Publication de deux nouveaux articles scientifiques du professeur Daniel Germain dans les revues Geomorphology et Earth Surface Processes and Landforms
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Auteurs | Daniel Germain et Jean-François Milot
Publié dans la revue Earth Surface Processes and Landforms
No. 5; Avril 2024; 1-16 - https://doi.org/10.1002/esp.5792
Résumé (en anglais)
Overcooled talus slopes are generally described as islands of sporadic permafrost
below the lower alpine limit of permafrost. The negative thermal anomaly of the ground
is mainly consecutive to the internal ventilation of the deposit, but it is also conditioned
by multiple factors as topography, slope aspect and incline, openwork
structure and coarseness of the deposit, air temperature, solar radiation and wind
regime. Therefore, the study of the spatiotemporal dynamics of ventilation processes
allows a better understanding of the phenomenon. At Cannon Cliff, New Hampshire
(USA), several field visits and environmental monitoring allowed us to describe the
varying nature and significance of the ventilation mechanisms that can be observed
at the ground surface and associated with both the intensity and direction of the airflows
in a talus debris accumulation/protalus rampart system. The thermal negative
anomalies are strong enough to lower the ground temperature to the point of preserving
ice during the late spring and summer seasons. The monitoring of the gradient
between external (air) and internal (talus) temperatures coupled with several
dendroecological and geomorphological analyses provided a complete environmental
picture of the impacts, feedback and extent of the phenomenon.
Auteur | Daniel Germain
Publié dans la revue Geomorphology
Numéro 455 (2024) 109201
Résumé (en anglais)
Vegetation colonization is known as an effective process for stabilizing talus slopes, but little quantitative data is available about the relationships between vegetation, sediment fluxes, and sediment storage. The results of a detailed analysis of a single active fine-grained scree slope show that the upper section, scattered with shrubby vegetation, represents an environment characterized by strong biogeomorphic feedbacks. Engineering species (Thuya occidentalis, Betula papyrifera, Cornus sericea, Salix caprea) are well adapted to high sediment mobility with different modes of reproduction and survival. White cedar has a high sediment trapping capacity (>22 m3 per individual) and generates a micro-relief of 80 cm on average. It is responsible for 99 % of the volume of sediment trapped by shrub vegetation, even though it represents 44 % of the total shrub population sampled. In contrast, the hardwoods species have a very low capacity for sediment trapping (<1 m3 per individual) and micro-relief generation (>20 cm). This is likely due to the morphology of the growth which, despite a strong capacity to produce stump rejections, remains limited in trapping sediment. The shrubby vegetation directly influences the trajectory of frost-coated clast flows, the dominant slope process. Nevertheless, the vegetation appears to be quite resilient and stable on a decadal scale, where even the occurrence of extreme debris flows had little impact. In the downslope section, the debris flows, frost-coated clast flows, and snow avalanches present original and circumstantial modalities of tree-line regression. If the upper slope remains of sufficient size to allow for the occurrence of high-magnitude geomorphic events, the tree line appears to be driven primarily by slope processes rather than climate. Although it may be surprising that recent warming lowers the tree line on the studied talus slope, this provides new insight into the complex and non-linear relationships between vegetation and talus slope processes.
