The tephra layers known with eruption ages play an important role in an investigation of tsunami history and archaeology in addition to volcanic history in Hokkaido, Japan. We investigated the event and tephra layers of the Late Holocene in the Pacific coast of western Hokkaido, where the stratigraphy of the Late Holocene has not been clarified. Surveys in coastal peatlands, mostly undisturbed deposits, have allowed for the discovery of thin tephra layers. The newly discovered tephra layers at the unexplored site were used to describe facies, observation under a polarization microscope, refractive index measurement of volcanic glasses, and chemical analysis, and correlated with the reported widespread tephras. We conducted wide-area field surveys and succeeded in revealing a wider distribution of tephra layers than previously known. The distribution of volcanic ash in the coastal area will contribute to the investigations of future volcanic and coastal hazards.
Keywords: Hokkaido; Komagatake volcano; Late Holocene; Pyroclastic fall deposit; Tarumae volcano; Tephra stratigraphy; Usu volcano.
© 2020 The Author(s).