Sliding mountains
Landslides have been taking place in the Himalaya mountains since time immemorial. In 1893, a landslide blocked the Birahiganga in Uttar Pradesh, forming a 350 m-high dam creating the vast Gohana lake. When a part of the dam toppled 10 months later, the levef of the Alaknanda rose by SO m and washed away the town of Srinagar, which was rebuilt later. When the flood wave reached Hardwar after two days, the level of the Ganga river rose by nearly four metres. Landslides often block the Himalayan rivers, forming dams and lakes. When these natural dams burst, they cause floods which trig- gers off more landslides. Floods in the Himalaya valleys are often associ-ated with this phenomenon.
Landslide dams are usually formed at the confluence of rivers. During downpour, even minor tribu-taries can bring enormous amounts of rubble to block the flow of major rivers. The same situation is now prevailing in Rudraprayag where the tributary Madhmaheshwar has blocked the Mandakini river in Monsoona village and formed a 2 sq km lake. A breach in the blockade might cause further flood in the downstream areas of the Alaknanda and the Ganga basin.