Scrambler Faces Avalanche Risk in Heatwave
@MartinRivers recounted a risky scramble from 980-1530m elevation amid rotten snow, avalanches, and a 12°C heatwave, describing how the dangerous conditions became "rewarding growth." The post highlights the increased avalanche risks that unseasonably warm weather creates for winter mountaineering.
Unseasonably warm temperatures dramatically increase the risk of wet slab avalanches. Meltwater from the snow surface percolates through the snowpack, weakening the bonds between layers and creating a dangerously unstable slab ready to slide. These avalanches are often powerful and destructive, capable of carrying large amounts of heavy, wet snow, rocks, and other debris. Heatwaves also accelerate the collapse of cornices, which are overhanging masses of wind-deposited snow on ridges. Rapid warming can cause these features to become unstable and break off, often triggering a larger slab avalanche on the slope below. Cornice falls are unpredictable and can break further back onto a ridge than expected, posing a significant threat to mountaineers. The term "rotten snow" often refers to a snowpack that has become isothermal, meaning its entire depth has warmed to 32 degrees Fahrenheit (0 degrees Celsius). This condition severely compromises the structural integrity of the snow, making it weak and slushy, which is a clear indicator of unstable and dangerous conditions. Traveling on such snow is hazardous as it loses its ability to support weight. A stable spring snowpack typically relies on a daily melt-freeze cycle, where the snow surface melts during the day and refreezes into a strong, supportive crust overnight. A heatwave disrupts this cycle. When temperatures remain above freezing for extended periods, especially overnight, the snowpack does not refreeze, leading to widespread instability and a heightened risk of avalanches.
