The glacierization of the cordilleras in Perú is directly related to the physical geography of the Andes, the elevation of the mountains, and the precipitation pattern. Generally speaking, the precipitation that falls on the glaciers comes from the Amazon and Paraná basins to the east of the mountains and falls as snow in the Andes because of the high elevations. The annual precipitation of snow in the highest cordillera is between 1,200 and 2,500 mm of water. This results in an annual accumulation of 2 to 3 m of snow between 5,000 and 6,000 m of elevation. The equilibrium line altitude that separates the accumulation area of glaciers from the lower ablation areas is between 4,800 and 5,100 m.
Hollin and Schilling (1981, p. 191) summarized the lowering of the snowline in the Peruvian Andes during the Pleistocene: "...the Pleistocene snowline was...4,000 m on the seaward side and 3,700 m on the landward side in northwest Perú; 4,300 m in central Perú; and 4,500 m in the southwest and 4,200 m in the northeast in a transect through Arequipa." Mercer and Palacios (1977) found evidence for a snowline of about 4,200 m for Nevado Auzangate in the Cordillera de Vilcanota in the last Wisconsinan and a snowline of 3,650 m for the coldest part of the Pleistocene; this compares with 4,600 m for the elevation of the modern glacier terminus. It is clear that the Andean mountains of tropical South America also experienced major climate cooling during the Pleistocene.
The Humboldt Current and the El Niño Current cause the unusual climatic conditions in Perú. The lowlands along the Pacific Coast have a hyperarid climate with infrequent rains and sparse to nonexistent annual precipitation. In contrast, the Andean highlands have alternating dry and rainy seasons and moderate precipitation. The eastern slopes of the Andes receive the greatest precipitation because of moisture from the vast Amazon basin, and precipitation continues throughout the year.
Because of these climatic variations, the flora and fauna in the arid coastal regions are completely dependent upon water from the Andean region (Dollfus, 1965). The glacierized areas in the Cordillera Occidental are very important as the unique sources of permanent water supply for the desertlike coastal areas of Perú.
Studies of ice cores from the Quelccaya ice cap in southern Perú by Ohio State University, in cooperation with Electroperú, have provided new data about climatic conditions during the last 1,500 years. The studies included measurement of oxygen and other isotopes, as well as the study of conductivity and microparticles in the ice cores (Thompson and Dansgaard, 1975; Thompson, Hastenrath, and Morales Arnao, 1979; Thompson, 1980; Thompson, Bolzan, and others, 1982; Thompson, Mosley-Thompson, Grootes, and others, 1984; Thompson, Mosley-Thompson, and Morales Arnao, 1984; Thompson, Mosley-Thompson, Bolzan, and Koci, 1985; Thompson, Mosley-Thompson, Dansgaard, and Grootes, 1986; Thompson and Mosley-Thompson, 1987, 1989; Thompson, Davis, and others, 1988).
The results of such paleoclimate studies, including those of Hastenrath (1967), Nogami (1972), Mercer and Palacios (1977), and Wright and others (1989), together with present-day climatic data, will lead to a more accurate understanding of climatic variability in the region. This information also should be helpful in planning the most cost-effective development of the hydrological resources of Perú.
The presence of glaciers in Perú was first mentioned in 1532 by Miguel de Astete, who was one of the members of the Hernando Pizarro Expedition; they crossed the Cordillera Blanca while traveling from Cajamarca to Pachacamac (Lima) (fig. 2). The first noted major glacier-related catastrophe was in 1702, when an outburst flood from a glacier lake destroyed part of the city of Huaraz. In 1725, floods again caused damage in Huaraz, and on the same day, an ice avalanche destroyed the town of Ancash. Antonio Raymondi described glaciers of the Cordillera Blanca in 1866 (Raymondi, 1873).
Glacier studies were begun in modern time by Ingeniero (Ing.) Jorge Broggi (Broggi, 1943, 1945) who, in 1927, commented on the influence of glaciers at the Raura Mines. Since 1932, several Austro-German expeditions led by P. Borchers and Professors Hans Kinzl and E. Schneider have surveyed and studied the Cordillera Blanca (Kinzl, 1935, 1942, 1964; Kinzl and Schneider, 1950) and Cordillera Huayhuash (Kinzl, Schneider, and Ebster, 1942; Kinzl, Schneider, and Awerzger, 1954); they made several accurate maps at scales of 1:200,000, 1:100,000, and 1:50,000 by using terrestrial photogrammetry. The expeditions also included observations of lakes and glaciers of the region (Kinzl, 1940).
In December 1941, a flood caused by the failure of a moraine dam at a lake in the Cordillera Blanca destroyed about 25 percent of the city of Huaraz. The catastrophe prompted the Instituto Geológico del Perú, under the direction of Ing. Jorge Broggi and the Commission of Cordillera Blanca Lakes, to begin a study and inventory of lakes and glaciers in the Cordillera Blanca. In addition, engineering projects were initiated to prevent or mitigate flood disasters caused by glacier-lake outbursts. This work has continued with some interruptions until the present (Fernandez Concha, 1957; Morales Arnao, B., 1969c).
Between 1944 and 1945, the Instituto Geológico del Perú extended its glacier studies to the Cordilleras Central, Vilcabamba, Carabaya, and Apolobamba (fig. 2). Between 1945 and 1972, the Corporación Peruana del Santa and the Regional Office of Electricity sponsored a number of studies that led to a series of reports on glaciers, glacial geology, and glacier lakes in the Cordillera Blanca: Oppenheim and Spann (1946), Heim (1947), Szepessy (1949, 1950), Trask (1952, 1953), Fernandez Concha (1957), Morales Arnao, B. (1962, 1966, 1969a, d), Petersen (1967), Ames (1969), Lliboutry (1977), Lliboutry, Morales Arnao, Pautre, and Schneider (1977), and Lliboutry, Morales Arnao, and Schneider (1977).
From 1966 to 1986, Ing. Benjamín Morales Arnao, initially with the Corporación Peruana del Santa and later with Electroperú, organized a special department of glacier studies (Kinzl, 1970); this department had as its primary objective the carrying out of studies of glaciers of the Cordillera Blanca and the planning of construction projects that would prevent catastrophic floods (Corporación Peruana del Santa, Electroperú, 1967-1995; Morales Arnao, B., 1969c, 1971; Schneider, 1969). The studies were begun in the northern part of the country. The Instituto de Geológia y Minería extended glacier studies to the entire country and had the goal of a complete inventory of glaciers and glacier lakes in Perú. The inventory was completed in 1988 (Hidrandina, 1988).
Starting in 1978, international agreements were signed with several institutions to support glacier studies, these included an arrangement with the Federal Institute of Technology, Zürich, Switzerland, to contribute Peruvian glacier data to the World Glacier Inventory Project, as well as cooperative research with Ohio State University on studies of paleoclimate from ice cores of the Quelccaya ice cap in the Cordillera de Vilcanota (Thompson, Mosley-Thompson, Grootes, and others, 1984) and from the Cordillera Blanca. More recently cooperative glacier studies have been established with the French Institute of Andean Studies and the Institute of Geography at the University of Innsbruck, Austria.
U.S. Geological Survey, U.S.Department of the Interior