We investigate the Gislá perched talus slope (Tröllaskagi peninsula, northern Iceland), from which a landslide (more specifically a debris avalanche) occurred in October 2020. Although this talus slope is located outside of the permafrost climatic boundaries, geomorphological evidence (i.e., molards in the landslide deposits) suggest that degradation of azonal permafrost could be among the destabilising factors of the landslide. The thermal dynamics of talus slopes is currently poorly understood, as air convection (the ‘chimney effect’) can play a role in the persistence of permafrost at the base of talus slopes. We use the software FEFLOW to run physical-based simulations of heat transfer within a cross-section of the Gislá talus slope, from -20,000 years to present. We explore the sensitivity of our model to document the initial porosity/ice content of the talus slope (0.3, 0.5 and 0.8), and the thermal conductivity (TC) of the rock phase (0.75, 1.1 and 1.75 W.m-1.K-1). Analysis of air temperature data show that the region has been undergoing a general temperature increase for the last ~ 40 years, supporting the possibility that permafrost degradation is among the destabilising factors of the landslide. Our temperature measurements show that a chimney effect indeed occurs at the Gislá talus slope. Although our modelling approach does not simulate air convection itself, permafrost persists at the base of the talus slope in all model scenarios. Increasing the initial porosity/ice content and decreasing the TC of the rock phase enhances persistence of permafrost in the Gislá talus slope. Our approach is unconventional as we initially know that ground ice was present in the Gislá talus slope at the time of the landslide; it attests that the permafrost dynamics in the talus slope is best represented by our most ice-conservative scenario – i.e., with a TC of 0.75 W.m-1.K-1
Modelling the thermal dynamics of perched permafrost talus slopes: insights from a recently destabilised site (Gislá landslide, October 6th 2020, Iceland)
Morino, Costanza;
2024
Abstract
We investigate the Gislá perched talus slope (Tröllaskagi peninsula, northern Iceland), from which a landslide (more specifically a debris avalanche) occurred in October 2020. Although this talus slope is located outside of the permafrost climatic boundaries, geomorphological evidence (i.e., molards in the landslide deposits) suggest that degradation of azonal permafrost could be among the destabilising factors of the landslide. The thermal dynamics of talus slopes is currently poorly understood, as air convection (the ‘chimney effect’) can play a role in the persistence of permafrost at the base of talus slopes. We use the software FEFLOW to run physical-based simulations of heat transfer within a cross-section of the Gislá talus slope, from -20,000 years to present. We explore the sensitivity of our model to document the initial porosity/ice content of the talus slope (0.3, 0.5 and 0.8), and the thermal conductivity (TC) of the rock phase (0.75, 1.1 and 1.75 W.m-1.K-1). Analysis of air temperature data show that the region has been undergoing a general temperature increase for the last ~ 40 years, supporting the possibility that permafrost degradation is among the destabilising factors of the landslide. Our temperature measurements show that a chimney effect indeed occurs at the Gislá talus slope. Although our modelling approach does not simulate air convection itself, permafrost persists at the base of the talus slope in all model scenarios. Increasing the initial porosity/ice content and decreasing the TC of the rock phase enhances persistence of permafrost in the Gislá talus slope. Our approach is unconventional as we initially know that ground ice was present in the Gislá talus slope at the time of the landslide; it attests that the permafrost dynamics in the talus slope is best represented by our most ice-conservative scenario – i.e., with a TC of 0.75 W.m-1.K-1
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