A giant section of a glacier on the Mont Blanc massif in the Alps is in danger of collapsing, experts warned on Wednesday, prompting the precautionary closure of two roads and the evacuation of mountain huts in northwestern Italy.
A block of about nine million cubic feet of the Planpincieux Glacier on the peak of Grandes Jorasses, a mountain on the French-Italian border, has splintered and could give way, according to Daniele Giordan, a geologist working for the Italian National Research Council.
Dr. Giordan, who is part of a team that has been monitoring the glacier since 2013, said by phone on Wednesday that though a fracture in the glacier was common after the warm summer months, the crack detected this time was alarmingly wide.
“This year, we noticed again the presence of a large crevasse,” he said. “The opening of this crevasse can create the collapse of a very large block.”
Dr. Giordan added, “A collapse that big could reach the bottom of the valley” in the form of a barreling ice avalanche that could endanger anybody on the mountain or on the road at the bottom of the valley.
Stefano Miserocchi, the mayor of the Italian resort town of Courmayeur, said he had issued a pre-emptive order to keep the area, which is popular with hikers, clear for the time being.
He added that the area under direct threat was uninhabited but that the authorities had nonetheless blocked part of the road connecting Courmayeur to the small settlement of Planpincieux for most of the day and night.
Though the risk of collapse is high, experts cannot be sure about when it will happen.
“The most important element now is temperature,” said Dr. Giordan, the geologist. A cold October could reduce the movement of the lower part of the glacier, he added, allowing the crevasse to close.
Dr. Giordan noted that such crevasses had happened before but that the volume of the block in peril had never been as big in the past.
Mr. Miserocchi, the Courmayeur mayor, said that climate change was “bringing changes and requires protection measures.”
“It’s a situation we have to live with and handle correctly,” he added.
Dr. Giordan said that the formation of the crevasse was not directly connected to climate change, but acknowledged that rising temperatures probably increased the frequency of such phenomena by making the glacier less stable.
About 10 percent of the Earth’s land area is covered by glaciers or ice sheets, according to a major United Nations report published on Wednesday that blames global warming for massive losses from ice sheets and glaciers in the past few decades.
“Many glaciers are projected to disappear regardless of future emissions,” the report said.
This week, dozens of people participated in a funeral march for the Pizol glacier in the Swiss Alps, while a study released in April by the European Geosciences Union, a nonprofit research organization, said in April that, “under strong warming, the Alps would be mostly ice-free by 2100.”
Daniel Farinotti, one of the authors of the study, said in a statement at the time, “Glaciers in the European Alps and their recent evolution are some of the clearest indicators of the ongoing changes in climate.”
“The future of these glaciers is indeed at risk, but there is still a possibility to limit their future losses,” he added.