Characteristics of ablation and heat balance in debris-free and debris-covered areas on Khumbu Glacier, Nepal Himalayas, in the pre-monsoon season

Ablation and heat balance were measured in debris-covered and debris-free areas of the ablation zone of Khumbu Glacier from 22 May to 1 June 1999. On the debris-free ice, the ablation rates ranged from 1.4 to 4.7 cm day -1 and were inversely correlated with the albedo. The contribution of turbulent heat flux to melting was very small, so net radiation accounted for about 98% of the incoming heat. Melting under debris decreased sharply with increasing thickness. Debris with thickness of 10 cm slowed melting to about 40% of that of bare ice with the same low albedo. The primary cause of melt reduction was the insulating effect of the debris. The heat stored in the debris layer during daytime was released to the atmosphere during night-time and warmed the air rather than being conducted downward to melt ice.