A. Meigs et J. Sauber, Southern Alaska as an example of the long-term consequences of mountain building under the influence of glaciers, QUAT SCI R, 19(14-15), 2000, pp. 1543-1562
Southern Alaska is a continent-scale region of ongoing crustal deformation
within the Pacific-North American plate boundary zone. Glaciers and glacial
erosion have dictated patterns of denudation in the orogen over the last s
imilar to 5 Myr. The orogen comprises three discrete topographic domains fr
om south to north, respectively: (1) the Chugach/St. Elias Range; (2) the W
rangell Mountains; and (3) the eastern Alaska Range. Although present defor
mation is distributed across the orogen, much of the shortening and uplift
are concentrated in the Chugach/St. Elias Range. A systematic increase in t
opographic wavelength of the range from east to west reflects east-to-west
increases in the width of a shallowly dipping segment of the plate interfac
e, separation of major upper plate structures, and a decrease in the obliqu
ity of plate motion relative to the plate boundary. Mean elevation decays e
xponentially from similar to 2500 to similar to 1100 m from east to west, r
espectively. Topographic control on the present and past distribution of gl
aciers is indicated by close correspondence along the range between mean el
evation and the modern equilibrium line altitude of glaciers (ELA) and diff
erences in the modern ELA, mean annual precipitation and temperature across
the range between the windward, southern and leeward, northern flanks. Net
, range-scale erosion is the sum of (1) primary bedrock erosion by glaciers
and (2) erosion in areas of the landscape that are ice-marginal and are de
glaciated at glacial minima. Oscillations between glacial and interglacial
climates controls ice height and distribution, which, in turn, modulates th
e locus and mode of erosion in the landscape. Mean topography and the mean
position of the ELA are coupled because of the competition between rock upl
ift, which tends to raise the ELA, and enhanced orographic precipitation ac
companying mountain building, which tends to lower the ELA. Mean topography
is controlled both by the 60 degrees latitude and maritime setting of acti
ve deformation and by the feedback between shortening and uplift, glacial e
rosion, and orographic effects on climate accompanying mountain building. (
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