In this Aug. 12, 2016, a block of ice is seen in the lagoon next to Pastoruri glacier in the Huascaran National Park in Huaraz, Peru. The melting of glaciers like the Pastoruri has put cities like Huaraz, located downslope from the glacier about 35 miles (55 kilometers) away, at risk from what scientists call a “glof,” or glacial lake outburst flood. A glof occurs when the weak walls of a mountain valley collapse under the weight of meltwater from a glacier. (AP Photo/Martin Mejia)
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