How can ice shape the land?

The surfaces of valley glaciers are littered with rocks which have tumbled down the mountainsides. Other rocks are frozen into the sides and bottoms of glaciers. These rocks turn the glaciers into gigantic files, because, as the glaciers move, the rocks scrape away at the land and gouge our more and more rocks. When the ice melts, steep sided, U-shaped valleys are striking evidence of the cutting power of glaciers.