Sheep and Taylor Mountains
Ancient Oceans

Glacial activity has shaped the present Centennial Range over its entire existence. Just as much as volcanic action and earth movement has created or built up these mountains, glacial erosion and weathering has given them character and worn them down. Obviously, mountain building must outpace erosion or we wouldn't see the mountains that we have today. We are currently in an interglacial period without glaciers. The last Glacial Maximum was about 22,000 years ago, but only 10,000 years ago the Centennial Valley may have still had glaciers. In fact, there have been over 10 glacial periods during the building of the Centennial Mountains over 2 million years, each of them creating glaciers that helped to carve the peaks and canyons even deeper.

Glacial activity acts in several ways to shape the landscape. Glaciers build up on mountain slopes and in valleys from an accumulation of snow in winter that exceeds the rate of melting in spring and summer. Over many, many years of cold climate, they get larger and more dense and eventually get so heavy that they begin to move by gravity down the valley often following a creek bed. The continued snow continues to accumulate at the top of the glacier so in extended cold times, the glacier replenishes itself to make a river of glacial ice (as this glacier in Switzerland). As it moves, this massive ice river or glacier plucks off rocks from the sides of the mountains, freezes rocks at the bottom which then travel with it creating abrasive bases digging the valley even deeper, and as it reaches a lower and warmer altitude it melts and deposits gravel, rocks and even large boulders (or erratics) making moraines and wide alluvial fans. Moraines can be created at the foot of a glacier or at the sides or both. These structures are often most identifiable as smoother hills with an assortment of rocks, gravel and boulders. Several can be seen within the Centennial Valley as evidence of these glaciers. Google Interactive Viewer

In the Centennial Valley, there are many glacier carved valleys. Some are U-shaped,Google Interactive Viewer indicating a larger, longer and older glacier but many are more V shaped and narrow, indicating steeper, and shorter glaciersGoogle Interactive Viewer. Most have a cirque (see diagram) or ampitheatre shaped depression at the base of the steepest part of the peak face. The face of Taylor Mountain in the Centennial Valley has no fewer than 6 glacier valleys with cirques. There is one glacial valley between Sheep Mountain and Taylor that has 4 cirques, and Sheep Mountain has 4 cirques. East of Taylor Mountain there are numerous valleys that were once carved by Glaciers, probably the largest being that on the southwest face of Mount Jefferson, the highest point in the Centennial Mountains at 10,216 feet.

As the Glaciers melt, the melt water can carve deep rivers or creeks which change the landscape. Here, in the Centennial Valley, the glaciers contributed to building up the valley floor with debris and by creating lakes and creeks that made the valley fill with sediments.

There are no longer any glaciers in the Centennial Valley, but some of the last remaining glaciers at this latitude are found not too far away in the Teton Mountain Range. The Teton Glacier is the largest but it is melting rapidly like most glaciers in the Northern Hemisphere today.

Since 1980, a significant global warming has led to glacier retreat in the Rocky Mountains and the rest of the world to become increasingly rapid and common, so much so that some glaciers have disappeared altogether, and the existence of a great number of the remaining glaciers of the world is threatened.

See examples of glacial geology in the Centennial Valley with our interactive Google Earth tool here.

Continue to the erosion section.

An interglacial period is an interval of warmer global average temperatures lasting thousands of years that divides consecutive glacial periods within an ice age. The current Holocene interglacial period has persisted since the end of the Pleistocene, about 11,400 years ago. During the 2.5 million year time span of the Pleistocene, many glacials have occurred at intervals of approximately 40,000 to 100,000 years. During these times there were often significant advances of continental ice sheets in North America and Europe. These long glacial periods were separated by more temperate and shorter interglacial periods. During the interglacial periods, (like the one we are in now) the climate warmed to temperatures similar to those today and the tundra receded northward following the ice sheets. Forests returned to areas that once only supported the unique tundra vegetation.
Glacial moraines are formed by the deposition of material from a glacier and are exposed after the glacier has retreated. These features usually appear as linear mounds of till, a non-sorted mixture of rock, gravel and boulders within a matrix of a fine powdery material. Terminal or end moraines are formed at the foot or terminal end of a glacier. Lateral moraines are formed on the sides of the glacier. Medial moraines are formed when two different glaciers, flowing in the same direction, coalesce and the lateral moraines of each combine to form a moraine in the middle of the merged glacier. Less apparent is the ground moraine, also called glacial drift, which often blankets the surface underneath much of the glacier downslope from the equilibrium line. Glacial meltwaters contain rock flour, an extremely fine powder ground from the underlying rock by the glacier's movement. Other features formed by glacial deposition include long snake-like ridges formed by streambeds under glaciers, known as eskers, and distinctive streamlined hills, known as drumlins.
An alluvial fan is a fan- or cone-shaped deposit of sediment crossed and built up by streams or debris flows, like from the bottom of glaciers. These flows come from a single point source at the end point of the fan. There are often overlaping cones from different flows on the same fan. Fans are most often found where a canyon draining from the mountains emerges out onto a flatter plain, and especially along fault-bounded mountain fronts.
The semiarid climate of Wyoming still manages to support about a dozen small glaciers within Grand Teton National Park, which all show evidence of retreat over the past 50 years. Schoolroom Glacier is located slightly southwest of Grand Teton is one of the more easily reached glaciers in the park and it is expected to disappear by 2025. Research between 1950 and 1999 demonstrated that the glaciers in Bridger-Teton National Forest and Shoshone National Forest in the Wind River Range shrank by over a third of their size during that period. Photographs indicate that the glaciers today are only half the size as when first photographed in the late 1890s. Research also indicates that the glacial retreat was proportionately greater in the 1990s than in any other decade over the last 100 years. Gannett Glacier on the northeast slope of Gannett Peak is the largest single glacier in the Rocky Mountains south of Canada. It has reportedly lost over 50% of its volume since 1920, with almost half of that loss occurring since 1980. Glaciologists believe the remaining glaciers in Wyoming will disappear by the middle of the 21st century if the current climate patterns continue.