THERMOKARST LAKE EVOLUTION IN A DISCONTINUOUS PERMAFROST ZONE NEAR WHITEHORSE YT, CANADA

Discontinuous permafrost underlies sections of the Takhini River Valley (TRV), located near Whitehorse YT, Canada. The TRV is a major agricultural area and highway corridor. Landforms in this area are dynamic due to localized frost heave and permafrost thaw. In the Yukon, climate change studies show an annual average temperature increase of 2^o C in the past 50 years - more than double the average increase in southern Canada (Streicker, 2016). While permafrost degradation is expected to increase over time as a direct result of this increase in air temperature (Streicker, 2016), previous studies suggest that vegetation, organic layer thickness, snow depth and soil moisture content are the more important variables for permafrost persistence in discontinuous permafrost zones (Burn, 1997). With permafrost melt we can expect increased ground instability and shifting topography and drainage patterns. This is visually observable through the reshaping of existing thermokarst landforms as well as the creation of new ones. The TRV floor is comprised of glaciolacustrine sediments deposited during the late Wisconsinan McConnell Glaciation (Hughes, 1989), and hosts clusters of thermokarst lakes – lakes formed by melting ice lenses resulting in ground subsidence. We visually characterized these lakes in the field and via aerial imagery (select years 1946 to 2016) for changes over time. We assessed qualitative characteristics such as lake size, structure and bank erosion. We did not observe any consistent temporal variation in lake formations that would correlate with increasing annual temperature. We did however determine that the aspect of thermokarst lake banks was a major contributor to erosion with south aspect banks showing significantly more activity. Further study can elucidate whether or not this is linked to increased sun exposure and heating resulting in earlier annual snow melt and elevated permafrost thaw rates.