Pelletier, J.D., Formation of oriented thaw lakes by thaw slumping, in review.

Abstract: In the classic model for oriented thaw lakes, sublittoral shelves form by wind-driven circulation near shorelines oriented perpendicular to the wind, protecting the adjacent banks from thaw and wave-cut erosion. Here I propose an alternative model based on thaw slumping, and test the model predictions against observations in northern Alaska. Thermal modeling illustrates that bank height controls the rate of thaw slumping because summertime thaw penetrates only decimeters into a tall bank but as much as tens of meters into a short bank. This effect also leads to oriented lakes because downslope banks are shorter than upslope banks. Bank-material texture also controls the rate of thaw slumping because fine-grained sediments drain slowly and maintain high pore pressures, resulting in lower critical angles for slumping. To test the thaw-slumping model quantitatively, I constructed a process-based numerical model that includes thaw slumping, lacustrine sediment dispersal, and thaw-driven lake-floor subsidence. The model predicts that lake orientations and aspect ratios are controlled by topographic aspect and slope, not by wind direction or intensity. This prediction does not distinguish between the thaw-slumping and wind-driven models, however, because topographic aspects and wind directions are perpendicular almost everywhere. The thaw-slumping model, however, further predicts inverse correlations between lake area and bank height, and lake area and bank-material texture. These correlations result from a positive feedback in which initially taller banks form in coarse-grained sediments, causing slow bank retreat and minor sediment infilling to form narrow, deep lakes over time. Simultaneously, initially shorter banks form in fine-grained sediments, causing rapid bank retreat and sufficient sediment infilling to counteract subsidence, resulting in wide, shallow lakes. The effect of bank-material texture is important for distinguishing between the two models because the wind-driven model predicts large lakes in coarse-grained sediments, while the thaw-slumping model predicts small lakes. An analysis of oriented thaw lakes in northern Alaska shows that systematically smaller, deeper lakes form in coarse-grained eolian sediments compared with those formed in fine-grained fluvial-marine sediments. This pattern strongly supports the thaw-slumping model.

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