HR: 11:50h
AN: C11E-07    [PDF]
TI: Slope Relaxation in Thaw Lake Terrain, NW Alaska.
AU: * Plug, L J
EM: lplug@dal.ca
AF: Department of Earth Sciences Dalhousie University, Life Sciences Centre, Halifax, NS B3H 4J1 Canada
AU: Werner, B T
EM: bwerner@ucsd.edu
AF: Complex Systems Laboratory, Cecil and Ida Green Institute of Geophysics and Planetary Physics, University of California-San Diego, La Jolla, CA 92093 United States
AB: Thaw-induced subsidence of the ground surface, localized in thaw lake basins, generates topographic relief of 1 to 20 m in regions of ice-rich permafrost. After lakes drain, basin relief is modified by gravity-driven slope processes and by re-inflation of the lake floor by peat accumulation and refreezing. Unlike slopes in temperate regions, where transport laws and rates have been estimated from measurements (eg., linear diffusion of topography and diffusion time constants), rates of slope relaxation over 10 - 10$^4$ y have not been measured in permafrost terrain. To investigate rates of permafrost slope relaxation, we conducted differential GPS surveys (resolution $\approx$ 1 cm) and constructed digital elevation models of bounding slopes for four lake basins ranging in age from modern (an actively expanding lake) to ~10$^4$ y, located in ice-rich aeolian Pleistocene silt on the Seward Peninsula, NW Alaska. Timing of lake drainage, marking the onset of slope relaxation, is constrained by radiocarbon ages of basal terrestrial peat samples collected from permafrost cores and stratigraphic exposures. The resulting chronosequence of slopes, each developed in similar materials and from a similar initial state, is then used to investigate time evolution of hillslopes in permafrost. Preliminary results indicate that 1) Total thaw basin relief ranges from 10--18 m; 2) Before and immediately following lake drainage, slopes display irregular, slump-dominated profiles with angle 35--60$\deg$; 3) After lake drainage, mid slopes evolve toward smooth cross- sectional and along-slope profiles consistent with diffusive transport; 4) Upper slopes exhibit gentle diffusive profiles near divides, but are marked by laterally-discontinuous steep 1--2 m high ramparts where merging into mid slope, which persist in the oldest basins. 5) Lower slopes are marked by sharp breaks where toes meet reinflating flat basin floors. Comparisons between measured slopes and transport model predictions are consistent with the view that permafrost slopes are characterized by a mixture of linear diffusive and nonlinear transport processes (eg., solifluction) that can maintain relief over long time periods.
DE: 1823 Frozen ground
DE: 1824 Geomorphology (1625)
DE: 9315 Arctic region
SC: Cryosphere [C]
MN: 2003 Fall Meeting