The Indian Himalaya belt is prone to various types of natural disaster due to its inherent nature and climatic conditions. Earthquakes ranging in severity, floods or flash flood, and glacial lake outbursts are common among other hazards. Monsoon is the time (almost every year) when few water-induced disasters take place in some form or another in various places across this mountain. Cloudbursts, that is sudden and violent rainfall, followed by flash floods are generally reported in the monsoon period. Such events are related to extreme hydrometeorolgical conditions leading to debris flow, landslide and eventually the blockade of river channels, which consequently wreak havoc downstream. The Alaknanda flood of 1970, considered to be the worst disaster of its kind in northwest India of the last century, was triggered by a cloudburst followed by flash flood in the downstream. The flash floods of Bhagirathi in 1978, Sutlej in 1993 and 2000 and Teesata in 1968 are further examples of similar events along the Indian Himalayan belt.
Most of the rivers in Himalayan terrain flow through narrow gorges abutting moderate to steep slopes with sharp bands and meet tributaries on steeper slopes. As the rivers flow downstream, the valley becomes comparatively wider and less steep. The occurrence of flash floods, particularly in narrow river valleys, is one of the most-feared consequences of major cloudbursts, landslides or glacial lake outburst. Rolling of debris by cloudburst or landslide along the constricted course of the rivers lead to a short-term damming of the river flow, resulting in the creation of temporary lakes, which can last anywhere from a few days to a few decades. When the backwater pressure of the lake exceeds the retention capacity of the barrier, the accumulated water gushes down stream with powerful force inundating otherwise safe settlements.
In 1893, a largest known landslide dam in the Central Himalaya blocked the Birahiganga to form a colossal...
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