3: Topography of Zao Volcano

   As a whole, near original surfaces are preserved in the younger edifices, while the older edifices are eroded. Additionally, many collapsed scarps are present, particularly on the edges of the volcanic edifices. Many of these are by landslide or collapse. The debris avalanche deposits are sometimes found in the direction of their openings. In this geological map, we indicate collapsed walls that are likely the sources of landslides and debris. In particular, the Sukawa Mudflow (Yagi et al., 2005) about 70 ka, the main source of which is Ryuzan Volcano of the Kita-zao Volcanoes, is composed of debris avalanche deposits. This mudflow is quite large in scale and is found from Zao Hot Springs area to the west, forming a flow mound. At the center of Zao Volcano, between Kumanodake and Kattadake, a horseshoe-shaped collapsed/eroded wall opening to the east with approximately 2 km in diameter is present and known as the Umanose Caldera (Sakayori, 1992). This caldera has been interpreted as an erosion caldera (Ban, 2013). The youngest cone Goshikidake has been formed in the caldera. The Okama crater lake is present with a clear crater shape, which is a crater lake of a pyroclastic cone Goshikidake. To the west of Okama and near Umanose, a normal fault occurs with an easterly dip and a north¬–northwest to south–southeast strike (Oba and Konda, 1989).

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