Gangotri’s rate of retreat slows to 10 m

In what should be a heartening news for environmentalists, the rate of retreat of Gangotri glacier, the source of the Ganga, has come down to 10m in 2015 from 22m in 2001.

Lucknow University professor Dhruv Sen Singh, who was part of the first and second Indian expeditions to the Arctic in 2007-08, has found this during his recent visit to Gangotri.

The glacier, he said, is no doubt retreating but the average rate of recession has come down. “Even if the present rate of retreat continues, it would take about 2,500 years for the complete disappearance of 30-km long glacier.”

Global warming is said to be responsible for melting of glaciers across globe, but Prof. Singh feels that the decreasing rate of retreat of Gangotri glacier indicates that global warming is not the only reason for melting of glaciers and that the fears of global warming appear to be exaggerated.

Prof. Singh’s findings support those of the Geological Survey of India, which recorded that the Gangotri glacier retreated at the rate of 22 metre per year (between 1985-2001) and 35 metres per year (between 1956-77).

Prof. Singh, who visited the Gangotri glacier in 2001 and the same spot this year in the same season, said, “The rate of retreat is normal because the melting of glacier is a normal physical process if the temperature is above zero degree Celsius.”

For measuring the retreat, Prof. Singh used “lateral moraines” as a base-point. He measured the distance between the snout (end point of glacier) and the base point through laser range finder. “The base point was the same both in 2001 and 2015. However, this time, I found that the glacier existed beyond the base point leading to a conclusion that the rate of retreat has reduced,” he explained.

Scientists had concluded in 2001 that the global warming is not the only factor responsible for rapid rate of retreat of Gangotri glacier, for which it has attracted international attention.

There are local factors responsible for the melting and retreating of the Gangotri.Firstly, he said, at Gaumukh, there is no fresh snow and it is covered with debris known as supra-glacier moraine. The albedo (ratio of incoming and outgoing solar radiation) is 70-80 per cent for fresh snow and only 30-40 per cent for the debris, a reason why the glacier melts at a rapid rate.

Secondly, it is found that the snout of the glacier is cracking and falling because of a geographical structure called lineament.

Thirdly, there are a number of supra-glacial lakes (lakes above glaciers) which cause high melting and lastly, some of its tributaries had become inactive and were contributing water instead of ice, leading to fluctuations in the rate of retreat of high mountain glacier.