Formation of oriented thaw lakes by thaw slumping

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 of a nonlinear relationship between bank height and bank retreat rate. Bank material texture also controls the rate of thaw slumping because fine-grained sediments drain slowly and maintain higher pore pressures than coarse-grained sediments, 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 and intensity. The thaw slumping model further predicts inverse correlations between lake area and bank height and between lake area and bank material texture. 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.