At least twelve climbers have died after being caught in avalanches triggered by a series of blizards in the Alborz Mountain Range to the north of Tehran in Iran. The first two fatalities were reported on Friday 25 December 2020, with another nine bodies being recovered by the Red Crescent on Saturday 26 December; a futher 14 climbers were rescued from the mountains, though one of these subsequently died, and another seven are still missing. The deceased are reported to include a political activist, an academic, a doctor and a mountaineering instructor.
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.
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