Figure 7.7 Fair Cirque glacier and rock glacier, Front Range, CO. U.S.A. (U.S.G.S)
Figure 7.8 Section
of the Monarch Lake topographic map. (U.S.G.S)
Scale 1: 24000 Contour Interval: 40 ft.
(North is to the top.)
| Most of you on this field trip have heard of glaciers, large natural accumulations of land ice that show evidence of movement either now, or sometime in the past. But how many of you know what a rock glacier is? To geomorphologists, rock glaciers represent a transitional phenomenon between glacial and non-glacial processes. The air photo below shows a much larger rock glacier (Labeled "RG')located a short distance from those found in Pawnee cirque. It extends away from Fair Glacier toward the north. You can discern its location by examining the topographic map. Notice how the contour lines bend outward away from the glacier toward Triangle Lake |
Figure 7.7 Fair Cirque glacier and rock glacier, Front Range, CO. U.S.A. (U.S.G.S) |
Figure 7.8 Section
of the Monarch Lake topographic map. (U.S.G.S) |
The Fair Cirque rock glacier is a tongue-shaped rock glacier like those found in Pawnee Cirque. Tongue-shaped rock glaciers in the Front Range are believed to be a result of rock debris burying marginally active cirque glaciers (Outcault and Benedict, 1965). The rock rubble insulated the ice, especially at the nose or terminus. Scan carefully across the surface of the rock glacier and you'll see a series of transverse ridges, ridges running horizontally across the surface, with intervening furrows. These features seem to indicate the presence of differential movement within the rock glacier. That is, compression and expansion is uneven leading to the creation of these features. White ( 1971) measured an average annual rate of downvalley movement of 9.7 cm.
Take a look at the north and northwest end of Triangle Lake in the air photo. You might notice a small ridge right by the water (to the right of the letter "M"). Now check your topographic map for its location. See how the 10,600 ft contour line on the east, south and west parallels the water and then the contour juts back on the north/northwest side. The part of the contour that juts back is the ridge which is a moraine.
Back to Pawnee rock glaciers
Back to Stop 7 Pawnee Cirque
Or jump to:
| Table of Contents
| Stop 1 Lodgepole Pine | Stop 2: Subalpine | Stop
3: Ecotone | Stop 4: Tundra |
| Stop 5: D1 | Stop
6: Isabelle Glacier | Stop 7: Pawnee
Cirque | Stop 8: Green Lakes Valley
| Wrap - up |
Created by Michael Ritter ( mritter@uwsp.edu ) Last revised June 25, 1997