干旱区生态环境知识资源中心

Glacial geologic evidence and radiocarbon-dated glacial deposits provide evidence of glacier fluctuations during the last 5 ka years in the Andes. Radiocarbon-dated moraines, morphological and stratigraphical studies permit the reconstruction of glacier fluctuations during the Holocene in the Valenzuela area of the Mendoza Andes valley located at 35 degrees S, in the upper Rio Grande basin. The Holocene record in this part of the Andes is mostly unknown, so this research is relevant for palaeoclimatic reconstructions in South America. In the Rio Valenzuela, glacier variations were dated in the El Azufre arid El Penon valleys. The first Neoglacial advance occurred at c. 5700 yr BP and a very close re-advance of similar magnitude occurred at 4700-4300 yr BP which formed well-preserved lateral-terminal moraines. The first Neoglacial advance occurred in the El Penon valley at c. 4400 yr BP and a well-preserved terminal moraine is observed. A second Neoglacial advance reached its maxima at c. 2500-2200 yr BP in the El Azufre and El Penon glaciers. A third, corresponding to the ’Little Ice Age’, culminated at c. 400 yr BP (c. AD 1451-1641 cal. yr) and 350 +/- 60 yr BP (C. AD 1460-1644 cal. yr) in the El Azufre valley The third Neoglacial advance is distinguished in the El Penon valley based on morphological characteristics, colour, freshness of the glacial deposits and the proximity to the active glacier. It is indicated by the Amarilla I, II, III lateral moraines. An estimation of the magnitude of snowline depression is obtained comparing the altitude of the present snowline with that of the reconstructed snow line for the first Neoglacial and ’Little Ice Age’ advances.