Report on Hakoneyama (Japan) — 8 August-14 August 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 8 August-14 August 2001
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2001. Report on Hakoneyama (Japan). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 8 August-14 August 2001. Smithsonian Institution and US Geological Survey.
35.233°N, 139.021°E; summit elev. 1438 m
All times are local (unless otherwise noted)
Elevated seismicity had been recorded at Hakone during June 2001 to at least 8 August. The seismicity was associated with a small amount of inflation that was centered at the volcano. Earthquake hypocenters occurred at depths less than 5 km beneath the volcano. A small swarm was also recorded under the northern end of the Ashino-ko (caldera lake). JMA noted that the change in activity might not be a precursor to an eruption since similar activity has occurred in the past that was not followed by an eruption.
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.