Andean alarm: climate crisis increases fears of glacial lake flood in Peru

Laguna Parón, at an altitude of 4,200 metres, is one of Peru’s most spectacular glacial lakes and the largest in the Cordillera Blanca mountains Photograph: Harriet Barber/The Guardian

Lake Palcacocha is high in the Cordillera Blanca range of the Peruvian Andes, sitting above the city of Huaraz at an altitude of about 4,500 metres. When the lake broke through the extensive moraines, or natural dams, holding it in place on 13 December 1941, it sent nearly 10m cubic metres of water and debris into the narrow valley towards the city, 1,500 metres below.

The result was one of the most devastating glacial lake outburst floods – or “GLOFs” – ever recorded. The force of the water altered the area’s geography for ever, and killed at least 1,800 people, and possibly as many as 5,000.