Report on Hakoneyama (Japan) — 2 October-8 October 2019
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 2 October-8 October 2019
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2019. Report on Hakoneyama (Japan). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 2 October-8 October 2019. Smithsonian Institution and US Geological Survey.
35.233°N, 139.021°E; summit elev. 1438 m
All times are local (unless otherwise noted)
On 7 October JMA lowered the Alert Level for Hakoneyama to 1 (the lowest level on a 5-level scale), noting that the number of volcanic earthquakes had decreased to background levels after a spike in seismicity was recorded in May. Inflation had been detected but had become almost stagnant after late August. Fumaroles in the Owakudani hot springs area continued to be active, with gas-and-steam plumes rising 100-400 m above their vents.
Geologic Background. Hakoneyama volcano is truncated by two overlapping calderas, the largest of which is 10 x 11 km wide. The calderas were formed as a result of two major explosive eruptions about 180,000 and 49,000-60,000 years ago. Scenic Lake Ashi lies between the SW caldera wall and a half dozen post-caldera lava domes that were constructed along a NW-SE trend cutting through the center of the calderas. Dome growth occurred progressively to the NW, and the largest and youngest of these, Kamiyama, forms the high point. The calderas are breached to the east by the Hayakawa canyon. A phreatic explosion about 3000 years ago was followed by collapse of the NW side of Kamiyama, damming the Hayakawa valley and creating Lake Ashi. The latest magmatic eruptive activity about 2900 years ago produced a pyroclastic flow and a lava dome in the explosion crater, although phreatic eruptions took place as recently as the 12-13th centuries CE. Seismic swarms have occurred during the 20th century. Lake Ashi, along with the thermal areas in the caldera, is a popular resort destination SW of Tokyo.