Scientists Warn of Himalayan Floods

More than 40 lakes high in the Himalayas, formed from rapidly melting glaciers, are expected to burst their banks in the next five years, sending millions of gallons of water and rock cascading on to settlements in the valleys below, scientists warned yesterday.

The lakes are growing larger and more unstable as rising temperatures in the world's highest mountain range, caused by global warming, lead to "a geological crisis", the scientists say.

The 44 dangerous lakes identified so far are in two countries - 20 in Nepal and 24 in Bhutan - formed from the meltwater of the region's thousands of retreating glaciers. There are thought to be hundreds more such liquid timebombs in India, Pakistan, Afghanistan, Tibet and China.

Millions of people live in the danger area.

Surendra Shrestha, Asian regional coordinator for the United Nations environment programme's early warning division, said: "These 44 could burst their banks with potentially catastrophic results for people and property hundreds of kilometres downstream."

Pradeep Mool, from the International Centre for Integrated Mountain Development, said action had only been taken in two places so far to try to avert the danger by lowering the water level and installing warning systems.

Tsho Rolpa lake in Nepal has grown sixfold since the 1950s and is now 2.6km long by 500 metres wide, with a depth of 107 metres.

It was formed as a glacier retreated, leaving a pile of frozen rock across the valley to form a dam. When the ice in the dam melts, it will become unstable.

Dr Mool said: "A flood from this lake could cause serious damage down to the village of Tribeni, 108km downstream, threatening 10,000 lives."

A £600,000 warning system will give local people between 15 minutes and four hours' notice of the dam bursting. "The best hope for the nearest people is to run up the side of the valley," Dr Mool said. "We have installed marks above which they should be safe."

Temperatures in the region have risen by 1C since the 1950s, causing thousands of glaciers to retreat by an average of 30 metres a year. The worst recorded collapse of one of these dams was in 1954, when 300,000 cubic metres of water and rock poured without warning into China in a 40 metre high flood surge from the Sangwang dam on the Tibet-Nepal border. The city of Gyangze, 120km away, was destroyed. The dead totalled many thousands.

"Glaciers have never been retreating at this rate, and lakes have never been forming so quickly," Dr Shrestha said. "For most of the Himalayas the risk is unknown, but it is very great. This is a seismic zone, and a catastrophic flood could be sparked by an earthquake."

Many of the retreating glaciers are in sensitive border areas and governments have been reluctant to allow scientists in to investigate. Another problem is that most of the lakes are at altitudes of 4,500 to 5,000 metres.

"This is a new and alarming threat," said Klaus Töpfer, UNEP's general secretary. "We now have another compelling reason to reduce emissions of greenhouse gases."