著者

安仁屋 政武

出版者

京都大学ヒマラヤ研究会・人間文化研究機構 総合地球環境学研究所「高所プロジェクト」

雑誌

ヒマラヤ学誌 : Himalayan Study Monographs (ISSN:09148620)

巻号頁・発行日

vol.11, pp.212-221, 2010-05-01

---

アンナプルナ山域の東側を限っているマルシャンディ川沿いにトレックした折り, 河岸堆積物, 河床, 斜面地形などを観察して, 天然ダムがあったと同定・推定できる場所を8カ所に認めた. 天然ダムは標高が低いところでは山腹崩壊による土砂が河道を閉塞してできた堰止め湖, 標高が高く支谷に氷河がある地域では氷河前進による氷河湖である. これらについて概説し, さらに典型的な土砂ダムとしてタル, 氷河ダムとしてマナンにあるガンガプルナ・タルを取り上げて若干の考察を行った.During the trekking in July-August 2009 along Marsyangdi River, east of the Annapurna Himal, Nepal, I observed sediments exposed along the riverbank, riverbed morphology and slope topography, thereby recognizing traces of natural dams at eight places (Fig. 1). Those located at lower altitudes were caused by landslides that blocked the riverbed, whereas those located at higher altitudes where glaciers exist in the tributary valleys were created by either glacier advance or landslide. Glaciers that advanced from tributary valleys into Marsyangdi River blocked the main stream together with lateral moraines, thereby having become natural dams. After briefly describing each of these natural dams at eight places, I discussed about two types of dams using typical ones. One is a typical landslide dam located at Tal, north of Chyamche, (Marked (2) in Fig. 1: Photos 1 & 2). 'Tal' in Nepalese means 'lake'; however, the lake has been completely filled up and villagers since have settled the flood plain. The other are two moraine dams formed by Ganggapurna Glacier at Manang (Marked (7) in Fig. 1 & 2: Photos 4, 5 & 6). Ganggapurna Tal, located on the right side of the main stream, is a current lake that is dammed by the terminal moraine of the Little Ice Age (LIA). Another moraine-dammed lake was formed when Ganggapurna Glacier made a strong advance before the LIA, thereby blocking Marsyangdi River by the lateral moraine (LM2, Fig. 2 & Photo 5) and ice. This dam has been long since completely filled up as seen in Photo 6.