Report on Asosan (Japan) — 28 April-4 May 2021
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
28 April-4 May 2021
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2021. Report on Asosan (Japan). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 28 April-4 May 2021. Smithsonian Institution and US Geological Survey.
32.884°N, 131.104°E; summit elev. 1592 m
All times are local (unless otherwise noted)
Volcanic tremor amplitude increased at Asoson at around 2100 on 2 May, prompting JMA to raise the Alert Level to 2 (on a scale of 1-5) at 2255. The public was warned to stay at least 1 km away from the crater. Sulfur dioxide emissions were low, at 200 tons per day on 3 May, and white steam plumes rose as high as 300 m above the crater rim.
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.