[S-VC32] Mitigation of volcanic disasters - basic and applied researches

[SVC32-11] Publication series of large-volume ignimbrites 2: Distribution Map of Shikotsu Ignimbrite, Central Hokkaido, Japan

*Shinji Takarada¹, Mitsuhiro Nakagawa², Mizuho Amma-Miyasaka², Takahiro Yamamoto¹, Tadashi Yamasaki¹, Yasuaki Kaneda³, Nobuo Geshi¹ (1.Geological Survey of Japan, AIST, 2.Hokkaido University, 3.Ibaraki University)

Keywords:Ignimbrite, Distribution Map, Large-volume, Shikotsu, Volcanic Disaster Mitigation

After the Tohoku earthquake in 2011, society has focused on geological events which can cause an infrequent but severe disasters. Mainly, massive eruptions with large-scale pyroclastic flows can generate disastrous impacts not only near the volcano but also over a wide area. Geological Survey of Japan (GSJ), AIST has started to publish a series of maps that display the distributions of large-volume ignimbrites, which erupted during the late Pleistocene in Japan, collaborating with Universities. The "Distribution Map of Large-volume Ignimbrite in Japan" series provides information on the distribution and characteristics of volcanic deposits from large-scale explosive eruptions based on the compiled results of geological field surveys carried out by GSJ and borehole data. Large-scale explosive eruptions and the related emplacement of ignimbrite deposits over vast areas have the potential to cause massive disasters, although such events are infrequent. The aim of publishing the distribution maps of large-volume ignimbrites in Japan is to place fundamental constraints on the impacts of large-scale eruptions that will help mitigate potential disasters in the future. "Distribution Map of Ito Ignimbrite and associated deposits, Aira Caldera, Japan," which is the first publication of this series, was published in Jan. 2022. The second publication, "Distribution Map of Shikotsu Ignimbrite and associated deposits, Shikotsu Caldera, Japan," was published in Dec. 2022. An outline of the Distribution Map of Shikotsu Ignimbrite is introduced.

"Distribution Map of Shikotsu Ignimbrite and associated deposits, Shikotsu Caldera, Japan," contains a 1:250,000 scale map of the distribution of the Shikotsu Ignimbrite in the area within ~40 km from Shikotsu Caldera, Central Hokkaido, Japan. Distributions of the Upper and Lower Units of the Shikotsu Ignimbrite are shown on the map. In addition to the distribution of the Shikotsu ignimbrite on the ground surface, this map also shows the subsurface distribution of the ignimbrite based on borehole data and publication data. The map also indicates point data of the distribution of the altitude and the thickness of the ignimbrite, the maximum size of pumice and lithic fragments in the ignimbrite, and the preferred orientation of the pumice fragments (Figure). The distribution of the Shikotsu 1 Tephra Fall deposit is also shown. The distribution map contains an explanation booklet that provides background geological information about the Shikotsu caldera and the sequence of the Shikotsu Eruption, as well as descriptions of the Shikotsu ignimbrite and associated deposits. The explanation booklet provides a pictorial of representative field occurrences of the Shikotsu Ignimbrite and associated deposits. All contents in PDF and GIS files can be downloaded from the website: https://www.gsj.jp/Map/JP/lvi.html.

GSJ plans to publish distribution maps for the series on large-volume ignimbrites in Japan: Aso-4, Aso-3, Toya, Ata, Kutcharo IV, Kutcharo I, Hachinohe, Ofudo, Koya, and Hakone-Tokyo ignimbrites. The "Distribution Map of Large-volume Ignimbrite in Japan" series will use a standard format to present the distribution of large-volume ignimbrites and associated ash fall deposits. These publications are expected to be used by researchers in universities and research institutes and will provide information about the possible extent of affected areas during future large-volume eruptions. This information could play a crucial role in disaster mitigation plans operated by national and regional governments and the construction of resilient infrastructure.

Takarada, S., Nakagawa, M., Amma-Miyasaka, M., Yamamoto, T., Yamasaki, T., Kaneda, Y. and Geshi, N. (2022) Distribution Map of Shikotsu Ignimbrite and associated deposits, Shikotsu Caldera, Japan. Distribution map of large-volume ignimbrites in Japan, no. 2, Geological Survey of Japan, AIST, 34p. (in Japanese with English abstract).