Thermokarst development can be complex, varying locally according to factors such as microtopography, ice content, erosion and the geotechnical properties of thawed sediment (Lawson 1986). A second cause of complexity is where permafrost soils experience alternating episodes of ice loss and gain. These are common where part of the ice-rich layer in near-surface permafrost episodically thaws due to changes in active-layer depth or lake levels and then re-forms (Sellmann et al. 1975; Shur et al. 2005), or where ice wedges experience alternate thermal erosion and pool-ice formation (Mackay 1988).
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