September 13, 2011

Glacier Retreat Kali Gandaki Headwaters, Nepal

Posted by Mauri Pelto

The headwaters of the Kali Gandaki River is in northern Nepal. The basin is identified as having 1025 glaciers covering 2030 square kilometers by ICIMOD. The largest hydropower project is the 144 MW Kali Gandaki A project. The dam is located in Mirmi and the water is then sent through a 6 km long tunnel to Beltari. The Kali Gandaki River is fed by the summer monsoon rains and glacier melt. The glaciers in the range are summer accumulation type. The monsoon precipitation in summer (June- September) provides 80 % of annual precipitation.
Ageta and Higuchi (1984) noted that on summer accumulation type glaciers, accumulation and ablation occur simultaneously in summer. The result is that glacier retreat does not impact streamflow as much, as in other glaciated alpine regions. This post will look at several glaciers north of the highest section of the Himalaya. The Kali Gandaki River passes between the 8000 meter peaks of Annapurna and Dhalaguri. North of these peaks the climate is drier and colder as the peaks act as a barrier to the incursion of warmer monsoonal air masses. The glaciers examined range in altitude from 6000 m to 5500 m. These are cold glaciers where the bulk of the glacier ice is below freezing. The cold based summer accumulation type glacier at the headwaters of the Kali Gandaki are quite susceptible to warming, because of the low elevation and their dependence on frequent summer snowfall events to keep the albedo of the glacier surface high. In the glaciers examined here a point of concern is the extent of the surface drainage systems. Cold-based glaciers move slower and have fewer crevasses as a result. In addition meltwater does not penetrate into the cold glacier ice. Therefore, meltwater tends to drain along the surface and the persistence of meltwater drainage is evident in the formation of channels. If the majority of a cold type glacier has these streams, this indicates a limited accumulation area, which will then lead to glacier retreat. An examination of each of the three glaciers below indicates that the extent of the meltwater channels is unusually large. The meltwater channels are indicated with red arrows. The images are from late October 2009 and in some cases new snow has already covered some of the stream channels which in two cases nearly reach the top of the glacier. This is not an equilibrium situation where meltwater channels cover more than 70% of an alpine glacier. this is an indication of an expanding melt area on these glaciers. A comparison of the middle glacier with a 2000 Landsat image indicates 200 meters of retreat in the last decade. Notice the lake that is at the terminus in 2000 below is now 250 meters from the terminus in the image. above. These glaciers are small compared to the large Himalayan glaciers like Khumbu, Imja or Gangotri, but have the same response to climate, significant retreat.