Last Glacial Maximum and deglaciation of Ampato volcanic complex, Southern Peru

Abstract

The last maximum glacier expansion in the Ampato Volcanic Complex (15º 49’ 09’’S; 71º 52’ 40’’W; max. altitude: 6,288 masl) is dated to 17,9 ± 0.1 – 16,8 ± 0.4 kyr with cosmogenic 36Cl isotope. The ice covered a total area of ~348 km2. In the Huayuray valley, located on the north side of the HualcaHualca volcano, the most northerly stratovolcano in the complex, the glacier surface area during this period was ~20.7 km2 and the paleoELA was situated ~4,980 m, i.e. ~820 m below 1955. Dating of a polished surface near the Ampato complex shows widespread deglaciation around 12,6 ± 0.4 kyr. However, there were several later phases of glacier re-advance; the age of one of these phases is estimated at 11,7 ± 0.2 kyr. In historical times, the retreat has been dominant, especially during the last decade.