Glaciers , the huge and seemingly sedate rivers of ice, are the source of life and, ironically, death too. These masses not only add to the serene and pristine beauty of the higher reaches of the Himalaya, they are also the source of north Indian rivers. Thus, with global warming on the rise and many glaciers retreating at an alarming rate, it is time to assess the potential of the glaciers, which are one of the least studied natural phenomena in India.

The rather crowded mountain regions of north India are vulnerable to the consequences of receding glaciers. "Cloudbursts, avalanches, landslides, glacial lake outburst floods ( glof s), mudflows and earthquakes. These natural hazards could increase in frequency,' says Bahadur. "If a glof occurs it can change the course of a river which can rise more than 10 feet and cause untold misery to all life forms in the Himalayan region.'

The thinning and retreat of Himalayan glaciers is resulting in the formation of new moraine-dammed lakes and the enlargement of existing ones. Small ponds on the surface of lower glacier tongues are also increasing in size and coalescing. The retraction of the glaciers leads to influx of huge quantities of water into glacier lakes. When the water level in the glacial lake rises, it breaches the dam formed of ice, boulders and sand (see diagram: Ready to burst ) .

Since 1956, a new lake has been noticed on the lower part of the Imja glacier below Lhotse. It has grown to about 50 hectares. There are now at least 50 ice-dammed and moraine-dammed lakes in the Dudh Kosi and Arun catchment area in eastern Nepal-southeastern Xizang in China. But while little is known about the frequency of collapse of these dams, their sheer number is impressive. A study of the Dig Tsho glof gives an idea of the extent of damage caused by such a disaster.

Several Himalayan glaciers are retreating, thus increasing the chances of glof s. Such hazards will, perhaps, hit India the hardest. Their effect on a ancient civilisation formed around the Indus and the Gangetic basins is anybody's guess. Vikram Chandra Thakur, wihg director, predicts that if the Himalayan glaciers continue to retreat at their current pace over the next 25 years, the Ganges will swell and then