Stratigraphy, distribution, and petrographic properties of Holocene tephras in Hokkaido, northern Japan

Thirty-one widespread visible Holocene tephras in Hokkaido, northern Japan, were identified and their stratigraphic relationships were examined. Among these, three tephras from Komagatake volcano (Ko-c1, Ko-c2, and Ko-g), three from Tarumae volcano (Ta-a, Ta-b, and Ta-c), Us-1663 from Usu volcano, Ma-b from Mashu volcano, and B-Tm from Baegdusan volcano (on the boundary between North Korea and China) cover a large area of southern and eastern Hokkaido and are thus useful tephras for correlating sedimentary records and Holocene phenomena. All tephras were identified on the basis of their mineral composition and the refractive indices and major elements of their glass shards. The volcanic glass samples were dehydrated before refractive index measurement by heating at 400 °C for 12 h. Most Holocene tephras in Hokkaido can be easily identified on the basis of the refractive indices and major element compositions of volcanic glass.