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Radiocarbon analyses of lake sediments from the Chirripo massif of Costa Rica indicate that glaciers last retreated about 10 000 yr BP. The 2 moraine complexes recognized on the massif apparently predate the M 111 advance on the volcanoes of central Mexico. Snowfall is unknown today in Costa Rica (Coen 1983), but during the Pleistocene snow fell and accumulated on the Chirripo massif in the Cordillera de Talamanca, forming several small glaciers. Ice-scoured basins, striated and smoothed rocks, and moraines have been mapped and described (Weyl 1956a, b , Hastenrath 1973, Bergoeing 1978, Barquero & Ellenberg 1982-83) but the chronology of ice growth and decay has remained a matter of speculation. Weyl (1956~1, b) first established the existence of a glacial episode on the Chirippo massif; based on the freshness of the glacial forms he suggested an age equivalent to the Wiirm-Wisconsin. Hastenrath (1973) identified 2 distinct sets of moraines on the massif: an older complex at valley exits that consists of up to 3 separate ridges and is composed of coarse, deeply weathered material, and a younger set of smaller moraines in the upper portions of the valleys characterized by finer material and a shallow humus layer. Hastenrath suggested that the larger and lower moraines belonged to the main period of glaciation, and that the smaller moraines upslope were appreciably younger and represented later, possibly recessional stages; however, he was unable to secure enough organic material within moraines to attempt radiocarbon dating. Here I report recent 14C determinations on lake sediments that provide the first evidence available as to the timing of deglaciation in the mountains of Central America. The radiocarbon dates and sediment stratigraphy indicate that both sets of moraines in the Chirripo highlands were deposited before 10000 yr BP (before present), and that the region has been ice-free throughout the

Timing of deglaciation in the Cordillera de Talamanca, Costa Rica