Deposits of Caldera-forming Eruptions and Post-caldera Eruptions of the Shikotsu Caldera, Hokkaido

Abstract

 The Shikotsu caldera in southwestern Hokkaido is a collapse caldera formed by a large ignimbrite eruption at around 46 ka. During the caldera-forming eruption, a large volume of ignimbrite was ejected from the caldera and spread in all directions. A part of the flow reached the city of Sapporo. After the caldera-forming eruption, Eniwa, Fuppushi, and Tarumae volcanoes were formed as post-caldera volcanoes. The area of Chitose and Tomakomai, located east of the Shikotsu caldera, has several key outcrops that reconstruct volcanic activities of the Shikotsu caldera. This outcrop is in Tomakomai, about 20 km southeast of the caldera. Within this outcrop, three layers of pumice-fall deposits from Tarumae volcano can be recognized on the pumice flow deposit of the caldera-forming eruption of the Shikotsu caldera. A dark-colored paleosol separating these eruption deposits shows a hiatus between these Plinian eruptions. In the distance, Tarumae volcano, one of the post-caldera volcanoes of the Shikotsu caldera, is visible.

(Photo: Mitsuhiro NAKAGAWA;

Explanation: Mitsuhiro NAKAGAWA and Nobuo GESHI)