An enormous landslide has dammed the very upper reaches of the Pareechu, a tributary of the Sutlej, in Tibet. Chinese authorities are reportedly open to a team of Indian engineers and hydrologists - an extraordinary gesture, and one that hints at the severity of the problem - to visit the 5 km lake that has built up behind the dam and assist with alleviative measures. Heavy rain and continuing bad weather have delayed this for two days however, and the situation is critical.

Landslides of rock and ice are reported to have created the huge lake, with millions of cubic meters of water piled up ready to burst through the block and rampage downstream. Such a flood could create havoc in towns as far as 350 km downstream, such as Rampur.

The Bhakra dam may not be overly affected as it has been severely short of water this year, with enough capacity left over to contain the expected flood.

Civil defense measures are being taken through the valley in Himachal, including emergency evacuation of at least 1,000 people already from places most at risk.

The unexpected severity of this problem should act as a warning to hydrologists and engineers who favour massive engineering works in glacial and seismically sensitive mountian areas. Failure of such systems is almost certainly doomed to be catastrophic, with gradients of river systems so steep that floods travel with massive speed and force, carrying millions of tonnes of mud, rock and ice with them, causing enormous damage for hundreds of kilometers.

The attached photograph shows the results of a similar glacial lake discharge in Nepal in 1985. The Dig Tsho lake near Mt Everest crashed through its dam following a massive avalanche off a nearby glacier that threw many tons of ice into its waters. The flood tore through 80 km of countryside, destroying millions of rupees worth of hydroelectric installations and 14 bridges. The countryside was devastated, leaving people homeless and without possibility of income, since the slopes above the riverbanks are devoid of arable features, as is typical of rocky mountain terrain.