A crisp, firm, outer surface upon snow. Basically, three types of snow crusts exist, formed by 1) the refreezing of surface snow, after melting and/or wetting, to form a hard layer of snow (sun crust, rain crust, spring crust); 2) the packing of snow into a hard layer by wind action (wind crust, wind slab); and 3) the freezing of surface water, however derived, to form a continuous layer of ice on top of snow (film crust, ice crust). A snow crust is designated as “breakable” or “unbreakable” according to its ability to support a person on skis.