Geography Reference
In-Depth Information
I rock glacier have shown a consistent increase in temperature with depth during the
past few decades. Some rock glaciers in the Alps, such as the Hochebenkar and the
Reichenkar rock glaciers, have shown increasing velocity since about 1990, the result of
warmer temperatures, which have accelerated melting of permafrost, causing warmer
ice to deform more quickly. In the San Juan Mountains of Colorado, some rock glaciers
appear to have become reactivated, overriding forests in their paths. This may possibly
be another effect of global warming: Ice that was previously too cold to flow effectively
has now warmed and can deform like a plastic. Rock glaciers with ground temperatures
close to 0°C flow faster compared to colder rock glaciers (Kääb et al. 2007; Janke and
Frauenfelder 2008). Continued monitoring of rock glaciers in other parts of the world
is necessary to help better understand global climate change, as well as monitor and
predict potential hazards associated with melting ice.
Fluvial Processes and Landforms
Since ancient times, mountains have been recognized as a source of water. Mountains
are the origin for most of the world's major rivers, and this water is more important to
human populations now than ever before, as discussed in Chapter 12. Irrigation, hydro-
electric power production, navigation, recreation, and domestic consumption are but a
few of the uses of mountain streams and reservoirs. The Danube, which rises in the Alps
and mountains of Eastern Europe, the great Indo-Gangetic rivers that originate in the
Himalayas, or the Nile, which rises in the mountains of East Africa and Ethiopia, are
of significant importance to the areas through which they flow. The hydrologic center
of the continental United States is in the Rocky Mountains near Yellowstone National
Park, where three great rivers (the Snake, the Colorado, and the Missouri) have their
sources. The downstream components of each of these are vital to the regions through
which they flow.
Running water is an important denudational agent in mountains. Material is continu-
ously transported downslope by rivers. Precipitation is greater in most mountains, and
this water has a high potential energy, owing to the presence of steep slopes and high
local relief. In addition, bare areas, with abundant surface material and little protective
vegetation, make mountain landscapes vulnerable to erosion by running water (Ding-
wall 1972). Much of the sediment load of streams is probably obtained from slopes ad-
jacent to small tributaries near the headwaters of drainage basins. In the Amazon Bas-
in, for example, it is estimated that 85 percent of the total stream load is provided by
just 12 percent of the drainage area, which is concentrated in tributaries in the Andes
(Bloom 1998). Streams also reach far beyond the mountains, serving as linkages to the
lowlands, and ultimately, to the sea. Mountains may be worn down primarily by frost
action and mass wasting, but if streams did not transport at least some of the material
away, the valleys would eventually be buried by the weathered material. The fact that
this does not happen is evidence for the importance of streams.
One would think that areas that have glaciers would more likely have rivers with in-
creased sediment loads, given glacial erosion and the amount of available water. It is
unclear, however, how glaciers link erosion and increased sediment load to rivers (Har-
bor and Warburton 1993). Fluvial specific sediment yield often does not correlate well
with glacial cover (Desloges and Gilbert 1998). The degree of glacial activity, therefore,
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