At first glance, Lake Palcacocha is the most peaceful of places. At 4,500 meters above sea level in the central Peruvian Andes, its turquoise waters and the bright blue sky contrast with the intense white ice of the glacier perched on the mountainside between them.
Stay a little longer, however, and this tranquility is interrupted by the noise of avalanches and blocks of ice and rock breaking off from Palcaraju, one of the peaks that surround the lake.
Each year, Palcaraju’s ice sheet shrinks and feeds Palcacocha, which in 42 years has swelled to 34 times its former volume, according to data from Peru’s National Water Authority.
As the lake grows, it becomes a latent threat to the residents of the nearby city of Huaraz: an increasingly likely overflow would trigger a flood that would sweep down the mountainside towards the city, a few kilometers below.
This has happened before, in 1941 — and as the Earth warms further, scientists believe it could happen again.
The 1941 Palcacocha flood
On 13 November 1941, one of the most tragic events in Peru’s history occurred. After a shuddering noise, giant waves of water, mud, and rock swept away everything in their path.
The tragedy began with the detachment of a block of ice from the snow-capped Palcaraju, which fell into Lake Palcacocha and caused it to overflow. The water flowed down towards a lower lake, Jiracocha, breaking its natural dam and creating a huge flood. It reached Huaraz below within 15 minutes, destroying a third of the city and claiming the lives of 1,800 people.
“The black water did not slide, but formed huge, inarticulate, boiling waves. Dense dust covered the scene. The sight was Dantesque. When I turned my face, my mother had disappeared.
Desperate, and god knows how, I climbed onto the roof of a house that was still standing,” Reynaldo Coral Miranda, a survivor of the tragedy, recounted to researcher Steven Wegner, in his 2014 history of the event, Lo que el agua se llevó (Gone with the Water).
Although the natural disaster caught Huaraz unawares, there had been warnings of the danger the years prior. In the 1930s, a scientist named Hanz Kinzl carried out studies of glaciers, indicating the risk of glacial lake outburst floods (GLOF) in several lakes, including Palcacocha....
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