The climatic snow line is a little above the highest peaks in this region (Mir Samir, 5 809 m, lat. 35° 35′ N., long. 70° 10′ E.) but steep north-facing slopes provide a topographie reason for small glaciers persisting, with a snow line a little below 4 900 in (16 000 ft). Snow accumulation at this height averages 1 300 kg m−2, most of this falling in late winter and spring. Gross ablation reaches 40 kg m−2 d−1. Net ablation (July–August), measured as stream discharge, averages 3 600 m3 d−1 = 9 kg m−2 d−1. Slow recession is the average condition. Halt stages at 4 800, 4 600 and 4 000 m are interpreted from the topography. Dating of moraines by lichen distribution indicates for the highest of these a minimum age of 400 years.
The vertical flux of heat and of water vapour were calculated through an air layer 30–100 cm over a melting firn surface for 24 h. The source of heat available at the surface expressed as a percentage of the total was: net radiation 87, condensation 5, forced convection 1, conduction through snow 6 and unexplained 1. The heat sink was: long-wave radiation 4, evaporation 6, forced convection 6, conduction into snow 2 and melting 82%.