Avalanches (pronounced avalan-CHEE) are natural phenomena found in mountainous areas that involve rapid movements of snow that pose serious threats to both people and property alike. Avalanches have the capacity to cause significant amounts of human and property damages every year, including debris slides or loose snow flows which can be initiated by collapsing weak layers of snowpack; once activated they can capture and transport rocks, trees, ice, etc. in their path.
Most avalanches are caused by snowpack dynamics; however, they can also be precipitated by human activities or earthquakes.
Avalanches can be large, destructive and often deadly avalanches; those spending winters exploring mountains for recreation and adventure need to understand this complex process in order to experience it safely.
Avalanches are one of the world’s deadliest natural hazards, capable of burying people alive, leveling buildings and roads and even killing backcountry skiers and snowboarders even when equipped with appropriate gear and knowledge.
While most people think of avalanches as being massive masses of snow moving quickly across terrain, they can occur at any size or speed. Avalanches also vary greatly in composition and form: slab avalanches can consist of tightly packed snow that compresses rapidly into slabs while loose snow avalanches are caused by weak layers collapsing underneath; they may even contain both elements together or simply consist of air as part of their composition.
Avalanches differ significantly from other geomorphic processes such as slush flows, mudslides and rock slides as well as serac collapses, while also differing from glaciers by typically only occurring in mountainous regions with an enduring snowpack during winter or spring months.
Historically, avalanches have claimed few victims; however, that is changing as more people explore remote backcountry terrain. Last winter alone in the US alone 34 people were killed by an avalanche, the highest total since 1980 and most were backcountry skiers or snowboarders familiar with their terrain at the time of death.
Climate variables associated with avalanches include temperature, snow water equivalent (SWE), maximum snow depth (HSmax) and winter precipitation. Figure 4a presents time series and boxplots of SWE, HSmax and precipitation for years with large avalanche activity versus control years; those years associated with larger avalanche events typically exhibit positive anomalies both for temperature and winter mean AO; positive phase of the latter may signal more frequent outbreaks of Arctic air over western North America while negative phases indicate fewer.