Like millions of their compatriots around the globe, the children of Courmayeur marched last Friday to protest against the climate crisis. The group of 160 or so pupils, some as young as six, turned out with banners and slogans, repeatedly shouting: “Ban plastic, save our planet.” But their most prominent placard message showed that for the youngsters of this small Italian resort town at the foot of Mont Blanc, the threat of climate change is particularly close to home. “You broke our glacier”, it read.

The activists were referring to Planpincieux, a glacier on the nearby Grandes Jorasses peak that is changing so rapidly that experts warned last week that a huge portion of ice was in danger of breaking away.

“We live here and can see the damage that climate change is doing,” said Matteo Pelliciotta, a teacher who helped on the march. “Every day, the glacier changes and becomes more grey in colour. This protest is more than just a message, it is a demand for politicians to take proper action.”

They can be assured that at least their mayor, Stefano Miserocchi, is taking the issue seriously. Miserocchi was quick to act last week when experts at the Fondazione Montagna Sicura (Safe Mountain Foundation) in the Aosta Valley said up to 250,000 cubic metres of ice were at risk of sliding off the Planpincieux. The glacier, which has been closely monitored since 2013, is always moving, but the size of a recent fracture and a significant increase in the speed at which the ice is melting raised the alarm. The area is popular with hikers, so as a safety precaution Miserocchi closed mountain refuges and part of a road upon which the ice could directly fall. Contrary to initial reports, only one home had to be evacuated. The other 10 or so in the hamlet beneath the glacier are empty holiday homes. But there is nonetheless deep unease. Can the glacier hold on? For how long?

“Each year you see how much the glacier changes,” Miserocchi told the Observer. “The average temperature has risen to the point where, in winter, ice is no longer being recreated because even though it snows, the temperature doesn’t get cold enough. Where there was once ice, there is now rock.”

Scientists are unable to predict when the mass of ice might collapse, but Miserocchi is not taking any chances as the glacier’s transformation has already cost lives. In August last year, a heavy storm unleashed a debris flow, killing an elderly couple when their car was swept from the road that is currently closed. Hundreds of people had to be evacuated from their homes. In January, a breakage in the wall of ice caused an avalanche, narrowly missing homes.

Safe Mountain Foundation experts are monitoring 184 glaciers in the Aosta Valley region. There are 4,000 glaciers across the Mont Blanc massif, the highest mountain range in Europe, which straddles Italy, France and Switzerland. Scientists predict that if emissions continue to rise at the current rate, the Alpine glaciers would shed half of their ice by 2050.

Facebook Twitter Pinterest A helicopter flies over the glacier above Val Ferret, a popular hiking area. Photograph: Antonio Calanni/AP

Fabrizio Troilo, a geologist at the foundation, reels off a list of historical disasters caused by collapsing glaciers. In 1965, two million cubic metres of ice and debris fell from the Allalin glacier in the Swiss canton of Valais, killing 88 workers at the Mattmark dam construction site below. Five years later, an earthquake triggered the collapse of an unstable glacier in Peru, burying the town of Yungay and killing more than 20,000 people. In 1892, 200,000 cubic metres of water and ice that had collected in a cavity on the Tête-Rousse glacier in France burst through the ice, triggering a flood that cost 175 lives.

More recently, a stream burst its banks in the Swiss resort of Zermatt in July, caused by glacial meltwater .

“These are rare events, but all glaciers under certain circumstances can have different behaviours that can be dangerous, not so much for climbers but for people living in the area,” said Troilo.

In Aosta alone, the team has recorded a massive loss of ice across the region’s glaciers, he added.

“We use all the latest technology … but it’s not easy to detect a lake that forms underneath the surface. For example, in Zermatt there was an outburst even though the glacier was being continuously monitored.”

As for the Planpincieux glacier, Troilo said that “everything is under control”, and in the worst-case scenario the ice would fall in the direction of the road and not on the cluster of homes in the area of Val Ferret.

Looking towards the glacier from the hamlet below, Rocco Raffaele, the manager responsible for the defence of the territory at Aosta’s regional authority, said news of the potential collapse probably wouldn’t have attracted as much attention had it not emerged during the week of the UN climate action summit in New York. The Italian prime minister, Giuseppe Conte, said the warning that part of Mont Blanc risked collapsing “must shake us all and force us to mobilise”.

“But the Alps have been feeling the effects of climate change for a long time,” said Raffaele. “As a glacier disappears, the material extracts beneath it become exposed, and when it rains, like it did in August last year, that material gets deposited down.”

In the event of a collapse, it would take less than two minutes for the mass to reach the municipal road.

“There is a danger, but that doesn’t mean you have to shut everything down,” said Raffaele. “It simply means being aware and understanding how to be responsible in the mountains.”

Facebook Twitter Pinterest Homes have been evacuated from underneath the glacier. Photograph: Yara Nardi/Reuters

But, as worried tourists frantically called hotels to inquire if they should cancel their trips to Courmayeur, those running tourism businesses were unhappy that the news had generated so much attention.

“This could be really damaging for us,” said Luca Savaglia from the Alpine Guides Society, which organises mountain excursions. “This particular glacier has always moved, and there are no hiking paths there, no climbing … we haven’t had any cancellations, but a lot of people have called to ask what is going on.”

Residents were also unhappy that newspapers gave the impression that their town was in danger, while Jean Pierre Fosson, secretary-general of the Safe Mountain Foundation, was left fuming after Greenpeace released an inaccurate statement.

“They said the situation was very dangerous in Courmayeur and that lots of homes were evacuated, but Planpincieux is 7km away from Courmayeur,” said Fosson. “We would never say a situation is not serious, but at the same time we have to give the correct information as we don’t want people living here to leave.”

But in a week during which millions of children took part in a global climate strike inspired by the Swedish activist Greta Thunberg, experts are pleased the news has helped draw attention to the vulnerability of glaciers. The children of Courmayeur were among the estimated one million young Italian protesters.

Raffaele said that the emotion galvanised by Thunberg now needed to be turned into concrete action. However, while children blame adults for breaking their environment, he advised them to also reflect on their own behaviour.

“My 10-year-old daughter keeps telling me to stop doing lots of things, such as keeping the tap running while brushing my teeth,” he said. “But she is the one who leaves the lights on and takes hot showers for 30 minutes. They have an awareness that is superior to ours, but they also need to change their habits.”