Report on Asosan (Japan) — March 1985

Scientific Event Alert Network Bulletin, vol. 10, no. 3 (March 1985)
Managing Editor: Lindsay McClelland.

Asosan (Japan) Moderate ash emission; volcanic flame

Please cite this report as:

Global Volcanism Program, 1985. Report on Asosan (Japan). In: McClelland, L (ed.), Scientific Event Alert Network Bulletin, 10:3. Smithsonian Institution. http://dx.doi.org/10.5479/si.GVP.SEAN198503-282110.

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Asosan

Japan

32.884°N, 131.104°E; summit elev. 1592 m

All times are local (unless otherwise noted)


Moderate ash-laden emissions from Naka-dake were occasionally observed in February and March. Gray plumes were seen on 8, 17-18, and 25-28 February. Ash accumulation on 26 February was 295 g/m at JMA's [Asosan Weather Station] (at the SW foot of Naka-dake [1.2 km from the crater]). On 1 March, the emission from the pit that had been active from January through February declined rapidly, although a new pit formed about 40 m N of the older one. Ash emission resumed the next day. Volcanic flame [from the pit on the crater floor was observed during visits] the nights of 6 and 25 March.

In late December, the press reported that volcanic tremors were continuously felt. However, JMA noted that average tremor amplitude was within the range of 0.1-0.3 µm through December and January. As of 1 April, tremor remained at about the same level.

Geologic Background. The 24-km-wide Asosan caldera was formed during four major explosive eruptions from 300,000 to 90,000 years ago. These produced voluminous pyroclastic flows that covered much of Kyushu. The last of these, the Aso-4 eruption, produced more than 600 cu km of airfall tephra and pyroclastic-flow deposits. A group of 17 central cones was constructed in the middle of the caldera, one of which, Nakadake, is one of Japan's most active volcanoes. It was the location of Japan's first documented historical eruption in 553 AD. The Nakadake complex has remained active throughout the Holocene. Several other cones have been active during the Holocene, including the Kometsuka scoria cone as recently as about 210 CE. Historical eruptions have largely consisted of basaltic to basaltic-andesite ash emission with periodic strombolian and phreatomagmatic activity. The summit crater of Nakadake is accessible by toll road and cable car, and is one of Kyushu's most popular tourist destinations.

Information Contacts: JMA.