When water-rich air in the atmosphere is cooled to well below 0° C, tiny ice crystals form. Depending on the conditions under which they are formed, over 6000 different crystal forms can occur. All have a uniform, hexagonal basic shape. If several crystals join together, snowflakes are formed. At temperatures around 0°C it snows large flakes, when it is extremely cold, only individual crystals. There are different types of fresh snow.
Powder - the freerider's dream
Powder falls in very small flakes when it is very cold. It consists of over 90% air and is therefore light and fluffy.
As powder snow is very dry, you cannot form snowballs from it. "Real? Powder snow forms the comparatively harmless loose snow avalanches. However, if there is catastrophic snowfall, as in the winter of 1998/99, the most dangerous avalanches can occur - dust avalanches.
If the snow falls under the influence of wind - and unfortunately this is almost always the case in the mountains - then the snow is no longer loose, but bound. Bound fresh snow can become a deadly trap as it forms slab avalanches.
If it snows in relatively warm temperatures, the flakes are large and the snow is moist and heavy.
Cardboard snow
Cardboard snow forms wet loose snow avalanches on very steep slopes. Unfortunately, the wet fresh snow is better suited to snowball fights than freeriding.
Graupel
Graupel grains are formed when water droplets freeze to ice crystals in the air. This creates small, airy spheres.
Rime
There are also snow crystals that do not fall from the sky, but form on the surface of the snow as surface frost - or on objects as hoar frost. Surface frost forms on clear nights. Moisture from the air crystallizes on the cold snow surface and forms leaf-shaped ice crystals. These can become very large, but are extremely fragile. If surface frost is snowed in by a layer of fresh snow, it acts like a ball bearing and provides the perfect avalanche slide surface. These snow-covered layers of frost, often only a few millimetres thick, are responsible for many avalanche accidents. Snow-covered surface hoar: perfect sliding surface for snow slabs!
Even more snow
Rough frost (also known as hoarfrost) always grows against the wind on objects that are supercooled in fog and wind, so that you can tell the direction of the wind.
Rain
Even in winter, it occasionally rains right up to the summit regions. While the powder-addicted freerider's heart gets heavy, the risk of avalanches rises sharply. Wet snow avalanches can break loose anywhere, often sliding directly onto the turf as ground avalanches.
The snow cover
The snow that falls during the winter accumulates on the ground. The snow cover consists of layers of different thicknesses made up of different types of snow. Snow crystals are very unstable and fragile formations. From the moment they are formed in the atmosphere until they melt, they are constantly changing. This is known as transformation or metamorphosis. These transformation processes influence the risk of avalanches, which is why it is important for freeriders to know the four transformation processes presented in the following articles.
Transformation by wind and pressure
Decomposing transformation
Building transformation
Melting transformation
