Formation of the Moraine-like Saneyama Ridge Underneath the Cirque on Mt. Tateyama, Northern Japanese Alps

Abstract

This study revealed the formation of the moraine-like Saneyama Ridge as determined by geomorphological and geological surveys. It is located underneath the cirque in the Jodosawa Valley extending northward through the northern Japanese Alps, between Mt. Tateyama (3,015 m) to the east and the Midagahara volcano (approximately 2,670 m) to the west. The Saneyama Ridge consists mainly of lahar deposits, formed after glaciers on Mt. Tateyama melted due to pumice fall from the Midagahara volcano, with subglacial tills above and below them. These sediments were widely deposited in the lower Jodosawa Valley during the early stadials (95–47±9 ka) of the last glacial period. The eastern part of these sediments was eroded by running water in the Jodosawa Valley during a period after the early stadials (47±9 ka) of the last glacial period and before the phreatic explosions (30–18 ka) that blew away the western part of the sediment. The Saneyama Ridge was thus formed by the remaining sediment between the eastern channel of and the western craters in the lower Jodosawa Valley.