[S-VC45] Active Volcanism

[SVC45-15] Preparatory process for the 2014 eruption in Ontake Volcano estimated from precise leveling (2006-2014)

*Masayuki MURASE¹, Fumiaki KIMATA², Rikio MIYAJIMA², Hitoshi, Y. MORI³, Yoshiko YAMANAKA⁴, Shinichiro HORIKAWA⁴, Kenjiro MATSUHIRO⁴, Takahiro OHKURA⁵, Shin YOSHIKAWA⁵, Hiroyuki INOUE⁵, Taketoshi MISHIMA⁵, Tadaomi SONODA⁶, Takeshi MATSUSHIMA⁷, Kazunari UCHIDA⁷ (1.Department of Geosystem, College of Humanities and Sciences, NIHON University, 2.Tono Research Institute of Earthquake Science, Association, 3.Institute of Seismology and Volcanology, Faculty of Science, Hokkaido University, 4.Graduate School of Encironmental Studies, University of NAGOYA, 5.Aso Volcanological Laboratory, Institute for Geothermal Sciences, Graduate School of Science, Kyoto, 6.Sakurajima Volcano Research Center, Disaster Prevention Research Institute, Kyoto University, 7.Institute of Seismology and Volcanology, Faculty of Sciences, Kyushu University)

Keywords:Ontake volcano, precise leveling

A preparatory process for the 2014 eruption in Ontake Volcano was estimated from vertical deformations detected by precise leveling. We installed leveling routes in the east part of Ontake volcano and conducted the precise leveling survey since 1999 (Kimata et al., 2004).
Here we focused on the vertical deformations during 2006-2014 to discuss the preparatory process for the 2014 eruption. Before 2006, slight uplift was detected just above the region of the most active earthquake cluster. The uplift, however, was detected around summit area after 2006. Despite the occurrence of eruption in 2007, slight uplift was continued to the 2009. The total value of the uplift during 2006 -2009 was about 1cm. The leveling survey was conducted with small part of the leveling routes in 2013. Although the result from the leveling survey with small distance is strongly affected by reference point, the result suggests that the slight uplift might be continued to the 2013. In the survey after 2014 eruption, the subsidence with about 1 cm was detected.
Based on the leveling results, possible preparatory process for the 2014 eruption in Ontake Volcano was as follows. The magma intruded to the shallow part of Ontake volcano in 2006 and small eruption occurred in 2007. The magma supply, however, was continued slightly after 2007 eruption and then 2014 eruption occurred. After 2014 eruption, magma with shallow part was deflated.