The Quaternary Glaciation of Chile: a Review
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Revista Chilena de Historia Natural 67: 369 - 383, 1994 The quaternary glaciation of Chile: a review La glaciaci6n cuaternaria de Chile: una revision CHALMERS M. CLAPPERTON Department of Geography, University of Aberdeen, Aberdeen AB9 2UF, Scotland ABSTRACT A review of literature on the Quaternary glaciations of Chile shows that repeated advances occurred in the central and southern Andes. However, radiocarbon dated sequences have been obtained only for the last glaciation in the Chilean Lakes Region and in the Paine and Magallanes regions of Patagonia. These suggest that glacier lobes from the icefields advanced at least five times during the last glaciation. Reconstruction of palaeo-snowlines indicates that the climatic belts during the glacial interval were basically similar to the modem, but that effective precipitation was greater in the north (arid) of Chile, and that the humid westerlies in temperate latitudes were displaced 5-6° to the north. Snow line descended 800-1 OOOm. While glaciers in the Lakes Region reached their maximum extension at ca.20-21,000 yr BP, those in the south and north of the country may have been more extensive at ca.27,000 yr BP, due to the greater humidity available. Some glacier lobes from the southemmost icefields of Chile were still expanded at ca.l2,000 yr BP and may have readvanced during the interval I 2,000-9000 yr BP. Key words: Southern Andes, glacier dynamics, paleo-snowlines, paleolakes. RESUMEN Una revision de la literatura sob re glaciaciones cuaternarias en Chile muestra, que en Ios Andes del centro y sur, han ocurrido repetidamente avances de glaciares. Sin embargo, secuencias fechadas radiocarbonicamente solamente se han obtenido para la ultima glaciacion en la Region de Ios Lagos yen !as regiones del Paine y Magallanes, en la Patagonia. Ellas sugieren que Ios lobulos glaciares de Ios campos de hielo avanzaron a! menos cinco veces durante la ultima glaciacion. La reconstruccion de !as paleolfneas de nieves indican que Ios cinturones climaticos durante la ectad glacial fueron basicamente similares a Ios actuales, pero la precipitacion efectiva fue mayor en el norte (ári do) de Chile, y que cl cinturon de Ios oestes de !as latitudes templadas se desplazo 5-6° a! norte. La lfnea de nieves descendio 800-1000 m. Mientras que Ios glaciares de la Region de Ios Lagos alcanzaron su extension maxima hace 20-21,000 años atras, aquellos del sur y norte del pafs pueden haber sido más extensos ea. de 27,000 afios, debido a la mayor humedad disponible. Algunos lobulos glaciares de Ios campos de hielo del extremo sur de Chile estaban aún expandidos hace 12,000 afios A.P. y pueden haber reavanzado entre 12,000 y 9,000 afios A.P. Palabras clave: Andes del sur, dinamica glaciar, paleolfneas de nieve, paleolagos. INTRODUCTION This paper reviews the state of knowledge about past glacier fluctuations throughout Observations on Quaternary glaciation in the Chilean Andes in an attempt to expose various parts of Chile have been made since problems that should be tackled to give a Darwin's visit in the 19th. Century. The better understanding of Quaternary Magellan region was commonly visited by glaciation in Chile, and its contribution to European scientists on their way to and studies of global climatic change. from Antarctica and this led to short reports about glacial features in the area (e.g. Nordeqskjld 1898, Quensel 1910). Topography, climate and modern snowline Subsequently, some classic works on Quaternary glaciation and glaciology in As in most of the Andes, the large-scale southernmost South America laid the topography of Chile has evolved primarily foundations for an understanding of the through late Cenozoic tectonics and glacial history of the southern Andes volcanic activity (Clapperton 1993a); (Caldenius1932; Briiggen 1950, Auer1956, denudational processes have shaped the Mercer 1976, Rabassa and Clapperton smaller-scale relief according to the 1990). climatic regime. 370 CLAPPERTON Extending approximately north-south primary climatic systems affecting Chile. across latitudes ca.l7°S-56°S, some In the south (lats.56°S-42°S) the constantly 4200km, the Chilean Andes contain a wet westerly system, with only slight number of different tectonic segments with changes in precipitation amount seasonally, distinctive topography. For example, brings totals in excess of 5000mm to sea between latitudes l8°S and 27°S Quater- level stations (Miller 1976). Such high nary-Recent volcanism has created the annual precipitation explains the presence highest relief, with more than 40 mountains of large icefields in southern Chile, with rising above 5500m altitude (Fig.l a); but outlet glaciers descending to sea level the mean topographic elevation is (Fig. le). ca.4000m. South of Nevada Ojos del Salado Between 42°S-31 os lat., in the so-called (6893m) at latitude 27°S, the Andes are 'Mediterranean-type' climatic zone, winter devoid of active volcanoes until latitude precipitation is brought by the seasonal 33° 27'S. Nevertheless, underplating of the movement northwards of the Polar Front continental edge by a buoyant part of the and associated cyclonic depressions. This N azca ocean crus tal plate has raised this nourishes glaciers and snowfields where segment of the Andes above a mean altitude altitude, topography and exposure provide of 4000m, culminating in Cerro Aconcagua suitable accumulation sites in these latitu- (6960m). des; but many parts of the mountains even Volcanic massifs appear again at latitude above 4000m altitude lose their snow cover 33°S, where Volcan Tupungatito (5628m) in summer because of high insolation and and Volcan Maipo (5264m) are two of the the relatively low total of mean annual highest, but a dramatic change in topo- precipitation (250mm). graphic elevation occurs at latitude 37°S, North of latitude ca.32°S mean annual south of which only Cerro Valentin (4058m) precipitation falls below 300mm, and comes at latitude c.46°50' S rises above 4000m, mainly in the austral winter as occasional and fewer than ten summits exceed 3000m. outbursts from cyclonic storms extend Here, thinner crust and the subduction northwards. Some precipitation may come regime have created a segment of highly to this part of the Chilean Andes in the fractured terrain with abundant volcanism; austral summer if convectional storms on but the mean altitude of the Andean crest is the Puno-Altiplano extend westwards (in- only ca.l800m. Many volcanic peaks rise vierno boliviano), but the annual amount above 2000m, as in Volcan Villarica from this source is generally insignificant. (2940m) and Volcan Osorno (2660m), both In this region, dominated by anticyclonic of which support small icecaps (Fig.lb). atmospheric circulation, intense radiation South of latitude 4 7°S, the volcanic systems and evaporation combined with low are more widely spaced but the mean precipitation totals cause the permanent topographic elevation rises to ea. 2500m snowline to lie above 6000m. Thus even and much of this is covered with the where mountains rise above the mean level Patagonian icefields (Fig.l c). of the atmospheric 0°C isotherm, commonly The climate of the Chilean Andes varies at ea. 4900-4700m in these latitudes (Fox from hyper-arid tropical in the north 1993), permanent snow and ice can not (lat.l rS-27°S) to hyper-humid temperate survive because of aridity and high at latitu.de ca.50°S. The precipitation insolation. Even the highest massif, which regime clearly controls local and regional rises to 6893m in Nevada Ojos del Salado, snowline altitudes and determines the has a patchy distribution of permanent distribution of modern glaciers. Fig. 2 snow, and glaciers no longer exist. illustrates the annual precipitation cha- Moreover, although the summit of racteristics for stations in different climatic Llullaillaco volcano culminates above regions of Chile and Fig. 3 shows the 6700m, it has no glaciers and supports only dramatic fall in snowline altitude from a small permanent snowpatch (Messerli et ca.6000m in the north to ca.250m in the al. 1993). Not only does the snowline south. This is due to the effect of the three altitude rise from east to west in these THE QUATERNARY GLACIATION OF CHILE 371 ... ,.. ,.. ,. .,. FiR. l.a Fig. lb ARGENTINA PATAGONIA ATLANTIC OCEAN ,. ,.. Fig. 1: General topography of the Chilean Andes L_______J00km ... and location of places mentioned in the text. Topograffa general de Ios Andes de Chile y ubicaci6n de Ios Fig. l.c lugares mencionados en el texto 372 CLAPPERTON 400 A 400 B SP 350 350 300 300 250 250 "'11.) 11.) .. :::"' u 11.) ~ 200 ~ 200 Ev ::i 150 ::i 150 100 100 50 ,_ .... , 50 '/ ------PA 0 0 JFMAMJJASOND JFMAMJJASOND Fig. 2: Mean monthly precipitation for selected stations representing the different climatic regions of Chile (after Miller, 1976). A. Stations south of 45°S: SP: San Pedro (47°43'S, 74°55'W) EV: Evangelistas (52°24'S, 75°06'W) PA: Punta Arenas (53°10'S, 70°54'W) B. Stations north of 45°S: PM: Puerto Montt (41°28'S, 72°57'W) Val: Valdivia (39°48'S, 73°14'W) CON: Concepci6n (36°40'S, 73°03'W) VAL: Valparafso (33°01'S, 71°38'W) LS: La Serena (29°54'S, 71°15'W) Precipitaciones medias mensuales de estaciones seleccionadas como representativas de diferentes regiones climticas de Chile (de acuerdo a Miller, 1976). A. Estaciones al sur de 45"S: SP: San Pedro (47"43'S, 74"55'W) EV: Evangelistas (52"24'S. 75"06'W) PA: Punta Arenas (53"10'S, 70"54'W) B.Estaciones al norte de 45"S: PM: Puerto Montt (41"28'S, 72"57'W) VAL: Valdivia (39"48'S, 73"14'W) CON: Concepci6n (36"40'S, 73"03'W) latitudes, but a clear gradient rises also 2500m until the region of humid westerlies from north to south between latitudes 30°S at ca.Iat.45°S.