As a glacier retreats, it may build a series of terminal moraines, marking pauses in the recession of the ice front. Streams issuing from the ice behind each new terminal moraine are incised more and more deeply into the older moraines and their outwash plains. Thus, new and younger layers of bouldery debris are spread at successively lower and lower levels. These surfaces are called outwash terraces.
Figure 8. East face of the Teton Range showing some of the glacial features, air oblique view. Cascade Canyon, the U-shaped valley, was cut by ice. The glacier flowed toward the flats, occupied the area of Jenny Lake (foreground), and left an encircling ring of morainal debris, now covered with trees. The flat bare outwash plain in foreground was deposited by meltwater from the glacier. The lake occupies a depression that was left when the ice melted away. National Park Service photo by Bryan Harry.
Figure 9. Cutaway view of a typical valley glacier.
Figure 10. Recently-built terminal moraine of the Schoolroom Glacier, a small ice mass near the head of the south fork of Cascade Canyon. The present glacier lies to the right just out of the field of view. The moraine marks a former position of the ice terminus; the lake (frozen over in this picture) occupies the depression left when the glacier wasted back from the moraine to its present position. Crest of the moraine stands about 50 feet above the lake level. Many of the lakes along the foot of the Teton Range occupy similar depressions behind older moraines. Photo by Philip Hyde.
Figure 11. Large ice-transported boulder of coarse-grained pegmatite and granite resting on Cretaceous shale near Mosquito Creek, on the southwest margin of Jackson Hole. Many boulders at this locality are composed of pegmatite rock characteristic of the middle part of the Teton Range. This occurrence demonstrates that boulders 40 feet in diameter were carried southward 25 miles and left along the west edge of the ice stream, 1,500 feet above the base of the glacier on the floor of Jackson Hole.
Just as the jagged ridges, U-shaped valleys, and ice-polished rocks of the Teton Range attest the importance of glaciers in carving the mountain landscape, the flat gravel outwash plains and hummocky moraines on the floor of Jackson Hole demonstrate their efficiency in transporting debris from the mountains and shaping the scenery of the valley.