Mer de Glace Grotto in Chamonix, France, Could Disappear Within 5 Years

The famous ice grotto at Chamonix’s Mer de Glace glacier — France’s largest glacier — could disappear within five years as record-breaking heat accelerates the French glacier’s retreat. The grotto has been a popular tourist attraction for 80 years and attracts around 280,000 visitors annually. Since 1946, the retreating glacier has shrunken the experience to a sad little grey lump among the debris of what was, for the grotto’s first 40 years, a remarkably stable wall of ice — before the melt accelerated sharply from the 1980s onward.

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Shrouded in geotextile tarps to reduce the melt, the grotto now can only be accessed via a series of ramps and metal steps. Once upon a time, visitors could walk straight across from the Montenvers railway station across the glacier to the grotto, now the glacier has retreated so far, it takes 600 steps across the ramps and stairs to reach the man-made cave. Glaciologist Luc Moreau fears that the grotto could be gone in the next five years.

But concerns about the grotto’s future are not new. In 2022, when a heatwave struck the European Alps, the grotto had to be closed for safety reasons as a rock band threatened to fall across the entrance. After some reconstruction, the grotto could reopen, but the event forced local authorities to consider what could be done to preserve access to the attraction over the medium and long term. Four years later, the problem has become considerably more acute: the glacier is now retreating so quickly that the grotto itself could become impossible to operate within just a few years. According to Moreau, the Mer de Glace glacier, has lost an extraordinary 8.5 meters (28 feet) of thickness since May 2026 alone. Since the 2022 heatwave, the glacier has lost approximately 60 meters (197 feet) of thickness at the measurement location, while its overall front has retreated more than a kilometer (0.6 miles) over the past two decades.

That pace is shocking and worth putting in context. A 2019 study published in the French scientific journal La Météorologie by glaciologist Christian Vincent and colleagues found that Mer de Glace lost an average of 45 meters (148 feet) of water-equivalent thickness — roughly 50 meters (164 feet) of ice — across the entire 20th century, or about 32% of its average thickness. Even then, the researchers noted the melt had “clearly accelerated” since 2002. Under the study’s moderate-emissions scenario, the glacier was projected to lose about 80% of its surface area by 2100, with its front retreating 7.2 kilometers (4.5 miles) between 2018 and 2100. Under the study’s most pessimistic scenario, assuming unchecked greenhouse gas emissions, the researchers projected Mer de Glace could largely disappear sometime between 2090 and 2100. Losing 60 meters (197 feet) of thickness in four years when it had lost only 45 meters (148 feet) in an entire century shows clearly how dramatically the melt is accelerating. The recent 8.5-meter loss during the current summer shows that the trend keeps picking up pace and tracks closer to that worst-case century-long trajectory than to the more moderate one — decades ahead of when the original model anticipated it.

The changes are impossible to miss for visitors arriving at Montenvers on the famous red railway from Chamonix. A gondola installed in 2024 takes tourists closer to the glacier, but the ice itself has dropped dramatically below the infrastructure built many years ago. A sign near the gondola shows where the glacier stood in 2018, highlighting just how quickly the landscape has changed.

The grotto is still a spectacular attraction, with visitors admiring the blue ice chambers carved into the glacier. But increasingly, the reality is sinking in for many tourists: they may never see the grotto again — at least not in its present shape and form. This realization is driving an increase in what experts refer to as “last-chance tourism.”

Not just the grotto is changing but the glacier itself has also changed appearance. Rather than the brilliant blue-white ice often associated with the Alps, much of the Mer de Glace is now covered by gray rock debris. Moreau explained that the glacier’s movement has slowed, meaning it is no longer transporting as much material away from its surface, causing the debris-laden appearance.

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The Mer de Glace is only one part of a much larger transformation occurring across the Mont Blanc Massif this summer. Geomorphologist Ludovic Ravanel has reported that around 450 rockfall and collapse events have been recorded across the massif this summer, describing the number as unprecedented. Extreme heat has repeatedly pushed the Alpine freezing level above 5,000 meters (16,400 feet), weakening permafrost that normally acts as a natural cement holding rock together.

The consequences have already been deadly. Three Czech mountaineers were killed by falling rocks in the Goûter Corridor in July, while a young French climber died after being struck by rockfall below the Aiguille de la Génépi on August 14. The instability became serious enough that authorities closed the Tête Rousse and Goûter refuges on August 11, effectively discouraging climbers from attempting Mont Blanc’s normal route, while the Compagnie des Guides de Chamonix also stopped guiding clients to the summit. The refuges reopened after two weeks, however, rockfall danger remains elevated.

For Ravanel, the problem extends beyond the immediate dangers to climbers. Ice that once covered northern faces is disappearing, exposing dark rock, while hanging glaciers are also becoming increasingly fragile. He described the transformation as the loss of a “millennial” natural heritage that also contains valuable information about the region’s climate history.

For the Chamonix Valley, where around 90% of the population depends on tourism, the transformation presents an uncomfortable challenge. The same mountains that support the local economy are changing rapidly because of the warming climate. For now, the Mer de Glace grotto remains open. Tourists can still descend to the ice, walk through the blue chambers and experience one of the Alps’ most iconic attractions. But the clock is ticking and Chamonix might have to farewell an attraction that has has welcomed visitors for 80 years.