北八ヶ岳，地獄谷火口底の氷塊と一時的な火口湖

概要

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Ground ice and temporary lake were studied in the Jigokudani Crater (N36°03′44.82″, E138°20′45.82″) in a northern area of the Yatsugatake Volcanic Chain (Kita-yatsugatake). The crater, which is about 30 m deep, is located at 2108 m a.s.l., and is surrounded by subalpine coniferous forest where the mean annual air temperature is about 3°C. The ground ice survived in summer mainly because cold air blew down through voids between andesite blocks composing the crater wall. The ice remained throughout 2009, although it melted completely in September 2010. In 2010, a crater lake appeared in May and disappeared in early August. This survival period of the lake was probably much longer than in other years. We consider that the melting of ground ice was promoted by the long-lasting lake having a slightly positive temperature which contacted the ice directly.