Three people have been confirmed dead following two avalanche incidents in Washington State this week. Joseph Simenstad, 32, from Issaquah in King Country died after being buried along with his wife, Sable, and Josh Winter, 24, while snowboarding near Mirror Lake, west of Cle Elum in Kittitas County, on Saturday 24 February 2018. The following day Declan Ervin, 17, and Niko Suokko, 18, both from Bellevue in King County, were caught in a second avalanche near Snoqualmie Pass in King County.
The scene of an avalanche that killed a man and injured two other people near Mirror Lake, Washington, on 24 February 2018. Kittitas County Sheriff's Department.
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.
Northwestern North America have seen a number of avalanche related incidents this winter, largely due to high levels of snowfall. This is, in turn caused by warmer conditions over the Pacific, which leads to higher rates of evaporation over the ocean, and therefore higher rates of precipitation over North America, which falls as snow in cooler upland regions. There are further concerns that as the climate warms in the coming months, the thawing of this snow will lead to further dangerous avalanches.
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