Snow sports are part of active tourism during winter season, when we can make the most of the white blanket surrounding ski slopes. However, this white layer isn't homogeneous but rather consists of multiple layers corresponding to different snowfalls that have accumulated.
For practising winter adventure sports, we can primarily distinguish between weak, poorly cohesive layers and strong, well-bonded layers. It's essential to evaluate different strata to ensure terrain stability and plan our route according to the snow type we'll encounter (see snow safety).
Highly cohesive snow
Once snow crystals settle, they begin changing shape, and these transformations determine the future resistance of the snow layer. When the snowpack temperature is uniform across all layers and not too low, the snow forms rounded crystals strongly bonded together. This creates a highly cohesive layer, very compact. These crystals are the most stable and persist for long periods.
If an outer layer of this type settles over a weaker one, there's significant avalanche danger, as the compact layer can break away and slide in blocks, causing a slab avalanche.
Powder snow
Also called "sugar snow". If there are temperature variations within the snowpack, the snow forms faceted crystals. These crystals don't create strong bonds, resulting in a weak, poorly cohesive layer. This snow has light consistency, not compact but loose, allowing quick gliding. Skiing on it creates "powder clouds" that give it its name.
Hard-packed powder
Consists of a compact base covered by a thin layer of powder snow. Common in ski resorts, where the compact base is created by snow groomers. Off-piste, it occurs when light snowfall lands on a very stable layer.
Depth hoar
When sugar snow gets buried under other layers, it's called depth hoar. Avalanches often occur when snow falls onto this layer, formed after a period of cold, clear weather.
Other snow types
- Virgin snow. Untouched by skiers or snow groomers.
- Groomed snow. Snow that has been compacted, for example by snow groomers. At ski resorts, grooming creates compact snow that's easier to ski on.
- Crust snow. Forms when there's significant temperature difference between day and night. At nightfall, surface snow cools first, water freezes and creates a very firm layer like a crust. Can also form from wind action on powder snow. One of the most difficult snow types for skiing.
- Slush snow. Not warm (despite the name), also called wet snow or mashed potato snow (without actual potatoes). Forms through the opposite process to crust snow. When daytime temperatures rise, snow melts creating a poorly cohesive layer with high water content. Also challenging for skiing.
- Surface hoar. A layer of snow or ice, typically very fragile, formed by water vapour condensation on snow surface. Usually forms on cold, clear nights - the solid equivalent of dew. Though usually forming a thin layer easily destroyed by wind or rain, it can gain consistency when bonding with other layers. Its instability depends on thickness, ranging from one millimetre to several centimetres.
- Granular snow. Snow whose flakes have transformed into grains that gradually fuse together.
- Sastrugi. Wind-formed snow layer with ridges or undulations.
- Firn. Very hard snow found in glaciers and perpetual snowfields.
- Artificial snow. Produced by snow cannons spraying atomised water that turns to snow at suitable temperatures. Once fallen, it transforms like natural snow through wind action, temperature changes etc.
