Stabilisation du paysage périglaciaire suite à un épisode de ravinement par thermo-érosion : implication pour la structure et la stabilité thermique du pergélisol de surface
Thermo-erosion gullies dissect the ice-wedge polygonal terrace in Qarlikturvik valley, Bylot Island (Nunavut), and gullies stay in the landscape as stabilized features following their catastrophic formation. After such disturbances, long-term transitions of the landscape in the continuous permafrost zone needs to be studied thoroughly to understand the recovery processes and new permafrost structure that results, and how it contrasts from pre-disturbance conditions. In this master’s thesis, we investigated how permafrost first formed and then went through a disturbance-stabilization transition. We also examined the processes that contributed to the recovery of surficial permafrost. Special attention was paid to the cryostratigraphic patterns of surficial permafrost due to landscape recovery. The thermo-erosion gully results from the partial erosion of an ice-wedge network, that previously developed in glaciofluvial sands and gravels, alluvial sediments and an organic matrix mixed with eolian silts. An area of 226 ± 22 m2 per linear meter of eroded permafrost was impacted by degradation and stabilization. Aggradational ice and rejuvenated ice wedges (found in the gully slopes) are two features indicative of permafrost stabilization lead by negative feedbacks acting on permafrost. On a one-meter deep profile, we learned that globally, drained polygons and slopes’ permafrost from both sides of the gully channel reached thermal conditions comparable to pre-degradation permafrost state. Regarding the drained polygons only, its surficial permafrost now has 1.2 time more latent heat than intact polygons, meaning more energy is necessary to induce its thawing. This modification in the permafrost structure suggests these stabilized drained polygons are in a better posture to face future climate warming compared with pre-disturbance permafrost. This study confirms the importance of long-term investigations of thermokarst terrain to understand landscape evolution in the context of climate change and puts to light permafrost resiliency.
cryostructures Permafrost Stabilization Aggradational ice Thermo-erosion gully Ice-wedge