

Hazards. Authorities in two towns and villages near Iwate closed the mountain to climbers on 26 June because of the likelihood of phreatic explosions at Nishi-Iwate.

According to a local newspaper (Iwate Nippo), a new hazard map was expected to be ready for distribution on 22 July, incorporating aspects of volcanology, disaster-protection, and Sabo engineering. The scenario assumes a phreatic eruption on the W side, perhaps as large as one at Nishi-Iwate that occurred 3,200 years ago. The presumed disaster areas would be subjected to both ashfalls and lahars. A theoretical 10-cm-thick ash deposit would occur in resort areas N and S of the volcano extending to 5 km from the possible eruption site, but the researchers postulated a lack of serious damage to buildings.

Information Contacts: Nishide Noritake, Volcanological Division, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan (Email: noritake.nishide@met.kishou.go.jp, URL: http://www.kishou.go.jp); Volcano Research Center, Earthquake Research Institute (ERI), University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113, Japan (Email: nakada@eri.u-tokyo.ac.jp); Nobuo Doi, Geothermal Engineering Co. Ltd., Japan (Email: doi@geothermal.co.jp).
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09/1998 (BGVN 23:09) Nearby M 6.2 earthquake on 3 September, but volcano still slumbering

A strong earthquake occurred 10 km SW of the summit of Iwate volcano at 1658 on 3 September. The Richter magnitude was 6.1 and the depth ~7 km. The mechanism was E-W compression on a reverse fault. A N-S-trending surface rupture appeared, despite the event's non-extreme magnitude. The aftershock area resulting from the earthquake differed from typical earthquakes on Iwate and the relationship between the earthquake and the volcano, if any, is not understood. This was the largest earthquake since August 1996 when a M 5.9 tremor struck.

A 3 September Reuters news article mentioned that a powerful earthquake took place, centered in the ski resort area of Shizukuishi, a mountainous region near Iwate volcano. The report claimed the epicenter was 5 km underground and police said that the event slightly injured at least nine people.

Information Contacts: Yukio Hayakawa, Faculty of Education, Gunma University, Aramaki, Maebashi 371, Japan (Email: hayakawa@edu.gunma-u.ac.jp); Reuters Limited, 1700 Broadway, New York, NY 10019 USA (URL: http://www.reuters.com/).
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10/1998 (BGVN 23:10) Seismic crisis ends on 3 November

Subsequent to the 3 September earthquake (BGVN 23:09), seismicity was low. Except for a few days, the number of tremors during October was <10/day, about the same level as in February-March 1998. The last tremor was observed on 3 November. This implies that the volcanic seismicity crisis (BGVN 23:09) has ended.

Information Contacts: Yukio Hayakawa, Faculty of Education, Gunma University, Aramaki, Maebashi 371, Japan (Email: hayakawa@edu.gunma-u.ac.jp).
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05/1999 (BGVN 24:05) A M 3.6 tectonic earthquake in September preceded ongoing seismic swarms

A large tectonic earthquake near Iwate on 3 September 1998 (BGVN 23:09) was followed by elevated rates of seismicity and ground deformation that declined in subsequent months (figure 3). In late 1998 volcanic tremor was recorded up to ten times per month and earthquakes around the Moho discontinuity occurred >10 times per month.

Figure 3. Daily numbers of earthquakes at Iwate (recorded at the Matsukawa station) during 1 January 1998-14 May 1999. Courtesy JMA.

At 1909 on 22 May 1999, a M 3.6 earthquake occurred around the W edge of Nishi-Iwate. The earthquake was followed 8 minutes later by another of M 2.2. These volcanic earthquakes were the largest of a swarm centered at 3-6 km depth. No episodes of tremor were observed and no surface manifestations were detected by video monitoring or during a helicopter flight.

The National Coordination Committee for Prediction of Volcanic Eruption said that the largest earthquakes in the swarm occurred in the W region of the volcano, where shallow (5-10 km in depth) low-frequency volcanic earthquakes had been increasing (figure 4). They also observed that deep (~30 km in depth) low-frequency earthquakes had been occurring regularly with some minor increases and decreases in frequency. GPS observation showed relatively low but steady ground-deformation in the western region of the volcano. Gas measurement showed an increase in below-ground temperature and also indicated the gas chemistry had become more magmatic since September 1998. Their conclusion was that Iwate was showing a slight increase in activity.

Figure 4. Hypocenters of earthquakes around Iwate during 1 April-13 May 1999. Courtesy JMA.

Information Contacts: Hiroyuki Hamaguchi, Faculty of Science, Tohoku University, Sendai 980, Japan (Email: hama@aob.geophys.tohoku.ac.jp); Kazuo Sekine, Sendai District Meteorological Observatory, Japan Meteorological Agency, 1-3-15 Gorin, Miyagino-ku, Sendai 983, Japan (Email: kazuo.sekine@met.kishou.go.jp); Volcano Research Center, Earthquake Research Institute (ERI), University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113, Japan (Email: nakada@eri.u-tokyo.ac.jp, URL: http://hakone.eri.u-tokyo.ac.jp/vrc/VRC.html).
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02/2000 (BGVN 25:02) Tremor event and earthquake swarm on 12 November 1999

At 1800 on 18 October 1999, the National Coordination Committee for Prediction of Volcanic Eruptions reported that the volcano's fumarolic area had expanded and the amount of steam had increased in the western part of Iwate volcano. New fumaroles have been observed since May on the N slopes of Mts. Ubakura-yama and Kurokura-yama and in the western stream of Ojigokudani (inside the erosion caldera). This fumarolic activity has intermittently increased since July, and ground temperatures between Mts. Kurokura-yama and Ubakura-yama also increased with time. Analyses of fumarolic gas collected between Ojigokudani and Mt. Ubakura-yama in August and October revealed a magmatic component. Although GPS measurements showed the end of the elongation trend observed since July, relatively large volcanic earthquakes occurred during May and June. Deep-seated (~30 km depth) low-frequency earthquakes, relatively deep-seated (6-13 km depth) low-frequency earthquakes, and shallow high-frequency earthquakes occurred under the eastern cone of Iwate. However, the overall level of seismicity has decreased compared to 1998 (figure 5).

Figure 5. Daily numbers of earthquakes at Iwate (recorded at the Matsukawa station) during 1 January 1998-13 November 1999. Courtesy of JMA.

On the evening of 12 November JMA issued a Volcano Advisory on Iwate after a 4-minute volcanic tremor (M 2.1) saturated local instruments starting at 2054. The event hypocenter was located 2-3 km below the Ubakura-yama and Kurokura-yama areas of western Iwate (figure 6). An earthquake swarm continued for 2 hours after the tremor event at a rate of 16-20 events/hour. Inspection from the air the following day did not show any major change in fumarolic activity or any deposition of new volcanic ash.

Figure 6. Hypocenters of earthquakes under the western section of Iwate during 11-12 November 1999. Courtesy of JMA.

On the evening of 16 November, the extended National Coordination Committee for Prediction of Volcanic Eruptions met in the city of Morioka, Iwate Prefecture, to review the events that occurred on the 12th. They noted that the tremor was similar in shape, amplitude, and duration to one (M 2.4) that occurred on 10 July 1999; hence it was considered likely that the two events occurred in the same place. Changes detected in tilt- and strain-meters located on the flank during the tremor were probably caused by subsurface ground faulting or fluid movement. After the tremor, however, no subsequent changes were observed. Neither the GPS-based, N-S traverse distance across the volcano nor the fumarole temperatures in the Ubakura-yama to Kurokura-yama region changed before or after the event. Fumarolic activity in western Iwate had increased since May as had the number of shallow earthquakes in the Ojigokudani area (erosion caldera). The tremor event on 12 November suggested a continuing possibility of a phreatic explosions in western Iwate.

Information Contacts: Kazuo Sekine, Sendai District Meteorological Observatory, Japan Meteorological Agency, 1-3-15 Gorin, Miyagino-ku, Sendai 983, Japan (Email: kazuo.sekine@met.kishou.go.jp); Hiroyuki Hamaguchi, Faculty of Science, Tohoku University, Sendai 980-8578 Japan (Email: hama@aob.geophys.tohoku.ac.jp, URL: http://www.sci.tohoku.ac.jp/); Setsuya Nakada, Volcano Research Center, ERI, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113, Japan (Email: nakada@eri.u-tokyo.ac.jp, URL: http://hakone.eri.u-tokyo.ac.jp/ vrc/VRC.html); Jun-ichi Hirabayashi, Kusatsu-Shirane Volcano Observatory, Tokyo Institute of Technology, Kusatsu, Agatsuma-gun, Gunma 377-17 Japan (Email: jhirabay@ksvo.titech.ac.jp, URL: http://131.112.25.6/).
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Viewed from the east, Iwatesan volcano has a symmetrical profile that invites comparison with Fuji, but on the west an older cone is visible containing an oval-shaped, 1.8 x 3 km caldera. After the growth of Nishi-Iwate volcano beginning about 700,000 years ago, activity migrated eastward to form Higashi-Iwate volcano. Iwate has collapsed seven times during the past 230,000 years, most recently between 739 and 1615 AD. The dominantly basaltic summit cone of Higashi-Iwate volcano, Yakushidake, is truncated by a 500-m-wide crater. It rises well above and buries the eastern rim of the caldera, which is breached by a narrow gorge on the NW. A central cone containing a 500-m-wide crater partially filled by a lake is located in the center of the oval-shaped caldera. A young lava flow from Yakushidake descended into the caldera, and a fresh-looking lava flow from the 1732 eruption traveled down the NE flank.

Summary of Holocene eruption dates and Volcanic Explosivity Indices (VEI).

Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
[ 1934 Jul ] [ 1935 ] Uncertain    
1919 Jul 15 (?) 1919 Jul 15 (?) Confirmed 1 Historical Observations W side of Onigajo caldera (O-jigokudani)
[ 1823 ] [ Unknown ] Discredited    
1732 Jan 22 1732 Oct (?) Confirmed 2 Historical Observations NE flank of Yakushi-dake
[ 1719 Feb (?) ] [ Unknown ] Discredited    
[ 1689 Jun 22 ] [ Unknown ] Uncertain 2  
[ 1687 Apr 14 ] [ 1687 Jul ] Uncertain 2  
1686 Mar 26 1686 Mar 27 Confirmed 3 Historical Observations
1450 ± 100 years Unknown Confirmed   Radiocarbon (uncorrected) Nishi-Iwate and Higashi-Iwate
1300 ± 50 years Unknown Confirmed 3 Tephrochronology Higashi-Iwate (Myoko-dake)
0150 (?) Unknown Confirmed   Radiocarbon (uncorrected) Higashi-Iwate
0350 BCE (?) Unknown Confirmed   Radiocarbon (uncorrected) Higashi-Iwate
0450 BCE (?) Unknown Confirmed   Radiocarbon (corrected) Nishi-Iwate (O-jigokudani area)
1150 BCE (?) Unknown Confirmed   Radiocarbon (uncorrected) Nishi-Iwate
1250 BCE (?) Unknown Confirmed 3 Radiocarbon (corrected) Higashi-Iwate
1500 BCE ± 300 years Unknown Confirmed   Tephrochronology Higashi-Iwate
1650 BCE (?) Unknown Confirmed   Radiocarbon (corrected) Nishi-Iwate (O-jigokudani area)
2000 BCE (?) Unknown Confirmed   Radiocarbon (corrected) Nishi-yama
2050 BCE ± 200 years Unknown Confirmed   Radiocarbon (corrected) Higashi-Iwate, W5 tephra
2700 BCE ± 200 years Unknown Confirmed   Tephrochronology Higashi-Iwate, W6a-d tephras
2950 BCE ± 50 years Unknown Confirmed   Radiocarbon (corrected) Nishi-Iwate, PHD5 tephra
3050 BCE (?) Unknown Confirmed   Radiocarbon (uncorrected) Higashi-Iwate
3250 BCE ± 500 years Unknown Confirmed 0 Tephrochronology
3750 BCE ± 100 years Unknown Confirmed   Tephrochronology Higashi-Iwate
4350 BCE ± 500 years Unknown Confirmed   Tephrochronology Higashi-Iwate
4450 BCE ± 500 years Unknown Confirmed 0 Tephrochronology Higashi-Iwate
4850 BCE ± 50 years Unknown Confirmed   Radiocarbon (corrected) Nishi-Iwate, PHD6 tephra
4900 BCE ± 100 years Unknown Confirmed   Radiocarbon (corrected) Higashi-Iwate
5650 BCE ± 50 years Unknown Confirmed   Radiocarbon (corrected) Nishi-Iwate, PHD7 tephra
6300 BCE ± 100 years Unknown Confirmed   Radiocarbon (corrected) Nishi-Iwate, PHD8 tephra
6450 BCE ± 1600 years Unknown Confirmed   Tephrochronology

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.


Synonyms

Ganju-san | Nambu-fuji | Iwate-fuji | Ganzyu-san | Iwate-Huzi | Nambu-Huzi | Iwate

Cones

Feature Name Feature Type Elevation Latitude Longitude
Higashi-Iwate Stratovolcano 2041 m 39° 50' 59" N 141° 0' 16" E
Inukura-yama Stratovolcano 1408 m
Mitsuishi-yama
    Mituisi-yama
Stratovolcano
Myoko-dake Stratovolcano 2000 m
Nishi-Iwate Stratovolcano
Onigajo
    Onigazyo
Stratovolcano 1706 m
Ubakura-yama Stratovolcano 1517 m
Yakushi-dake Stratovolcano 2041 m 39° 50' 59" N 141° 0' 16" E

Craters

Feature Name Feature Type Elevation Latitude Longitude
Ohachi
    Ohati
Crater
Okama Crater
Omuro Crater
Onashiroko Crater

Thermal

Feature Name Feature Type Elevation Latitude Longitude
Amikake Spa Thermal
Matsukawa Spa Thermal
Ojigoku
    Ozigoku
Thermal
Iwate volcano displays two summit peaks when viewed from the SE. Yakushi-dake (right) forms the summit of Iwate, and is a younger cone that was constructed over the eastern rim of Nishi-Iwate caldera, the left-hand peak. Historical eruptions, mostly from the 500-m-wide summit crater of Yakushi-dake and vents on its flanks, have been recorded since the 17th century.

Photo by Lee Siebert, 1977 (Smithsonian Institution).
Seen from the SW, Iwate stratovolcano on Japan's northern island of Honshu, has an elongated profile. The extensively dissected Onogajo volcano forms the older, western part of Iwate and is truncated by the 1.8 x 3 km Nishi-Iwate caldera. The smoother slopes at the right are formed by ejecta from the younger Yakushi-dake cone, which was constructed on the eastern rim of the caldera.

Photo by Hidenori Togari, 1994 (Hokkaido University).
The Nishi-Iwate caldera is seen here from the summit of Yakushi-dake, a cone constructed on the eastern rim of the caldera. Onoshiroko lake fills the nested crater of Okama in the center of the caldera, which is breached to the NW.

Photo by Hidenori Togari, 1994 (Hokkaido University).
Yakushi-dake, the central cone of Iwate volcano, is viewed here from the north. The undissected cone of Yakushi-dake is the youngest feature of Iwate volcano. A lava flow was erupted from a NE-flank vent in 1719.

Photo by Hidenori Togari, 1994 (Hokkaido University).
Yakushi-dake (center), the summit cone of Iwate volcano was constructed at the eastern end of the elongated Nishi-Iwate caldera. The north and south rims of the 1.8 x 3 km caldera form the ridges at the left and right, respectively. Both Yakushi-dake and a cone in the western caldera have been active in historical time.

Photo by Hidenori Togari, 1994 (Hokkaido University).
The vegetation-poor Yakebashiri lava flow descended the NE flank of the Yakushi-dake summit cone of Iwate volcano in 1719. The basaltic-andesite aa Yakebashiri flow, the youngest lava flow from Iwate, was erupted from a vent on the upper NE flank and traveled down to about the 550-m altitude, 3.5 km from the vent.

Photo by Hidenori Togari, 1993 (Hokkaido University).

The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography. Discussion of another volcano or eruption (sometimes far from the one that is the subject of the manuscript) may produce a citation that is not at all apparent from the title.

IAVCEI, 1973-80. Post-Miocene Volcanoes of the World. IAVCEI Data Sheets, Rome: Internatl Assoc Volc Chemistry Earth's Interior..

Itoh J, 1998. The eruption history of Iwate volcano in the Edo period, based on the historical documents. Bull Volc Soc Japan (Kazan), 43: 467-481 (in Japanese with English abs).

Japan Meteorological Agency, 2013. National Catalogue of the Active Volcanoes in Japan (fourth edition, English version). Japan Meteorological Agency.

Japan Meteorological Agency, 1996. National Catalogue of the Active Volcanoes in Japan (second edition). Tokyo: Japan Meteorological Agency, 502 p (in Japanese).

Kudo T, Hoshizumi H, 2006-. Catalog of eruptive events within the last 10,000 years in Japan, database of Japanese active volcanoes. Geol Surv Japan, AIST, http://riodb02.ibase.aist.go.jp/db099/eruption/index.html.

Kuno H, 1962. Japan, Taiwan and Marianas. Catalog of Active Volcanoes of the World and Solfatara Fields, Rome: IAVCEI, 11: 1-332.

Nakano S, Yamamoto T, Iwaya T, Itoh J, Takada A, 2001-. Quaternary Volcanoes of Japan. Geol Surv Japan, AIST, http://www.aist.go.jp/RIODB/strata/VOL_JP/.

Tanaka S, Hamaguchi H, Ueki S, Sato M, Nakamichi H, 2002. Migration of seismic activity during the 1998 volcanic unrest at Iwate volcano, northeastern Japan, with reference to P and S wave velocity anomaly and crustal deformation. J Volc Geotherm Res, 113: 399-414.

Volcano Types

Complex
Caldera
Pyroclastic cone(s)

Tectonic Setting

Subduction zone
Continental crust (> 25 km)

Rock Types

Major
Basalt / Picro-Basalt
Andesite / Basaltic Andesite

Population

Within 5 km
Within 10 km
Within 30 km
Within 100 km
439
18,462
415,920
2,976,795

Affiliated Databases

Large Eruptions of Iwatesan Information about large Quaternary eruptions (VEI >= 4) is cataloged in the Large Magnitude Explosive Volcanic Eruptions (LaMEVE) database of the Volcano Global Risk Identification and Analysis Project (VOGRIPA).
WOVOdat WOVOdat is a database of volcanic unrest; instrumentally and visually recorded changes in seismicity, ground deformation, gas emission, and other parameters from their normal baselines. It is sponsored by the World Organization of Volcano Observatories (WOVO) and presently hosted at the Earth Observatory of Singapore.
EarthChem EarthChem develops and maintains databases, software, and services that support the preservation, discovery, access and analysis of geochemical data, and facilitate their integration with the broad array of other available earth science parameters. EarthChem is operated by a joint team of disciplinary scientists, data scientists, data managers and information technology developers who are part of the NSF-funded data facility Integrated Earth Data Applications (IEDA). IEDA is a collaborative effort of EarthChem and the Marine Geoscience Data System (MGDS).
Smithsonian Collections Search the Smithsonian's NMNH Department of Mineral Sciences collections database. Go to the "Search Rocks and Ores" tab and use the Volcano Name drop-down to find samples.