Eventually the rock will break away. This a valley which was V-shaped but has been eroded by ice. The velley sides are steeper and the valley floor flatter after the ice melts. Hence the name U-shaped valleys. Hanging Valleys - These occur when glaciers at higher levels than the main valley didn't experience such powerful erosion.
Tributary streams enter the valley as waterfalls from hanging valleys.
The following links are to web sites containing case study infomation about Helvellyn, an area containing glaciated landforms in the Lake District, England.