sentence: Some valleys are made by glaciers which are slow-moving rivers of ice.
sentences_before: A 'valley' is a type of landformation. Valleys often start as a downward fold between two upward folds in the surface of the Earth. A valley is made deeper by a stream of water or a river as it flows from the high land to the lower land, and into a lake or sea.
sentences_after: When a valley is made deeper or wider by water or ice, this is called erosion. Wind can also make valleys larger by erosion.
concept_name: valley
headings: Valley