36.63 N, 138.55 E
summit elevation 2176
Kusatsu-Shirane volcano is located 150 km NW of Tokyo. Three craters (Karagama, Yugama, Mizugama) are located on the summit of Shirane pyroclastic cone.
Yugama (hot-water cauldron") contains the most active vent. The water is highly acidic (pH = 1.2 ) and mineralized (approximately 1% salt). The lake is about 270 m in diameter and 27 m at the deepest point. The present surface temperature of the lake water is always above that of the atmosphere, which is from below 0 ° C in winter to 24°C in summer. During 1910 to 1918, water temperatures reached a maximum of 100°C. Subaqueous fumaroles with molten sulfur pools exist in the center of the lake.
Historic eruptions at Kusatsu-Shirane volcano have been phreatic through, or close to the crater lakes.
An eruption occurred at Kusatsu-Shirane Volcano on 7th February 1996. The ice sheet was broken a sudden discharge of fluid at the bottom of the lake. Debris of ice sheet the thickness of which was 20 to 30 cm washed ashore.
In 1989 a small eruption occurred in Yugama Crater. Small amounts of volcanic ash deposited on the frozen surface of Yugama Crater.
Kusatsu-Shirane Volcano erupted phreatically five times in 1982 and 1983. Eruptions occurred on 26th October 1982, 29th December 1982, 26th July 1983, 13th November 1983, and 10th December 1983. The water temperature at Yukama crater lake increased greatly to 55.5 deg C after the first eruption, but was not affected by later eruptions.
A phreatic eruption occurred at Mizugama Crater.
The 1942 eruption of Kusatsu-Shirane volcano was followed by a quiet period for the next 34 yr, interrupted only by a small eruption in 1958.
The eruption in 1942 occurred in a different location from most activity at the volcano. An group of small craters opened on the north flank of Mizugama Crater, and a second array formed on the south flank of Yugama Crater.
This was the largest historical eruption at Kusatsu-Shirane volcano, producing a 20 cm deposit of volcanic ash 2 km east of Yugama Crater.
1989, 1982-83, 1976, 1958, 1942, 1939, 1938?, 1937, 1934, 1933?, 1932, 1927, 1925, 1905, 1903?, 1902, 1900, 1897, 1882, 1805.