A rapid flow of snow down a slope, triggered when an unstable layer within the snowpack fails, often set off by additional snow load, warming temperatures, or the weight of a skier or animal crossing the slope. Avalanches range from small, harmless sloughs to massive slab avalanches capable of destroying buildings and burying entire valleys, and are among the most significant natural hazards in mountainous, snow-covered regions worldwide.
Facts
PeriodicityMost frequent in winter or spring, though avalanches may occur at any time of year in any mountain range with an enduring snowpack. 1 ScaleSized in North America on the D-scale (destructive force) and R-scale (relative to the avalanche path), both running 1 to 5 with half sizes used on the D-scale; Canada uses its own size classification based on consequences. 1 First DescribedSystematic attempts to model avalanche behavior date from the early twentieth century, notably the work of Professor Lagotala in preparation for the 1924 Winter Olympics in Chamonix, later developed by A. Voellmy and published in 1955 as On the Destructive Force of Avalanches. 1 Identification
Distinguishing AppearanceA rapid flow of snow down a slope, occurring as tightly packed slab avalanches or as loose flowing snow, capable of capturing and moving ice, rocks and trees. 1 Connections
Associated With
Strong seismic shaking from an earthquake is a well-documented direct trigger of snow avalanches on unstable slopes.
The rapid temperature rise and snowmelt a foehn wind brings on its lee-side descent is a well-documented direct trigger of wet-snow avalanches in mountain regions.
Sources
1. Avalanche (Wikipedia)
WikipediaWikipedia 'Avalanche', lead section
An avalanche is a rapid flow of snow down a slope, such as a hill or mountain.
Wikipedia 'Avalanche', United States classification for avalanche size section
The size of avalanches are classified using two scales; size relative to destructive force or D-scale and size relative to the avalanche path or R-scale. Both size scales range from 1 to 5.
Wikipedia 'Avalanche', Modeling section
Attempts to model avalanche behaviour date from the early 20th century, notably the work of Professor Lagotala in preparation for the 1924 Winter Olympics in Chamonix.
Wikipedia 'Avalanche', lead section (periodicity sentence)
They are most frequent in winter or spring, but may occur at any time of the year.
Wikipedia 'Avalanche', lead section (distinguishing-appearance sentence)
An avalanche is a rapid flow of snow down a slope, such as a hill or mountain.
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