Recent Avalanche Fatalities
Avalanches have recently caused multiple fatalities across various regions. This week, at least eight individuals died in California's Sierra Nevada mountains, three in the French Alps, and two on the Italian side of Mont Blanc. One person remains missing from the Lake Tahoe back country incident, marking it as one of the deadliest single avalanches in US history.
In Europe, over 90 avalanche-related deaths have occurred since October, significantly higher than the 36 deaths recorded in the same period last year, according to European Avalanche Warning Services. France and Italy have experienced the majority of these fatalities.
Japan has also reported avalanche deaths this season, alongside blizzards and chairlift accidents.
Understanding Avalanches
Avalanches are primarily categorized into two types: "loose snow avalanches," which involve surface-level snow moving downhill from a single point, and "slab avalanches," which are less predictable and more hazardous.
Craig Sheppard, program manager for the Mountain Safety Collective, explains that slab avalanches result from the interaction of different layers within a snowpack. Weather breaks can alter snow crystals; some conditions strengthen snow grains, while others weaken them. An unstable situation arises when a weak layer forms beneath a strong layer.
When snowfall is absent for a period, surface snow exposed to daily warming and nightly cooling can develop "facets" or weak crystals. Subsequent fresh snowfall can then rest on this unstable layer. Tyson Millar, an avalanche safety expert from Protect Our Winters, compares this faceted snow to "ball bearings in the layers of snow." This phenomenon was observed in Europe and the West Coast of North America this season, characterized by minimal snowfall in January followed by heavy snow in February. Japan, conversely, experienced consistent heavy snowfall throughout the season.
Geographical Considerations
Avalanches are less frequent in Australia due to its "maritime snowpack," which is influenced by proximity to the ocean. This differs from the intercontinental or continental snowpacks found inland, such as in the Rocky Mountains.
Sheppard notes that Australian dangers are more related to whiteout conditions and hazardous surface crusts on steep, icy slopes.
New Zealand and coastal North American resorts like Whistler, Canada, also exhibit maritime snowpack characteristics. However, Japan, despite being an archipelago, receives substantial wind from Siberia, rather than warm, moist ocean air.
Associate Professor Nathalie Vriend at the University of Colorado Boulder indicates that slopes between 25 and 40 degrees carry the highest avalanche risk, aligning with ideal skiing conditions.
Slopes under 25 degrees typically experience minor slips, while those over 40 degrees generally do not accumulate enough snow to pose an avalanche risk.
Climate Change Influence
Global warming can reduce avalanche frequency by decreasing overall snow accumulation. However, climate change also contributes to increased avalanche frequency and intensity through other mechanisms.
Professor Steven Sherwood at the University of NSW Climate Change Research Centre states that ski seasons globally are shortening due to higher temperatures, leading to more variable snow patterns. This includes less frequent, but potentially heavy, snowfalls, and a higher proportion of rain instead of snow. Lower altitudes may experience increased rain, including rain falling on existing snow, while higher altitudes could see softer snow.
Sheppard identifies snow season variability, extended periods without snowfall, temperature fluctuations, rain on snow, and soft snow as factors that elevate avalanche risk.
A 2018 paper in PNAS linked an increase in avalanche activity in the Himalayas to concurrent climate warming, contradicting the assumption that warming reduces snow and thus fewer avalanches.
A 2024 peer-reviewed article in Nature Reviews Earth & Environment suggests that climate change could affect the number, magnitude, flow regime, release, type, and seasonality of avalanches, as well as the types of terrains susceptible to them.
The paper projected a rise in wet avalanches, often resulting from thaw conditions where slushy snow slides over bonded snow, in the French Alps, central Rocky Mountains, and western Norway.
Researchers emphasized the need for more data to fully comprehend climate change's impact on avalanche risk, including indirect factors like treeline elevation shifts or glacier retreat.