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Matell, Nora, 2009

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Matell, Nora, 2009, Shoreline erosion and thermal impact of thaw lakes in a warming landscape, Arctic Coastal Plain, Alaska: University of Colorado, Boulder, M.S. thesis, 94 p.

Abstract

Warming air temperatures in the Arctic are modifying thermokarst processes along Alaska's Arctic Coastal Plain. The numerous thaw lakes that are the most visible surface feature in the region are formed by thermokarst processes and stand to be altered as warming continues. In addition to a large ecological role, thaw lakes may act as a source of atmospheric carbon, releasing methane and carbon dioxide previously stored in the underlying permafrost. In this study, I investigate how the subsurface thermal structure may change under a warming climate and how this could affect thermoerosion, and place bounds on what erosional changes have occurred or are occurring along the lakeshores of Arctic Coastal Plain thaw lakes near Drew Point, Alaska. I employ a 1-D numerical model to investigate the subsurface thermal impact of thaw lakes of various depths. Most thaw lakes in the region are shallow (<~2 m deep) and are not underlain by taliks (unfrozen ground). The modeling suggests that under a warming scenario, the number of lakes that do not freeze to their bottoms during the winter, and are therefore underlain by taliks, will increase. Using a 2-D thermal model, I explore the subsurface thermal structure between two nearby lakes. While the interlake ground remains frozen, permafrost temperatures do warm significantly, suggesting that this may increase the potential for thermokarst breaches between adjacent lakes. To constrain shoreline erosion, I combine remote sensing with field observations. My remote sensing results indicate that any changes in lake size between the 1970s and 2000s are within the margin of error for Landsat images, and that hydrologically driven changes in lake levels are sufficient to obscure any long-term erosion signal. Field results indicate that lakeshore erosion is indeed occurring, although rates are highly variable over short distances. Using time-lapse images of summer lakeshore position that record 1-5 m of erosion over 5 weeks, I propose that lakeshore erosion occurs by a process of thermally driven bank undercutting, slumping, and disaggregation.

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