Browsing by Autor "Yves Arnaud"

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Analyse de la structure d'un glacier rocheux du domaine tropical (Caquella, sud-Lipez, Bolivie)
(Société hydrotechnique de France, 2001) Denis Fabre; Bernard Francou; Vincent Jomelli; Brigitte Kaiser; Yves Arnaud; Bernard Pouyaud; Claudio Smiraglia; François Valla
Click to increase image sizeClick to decrease image sizeThe Caquella rock glacier (5960-5400 m asl), by the size (one kilometre long) is probably the most important active rock glacier in the Inner Tropics. In this arid high mountain environment glaciers are lacking and rock glaciers represent, with the salt lakes, the best indicators of the climatic variability. Moreover, they behave as water reservoirs in the present hydrological cycle marked by very scarce precipitation. Direct observations and geoelectrical soundings make it possible to identify interstitial ice in the permafrost. Nevertheless, the resistivity curve profile, the ice distribution in the debris mass as well as observations from the surface topography, bring clear evidences that this rock glacier is in recession. The Caquella rock glacier results from a long evolution, which has probably its origin in the early Holocene. Presence of a very recent moraine in the upper part suggests presence of ELA on the rock glacier during the Little Ice Age.
El Niño‐Southern Oscillation (ENSO) influence on a Sajama volcano glacier (Bolivia) from 1963 to 1998 as seen from Landsat data and aerial photography
(American Geophysical Union, 2001) Yves Arnaud; Frédéric Muller; Mathias Vuille; Pierre Ribstein
Sajama volcano, located in the Bolivian Altiplano, is the southernmost tropical glacier and, owing to its situation, approximately 100 km east of the Pacific coast, is well suited to study the El Niño‐Southern Oscillation phenomenon. Landsat data from 1972 to 1998 and a 1963 aerial photograph are used to monitor the snow line fluctuations on a selected part of Sajama volcano. We assume that a few months after the rainy season, the snow line is representative of the previous rainy season, if no recent snowfall has occurred. By observing precipitation from the stations surrounding Sajama volcano and by verifying snow presence on surrounding summits, we detect images with recent snowfall likely to disturb the climatic significance of the snow line. A snow line evolution model takes into account the different image acquisition dates and adjusts the snow line elevation accordingly for the middle of the dry season. A progressive rise of the snow line elevation is observed from 1963 to 1998 with a sustained rise from 1984 to 1990. The snow line altitude is related to the Southern Oscillation Index. Even after the high precipitation of the 1996–1997 wet season, the following El Niño 1997–1998 leads to a substantial rise of the snow line. The snow line elevation is related primarily to the total rainy season precipitation and to a lesser degree to the maximum monthly mean temperature of the warmest month, thus confirming a greater snow line sensitivity to precipitation than to temperature.
Glacier mass balance determination by remote sensing in the French Alps: progress and limitation for time series monitoring
(2004) J.-P. Dedieu; Antoine Rabatel; Christian Vincent; François Valla; Emmanuel Thibert; Yves Arnaud
This paper presents an approach founded on an indirect methodology to determine the distribution of mass balance at high spatial resolution using remote sensing and ground stakes measurements. A recent time series of images from optical and SAR data are selected on 3 outlet glaciers well suited in the French Alps to evaluate the accuracy of the computed mass balance. The method is based on the snowline determination as a proxy of the equilibrium line altitude (ELA). The key of the transfer is the activity coefficient (db/dz) for the annual mass balance calculation. Comparison between measured and computed mass balance provide a good correspondence (R/sup 2/=0.90) and allows extending the method on large-scale areas. The limitations are cloudiness for optical data and high slope distortion on SAR images.
Reduced melt on debris-covered glaciers: investigations from Changri NupGlacier, Nepal
(Copernicus Publications, 2016) Christian Vincent; Patrick Wagnon; J. M. Shea; Walter W. Immerzeel; Philip Kraaijenbrink; Dibas Shrestha; Álvaro Soruco; Yves Arnaud; Fanny Brun; Étienne Berthier
Abstract. Approximately 25 % of the glacierized area in the Everest region is covered by debris, yet the surface mass balance of debris-covered portions of these glaciers has not been measured directly. In this study, ground-based measurements of surface elevation and ice depth are combined with terrestrial photogrammetry, unmanned aerial vehicle (UAV) and satellite elevation models to derive the surface mass balance of the debris-covered tongue of Changri Nup Glacier, located in the Everest region. Over the debris-covered tongue, the mean elevation change between 2011 and 2015 is −0.93 m year−1 or −0.84 m water equivalent per year (w.e. a−1). The mean emergence velocity over this region, estimated from the total ice flux through a cross section immediately above the debris-covered zone, is +0.37 m w.e. a−1. The debris-covered portion of the glacier thus has an area-averaged mass balance of −1.21 ± 0.2 m w.e. a−1 between 5240 and 5525 m above sea level (m a.s.l.). Surface mass balances observed on nearby debris-free glaciers suggest that the ablation is strongly reduced (by ca. 1.8 m w.e. a−1) by the debris cover. The insulating effect of the debris cover has a larger effect on total mass loss than the enhanced ice ablation due to supraglacial ponds and exposed ice cliffs. This finding contradicts earlier geodetic studies and should be considered for modelling the future evolution of debris-covered glaciers.