Recent glacier variations and snow line changes in central Chile
Andrés Rivera (Departamento de Geografía, Universidad de Chile and Centro de Estudios Científicos, CECS)
Gino Casassa and Cesar Acuña (Centro de Estudios Científicos, CECS)
Rosemary Vieira (Universidade Federal do Rio Grande do Sul, Brasil)Glaciers in the Chilean central Andes (28°- 41° S) have shown a significant frontal retreat during the last 4 decades, additionally, they present an important reduction of their surfaces. This process is believed to be a clear response to the temperature increase observed at weather stations holding the longest records in the area (Rosenblüth et al., 1997), the decrease in the amount of total annual precipitation (DGA, 1999) and the increase in the elevation of the snowline in that region (Figure 1).
Despite the generalized trend of retreat, significant differences are observed among the glaciers considered for this study. Their response to climatic variations depend upon local factors, such as the geometry of the valley, shape of terminal front, type of moraine material covering the ice and the hipsometry of the glacier basin.
Table 1 shows the glaciers considered for this work. They have been assessed using historical aerial photographs and regular cartography from the Chilean Instituto Geográfico Militar (IGM).
The Juncal Sur Glacier (Table 1) shows the largest retreat, approximately -50 m a-1 from 1955 to 1997. On the northern slope of the same mountain, Monte Juncal, lies the Juncal Norte Glacier which presents the smallest retreat in central Chile for the same period, namely -4 m a-1 (Table 1). The probable cause for the small retreat of Juncal Norte glacier is the abrupt topography surrounding the terminal front, which produces significant shade effects that reduce ablation.
The Cipreses Glacier, located in the Cachapoal basin, represents an important case in central Chile. As shown in figure 2, this glacier has shown a constant retreat, stressed during the last decades when its retreat rate has tripled.
In the south central region of the country, recent variations of glaciers of Monte Tronador have been studied. This mountain has a large ice surface which flows towards Argentina and Chile, where several tongues covered by moraine material are located at the feet of impressive ice cascades.
Among the glacier tongues flowing towards Chile, of special mention are the glaciers Casa Pangue and Blanco Chico, with rates of retreat of -32 m a-1 during the period 1961-1995. The Blanco Chico glacier showed in 1955 a very stable position on a visible moraine with a calving front in a proglacial lake. However, as the glacier retreated from this pinning point, the retreat accelerated because of increased calving, creating a more than 2 km long lake in an area previously occupied by ice.
Provided the current climatic trend continues, present retreat rates and surface losses will result in the disappearance of a number of small and medium sized glaciers, as it is now happening with G32 and G30 glaciers in the Maipo basin (Table 1).
References
DGA, 1999. Política Nacional de Recursos Hídricos. Documento de Discusión. Ministerio de Obras Públicas / Dirección General de Aguas, Santiago, 49 pp.
Rivera, A., Acuña, C., Casassa, G. and Bown, F. 2002. Use of remote sensing and field data to estimate the contribution of Chilean glaciers to the sea level rise. Annals of Glaciology, 34: 367-372.
Rosenbluth, B., Fuenzalida, H. and Aceituno, P. 1997. Recent Temperature Variations in Southern South America. International Journal of Climatology, 17, 67-85.
Table 1. Glacier surface changes and normalization to 51 years in Chile (Rivera et al. 2002) Name of the glacier Location in Geographical coordinates Aspect Study
PeriodOriginal
surface
AreaFinal
surface
AreaTotal
Area
ChangeLost-area ratio Loss:
51 yearsFrontal variations
rateLatitude S Longitude W years km2 km2 km2 % km2 m a-1 Tronquitos 28º32` 69º43` SW 1955-84 4.6 4.0 -0.52 -11.4 -0.46 -14 Juncal Norte 33º02` 70º06` N 1955-97 9.0 8.8 -0.22 -2.5 -0.27 -4 Juncal Sur 33º05` 70º06` S 1955-97 25.6 22.8 -2.8 -10.9 -3.40 -50 Risopatron 33º08` 70º05` W 1955-97 5.4 4.9 -0.53 -9.8 -0.64 -13 Olivares Beta 33º08` 70º11` SW 1955-97 -1.2 -21 Olivares Gama 33º08` 70º10` SW 1955-97 14.7 13.5 -1.2 -8.2 -1.46 -12 G30 33º08` 70º08` S 1955-97 1.3 0.9 -0.4 -31.0 -0.49 -12 G32 33º08` 70º07` S 1955-97 1.4 0.7 -0.72 -50.7 -0.87 -13 Esmeralda 33°14' 70°13' N 2000* 4.8 Cipreses 34º33` 70º22` W 1955-97 40 39.4 -0.57 -1.4 -0.78 -27 Universidad 34º42` 70º20` SW 1955-97 -18 Casa Pange 41º08` 71º52` N 1961-95 7 6.4 -0.6 -8.6 -0.90 -32 Blanco Chico 41º09` 71º55` W 1961-95 7 6.6 -0.4 -5.7 -0.60 -32 Verde 41º12` 71º50` S 1961-95 8.1 8.0 -0.13 -1.6 -0.20 -13 Cerro Blanco 48°20' 72°15' W 1945-97 12.3 11.8 -0.48 -3.9 -0.46 -25 Note:* Frontal and areal variations of Esmeralda glacier have not been studied The copyright for content on this website is held by Laboratorio de Glaciologia, except for material provided by other organisations, where copyright ownership is indicated. Downloading material from this website is permitted, for non-commercial purposes and only if the source is indicated (www.glaciologia.cl).
