The Marmolada Glacier in the Alps of northern Italy, where 11 people died on July 3 when part of the ice collapsed into a massive avalanche, may crumble even more before Europe’s brutally hot summer ends. 

Glaciologists are tracking a new crack, about 650 feet long and more than 100 feet wide, that has appeared in a different part of the glacier, intensifying concerns that such unpredictable threats could become more frequent and widespread as global warming intensifies heat waves and deprives the icefields of the snow needed to replenish them. On average, high mountain areas are warming at least twice as fast as the rest of the planet.

In the July 3 collapse, a slice of ice about 250 feet wide and 80 feet high broke off and raced hundreds of feet downhill in an avalanche that crushed hikers on a trail far below the glacier. The sudden disintegration of part of the Marmolada glacier was completely unexpected. Concerns about abrupt glacial destabilization had been growing, however, and were amplified again by hikers in Kyrgyzstan less than a week later when they recorded another massive glacier collapse on July 8 in the Tien Shan Mountains. 

The recent collapses suggest that not all glaciers will disappear in a quiet trickle of water. Some, in their death throes, may release giant torrents of ice, water, rock and mud that can destroy anything in their paths, including roads, towns or mountain reservoirs. 

Climate and glacier models can predict the long, slow retreat of glaciers over decades, but little is known about how they will behave as they finally disappear, said Giovanni Baccolo, a glacier researcher at the University of Milano-Bicocca and editor of the European Geosciences Union cryosphere blog.

The Marmolada was considered to be a relatively risk-free glacier. “But non-linear failure of small glaciers may become increasingly common in the near future,” Baccolo posted on Twitter. This summer could go down as the worst-ever in the records of alpine glaciers’ decline, he said.

“Before 2022, the summer that has long been cited as the worst for alpine glaciers was 2003,” he said, noting that the frequency of such events appears to be increasing. “So 20 years have passed to have another dramatic year for glaciers. I really hope that the next one will be in 2040 or so but my fear is that because of climate change it will occur sooner.”

Glacier scientists taking measurements right now “are all sure that many records of thickness reduction of ice will be beaten,” he said.

On several glaciers, researchers have already documented the disappearance of two meters of ice this season, an amount that typically isn’t observed until the end of the summer, he said.

“By the end of this summer, many glaciers will look different than they did before,” he added.

Nobody could have predicted the Marmolada glacier collapse, he said, but he anticipates the event will help glaciologists understand more about the final stages of alpine glacier decline. 

“I guess that we should strive to learn something from this tragic event,” he said. “Looking at the lower part of many glaciers, there are signs of collapses because of ice melt. Glaciers are literally being destroyed by this crazy summer that is following an extremely dry winter, at least in the southern flank of the Alps.”

Preceding the Marmolada collapse, he said, temperatures around the glacier stayed above 32 degrees Fahrenheit for more than 20 days, with no nighttime relief from the above-freezing conditions. 

“We know perfectly how glaciers react to climate change and we have also made predictions of their evolution in future years, but we still do not know too much about the final phases of a glacier,” he said. “In many cases the ice just finishes, in other cases the glacier can collapse because of its excessive weakening related to melt.”

“It is very likely that in the future these events will be more frequent,” he said.

Trickle-Down Hazards

There are many ways that warming can introduce instabilities in high-altitude and high-latitude systems, said Richard Alley, a Penn State geoscientist well known for his research on how global warming will affect the frozen parts of the planet.

“I mostly work on a really big one, the possibility that West Antarctica will destabilize and give us an additional 3 meters or so of sea-level rise a lot faster than generally expected,” he said. “But there are shorter-term, more-local impacts. The transition from cold, icy mountains to whatever we will have in the future involves a lot of disturbance, and things often move when they are disturbed.”

In some cases, the glaciers may simply be coming unstuck from their beds, he said.

“If you are old enough to recall defrosting a non-frost-free refrigerator, or if you’ve ever tried to shovel a driveway with ice frozen to the pavement, you know how hard it is to remove ice frozen to something,” he said. “Some high mountains are cold enough that the glaciers are frozen to their beds. Thawing the freezer, or the driveway, or the bed of the glacier, makes motion much easier. For the freezer and the driveway this may make you happy; for people below the glacier, it may make them very unhappy.”

Some impacts of warming on a glacier are hidden beneath the ice. Extra meltwater from warming can wedge open crevasses and additionally lubricate an already-thawed bed, in some cases pushing a huge mass of ice that can slide more easily off the hillside, as is suspected in the Marmolada collapse.

In addition to the collapse of the glaciers themselves, Alley said their disintegration also affects surrounding landscapes. For example, when a valley glacier melts, it can no longer support loose rocks on the canyon walls, making them more susceptible to rock- and landslides.

Glaciers also are often surrounded by moraines—loose rock and soils that they’ve excavated from the mountains. As some glaciers retreat, their meltwater forms lakes behind the moraine, with the pressure on the natural dams increasing as the water rises.

“Engineers tend to frown on dam construction from loose materials—rapid failure is possible,” Alley said. “So, retreating glaciers can leave lakes primed to cause outburst floods.”

Melting Glaciers Destroy Themselves

Meltwater from glaciers plays a key role in their future, and the increase in heatwaves is swelling the amount of water that can be transferred to the glacier bed, said Etienne Berthier, a glaciologist with the French National Center for Scientific Research.  

“Water is really the key factor for triggering a glacier collapse,” Berthier said. “Overall, its effect will depend on the capabilities of the glacier system to evacuate this extra meltwater. If the drainage system is well developed and the glacier ice is at the melting point, water will be easily drained out of the system. Otherwise, water can be stored under the glaciers, in lakes, pockets or as a film, and it can increase pressure and trigger glacier destabilization.”

Berthier was co-author of a landmark 2018 research paper in Nature Geoscience that identified climate change as one of the factors in the dramatic collapse of two Himalayan glaciers in Tibet in 2016.  

With a warming climate and increasing heat waves, “it’s quite clear we are seeing more meltwater in places where we didn’t see it before,” said Swiss glacier scientist Matthias Huss. “As soon as you get water percolating into crevasses making its way to the glacial base where it can lubricate the base of the ice, it is a very powerful trigger for such events.”

But, all the glaciers baking in the current heat wave are not going to collapse, he said. 

“This is not something that is completely new,” he said. “Deadly and destructive glacier collapses also happened in much colder climate that were not related to human-caused global warming, and it’s difficult to say if they’ve increased in frequency. One hundred years ago, this event in Kyrgyzstan might have gone unnoticed.”

Climate models don’t really make predictions for single glaciers in high regions, said Jordi Bolibar, a postdoc researcher at the Netherlands Institute for Marine and Atmospheric research, who recently co-authored a paper that explores the nonlinear sensitivity of glaciers.

The challenges of modeling the collapse of individual glaciers is that they are still very rare on a global scale. Scientists currently assume that such sudden catastrophic alpine glacier events don’t have a big effect on things like overall water resources or global sea level rise. But, he said, that’s based on what’s known about the past, “when there were fewer temperature extremes than now.”

In the warmer decades ahead, he said, some steep ice flows will become detached from the bases that buttress them from below, which could make them more susceptible to catastrophic collapse. And as glaciers currently surviving at very high elevations move and melt into new shapes, they may enter steeper zones where they would be more prone to falling.

The High Mountain Areas chapter of the 2019 Special Report on the Ocean and Cryosphere from the Intergovernmental Panel on Climate Change found with high confidence that global warming increases instabilities of all sorts in the mountains.

With glaciers appearing to collapse more often, more granular modeling of individual glaciers might prove helpful, Bolibar said.

Early warnings, of glacial collapses, rockslides and outburst floods, could save lives.

During the current shift from a relatively stable, post-ice age climate to whatever is coming, “the critical period is the transition, from one state to another,” Huss said. “In this transition we’ll be seeing a lot of instabilities. We’ll be seeing more of such new situations, that were unknown before, or even unthinkable. At the moment it seems there might be a trend, and the heat waves of the last days might be the last trigger.”