Circular soil - Enkeido

...Soil with gravel structured is classified as soil with a pattern formed by the separation of gravel in the soil, soil with no gravel or with poor selection and a pattern formed by the soil, and soil with vegetation covered is classified as soil with vegetation covered. Furthermore, soil is classified according to the planar shape as circular, polygonal, net, striped, and stepped, and the two are combined and called gravel stepped soil, soil polygonal soil, and vegetation covered circular soil. The size of the soil is small in tropical mountain areas with shallow freezing depth and temperate mountain areas such as Japan, and most of them are about a few centimeters to 1 meter in diameter or width, but huge polygonal soils with sides of tens of meters are distributed in the permafrost zones of Alaska and Siberia. ...

*Some of the terminology explanations that refer to "circular soil" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…土中の礫（れき）がより分けられて模様を作っているものを礫質構造土，土中に礫を含まないか，あっても淘汰が不良で，土が模様を作っているものを土質構造土，植物に覆われたものを植被構造土として区別する。さらに平面形によって円形土，多角形土，網状土，縞状土，階状土に分け，双方を組み合わせて礫質階状土，土質多角形土，植被円形土などと呼ぶ。その大きさは凍結深度の浅い熱帯山地や，日本のような温帯山地で小さく，直径または幅が数cmから1m程度のものが多いが，アラスカやシベリアの永久凍土地帯には，1辺が数十mの巨大多角形土が分布する。…

※「円形土」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。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報