From rockfall to ice avalanches: how climate change has altered natural hazards in the Alps.
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Climate change is intensifying natural hazards in the mountains in many places, posing particular challenges for the Alpine region. This is the result of a study jointly coordinated by SLF permafrost expert Samuel Weber and glaciologist Mylène Jacquemart from WSL and ETH Zurich as part of the WSL research programme CCAMM. "Our observations clearly underline the effects of climate change on mass movements in the mountains," says SLF scientist Samuel Weber. The international team has evaluated more than three hundred scientific papers from the past three decades. "We focused on the processes that occur most frequently in the Alps: rockfall, rock avalanches, debris flows, ice- and snow avalanches," says Jacquemart, explaining the approach. The results:
- Rockfall: Activity has increased in recent decades, but only in the high Alpine region. There, the permafrost is thawing (see box) and the glaciers are retreating. This weakens the rock on a widespread basis and encourages the release of stones and rock masses.
- Rock avalanche: There is comparatively little data available for these major events. "Even if a clear statement is not yet possible, there are many indications that large rock avalanches occur more frequently today," says Weber.
- Debris flows: The number of heavy precipitation events that can trigger debris flows has clearly increased. "But only half of the studies examined indicate an increase in debris flows," says Jacquemart. However, there are signs of more activity above the tree line and in areas not previously affected. Due to the retreat of the glaciers and increased rockfall, there is more loose material available that rainfalls can set in motion.
- Avalanches: "Activity is declining at low altitudes because the amount of snow is decreasing. At high altitudes, on the other hand, avalanche activity has increased slightly," explains Weber. At the same time, the avalanches are changing their characteristics. Dry avalanches occur less frequently on average these days, while wet snow avalanches are more common.
- Ice avalanches: In many places, ice avalanches are disappearing along with the glaciers. However, regional observations indicate that larger ice avalanches have been occurring more frequently since the turn of the millennium. "Where and how exactly ice avalanches are changing needs to be investigated further," admits Jacquemart.
None of this comes as a surprise. Jacquemart and Weber refer to the first IPCC assessment report from 1990, which had already predicted an increase in alpine hazards due to climate change. The researchers expect snow and ice avalanches to become rarer by the end of the 21st century as warming continues. At the same time, the permafrost will continue to warm, even at high altitudes. The researchers therefore assume that rockfalls, debris flows and landslides will become more frequent. "This change poses major challenges for society in the Alpine region," emphasize Jacquemart and Weber.
What is ... permafrost?
Permafrost is ground such as rock, debris or moraine that has temperatures below 0°C throughout and is therefore permanently frozen. Permafrost covers some five percent of Switzerland’s territory and is mainly found in scree slopes and rock walls in cold locations at elevations above 2,500 metres above sea level.
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