In Simple Terms
A new study found that many ski areas in the northern French Alps overlap with huge slopes of rock that are slowly shifting. That does not mean a collapse is about to happen, but some of the slopes are moving now. Mapping and monitoring them can help experts understand which places need closer attention.
When a Slope Looks Still, It May Be Slowly Changing
Not every mountain hazard begins with an obvious collapse or rocks tumbling down where people can see them. Some slopes undergo deep, slow changes within the rock itself. The rock may shift little by little over a very long period—over centuries or even thousands of years. That does not mean a major collapse is scheduled to happen, or that one is imminent.
But slow movement does not make the process unimportant. Under certain conditions, a rock mass that has gradually changed shape can eventually fail quickly and on a large scale. The result could be a rockfall or a broad flow of rock in a massive landslide. That is why locating these areas is an essential step in understanding the hazard, even when the mountain’s surface shows no dramatic warning signs.
The study by S. Blondiau and Y. Gounelle focuses on what is known as deep-seated gravitational slope deformation. The researchers use the term rock-slope deformation for these areas. They are not describing a single small crack, but a large mass of rock that is slowly changing under the pull of gravity. This kind of deformation does not automatically mean a disaster will occur. It does, however, make it important to distinguish relatively stable slopes from those that may warrant closer monitoring.
A Broad Survey of Ski Areas in the Northern French Alps
The researchers chose the northern French Alps, a region with 116 ski areas. Rather than focusing on a single location or isolated incident, they compiled a map of rock-deformation sites and compared them with the ski areas. Their survey identified 888 areas of rock-slope deformation across the study region. This makes it possible to consider the issue as a regional challenge, rather than as an isolated concern at one resort.
Of the 888 areas, 206 overlap with the boundaries of ski areas. In total, 69 of the 116 ski areas are affected by this geographic overlap. This is a significant overlap between the region’s geology and the recreational use of its mountains. But an overlap on a map does not mean that every part of a resort faces the same hazard, nor does it prove that a collapse will occur. It identifies locations that merit closer investigation.
Maps help put the issue in its geographic context. Is a deformed slope above a populated or frequently used area? Does its extent reach ski facilities? Which locations should be prioritized for monitoring? The inventory figures cannot answer all these questions on their own, but they provide a basis for comparing sites. They also help ensure that attention is not limited to places where rock movement has already been clearly observed or a known incident has occurred.
Les Menuires Shows How Extensive the Overlap Can Be
One of the cases highlighted in the study is the ski resort of Les Menuires, where a rockslide area lies above the town and resort. The researchers calculated that 86% of the ski area at Les Menuires is affected by rock-slope deformation zones. This figure refers to the share of the ski area covered by the deformation zones. It does not mean that 86% of the resort will collapse or that every part faces the same level of risk.
The example matters because it shows how extensive a deformation zone can be in relation to a tourist resort. To a visitor, the slope may look ordinary, while geological maps reveal a large mass of rock that is slowly changing. That is why it is useful to combine knowledge of the underlying terrain with information about where people are active. The resort’s administrative boundaries, or the mountain’s appearance from the surface, are not enough on their own to show the full extent of the overlap.
The 86% figure also illustrates why such numbers need to be read carefully. It describes how much of the ski area at this particular site overlaps with deformation zones; it does not indicate the likelihood of a collapse or how large one might be. To assess the actual hazard, experts need to know whether the rock mass is moving now, how that movement is distributed, and what could be affected if a collapse occurred. The study places this example in a broader picture that includes dozens of sites, but it does not reduce the assessment of each location to a single percentage.
Satellite Monitoring Adds Another Layer of Information
After identifying the areas that overlap with ski resorts, a more specific question follows: which sites are showing signs of movement now? The study points to the possible use of InSAR, a technique that compares radar measurements collected by satellites to detect changes in the ground’s surface. These measurements can help reveal slow movement that may be difficult to spot by eye or during a brief visit to a site.
According to the researchers’ analysis, signs of ongoing deformation were detected at 43 of the 69 ski areas affected by the overlap. This does not mean that those 43 sites are certain to collapse, nor does it prove that the other sites are free of risk. It does, however, provide information that can help set monitoring priorities. Detecting movement draws attention to locations where the slope’s behavior needs to be understood more precisely, while the other sites also require appropriate assessment.
Movement measurements address only part of the problem. Detecting a change in the surface does not, by itself, reveal when a major collapse might happen, and it does not prove that every slow-moving slope will suddenly fail. The signals also need to be interpreted in the right geological and field context. InSAR is therefore not a standalone solution, but one of several tools that can contribute to hazard detection and monitoring.
Finding a Hazard Is Not the Same as Assessing Its Impact
Managing slopes requires more than knowing that rock deformation is present. It is also important to understand the nature and extent of the movement and to consider what kind of failure might occur, from falling rocks to a major rockslide. The study emphasizes that effective hazard management calls for a range of approaches, rather than reliance on a single technology or map.
This distinction matters to ski resorts and to anyone planning how mountain land should be used. An overlap map can show where deformation zones lie in relation to ski areas, while movement monitoring provides information about ongoing changes. Turning these findings into a hazard assessment requires a closer look at the characteristics of each location, followed by a decision about whether more monitoring or other appropriate measures are needed. The available material does not provide a detailed list of such measures, so it would not be reasonable to assume that one action would suit every site.
The findings should not be read in a way that either causes alarm or dismisses the issue. The figures do not say that all 69 ski areas face an imminent collapse, or that each of the 206 deformation zones will affect people or infrastructure in the same way. They show that many ski areas overlap geographically with deformed rock slopes, and that some of these sites display detectable movement. That is enough to justify systematic attention, but not to make a uniform judgment about every resort.
Climate and Human Activity Shape the Risk Picture
The study places slope deformation in a broader context, where natural hazards intersect with the presence of large numbers of people at high elevations. Skiing draws visitors into mountain environments, while slope conditions change under the influence of multiple factors. The source links the increase in rock-slope failures to climate change. When changing hazards coincide with people and activities in the same places, assessing risk becomes a matter of understanding both the geology and how the mountains are used.
This does not mean that climate change alone explains every instance of rock movement, or that every resort is experiencing the same increase in risk. The key point is that hazard patterns and human presence can change at the same time, making outdated assumptions inadequate. In heavily used mountain areas, identifying deformation zones and tracking which ones are moving can help build a more current understanding of conditions.
That is why the maps are useful beyond academic description. They direct attention to places where slowly moving slopes overlap with areas people visit, and provide a foundation for more systematic monitoring. One question remains open: will this inventory lead to a broader approach to managing threats at ski resorts, combining monitoring with site-by-site assessment based on local conditions?
The Bottom Line
A 2026 study by S. Blondiau and Y. Gounelle, published in the journal Environmental Management, documents extensive overlap between rock-slope deformation zones and ski areas in the northern French Alps. Of 888 mapped deformation zones, 206 overlap with ski areas, affecting 69 of the region’s 116 areas. InSAR analysis found signs of ongoing movement at 43 of those sites. Les Menuires illustrates the scale of the overlap: deformation zones affect 86% of its ski area.
These results do not predict an imminent collapse, and they do not mean that every location faces the same level of risk. They do show why slowly moving slopes deserve serious attention, particularly when they are close to places people use. Geographic mapping and satellite monitoring offer an important starting point, but managing the hazard requires multiple tools and careful assessments that account for the differences between sites.