Report on Hakoneyama (Japan) — 1 July-7 July 2015
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 1 July-7 July 2015
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2015. Report on Hakoneyama (Japan) (Sennert, S, ed.). Weekly Volcanic Activity Report, 1 July-7 July 2015. Smithsonian Institution and US Geological Survey.
35.233°N, 139.021°E; summit elev. 1438 m
All times are local (unless otherwise noted)
According to a news article a drone that surveyed the Owakudani hot spring district at Hakoneyama recorded damage to three hot spring supply facilities; an exclusion zone for visitors was in effect due to increased seismic activity and an Alert Level raise to 2 (on a 5-level scale) on 6 May. At 1230 on 30 June a small-scale eruption occurred and the Alert Level was raised to 3. On 1 July a news article noted another small-scale eruption (occurring between 0400 and 0500), and JMA reported that ash deposits were visible with the webcam. During fieldwork on 2 July, scientists confirmed new fumaroles at Owakudani that were vigorously emitting white plumes; the new fumaroles had formed during 29-30 June. White fumarolic plumes continued to be emitted through 5 July.
Geological Summary. 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.