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Glaciers

Kibo's diminishing ice cap exists because Kilimanjaro is a little-dissected, massive mountain that rises above the snow line. The cap is divergent and at the edges splits into individual glaciers. The central portion of the ice cap is interrupted by the presence of the Kibo crater. The summit glaciers and ice fields do not display significant horizontal movements because their low thickness precludes major deformation.

Geological evidence shows five successive glacial episodes during the Quaternary period, namely First (500,000 BP), Second (greater than 360,000 years ago to 240,000 BP), Third (150,000 to 120,000 BP), Fourth (also known as "Main") (20,000 to 17,000 BP), and Little (16,000 to 14,000 BP). The Third may have been the most extensive, and the Little appears to be statistically indistinguishable from the Fourth.

A continuous ice cap covering approximately 400 km (150 sq mi) down to an elevation of 3,200 m (10,500 ft) covered Kilimanjaro during the Last Glacial Maximum in the Pleistocene epoch (the Main glacial episode), extending across the summits of Kibo and Mawenzi. Because of the exceptionally prolonged dry conditions during the subsequent Younger Dryas stadial, the ice fields on Kilimanjaro may have become extinct around 11,500 years BP. Ice cores taken from Kilimanjaro's Northern Ice Field (NIF) indicates that the glaciers there have a basal age of about 11,700 years, although an analysis of ice taken in 2011 from exposed vertical cliffs in the NIF supports an age extending only to 800 years BP. Higher precipitation rates at the beginning of the Holocene epoch (11,500 years BP) allowed the ice cap to reform. The glaciers survived a widespread drought during a three century period beginning around 4,000 years BP.

In the late 1880s, the summit of Kibo was completely covered by an ice cap about 20 km (7.7 sq mi) in extent with outlet glaciers cascading down the western and southern slopes, and except for the inner cone, the entire caldera was buried. Glacier ice also flowed through the Western Breach. The slope glaciers retreated rapidly between 1912 and 1953, in response to a sudden shift in climate at the end of the 19th century that made them "drastically out of equilibrium", and more slowly thereafter. Their continuing demise indicates they are still out of equilibrium in response to a constant change in climate over the past century.

In contrast to the persistent slope glaciers, the glaciers on Kilimanjaro's crater plateau have appeared and disappeared repeatedly during the Holocene epoch, with each cycle lasting a few hundred years. It appears that decreasing specific humidity instead of temperature changes has caused the shrinkage of the slope glaciers since the late 19th century. No clear warming trend at the elevation of those glaciers occurred between 1948 and 2005. Although air temperatures at that elevation are always below freezing, solar radiation causes melting on vertical faces. Vertical ice margin walls are a unique characteristic of the summit glaciers and a major place of the shrinkage of the glaciers. They manifest stratifications, calving, and other ice features. "There is no pathway for the plateau glaciers other than to continuously retreat once their vertical margins are exposed to solar radiation." The Kilimanjaro glaciers have been used for deriving ice core records, including two from the southern icefield. Based on this data, this icefield formed between 1,250 and 1,450 years BP.

Almost 85 percent of the ice cover on Kilimanjaro disappeared between October 1912 and June 2011, with coverage decreasing from 11.40 km (4.40 sq mi) to 1.76 km (0.68 sq mi). Between 1912 and 1953, there was about a 1.1 percent average annual loss of ice coverage. The average annual loss for 1953 to 1989 was 1.4 percent, while the loss rate for 1989 to 2007 was 2.5 percent. Of the ice cover still present in 2000, almost 40 percent had disappeared by 2011. Ice climber Will Gadd noticed differences between his 2014 and 2020 climbs. The glaciers are thinning in addition to losing areal coverage, and do not have active accumulation zones; retreat occurs on all glacier surfaces. Loss of glacier mass is caused by both melting and sublimation. While the current shrinking and thinning of Kilimanjaro's ice fields appear to be unique within its almost twelve-millennium history, it is contemporaneous with widespread glacier retreat in mid-to-low latitudes across the globe. In 2013, it was estimated that, at the current rate of global warming, most of the ice on Kilimanjaro will disappear by 2040, and "it is highly unlikely that any ice body will remain after 2060".

The Furtwangler Glacier on Kilimanjaro is a remnant of the ice cap that once covered the mountain. This has retreated dramatically over the last century with over 80 percent glacial retreat. The glacier is named after Walter Furtwangler, who along with Ziegfried Koenig, was the fourth to ascend to the summit of Kilimanjaro in 1912.

A complete disappearance of the ice would be of only "negligible importance" to the water budget of the area around the mountain. The forests of Kilimanjaro, far below the ice fields, "are essential water reservoirs for the local and regional populations".