LATE-QUATERNARY GLACIATION AS A PROXY FOR CLIMATE-CHANGE IN THE CENTRAL ANDES

The glacial history of the central Andes is used to reconstruct climat ic changes during the last 20,000 years. The depression of the equilib rium-line altitude of glaciers is determined to quantitatively reconst ruct these changes. The results indicate that late-Pleistocene glaciat ion culminated between 14,000 and 12,000 yr B.P At this time equilibri um-line altitudes in the Eastern Cordillera of Bolivia were depressed on average 300 m in response to an increase in precipitation and a tem perature reduction of 3.5-degrees +/- 1.6-degrees-C. Between 12,000 an d 10,000 yr B.P. deglaciation proceeded rapidly and several stages of recessional moraines were deposited. By 10,000 to 8,000 yr B.P. glacie rs in most valleys were near their modern extents. In the late-Holocen e glaciers advanced again because of colder conditions and maize produ ction may have been limited as indicated by the ethnobotanical evidenc e from archaeological sites in the Mantaro River valley of central Per u.