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The Eroding Himalayas
|by V. K. Joshi (Bijji)|
Compared to 4500 billion year old history of the earth, the 20 million year old Himalayas are very young. They are as young as an eight month old child in the life span of a man. Like a child the Himalayas too are hyperactive. How the hyperactive Himalayas are eroding fast, particularly in Himachal Pradesh, Nepal and elsewhere and spelling doom for the mountain states and the plains below makes an interesting reading.
Imagine a table full of whisky glasses, some filled and some empty. Try to push the table. The vibration can cause some of the glasses to topple. Compared to Himalayas this table is stable as the top which has the fragile glasses is flat. The Himalayas with their steep slopes are most unstable. A slight vibration can send the rocks and boulders toppling down. To cap it all if these slopes are enriched with water during rains lot more material tends to slide down due to lubrication. Above all if there is an improper drainage then the rain water that percolates inside the mountain tries to come out and generates a pore pressure on the surface, which breaks at the weakest spots and water gushes out. It carries lots of material down in the form of a massive landslide, damaging whatever lies in its way. Many times this mass of material including rock boulders, trees, soil and scree after reaching the valley chokes the stream and a dam is created. This artificial dam bursts if the pressure of water column behind exceeds a limit. Result is a flash flood in downstream areas.
Natural reasons apart, man tries his best to keep the Himalayas unstable. For example, slate has been used since ages as a roofing material Of late the craze for slates from Dhauladar range in Himachal Pradesh has increased. Consequently 40 matured cedar trees are hacked everyday in Bhagsu slate quarries in Mcleodganj, near Dharamshala. Similarly The Khaniara quarry operates in an area of 12.5 hectares put of a total of 625.42 hectare area of the village. This quarry generates an annual income of Rs 70 lakhs reports a journalist Devinder Sharma from Dharamshala. Dhauladar ranges face extremes of weather. During the winters they are under a white cover of snow. During rainy season they face severe rains as well. Both snow and rain are active agents of erosion. Hence the mountains in the quarry area bereft of trees and soil cover are left at the mercy of the forces of nature to erode freely. Khaniara mines are more than a century old. One George Berkley Shaw floated the Kangra Valley Slate Company. Since then the mining was going on. The villagers vehemently protested and the British agreed to stop mining. Alas during the post Independence era mining was resumed and now a stage has reached when the toe of the mountain has been completely mined. Imagine if the carpet on which you are standing is pulled out suddenly! The impact of removing the toe of a hill slope on a mountain is like that only.
The vulnerability of the Himalayas is not reduced even if large parts are not exploited by the human beings to extract natural resources like slate. Nepal for example, has a landslide which is the largest so far recorded. This landslide had mobilized material to the tune of 15 cubic kilometers. Fortunately it occurred 30,000 years ago, claim the geologists in Langtang valley. Similarly the locals in Pokhara valley claim their elders discussing about many large landslides due to excessive rains in 1934. The situation, instead of improving has worsened over the years.
Image-1. Erosion near the Mount Everest (c) Gettyimages.com
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07/06/2011 19:10 PM
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