Browsing by Autor "Bernard Francou"

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10 year surficial velocities on a rock glacier (Laurichard, French Alps)
(Wiley, 1992) Bernard Francou; Louis Reynaud
Abstract A survey of painted lines on the top and frontal zone of a talus rock glacier allows one to present a longitudinal profile of the surficial velocity distribution. Measurements were taken over a 8–12 year period at regular intervals and the results now provide information on the variability of displacements. In the upper zone a recent slowing of movement coincides with negative mass balance of local glaciers. Discussion focuses on the variations in velocity of the rock glaciers over the short time‐scale.
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.
Comment on tc-2022-70
(2022) RubÃ©n Basantes-Serrano; Antoine Rabatel; Bernard Francou; Christian Vincent; Álvaro Soruco; Thomas Condom; Jean Carlo RuÃz
Abstract. We present a comprehensive study of the evolution of the glaciers on the Antisana ice cap (tropical Andes) over the period 1956–2016. Based on geodetic observations of aerial photographs and high-resolution satellite images, we explore the effects of morpho-topographic and climate variables on glacier volumes. Contrasting behaviour was observed over the whole period, with two periods of strong mass loss, 1956–1964 (−0.72 m w.e. yr−1) and 1979–1997 (−0.82 m w.e. yr−1), and two periods with slight mass loss, 1965–1978 (0.10 m w.e. yr−1) and 1998–2016 (−0.26 m w.e. yr−1). There was a 42 % reduction in the total surface area of the ice cap. Individually, glacier responses were modulated by morpho-topographic variables (e.g. maximum and median altitude and surface area), particularly in the case of the small tongues located at low elevations (Glacier 1, 5 and 16) which have been undergoing accelerated disintegration since the 1990s and will likely disappear in the coming years. Moreover, thanks to the availability of aerial data, a surging event was detected on the Antisana Glacier 8 (G8) in the 2009–2011 period; such an event is extremely rare in this region and deserves a dedicated study. Despite the effect of the complex topography, glaciers have reacted in agreement with changes in climate forcing, with a stepwise transition towards warmer and alternating wet–dry conditions since the mid-1970s. Long-term decadal variability is consistent with the warm–cold conditions observed in the Pacific Ocean represented by the Southern Oscillation index.
Comment on tc-2022-70
(2022) Rubén Basantes-Serrano; Antoine Rabatel; Bernard Francou; Christian Vincent; Álvaro Soruco; Thomas Condom; Jean Carlo RuÃz
We present a comprehensive study of the evolution of the glaciers in the Antisana ice cap (tropical Andes) over the period 1956–2016. Based on geodetic observations of aerial photographs and high-resolution satellite images, we explore the effects of morpho-topographic and climate variables on glacier volumes. Contrasting behavior was observed over the whole period, with two periods of strong mass loss: 1956–1964 and 1979–1997, and two periods with slight mass loss: 1965–1978 and 1997–2016. There was a 42 % reduction in the total surface area of the ice cap. Individually, glacier responses were modulated by morpho-topographic variables (e.g., maximum and median altitude, and surface area), particularly in the case of the small tongues located at low elevations (Glacier 1, 5, and 16) which have been undergoing accelerated disintegration since the 1990s, and will likely disappear in the coming years. Moreover, thanks to the availability of aerial data, a surging event was detected in the Antisana G8 in the 2009–2011 period; such an event is extremely rare in this region and deserves a dedicated study. Despite the effect of the complex topography, glaciers react in agreement with changes in climate forcing, with a stepwise transition towards warmer and alternating wet/dry conditions since the mid-1970s. Long-term decadal variability is consistent with the warm/cold conditions observed in the Pacific Ocean represented by the Southern Oscillation Index.
COMPARACIÓN DE MÉTODOS PARA ESTIMAR EL BALANCE DE MASA DEL GLACIAR DE ZONGO, BOLIVIA (16º S, 68º O)
(Universidad Nacional de La Plata, 2014) Álvaro Soruco; Christian Vincent; Bernard Francou; Antoine Rabatel
La serie más larga y continua de mediciones de balance de masa en la Zona Intertropical de Sud América corresponden al glaciar de Zongo, Bolivia. Las mediciones fueron iniciadas en 1991, empleando tanto el método glaciológico como el hidrológico. Los resultados muestran discrepancias en los balances de masa obtenidos por ambos métodos. Con el objetivo de verificar estos balances de masa, se realizó un nuevo balance de masa mediante el método fotogramétrico, que fue comparado con los métodos glaciológico e hidrológico ya existentes. Los resultados de esta comparación entre balances de masa obtenidos con el método hidrológico y fotogramétrico son equivalentes, mientras que la comparación de los resultados obtenidos entre estos y el método glaciológico, están en desacuerdo. Esta diferencia, se atribuye a la imposibilidad de realizar mediciones adecuadas con el método glaciológico en las zonas de difícil acceso del glaciar de Zongo, las cuales son simplemente interpoladas en la estimación del balance de masa neto específico. Los resultados muestran, en general, que el glaciar Zongo ha estado muy cercano a un estadio de equilibrio entre 1956 y 1963; ganó masa entre 1963 y 1975 de manera significativa (3.86 m eq. agua) y a partir de 1975, los balances de masa son negativos. Por otra parte, se han extendido las observaciones del balance de masa del glaciar de Zongo para los últimos 50 años (1956-2006).
Contribution of glacier runoff to water resources of La Paz city, Bolivia (16° S)
(Cambridge University Press, 2015) Álvaro Soruco; Christian Vincent; Antoine Rabatel; Bernard Francou; Emmanuel Thibert; Jean Emmanuel Sicart; Thomas Condom
Abstract The supply of glacier water to La Paz city, Bolivia, between 1963 and 2006 was assessed at annual and seasonal timescales based on the mass-balance quantification of 70 glaciers located within the drainage basins of La Paz. Glaciers contributed ∼15% of water resources at an annual scale (14% in the wet season, 27% in the dry season). Uncertainties in our estimation are related to the assumed constant precipitation (∼0.5% for ice-free areas and up to 6.5% for glaciated areas), the constant runoff coefficient (∼1%), the surface areas of the glaciers and catchments (∼5%) and the mean mass-balance uncertainty of the 21 glaciers used to obtain the mass balance of the 70 glaciers (12% of the total discharge). Despite the loss of 50% of the glacierized area during the study period, runoff at La Paz did not change significantly, showing that increase in ice melt rates compensated for reduction in the surface area of the glaciers. In the future, assuming complete disappearance of the glaciers and no change in precipitation, runoff should diminish by ∼12% at an annual scale, 9% during the wet season and 24% during the dry season.
Current state of glaciers in the tropical Andes: a multi-century perspective on glacier evolution and climate change
(Copernicus Publications, 2013) Antoine Rabatel; Bernard Francou; Álvaro Soruco; Jesús Gómez; Bolívar Cáceres; J. L. Ceballos; Rubén Basantes-Serrano; Mathias Vuille; Jean‐Emmanuel Sicart; Christian Huggel
Abstract. The aim of this paper is to provide the community with a comprehensive overview of the studies of glaciers in the tropical Andes conducted in recent decades leading to the current status of the glaciers in the context of climate change. In terms of changes in surface area and length, we show that the glacier retreat in the tropical Andes over the last three decades is unprecedented since the maximum extension of the Little Ice Age (LIA, mid-17th–early 18th century). In terms of changes in mass balance, although there have been some sporadic gains on several glaciers, we show that the trend has been quite negative over the past 50 yr, with a mean mass balance deficit for glaciers in the tropical Andes that is slightly more negative than the one computed on a global scale. A break point in the trend appeared in the late 1970s with mean annual mass balance per year decreasing from −0.2 m w.e. in the period 1964–1975 to −0.76 m w.e. in the period 1976–2010. In addition, even if glaciers are currently retreating everywhere in the tropical Andes, it should be noted that this is much more pronounced on small glaciers at low altitudes that do not have a permanent accumulation zone, and which could disappear in the coming years/decades. Monthly mass balance measurements performed in Bolivia, Ecuador and Colombia show that variability of the surface temperature of the Pacific Ocean is the main factor governing variability of the mass balance at the decadal timescale. Precipitation did not display a significant trend in the tropical Andes in the 20th century, and consequently cannot explain the glacier recession. On the other hand, temperature increased at a significant rate of 0.10 °C decade−1 in the last 70 yr. The higher frequency of El Niño events and changes in its spatial and temporal occurrence since the late 1970s together with a warming troposphere over the tropical Andes may thus explain much of the recent dramatic shrinkage of glaciers in this part of the world.
Degree-day melt models for paleoclimate reconstruction from tropical glaciers: calibration from mass balance and meteorological data of the Zongo glacier (Bolivia, 16&lt;b&gt;°&lt;/b&gt; S)
(2011) Pierre‐Henri Blard; Patrick Wagnon; Jérôme Lavé; Álvaro Soruco; Jean‐Emmanuel Sicart; Bernard Francou
Abstract. This paper describes several simple positive degree-day models (hereafter referred as "PDD models") designed to provide past climatic reconstruction from tropical glacier paleo-equilibrium altitude lines (paleo-ELA). Several ablation laws were tested and calibrated using the monthly ablation and meteorological data recorded from 1997 to 2006 on the Zongo glacier (Cordillera Real, Bolivia, 16° S). The performed inversion analyses indicate that the model provides a better reconstruction of the mass balance if the ablation is modeled with different melting factors for snow and ice. The inclusion of short-wave solar radiations does not induce a substantial improvement. However, this type of model may be very useful to quantify the effects of local topographic (orientation, shading) and to take into account incoming solar radiation changes at geological timescale. The performed sensitivity test indicates that, in spite of the uncertainty in the calibrated snow-ice ablation factors, all models are able to provide paleotemperatures with ~1 °C uncertainty for a given paleoprecipitation. This error includes a 50 m uncertainty in the estimate of the paleoELA. Finally, the models are characterized by different precipitation-temperature sensitivities: if a similar warming is applied, model including different ablation factors for snow and ice requires a lower precipitation increase (by ∼15 %) than others to maintain the ELA.
El rápido retroceso de los glaciares en los Andes tropicales: Un desafío para el estudio de la dinámica de los ecosistemas de alta montaña
(2013) Bernard Francou
Etude des précipitations et de la fonte sur un glacier tropical: le glacier du Zongo, Bolivie, 16°S
(Taylor & Francis, 2003) Jean Emmanuel Sicart; Pierre Ribstein; Bernard Francou; Robert Gallaire
Résumé Cet article présente les relations entre les précipitations et la fonte sur le glacier du Zongo en Bolivie où l'ablation et l'accumulation sont maximales en saison des pluies (été austral). Les nuages, provenant du bassin amazonien, donnent des précipitations à midi dans les vallées, puis dans l'après-midi en montagne. Lors de l'installation de la saison des pluies de septembre à décembre, les chutes de neige recouvrent temporairement la glace en fusion. Par effet d'albédo, l'énergie solaire absorbée et la fusion varient beaucoup et atteignent leur maximum lorsque le couvert neigeux est réduit. Au cœur de la saison des pluies de janvier à mars, la neige reste à basse altitude sur le glacier, l'albédo est fort et la fonte diminue. La saison sèche de mai à août est une période de faible ablation. La fonte sur les glaciers tropicaux dépend fortement de la répartition saisonnière des précipitations, par l'augmentation d'albédo due aux chutes de neige d'été.
Glacier recession on Cerro Charquini (16° S), Bolivia, since the maximum of the Little Ice Age (17th century)
(Cambridge University Press, 2006) Antoine Rabatel; Abraham Machaca; Bernard Francou; Vincent Jomelli
Abstract Cerro Charquini, Bolivia (Cordillera Real, 5392 ma.s.l.) was selected as a site to reconstruct glacier recession since the maximum of the Little Ice Age (LIA) in the central Andes. Five glaciers, located on differently exposed slopes, present comprehensive and well-preserved morainic systems attributed to former centuries. The moraines were dated by lichenometry and show a consistent organization on the different slopes. The past geometry of the glaciers was reconstructed using ground topography and aerophotogrammetry. Lichenometric dating shows that the LIA maximum occurred in the second half of the 17th century, after which the glaciers have receded nearly continuously. Over the last decades of the 20th century (1983–97), recession rates increased by a factor of four. On the northern and western slopes, glaciers receded more than on the southern and eastern slopes (by 78% and 65% of their LIA maximum area, respectively). The mean equilibrium-line altitude (ELA) rose by about 160 m between the LIA maximum and 1997. Recession rates were analysed in terms of climatic signal, suggesting that glacier recession since the LIA maximum was mainly due to a change in precipitation and that the 19th century may have been drier. For the 20th century, a temperature rise of about 0.6°C appears to be the main cause of glacier recession. Recent climatic conditions from 1983 to 1997 correspond to a mass deficit of about 1.36m w.e.a –1 . If such conditions persist, the small glaciers below 5300ma.s.l. in the Cordillera Real should disappear completely in the near future.
Glacier shrinkage and water resources in the Andes
(Wiley, 2005) Bernard Francou; Anne Coudrain
For more than a century glaciers around the world have been melting as air temperatures rise due to a combination of natural processes and human activity. The disappearance of these glaciers can have wide‐ranging effects, such as the creation of new natural hazards or changes in stream flow that could threaten water supplies Some of the most dramatic melting has occurred in the Andes mountain range in South America. To highlight the climatic and glacial change in the Andes and to encourage the scientific community to strengthen the glacier observation network that stretches from Colombia to the Patagonian ice fields, the Instituto Nacional de Recursos Naturales (INRENA), Perú, and the Institute of Research and Development (IRD), France, recently organized the second Symposium on Mass Balance of Andean Glaciers in Huaráz,Perú.
Glaciers and Climate in the Andes between the Equator and 30° S: What is Recorded under Extreme Environmental Conditions?
(Springer Nature (Netherlands), 2003) U. Schotterer; Martín Grosjean; Willibald Stichler; Patrick Ginot; C. Kull; H. Bonnaveira; Bernard Francou; H. W. Gäggeler; Robert Gallaire; Georg F. Hoffmann
Glaciers of the Tropical Andes: Indicators of Global Climate Variability
(Springer Nature (Netherlands), 2005) Bernard Francou; Pierre Ribstein; Patrick Wagnon; Edson Ramírez; Bernard Pouyaud
Heavy metals in ancient tropical ice: initial results
(Elsevier BV, 2001) Christophe Ferrari; Thomas Clotteau; Lonnie G. Thompson; Carlo Barbante; Giulio Cozzi; Paolo Cescon; Sungmin Hong; Laurence Maurice; Bernard Francou; Claude F. Boutron
Monthly balance and water discharge of an inter-tropical glacier: Zongo Glacier, Cordillera Real, Bolivia, 16° S
(Cambridge University Press, 1995) Bernard Francou; Pierre Ribstein; Ronald Saravia; Eric Tiriau
Abstract Measurements of mass balance were performed every month on Zongo Glacier. Bolivia. Simultaneously, water-discharge, temperature and precipitation data were obtained. The first year of the survey, 1991–92. was marked by an ENSO (El Niño-Southern Oscillation) event with high temperature and low precipitation, whilst the following year, 1992–93, was normal. Results point to the early and late wet season (October-December and March–May: as playing a critical role in the determination of the annual mass balance. The wet season is the warmest period of the year and consequently the duration of the wet season is a highly relevant variable in determining mass balance. Both glaciological and hydrological methods for the determination of the mass balance provide similar results. Our study confirms dial ENSO events have a major influence on the rapid glacier retreat currently affecting this part of the Andes.
Monthly balance and water discharge of an inter-tropical glacier: Zongo Glacier, Cordillera Real, Bolivia, 16° S
(Cambridge University Press, 1995) Bernard Francou; Pierre Ribstein; Ronald Saravia; Eric Tiriau
Abstract Measurements of mass balance were performed every month on Zongo Glacier. Bolivia. Simultaneously, water-discharge, temperature and precipitation data were obtained. The first year of the survey, 1991–92. was marked by an ENSO (El Niño-Southern Oscillation) event with high temperature and low precipitation, whilst the following year, 1992–93, was normal. Results point to the early and late wet season (October-December and March–May: as playing a critical role in the determination of the annual mass balance. The wet season is the warmest period of the year and consequently the duration of the wet season is a highly relevant variable in determining mass balance. Both glaciological and hydrological methods for the determination of the mass balance provide similar results. Our study confirms dial ENSO events have a major influence on the rapid glacier retreat currently affecting this part of the Andes.
New insights into the decadal variability in glacier volume of a tropical ice cap, Antisana (0°29′ S, 78°09′ W), explained by the morpho-topographic and climatic context
(Copernicus Publications, 2022) Rubén Basantes-Serrano; Antoine Rabatel; Bernard Francou; Christian Vincent; Álvaro Soruco; Thomas Condom; Jean Carlo Ruíz
Abstract. We present a comprehensive study of the evolution of the glaciers on the Antisana ice cap (tropical Andes) over the period 1956–2016. Based on geodetic observations of aerial photographs and high-resolution satellite images, we explore the effects of morpho-topographic and climate variables on glacier volumes. Contrasting behaviour was observed over the whole period, with two periods of strong mass loss, 1956–1964 (−0.72 m w.e. yr−1) and 1979–1997 (−0.82 m w.e. yr−1), and two periods with slight mass loss, 1965–1978 (0.10 m w.e. yr−1) and 1998–2016 (−0.26 m w.e. yr−1). There was a 42 % reduction in the total surface area of the ice cap. Individually, glacier responses were modulated by morpho-topographic variables (e.g. maximum and median altitude and surface area), particularly in the case of the small tongues located at low elevations (Glacier 1, 5 and 16) which have been undergoing accelerated disintegration since the 1990s and will likely disappear in the coming years. Moreover, thanks to the availability of aerial data, a surging event was detected on the Antisana Glacier 8 (G8) in the 2009–2011 period; such an event is extremely rare in this region and deserves a dedicated study. Despite the effect of the complex topography, glaciers have reacted in agreement with changes in climate forcing, with a stepwise transition towards warmer and alternating wet–dry conditions since the mid-1970s. Long-term decadal variability is consistent with the warm–cold conditions observed in the Pacific Ocean represented by the Southern Oscillation index.
New insights into the decadal variability in glacier volume of an iconic tropical ice-cap explained by the morpho-climatic context, Antisana, (0°29’ S, 78°09’ W)
(2022) Rubén Basantes-Serrano; Antoine Rabatel; Bernard Francou; Christian Vincent; Álvaro Soruco; Thomas Condom; Jean Carlo Ruíz
Abstract. We present a comprehensive study of the evolution of the glaciers in the Antisana ice cap (tropical Andes) over the period 1956–2016. Based on geodetic observations of aerial photographs and high-resolution satellite images, we explore the effects of morpho-topographic and climate variables on glacier volumes. Contrasting behavior was observed over the whole period, with two periods of strong mass loss: 1956–1964 and 1979–1997, and two periods with slight mass loss: 1965–1978 and 1997–2016. There was a 42 % reduction in the total surface area of the ice cap. Individually, glacier responses were modulated by morpho-topographic variables (e.g., maximum and median altitude, and surface area), particularly in the case of the small tongues located at low elevations (Glacier 1, 5, and 16) which have been undergoing accelerated disintegration since the 1990s, and will likely disappear in the coming years. Moreover, thanks to the availability of aerial data, a surging event was detected in the Antisana G8 in the 2009–2011 period; such an event is extremely rare in this region and deserves a dedicated study. Despite the effect of the complex topography, glaciers react in agreement with changes in climate forcing, with a stepwise transition towards warmer and alternating wet/dry conditions since the mid-1970s. Long-term decadal variability is consistent with the warm/cold conditions observed in the Pacific Ocean represented by the Southern Oscillation Index.
Pb and Sr isotopes from an ice-core provides evidence for changing atmospheric conditions at the Sajama icecap, South America
(Springer Science+Business Media, 2003) K. J.R. Roman; Sang-Bum Hong; G. Bulion; Laurie J. Burn; C.F. Boutron; Christophe Ferrari; Lonnie G. Thompson; Laurence Maurice; Bernard Francou
Measurements of Pb and Sr isotopes and Pb, Sr, Ba and Rb concentrations in ice-core samples from the Sajama icecap in Bolivia were made to investigate the changing environmental conditions in the region over the past 22 ky.. The Pb isotopic measurements indicate there has been a significant change in the 206 Pb/ 207 Pb ratio in the ice by 1700 AD which can be attributed to human activity. This change was also accompanied by increasing Pb/Ba ratios that reach ∼10 times natural values by the beginning of the 20 th century, confirming an increase of anthropogenic Pb levels. Sr and Rb concentrations are highly enhanced in 3 ky and 0.5 ky BP ice relative to the upper-crustal rock indicating a different origin for a significant proportion of the dust in these samples. Likely sources of this dust are dry lake beds that occur on the Altiplano as a result of changing climatic conditions. This dust adds to the background level of dust accumulating on the Sajama icecap.