Dating Neoglacial evente in Monte San Lorenzo, Argentina, using lichenometric methods

GARIBOTTI, I.A.; VILLALBA, R.

Uspallata

Workshop; Science Meeting IAI CRN 2047B, Documenting, understanding and projecting changes in the hydrological cycle in the America Cordillera; 2013

IANIGLA

Monte San Lorenzo (47°35′S, 72°18′W) is the highest mountain (3706 m) in the Argentinean southern Patagonian Andes. Two major glaciers, Glaciar San Lorenzo Sur and San Lorenzo Este, named according to Mercer (1968), are the largest ice bodies in the Argentinean sector of Monte San Lorenzo. These glaciers present large and conspicuous arcuate Neoglacial moraines. At each glacier, we mapped the sequence of moraines and dated the glacier deposits using lichenometric techniques. Historical terrestrial and aerial photographs are available for the area, as well as a radiocarbon date of organic material (Mercer, 1968) in an outer moraine of Glaciar San Lorenzo Este. Combination of this information with lichenometric dating has allowed a multi-proxy approach for dating glacier fluctuations. Lichenometric measurements provide similar dates for the set of glacier deposits at both glaciers, indicating four major Neoglacial advances with minimum dates estimated at 4900 years BP, 2600 years BP, 1800 years BP and 200-50 years BP. Concordance between lichenometric dates, historical aerial and terrestrial photographs, and the radiocarbon dating of the most external deposit, suggests that the established chronology for Neoglacial fluctuations of Monte San Lorenzo glaciers is consistent. In addition, our results show that lichenometric methods are reliable for dating landforms related to Neoglacial events. The estimated scenario of glacier fluctuations at Monte San Lorenzo is in agreement with both chronologies proposed for glacier fluctuation in the Patagonian Andes during the last 5 millennia (Mercer 1968, Aniya 1996). Dates estimated for the earlier event coincide with the Neoglacial Advance I proposed by Mercer. It is followed by two minor events that corresponded to the Neoglacial Advances II and III according to Aniya. Finally, both glaciers experienced 2 to 3 re-advances during the Little Ice Age period (Neoglacial Advance IV).