Located in the Cordillera Oriental section of the Andes mountains in Peru, the cap covers an area of 42.8 square kilometres (16.5 sq mi) with ice up to 200 metres (660 ft) thick.

At the beginning of the Holocene the ice cap shrank to a size smaller than present day; around 5,000 years ago, a neoglacial expansion began.

After reaching a secondary highstand (area expansion) during the Little Ice Age, Quelccaya has been shrinking due to human-caused climate change; in particular the Qori Kalis Glacier has been retreating significantly.

[30] A 1974 map shows a homestead on the Huancané River southwest from Quelccaya, about 12 kilometres (7.5 mi) from the ice margin.

It has decreased over time,[13] and by 2009 it had shrunk to 42.8 square kilometres (16.5 sq mi) making it smaller than the ice on Coropuna,[44][45] which is not declining as quickly.

[50] On the southern and western sides, parts of the ice cap end at steep cliffs like those in polar regions.

[54] On the southern side, the ice cap ends in four cirques with icefalls at their head and four sets of moraines downstream.

[69] The ice of Quelccaya does not appear to have been particularly erosive during the late Holocene, as indicated by the preservation of plant remains below it.

[77] Sulfate and nitrate are also found and may originate in the Amazon;[78] their concentrations at Quelccaya resemble these of snow in Andean regions.

[84] As reported in 1979, 1981 and 2013, there is little energy available at the top of the Quelccaya ice cap as outgoing and incoming radiation are essentially balanced.

[92][93] Moraines from glaciers lie in the valleys radiating from the ice cap and contain alluvial deposits and peat bogs, ponds and wetlands within depressions.

[1][36] As a consequence of global warming, temperatures on the summit of Quelccaya sometimes rise above freezing, accelerating the shrinkage of the ice cap.

[27][137] The vegetation in the region is known as puna grassland;[138][52] above 4,300 metres (14,100 ft) elevation it is defined as "super-Puna", and consists of herbs and shrubs such as Plantago and trees like Polylepis which grow to the ice cap and often have a krummholz appearance.

Sediment cores in lakes and peat,[53] mapping of moraines, radiocarbon and cosmogenic isotope dating have been used to infer past states of the ice cap,[146] and since 1976 Quelccaya is regularly reconnoitered.

[13][117] The American paleoclimatologist Lonnie Thompson and the Ohio State University (OSU) have been monitoring Quelccaya since 1974 and the ice cap has been investigated for its glaciology and for both its past and present climate.

[48] Because of the lack of seasonal temperature variations and of synoptic weather patterns, tropical glaciers may primarily record secular climate change.

[186][187] During the maximum extent the ice reached down to elevations of 4,500 metres (14,800 ft) as the equilibrium line altitude decreased by 360 metres (1,180 ft);[188] this change in the equilibrium line altitude is considerably less than the decrease found elsewhere in the Peruvian Andes and may reflect topographical controls on glacier expansion.

[189][190][192][193] By 13,600–12,800 years ago Quelccaya had retreated concomitant with global glacier shrinkage at the end of the last glacial maximum.

[201][202] It is possible that during the mid-Holocene Quelccaya was ice-free altogether;[203] peat deposits and ice cores indicate that it was reduced or even absent then.

[206][207] The ice cap began to grow again at a time of global climate change, 5,000 years ago, which included the drying of the Sahara at the end of the African humid period and wetter and colder conditions in the extratropics.

[227][232] This dominance of temperature over precipitation in determining ice cap size and glacier length has been replicated by modelling.

[235] Between 1980 and 2010, the ice cap shrank at a rate of 0.57 ± 0.1 square kilometres per year (0.220 ± 0.039 sq mi/a) with a loss of 30% of its area between 1979 and 2014.

[239] At the northwestern and southeastern ends of the ice cap, the retreat has reached the plateau that Quelccaya sits on.

[243] True fluctuations also occur, such as an advance of part of Quelccaya's southern margin reported in 1977 which bulldozed peat deposits,[17][244] a pause of the Qori Kalis glacier between 1991 and 1993 probably linked with the global cooling caused by the Philippine Pinatubo eruption in 1991,[245] a slow-down in the mid-2000s and an overall higher rate of retreat since 2000.

[53] The rate of retreat is higher than at the end of the last ice age and the glacier responds quickly to climate alterations.

[9] Similar retreats have been observed at other tropical glaciers, and are linked to the increase in global temperatures caused by industrial greenhouse gas emissions.

[251] The freezing level regularly rises above the summit of Quelccaya, and in recent ice cores, meltwater infiltration has become apparent.

[56][252] Consequently, oxygen isotope ratios are no longer preserved in the ice; while this infiltration has smoothened the record only to a certain depth[253][254][255] and particle-based records are unaffected,[256] it illustrates the threat that climate change is creating for the existence of climate archives in ice cores.

[257] Alpine life is quickly advancing into the terrain left by ice,[140] and the retreat has exposed plant remains that had been overrun during a glacier expansion that occurred 5,000 years ago.

The population in the region is for the most part rural with low socioeconomic status, and as such is highly vulnerable to the effects of climate change.