Global warming has melted one of Mount Everest's most-visited glaciers into a vast and growing lake that now poses a threat to villagers and trekking tourists, scientists have warned.
A study of glacial melting in the high Himalaya found that the Imja glacier has melted from solid ice in the mid-1950s to a one and a half mile long lake today.
Scientists from Nepal's International Centre for Integrated Mountain Development (ICIMOD) said the lake is growing by just under 50 metres per year and is in danger of bursting its banks - a 31 metre-high dam of rocks and stones - and flooding nearby villages and trekking routes.
They predicted that more than 7,500 people would be affected by the floods, including tourists hiking along the popular Everest Base Camp route.
The study compared photographs taken from the 1956 Swiss Everest expedition, which showed no evidence of a lake on the glacier, to later pictures that revealed the creation of a large lake.
"Photographs taken in the 1950s demonstrate that, except for several small melt ponds, no lake existed at that time. By 1984 a lake of approximately 0.4 square kilometres had formed," the report said.
One of the authors, Pradeep Mool, a leading Himalayan glacier expert, said the study had been aimed at establishing which of the region's "potentially dangerous" glacial lakes could burst in the future.
Global warming was the cause of the glacier's rapid meltdown and transformation into a lake.
"Without the warming the ice will not melt. The rate of melt has increased because of exposure to atmospheric warming in the last few decades. It's a very beautiful lake but it is one of the lakes in potential danger of an outburst [of water]," he said.
The research, including scientific photography and the use of remote sensors, was conducted in one of the most dangerous parts of the high Himalaya and one of the researchers was killed in an accident while collecting the data.