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Report on Asosan (Japan) — January 1980


Scientific Event Alert Network Bulletin, vol. 5, no. 1 (January 1980)
Managing Editor: David Squires.

Asosan (Japan) Short explosive eruption; 1979 activity reviewed

Please cite this report as:

Global Volcanism Program, 1980. Report on Asosan (Japan) (Squires, D., ed.). Scientific Event Alert Network Bulletin, 5:1. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198001-282110



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

All times are local (unless otherwise noted)

Activity stopped on 28 November after strong ash emission through most of the month (table 2). Between June and November, ash caused about 1 billion yen ($4 million) in damage to crops and forests. No further ashfalls were observed until an explosion at 2107 on 26 January deposited 3 cm of ash and fist-sized scoria on the rim of Naka-dake, the source crater. A small amount of ash fell on Aso-machi town, at the base of the volcano. The explosion caused no damage, and the volcano returned to quiescence the next day.

Table 2. Monthly ashfall in thousands of tons, June-December 1979, as estimated by personnel from JMA's [Aso-san Weather Station].

Month Ashfall (tons)
Jun 1979 1,420,000
Jul 1979 1,620,000
Aug 1979 1,590,000
Sep 1979 300,000
Oct 1979 970,000
Nov 1979 3,270,000
Dec 1979 0
TOTAL 9,170,000

Geological Summary. 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 km3 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 CE. 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.