Japan Geoscience Union Meeting 2015

Presentation information


Symbol S (Solid Earth Sciences) » S-VC Volcanology

[S-VC45] Active Volcanism

Thu. May 28, 2015 11:00 AM - 12:30 PM 304 (3F)

Convener:*Yosuke Aoki(Earthquake Research Institute, University of Tokyo), Chair:Teruki Oikawa(Institute of Earthquake and Volcano Geology, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology), Masayuki Murase(Department of Geosystem, College of Humanities and Sciences, NIHON University)

11:00 AM - 11:15 AM

[SVC45-10] Eruption sequence of Ontake-san (Ontake Volcano) 2014 eruption, based on the images and the field survey.

*Teruki OIKAWA1, Mitsuhiro YOSHIMOTO2, Setsuya NAKADA3, Fukashi MAENO3, Yoshihiro ISHIZUKA1, Yoshihiro TAKESHITA4, Jiro KOMORI5, Taketo SHIMANO6, Yasuhiro ISHIMINE7 (1.GSJ/AIST, 2.Mount Fuji Research Institute, Yamanashi Prefectural Government, 3.ERI, Univ. Tokyo, 4.Education, Shinshu Univ., 5.Teikyo Heisei Univ., 6.Social and Environmental,Tokoha Univ., 7.Department of Health Crisis Management, National Institute of Public Health)

Keywords:Ontakesan, Ontake Volcano, eruption sequence, recording images, interviews

Over 60 casualties including missing people were recorded in a phreatic eruption at Mount Ontake (3, 067 m) on 27 September 2014, 11:52. We clarified the eruption sequence of the 2014 eruption, based on the recording images (photographs and videos from climbers), the interviews with Workers in the mountain huts, and the field survey of the summit area. The onset of eruption was sudden without any clear surface precursory phenomena such as ground rumbling and strong smell of sulfur. The eruption started with pyroclastic surges descending about 2.5 km from the craters to SW and moving horizontally about 1 km to N and W beyond summit ridges. That time, rock fragments up to 50 cm showered densely on the summit area: 20-30 cm-across fell about 1.3 km away from the craters. In the summit area, the first 30 minutes of the eruption there was a violent falling rock fragments. Then, the number of falling rock fragments become gradually less. At that time, the plume rose up to maximum high (7 km above the summit); mud rain has been falling from the plume. In about 16:00 after, Lahar generated by the hot water overflowing from the crater, flowed down the Jigoku-dani.