Tuesday 28 December 2021

Avalanche kills skier in Colorado.

A skier has died following an avalanche at Cameron Pass in Colorado on Friday 24 December 2021, according to the Colorado Avalanche Information Center. The skier, who has not yet been named, was with a companion when he was buried by the event, and despite being dug out promptly, did not survive. The avalanche was about 50 m wide, and is thought to have been caused by the failure of a layer of faceted snow 30-100 cm beneath the surface at a point where the slope steepens sharply. This had been covered by a recent snowfall, and would not have been apparent to the skiers. This is the first fatality of the 2021-22 ski season in Colorado; twelve people are thought to have died in avalanches in Colorado in the winter of 2020-21, the majority of them while skiing.

The crown of the 24 December 2021 Cameron Pass avalanche. Lucas Mouttet/Colorado Avalanche Information Center.

Avalanches are caused by the mechanical failure of snowpacks; essentially when the weight of the snow above a certain point exceeds the carrying capacity of the snow at that point to support its weight. This can happen for two reasons, because more snow falls upslope, causing the weight to rise, or because snow begins to melt downslope, causing the carrying capacity to fall. Avalanches may also be triggered by other events, such as Earthquakes or rockfalls. Contrary to what is often seen in films and on television, avalanches are not usually triggered by loud noises. Because snow forms layers, with each layer typically occurring due to a different snowfall, and having different physical properties, multiple avalanches can occur at the same spot, with the failure of a weaker layer losing to the loss of the snow above it, but other layers below left in place - to potentially fail later.

Diagrammatic representation of an avalanche, showing how layering of snow contributes to these events. Expedition Earth.

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