A LATE-HOLOCENE (LESS-THAN-2600 BP) GLACIAL ADVANCE IN THE SOUTH-CENTRAL ANDES (29-DEGREES-S), NORTHERN CHILE

Radiocarbon dates and relative ages of soils on moraines provide evide nce of a substantial late-Holocene (>2600 BP) readvance of glaciers in the western part of the arid Andes at 29 degrees S. The glacier in th e Encierro valley, northern Chile, reached about 60% of its late-Pleis tocene extent. The equilibrium line altitude ELA during this advance r emained between 4250 and 4500 m which is above the modern 0 degrees C isotherm of the free atmosphere during summer. It is suggested that, g iven the specific climate at high elevations in the extremely arid And es, a substantial increase in effective moisture is sufficient to expl ain this advance, whereas no significant temperature depression was ne eded. This compares favourably with the regional late-Holocene climati c history, when lake levels were higher and effective moisture greater than today between 3000 and 1800 BP. Judging from regional palaeodata , we suggest that this late-Holocene humid spell was most likely relat ed to increased Westerly moisture sources from the Pacific.