Mountain Landforms and Geomorphic Processes - Mountain Geography: Physical and Human Dimensions - page 230

buttressing of rock slopes, and formation of hanging valleys. Periglacial processes, or
cold climate processes without the presence of glacial ice, may further diminish relief,
although mass wasting is often very slow. Aggradation of deposits at lower elevations
will bury channels in alluvium, thus further reducing relief.
The mechanics of glacier erosion are insufficiently known. Glaciers are likely better
transporters of material, thus providing further uncertainty as to an isostatic response
of mountains (Caine 1986). Worldwide denudation rates in nonglacierized basins, not in-
cluding some of the world's most active mountain belts, have indicated that no obvious
relationship exists between precipitation or mean annual temperature and total denud-
ation. In addition, topographic relief alone does not result in high rates of denudation.
Denudation rates are highest in areas of rejuvenation, and the rates of weathering co-
vary primarily with physical erosion and much less with temperature or precipitation
(von Blanckenburg 2005).
Again, the link between process and resulting form is poorly developed and contin-
ues to puzzle geomorphologists. Spatial scale will continue to play an important role in
future studies. As our ability to comprehend fluvial incision processes as well as glacial
erosion and transport improve, so will our understanding of mountain growth (Tuck-
er and Slingerland 1996; Hartshorn et al. 2002; Hovius et al. 2000). As more detailed
observations become available, mountain geomorphologists will hopefully be able to
“scale up” to answer such regionalized questions.
Hillslope Components
The basic components of the mountain landscape are the upland surfaces, the valley
bottoms, and the slopes that connect them. Slopes are of the utmost importance, since
they occupy the greatest area, provide a link between uplands and valley floors, and
result in a high degree of energy transfer. Geomorphic processes are intensified in the
presence of steep slopes and a mountain climate. While precipitation is often the major
factor at intermediate altitudes, low temperatures become the dominant environmental
feature at higher altitudes and give rise to glacial, nivational, and periglacial systems
(Washburn 1980; Embleton and King 1975; Barsch and Caine 1984). The glacial system
is one in which ice acts directly to shape the land. It generally occurs at the highest
elevations (Benn and Evans 1998). Nivation, a special set of processes (and sometimes
forms) that result from the presence of snow patches, is dominated by frost action and
the downslope movement of earth material by gravity (mass wasting). The snow patch
is not doing the work; rather, freezing and running water intensify erosion and trans-
port, thus often hollowing a hillslope. Once begun, this is a self-perpetuating process:
The larger the depression, the more snow that will accumulate, and the longer it will
take to melt in summer, thereby increasing its erosive effect. Nivation processes are
best developed at the snowline. The periglacial system is characterized by nonglacial,
cold climatic conditions as well as frost action and mass wasting processes.
Since the processes that operate within these systems are often not mutually exclus-
ive, others have devised broader classifications that focus on material fluxes. Barsch
and Caine (1984) divided mountains into (1) a glacial system, (2) a coarse-grained
debris system, (3) a fine-grained debris system, and (4) the geochemical system. Active
glaciers in the glacial system have the greatest erosion potential (Embleton and King