High in the Peruvian Andes, the glacier-fed lake Laguna 513 brims with meltwater atop a populated valley in a region prone to earthquakes. Scientists warn that if a giant chunk of ice from the Hualcan glacier breaks off it could trigger a tsunami-like wave in Laguna 513 and send a lethal torrent of water cascading down the valley.
It has happened before in the Andean nation. In 1970, a 7.9 magnitude earthquake shook ice blocks into highland lakes and unleashed an avalanche that buried the town of Yungay and killed more than 20,000 people.
Peru has more tropical glaciers than any other nation but rising temperatures linked to global warming have helped shrink the ice masses by up to 40 percent, filling existing lakes to the brim and spawning hundreds of new ones. As the glaciers retreat, the ice contorts and fissures and lumps fall off.
"People don't think these lakes are dangerous and they are not taking precautions," glacier expert Christian Huggel said, as avalanches thundered high up on Hualcan and shards of glacier collapsed into the lake. In the Peruvian capital, Lima, nearly 200 governments are meeting this week to thrash out a rough draft of a deal to cut carbon emissions in a bid to ward off more warming. The deal is due to be agreed in Paris in late 2015.
World greenhouse gas emissions are rising fast and it may be years before they start falling, prompting glaciologists to urge Peru to act fast to protect towns and villages in danger.
In a first for Peru, four underground sensors around the perimeter of Laguna 513 have been installed to detect movements while cameras snap shots of the lake's surface.
If a large ice block disturbs the lake surface, alarms wail in government offices in Carhuaz, a town of 13,000 in the valley below Laguna 513. Local schools conduct evacuation drills along pre-planned routes to higher ground.
VULNERABLE
Glaciologist Cesar Portocarrero said Peru has been slow to reinforce dams, build levies, install sirens and prepare escape routes in high risk zones.
Laguna 513 is the country's only lake with an adequate flood warning system out of 15 flagged as dangerous, said Alejo Cochachin, a glaciologist with Peru's state water authority.
Lake Palcacocha bulges above the city of Huaraz, the capital of the Ancash region with a population of 150,000.
A rim of sediment is all that holds in its 17 million cubic meters of water - enough to fill 6,800 Olympic swimming pools and a third more than it contained 40 years ago.
Plans to drain the lake to safer levels, reinforce its walls and install sensors have faced years of delay.
"I envy Carhuaz," said Huaraz civil defense official Johnny Salazar.
Salazar said his request to the regional authorities for 3 million soles ($1 million) to finance a flood warning system similar to Laguna 513's was rejected because of a lack of funds.
Ancash, home to Peru's biggest copper mine Antamina, receives about 1 billion soles annually in mining revenues.
"With all those millions and we cannot put 3 million into saving lives. It's absurd!" Salazar said.