A second photo from the western Alaska Range shows additional erosional features common to glaciers. Between two glaciated valleys a knife edge ridge is often formed called an arête. Where a mountain peak is surrounded by glaciers on all sides a pyramid-shaped horn is formed; the Matterhorn in Switzerland is the most famous example of this.
A large glacier occupying a valley and beginning at the headwaters of that valley is referred to as a trunk glacier. Smaller glaciers, sourced by smaller drainages, will enter the trunk glacier from the side. Often these smaller glaciers will cascade into the trunk glacier over an ice fall. When these glaciers melt they will leave behind U-shaped valleys and a steep hanging valley where the ice fall occurred.
It is difficult to fathom the erosional power of a glacier. At its maximum extent, the glacier that occupied Little Cottonwood Canyon was over twelve miles long, one to two miles wide with a thickness of 1,000-2,000’ of ice. A typical rate of movement along this glacier would be 5 to 10 feet/day, however; a surging glacier can travel in excess of 100 feet/day. Glaciers of this scale remove hundreds of feet of bedrock from the bottom and sides of a stream valley. They also smooth out irregularities in the valley bottom forming a consistent gradient.
| Merging glaciers in the western Alaska range display dramatic glacial features. |