Central Andes (Between Lat 31° and 35°S.)

As mentioned earlier, the Central Andes have large glaciers covering about 2,200 km², but very few people have ever come close to them. In spite of the proximity of the city of Santiago, the Central Andes have virtually no inhabitants (the large Maipo valley being an exception) and very few roads. Hiring mules has become very expensive. Unless a helicopter is chartered, a visit to the Cerro/Volcán Tupungatito, perhaps the most picturesque journey in the Central Andes, requires 8 days, with 6 of those days on muleback following a sometimes giddy and dangerous track along the Río Colorado. On the Argentine side, the glaciers are even farther from any road.

The two best Landsat MSS images that cover the Cordillera Central are reproduced in figures 9 and 10. From the images, a sketch map of the Cerro (Volcán) Tupungato-Nevado de los Piuquenes area has been drawn (fig. 11); the sketch map improves upon the information included in the 1:150,000-scale map published by Lliboutry (1956). A cross section of the same area is given in figure 6. Some of the major advances to the glaciological and geographical knowledge of the region gained from the Landsat images are provided in the following paragraph.

Figure 9.--Annotated Landsat MSS false-color composite image (2418-13414, bands 4, 5, and 7; 15 March 1976; Path 249, Row 83) of the Central Andes between Santiago and Mendoza.

Figure 10.--Annotated Landsat MSS false-color composite image of the Central Andes south of figure 9.

Figure 11.--Cerro (Volcán) Tupungato-Nevado de los Piuquenes area in the Central Andes, 50-85 km east of Santiago. Features have been delineated on the basis of published maps and analysis of Landsat images. The area shown by the small "v" pattern is a lava field erupted from Cerro/Volcán Tupungatito. Glaciers are shown in green, and the dotted areas are debris-covered glaciers or rock glaciers. The thick gray lines show ridgelines, the hachured gray lines show cliffs or depressions. The map projection is the same as the one for Landsat image 2022-13455 (13 February 1975; Path 249, Row 83). The coordinates are inferred from Paso de Las Pircas, Portezuelo del Tupungato, and Portezuelo de/Paso Piuquenes as given in Carta Nacional (scale 1:500,000, Instituto Geográfico Militar de Chile), although with such a map projection, the scale can only be approximate. Elevations are from several different sources and are derived from Lliboutry's 1:150,000-scale map (Lliboutry, 1956). The border between Chile and Argentina follows the main ridgeline (+++ where ridgeline is not continuous). Names in italics and names enclosed in quotation marks are names that are not listed in the gazetteers for Argentina (U.S. Board on Geographic Names, 1992a) and Chile (U.S. Board on Geographic Names, 1967, 1992c). Abbreviations: Co., Cerro, mountain; Nev., Nevado, snow- and (or) ice-capped mountain; E., Estero, creek (in Chile); and A., Arroyo, creek (in Argentina); and Q., Quebrada, creek. Paso is a cross-border pass and mule track; Pzo., Portezuelo, is any other pass.

Glaciar de los Polacos on the east slope of Cerro Aconcagua, at the head of Arroyo Relincho, is much broader and longer than previously suspected, with a length of 5.6 km (fig. 9, no. 3). Cordillera del Tigre has much more complex topography than is depicted on Argentine charts. Glaciers of the Cordón del Plata are much more important than realized by Mercer (1967, p. 100); the main glacier is 8 km long. East of Cerro Marmolejo (fig. 9), a debris-covered glacier exists at the head of Arroyo Piedras Negras. Arroyo los Plomos does not come from Cerro Marmolejo. Meltwater from the large debris-covered glacier east-northeast of Cerro Marmolejo drains through Arroyo Barroso instead. Lastly, the east glacier of Cerro Marmolejo, at the head of Arroyo Barroso, is much longer than previously thought; it is about 10 km long. On the east slope of Volcán San José the two bare glacier tongues are in fact linked and continue as a debris-covered glacier until 9 km from the crater (fig. 10). Just south of Volcán Maipo, Cerro Listado (4,850 m) contains several glaciers; the main one is in the drainage basin of Río Bayo. Its ice cover is similar to the one of Nevado de Arhüelles (4,840 m), just north of Volcán Maipo.

Glaciers of the Central Andes can be quite large for such moderate latitudes, sometimes as much as 14 km long. Some of them, such as the ones on the plateau that gently descends from 4,700 m to 3,800 m at the head of Río Olivares (see southwestern part of fig. 9 for general location), have no cover of morainic debris along nearly their entire length. But many other glaciers have morainic cover in their lower part or sometimes over almost their entire length, such as Glaciar Horcones Inferior (no. 4 south of Cerro Aconcagua in fig. 9), Glaciar del Tunuyán (see fig. 12), or Glaciar Cachapoal (south of Picos del Barroso) (central part of fig. 10 and fig. 13). In the standard false-color satellite images, the debris-covered glaciers appear as dark green (not to be confused with the lighter green of large thalwegs without vegetation). Where the morainic debris-cover consists only of rocky blocks, as at the terminus on the right side of Glaciar Universidad (lat 34°40'S., fig. 10), the false color appears as dark blue.

Figure 12.--Vertical aerial photograph of glaciers at the head of Río Tunuyán (from IFTA, 1973). The very long (20.2 km) glacier shown south of Cerro (Volcán) Tupungato on Lliboutry's 1:150,000-scale map (Lliboutry, 1956) is, in fact, formed by three successive glaciers: (1) Glaciar Sur del Tupungato, which enters at the upper right-hand corner of the photograph; (2) an unnamed glacier located between Nevado sin Nombre (6,000 m) (just off the top of the photograph) and Cerro Alto (6,111 m) (off bottom left of photograph), which contains a large névé; and (3) a glacier located in a deep cirque between Cerro Alto and Nevado de los Piuquenes (6,017 m) (see fig. 11) that may be named Glaciar del Tunuyán. The two latter glaciers are heavily debris-covered and contain small supraglacier lakes and a distinct thermokarst facies (note especially the course of the creeks flowing from the west). In the unnamed glacier, festooned areas of bare glacier ice show the diagnostic evidence of surge behavior.

Mercer (1967), in his "Southern Hemisphere Glacier Atlas," gathered all the available information on the glaciers in South America. However, the information derived from individuals who have little knowledge of glaciers must be used with caution because, in general, they do not recognize debris-covered glaciers as glaciers. For instance, they did not realize that the huge field of rubble at the head of Río Cachapoal is actually a debris-covered glacier, 12 km long, the longest one on the Chilean side of the Central Andes (fig. 13) (see west edge of fig. 10 for general location).

Figure 13.--Glaciar Cachapoal, the largest debris-covered glacier in Chile, is 12 km long. The glacier is entirely covered with debris that is indistinguishable from its left margin. The rocky wall in the background of the photograph marks the border between Chile and Argentina. The foreground is at an elevation of about 2,400 m. The mountain around which Glaciar Cachapoal flows is 4,500 m high.

At the foot of rock walls, "ice-debris glacierets" commonly are found, where a new layer of ice forms most winters, and a layer of rubble falls down (or appears at the surface) each summer. In many glacier tongues, clean ice is superimposed on a very thick layer of dragged and sheared debris-layered ice. The latter may have been either a frozen soft bed (permafrost) or an "ice-debris glacieret," but in both cases, it has been dragged and sheared during a glacier advance or a glacier surge (Lliboutry, 1954a, 1956, 1965, 1986). Near the terminus, where melting reaches the lower debris-laden layer, a thick ablation moraine forms.

Where ice has melted (see the section on "Rock Glaciers" below), a continuum (all intermediate cases are possible) exists between a debris-covered glacier, an ice-debris glacier, and a rock glacier. It is possible to make separate inventories of glaciers (covered or not) on the one hand and of rock glaciers (with or without some ice included) on the other hand. For this reason, all young rock glaciers are listed in the glacier inventories. Consequently, in table 7, the area of covered glaciers is overestimated.

The first glacier inventory, based on sketches drawn by Chilean andinistas (mountaineers), personal exploration, and Trimetrogon aerial photographs, is found in Lliboutry (1956). Glacier inventories based on the Chilean aerial photographic coverage of 1955-56 have been made by C. Marangunic (basins of Río del Plomo and Río Cachapoal) and by G. Casassa (Chile). Glacier inventories based on the Argentine aerial photographic coverage of 1980-81 have been made by C. Aguado (Río de los Patos basin), by L. Espizúa (most of Río Mendoza and Río Tunuyán basins), and by D. Cobos (Río Atuel basin). Except for the inventory available in Corte and Espizúa (1981), all these inventories remain unpublished.

Table 7.--Total glacier area in the Central Andes

[Given in square kilometers. Data for Chile from Valdivia (1984); data for Argentina from Espizúa and Aguado (1984)]