Kusatsu-Shiranesan

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  • 36.618°N
  • 138.528°E

  • 2165 m
    7101 ft

  • 283120
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25 June-1 July 2014

JMA reported that deformation of Kusatsu-Shiranesan’s crater and the elevated temperatures which began earlier in March, continued during 25-30 June. This activity has been focused in the area immediately of N of Mizugama crater. Some seismicity was also reported, although tremor was absent. The Alert Level remains at 2 (on a scale of 1-5).

Source: Japan Meteorological Agency (JMA)

Index of Weekly Reports


2014: June

Weekly Reports


25 June-1 July 2014

JMA reported that deformation of Kusatsu-Shiranesan’s crater and the elevated temperatures which began earlier in March, continued during 25-30 June. This activity has been focused in the area immediately of N of Mizugama crater. Some seismicity was also reported, although tremor was absent. The Alert Level remains at 2 (on a scale of 1-5).

Source: Japan Meteorological Agency (JMA)


18 June-24 June 2014

JMA reported that anomalous temperatures and deformation of Kusatsu-Shirane’s crater, which began earlier in March, continued during 13-20 June. This activity has been focused in the area immediately of N of Mizugama crater. Elevated seismicity was also reported, although tremor was absent. The Alert Level was raised to 2 (on a scale of 1-5).

Source: Japan Meteorological Agency (JMA) via the Volcano Research Center


Index of Monthly 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.

03/1976 (GV 1975) Small eruption from Mizugama Crater

09/1976 (SEAN 01:12) Three people killed by hydrogen sulfide

10/1982 (SEAN 07:10) Phreatic explosion; volcanic tremor

11/1982 (SEAN 07:11) Lake temperatures measured after explosion

12/1982 (SEAN 07:12) Volcanic tremor, phreatic explosion

04/1983 (SEAN 08:04) Small phreatic explosion; harmonic tremor

05/1983 (SEAN 08:05) 9 March activity was only seismic

07/1983 (SEAN 08:07) Small plume emitted; volcanic tremor; A-type events

10/1983 (SEAN 08:10) Explosions eject large tephra

12/1983 (SEAN 08:12) Summit explosions and seismicity

01/1984 (SEAN 09:01) 1983 activity summarized

06/1986 (SEAN 11:06) Increase in microearthquakes since 1984

10/1987 (SEAN 12:10) Earthquakes increase to five times monthly average

10/1988 (Ref 1989) Seismicity during September-October 1988; tremor in January 1989 associated with phreatic emissions

02/1990 (BGVN 15:02) Highest amplitude tremor since 1982-83 activity, but no eruption

05/1990 (BGVN 15:05) Seismicity remains high; high-amplitude tremor continues

06/1990 (BGVN 15:06) Continued vigorous seismicity

07/1990 (BGVN 15:07) More frequent volcanic earthquakes and tremor

08/1990 (BGVN 15:08) Seismicity remains strong

09/1990 (BGVN 15:09) Seismicity remains strong

10/1990 (BGVN 15:10) Continued high seismicity but no surface changes

11/1990 (BGVN 15:11) Strong seismicity continues but no surface changes

12/1990 (BGVN 15:12) Continued vigorous seismicity

01/1991 (BGVN 16:01) Continued seismicity but no change in surface activity

02/1991 (BGVN 16:02) Continued seismicity but no surface changes

03/1991 (BGVN 16:03) Brief peak in seismicity

04/1991 (BGVN 16:04) Continued seismicity

02/1996 (BGVN 21:02) Minor hydrothermal ejection in Yu-gama crater

07/1996 (BGVN 21:07) Seismic activity increases

02/2013 (BGVN 38:02) Minor tremor and small earthquakes during 2011-2012


Contents of Monthly Reports

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

All times are local (= UTC - 9 hours)

03/1976 (GV 1975) Small eruption from Mizugama Crater

[JMA notes that a small eruption from Mizugama Crater occurred at about 1800 on 2 March 1976. A new crater 50 m in diameter and 10 m deep was formed in the NE part of Mizugama Crater.]

Information Contact: Japan Meteorological Agency, Tokyo.

09/1976 (SEAN 01:12) Three people killed by hydrogen sulfide

[On 3 August] a high school teacher and two students were overcome and killed by H2S, which is emitted in considerable quantities [from fumaroles on the NW side of Motoshirane-san, 2 km SSW of Yugama Crater]. The gas had concentrated in a bowl-shaped area during a light rain on a nearly windless day.

Further Reference. Ossaka, J., and others, 1980, Variation of chemical composition in volcanic gases and waters at Kusatsu-Shirane volcano and its activity in 1976: BV, v. 43.

Information Contact: JMA, Tokyo.

10/1982 (SEAN 07:10) Phreatic explosion; volcanic tremor

A brief phreatic explosion from three vents on 26 October ejected a dark column that rose 100 m above the lakes in two summit craters, Yugama and Karagama (figure 1). Onset time of the explosion was uncertain, but the seismograph at the Maebashi District Meteorological Observatory, 1.1 km NE of Yugama, began to record volcanic tremor with an amplitude of 0.2 µm at 0855. Gray plumes were recognized at 0905. The tremor gradually increased in amplitude and peaked about an hour after onset.

Figure 1. Map of the summit region of Kusatsu-Shirane. Small circles indicate fumaroles; the other marks represent vents active since the 27 October 1982 eruption. An 'x' indicates an emission point of the 26 October 1982 eruption plume. The large open circle is Pit No. 6; the concentric circles are Pit No. 7. The solid circle is a new pit that formed on 13 November. Pits No. 2 and 3 (not shown) are on the W inner wall of Yugama. Courtesy of JMA.

Activity at Karagama ended at 0920, only 15 minutes after it was first recognized, and at 0930 activity at Yugama was reduced to white vapor emission (which ended the next day). Volcanic tremor, however, continued at peak levels for a few hours then gradually weakened, ceasing at 0124 on 30 October. A swarm of volcanic earthquakes lasting 5 hours was recorded on 26-27 October, and there was another minor swarm on [27] October.

JMA reported that a strong wind carried ash from as far as 3 km to the SE; ash was 1 mm thick on the crater rim. Tokiko Tiba reported a maximum of 3 cm of ash in the summit area. The total volume of ejecta was estimated to be 2,800-3,400 tons. No damage was reported. As of 2 November no further eruptions had been reported, and fumarolic activity in Yugama had declined. . . .

Information Contacts: T. Tiba, National Science Museum, Tokyo; JMA, Tokyo.

11/1982 (SEAN 07:11) Lake temperatures measured after explosion

Temperatures measured in the lake in Yugama Crater for 6 days following the 26 October explosion [were: 14°C on 26 October, 46°C on 27 October, 55°C on 28 October, 56°C on 29 October, 48°C on 30 October, and 39°C on 31 October.]

Information Contacts: Y. Sawada, Meteorological Research Institute, Ibaragi; D. Shackelford, CA.

12/1982 (SEAN 07:12) Volcanic tremor, phreatic explosion

At 0538 on 29 December, after 64 days of quiescence, a phreatic explosion from the pit formed in the 26 October explosion ejected a gray plume that rose about 300 m above the rim of Yugama Crater. The plume was 700 m above the rim by 1300, then suddenly declined about 1500. The seismograph at the Maebashi District Meteorological Observatory, 1.1 km NE of Yugama, began to record volcanic tremor 46 minutes before the explosion. Maximum amplitude was 2.1 µm. Tremor ended at 1538, but resumed at 1900 and continued until 1500 the next day. Ash traveled as far as 4 km, mainly NE. Scattered blocks and ejecta carried by spraying water were observed around the pit, including clay material on 30 December. No damage was reported. As of 5 January, no further explosions had been reported, but tremor had been continuous since 2 January.

Information Contact: JMA, Tokyo.

04/1983 (SEAN 08:04) Small phreatic explosion; harmonic tremor

. . . Local seismicity had declined after the December activity, but increased in early January (see table 1), when 91 volcanic earthquakes and 44 tremor events were recorded. After mid-January no tremor events were recorded, but the number of volcanic earthquakes was greater than background level in early March.

At 0459 on 9 March the seismograph at Maebashi District Meteorological Observatory recorded a swarm of volcanic earthquakes that lasted only a few minutes. JMA scientists noted that these earthquakes were similar in wave form to those recorded during previous eruptions. . . . In April, activity was limited to occasional white vapor ejections. On 10 April, one vapor plume rose to 60 m above Yugama Crater. Volcanic tremor, possibly accompanied by vapor ejections, was observed 9-12 and 19-20 April.

Information Contact: JMA, Tokyo.

05/1983 (SEAN 08:05) 9 March activity was only seismic

Tokyo Institute of Technology personnel visited the volcano on 12 March to investigate a report of a small phreatic explosion from Pit No. 7 on 9 March [originally reported in 8:4]. A brief swarm of volcanic earthquakes had been recorded at 0459 that day at the Maebashi District Meteorological Observatory. The Institute team found no fresh ash. Although ash was reported to have fallen on the frozen crater lake, another observer said that the lake was not frozen on 9 March. The team concluded that the 9 March activity had been only seismic.

Information Contact: JMA, Tokyo.

07/1983 (SEAN 08:07) Small plume emitted; volcanic tremor; A-type events

On 26 July a small phreatic explosion occurred at the NW rim of Yugama Crater, at the volcano's summit. JMA personnel observed the eruption, at Pit No. 6, formed during the 26 October phreatic explosion and the site of a similar explosion on 29 December. Volcanic tremor (amplitude 0.2-0.3 µm) started at 1031. About 1110, the dominant frequency of the tremor decreased and white vapor was ejected. Volcanic rumbling intensified at 1140; about 1/3 of the crater lake was covered with ash by 1150. Accompanied by strong rumbling, a dark plume was ejected at [1204]; it had risen above the crater rim by [1212]. Volcanic tremor returned to a higher frequency at 1213, but shifted back to lower frequency about 20 minutes later. Emission of a white vapor plume that rose to about 100 m above the pit was continuous in the afternoon. Volcanic tremor ended at 1720. The plume weakened suddenly at 1730.

Local seismicity had been at a high level since last autumn. Seismographs recorded 209 volcanic earthquakes in June and 227 in July. On 22 July, swarms of A-type earthquakes occurred. After the 26 July eruptive episode, seismicity declined slightly but remained above background level.

Information Contacts: JMA, Tokyo; T. Tiba, National Science Museum, Tokyo.

10/1983 (SEAN 08:10) Explosions eject large tephra

UPI reported that thunderous explosions ejected tephra on 13 November at 1144. [Blocks fell a few hundred meters from the vent; original press reports of a more distant fall of large tephra were incorrect.] Tephra [reached a town] (Nakanojo) 40 km SE of the volcano. A "secondary" eruption occurred 25 minutes later. No injuries were reported.

Information Contact: UPI.

12/1983 (SEAN 08:12) Summit explosions and seismicity

Summit explosions from Kusatsu-Shirane occurred on 13 November and 21 December. Precursory seismic activity began with a large-amplitude discrete event on 2 November. Tremor was continuous between 0700 and 2000 on the 10th. Stronger tremor was recorded at 1722 on the 12th. Its mean amplitude on the seismograph, initially 1.9 µm, gradually increased to more than 5.0 µm at 2000, when the wave form of the tremor became similar to one that had accompanied a mud at Aso Volcano. Tremor gradually declined during the early morning of 13 November.

Explosions occurred 13 November at 1144 and 1208 from small vents (Pits No. 6 and 7) on Yugama Crater's [N] wall and a new pit that appeared about 50 m E of Pit No. 6. [During a 22 December inspection] Tokyo Institute of Technology personnel found that a [45] cm-wide, 45 m-long fissure on the N wall of the adjoining Karagama Crater had also ejected ash. JMA noted that the line extending SW from Pit No. 6 across Karagama Crater's N wall has been active since the eruption of October 1982.

Lapilli were scattered as much as 600-700 m S of Yugama. Ash was carried 30 km downwind although most fell into the lake in Yugama Crater. The second explosion was accompanied by a ground shock of intensity III (JMA Scale) at the rest area 700 m S of Yugama. Signals from the seismograph at the Maebashi District Meteorological Observatory stopped immediately after this explosion. A field survey revealed that [blocks] had made many craters 1-3 m in diameter and 50 cm deep on the upper SE outer slope of Yugama. The buried seismograph cable seemed to have been cut by one of these [blocks].

Seismic activity increased again 18-19 December, when 32 and 31 discrete events were recorded. After a brief period of activity from 0954-1007 on the 21st, continuous tremor resumed at 1022. The tremor, accompanied by some large discrete events, saturated the seismograph from 1035-1105, then gradually declined, ending at 1220.

A Kusatsu town employee working S of Yugama first noticed the sound of vapor emission at 1010; 20 minutes later he observed a dark plume containing mud and lapilli rising 300 m above the crater rim. Ash traveled 400-500 m SE, darkening frozen Yugama Lake. Eruptive activity began to decline about 1100. Tokyo Institute of Technology personnel found that the eruption sites were Pits No. 2 and 3 on the W inner wall of Yugama. A small amount of ash was also ejected from the fissure in Karagama Crater that was active in November.

Information Contact: JMA, Tokyo.

01/1984 (SEAN 09:01) 1983 activity summarized

1983 activity is summarized in table 1; locations are on figure 1.

Table 1. Seismic activity at Kusatsu-Shirane, 1983. Courtesy of JMA.

    1983      Discrete       Continuous            Remarks
           Seismic Events      Tremor

    Jan    Observed swarms   Observed              Rumbling at the summit.
    Mar    Observed swarms   --                    Increased fumarolic
                                                     activity at Pit No. 2.
    Apr    --                Observed              White plumes from Pits No.
                                                     2, No. 7, and a fumarole
                                                     on the N inner wall of
                                                     Yugama; N edge of frozen
                                                     Yugama lake melted.
    Jun    Observed swarms   --                    --
    Jul    Observed swarms   Almost at noise       Small eruption at Pit No.
                               level                 6, NW wall of Yugama, on
                                                     26 July; small amount of
                                                     ash.
    Nov    Observed swarms   Observed during       Explosive eruption at NW
                               eruptive activity     inner wall of Yugama and
                                                     at Karagama on 13 Nov; a
                                                     larger amount of ejecta.
    Dec    Observed swarms   Observed during
                               eruptive activity

Further Reference. The 1982-1983 eruptions of Kusatsu-Shirane volcano, in XIX IUGG General Assembly, 1987, Report on volcanic activities and volcanological studies in Japan for the period from 1983 to 1986, p. 5-8.

Information Contact: JMA, Tokyo.

06/1986 (SEAN 11:06) Increase in microearthquakes since 1984

Monthly frequency of microearthquakes recorded at the volcano reached 96 in June, the highest since the active phase of 1982-84. A gradual increase in seismicity began last year (figure 2).

Figure 2. Monthly seismicity at Kusatsu-Shirane, 1978-86. Arrows indicate five eruptions in 1982 and 1983.

Information Contact: JMA.

10/1987 (SEAN 12:10) Earthquakes increase to five times monthly average

Many small volcanic earthquakes were recorded 14-19 October by the seismograph 1 km NE of Yugama, the largest of the three crater lakes. The monthly total of volcanic earthquakes reached 114, compared to the monthly average of less than 20. Seismic activity declined to a low level after 22 October. Epicenters were estimated to be several hundred meters E of Yugama. JMA's Mobile Volcanological Observation Team established two additional seismographs and began 10 days of observation on 18 October. No significant changes in fumarolic activity were observed during field surveys on 23 and 26 October.

A phreatic explosion from Yugama crater ejected 20-cm blocks to 600-700 m from the crater lake on 13 November 1983. Small phreatic explosions occurred from Yugama and Karegama (the E crater lake) on 26 July and 21 December 1983.

Information Contact: JMA.

10/1988 (Ref 1989) Seismicity during September-October 1988; tremor in January 1989 associated with phreatic emissions

[Ida and others (1989) report that swarm-like seismicity began at the end of September 1988 and continued through October, with most located events centered SE of Mizugama crater. Hypocenters remained in the same area during the following period, but focal depths shallowed and episodic volcanic tremor became more frequent. Continuous volcanic tremor began suddenly on 6 January 1989 and lasted for almost 24 hours. The tremor was associated with emission of steam or water from the NW part of Yugama Crater, which distributed a small amount of ash over the crater lake.]

Reference. Ida, Y., Osada, N., Sawada, M., Koyama, E., and Kagiyama, T., 1989, Seismological Study Based on Recently Installed Permanent Stations and a Small Eruptive Event on January 6, 1989 at Kusatsu-Shirane Volcano: Bulletin of the Earthquake Research Institute, University of Tokyo, v. 64, p. 325-345 (in Japanese with English abstract and figure captions).

02/1990 (BGVN 15:02) Highest amplitude tremor since 1982-83 activity, but no eruption

Volcanic tremor began at about 1445 on 27 January and continued through 1 February. The largest amplitude was about 0.2 µm. A field survey on 2 February found no new ash deposition around the crater. Water discoloration in Yugama crater lake was observed as usual.

Volcanic tremor resumed at 0019 on 12 February and continued until 0417 the next day. Additional tremor episodes occurred on 18 and 24 February. Amplitudes of 1.3 µm on 18 January and 1.1 µm on 24 February were the highest recorded since the last eruption in 1982-83. The number of discrete volcanic earthquakes also increased between 17 February and 7 March.

Information Contact: JMA.

05/1990 (BGVN 15:05) Seismicity remains high; high-amplitude tremor continues

Seismic activity remained at the highest levels since the 1982-83 eruptive period. The daily number of earthquakes has remained high since increased seismicity began in mid-February (figure 3). The number and amplitude of tremor episodes also remained high with one in January, six in February, two in April, and nine in May. Water discoloration in Yugama crater lake, first noted in February, was usually evident through May (during 13 of 19 visits January-May).

Figure 3. Daily number of recorded earthquakes at Kusatsu-Shirane, 1978-June 1990. Arrows mark eruptions. Courtesy of JMA.

Information Contact: JMA.

06/1990 (BGVN 15:06) Continued vigorous seismicity

The number of volcanic earthquakes persisted at a high level as of early July. Six volcanic tremor episodes were recorded in June. No eruption occurred and fumarolic activity in and around the active crater rim has remained unchanged.

Information Contact: JMA.

07/1990 (BGVN 15:07) More frequent volcanic earthquakes and tremor

The number of volcanic earthquakes . . . remained at high levels as of 8 August, with 212 earthquakes in June and [243] in July. Twelve volcanic tremor episodes were recorded by the seismograph 1.1 km NE of Yugama Crater.

Information Contact: JMA.

08/1990 (BGVN 15:08) Seismicity remains strong

During August, 171 earthquakes . . . and 35 tremor episodes . . . were recorded. Tremor amplitude ranged from 0.0 to 1.3 [µm].

Information Contact: JMA.

09/1990 (BGVN 15:09) Seismicity remains strong

Seismicity has remained at high levels . . . . During September, 184 earthquakes . . . and 44 volcanic tremor episodes . . . were recorded. Tremor amplitude also decreased from as much as 1.3 µm in August to 0.1-0.5 µm in September.

Information Contact: JMA.

10/1990 (BGVN 15:10) Continued high seismicity but no surface changes

Seismicity has remained at high levels . . . (figure 4). During October, 213 earthquakes (up from 184 in September) and 29 tremor episodes . . . were recorded. Tremor amplitudes were similar to previous months. Earthquakes were centered 1 km E of . . . Yugama Crater. Seismicity remained similar as of 14 November. No changes in surface activity were observed.

Figure 4. Monthly number of earthquakes at Kusatsu-Shirane, January 1978-October 1990. Arrows at top of figure mark eruptions. Courtesy of JMA.

Information Contact: JMA.

11/1990 (BGVN 15:11) Strong seismicity continues but no surface changes

Seismicity has remained at high levels since February (figure 4). During November, 117 earthquakes and 27 volcanic tremor episodes were recorded . . . . Seismicity remained similar in early December. No changes in surface activity were observed.

Information Contact: JMA.

12/1990 (BGVN 15:12) Continued vigorous seismicity

Seismicity has remained at high levels since mid-February. During December, [101] earthquakes . . . and 11 tremor episodes . . . were recorded.

Information Contact: JMA.

01/1991 (BGVN 16:01) Continued seismicity but no change in surface activity

Seismicity has remained at high levels since February 1990. During January, 92 earthquakes and 24 volcanic tremor episodes were recorded . . . . No changes in surface activity were observed. Similar activity was noted in early February.

Information Contact: JMA.

02/1991 (BGVN 16:02) Continued seismicity but no surface changes

Earthquakes and tremor activity continued at levels similar to previous months. No changes in surface activity were observed.

Information Contact: JMA.

03/1991 (BGVN 16:03) Brief peak in seismicity

Seismicity continued at high levels through mid-April, after [131] recorded earthquakes and 11 tremor episodes in March. A sharp, brief increase in seismicity on 9 March (42 recorded earthquakes), prompted the JMA to issue a notice ("Extra Volcanic Information"), the first since August. No changes in surface activity were observed.

Information Contact: JMA.

04/1991 (BGVN 16:04) Continued seismicity

In April, seismicity remained similar to previous months, with a total of 110 earthquakes and one tremor episode recorded . . . (figure 5). No surface activity was observed.

Figure 5. Daily number of recorded earthquakes (top) and tremor episodes (bottom) at Kusatsu-Shirane, January 1989-April 1991. Courtesy of JMA.

Information Contact: JMA.

02/1996 (BGVN 21:02) Minor hydrothermal ejection in Yu-gama crater

According to Kusatsu-Shirane Volcano Observatory (Tokyo Institute of Technology), at 1044 on 7 February geophysical changes occurred. A hydrophone submerged in Yu-gama pond recorded large amplitude sound waves and a meter registered water-level changes. Observers on 14 and 24 February saw discolored water near the NW part of the pond's surface and pieces of broken ice, 20-30 cm in size, along the shore. Therefore, on 7 February, a small magnitude ejection might have occurred at the pond. When a similar phenomenon was last observed, 6 January 1989, it was ascribed to hydrothermal activity.

Information Contact: Volcanological Division, Japan Meteorological Agency, 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan

07/1996 (BGVN 21:07) Seismic activity increases

According to the Kusatsu-Shirane Volcano Observatory, Tokyo Institute of Technology, many small earthquakes were detected near the vent on 8 July.

Information Contact: Volcanological Division, Japan Meteorological Agency, 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan

02/2013 (BGVN 38:02) Minor tremor and small earthquakes during 2011-2012

On 7 February 1996, hydrophone data and water level changes suggested that a small hydrothermal ejection may have occurred at Kusatsu-Shirane (also known as Kusatsu-Shiranesan) at Yugama crater’s pond (BGVN 21:02). Several months later, on 8 July, numerous small earthquakes were detected by the Kusatsu-Shirane Volcano Observatory (BGVN 21:07). The volcano is about 150 km NW of Tokyo (figures 6 and 7; also refer to the sketch map in figure 1, SEAN 07:10). This report summarizes seismicity between May 2011 and February 2013 based on available reports from the Japan Meteorological Agency (JMA).

Figure 6. A sketch map showing the location of Kusatsu-Shirane (Kusatsu-Shiranesan) in Honsho, Japan. Courtesy of JMA.
Figure 7. An aerial photo of Kusatsu-Shirane, as viewed from the S. The photo, taken on 29 May 2008, shows the overlapping pyroclastic cones and two of the three crater lakes. Courtesy of Flickr user rangaku1976.

On 27 May 2011, tremor was detected at Kusatsu-Shirane; no further information was provided. During 5-7 June 2011, an elevated number of microearthquakes with low amplitude occurred around Yugama crater (the main crater). No volcanic tremor or significant deformation was detected during this time. Thereafter, activity gradually diminished to background levels.

Field surveys during 27-29 June and 12-13 July 2011 revealed that elevated thermal anomalies persisted inside Yugama crater’s N flank, the N fumarole area, and the slope located N to NE of Mizunuma crater. Ground temperatures around fumaroles remained high.

On 18 July 2011, a short period of tremor (duration 2.5 min) was detected. No change in fumarole activity was observed.

On 10 August 2011, an aerial survey was conducted in cooperation with Gunma prefecture. The survey found that the distribution of thermal anomalies and fumaroles in Yugama crater and the N fumarole area had not changed.

During 16-18 August, an elevated number of microearthquakes with low amplitude occurred near and to the S of Yugama crater. Significant deformation was not detected. Seismicity remained at background levels during the other days in August. High temperatures persisted on the N flank inside the main crater.

A field survey on 8 March 2012 found that the high temperatures on the N slope of Mizugama crater and the N fumarole area were the same as those found during a previous survey conducted during 27-29 June 2011. Very weak steam plumes at the N fumarole area of Yugama were sometimes observed by a camera at Okuyamada, though bad weather and mechanical trouble prevented their observation for long periods. The ground temperature in the fumarole area NE of Yugama crater remained elevated since its rapid rise in May 2009, despite occasional fluctuations.

According to JMA, the occurrence of small amplitude volcanic earthquakes occasionally increased during March 2012. The hypocenters were located just beneath the S part of Yugama crater. No tremor or significant crustal change was noted in GPS data.

During 1-2 April 2012, seismicity increased slightly, then subsided. No tremor, change in fumarole activity, or crustal change was observed, and no further reports have been issued on activity at Kusatsu-Shirane as of February 2013.

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); rangaku1976, Flickr (URL: http://www.flickr.com/photos/rangaku1976/).

The summit of Kusatsu-Shiranesan volcano, located immediately north of Asama volcano, consists of a series of overlapping pyroclastic cones and three crater lakes. The andesitic-to-dacitic volcano was formed in three eruptive stages beginning in the early to mid Pleistocene. The Pleistocene Oshi pyroclastic flow produced extensive welded tuffs and non-welded pumice that covers much of the east, south and SW flanks. The latest eruptive stage began about 14,000 years ago. All historical eruptions have consisted of phreatic explosions from the acidic crater lakes or their margins. Fumaroles and hot springs that dot the flanks have strongly acidified many rivers draining from the volcano. The crater was the site of active sulfur mining for many years during the 19th and 20th centuries.

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

Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
[ 1989 Jan 6 ] [ 1989 Jan 6 ] Uncertain 1   NW part of Yu-gama
1983 Jul 26 1983 Dec 21 Confirmed 1 Historical Observations Yu-gama, Kara-gama
1982 Oct 26 1982 Dec 29 Confirmed 1 Historical Observations Kara-gama, Yu-gama
1976 Mar 2 1976 Mar 2 Confirmed 1 Historical Observations NE corner of Mizu-gama Crater
1958 Dec 31 ± 365 days Unknown Confirmed 1 Historical Observations Yu-gama
1942 Feb 2 Unknown Confirmed 1 Historical Observations Fissure east and south of Yu-gama
1941 Jan 19 1941 Jan 19 Confirmed 1 Historical Observations
1940 Apr 7 1940 Sep 13 Confirmed 1 Historical Observations
1939 Feb (?) 1939 Aug 28 (?) Confirmed 1 Historical Observations Yu-gama
1938 Jul 17 (?) 1938 Oct 5 (?) Confirmed 1 Historical Observations Yu-gama
1937 Nov 27 1938 Feb 16 (?) Confirmed 1 Historical Observations Yu-gama
1934 Unknown Confirmed 2 Historical Observations
[ 1933 ] [ Unknown ] Uncertain    
1932 Oct 1 1932 Nov Confirmed 3 Historical Observations NE part of Yu-gama, SE outer rim
1927 Dec 29 1927 Dec 31 Confirmed 2 Historical Observations N Yu-gama & S outer rim (in 1927, not 1928)
1925 Jan 22 (?) 1925 Jan 30 Confirmed 2 Historical Observations Northern part of Yu-gama
1905 Oct 1905 Oct Confirmed 2 Historical Observations Yu-gama
[ 1903 ] [ Unknown ] Uncertain    
1902 Jul 15 1902 Sep 24 Confirmed 1 Historical Observations North side of Yumi-ike
1900 Oct 1 1900 Oct 1 Confirmed 1 Historical Observations NE part of Yu-gama
1897 Jul 8 1897 Aug 16 Confirmed 2 Historical Observations NE part of Yu-gama
1882 Aug 6 1882 Aug 16 (in or after) Confirmed 2 Historical Observations Yu-gama, NE end of Kara-gama
1805 Unknown Confirmed 2 Historical Observations Yu-gama
1470 ± 150 years Unknown Confirmed   Radiocarbon (uncorrected)
0050 (?) Unknown Confirmed 2 Tephrochronology Yu-gama, Tephra layer 13.7D
0550 BCE (?) Unknown Confirmed 3 Tephrochronology Yu-gama, Tephra layer 13D
1120 BCE ± 150 years Unknown Confirmed 4 Radiocarbon (uncorrected) Moto-Shirane
3750 BCE (?) Unknown Confirmed 2 Radiocarbon (corrected) Shirane
6270 BCE ± 200 years Unknown Confirmed   Radiocarbon (uncorrected)
6550 BCE (?) Unknown Confirmed 3 Radiocarbon (corrected) Shirane

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
Kusatu-Sirane | Kusatsu-Shirane


Cones
Feature Name Feature Type Elevation Latitude Longitude
Aino-mine Cone 2110 m 36° 38' 0" N 138° 32' 0" E
Moto-Shirane Cone 2176 m 36° 37' 0" N 138° 32' 0" E
Shirane-san Cone 2162 m 36° 39' 0" N 138° 32' 0" E


Craters
Feature Name Feature Type Elevation Latitude Longitude
Kara-gama Crater 2040 m 36° 38' 0" N 138° 32' 0" E
Mizu-gama Crater 2050 m 36° 39' 0" N 138° 32' 0" E
Yu-gama Crater 2040 m 36° 38' 0" N 136° 32' 0" E
Yumi-ike Maar 2020 m 36° 38' 0" N 138° 32' 0" E


Domes
Feature Name Feature Type Elevation Latitude Longitude
Futago-yama Dome 2154 m 36° 37' 0" N 138° 32' 0" E


Thermal
Feature Name Feature Type Elevation Latitude Longitude
Bandaiko Hot Springs Hot Spring
Jinetsu Hot Springs Hot Spring
Jizo Hot Springs Hot Spring
Jyobu Hot Springs Hot Spring
Kagusa Hot Springs Hot Spring
Karabuki Thermal
Kitagawa Thermal
Manza Hot Springs Hot Spring
Sainokawara Hot Springs Hot Spring
Sesshogawara Thermal
Shakunage Hot Springs Hot Spring
Shirahata Hot Springs Hot Spring
Shiranezawa Thermal
Tachibana Hot Springs Hot Spring
Yubatake Hot Springs Hot Spring
The crater rim of Kusatsu-Shirane volcano is seen here from the top of a satellitic cone to its south. The diagonal line ascending the cone at the center is a trail leading to the crater lake of this frequently visited volcano. The slopes of the cone are kept largely unvegetated by frequent phreatic explosions from three overlapping craters. Eruptions have been recorded since the early 19th century.

Photo by Lee Siebert, 1977 (Smithsonian Institution).
The summit of Kusatsu-Shirane volcano is cut by three craters, the largest of which is Yu-gama, filled by a turquoise lake. Rafts of yellow sulfur float on the surface of the acidic lake. This 1977 view looks across the lake from the SW-most crater, Kara-gama, to the NE-most crater, Mizu-gama, located beyond the notch at the left. Small-to-moderate phreatic explosions have occurred from all three craters during historical time. The colorful crater lake of Kusatsu-Shirane is a major tourist destination, as are hot spring resorts on the volcano's flanks.

Photo by Lee Siebert, 1977 (Smithsonian Institution).
The turquoise waters of Yu-gama, one of three craters at the summit of Japan's Kusatsu-Shirane volcano, are a popular tourist destination. Yellow rafts of sulfur float on the surface of the acidic lake, which prior to an eruption in 1882, was clear, with forested walls. Frequent phreatic explosions have occurred from Yu-gama and the two other summit craters during historical time. This 1981 photo was taken from the south crater rim.

Copyrighted photo by Dick Stoiber, 1981 (Dartmouth College).

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.

Hayakawa Y, Aramaki S, Shimozuru D, Ossaka J, 1981. Kusatsu-Shirane volcano. In: Aramaki S (ed) {Symp Arc Volcano Field Excur Guide to Fuji, Asama, Kusatsu-Shirane and Nantai Volcanoes}, Tokyo: Volc Soc Japan, 1: 49-63.

Hayakawa Y, Yui M, 1989. Eruptive history of the Kusatsu Shirane volcano. Quat Res, 28: 1-17 (in Japanese with English abs).

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

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

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/.

Suzuki T, 1996. Discharge rates of fallout tephra and frequency of plinian eruptions during the last 400,000 years in the southern Northeast Japan arc. Quat Internatl, 34-36: 79-87.

Uto K, Hayakawa Y, Aramaki S, Ossaka J, 1983. Geologic map of Kusatsu-Shirane volcano. Geol Surv Japan, 1:25,000 geol map.

Volcano Types

Stratovolcano(es)
Pyroclastic cone(s)
Lava dome

Tectonic Setting

Subduction zone
Continental crust (> 25 km)

Rock Types

Major
Andesite / Basaltic Andesite
Dacite

Population

Within 5 km
Within 10 km
Within 30 km
Within 100 km
4,485
14,296
434,049
5,947,593

Affiliated Databases

Large Eruptions of Kusatsu-Shiranesan 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.