HR: 16:15h
AN: T22E-02 INVITED     [PDF]
TI: Insights into the evolution of tectonically-active glaciated mountain ranges from digital elevation model analyses
AU: * Brocklehurst, S H
EM: shb@cires.colorado.edu
AF: Department of Earth Sciences, The University of Manchester, Manchester, M13 9PL United Kingdom
AU: Whipple, K X
EM: kxw@mit.edu
AF: Department of Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, MA 02139 United Kingdom
AB: Glaciers have played an important role in the development of most active mountain ranges around the world during the Quaternary, but the interaction between glacial erosion (as modulated by climate change) and tectonic processes is poorly understood. The so-called glacial buzzsaw hypothesis (Brozovic et al., 1997) proposes that glaciers can incise as rapidly as the most rapid rock uplift rates, such that glaciated landscapes experiencing different rock uplift rates but the same snowline elevation will look essentially the same, with mean elevations close to the snowline. Digital elevation model-based analyses of the glaciated landscapes of the Nanga Parbat region, Pakistan, and the Southern Alps, New Zealand, lend some support to this hypothesis, but also reveal considerably more variety to the landscapes of glaciated, tectonically-active mountain ranges. Larger glaciers in the Nanga Parbat region maintain a low downvalley gradient and valley floor elevations close to the snowline, even in the face of extremely rapid rock uplift. However, smaller glaciers steepen in response to rapid uplift, similar to the response of rivers. A strong correlation between the height of hillslopes rising from the cirque floors and rock uplift rates implies that erosion processes on hillslopes cannot initially keep up with more rapid glacial incision rates. It is these staggering hillslopes that permit mountain peaks to rise above 8000m. The glacial buzzsaw hypothesis does not describe the evolution of the Southern Alps as well, because here mean elevations rise in areas of more rapid rock uplift. The buzzsaw hypothesis may work well in the Nanga Parbat region because the zone of rapid rock uplift is structurally confined to a narrow region. Alternatively, the Southern Alps may not have been rising sufficiently rapidly or sufficiently long for the glacial buzzsaw to be imposed outside the most rapidly uplifting region, around Mount Cook. The challenge now is to understand in detail why glaciers exhibit this range of behavior; why large glaciers apparently erode more efficiently than small glaciers, what are the processes that control the development of periglacial hillslopes, and why the rates of erosion on these hillslopes might be limited.
DE: 1824 Geomorphology (1625)
DE: 1827 Glaciology (1863)
DE: 8102 Continental contractional orogenic belts
DE: 8107 Continental neotectonics
SC: Tectonophysics [T]
MN: 2003 Fall Meeting