Japan Geoscience Union Meeting 2019

Presentation information

[J] Poster

S (Solid Earth Sciences ) » S-VC Volcanology

[S-VC39] Hydrothermal systems of volcanoes

Mon. May 27, 2019 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall8, Makuhari Messe)

convener:Yasuhiro Fujimitsu(Department of Earth Resources Engineering, Faculty of Engineering, Kyushu University), Wataru Kanda(Volcanic Fluid Research Center, School of Science, Tokyo Institute of Technology), Takeshi Ohba(Department of chemistry, School of Science, Tokia University)

[SVC39-P09] Numerical model of the hydrothermal system at the Akakura Caldera in Kurikoma Area

*Yasuhiro Fujimitsu1, Daichi Yoshioka2 (1.Department of Earth Resources Engineering, Faculty of Engineering, Kyushu University, 2.Department of Earth Resources Engineering, Graduate School of Engineering, Kyushu University)

Keywords:hydrothermal system, numerical modeling, caldera

The Akakura Caldera is located at the southern part of Kurikoma Area, and is one of the old calderas in Tohoku District. It was formed by the huge pyroclastic flow about 3 million years ago. This study conducts numerical simulations of the hydrothermal system development that is modeled after the Akakura Caldera. In the numerical modeling, the structures such as a magma chamber that was associated with the formation of the caldera structure (Magma 1), high permeable fracture zone associated with a reverse fault and a circular fracture, impermeable layers filled with quartz and fracture clouds were considered and emplacement of a magma chamber that generated the post-caldera volcanic activity of 0.8 to 1.4 Ma (Magma 2) was also included. The calculation period was 3 million years from the emplacement of Magma 1 to the present and Magma 2 was emplaced 2.2 million years after the emplacement of Magma 1. The initial temperature of Magmas 1 and 2 was set as 1000 deg C. For the size of Magma 2, two kinds of diameter (2.5 km and 3.5 km) were adopted for the modeling. As a result, it was indicated that a supercritical geothermal fluid region still remains at the depth of 5 km until about 100 thousands years after the emplacement of Magma 2. It is inferred that a high enthalpy hydrothermal system can exist at a piston-cylinder type caldera with a post-caldera volcanic activity like the Akakura Caldera until about 10 thousands years after the commencement of the post-caldera volcanic activity.