Rill

Japanese: rill

…Rain that falls on a slope collects in small depressions as it flows down, forming countless streams. These streams are called rills, and as the water collects with each rain, it erodes them deeper, forming small V-shaped valleys with steep valley walls. Furthermore, valley head erosion also occurs, increasing the length of the valley. …

From [Erosion]

…Rain wash is the process by which rainwater directly erodes the land. Rain erosion includes splash erosion, in which rainwater collides with the soil and moves it; rill erosion, in which rainwater flows over the ground and turns into rills, which move the soil particles and create shallow depressions in the ground; sheet erosion, in which numerous rills cover the ground and spread out, resulting in shallow erosion of the land as a whole; and gully erosion, in which rills gather and carve gullies. Rain erosion is most noticeable on gentle slopes such as the foothills of volcanoes, flat surfaces such as continental plateaus, and terraced surfaces, and occurs in places relatively higher than the head of a river valley. …

*Some of the terminology explanations that mention "rill" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…斜面に降った雨は流下する途中でわずかな凹地に集中し，無数の流れの筋をつくる。この筋は細溝（さいこう）(リルrill)と呼ばれ，雨のたびに水が集中して深く削られ，急な谷壁を持つV字型の小谷が形成される。さらに谷頭浸食も加わって，谷の長さも大きくなる。…

【浸食作用】より

…雨食rain washは雨水が直接に土地を削り取る作用で雨洗ともいう。雨食には降雨が衝突して土を動かす雨滴浸食splash erosion，雨水が地表を流れて細流(リルrill)となり，土粒が動かされて地面に浅いくぼみがつく細流浸食(rill erosionリル･エロージョン)，幾多の細流が地面を覆って広がる布状洪水sheet floodによって土地が全体的に浅く削られる布状浸食sheet erosion，さらに細流が集中して雨裂(雨溝，ガリーgully)を刻むガリー浸食gully erosionが含まれる。雨食が目だって作用するのは火山麓のような緩傾斜面や大陸台地のような平たん面や段丘面などであり，河川の谷頭よりも相対的に上位にあたる場所におこる。…

※「rill」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

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