Report on Asosan (Japan) — 29 April-5 May 2015
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 29 April-5 May 2015
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2015. Report on Asosan (Japan). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 29 April-5 May 2015. Smithsonian Institution and US Geological Survey.
32.884°N, 131.104°E; summit elev. 1592 m
All times are local (unless otherwise noted)
JMA reported that, based on seismic data, the eruption from Asosan’s Nakadake Crater that began on 25 November 2014 continued during 27 April-1 May. Ashfall was reported in areas to the SE and NE on 27 April. Field surveys were conducted on 27 April and 1 May; observers noted an off-white plume rising from the vent. A plume rose as high as 1.2 km above the crater rim on 29 April. The Alert Level remained at 2 (on a scale of 1-5).
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 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.