Figure 21 Glaciers can carve out large U-shaped valleys, such as this one in Glacier National Park, Montana.
Glaciers also widen and deepen the valleys through which they flow. When glaciers flow through V-shaped valleys cut by running water, they widen them into U-shaped valleys. Glacial valleys are U-shaped because the moving ice scours the entire valley, eroding rock from the valley's bottom and sides. Glacier National Park, shown in Figure 21, contains many U-shaped valleys that were carved by glaciers.
Unlike valley glaciers, continental glaciers tend to level large surface areas through the scraping and grinding of thick ice. Continental glaciers can enlarge and deepen natural depressions in the surface. These depressions then fill with water when the glaciers retreat. The Great Lakes and the Finger Lakes in New York are examples of glacial lakes that formed by this process.
Features Formed by Glacial Deposition
A glacier gathers and transports a huge amount of rock and soil as it moves. 
When a glacier melts, it deposits its load of sediment, creating a variety of landforms. Glacial sediment is called till. Till is an unsorted mixture of sediment containing fragments of many sizes. Giant boulders, gravel, sand, and pulverized rock dust are all found in till. Glaciers deposit till as they melt. The till forms moraines, mounds of sediment at the downhill end of the glacier and along its sides. As the How It Works box on page 722 explains, glacial deposits leave many traces in the landscape.
What are moraines?
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