Remote Sensing and Digital Reconstruction of Pre-Late-Glacial to Recent Glaciers in the Cordillera Huayhuash, Perú
Joan M. Ramage, Lehigh University
collaborating with Don Rodbell, Union College and students at Lehigh and Union. There are several others involved too... I'll add more when I get a chance to make this fancier!
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Glacier equilibrium line altitude (ELA) estimates in the tropical Andes vary widely, due in part to uncertainty of the age of glacial features used to determine the ELAs and in part due to real differences in ELAs throughout the Andean cordillera. There is a large ELA difference or steep gradient between the Cordillera Blanca and the Junin plain. The little-studied Cordillera Huayhuash, Perú (~10°15' S) lies in between these regions, and provides an opportunity to determine, with good age control, paleo-ELAs from four major past glaciations and their subdivisions, including constraining the extent and ELA from the last glacial maximum (LGM). Little of this type of work has been done in the Cordillera Huayhuash, although good maps have been produced since the 1930s (Kinzl 1954). In June 2003, I was part of a team of geologists and students that conducted a pilot study to map glacial features, determine the glacial chronology using cosmogenic ages of moraine ridges, and reconstruct paleo-ELAs in the Jahuacocha valley, headwaters of the Rio Achin, on the western flank of the Cordillera Huayhuash. Four major moraine sets, comprising a minimum of ten ridges, were mapped in the Jahuacocha valley, a major valley draining the cordillera (Ramage et al. 2003). This project is a study to map the 4 major glacial stages, date each of the moraines (funded separately), and reconstruct the paleo ice cover and ELAs from each interval. Moraines will be mapped using global positioning system units, aerial photographs, Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite data, and the recently-released shuttle radar topography mission (SRTM) digital elevation model for South America. In addition, rock samples will be collected from moraine ridge tops to determine cosmogenic ages. Cosmogenic ages will help to determine which of the ridges correspond to the LGM, and will help to put the older moraines in a chronologic context. Glacial lake cores may contain material to help constrain the moraine ages further; for example deformed lake sediments within one of the (probable) late-glacial moraines indicates a period of advance after a significant still-stand. From the mapped moraine positions and valley shapes we reconstruct probable glacier area and ELA for each stage. By combining the reconstructions from the Jahuacocha valley with the LGM extent and ELAs across the Cordillera Huayhuash the project will provide an improved understanding of the spatial gradients in ELA and ELA depression at a critical tropical location.
for more information, contact Joan Ramage