Mountain Landforms and Geomorphic Processes - Mountain Geography: Physical and Human Dimensions - page 231

1975; Barsch and Caine 1984). In the coarse-grained system, sediment is transferred
from the cliffs to depositional features through rockfalls, landslides, or avalanches.
Mass-movement landforms typically are present in the coarse debris system. The fine-
grained sediment system is an open system that has both internal and external inputs
fed from erosion of local soils or eolian (wind) deposition of dust. The geochemical sys-
tem involves solution weathering. Bedrock and surficial geology as well as nivation and
fluvial processes all play important roles in the geochemical system (Darmody et al.
2000; Sueker et al. 2001). Other coarse-grained periglacial landforms, such as rock gla-
ciers, have the potential to alter stream geochemistry by storing and releasing solutes
(Williams et al. 2007).
Other classifications of alpine hillslopes have also been formulated. Caine (1974) cat-
egorized hillslopes in the Rocky Mountains into (1) interfluves, (2) free-face, (3) talus,
(4) talus foot, (5) valley floor, and (6) stream channel components (Fig. 5.3). Interfluves
are convex surfaces where slow mass wasting and soil creep dominate. The free-face
consists of steep bedrock cliffs, where rapidly moving rocks are free to fall and bounce.
The talus component experiences less rapid movement than the free-face since it accu-
mulates alluvial and avalanche material. At the talus foot, landforms such as rock gla-
ciers can be found. The valley floor also experiences mass wasting and overland flow,
with some areas having relatively rapid movement. In Colorado, most valley floors are
inactive, and it is rare that elastics ever reach them. In the stream channel, there is also
insignificant input from upper slopes.
The Colorado Front Range has been intensively studied, but still provides a problem
when linking geomorphic systems. Uncertainty is created when the systems are ex-
amined at the basin scale. Consider the hillslope categories mentioned above. At Niwot
Ridge, lowering is at a rate less than 0.01 mm/yr, but cliff retreat is about 0.76 mm/yr.
This suggests that Indian Peaks are relatively inactive and shows that zones of higher
activity are surrounded by inactive zones with poorly developed linkages within basins.
The interfluves, valley sides, and stream network should be viewed as independent en-
tities with respect to coarse debris movement. There should be more coarse debris
throughout the system, but this is not the case, because the system does not cascade all
the way down (Gerrard 1990). At present, the hillslope sediment budgets are dominated
by internal transfer of coarse debris within the free-face and talus components. Even
where fine sediment is involved in movement, it is not transported out of the slope sys-
tem, except possibly by high winds (Caine 1986). Mountain landscapes that were glaci-
ated during the Pleistocene often have contemporary denudation rates that are an order
of magnitude lower than the global maxima. Sediment storage dominates in a postgla-
cial landscape with poor connections between fluvial systems and surrounding slopes,
reflecting the extreme difference between valley and ridge lowering (Small et al. 1997;
Anderson 2002). However, it is difficult to measure processes at the basin scale. Often
these measurements are obtained for a few localized areas and then generalized for the
entire basin. Remote sensing and GIS show promise in upscaling local measurements to
regional assessments based on classification techniques.
The mountain landscape is characterized by instability and variability. Rock-strewn
surfaces resulting from rapid, short-lived physical weathering are prevalent; exposed
soil is continually being transported downslope. This is commonly observed in the rush-
ing waters of alpine streams and in the movement of entire slopes. If you have ever