Unzen volcano alarms Japan

Added: 12/30/2005

Japan is located along the circum-Pacific volcanic belt; therefore, there is a great number of volcanic areas. It is interesting to note that of the eight hundred and forty active volcanoes in the world, Japan has almost 1/10 of them (approximately eighty), although Japan has only 1/400 of the world's land area. An abundance of volcanoes has both negative and positive aspects: volcanoes are dangerous and devastating for the civilization and, at the same time, they make money, since crowds of tourists go to see them all year round.

The Unzen Volcano is situated in the Shimabara Peninsula, Kyushu, Southwest Japan. This is a decade volcano, consisting of thick lava flows/domes and collapsed materials. Two historical eruptions produced huge masses of an andesite lava flow and a dacite lava flow in 1663 and 1792. Earthquakes occurred before and during the 1792 eruption, and a large earthquake after the eruption triggered a large-scale collapse of an old lava dome; the dry avalanche and the resultant tsunami took fifteen thousand people's lives. It has been Japan's worst ever volcanic disaster. After the 1792 eruption, the Unzen was dormant for nearly two hundred years.

The present active center, Mt. Fugen, is only six km away from the center of the Shimabara City with forty five residents, the biggest city around the volcano. The eruption occurred in 1990, which was preceded by a number of earthquakes that began in November, 1989. The tremor was noted four months before the first eruption. In late January, 1991, a continuous tremor was noted beneath the volcano and the eruption followed on February 12, 1991.

Since May, 1991, the dome growth continued and dome-collapse pyroclastic flows happened frequently, while around ten thousand pyroclastic flows were counted. Forty-four people, including French and American volcanologists, were killed by the pyroclastic flows, and more than two thousand buildings were destroyed by the pyroclastic flows and lahars. The dome continued to grow for four more years; hence, the eruptions regularly appeared for five years.

Japanese scientists keep closely monitoring Unzen as a candidate for the long-lived dome growth. A special issue on "Unzen eruption: Magma Ascent and Dome Growth" was published from Elsevier (Journal of Volcanology and Geothermal Research, vol. 89, nos.1-4, 1999) and other papers continue to be published. A scientific research project at Unzen with drilling into the volcanic body started in April, 1999, in order to understand an eruption mechanism and a magmatic activity of magma at Unzen and to count a volcanic disaster that a future eruption can bring about. The volcano was designated a Decade Volcano in 1991 as a part of the United Nations' International Decade for Natural Disaster Reduction due to its history of furious activity and location in a densely populated area.

Another volcano, famous for its violent activity in Japan, is Sakurajima. Sakurajima is an active volcano and a former island, since the eruption of 1914 connected it to the Osumi Prefecture. There has been a great eruption and an activity of the volcano continues today, throwing out large amounts of volcanic ash. The Sakurajima Volcano Observatory was set up in 1960 to monitor eruptions. Studying and monitoring of the volcano and predictions of large eruptions are particularly important, since Sakurajima is located in a densely populated area with Kagoshima's six hundred thousand people only a few kilometers from the volcano.

Unzen and Sakurajima are the best-studied volcanoes in the world, for their research is of vital importance for the human population of close areas and the information about them can help understand the nature and character of volcanoes in general, though each volcano and its behavior are unique.

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