The Kobui Terrace in the vicinity of the Esan Volcano, southeastern part of the Oshima Peninsula, Hokkaido, is formed of the Kobui Formation consisting of sand and volcanic ash. This is underlain with unconformity by the Tertiary sediments and superposed with unconformity by the Menagawa Volcanic Ash. The Kobui Formation contains the drift woods of Picea, Abies and Larix and the associated pollen flora. The terrace can be traced from the foot of the Esan Volcano westwards to near Hakodate City, where three terraced plains are developed. The Kobui Terrace continues to the middle terrace among them. The Kobui Formation can be dated as the Last Interglacial Stage. On the southern foot of the Esan Volcano, the Kobui Formation comprises beds of ejecta originated from the somma of the volcano and the lava of the central cone overlies the Kobui Terrace. This lava partly flowed into the valleys dissected on the terrace plain. The central cone of the Esan Volcano may be dated as the Last Glacial Stage or as Recent.
