Deadliest single avalanche

The deadliest single avalanche on record took place on 13 December 1916, near the Gran Poz summit of Monte Marmolada, Italy. This summit was one of the most fiercely contested positions on the Alpine Front of World War I, with thousands of Austro-Hungarian and Italian soldiers living in trenches and shanty-town-like camps on the rocky slopes around the peak. At roughly 5:30 a.m. local time, a massive avalanche tore through the encampment of the 1st Battalion, Kaiserschützen Regiment III (3rd Imperial Rifle Regiment), burying or crushing the wooden barrack buildings. At least 332 people were in the camp at the time of the avalanche, including 230 from the Imperial Rifles and a further 102 from the battalion's Bosnian support company. Figures for the eventual death toll vary from 270 to 330.

The winter of 1916/17 saw the heaviest snowfall of the 20th century in the Tyrolean Alps. One rain gauge recorded 143.2 cm of precipitation between November 1916 and January 1917, with a further 56 cm between March and April 1917.

The Gran Poz disaster was just one of many deadly avalanches recorded on 13 December 1916, a day that is rememebered as "White Friday". They were triggered by a particularly intense burst of snowfall that occured when a warm and humid air mass was pushed north into the mountains from the Mediterranean coast.

For many years, the avalanches of White Friday were reported to have killed around 10,000 men, but recent research published in 2016 by historians and meteorologists at the University of Bern in Switzerland has refuted this. The researchers found that only 1,300 Austro-Hungarian soldiers were reported killed (from all causes) in that sector during the first two weeks of December 1916, and that no contemporary reports gave casualty figures (including injured) higher than 2,000 for the 13 December avalanches. The figures for the Italian Army were harder to find, but casualty numbers were thought to have been similar.

The researchers also noticed that 13 December 1916 – "White Friday" – was actually a Wednesday.

Both the 1962 and 1970 Huascarán avalanches killed more people (death tolls estimated at 4,000 and 22,000, respectively), but neither were avalanches in the traditional sense. In both cases, ice falls from glaciers around the mountain triggered a cascading sequence of mudslides and rockfalls. These built up to form a colossal wave of rock and ice that scoured the land for a distance of 5 kilometers destroying several towns.