Glacial melt is a popular topic in global warming discussions, with its contribution to rising sea levels and shrinking freshwater supplies among the main concerns. But for mountainous communities in Peru, such long-term worries are obscured by a much more imminent threat – glacial lake outburst flows, called GLOFs – poised just above them.

Last month, the Risk Management Office of the Peruvian Municipality of Huaraz sounded the alarm that glacial lake Palcacocha had once again swollen above its record volume of 17 million cubic meters of water (about 612 million cubic feet). At such levels, local authorities feared the lake could suddenly burst and send waves, liquid mud, blocks of ice and chunks of rock roaring down the Santa River valley into the quiet city of Huaraz, population 117,774.

Lake Palcacocha sits below the Palcaraju and Pucaranra glaciers in Peru’s snow-capped Cordillera Blanca at 14,967 feet above sea level – barely 15 miles northeast of the city.

Glacial lakes are formed by the accumulation of meltwater from nearby glaciers over a period of time. The problem is that these lakes are usually enclosed in moraine – loose, unconsolidated rocks and debris resulting from glacier retreat – that can be easily eroded by avalanches and big swells.

The thought of 17 million cubic meters of water (roughly the contents of 240,000 Olympic swimming pools) and associated debris storming down the valley has prompted nearby towns to call on the government to take pre-emptive measures to secure the lake.

But it’s not just Lake Palcacocha. Many glacial lakes in the Cordillera Blanca region have seen their volumes go up in recent years, and new lakes are forming.

“This past decade has been very dynamic,” said Peruvian glaciologist Benjamin Morales, referring to lake formation and glacial floods as a result of increased thaw in the region. “Luckily, they haven’t been as catastrophic as in the past, but they remain a big concern,” he said.

A history of disaster

Flanked by the Cordillera Blanca to the east and the Cordillera Negra to the west, the city of Huaraz is no stranger to GLOFs – nor is any city in the region, for that matter.

The oldest records of glacial lake outbursts – or “aluviones” – date back to the 16th century with stories about avalanches and glacial floods burying the old cities of Huaraz and Ancash. But local experts believe such events are a big part of Peru’s history.

“There are myths, legends, that have been passed along through generations in places where there hasn’t been any avalanches for centuries,” said glacial engineer César Portocarrero.

In 1941, a huge chunk of ice from the Palcaraju glacier fell into Lake Palcacocha, creating a wave so big it breached the moraine and dumped billions of gallons down the Callejón de Huaylas, or the Santa River valley, into Huaraz. In a matter of minutes, about a third of the city was under water and more than 5,000 people were killed.

Lake Palcacocha’s outburst in 1941 set the foundations for the creation of a government glaciology unit, Portocarrero said, with an office in Lima established to supervise such threats. But it wasn’t until the 1970 avalanche disaster – prompted by a 7.9 Richter scale earthquake – which buried the city of Yungay and killed more than 20,000 people, that the Unit of Glaciology and Lake Safety was created, he explained.

After the 1970 tragedy, the government started pouring money into the study of glaciers and engineering work to stabilize hazardous lakes, such as Palcacocha.

Security work starts, but then slows

“We have the best technology in the world to drain dangerous glacial lakes,” Morales said.

Out of necessity, local communities developed primitive ways to partially drain hazardous lakes, mainly slicing open parts of the moraine to let the water flow. Through the years, particularly after the government’s boost in the 1970s, these practices have been perfected and further developed.

The standard procedure is to carefully cut through the moraine and let the lake drain, allowing its water level to descend an average of 20 meters (about 65 feet) under the natural level. Then, a concrete dam with a sluice – or floodgate – is built to reinforce the moraine and maintain a steady flow. This way, in case of an avalanche or a block of ice plunging into the lake, there is a safety margin to contain erosive lake swells.

As an engineer specializing in geological risks, Morales led the construction of the drainage system in Palcacocha in the ’70s. Back then, the lake was considerably smaller and, by the time they were done, it was left with a little more than 500,000 cubic meters of water, he said.

Between the ’70s and early 2000, more than 35 security dams were built in the Cordillera Blanca. And to this day, none of them has collapsed.

What’s more, Peru’s way of tackling the risks of glacial floods has drawn attention from field experts around the world. According to Morales, they come to Peru to study the work.

“One of our engineers has been chosen as adviser for this kind of work in Nepal – which has been having similar problems [with their lakes],” he said.

For the last couple of years Portocarrero has been involved in discussions with the local government and mountain communities in Nepal to help tackle the growing threat of GLOFs in the Himalayas.

But building dams in such remote terrains and at altitudes well above 13,123 feet is difficult and very expensive. Changes in the government’s political priorities since 2000 have stalled security work in Peruvian glacial lakes, Morales said.

But as climate change makes glaciers melt faster, glacial lake monitoring and reinforcement are more necessary than ever, he said.

‘Altitude is everything’

“All of the world’s glaciers are melting,” Morales said. “Some more than others.”

According to a recent study, glacier retreat in the tropical Andes over the last three decades is unprecedented since the maximum extension of the Little Ice Age between the 17th and 18th centuries.

The Andes hosts more than 99 percent of all tropical glaciers, with more than 70 percent concentrated in Peru alone. Tropical glaciers are extremely sensitive to increases in temperature, mainly because glacial ablation – or melt – in the tropics occurs all year round on the lowest part of the glaciers, the study explained.

“Altitude is everything,” Morales said, with glaciers at 15,419 feet above sea level melting faster than those found at, say, an altitude of 19,685 feet.

“At 4,700 meters about 15,419 feet, we’ve registered temperatures reaching 15 degrees Celsius about 59 degrees Fahrenheit during the day, and you can see water running down the glacier,” Morales said. During nightfall, temperatures drop enough for the ice to freeze, but the loss in mass volume during prolonged daylight hours takes its toll, he added.

When glaciers melt, water sometimes seeps through the cracks and reaches the rock. There, the meltwater acts as a lubricant separating the ice glued to the rock and causes glaciers to slip, or move.

As global warming pushes Peru’s tropical glaciers to melt faster, glacial lakes will continue to form and grow. What’s more, the accelerated melt will tend to make glaciers more unstable, increasing the chances of flood-generating avalanches.

“No other country in the world has experienced so many avalanches over glacial lakes, that have resulted in GLOFs, such as Peru,” Morales said.

As a result, veteran glaciologists and researchers have been trying to push the government to create a special unit to take over the monitoring of glaciers and security construction work. “We must convince them this is necessary,” Morales said.