Estimating surface water availability in high mountain rock slopes using a numerical energy balance model

Water takes part in most physical processes that shape the mountainous periglacial landscapes and initiation of mass wasting. An observed increase in rockfall activity in several mountainous regions was previously linked to permafrost degradation in high mountains, and water that infiltrates into rock fractures is one of the likely drivers of these processes. However, there is very little knowledge on the quantity and timing of water availability for infiltration in steep rock slopes. This knowledge gap originates from the complex meteorological, hydrological and thermal processes that control snowmelt, and also the challenging access and data acquisition in the extreme alpine environments. Here we use field measurement and numerical modeling to simulate the energy balance and hydrological fluxes in a steep high elevation permafrost affected rock slope at Aiguille du Midi (3842 m a.s.l), in the Mont-Blanc massif. Our results provide new information about water balance at the surface of steep rock slopes. Model results suggest that only ~25 % of the snowfall accumulates in our study site, the remaining ~75 % are redistributed by wind and gravity. Snow accumulation depth is inversely correlated with surface slopes between 40&deg; to 70&deg;. Snowmelt occurs between spring and late summer and most of it does not reach the rock surface due to the formation of an impermeable ice layer at the base of the snowpack. The annual effective snowmelt, that is available for infiltration, is highly variable and ranges over a factor of six with values between 0.05&ndash;0.28 m in the years 1959&ndash;2021. The onset of the effective snowmelt occurs between May and August, and ends before October. It precedes the first rainfall by one month on average. Sublimation is the main process of snowpack mass loss in our study site. Model simulations at varying elevations show that effective snowmelt is the main source of water for infiltration above 3600 m a.s.l.; below, direct rainfall is the dominant source. The change from snowmelt-dominated to rainfall-dominated water availability is nonlinear and characterized by a rapid increase in water availability for infiltration. We suggest that this elevation of water availability transition is highly sensitive to climate change, if snowmelt-dominated permafrost-affected slopes experience an abrupt increase in water input that can initiate rock slope failure.</p

Assessing the sensitivity of steep rock slope permafrost to water infiltration under various fracture geometries: a numerical approach

International audienceWater infiltration and circulation in frozen bedrock fractures may enhance heat transport from the surface to the permafrost body and play a role in rock slope failure. However, such processes occurring in steep rock slope permafrost are difficult to investigate because of their non-linearity and anisotropy. In this communication, we will present recent developments conducted in the frame of the WISPER project (“Water and Ice related thermo-mechanical processes in the fractures of Steep alpine bedrock Permafrost”, funded by the French National Agency for Research). The FeFlow® (DHI-WASY) software is used to model and study the coupled heat and mass transfer in a simple alpine geometry that typically represents steep rock slope affected by permafrost and seasonal freeze and thaw cycles at c.a.3500 m a.s.l. Using a synthetic annual forcing for rock surface temperature, several case studies are implemented to investigate the sensitivity of permafrost degradation to various fracture networks features: width and density, orientation, angle, shape, amount and seasonality of the input water flux. The thermal and hydrogeological variables (notably temperature fields, and hydrostatic pressures), are compared to a base case without any fracture, in order to assess their sensitivity to the studied parameters. The comparison between these theoretical simulations and field measurements is considered through a number of diagnostic variables of the infiltrating water. The prospective framework to carry out field measurements and compare with the simulations will be presented

Monitoring steep rock wall permafrost using electrical resistivity and induced polarisation: Part 2: preliminary inversion results of a year-round series of measurements

International audienc

Main advances and perspectives in high mountain permafrost and steep rock slopefailures research in the French Alps

International audienc

Hydrological processes and thermal dynamics in high mountain permafrost

International audienc

Hydrological processes and thermal dynamics in high mountain permafrost-affected rock walls

International audienc

Real-time monitoring of snowmelt infiltration in steep permafrost-affected rock slopes using fluorescent dyes

International audienceLittle is known about the connectivity between surface water and subsurface fractures in steep permafrostaffected rock slopes. Here we present a novel high-elevation field experiment designed to monitor real-time infiltration in rock fractures at Aiguille du Midi (3842 m a.s.l), in the Mont-Blanc massif. An existing tunnel that was carved for access to visitors, allows the collection of water directly from fractures that cross the tunnel walls. We monitored the water flow rate, temperature, and electrical conductivity in two adjutant fractures. In addition we installed a fluorescence probe and inserted two different fluorescent dyes: amino-acid-G and sulphorhodamine-B, into snow patches at the surface, in two locations directly above the fractures (5-15 m) to track the water source. We sampled water from the monitored fractures and other locations in the tunnel

Monitoring steep rock wall permafrost using electrical resistivity and induced polarisation: Part 1: installation, instrumentation

International audienc

Analyse des écroulements de 2020 au Vallon d'Étache (Haute Maurienne) et à la Crête des Grangettes (Ecrins) : les dernières avancées de la recherche sur le permafrost des versants raides

International audienc