Glaciers sculptured all sides of Jackson Hole and filled it with ice to an elevation between 1,000 and 2,000 feet above the present valley floor. The visitor who looks eastward from the south entrance to the park can see clearly glacial scour lines that superficially resemble a series of terraces on the bare lower slopes of the Gros Ventre Mountains. Southward-moving ice cut these features in hard rocks. Elsewhere around the margins of Jackson Hole, especially where the rocks are soft, evidence that the landscape was shaped by ice has been partly or completely obliterated by later events. Rising 1,000 feet above the floor of Jackson Hole are several steepsided buttes (figs. [13] and [55]) described previously, that represent “islands” of hard rock overridden and abraded by the ice. After the ice melted, these buttes were surrounded and partly buried by outwash debris.
Figure 12. “The Potholes,” knob and kettle topography caused by melting of stagnant ice partly buried by outwash gravel. Air oblique view north from over Burned Ridge moraine (see [fig. 61] for orientation). Photo by W. B. Hall and J. M. Hill.
The story of the glaciers and their place in the geologic history of the Teton region is discussed in more detail later in this booklet.
Figure 13. Radar image of part of Tetons and Jackson Hole. Distance shown between left and right margins is 35 miles. Lakes from left to right: Phelps, Taggart, Bradley, Jenny, Leigh, Jackson. Blacktail Butte is at lower left. Channel of Snake River and outwash terraces are at lower left. Burned Ridge and Jackson Lake moraines are in center. Lava flows at upper right engulf north end of Tetons. Striated surfaces at lower right are glacial scour lines made by ice moving south from Yellowstone National Park. Image courtesy of National Aeronautics and Space Administration.
MOUNTAIN UPLIFT
Mountains appear ageless, but as with people, they pass through the stages of birth, youth, maturity, and old age, and eventually disappear. The Tetons are youthful and steep and are, therefore, extremely vulnerable to destructive processes that are constantly sculpturing the rugged features and carrying away the debris. The mountains are being destroyed. Although the processes of destruction may seem slow to us, we know they have been operating for millions of years—so why have the mountains not been leveled? How did they form in the first place?
Kinds of mountains
There are many kinds of mountains. Some are piles of lava and debris erupted from a volcano. Others are formed by the bowing up of the earth’s crust in the shape of a giant dome or elongated arch. Still others are remnants of accumulated sedimentary rocks that once filled a basin between preexisting mountains and which are now partially worn away. An example of this type is the Absaroka Range 40 miles northeast of the Tetons (figs. [1] and [52]).