Snow, Ice and Verticality in the Karakoram

Abstract

The distribution of perennial snow and ice in the Karakoram Himalaya is examined and its area–altitude relations. The presence and extent of snow and ice are shown to depend upon, and be positively correlated with, interfluve heights. The elevations and extent of the highest altitude terrain are of decisive significance. The size, length and lowest reach of glaciers increase as elevation increases up to the highest watersheds. In the Central Karakoram, the ‘glaciation level’, or minimum elevation needed to generate a glacier, is found at about 5,250 m on north-facing slopes and 5,500 m on south-facing slopes. At the western margins, the averages are 4,600 m and 5,200 m, respectively. They rise eastwards by about 1,200 m and 900 m to the highest glaciation levels found in the eastern margins of the Karakoram. A main set of the 42 largest valley glaciers is introduced, with basin areas exceeding 130 km² and ice streams over 16 km in length. These have exceptional elevation ranges, five spanning more than 5,000 m and 34 more than 3,000 m. Their long profiles exhibit two main features. Most of the vertical descent is accomplished in less than 10 % of ice stream lengths, mainly in icefalls in the upper parts of the basins. However, their longest sections, in the middle and lower reaches, are of relatively gentle gradient. Some 85 % of main ice stream areas lie between 4,000 and 6,000 m, the critical elevation zone in terms of ice cover. This must be balanced against the extreme high elevations of their watersheds and also the exceptionally low termini of many Karakoram glaciers compared to most in the Greater Himalayan Region.