Chronology and climatic interpretation of glaciers' fluctuations in the Bolivian Andes (16°S) since the Little Ice Age Maximum (17th century)

• Main Author: Rabatel, Antoine
• Other Authors: Laboratoire de glaciologie et géophysique de l'environnement (LGGE), Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Université Joseph-Fourier - Grenoble I, Bernard Francou([e-mail])
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2005
• Subjects: Glacier fluctuations; lichenometry; Little Ice Age; Bolivia; Fluctuations glaciaires; moraine; lichenométrie; Petit Age Glaciaire; Paléoclimat; Andes; Bolivie; [SDU.OTHER]Sciences of the Universe [physics]/Other; Ela; Ice cap; ice core
• Online Access: https://theses.hal.science/tel-00012124; https://theses.hal.science/tel-00012124/document; https://theses.hal.science/tel-00012124/file/Rabatel2005These.pdf

The evolution of about fifteen glaciers of the Bolivian Eastern Cordillera (16-17°S; 68°W), since their Little Ice Age (LIA) maximum till the late 20th century, has been reconstructed on the basis on ten main moraines observed on the glacier forelands and six aerial photographs. A correspondence between the moraines from a glacier margin to another has been established using geomorphological criteria. These moraines have been dated by lichenometry (Rhizocarpon geographicum s.l.) using a new statistical method based on the extreme values theory. Glacier maximal extent has been dated from the second half of the 17th century. Glaciers kept, until the first half of the 18th century, a quite similar position. From the 1730s – 40s, they began to retreat nearly continuously. The most important moraines attest to periods of standstill or small advances which were never strong enough to remove former moraines. Glacier retreat accelerated during the late 19th and early 20th centuries. Over the 20th century retreat remains fast. Over the whole studied period, glaciers lost about 60% of their maximal extent and the ELA rose by about 135 m. Moraines' dating as well as Bolivian glaciers' evolution since the late 19th century are in good agreement with data available in other places of the tropical Andes such as in Peru and Equator. A synchronism in glacier evolution at a regional scale due to a common climatic forcing can be stressed. We suppose that the Bolivian glaciers' maximal extent was forced by enhanced precipitation (20 to 30% higher than current mean) and reduced temperature (0.4 to 0.6°C lower than current mean). In addition, we can note the concomitance between periods of low solar activity and periods of glacier advances. Retreat from the first half of the 18th century could be mainly due to a decrease in precipitation. These hypothesis agree with the results obtained from the scarce climate proxies available in this part of the Andes such as the ice core retrieved in the southern Peru Quelccaya ice cap. During ...