It's strangely calming to watch the Imja glacier lake grow, as chunks of ice part from black cliffs and fall into the grey-green lake below.

But the lake is a high-altitude disaster in the making – one of dozens of new danger zones emerging across the Himalayas because of glacier melt caused by climate change.

If the lake, situated at 5,100m in Nepal's Everest region, breaks through its walls of glacial debris, known as moraine, it could release a deluge of water, mud and rock up to 60 miles away. This would swamp homes and fields with a layer of rubble up to 15m thick, leading to the loss of the land for a generation. But the question is when, rather than if.

Mountain regions from the Andes to the Himalayas are warming faster than the global average under climate change. Ice turns to water; glaciers are slowly reduced to lakes.

When Sir Edmund Hillary made his successful expedition to the top of Everest in 1953, Imja did not exist. But it is now the fastest-growing of some 1,600 glacier lakes in Nepal, stretching down from the glacier for 1.5 miles and spawning three small ponds.

At its centre, the lake is about 600m wide, and according to government studies, up to 96.5m deep in some places. It is growing by 47m a year, nearly three times as fast as other glacier lake in Nepal.

"The expansion of Imja lake is not a casual one," said Pravin Raj Maskey, a hydrologist with Nepal's ministry of irrigation.

The extent of recent changes to Imja has taken glacier experts by surprise, including Teiji Watanabe, a geographer at Hokkaido University in Japan, who has carried out field research at the lake since the 1990s.

Watanabe returned to Imja in September, making the nine-day trek with 30 other scientists and engineers on a US-funded expedition led by the Mountain Institute. He said he did not expect such rapid changes to the moraine which is holding back the lake.

"We need action, and hopefully within five years," Watanabe said. "I feel our time is shorter than what I thought before. Ten years might be too late."

Unlike ordinary flash floods, a glacier lake outburst is a continuing catastrophe.

"It's not just the one-time devastating effect," said Sharad Joshi, a glaciologist at Kathmandu's Tribhuvan University, who has worked on Imja. "Each year for the coming years it triggers landslides and reminds villagers that there could be a devastating impact that year, or every year. Some of the Tibetan lakes that have had outburst floods have flooded more than three times."

But mobilising engineering equipment and expertise to a lake 5,100m up and several days' hard walking away from the nearest transport hub is challenging in Nepal, one of the poorest countries in the world. People living in the small village of Dingboche below the lake say scientists and government officials have been talking about the dangers of Imja for years.

Some years ago one of the visiting experts was so convincing about the dangers of an imminent flood that the villagers packed up all their animals and valuables and moved to the next valley. They came back after a week when the disaster did not materialise, but say it's hard to dismiss the idea that there could be a flood one day.

"When I was 21 I went to the lake and it was black and really small," said Angnima Sherpa, who heads a local conservation group in Dingboche. "Two years ago I went there and it was really big. I couldn't believe it could get so big. It was really scary."

But scientists and engineers still cannot agree on whether to rate Imja as the most dangerous glacier lake in the Himalayas, or a more distant threat.

Mobilising international assistance for large-scale engineering projects during a global recession is also difficult. The Mountain Institute's initiative was to call in experts from the Andes, where Peruvians have developed systems for containing glacier floods since a disaster in the 1940s killed nearly 10,000 people.

Cesar Portocarrero, who heads the department of glaciology at Peru's national water agency, has overseen engineering works to drain more than 30 glacier lakes, building tunnels or channels to drain the water and reduce the risk of flooding.

But he conceded it would be an enormous challenge to apply these methods at Imja.

"It's not easy to say 'we are going to siphon the water out of the lake'," Portocarrero said. "Where do you find the people who can work at high altitudes? How do you move in the equipment? What do you do in bad weather? You have to have exhaustive planning." There are also other contenders for immediate action, with some 20,000 glacier lakes across the Himalayas, although many are concentrated in the Everest region. Bhutan alone has nearly 2,700.

Three of those, known as the Lunana complex, are practically touching, increasing the possibility of cascading floods far more devastating than any rupture at Imja.

"If the barrier fails between them we are going to have a massive glacier lake outburst flood," said Sonam Lhamo, a geologist for the Bhutanese government.

The United Nations Development Programme and other agencies have supported a project to drain the lakes but those funds are running out.

John Reynolds, a British engineer and expert on glacier lakes who has worked in Nepal, argues that the international community has focused on Imja because of its proximity to Everest and trekking routes popular with western tourists. He says there are other, more hazardous lakes elsewhere.

The Nepali government ranks Imja among the six most dangerous glacier lakes in the country largely because it is growing so quickly. More than 12 other such lakes are also seen as high risk.

But Reynolds argued: "Just because a lake is getting bigger doesn't necessarily mean that it is getting more hazardous. As the climate is changing, generally speaking more glacial lake systems are forming.

"The question is how to decide which ones are hazardous now and which ones have the propensity to become hazardous in the future."

Imja, though fast-growing, is held in by a relatively wide moraine, which makes it secure in comparison to some others.

Most glacial lake floods begin as high-altitude tsunamis. A large block of ice falling from a glacier at great height sets off a series of giant waves that wash over the moraine.

That's not such a risk for Imja. The glaciers feeding the lake are gradual in slope, which reduces the risk of a large chunk of ice falling from a great height and setting off large waves.

Watanabe concedes the geography of the lake could keep disaster at bay, at least in the next year or two. But, he says, there are signs that an outlet channel at the bottom of the lake may be widening dangerously.

Reynolds said Nepal and the international community need to think of a Himalaya-wide action plan.

"As the climate is changing more glacial lake systems are forming," he said. "The question is how to decide which are hazardous now and which are going to become hazardous in the future."