An avalanche is a rapid flow of snow down a slope, such as a hill or mountain.
A powder snow avalanche in the Himalayas near Mount Everest.
Heavy equipment in action after an avalanche has interrupted service on the Saint-Gervais–Vallorcine railway in Haute-Savoie, France (2006).
The terminus of an avalanche in Alaska's Kenai Fjords.
Alaska Railroad track blocked by a snow slide
Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughout its life cycle, starting when, under suitable conditions, the ice crystals form in the atmosphere, increase to millimeter size, precipitate and accumulate on surfaces, then metamorphose in place, and ultimately melt, slide or sublimate away.
Norwegian train plowing through drifted snow
Cold northwesterly wind over Lake Superior and Lake Michigan creating lake-effect snowfall
Freshly fallen snowflakes
An early classification of snowflakes by Israel Perkins Warren