Browsing by Autor "Bernard Pouyaud"

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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.
Données isotopiques (<sup>87</sup>86/Sr) et changements hydrologiques depuis 15 000 ans sur l'Altiplano andin
(Taylor & Francis, 2002) Anne Coudrain; M. Loubet; Thomas Condom; Amal Talbi; Pierre Ribstein; Bernard Pouyaud; Jorge Quintanilla; Claudine Dieulin; Bernard Dupré
Résumé Actuellement, le bassin sud (17°-22°S, 126 000 km2) de l'Altiplano reçoit environ 39.4 × 109 m3 an−1 d'eau, dont 4% proviennent du bassin nord (14°-17°S) par le Rio Desaguadero. Le rapport 87Sr/86Sr des écoulements de surface actuels présentent des valeurs distinctes sur les deux bassins permettant d'utiliser ce traceur pour reconstituer des conditions hydrologiques passées contrastées du bassin sud. Pour la période aride de 10 000 à 2000 ans BP, les données acquises et la modélisation du transport de strontium dans un aquifàre renforcent les Hypothàses d'une valeur des précipitations de 80% de l'actuel et de l'absence d'alimentation significative du bassin sud par le Rio Desaguadero. Pour les hauts niveaux d'eau de la phase lacustre Tauca, vers 15 000 ans BP, les données hydrologiques et isotopiques indiquent que pour une alimentation totale estimée à 110 109 m1 an1 les apports du bassin nord pouvaient être limités à 5%.
Glaciers of the Tropical Andes: Indicators of Global Climate Variability
(Springer Nature (Netherlands), 2005) Bernard Francou; Pierre Ribstein; Patrick Wagnon; Edson Ramírez; Bernard Pouyaud
Potential for climate variability reconstruction from Andean glaciochemical records
(Cambridge University Press, 2002) Patrick Ginot; Margit Schwikowski; U. Schotterer; Willibald Stichler; H. W. Gäggeler; Bernard Francou; Robert Gallaire; Bernard Pouyaud
Abstract In order to select glacier sites suitable for the reconstruction of short-term climate variability, chemical constituents of shallow cores from Chimborazo, Ecuador, Illimani, Bolivia, and Cerro Tapado, Chile, were analyzed to determine if they represent the climate and atmospheric conditions of the particular area. Pronounced variations were observed in the Chimborazo core, which were attributed to the seasonal occurrence of wet and dry periods. Using chemical tracers, the Pacific and the Amazon basin were identified as the two principal sources of atmospheric moisture. In the Illimani record, seasonality is obvious but is less regular than in the Chimborazo core. Chemical tracers point to the Amazon basin as a moisture source. Post-depositional sublimation masks a possible atmospheric signal in the glaciochemical records from Cerro Tapado. the arid conditions and a prevailing high condensation level also cause little variability in the stable-isotope content. Irregular, more negative δ 18 O values occur during the humid phases of El Niño events. Despite alterations due to sublimation, chemical tracers indicate the Pacific Ocean as a main moisture source for precipitation preserved on Glaciar CerroTapado.
Small glaciers disappearing in the tropical Andes: a case-study in Bolivia: Glaciar Chacaltaya (16<sup>o</sup> S)
(Cambridge University Press, 2001) Edson Ramírez; Bernard Francou; Pierre Ribstein; Marc Descloîtres; Roger Guérin; Javier Mendoza; Robert Gallaire; Bernard Pouyaud; Ekkehard Jordan
Abstract Glaciar Chacaltaya is an easily accessible glacier located close to La Paz, Bolivia. Since 1991, information has been collected about the evolution of this glacier since the Little Ice Age, with a focus on the last six decades. The data considered in this study are monthly mass-balance measurements, yearly mappings of the surface topography and a map of the glacier bed given by ground-penetrating radar survey. A drastic shrinkage of ice has been observed since the early 1980s, with a mean deficit about 1 m a −1 w.e. From 1992 to 1998, the glacier lost 40% of its average thickness and two-thirds of its total volume, and the surface area was reduced by >40%. With a mean estimated equilibrium-line altitude lying above its upper reach, the glacier has been continuously exposed to a dominant ablation on the whole surface area. If the recent climatic conditions continue, a complete extinction of this glacier in the next 15 years can be expected. Glaciar Chacaltaya is representative of the glaciers of the Bolivian eastern cordilleras, 80% of which are small glaciers (<0.5 km 2 ). A probable extinction of these glaciers in the near future could seriously affect the hydrological regime and the water resources of the high-elevation basins.