'Little Ice Age' Glacier Fluctuations, Gran Campo Nevado
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The Holocene 15,1 (2005) pp. 20–28 ‘Little Ice Age’ glacier fluctuations, Gran Campo Nevado, southernmost Chile Johannes Koch1* and Rolf Kilian2 (1Department of Earth Sciences, Simon Fraser University, Burnaby, BC V5A 1S6, Canada;2Lehrstuhl fu¨r Geologie, FB VI, Universita¨t Trier, 54286 Trier, Germany) Received 8 May 2003; revised manuscript accepted 1 January 2004 Abstract: Moraine systems of Glaciar Lengua (unofficial name) and neighbouring glaciers of Gran Campo Nevado (53S) in the southernmost Andes were mapped and dated by dendrochronological means. They were formed around AD 1628, 1872=1875, 1886, 1902, 1912 and 1941 with the advance in the 1870s being calendar dated. Recessional moraines within each moraine system correspond to brief standstills or minor readvances. A significantly older moraine could not be directly dated by dendrochronological methods as the forest on it was assumed to be second-generation or older. From soil-formation rates, it is assumed that this moraine was formed at some time between AD 1280 and 1460, a time in which many other glaciers in Patagonia formed moraines. Overall, fluctuations of Glaciar Lengua show a strong synchronicity to other glaciers in the Patagonian Andes between 41S and 55S. This study suggests that Glaciar Lengua and possibly all glaciers of Gran Campo Nevado reached their Holocene maximum during the ‘Little Ice Age.’ Key words: ‘Little Ice Age’, glacier variations, dendrochronology, southernmost Andes, late Holocene. Introduction to topographic-climatic effects and glacier dynamics (Warren and Sugden, 1993; Holmlund and Fuenzalida, 1995), further The ‘Little Ice Age’, a period during the last millennium in studies are needed to establish a complete picture of the which glacier cover was generally more extensive (Grove, Holocene glacial chronology in Patagonia. In all previous 1988), is a phenomenon recorded in all mountainous areas of studies, glacial advances were dated to the ‘Little Ice Age’ the world (e.g., Luckman, 2000; Holzhauser, 1985; Wiles (LIA). However, studies concerningspecifically the LIA are et al., 1999; Villalba, 1994). These glacier fluctuations seem very few (Villalba et al., 1990; Harrison and Winchester, to be synchronous on a centennial scale alongthe pole- 1998; 2000; Winchester and Harrison, 2000; Winchester et al., equator-pole I transect (alongthe Americas). However, long 2001; Strelin and Casassa, unpublished data) and therefore stretches alongthe Cordillera remain uninvestigated.There- more detailed LIA chronologies would be welcome (Luckman fore, Luckman and Villalba (2001: 136) pointed out that ‘there and Villalba, 2001). remains a significant need for detailed, well-dated records of [‘Little Ice Age’] glacier fluctuations’. Gran Campo Nevado is a small ice cap (approximately 200 Study area km2) in the southernmost Andes (53S; Figure 1). It is located between the Hielo Patagoonico Sur (48200 to 5130’S) and the The investigated Andean area at 53S is characterized by Cordillera Darwin (54À55S), both of which have been the deeply incised fiords and islands with their highest elevations focus of glaciological studies (e.g., Warren and Sugden, around 2000 m (Figure 1). The northÀsouth trendingAndes 1993; Casassa, 1995; Holmlund and Fuenzalida, 1995). form an orographic barrier to the very strong and prevailing However, due to relatively difficult access only a few studies westerlies, leadingto annual precipitation in excess of 6000 on Holocene glacier activity have been carried out (e.g., mm (Schneider et al., 2003). Precipitation is evenly Mercer, 1968; 1970; 1982; Clapperton and Sugden, 1988; distributed throughout the year and the area is characterized Aniya, 1995; 1996; Kuylenstierna et al., 1996). As recent varia- by cool summers and mild winters. tions of Patagonian glaciers are highly localized, probably due Glaciar Lengua, as well as approximately 25 other unnamed outlet glaciers of Gran Campo Nevado, has not been subject to any study known to the authors. Glaciar Lengua is located *Author for correspondence: (e-mail: [email protected]) west of Bahia Bahamondes on Canal Gajardo, a fiord connect- # 2005 Edward Arnold (Publishers) Ltd 10.1191/0959683605hl780rp Johannes Koch and Rolf Kilian: ‘Little Ice Age’ glacier fluctuations, Gran Campo Nevado, Chile 21 Figure 1 Location of Glaciar Lengua. The small map in the top right shows the location of the study site with the Hielo Patagoonico Sur to the north, and Cordillera Darwin in the south. The main map shows the location of Gran Campo Nevado in relation to Estrecho de Magallanes and Seno Skyringand the map of Gran Campo Nevado ice cap (lower right)includes the names mentioned in the text. ingSeno Skyringin the northeast with the Estrecho de Magal- on moraine A, with forest on moraine B appearingto be lanes to the southwest (Figure 1). The valley between the gla- slightly younger, lacking the fallen trunks and stumps of cier front and Bahia Bahamondes is mainly occupied by a bar moraine A. The forest cover on interveningmoraine systems of Holocene sediments. The well-drained parts of the bar are (moraines C and D) represents intermediate succession stages forested by Magellanic Rainforest, with the remaining area with Nothofagus antarctica and N. betuloides codominating. covered by Magellanic Moorland. Forests are dominated by Nothofagus betuloides (Mirb.) Blume with Nothofagus antarc- tica (Forst) Oerst, Pilgerodendron uviferum (D. Don) Florin and Drimys winteri J.R. & G. Forst beingminor components. Methods The moraine systems in the glacier foreland of Glaciar Lengua were mapped during the austral summer of 2000. The formation of the moraines was dated by dendrochronolo- The outermost moraine lies approximately 900 m in front of gical means. The age of the oldest tree on a moraine provides a the present glacier snout. The geomorphic and vegetational minimum estimate for moraine formation and stabilization evidence show four distinct moraine complexes lyingwithin (Sigafoos and Hendricks, 1969; McCarthy and Luckman, 300 m of each other (moraines BÀE; Figure 2). A fifth moraine 1993). On the foreland, tree invasion appears to be uniform system (moraine A) was found only on the north side of Rio and at an early stage in succession. One problem is that, due Lengua. The moraine systems dam Lago Lengua, a small lake to the very dense forest cover on all moraines, it is possible that drained by Rio Lengua. Rio Lengua has breached all the the oldest trees were not always sampled and dated. Two moraine systems and its course has changed since the last increment cores were extracted from several trees on each mor- glacier advance. Each moraine complex is better defined north aine usinga 4.3 mm diameter increment borer. By removing of Rio Lengua, whereas the south side has been modified by two cores, data are replicated and the possibility of missing fluvial activity. All moraine systems comprise complex rings or ‘false’ rings is reduced (Stokes and Smiley, 1968). multiple moraines and push moraines; for example, moraine Cores were mounted and prepared for analysis by sandingwith C has four distinct ridges within the main moraine complex progressively finer grades of sandpaper to enhance the defi- (Figure 3). It is therefore assumed that during the general nition and contrast of annual tree-ringboundaries. Ringswere recession of Glaciar Lengua there were various standstills measured with a precision of Æ 0.01 mm. Trees damaged or and minor readvances. tilted by a glacier advance provide additional age controls on All moraine systems are extensively covered by dense forest moraines and trees killed by a glacier advance can be used to (Figure 4). However, each system shows a different succession develop floatingchronologiesthat can be crossdated with stage (Figure 3), ranging from pioneer Nothofagus antarctica livingchronologies,with the year of death providinga forest on the innermost moraines (moraine E) to primary minimum age for the moraine. Discs were cut from any Magellanic Rainforest dominated by Nothofagus betuloides damaged or killed trees found on the moraines and analysed 22 The Holocene 15 (2005) Figure 2 Geomorphic map of Glaciar Lengua and its surroundings. Shown are the mapped and dated moraine systems AÀE with the transect across the moraines in white (Figure 3). The insert map shows the mapped moraines AÀE and the location of samplingsites numbered 1 À9. The bold lines indicate the major moraines, while the lighter lines indicate minor moraines formed by standstills and=or readvances. Contour intervals are 100 m. Figure 3 Cross-section of the moraine systems of Glaciar Lengua. The sketch is approximately to scale with a slight vertical exaggeration. The length of the transect is approximately 300 m and the height of the biggest moraine is approximately 25 m.The location of the transect is shown in Figure 2. The different succession stages are indicated by different heights of vegetation cover. in the same way as the cores. However, four radii were be corrected for (McCarthy et al., 1991; Winchester and measured on the discs to improve the certainty of the crossdating. Harrison, 2000). We used the method proposed by A livingtree-ringchronologywas formed from all trees Winchester and Harrison (2000). To establish age=growth growing on the various moraines. The series was checked relationships below coringheights,15 small trees were cut and verified by the International Tree-RingData Bank at ground level. Each tree’s local environment, its height (ITRDB) software program COFECHA and crossdated and basal ringcount were recorded. Furthermore, where (50-year dated segments lagged by 25 years, with a critical level applicable, trees with sections suggesting stressful growth of correlation [99%] set at 0.32), thus creatinga master ring- conditions (e.g., narrow rings or compression wood) were width chronology (Holmes, 1983). A floating chronology was recorded. Ages of trees below core height were then based developed from a killed tree includingthe bark. The floating on the characteristics of the rings nearest the central pith series was crossdated against the living chronology using and the recorded details for each tree.