Climate change has turned Peru's glacial lake into a deadly flood timebomb

Lake Palcacocha is swollen with water from melting ice caps in the Cordillera Blanca mountains. Below, 50,000 people live directly in the flood path

Nestled beneath the imposing white peaks of two glaciers in Peru's Cordillera Blanca, the aquamarine Lake Palcacocha is as calm as a millpond. But despite its placid appearance it has become a deadly threat to tens of thousands people living beneath it as a result of global warming.

A handful of residents of Huaraz, the city below the lake, can recall its destructive power. In 1941 a chunk of ice broke away from the glacier in an earthquake, tumbling into the lake. The impact caused a flood wave which sent an avalanche of mud and boulders cascading down the mountain, killing about 1,800 people when it reached the city.