No abstract

The highly fissile lithology of the rockwalls and the diversity of mass-wasting processes provide a specific character to the active talus slopes of the northern Gaspé Peninsula since deglaciation. At a regional scale, the geology of the rockwalls, the patterns and modalities of deglaciation and the evolution towards a cold temperate morphoclimatic regime in a maritime context still influence the geomorphological dynamics of scree slopes today. At a local scale, the south-north orientation of the main coastal valleys influences insolation and exposure to prevailing winds, which in turn influence the snow cover regime and the occurrence of freeze-thaw cycles. The statistical analyses carried out from the mapping of 43 talus slopes and their geometric variables allowed the identification of significant environmental factors for the characterization of the dominant geomorphic processes: snow avalanches, frostcoasted clast flows, debris flows and rockfalls. Slope aspect appears to be a key parameter in the nature of the processes acting on the talus slopes. East-and northfacing talus slopes are generally covered by a significant snowpack in winter and the dominant processes are snow avalanches and debris flows. West-and south-facing talus slopes face prevailing winds and insolation and are subject to frost-coated clast flows, the main driver for forest regression, and rockfalls. However, the evolution of scree slopes in forested environments remains extremely complex due to the multiscale components that affect their evolution in the short, medium and long term.

<p>Scree slopes offer an environment conducive to the occurrence of several gravity-driven geomorphic processes, the frequency and magnitude of which are highly variable in time and space. These processes locally prevent vegetation colonization, despite the climatic warming that favors a general progression and consolidation of forest fronts, and this from an altitudinal as well as a latitudinal point of view. The position of the forest front is therefore due, in addition to the climate, to the geomorphological dynamics of mass transfer processes on these steep slopes. Rarely observed in a cold temperate climate, at low altitude and enclosed in the forest environment, this makes the Northern Gaspé region (Province of Quebec, Eastern Canada) unique and complex for studying the interactions between geomorphic processes, talus slope geometry and morphology and forest dynamics during the Holocene.</p><p>The mapping inventory of 43 active talus slopes in the coastal valleys of the Northern Gaspé, and their geometric characteristics, allowed the identification of statistically significant variables that explain scree slope morphology in relation to two groups of dominant geomorphic processes, namely: 1) snow avalanches and debris flows, and 2) frost-coated clast flows and rockfalls. The first group is found on East and North facing slopes while the second is found on West and South facing slopes. The variables indicative of high geomorphic activity (active area, altitudinal treeline, Ho/Hi ratio) all suggest increased geomorphic activity on West and South facing slopes. Conversely, the East and North facing slopes are largely stabilized, but occasionally disturbed by debris-flow channels and snow-avalanche corridors. The location and intensity of these disturbances depend essentially on the morphology of the rockwall and the talus slope, in addition to climatic parameters.</p><p>The evolution of the West and South facing slopes is more complex as geomorphic processes have continued to disrupt the vegetation colonization, started 7250 years BP, on the slopes where the rockwalls are still active. However, the reasons for the presence or absence of frost-coated clast flows having a notable impact on the sediment budget and the altitudinal treeline remain unclear.</p>