In the shadow of a melting glacier

Climate change causes glacial lake to burst its banks seven times in three years.

The Cachet 2 glacial lake in Chile has drained and refilled seven times in three years.
CECS and Jonathan Leidich (PAEX), 2008.The people living beside the Colonia River in the Aysén region of Chilean Patagonia are under constant threat of a sudden catastrophic flood sweeping down from the mountains above them.

The region has experienced an unprecedented seven events called glacial-lake outburst floods since April 2008. Each time, Lake Cachet 2, which lies on the Colonia glacier, has drained its 200 million cubic metres of water in a matter of hours into the Colonia Lake and River, sending the water on to the river's confluence with Baker River, Chile's largest in terms of volume, and generating a wave as far as 25 kilometres upstream and 100 kilometres downstream to the Pacific Ocean.

"You can review the scientific literature and you will notice that these phenomena are known worldwide in the Himalayas, the Alps, but the difference here, and what is striking, is its recurrence," says Fabián Espinoza, regional director of the country's Bureau of Water Management.

The most recent flood was on 4 March this year. The water level in Colonia Lake rose 3.5 metres in just 28 hours and divided the region in two after cutting across the Austral Highway, the main north-south route in Aysén. The Baker River doubled in volume.

Glaciologist Gino Casassa of the Center for Scientific Studies (CECS) in Valdivia has studied the floods in collaboration with the Chilean Meteorological Office. After three years, he has a clear culprit in mind: the repeated opening and closing of a tunnel 8 kilometres beneath the Colonia glacier, connecting Lake Cachet 2 above the glacier and Colonia Lake below it1.

But why has this phenomenon occurred repeatedly over the past few years in Cachet 2? Casassa's answer is climate change: "The glaciers of Patagonia in general have receded and thinned greatly during the past decades," he says. "The lakes grow at the expense of the ice and generate situations in which there is a danger of draining. In the case of the Colonia glacier, this thinning has weakened the natural dam the glacier constitutes."

César Portocarrero, head of the Department of Glaciology and Water Resources at the National Water Authority of Peru, has studied this phenomenon elsewhere in the Andes. He agrees with Casassa. "We can affirm that there is a direct relation between climate change and the phenomena that have been occurring," he says. "The water generated by the melting of the glaciers circulates between the glacier and rock and serves as a lubricant for the shifting of the ice mass."

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