Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Oral

S (Solid Earth Sciences) » S-EM Earth's Electromagnetism

[S-EM17] Geomagnetism, Paleomagnetism and Rock Magnetism

Mon. May 21, 2018 10:45 AM - 12:15 PM A03 (Tokyo Bay Makuhari Hall)

convener:Nobutatsu Mochizuki(Priority Organization for Innovation and Excellence, Kumamoto University), Hisayoshi Shimizu(Earthquake Research Institute, University of Tokyo), Chairperson:Hoshi Hiroyuki(Department of Science Education, Aichi University of Education), Mochizuki Nobutatsu(熊本大学)

11:15 AM - 11:30 AM

[SEM17-09] Paleomagnetic study on the pyroclastic deposits of the Shikotsu caldera-forming eruption: Estimating the temporal gaps between the eruption phases

*Nobutatsu Mochizuki1, Takeshi Hasegawa2, Mitsuhiro Nakagawa3 (1.Priority Organization for Innovation and Excellence, Kumamoto University, 2.Department of Earth Sciences, College of Science, Ibaraki University, 3.Department of Natural History Sciences, Graduate School of Science, Hokkaido University)

Keywords:paleomagnetic direction, paleomagnetic secular variation, non-welded pyroclastic flow deposit, caldera-forming eruption

We reported a preliminary paleomagnetic results of the pyroclastic deposits of the 40 ka Shikotsu caldera-forming eruption. Geological observation on the pyroclastic deposits indicated that these volcanic deposits were classified into five eruption phases. In order to estimate a possible temporal gap between these eruption phases, we conducted paleomagnetic measurements of the pyroclastic flow deposits and surge deposits. Non-welded pyroclastic flow deposits and surge deposits were collected using an improved sampling procedure; a cube guide was firstly fixed to the outcrop, and subsequently a cube was put into the outcrop trough the cube guide, and then the orientation of the cube was precisely measured on the front plane of the cube guide. The phases 2 and 3 of non-welded pyroclastic flow deposit have indistinguishable paleomagnetic directions, suggesting that these two phases occurred within the order of tens years. The paleomagnetic direction of the phase 4 of non-welded pyroclastic flow deposit is distinguishable from that of phase 3, suggesting a temporal gap between phases 3 and 4 is about 100 years. These paleomagnetic data will contribute to estimating the temporal sequence of the process of the Shikotsu caldera-forming eruption.