I was wondering what information you could give me about the eruptions Usu in Japan. What type of Volcanoe is it? What is its present condition? Any information you could send would greatly benefit me.

rockyTim

Hi Tim,

Usu is an interesting volcano. What I'm telling you comes from a book called "Global Volcanism 1975-1985" by Lindsay McClelland and others, plus some reports from the Global Volcanism Network since 1985.
Usu is on Hokkaido and has erupted six times since its biggest eruption in 1663. Many of the Usu eruptions start out as explosive events which are then followed by long periods of lava dome growth. Usu is (not surprisingly) a complex of numerous domes, most of which have names.
Usu had a large explosive eruption in August of 1977. It was preceded by lots of seismicity and forced the evacuation of almost 30,000 people from nearby towns. The main explosive activity was over in about a week with weaker ashand steam explosions continuing for months. By September a new dome was growing, but it was growing underground. Such a dome is called a "cryptodome". It had bulged the gound surface upward by 70 m by late september. At times during October the cryptodome was growing by up to 60 cm per day! By mid-1979 the rate of growth had declined to less than 10 cm/day.
Well, I couldn't find any mention of Usu in the GVN bulletins from 1989 until now so I guess it isn't doing much. For an overview of the volcano you can look for these two articles:
Yokoyama, Yamashita, Watanabe, and Okada (1981). "Geophysical Charactistics of Dacite Volcanism--1977-1979 eruption of Usu Volcano" in the Journal of Volcanology and Geophysical Research (volume 9, pages 335-358). Katsui, Komuro, and Uda (1985). "Development of faults and growth of Usu-Shinzan cryptodome in 1977-1982 at Usu Volcano, North Japan" in the Journal of the Faculty of Science, Hokkaido University, Series 4 vol. 21, pages 339-362.
Hopefully this will give you some hints of where to look for even more information.

Sincerely,

Scott Rowland 

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