Holocene variations of Ameghino Glacier, southern Patagonia

Abstract

This study reports new data concerning the Holocene glaciation of Ameghino Glacier, an eastern outlet of the Southern Patagonia Icefield. The lowest 7 km of the valley occupied by Ameghino Glacier is now ice-free, of which the upper 3.7 km is a moraine-dammed proglacial lake. Many glacial features are present in the Ameghino Valley. Across the valley floor, four terminal moraines have been identified, each representing a Neoglacial advance. Prominent vegetation trimlines are associated with the youngest of these moraines (M IV) which dammed the proglacial lake. Samples for 14 C dating collected at the trimlines and from the valley floors indicate that the formation of M IV, the culmination of the recent maximum glaciation, occurred c. AD 1600-1700, and that deposition of the valley train occurred c. AD 1500. Large standing trees which were buried and killed by this period of deposition have subsequently been exhumed by river erosion. The glacier may have remained at the trimline level until around AD 1870-1880, the date obtained by Nichols and Miller (1951) from dendrochronological analyses. The number of Neoglacial advances (4) identified in the Ameghino Valley is the same as that recently identified at two other Patagonian glaciers, Upsala and Tyndall, and the date of the latest glacial episode, the 'Little Ice Age', is found to be synchronous. However, the ages of the earlier three Neoglacial episodes remain unknown.