284 THE ANDES OF SOUTHERN PERU 



is not a simple volcano but a composite cone with five main sum- 

 mits reaching well above the snowline, the highest to an elevation 

 of 21,703 feet (6,615 m.). It measures about 20 miles (32 km.) in 

 circumference at the snowline and 45 miles (72 km.) at its base 

 (measuring at the foot of the steeper portion), and stands upon 

 a great tributary lava plateau from 15,000 to 17,000 feet above 

 sea level. Compared with El Misti, at Arequipa, its volume is 

 three times as great, its height two thousand feet more, and its 

 access to ocean winds at least thirty per cent more favorable. El 

 Misti, 19,200 feet (5,855 m.) has snow down as far as 16,000 feet 

 in the wet season and rarely to 14,000 feet, though by sunset a 

 fall of snow may almost disappear whose lower limit at sunrise 

 was 16,000 feet. Snow may accumulate several thousand feet be- 

 low the summit during the wet season, and in such quantities as 

 to require almost the whole of the ensuing dry season (March to 

 December) for its melting. Northward of El Misti is the massive 

 and extended range, Chachani, 20,000 feet (6,100 m.) high; on the 

 opposite side is the shorter range called Pichu-Pichu. Snow lies 

 throughout the year on both these ranges, but in exceptional sea- 

 sons it nearly disappears from Chachani and wholly disappears 

 from Pichu-Pichu, so that the snowline then rises to 20,000 feet. 

 It is considered that the mean of a series of years would give a 

 value between 17,000 and 18,000 feet for the snowline on all the 

 great mountains of the Arequipa region. 3 This would, however, in- 

 clude what is known to be temporary snow; the limit of "per- 

 petual" snow, or the true snowline, appears to lie about 19,000 

 feet on Chachani and above El Misti, say 19,500 feet. It is also 

 above the crest of Pichu-Pichu. The snowline, therefore, appears 

 to rise a thousand feet from Coropuna to El Misti, owing chiefly 

 to the poorer exposure of the latter to the sources of snowy pre- 

 cipitation. 



It may also be noted that the effect of the easy access of the 

 ocean winds in the Coropuna region is also seen in the increasing 

 amount of vegetation which appears in the most favorable situa- 



* S. I. Bailey, Peruvian Meteorology, 1888-1890. Ann. Astron. Observ. of Har- 

 vard Coll., Vol. 39, Pt. I, 1899, pp. 1-3. 



