Complete the Words

Many of the most dramatic valleys in mountain regions were shaped not by rivers but by glaciers. As a glacier (1)sli___ downhill, (2)ro___ (3)fro___ (4)in__ the (5)bot___ of the ice (6)scr___ the (7)gro___ (8)ben____ it like a (9)gi___ file, (10)wide____ and deepening the valley floor. Because ice fills the whole valley rather than a narrow channel, glaciers leave behind a broad U shape, while rivers usually cut a narrower V. When the ice finally melts, these valleys are often left with steep walls, flat floors and, in many cases, long lakes.