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Relationship between caldera structure and associated pyroclastic flows: The case of the Atosanupuri volcano, eastern Hokkaido, Japan

Akiko Matsumoto1, Mitsuhiro Nakagawa1, Hiroshi, Kishimoto1,2, Kenta Ueno1, Takeshi Hasegawa3, and Kentaro Takeda1,4

  • Affiliations: 1Graduate School of Science, Hokkaido University, Japan; 2Japan Meteorological Agency; 3College of Science, Ibaraki University, Japan; 4Japan Petroleum Exploration Co., Ltd. 

  • Presentation type: Poster

  • Presentation time: Friday 16:30 - 18:00, Room Poster Hall

  • Poster Board Number: 137

  • Programme No: 3.4.21

  • Theme 3 > Session 4

Abstract

Atosanupuri volcano, located in eastern Hokkaido, Japan, is one of the post-caldera volcanoes of the Kutcharo caldera volcano. The volcano consists of the somma, the inflectional caldera (6 * 3.5 km in total length: Atosanupuri caldera) and several lava domes. Its activity started after the 40 ka Kutcharo pyroclastic flow I eruption: the somma lavas extruded and a large pyroclastic flow (Atosanupuri pyroclastic flow: Ap) erupted to form the Atosanupuri caldera. Several lava domes were then built in and around the caldera. Although it is considered that the Ap eruption was accompanied by the formation of the caldera, its eruption scale and sequence are still unknown. To clarify the whole sequence of the Ap eruption, we investigated the tephra stratigraphy in the distal area and correlated the distal tephra with the proximal Ap deposits based on the petrological characteristics of their juvenile materials. The results show that the Ap eruption was not a single event, but a series of VEI 4-5 eruptions over 10 kyrs (ca. 40 km3 in total volume), and that three magma systems were active in turn. According to the topographic map made from the 1 m DEM data, the Atosanupuri caldera seems to consist of multiple calderas and craters. This feature is consistent with multiple pyroclastic eruptions: i.e., the Atosanupuri caldera is a composite caldera. The Ap eruption is comparable in scale to the caldera-forming eruptions in general. Therefore, it would be better to re-examine its implication in the caldera cycle of the Kutcharo caldera volcano.