Autor: Gerardo Zegers (University of Calgary)

The Importance of Gravel-Size Sediments in Permafrost Occurrence in Mountain Environments.

Abstract:

Permafrost is a key component of the cryosphere, influencing energy exchanges, hydrological processes, and natural hazards. In mountainous areas, permafrost occurrence is affected by complex topography and surficial geology, resulting in significant spatial heterogeneity. In discontinuous alpine permafrost zones, the lowest active permafrost is typically found in gravel-size sediments. These surficial sediments create a unique thermal regime that allows permafrost to persist even under positive mean annual air temperatures. This study investigated the role of gravel-size sediments in permafrost occurrence in the Canadian Rockies using fieldwork and numerical modelling. Ground surface temperature sensors were deployed at various elevations, ranging from 2000 m.a.s.l. to 2500 m.a.s.l., revealing that areas with larger sediments have lower ground temperatures than zones with finer sediments. Additionally, a new version of the hydrogelogical GeoTOP model was developed to improve the prediction of permafrost occurrence in surficial sediments by incorporating natural convection in the ground energy balance. The model was tested in a talus slope located at Lake O'Hara basin in the Canadian Rockies, and the results showed that natural convection plays an essential role in the thermal regime of gravel-size sediments. These findings enhance our understanding of permafrost dynamics in mountain environments and provide a valuable tool for studying the effect of permafrost thaw on groundwater discharge. Future work will focus on understanding the impact of climate change on permafrost and groundwater discharge in these environments.