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Quaternary Volcano > Active Volcanoes > Kusatsu-Shirane
Kusatsu-Shirane Volcano   textgeologicmap3Dgeologicmap
Eruptions of historical times

   In contrast to nearby Asama Volcano, historical records are scarce for Kusatsu-Shirane Volcano. The oldest is the activity of Yugama in 1805 ( 2nd year of Bunka ). In historical times, only phreatic eruptions around explosion craters such as Yugama, Mizugama, Karegama, and Yumi-ike, are known, but no record of lava flow or pyroclastic flow. In the thirteen activities described below for 180 years, 10 eruptions occurred within a time spanning for 61 years from 1882 to 1942.

Eruption in 1805 ( 2nd year of Bunka )
   It seems that phreatic eruption occurred at Yugama resulting in a large amount of ash fall in Nagano Prefecture in the west and many trees dead.

Eruption of 1882 ( 15th year of Meiji )
   For 77 years since 1805, Kusatsu-Shirane Volcano seemed to be quiet and periphery of Yugama was covered by trees and grass. From the beginning of July intermittent sound was heard and on 6th of August eruption started from just west of Yugama. Many explosion craters were formed with ejection of large and small blocks, ash, and mud. In the center of Yugama was formed a small sulfur hill. The activity continued for several days and after this water of Yugama, Mizugama, and Karegama became acid.

Eruption in 1897 ( 30th year of Meiji )
   Many sounds were heard since January. It became very frequent from the beginning of June. From afternoon of July 7th, sound became violent and about 4:00 on 8th NE wall of Yugama exploded with ejection of large blocks. Several hundred meters around Yugama was covered by fallen ash. An hour later SW side of Yugama exploded with ejection of hot water and mud to about 150 m high which continued for 3 hours. At 5:00 on July 31st explosion occurred again and one laborer at sulfur works was injured. Several fumaroles with diameter of about 10 m were formed and a crack of about 10 m long was observed. At 2:00 on August 2nd sound became frequent and exploded at sunrise. At 14:00 on September 9th exploded again, one person injured. The sound activity continued till 16th with small explosions.

Eruption in 1900 ( 33rd year of Meiji )
   Small explosion on October 7th. Details not known.

Eruption in 1902 ( 35th year of Meiji )
   At about 16:00 on July 15th, NE shore of Yumi-ike exploded. Explosion crater surrounded by deposits in cone shape formed ejecting steam and blocks. Small explosion at the same spot on August 20th. Small explosion crater formed just outside of above crater on September 4th with 3 cm ash fall at Manza Hot Spa. At 19:00 on September 17th explosion occurred again at the same spot and considerable ash fall in 20 minutes. Explosions on 23rd and 24th, and the activity continued till December. Water in Yumi-ike became acid and undrinkable.

Eruption in 1905 ( 38th year of Meiji )
   Small explosion in October. Details not clear.

Eruption in 1925 ( 14th year of Taisho )
   On January 22nd upper part of north wall of Yugama exploded ejecting ash and blocks and formed explosion crater of the size 20 m long and 7 m wide. Ash fall thickness at 3 km in the SE was 10 to 20 cm.

Eruption in 1927 ( 2nd year of Showa )
   At 7:00 on December 29th and at 9:00 on December 30th sounds were heard and on the following day at 11:00 explosion occurred. A crack 100 m long was formed at the bottom of north wall of Yugama. Also many large and small cracks were formed outside slope of SE wall. Abundant blocks, ash, mud, and gas were ejected resulting in lowering of water level in Yugama by 14 m.

Eruption in 1932 ( 7th year of Showa )
   At 14:00 on October 1st explosion occurred with no warning sign, and formed over 10 large and small explosion craters on NE wall of Yugama. The largest crater was 50 m across and the crack extended beyond SE wall reaching 500 m long altogether. Steam and gas erupted from many places of the crack. Two laborers digging for sulfur were killed by cinder and seven injured. At 2:30 on 4th exploded again with black smoke column and ash fall continued in Sesshogawara till evening. At 3:00 on 6th black smoke rose and ash fall furious. At 6:40 on 8th small explosion occurred, and 3:00 on 14th seven fumaroles of about 2 m diameter each were formed along cracks extending outside of Yugama and black smoke rose furiously. Several small explosions occurred from 16th to 17th.

Eruptions in 1937 to 1939 ( 12th to 14th year of Showa )
   Explosion commenced on November 27th 1937 repeated 10 strong times till February 16th 1938. Thereafter became slightly quiet, but again became active following small explosion on October 5th and repeated notable explosions in March, April, and May 1939. Particularly those in April 1939 brought much ash fall in Kusatsu and Naganohara Townships.

Eruption in 1942 ( 17th year of Showa )
   Small explosion on February 2nd at Yugama. Smoke rose. Building near the crater suffered damage.

Eruption in 1976 ( 51st year of Showa )
   Small explosion at north wall of Mizugama at the beginning of March ejecting large and small blocks.

Eruption in 1982 ( 57th year of Showa )
   At about 9:00 on October 26th small explosion occurred at Yugama and west wall of Karegama. Small amount of black ash was ejected from Karegama and after 20 minutes became quiet. Yugama ejected black ash from several points. The ash was blown by strong NW wind resulting in ash fall in SE directions. The ash reached Sesshogawara. Up to head-sized blocks were ballistically ejected toward crater floor of Mizugama.

   Volcanic tremors became frequent again from around December 20th, and at around 4:30 of December 29th phreatic explosion occurred. The smoke rose up to 700 m and ash fell 4 km away in NE direction. Large and small blocks up to 40 cm across were ejected in east and west directions. In January 1983 the smoke and tremors still continued.

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