When the glacier is moving down the side of the valley it scrapes of the rocks. The grinding changes the shape of the valley so that it is rounded.
A U-shaped valley, also known as a glacial trough, is a large valley with steep sides, and with a wide, flat valley floor. It is formed, as the alternative name suggests, by glacial activity in the...
melting glacier
U-shaped valleys are generally formed by the erosive effects of moving glaciers.
glaciers