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Magma residence time of magma chambers at shallow crustal depths in past caldera eruptions in Japan

Yoshiyuki Yasuike 1, Nobuo Geshi2, Keiko Matsumoto3, Ikuko Yamada3, Popa Razvan-Gabriel4, Bachmann Olivier4

  • Affiliations:  1Division of Research for Earthquake and Tsunami, Nuclear Regulation Authority, Japan;2Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University, Japan;3Research Institute of Earthquake and Volcano Geology, The National Institute of Advanced Industrial Science and Technology, Japan;4Institute of Geochemistry and Petrology, ETH Zürich, Zürich, Switzerland 

  • Presentation type: Talk

  • Presentation time: Thursday 11:00 - 11:15, Room R380

  • Programme No: 3.11.3

  • Theme 3 > Session 11

Abstract

In Japan, caldera volcanoes that can cause catastrophic eruptions are located in southern Kyushu, Hokkaido, and northern Tohoku. In volcanic hazard assessment for nuclear facilities, it is important to evaluate the activity potential of caldera volcanoes. In order to establish a method for evaluating it, we conducted material science studies focusing on the accumulation process of magma chambers as a preparation process for past caldera forming eruptions in Japan. The accumulation depth of magma reservoirs, magma accumulation time, and magma residence time just before eruption were estimated for the past active caldera volcanoes. These magma accumulation conditions were estimated using orthopyroxene, which is basically the same crystal. Magma accumulation time was also estimated by the U/Th method using ilmenite. As a result, it was estimated that the upper surface depth of magma chambers in the studied caldera volcano is 4 to 8 km, the crystal ages obtained by the elemental diffusion and U/Th methods are consistent with each other, and the magma accumulation time scales are long, ranging from several thousands to several tens of thousands of years. The residence time of magma chambers in the shallow crust was estimated to be at least several hundred to several thousand years. Based on the obtained information on the preparatory process of caldera eruptions, we propose a caldera activity assessment method for nuclear facilities on caldera volcanoes that combines geophysical surveys and eruption scenarios.