Robert Rodriquez/CNET

Climate change has made the world's deadliest lake way more dangerous

For Earth Day 2021, we revisit the epic, decades-long battle to tame a lake so swollen it threatens to wipe out an entire city center.

Editors' note: For Earth Day 2021, we're checking in on progress made in confronting climate change. In this story, Eric Mack investigates the complicated challenges facing people in Peru living under the constant threat of glacial lake outburst floods. Since the story originally came out in late 2019, the danger has seemingly increased in the Andes, as evidenced by a deadly flood triggered from a melting glacier near Machu Picchu in 2020.

I'm standing on a 45-year-old dam high in the Peruvian Andes, gripped by a mix of awe and terror.

The glacial waters of Lake Palcacocha lap at the 25-foot-tall structure. Billions of gallons of meltwater stretch a mile back to the foot of the ice-capped peaks of Palcaraju and Pucaranra that top out at 20,584 feet.

Scientists and historians believe a huge chunk of glacial ice cap fell into Lake Palcacocha one day in 1941. The instant displacement of millions of gallons of water triggered a massive wave that crashed through a natural barrier. Water, mud, rocks and debris surged into the canyon below and into the streets of Huaraz, the largest city in this part of the Andes and a tourist destination.

The violent rush hit with practically no warning and killed at least 1,800 people.

It could happen again, at any moment. And if it does, the outcome is likely to be much worse.


Small dams were built around Lake Palcacocha in the 1970s, when it was a fraction of its current volume.

Eric Mack/CNET

The dam I'm standing on hasn't changed since it was built in the 1970s, yet rising temperatures have melted surrounding glaciers, causing the volume of Lake Palcacocha to swell. The lake now holds more than 34 times the volume it did in the early '70s. Meanwhile, Huaraz has reached 120,000 residents. And the number of people living directly in Lake Palcacocha's flood path has grown to tens of thousands.

That's why there are construction crews in bright orange uniforms on a hillside overlooking the lake behind me. And that's why I'm here. I want to see firsthand how the people of the Andes are addressing increasing risks amplified by  climate change  and working through the unexpected challenges along the way.  

After years of seemingly inexplicable delays, the regional government has finally begun constructing a new high-tech early warning system to continuously monitor the lake and quickly relay emergency alerts to Huaraz and other downstream communities.

Right now watchmen like Victor Morales play the role of early warning system. A thin, middle-aged and friendly man wearing a baseball cap, Morales spends days and nights in a small cabin perched next to the construction site, a literal stone's throw from where the killer wave broke through a rocky ridge decades ago. His job is simply to listen and watch, with radio in reach, for any avalanche or other threat that could unleash a major flood. 


The view from the current watch point above Lake Palcacocha, where a new early alert system is being constructed.

Eric Mack/CNET

Morales sets out coffee for us on a small, rickety table in front of his quarters, a welcome salve for the biting winds. 

We sip slowly as Morales recounts the small avalanches he's seen or heard in recent weeks. He points out a huge boulder on the far side of the lake that tumbled down the glacier, stopping just short of the water. Moments later, he calmly points across the lake and says to me at a volume just barely louder than the wind:

"Mira, avalancha."

A steady stream of snow slides down the glacier and into the far side of the lake. It's small, and the effect on the water is barely perceptible among the wake generated on its surface by the wind. I ask Morales how often he witnesses bigger slides.

"Todos los dias," he tells me with a wave of his hand. 

Every day.

Ending an era of inaction

Average temperatures in Peru have increased by about 4 degrees Fahrenheit (2.2 degrees Celsius) since the late 1800s, and the nation's glaciers have lost as much as 90 percent of their mass. At Lake Palcacocha, melting has added perhaps 4 billion gallons of water to the lake, which is just waiting to breach the dam when the next hunk of hulking ice cap plunges into its depths. 

Over the past year, Inaigem -- or the National Research Institute on Glaciers and Mountain Ecosystems -- has made it possible for the world to monitor Lake Palcacocha along with watchmen like Morales, at least during daylight hours. The agency has installed a webcam that streams a live image of the lake to its offices in Huaraz and to YouTube.

The camera has caught a few significant but non-threatening avalanches sending ice and snow into the water, causing the lake to roil around its rim like a bathtub disturbed by rowdy children. The videos make national news and raise the anxiety level in Huaraz.


Ted Alexander is a mountain guide and entrepreneur in Huaraz who has advocated for more monitoring of the lake for years.

Ted Alexander

"We have a radio and we're in communication with those guys at the lake," Ted Alexander, an American expat and business owner in Huaraz, tells me. He says the private school he co-founded is in the potential flood zone. "I built a bridge and we have our evac route. We plan and we do drills every single month."

Alexander is a large, muscular guy with close-cropped graying hair and biceps the size of my neck. The mountain guide and entrepreneur greets me in the doorway of his restaurant with a weathered backpack in one hand and a beat-up bicycle helmet on his head. As we talk on the sidewalk patio near the center of Huaraz, he keeps his sunglasses on and slams two tall glasses of milk with a shot of espresso.

Alexander has been active in the collaborative push among nonprofits, local leaders and governments for an early warning system. He becomes visibly upset talking about his struggles navigating the local bureaucracy, pausing a few times to soften his voice and gently shoo away elderly panhandlers, handing them a few coins.

"The thing that sort of fired me up was that it was treated, and it still is being treated, as though we're building a playground," Alexander says.

The process of installing an alert system has dragged on for years. Everyone I talk to tells me this slow pace is expected within Peru's often labyrinthine bureaucracy, but it's still befuddling given the clear risk.

"It's a very [small] investment to secure a city of over 100,000 people and it took five years," explains Jorge Recharte, director of The Mountain Institute, which advocates to protect the livelihoods and cultures of mountain people in the Andes and around the world.


Installation of a new alert system at Lake Palcacocha.

Eric Mack/CNET

Installing an early warning system, along with educating the public about evacuation routes in case of a flood, could provide an extra half hour or so for people in Huaraz to get out of the way of a massive mudslide. That's not enough time to save property built in the flood zone, but it could save thousands of lives.

But Palcacocha is just one of many bloated lakes high in the Peruvian Andes with the potential for catastrophic flooding. The story of what happened after another glacial lake sent a torrent downstream less than 10 years ago may help explain why it's taken so long for mitigation measures to be put in place here.


Sunset at Carhuaz plaza. 

Eric Mack/CNET

Best-laid plans

An hour's drive down the Santa River valley is the smaller town of Carhuaz, centered on a picturesque plaza ringed by heladerias selling dozens of flavors of ice cream. 

Over the scene looms Hualcan, another 20,000-foot, ice-capped peak. Several glacial lakes sit at its base, including three directly above Carhuaz. The largest is called simply Laguna 513. In 2010 a block of ice calved off one of Hualcan's glaciers and plummeted into the lake, sending a freshwater tsunami toward the valley below. The water careened down the steep slopes, picking up mud and boulders as it hurtled in the direction of grassy pastures below. 

The flood carried away livestock and buildings and swamped part of the municipal water system before just missing Carhuaz and its 12,000 residents. Luckily, no one was killed, but the rushing waters frayed many nerves. 

"The mudslide destroyed everything it could," one resident told Peru's La Republica newspaper in 2010.

Following the close call, Peruvian and European scientists and engineers visited Laguna 513. Researchers published academic papers on the flooding. The Swiss government, the University of Zurich and the nonprofit CARE Peru eventually teamed up to install a high-tech early warning system that included sensors, cameras and communications relay antennas.  

It was designed to provide enough warning for people in Carhuaz and nearby to get out of the way of an incoming flood and to serve as a model for other threatened communities, like Huaraz.


The evacuation plan for a flood hitting Carhuaz.

Eric Mack/CNET

The system was in place by 2013, and for a while everyone was satisfied. It was even presented as a successful case study at a "Technology for Development" conference. But within months of that victory lap, the entire project was undone. 

A double whammy of drought and damaging frost struck the farming communities around and above Carhuaz that year. Rumors began to spread that the warning system was somehow blowing away rain clouds or controlling the weather. That fall, a group from the local farming villages hiked up to the lake and destroyed the equipment.

Within a few days, it began to rain.

What led to residents destroying harmless equipment designed to protect them? I have spoken to over a dozen people directly or indirectly involved in this strange saga. Several more refused to discuss it.  

Reasons they mention include indigenous beliefs, long-held superstitions, ineffective communication between project leaders and local communities, language barriers, jealousy over contracts awarded for the construction of the system and manipulation of all of the above by local politicians for their own ends.

The theme that emerges from these conversations is ironically simple: In a nutshell, it's complicated. 


The massive mountain Hualcan towers over an agricultural plateau with Carhuaz lying in the valley below.

Johanna DeBiase

A la laguna

To begin to understand the complications, I want to see for myself the path the mudslide took almost a decade ago from Laguna 513. But there's no road to the lake and this time my wife and daughter will be part of the tour. I need a guide. 

"How y'all doin'? I'm Preston. I hear you're looking to go for a hike."

Preston isn't quite the native Peruvian guide I imagined. He's tall, thin and in his 20s with curly, blond hair and glasses. He wears a khaki vest with a patch reminiscent of the Boy Scouts that reads "Cuerpo de Paz" (Peace Corps) and a name tag that spells out "Preston Anderson." He speaks with a Texas accent rather than in a South American dialect.

Enlarge Image

Laguna 513 in all its rugged beauty.

Eric Mack/CNET

Preston and the folks in the Carhuaz city offices who introduced us aren't concerned about the threat of flooding from the lakes looming above us. They're working together to develop a Laguna 513 hiking trail to rival the other glacial lake tours that are key to the region's tourism industry.

"People here figure if [a major flood] was going to happen, it would have happened in 1970," Preston tells me later.

That year, on May 31, a devastating, magnitude 7.9 earthquake rocked northern Peru. The tremor destabilized Mount Huascaran, the towering 22,205-foot zenith of the Peruvian Andes, causing an avalanche of rock, ice and snow that buried much of the town of Yungay, only 15 miles from Carhuaz. Over 20,000 people were killed and the site remains a giant, eerie graveyard.

In the years that followed, engineers set to work draining the more threatening glacial lakes, including 513. A series of small tunnels were dug to lower the lake's level, and some credit those efforts with preventing casualties from several avalanches into the lake over the years, including the massive wave in 2010.

I'm no mountaineer, but I've done plenty of hiking from the Himalayas to Alaska to the Olympus Range in Greece. And the 5-mile, 3,000-foot-climb to Laguna 513 is simply one of the most breathtaking hikes I've ever done. 

Following Preston across a green pasture strewn with cattle and wildflowers, Hualcan's ice cap sits perched on its throne above, a reminder of who is truly in charge of all fates here. 

We break for lunch at Laguna Yanahuanca, where a single narrow waterfall flows over a rock outcropping several stories tall. I try not to imagine what it looked like the moment a torrent of destructive muddy flood waters cascaded over it, just nine years earlier, with enough force to toss large boulders over the edge and into the now serene lake.

Watching my daughter climb nearby boulders, I think about an avalanche that killed two skiers in January at Taos Ski Valley's Kachina Peak near my home in northern New Mexico. 

The day before it hit, I'd planned to ski the same chutes where the accident occurred, but I was turned back by low visibility and an unseasonably warm, wet storm on top of the mountain ridge. That heavy precipitation weighed down on the weaker early season snow until a huge slab was released. 

I was just a day off from being one of those skiers.

An increase in unusually wet winter storms like these are another consequence of our warming climate. Warmer air in the atmosphere can hold more of the moisture it picks up from warming oceans, which later gets dumped on land as precipitation. Here, in the Andes, higher average temperatures result in destabilized glaciers that in turn destabilize everything below them with the threat of far more destructive avalanches. 

I push away all thoughts of falling snow and boulders for the moment and we press on beyond 14,000 feet in elevation. Our pace slows and a few snowflakes begin to fall. One last push leads to the top of the natural moraine dam overlooking the majestic glacial blue waters of 513. An island of ice and snow floats in the middle of the water, evidence of a very recent slide. 

The remnants of the early warning system can be seen on the far side of the bowl. Unlike at Lake Palcacocha, there is no one around keeping watch over the lake. 

If a big avalanche hit, we'd be the first to know. But that would also be the last anyone heard of us.

Perhaps it's the hulking presence of Hualcan before us, but Lake 513 doesn't seem that big. The catch: It's deceptively deep. The bright glacial blue of the water masks dark depths of over 360 feet. There's a lot of water lurking below us, and above Carhuaz.

During our hike, I ask Preston what people in Carhuaz have told him about the early warning system installed at Lake 513 and what happened to it. He's been told nothing. 

I was informed in advance of coming here that this might be the case. I visited the Swiss Agency for Development Cooperation in Lima (the Swiss equivalent of USAID). Martin Jaggi, head of cooperation, told me there had been a transition to a new municipal government in Carhuaz around the time the warning system was destroyed. 

He suspects the new administration may not have been fully debriefed on the system's backstory. In fact, the new municipal government never followed up with the Swiss office about the system or responded to letters sent from Lima. They also never responded to my requests for comment, nor did the previous mayor or other officials who were in office when the system was destroyed.


Life goes on in Carhuaz.

Eric Mack/CNET

After our hike, I send Preston a link to a 2017 article in the obscure journal EcoAmericas detailing the story of the early warning system's fate. I ask what he thinks about the whole drama that predated his arrival in Carhuaz by a couple of years. 

He wonders if more could have been done to help educate the local communities about the aims of the project and the equipment that would help achieve those goals.

"Any local development requires the participation and advocacy of the community or they just don't work. I'm not surprised they kept tearing things down -- they don't know or trust these people implementing these systems," he tells me.

Jaggi acknowledges there may not have been sufficient buy-in from locals.

"We didn't make the right analysis of the social and political context of the different groups and we didn't manage to include all of them so that we make sure that the system will work," he says.

A history of mistrust and misunderstanding


The village of Hualcan, between Carhuaz and Laguna 513.

Eric Mack/CNET

What happened to the early warning system at Laguna 513 wasn't an isolated event. 

Jesus Gomez, Inaigem's glacier research director, was working at the sprawling Huascaran National Park years ago when confronted by a large group of residents. They demanded that an automated weather station installed at the glacier be removed for fear it was controlling the weather. 

"I tried to explain that this equipment…  cannot make it rain or not rain," he says. "But obviously it is not what people believe. They did not want to understand."

Eventually the equipment was removed from the area and installed somewhere else, Gomez said.

In late July, just weeks after I left Peru, there was another incident in the village of Musho, located between Carhuaz and Yungay and below the Huascaran glacier. Villagers became suspicious of a team of scientists, led by respected Ohio State University paleoclimatologist Lonnie Thompson, working to take ice cores from the summit of the glacier.

Rumors spread that the researchers might secretly be working for mining companies and their work could pollute the area's water. Locals ordered the team off the mountain within 12 hours -- an impossible deadline given the tons of equipment and ice cores left near the 22,205-foot summit.

The team was eventually given five days to extricate itself from the mountain. With the help of a helicopter from the Peruvian government, the researchers and their ice cores made it back to Ohio. 

"In many rural areas, be it Bolivia, Peru or Papua, glaciers are gods," Thompson says in the above video from Ohio State. "They are holy places. And as scientists, we need to operate with respect for those cultures."

Before visiting Carhuaz, I ask a group of scientists and other professionals working at the Inaigem offices in Huaraz what lessons can be learned from the fate of the early warning system for Laguna 513.

"As government and researchers, we don't make enough effort to inform the people what is happening," says Beatriz Fuentealba, Inaigem's research director for mountain ecosystems. "Why is climate changing? What happens with the rain and precipitation? This is one part of the problem."


The Rio Quilcay runs through center of Huaraz. This channel was flooded by Lake Palcacocha in 1941 and could face the same devastation at any moment.

Eric Mack/CNET

Adding to this issue: The ironic coincidence that after the equipment at Laguna 513 was destroyed, the rains came within a few days. Everyone I spoke to in Peru believed this was just a coincidence, but that doesn't make it a unanimous opinion throughout the region.

Villagers outside "Huaraz know about these problems," says Jenny Menacho Agama, a capacity building specialist working with Inaigem. "And they say: 'They destroyed it and then it started raining.' And this is a case they use as evidence."

Fuentealba, Agama and others working on the problem worry the same fate could befall the new, more sophisticated warning system being constructed right now at Lake Palcacocha.

Fuentealba told me about a visit to the village of Macashca, south of Huaraz, where a group of local women said they believed the glaciers could become active and cause slides themselves.

"They say, 'Probably the basin activates when a lot of engineers and outsiders visit… The glaciers become jealous because we introduce a lot of people,'" she recalls. "I'm not sure if this is a majority view, but the ladies spoke to me in a serious manner. They were not joking."

Replacing a toy with a serious tool

It's just a short walk from the Inaigem offices to the Rio Quilcay, a small river flowing through the middle of Huaraz that traces its waters to Lake Palcacocha. Deadly waters could race down this channel at just about any moment as they did in 1941. Efforts to prevent people and businesses from rebuilding in the area failed in the 1940s and 1950s. Today, it's a lively part of town with parks along the banks of the river. Vendors on the several bridges over the water also make it a popular place for students, workers and just about anyone else to grab lunch or ice cream. 


Cesar Portocarrero at his home in Huaraz.

Eric Mack/CNET

Cesar Portocarrero lives nearby in a stately home with a dark wrought-iron fence and bushes concealing his porch from the view of the many passersby. To him, the best plan of action is obvious: The lake must be lowered.

Portocarrero is something of a legend when it comes to glacier conservation and engineering solutions for often dangerous glacial waters. He's worked around the world, whether at home in the Andes or in the Himalayas of Nepal. 

Now in his 70s and walking with a cane, he escorts me to his home office, where the walls are adorned with shelves of books about engineering and his Sir Edmund Hillary Mountain Legacy Medal.

He shows me newspaper clippings from the 1960s about the glaciers now looming above us and weaves in anecdotes about his grandchildren. 

Portocarrero is working for the regional government in Ancash. One of his projects is to lower the waters of Lake Palcacocha, which he hopes could significantly reduce the risk of a flood reaching Huaraz. Currently there's a series of large pipes that were installed in the dam several years ago with the goal of lowering the water level, but they have proven capable of only lowering it by a few meters.

"To me that's more like a toy," the often brutally frank Portocarrero tells me. "The real work that could reduce the hazard and the danger is to really reduce the volume."


A series of pipes at Lake Palcacocha currently lower its level by a few meters.

Eric Mack/CNET

He estimates more involved engineering work to lower the water level by at least 20 meters could begin in the next few years.

"We should start right now, but bureaucracy is terrible," he says.

Portocarrero describes his recent bureaucratic struggles in as much detail as his accomplishments, which include reducing the risks from all the dangerous lakes I visit during my time in Peru. 

His work draining lakes like Laguna 513 and the gorgeous Lake Paron above the city of Caraz to the north of Carhuaz is credited with saving thousands of lives and millions of dollars. But big engineering projects take years, and climate change is making it hard to keep up with the rise in meltwater. What's worse, Portocarrero doesn't see a fresh crop of young Peruvian engineers to take the place of his generation. Above all, he says the bureaucracy is his biggest challenge, even bigger than climate change.


Lake Paron.

Eric Mack/CNET

I've now spent more than a year researching the risk of a tragic glacial lake outburst flood in towns like Carhuaz and Huaraz, as well as the challenges facing the efforts to do something about it. As with other efforts to reduce and adapt to climate change worldwide, there's a sense of hopelessness and a dearth of simple solutions.

Like climate change itself, the problem seems too large and insidious to attack with the limited resources at hand. The whole thing feels a bit too far gone. 

Then there is Saul Lliuya.  

David versus Goliath

Saul Lliuya is a farmer and mountain guide attached to what could be a revolution in how we deal with climate change. 

He's suing Germany-based energy giant RWE, arguing that the company's climate-altering emissions are a threat to him, his property in Huaraz and many of his neighbors. RWE has no direct link to Huaraz, but its emissions, Lliuya argues, are affecting the entire planet. The suit cites Portocarrero's plan to drain the lake as the best remedy and asks that RWE pay for a portion of the estimated $4 million project based on RWE's portion of greenhouse gas emissions during the industrial era. 


Saul Lliuya


That portion works out to around $20,000, a trivial amount to any big corporation, but it would set a precedent that could make energy and extraction companies liable for billions and trillions over the long haul if it were to spread to courts worldwide. 

It's the ultimate David versus Goliath story.

I meet Lliuya in a park in central Huaraz. He is small but strong, a trait I've noticed in many Peruvian mountain guides during my time here. 

"I have been working at the mountain for 16 years. ... I live near the mountain at my country house," he tells me. "We want more climate justice, in the sense that those of us who have not contaminated so much are suffering the consequences of what has been provoked by others at other places."

The saga has been running for four years now. An appeals court in Germany has agreed to accept the case, which is further along than many thought it would get.

"When we started with the case, I received a lot of criticism. They thought I was crazy, that I was selling the lake," Lliuya explains. "But as time has advanced, people have started to understand that there is hope. Hopefully we will win."

The COVID-19 pandemic has further delayed the case by making it nearly impossible for investigators from Europe to travel to Peru to evaluate the state of Lake Palcacocha, among other things. 

It's now been over a year and a half since my last reporting trip to Peru, and there has been some progress made at home and abroad. A new, high-tech avalanche mitigation system has been installed on Kachina Peak here in New Mexico, and the government in Ancash announced that the early warning system for Lake Palcacocha was finally 100% complete in February of this year. 

Meanwhile, Lliuya continues to wait for his day in court in Europe. 

"We have to dream that in the future, things change for our good," he told me as we shared a bench in tiny Parque Ginebra in central Huaraz. "I know it is very difficult because it has to do with politics and the economy. … The challenge is big, but I believe it can be done."

First published Dec. 12, 2019.