Fig. 258.—The Valley of the American Fork. A V-shaped non-glaciated valley in the Wasatch Mountains of Utah. Compare [Fig. 259]. (Church.)
Fig. 259.—U-shaped valley resulting from glaciation. Little Cottonwood Canyon, Wasatch Mountains. (Church.)
Fig. 260.—Contrast between glaciated topography below and non-glaciated topography above. The minarets in the Sierras, Cal.
Fig. 261.—Contrast between glaciated topography below, and non-glaciated topography above. Needles Mountains, from slope west of Hidden Lake. (Cross, U. S. Geol. Surv.)
The deepening of a valley by glacial erosion may throw its tributaries out of topographic adjustment. Thus if a main valley is lowered 100 feet by glacial erosion while its tributary is not deepened, the lower end of the latter will be 100 feet above the former when the ice disappears. Such a valley is called a hanging valley (Figs. [262] and [263]). Such valleys are of common occurrence in regions recently glaciated, but now ice-free. Examples are common in the western mountains of North America and elsewhere.
Ice-caps which overspread the surface irrespective of valleys and hills, tend to reduce the angularities of the surface. Hills and ridges are cut down and smoothed (Figs. [264] and [265]); but since valleys parallel to the direction of movement are deepened at the same time, it is doubtful if the relief of the surface is commonly reduced by the erosion of an ice-cap.