During 2013, the activities of French periglacial communities and permafrost researchers were undertaken in a wide range of approaches (geomorphological field study, physical modelling and numerical approach) and cover several areas (Spitsbergen, Iceland, Central Norway and Central Yakutia (Russia).
The hydrological and hydrogeological instigations carried out on the Austrelovénbreen catchment (western Spitsbergen) are still going on in 2013 and also in 2014. The projects CRYOSENSORS / GRAAL result from the collaboration of 3 French laboratories : IDES (Univ Paris-Sud / CNRS), THEMA and FEMTO (Univ. de Franche Comté/CNRS). The research work is funded by the National Research Agency of France (ANR), by the GDR Mutations polaires (CNRS) and by IPEV (French Polar Institute).
The Austre Lovén glacier catchment (10 km2) has conditions highly favorable for hydrological investigations because the drainage system forms a well-defined outlet downstream. The project aims to study both hydrological and glaciological mass-balances of the catchment. In 2013 like in 2012, field-work was conducted in order to study the water exchanges between river water and the supra-permafrost water-table. For this purpose, several monitoring have been undertaken in rivers as well as in groundwater thanks to 2 lines of piezometers (physicochemical characteristics of surface and ground-water, potentiometric level, soil temperature, geophysical investigations). The results show a seasonal evolution of the hydrographs closely linked to climatic factors. Although the meltwater from snow and glacier ice strongly contributes to the outlet flows, the discharge of subglacial river and that of the suprapermafrost water-table also controls the fluxes by constituting the river base flow, chemically more mineralized than other end-members. The new piezometers set up in Spring 2013 in the proglacial area have confirmed that the water-table reaches a thickness of 1.50 m thick for an active layer depth of 2.50 m at maximum. The contribution of the water -table towards the rivers may constitute around 10 to 20% of the total annual discharge. The increase of the active layer and therefore that of the volume of groundwater stored into the shallow, supra-permafrost aquifer may lead in the future to the increase of the contribution of groundwater, more chemically enriched, to the runoff at the outlet of land- based glaciers in the Arctic.
Figure 1. Drilling of piezometers in the proglacial area of Austre Lovén glacier close to Ny-Ålesund- Svalbard (April 2013). The piezometers are equipped with CTD probes and temperature loggers (0.5 to 4.5 m deep) – photos taken by Christelle Marlin.
In 2013, the French-Icelandic research team, with Denis Mercier, Etienne Cossart, Armelle Decaulne, Julien Coquin, Thierry Feuillet, Helgi Páll Jónsson and Þorsteinn Sæmundsson, has developed researches on the deglaciation and subsequent landsliding in the Skagafjördur area, northern Iceland. The role of paraglaciation (debuttressing, influence of post-glacial rebound) is examined and has been compared with the one of classic factors (topography, lithology, etc.) in terms of landslide occurrence and location, using a spatial analysis based on a chi-square test. Results show that landslides are over- represented in areas where post-glacial rebound was at its maximum, with a stronger concentration of landslides in the northern part of the fjord. Also, the distribution of landslides does not show any clear relationship with the pattern of glacial debuttressing. Tschuprow coefficient highlights that the influence of post-glacial rebound on landslide location is higher than the combined influence of slope gradient, curvature or geological structure. This result is supported by evidence for landslides timing in the area: most landslides occurred during the first half of the Holocene, and a period of hillslope instability was initiated when the post-glacial uplift was at its maximum. Finally, the mechanisms that link post-glacial rebound and landsliding as well as the geomorphic impacts of landslides, are investigated.
Figure 2. Photo: view of the source-area and partial body of the Vatnaöxl postglacial landslide, W of Sauðárkrókur (photo D. Mercier).
French Norwegian research team
In 2013, the French-Norwegian research team, with Armelle Decaulne, Achim A. Beylich and Katja Laute, applied tree-rings methods to snow-avalanche occurrence in two U-shaped valleys of Western Norway, Bødalen and Erdalen.
In Bødalen, the analyses of the tree-ring patterns of 91 trees highlight four extreme snow-avalanche events, extending over the entire valley floor and up to a distance of 800 m from the foot of the slope,
during the 20th century and at the beginning of the 21st century. Return periods of 15 to 20 years for the most extreme events are extracted from the analyses, and recurrence intervals of 10 to 15 years for avalanches presenting distinct deposition lobes uphill of the distal torrent. Results obtained by tree- ring analyses are successfully compared with available documents at different spatial and temporal scales. Rock-face snow-avalanche occurrences in the area, of small to medium size, are associated with heavy wintry precipitation combined with strong winds. However this normal situation is not valid for extreme snow avalanches crossing the path investigated in the paper, which result from the outlet glacier located in the starting zone; this glacier commands spatial and inter-annual variations of snow accumulation in the departure zone.
Figure 3. Photo: view of Bødalen study site, Norfjord, Western Norway (photo A. Decaulne).
In Erdalen, investigations conducted on one path (with a maximum runout distance shorter than the one investigated in Bødalen) reconstruct 17 snow avalanche winters since the 1930s, and 7 winters regarded are extreme for their snow-avalanche activity. Calculation of frequency provides return period ranging from 4.4 to 33 years. Induced spatial extent of snow-avalanche events induces flow- like snow avalanches with limited extent around the tree-less parts of the cone with a return period under 6 years, the cone is totally covered and the distal tree-limit overpassed with a return period of 16 to 33 years.
During past years, Christophe Grenier and Emmanuel Mouche from LSCE (Laboratoire des Sciences du Climat et de l'Environnement) has been developing activities in numerical modeling for permafrost issues involving coupled thermal transfer with water flow in the Cast3M code (www-cast3m.cea.fr). During the last two years, this modeling activity was complemented by laboratory experiments and field work involving collaborations with François Costard, Nicolas Roux and Antoine Sejourne at IDES (Interactions et Dynamique des Environments de Surface, Orsay) and Alexander Fedorov and Pacha Konstantinov from Permafrost Institute in Yakutsk (Yakutia, Russia). The topic studied concerns the evolution of river taliks in the context of climate change with a joint approach combining numerical simulation, analogical experiments in cold room. The field study focuses on the evolution of the soil - river continuum in an Alas valley in Yakutia. The site was equipped in 2012 with thermal, hydrological & hydrogeological sensors and the water properties and isotopic signatures were monitored. The first year of data was obtained during September 2013 field study. The main results will be presented during the next EUCOP meeting in 2014. The experimental study in cold room at IDES addresses the same issue of river – soil interaction considering a channel with a “river” flowing on a frozen porous medium. The first purpose is to identify the main controlling parameters for the progression of the 0°C isotherm into the frozen material based on thermal monitoring of the system. The second objective is to simulate the experiment with Cast3M code and identify the appropriate boundary conditions, parameters and finally validate the code for such purposes. This was the topic of the Roux et al. communication at the AGU meeting in San Francisco, December 2013.
Another line of action concerns the development of coupled Thermo-Hydrological codes. While a larger amount of publications appear on such issues, the resolution of such a coupled non-linear system with phase change still remains a difficult issue: this year, LSCE proposed and launched a TH code intercomparizon exercise to 1°) evaluate and validate codes by means of intercomparizon on test cases and experimental studies, 2°) create a research community around such issues to exchange and improve codes in view of more realistic system simulations. The INTERFROST benchmark was presented in various places this year including in particular the EGU (Vienna) and AGU (San Francisco) meetings. A web site is under construction to host the exercise at (https://wiki.lsce.ipsl.fr/interfrost). Please consider joining the benchmark.
Figure 4. Setup for the cold room experiment at IDES: water flows in a channel made on a frozen and saturated sand unit with temperature monitoring.
Report prepared by François Costard (firstname.lastname@example.org)