Thermokarst in Alaska

M. T. Jorgenson
ABR, Inc., Fairbanks, AK 99709
Y. L. Shur
Department of Civil Engineering, University of Alaska Fairbanks
T. E. Osterkamp
Geophysical Institute, University of Alaska Fairbanks

Abstract

Knowledge of the varying surface patterns (landforms), extent, and expansion rate of thermokarst is essential to understanding the response of northern ecosystems to climate change and human impacts. Field studies and airphoto analysis have revealed 22 thermokarst landforms associated with varying heat and mass transfer processes, terrain conditions, and ground ice. These include deep and shallow thermokarst lakes, thaw-lake basins, thaw-lake sinks, thermokarst pits, thermokarst troughs and pits, collapsed pingos, thermokarst shore bogs, thermokarst bogs and fens, thermokarst gullies, thermokarst water tracks, beaded streams, thaw slumps, detachment slides, sink holes and tunnels, glacial thermokarst, collapse-block shores, block landslides, thermokarst conical mounds, irregular mounds, and nonpatterned thawed ground. The extent of permafrost degradation was assessed using airphotos taken across the discontinuous zone, revealing 5% of the area has thermokarst, 62% has permafrost, 21% is unfrozen with no recent permafrost, and 12% remains undetermined. In continuous permafrost of arctic Alaska, thermokarst terrain was evident on 13.5% of the area, and 1.5% was unfrozen under deep non-thermokarst lakes. The rate of degradation based on airphoto analysis at four sites revealed the area affected by thermokarst increased 3.5 8 % over ~50-yr.

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