Response of Permafrost Terrain to Disturbance: A Synthesis of Observations from Northern Alaska, U.S.A.

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Abstract
Former exploratory drilling sites in the National Petroleum Reserve-Alaska, are examples of the long-term physical modifications resulting from disturbance of perennially frozen terrain. Camp construction and drilling activities in the late 1940s/early 1950s resulted in disturbances which can be grouped by their first modification to the site and its thermal regime: trampling of vegetation, killing the vegetative cover, removal of the vegetative meat, or removal of the vegetation and soil. Removal of the vegetation led to the most extensive modifications at all sites, but the subsequent response to disturbance between sites varied with primarily four factors: (1) ground ice volume, (2) distribution and size of massive ground ice, (3) material properties during thaw, and (4) relief, including progressive changes during thaw subsidence. Variations in response time resulted from the influence of these factors on the type and activity of degradational processes that ensued. Terrain underlain by ice-poor sediments that are stable upon thawing, for example, was altered only by thaw subsidence and consolidation, while ice-rich sediments that are unstable at thaw were extensively modified by a complex interaction of slumping, sediment flow, and thermal and mechanical erosion. Drainage promoted meltwater erosion, whereas undrained areas were modified significantly less and attained stability more rapidly. Physical stability is required for growth of vegetation and thermal equilibration, and has taken over 30 yr to attain in ice-rich, thaw-unstable areas. Ice-poor, thaw-stable materials in undrained or low relief areas required an estimated 5 to 10 yr for stability; thaw depth measurements suggest that certain of these areas have also equilibrated thermally.

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