Initiation The initiation of a thaw lake begins with the degradation of ice-rich permafrost. The natural inception of thermokarst lakes can be demarcated into two separate processes; whether in continuous or discontinuous permafrost. In continuous permafrost, water accumulates when ice veins and polygonal ground are present. Through discontinuous permafrost, it is when thaw occurs in palsas (frozen peat cores) or in lithalsas (mineral core mounds). Permafrost degradation is typically linked to a surface disturbance, either natural or artificial, in combination with site-specific factors, such as permafrost ice-content, ground temperature, etc.
Development/expansion Development of thaw lakes tends to be slow at first, but once the average lake bottom temperature exceeds the lake ceases freezing to the bottom and thaw becomes continuous. The lake grows as ice thaws, which may result in the slumping of shorelines or submergence of vegetation, which is why thaw lakes in the boreal forest tend to be surrounded by "drunken trees". It should be specified that "drunken trees" (also known as "drunken forests") occur within
Yedoma regimes. This feature is not present throughout all thermokarst regions. Upon expansion in this stage, thermokarst lakes often take on an elongated shape with ordered alignment in the long axis. If lakes form in an area of ice-rich permafrost, coalescence of several smaller lakes may occur, producing a larger body of water, magnifying the thermal disturbance. Development may be further facilitated by lateral bank erosion. Additionally, thermal abrasion of thermokarst lake edges can expand the lake size, as well as lake bottom subsidence. Oriented morphology of lakes can take on shapes such as "elliptical, egg-shaped, triangular, rectangular, clam-shaped, or D-shaped", and commonly occur in terrain with sandy sediments. Polemic scholastic discussions pertaining to development of lakes’ shapes are commonplace throughout the literature on orientation and morphology of thermokarst lakes. However, there are clearly a multitude of reasons beyond wind movement only, that contribute to the shape of lakes. Grosse
et al. (2013) summarize endogenous and exogenous elements that are key factors in orientation including: • Redistribution of littoral shelves by wind creating insulation, • arrangement of polygonal ice-wedges producing thawing, and • erosion from fluvial channels causing inhomogeneous sediments.
Drainage Before complete drainage, lake edges recede through
retrogressive thaw slumps (RTS) and subaerial debris flows. Actual drainage may be triggered by fluvial erosion or expansion of adjacent basins at inland locations. In coastal areas, drainage may be due to coastal retreat leading to thermal abrasion or erosion due to wave action. More gradual drainage (partial or complete) may be caused by local permafrost degradation and erosion. Lakes stop growing once drainage is initiated, and eventually depressions are filled by sediments, aquatic plants or peat. Another option for the fate of a drained thaw lake is that the active layer surrounding the lake deepens to below water level once ground ice is exhausted, allowing for a residual lake to remain. ==Gallery==