Downward erosion - Downward erosion

… As river erosion progresses, the riverbed lowers and the valley widens. River erosion that lowers the riverbed is called incision or deepening, and river erosion that acts at a slight angle is called lateral erosion, but lateral erosion works diagonally downward rather than horizontally. Therefore, the widening of the valley is not caused only by lateral erosion, but is the result of the material that makes up the slope moving downward and then being carried away by the flowing water while incising it. …

*Some of the terminology explanations that refer to "downward erosion" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…　河食の進行につれて河床は低下し，谷幅は広がる。河床を低下させるような河食を下刻（かこく）または下方浸食deepeningとよび，多少とも斜めに働きかける河食を側刻または側方浸食lateral erosionとよぶが，側刻は水平方向というよりは斜め下方に働く。したがって谷幅の拡大は側刻だけが原因ではなく，斜面を構成する物質が下方へ移動した後に流水が下刻を行いながら運び去った結果である。…

※「下方浸食」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