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

A tale of two lakes: a multi-proxy comparison of Lateglacial and Holocene environmental change in Cappadocia, Turkey

Individual palaeoenvironmental records represent a combination of regional-scale (e.g. climatic) and site-specific local factors. Here we compare multiple climate proxies from two nearby maar lake records, assuming that common signals are due to regional-scale forcing. A new core sequence from Nar Lake in Turkey is dated by varves and U–Th to the last 13.8 ka. Markedly dry periods during the Lateglacial stadial, at 4.3–3.7 and at 3.2–2.6 ka BP, are associated with peaks in Mg/dolomite, positive δ18O, elevated diatom-inferred electrical conductivity, an absence of laminated sediments and low Quercus/chenopod ratios. Wet phases occurred during the early–mid Holocene and 1.5–0.6 ka BP, characterized by negative δ18O, calcite precipitation, high Ca/Sr ratios, a high percentage of planktonic diatoms, laminated sediments and high Quercus/chenopod ratios. Comparison with the record from nearby Eski Acıgöl shows good overall correspondence for many proxies, especially for δ18O. Differences are related to basin infilling and lake ontogeny at Eski Acıgöl, which consequently fails to register climatic changes during the last 2 ka, and to increased flux of lithogenic elements into Nar Lake during the last 2.6 ka, not primarily climatic in origin. In attempting to separate a regional signal from site-specific ‘noise’, two lakes may therefore be better than one

Avant-propos

Malet Emmanuel, Astrade Laurent. Avant-propos. In: Collection EDYTEM. Cahiers de géographie, numéro 19, 2017. Monitoring en milieux naturels. Retours d’expériences en terrains difficiles. pp. 4-5

Monitoring en milieux naturels, retours d’expériences en terrains difficiles.

National audienc

Monitoring en milieux naturels, retours d’expériences en terrains difficiles.

National audienc

Monitoring des régimes thermiques des sols en montagne. Expériences alpines actuelles.

Recording the temporal and spatial (in three-dimension) changes in soil temperatures is not new. It is part of a long scientific tradition. The interest of monitoring the thermal regimes of soils today for questions of plant ecology but also for understanding the dynamics of storage/ release of soil organic matter is presented here in particular in mountain areas. After a brief presentation of the current techniques for monitoring these temperature regimes in soils (material, operational difficulties ...), the article presents some current alpine experiments of network of measurement of these regimes.L’enregistrement des évolutions temporelles et spatiales des températures des sols n’est pas une nouveauté. Il s’inscrit dans une longue tradition scientifique. Le suivi des régimes thermiques des sols apporte des éléments de réponse à des questions d’écologie végétale, mais permet aussi de mieux comprendre les dynamiques de stockage/ déstockage des matières organiques, en particulier en zone de montagne. Après une courte présentation des techniques de monitoring, l’étude de ces rédimes de températures dans les sols (matériel, difficultés opérationnelles) est illustrée par quelques expériences alpines en cours dans les Hautes-Alpes (vallon de Roche Noire) , en haute Tarentaise (profils de Bourg-Saint-Maurice) et dans le haut Faucigny (bassin versant du lac d’Anterne).Poulenard Jerôme, Choler Philippe, Malet Emmanuel. Monitoring des régimes thermiques des sols en montagne. Expériences alpines actuelles. In: Collection EDYTEM. Cahiers de géographie, numéro 19, 2017. Monitoring en milieux naturels. Retours d’expériences en terrains difficiles. pp. 279-290

OECD International Standard Problem ISP-47 on containment thermal-hydraulics—Conclusions of the TOSQAN part

International audienceThe main objective of the ISP-47 is to assess the capabilities of Lumped-Parameter and ComputationalFluid Dynamics codes in the area of nuclear containment thermal-hydraulics. Three experimentalfacilities TOSQAN, MISTRA and ThAI were involved in this project. The present paper summarizes thespecifications, the results and the conclusions obtained for the TOSQAN open benchmark exercise.Wall condensation, steam injection in air or air/helium atmospheres, and buoyancy were addressedunder well-controlled initial conditions in the simple TOSQAN geometry. Detailed gas velocity and gasconcentration (air, steam and helium) fields were obtained for the first time in such an exercise.It is found that the model predictions fit with a generally good accuracy the experimental resultsobtained during condensation steady-state conditions, but the flow conditions in the transition regimeare not well reproduced by the calculations: some of the major transient phenomena are not alwayscorrectly modelled and if so, the transient evolutions or the levels of the concerned variables are not thesame in the calculations and in the experiment. Furthermore, two kinds of measurements were specificfor TOSQAN: boundary layer measurements and turbulence variables, which were addressed for the firsttime in such an exercise. It is concluded that more sophisticated modelling in CFD codes for the boundarylayers should be developed and that turbulence variables should be addressed more intensively in furtherexercises

Du blanc au dessus du vide. Monitoring multi-paramètres de la formation et de l'évolution d'un pont de neige au-dessus d'une crevasse sur un glacier alpin

On glaciers, snow bridges that form above crevasses allow mountaineers and skiers to cross them easily, but their break represents a high risk of potentially fatal falls for practitioners. To understand the formation and evolution of these fragile structures, we sat up instrumentation at 3450 m a. s. l. in the Mont Blanc massif. The device, whose installation required complex logistics, surveys the main meteorological parameters several times a day. Moreover, the geometry of the snow bridge is surveyed by an automatic camera while an extensometer measures the evolution of the opening of the crevasse. Although the ensemble is well suited to the conditions of the high mountain environment, its maintenance is delicate due to the strong instability of the environment (movements of the glacier, extreme weather conditions) while processes unexpected as important (wind filling of the crevasse) are challenging a part of the planned instrumentation (e. g. automatic photo inside the crevasse).Sur les glaciers, les ponts de neige qui se forment au-dessus des crevasses permettent aux alpinistes et aux skieurs de les traverser facilement mais leur rupture éventuelle fait supporter un risque élevé de chute potentiellement mortelle aux pratiquants. Pour comprendre la formation et l’évolution de ces structures fragiles, une instrumentation a été mise en place à 3450 m d’altitude dans le massif du Mont Blanc. Le dispositif, dont l’installation a requis une logistique complexe, relève plusieurs fois par jour les principaux paramètres nivo-météorologiques. Par ailleurs, un appareil photo automatique suit la géométrie du pont de neige tandis qu’un extensomètre mesure l’évolution de l’ouverture de la crevasse. Si l’ensemble apparait bien adapté aux conditions de la haute montagne, sa maintenance est toutefois rendue délicate par la forte instabilité du milieu (mouvements du glacier, conditions météorologiques extrêmes) tandis que des processus non pressentis comme importants (remplissage éolien de la crevasse) remettent en question une partie de l’instrumentation prévue (photo automatique à l’intérieure de la crevasse).Ravanel Ludovic, Malet Emmanuel, Batoux Philippe. Du blanc au-dessus du vide. Monitoring multi-paramètres de la formation et de l’évolution d’un pont de neige au-dessus d’une crevasse sur un glacier alpin. In: Collection EDYTEM. Cahiers de géographie, numéro 19, 2017. Monitoring en milieux naturels. Retours d’expériences en terrains difficiles. pp. 69-75