185 Quaternary Geology/Geomorphology

Wednesday, 31 October 2007
8:00 AM - 12:00 PM

LATE PLEISTOCENE GLACIAL ACTIVITY ON NEVADO SAJAMA, WESTERN CORDILLERA, BOLIVIA

Paper number: 185-14
Program: Technical Sessions
Time: 11:30 AM – 11:45 AM

Authors

Abstract

In the Eastern Cordillera, Bolivia, the 0o C isotherm intersects glaciers near the equilibrium line altitude (ELA). In the Western Cordillera, Bolivia, the 0o C isotherm is up to 1000 m below the termini of the glaciers (Klein et al., 1999). Thus, it has long been hypothesized that glaciers in the Eastern Cordillera are more sensitive to temperature changes while glaciers in the Western Cordillera are more sensitive to precipitation changes (Hastenrath, 1971). Accordingly, if the glaciers in the Eastern and Western Cordilleras respond to different forcings, then it is possible if not likely that the two areas have different glacial chronologies.

In order to test this hypothesis, geomorphic mapping and 36Cl exposure age dating of glacial deposits at Nevado Sajama, Western Cordillera, Bolivia were undertaken. Results indicate glaciers reached a maximum extent between roughly 16.9 ka and 10.2 ka during the global late glacial period,. Geomorphic evidence suggests that during this maximum advance some glaciers on the mountain were wet based while others were frozen to their beds. Identification of wet vs. frozen bed conditions allowed for the estimation of the elevation of the 0o C isotherm and a temperature depression of 3.9 - 4.8 oC from modern conditions. Additionally, an increase in annual precipitation of 42 - 65 % is estimated based on modern relationships between normalized snowline and precipitation.