February 16, 2012

Ngozumpa Glacier Retreat Tongue Disintegration, Nepal

Posted by Mauri Pelto

Ngozumpa Glacier (also Ngozumba) is a large debris covered valley glacier draining south from Cho Oyu and Gyanchung Kang one valley west of the Khumbu valley. The lower 10 kilometers of this glacier is heavily debris covered, similar to the Khumbu Glacier and Imja Glacier. Above image from Doug Benn. From the terminus at 4700 meters to 4900 meters a distance of 8 kilomters the glacier is increasingly riddled with supraglacial lakes (lakes on top of glacier) as this section downwastes. Velocity in this reach is less than 5 meters/year, essentially stagnant. The snowline of the glacier has been at nearly 6000 meters in recent years. On the following image the snowline (blue dots), accumulation areas (A) and terminus blue arrow are indicated. It is evident that more than 50% of this glacier is debris covered. An examination of Landsat imagery from 1992, 2000 and 2009 indicates the expansion of these lakes near the terminus. These lakes (S) in the 2010 (Goggle Earth imagery) are beginning to coalesce and look to be creating a proglacial lake (lake at front of glacier) at the terminus of the glacier. Benn et al (2001) examining the supraglacial lakes hypothesized that the glacier was close to forming a moraine dammed proglacial lake. This is a scenario very similar to what has developed on Menlung Glacier, which is just over the pass into Tibet from the Ngozumpa. Further upglacier the surface of the glacier is riven with more lakes amidst the debris covered relatively stagnant ice. Further upglacier the thinning is evident in the expansion of a bedrock knob in the midst of the glacier (A), the decrease in surface elevation compared to the lateral moraine-trimline (L) and the quite high equilibirum line for 2009 (E). The higher snowlines at Nup La on an eastern branch of the glacier indicates that thinning is occurring high on the glacier and will lead to further retreat. Strong thinning in the accumulation zone, though less than the ablation zone, of Khumbu Glacier was found by Bolch et al(2011)