Report on Asosan (Japan) — 14 August-20 August 2019
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 14 August-20 August 2019
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2019. Report on Asosan (Japan) (Sennert, S, ed.). Weekly Volcanic Activity Report, 14 August-20 August 2019. Smithsonian Institution and US Geological Survey.
32.8849°N, 131.085°E; summit elev. 1592 m
All times are local (unless otherwise noted)
JMA reported that increased eruptive activity at Asosan that began on 28 July paused at 1110 on 16 August. An eruptive event was recorded at 1627 on 18 August; elevated eruptive activity continued at least through 19 August. The Tokyo VAAC reported that the eruptive event on 18 August produced an ash plume that rose to 2.1 km (7,000 ft) a.s.l. Ash plumes rose to 1.5-2.1 km (5,000-7,000 ft) a.s.l. and drifted N and NW during 19-20 August. The Alert Level remained at 2 (on a scale of 1-5).
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.