Arras (topography) - Arras

...Slopes are distributed with solifluction lobes, which are tongue-shaped structures with slight undulations of several tens of centimeters at the front of the solifluction, and layered slope deposits consisting of alternating layers of fine-grained material less than a few millimeters in size and rock fragments several centimeters in size. In permafrost zones, landforms such as ice wedges, which are frozen water that fills frost cracks, huge polygonal soils with diameters of several tens of meters, palsas, which are mounds of peat with thin layers of ice and several meters in diameter to several tens of meters in height, large hills with ice blocks inside, pingos, ice agglomerates accumulated under the ground surface, and shallow basins and thawing lakes formed by melting ice agglomerates, are developed. In the cross section of the frozen soil phenomenon, thaw mixing phenomena such as involutions, which are complexly distorted folding and intrusion structures, and the rising of gravel in the soil with its long axis oriented vertically, are seen. ...

*Some of the terminology explanations that mention "Aras (terrain)" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…斜面にはソリフラクションの前面が高さ数十cmの微起伏をもって舌状にのびたソリフラクションローブsolifluction lobe，数mm以下の細粒物質と数cm大の岩片が互層をなす成層斜面堆積物が分布する。永久凍土地帯では，凍結割れ目を満たす水が凍った氷楔（ひようせつ）ice wedge，それが作る径数十mの巨大多角形土polygons，氷の薄層をもつ径数m～数十m，高さ数mの泥炭の高まりであるパルサpalsa，さらに大型で中に氷塊をもつ小丘ピンゴpingo，地表下に集積した集塊氷，それが溶けてできた浅い盆地アラスalasや融解湖などの地形が発達する。凍土現象の断面には，インボリューションinvolutionという複雑にゆがんだ，褶曲･貫入構造や，土中の礫が長軸を垂直方向に向けた礫の立ち上がりなどの，融凍攪拌現象がみられる。…

※「アラス（地形）」について言及している用語解説の一部を掲載しています。

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