I need information about the volcano Unzen in Japan. I would be really glad if you could tell me everything you know about it. I think this program you have here is really good and I know that I'm going to use it a lot.

rocky Jakob - Iceland, Europe

Hi Jakob,

Everything that I know about Unzen is not very much. I can tell you that it is one of Japan's most active volcanoes. It is what is called a strato-volcano, made up of layers of both ash and lava flows, and that when it erupts it is usually explosive. The products of volcanoes like Unzen are thick viscous lava flows, ash, and pyroclastic flows. A pyroclastic flow is a mix of hot gas and ash that goes racing down the flanks of the volcano. Pyroclastic flows are sometimes up to 600 degrees C, and move at up to 200 km/hour.

The most recent eruption sequence began with increased seismicity in the fall of 1990. Some small eruptions began in spring of 1991, with some small explosions and small pyroclastic flows and mud flows, and most of Shimabara city, at the base of Unzen, was evacuated. In June of 1991 a pyroclastic flow went farther than the previous ones and killed a bunch of television news people, local residents, and 3 volcanologists. Since then a lava dome has been growing at the summit, and every few days part of the dome collapses off and rumbles down the slopes as a small pyroclastic flow.

In 1792 a huge piece of the volcano broke off and avalanched into the Ariake Sea. About 14,500 people were killed, mostly by tsunami that washed all the nearby coastlines.

There is a recent book called Volcanoes of the World, by Tom Simkin and Lee Seibert, and it might be a good place for you to start looking for basic information about Unzen.

I hope this helps to give you a start. Thank you for your kind words about the VolcanoWorld home page.

Sincerely,

Scott Rowland, University of Hawaii 

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