Lake Tilicho is located in the Annapurna Region and is one of the highest glacial lakes in the world. Credit: Santosh Pokhrel Glaciers Large parts of the Himalayas are covered by glaciers. Although these glaciers are only a pale shadow of their former selves, they are still significant enough to cause certain environmental problems. The glaciers and the melt waters released by them are a major source of erosion in the barren areas having little vegetative cover. Receding glaciers leave behind unconsolidated debris which may become the source material for landslides in the near future.

Ice walls of the Great Gangotri glacier, Garhwal, India. Credit: Karamjeet Singh

When glaciers recede, they leave behind debris called terminal moraine. However, vast areas are left open by these retreating glaciers, which tend to remain barren for a considerable period of time. There is large-scale erosion, more so during this period as the erosive power of the morainic material is more than that of the moving body of ice.

Moraines may block the passage of the meltwater, act as dams and form morainal (glacial) lakes. Many lakes in the Trans Himalayan regions trace their origins to the glaciers. There are many beautiful glacial lakes in the Nepal Himalayas such as Tilicho Lake, Rara Lake and Gokyo Lake.

Gokyo lake, having glacial origins Credit: Rajesh Shrestha

Sometimes, this debris dam gives way, causing the water to drain away with considerable force. This results in heavy flash flooding. Two such accidents occurred in 1980 and 1985 in Nepal that swept away many roads and bridges and killed many people and initiated numerous land slides.