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

In the Eastern Cordillera, Bolivia, the 0^o C isotherm intersects glaciers near the equilibrium line altitude (ELA). In the Western Cordillera, Bolivia, the 0^o 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 0^o 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.