ヤク-チャ(シベリア),バロ-(アラスカ),マッケンジ-デルタ(カナダ)におけるいくつかの典型的な永久凍土地形 (ノルデンショルド北氷洋周航百年記念シンポジウム)

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Scientific expeditions in permafrost regions were carried out at Yakutia, Siberia in the middle of August, 1972 and at Barrow, Alaska and Tuktoyaktuk, Mackenzie Delta in the summers of 1974 and 1977. I Yakutia, Siberia Field observations were conducted on permafrost around Lake Surdakh, which is located 250km northeast from Yakutsk, Siberia. Lake Surdakh is an alas, which is a depression formed by a thermokarst development in which local deep thawing has taken place in permafrost masses accompanied by the melting of ground ice. The shape of the alas is nearly round and the diameter of Lake Surdakh is about 4km. The lake is surrounded from all sides by a larch forest. The height of the basin cliffs is about 20m. At some places along the cliffs underground ices are exposed. The top of the ices is 1.5m below the top of the cliffs and the ices sink into the ground in a wedge-like shape. Observations were made as to the exposed ice, the soil around the exposed ice and the forest above the ground, and also on the some alases in the vicinity. II Barrow and Tukutoyaktuk Field observations were conducted on high center polygons, pingos, ice wedges and exposed massive ground ice, all of which showed characteristic land feature of the tundra area composed of permafrost. a. High center polygon Spreading gregariously, high center polygons formed an orthogonal net pattern near Footprint Creek, 3km southwest of NARL, Barrow. Each mound was 5-10m in width and 50-100cm in height. A crack ran along the trough between two neighboring mounds. The surface at the raised center of a mound was covered with vegetations including willow, birch and crowberry. Core samples showed the structures of layers; namely, the upper layer of 5-10cm in thickness was composed of mixture of roots, organic material, and silt, while the layer underneath was composed almost of ice-richpeat, which had such an extremely high water content as amounts to 1000-2000%, the ice being uniformly contained not in the form of ice lenses. Meanwhile, as for the trough, its surface was covered with gramineae or formed puddles, while the layer above the depth of 40-50cm was composed of silty soil and contained distinct ice lenses, whereas the layer below this depth was composed of ice, which was polycrystalline with ice crystals several cm in length and almost stretching vertically. Polygons studied by the authors exemplified the type of ice-wedge polygons.
社団法人東京地学協会の論文

著者

木下誠一
北海道大学低温科学研究所

ヤク-チャ(シベリア),バロ-(アラスカ),マッケンジ-デルタ(カナダ)におけるいくつかの典型的な永久凍土地形 (ノルデンショルド北氷洋周航百年記念シンポジウム)

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