bod-kin crystals                          plank crystals                            small stars

Snow crystals are created under various temperatures. Crystals structure are formed according to the temperature  - see the survey below:

from            to

- 4            -   8      bod-kins

- 8            - 12      planks

- 12          - 18      small stars 

- 18          - 25      space stars

- 25          - 40      short prisms

Essential forms of snow crystals 

These forms can be combinated each other. This depends on humidity circumstances in the atmosphere. There were described more than 21 thousands of various crystal forms. The science - known as snow crystalography - studies presence and existence of such appearances.

Nakay classification of snow crystals

According to latest notions, it is obvious that each snow crystal differs in details. At the temperature, near to freezing point, the crystals are joined and so the flakes are created.

Special sorts of snow

Surface hoar-frost

It is created by vapour or hardly cold surface of snow covering or subjects, mostly during very cold, calm and clear nights. During snowing up, it presents dangerous slipping layer for new belts of snow, situated over it.

                                    Surface hoar-frost                       Surface hoar-frost

Hails

These are of round forms. They were not created by crystalisation, but frozing of water drops to snow crystals in the atmosphere. They have no essential influence to avalanches.

Ice-accretion

It is created within windy weather from small frozen drops on luff-side of very cold subjects.  

                                                           Ice-accretion on rocks            

Change of snow crystals

Since its creation until complete thaw, the snow is  always changing. Snow lives, the experts say. They are distinguished the sorts of snow changing, such as:

Change by means of  decomposition - destructive metamorphose

Change by means of growing up - constructive metamorphose

Change by means of thaw - corn snow

We do not speak about snow crystals at these changes but about snow grains, as the crystal grate is disappearing.

Destructive change

The crystals of new snow - during its fall in the atmosphere - are (under influence of wind) broken and deformed. They receive a form of powder-snow fragment. After snow-fall, the destruction of crystals continues, under the influence of upper layers, in connection with the temperature of - 3 to - 5 degrees, and in consequence of steaming of vapours it comes, via the stage of cup-shaped snow, to round snow corns. These snow corns are very small. The fastening of each neighbouring corns is good. The layers created with roundcorned snow heave mostly sufficient strength, so they form stabilizating element of snow covering.

                 New snow                                Felted snow                        Roundcorned snow

Constructive change

At small snow covering height and big temperature difference between soil surface (this is nearly approaching 0 degrees) and snow cover surface, there is a movement of vapours so big that it occurs to quick arise of snow corns of angular forms and are bigger - so called movable snow. The proceeding of growth is dependent on longdated low temperatures (-10 degrees and less) and temperature fall in snow-layer ( the temperature of snow covering layer in C degrees is to be divided with height of snow covering in cm). The conditions for constructive change of snow start at temperature fall of 0,25 degrees C/cm, with growing fall the constructive change starts to be more intensive.

                                                           Angular-corned snow

Big temperature fall between layers

As a final result of this change, there  is so called hollow-snow. It has considerably great angular and hollow corn, reminding on small cups. The corns of hollow and movable snow  among each other do not have practically any cohesion. The layers formed with these flakes present ideal slipping surface for upper situated layers.

                                                             Hollow ice-accretion

Change by means of thaw

When the snow warms over 0 degrees, the water starts to be released and enters among  separate snow corns, lets down the cohesion among them and whole layers, too. At  repeated frozen temperature, there are established straight ice-bindings among snow corns - bridges, so the whole layer is stabilized  expressively. The repetition of this proceeding is known as corn snow formation.

                                                                  Snow corns

The separate parts of these  snow proceedings can be combinated in various forms, depending on weather conditions.

Snow covering

All weather stages and changes manifest  snow layers. Each snow layer has its specific characteristics: sort of snow corns, hardness, humidity, adhesion, optical characteristics, etc.

Description of some essential snow layers:

New snow: layers of new snow are created from snow crystals, where the crystalic grate is visible. There are mostly layers, established during final period of snow-fall.

Free snow: in this layer, any snow corn is movable, without binding to neighboring corns. This layer does not allow long distance tension  transfer in snow covering. It could be dry powder snow or wet snow. A natural  showering angle of free snow is 47 degrees. If it does not remain snow-trace during your arise on ski, it is free snow. It is a similar proceeding when you take snow-freestone on a pan, we shake with pan, and snow-freestone is scattered, it is also a free snow.

Hardened (bounded) snow: billions of snow corns are bounded each other and are not free movable. This enables long distance tension transmission in snow covering. The stabilization of all layers of hard snow depends on hardness of snow layers and its adhesion to the lower layers.

Snow  beaten by wind: it is to be found on luff-sides. While walking along boards of snow beaten boards, you can hear a hollow sound. The boards are mostly very fragile, after breaking you can hear always typical sound „whumm“. It signalls bad board stability.

Under by wind hardened board, we find often soft snow layer, the adhesion of which is very low.

Blown snow: is set aside under ranges on calm places of slopes, in form of snow pillows.

Wind speed slowing on calm places behind ranges, enables big accumulation and partial snow hardness. This hardness is mostly unsufficient, snow pillows and snow-drifts belong to very dangerous avalange formations.

Layers of movable and hollow snow: it is most dangerous and less adhesive layer. It acts for upper layers as a fountain pen. While digging snow profile, the layer strews as a sugar and its hardness is minimal.

Snowed layer of surface hoar frost: it has similar characteristics as a layer of movable snow.

Ice layer: the adhesion of upper layers is drastically decreased.

Crust of frozen corned snow: it acts as a stabilization factor in snow cover. However, it is dangerous for the upper layer of new snow.

Physical Characteristics of Snow:

The temperature of snow layer situated near to the soil, has mostly a temperature nearly to 0 degrees. At the surface, the snow cover is similar to the temperature of the air. During arrival of warm and wet weather in spring months, the temperature moves around 0 degrees in the whole profile. Snow works as a good temperature insulator, it is twice better as pine wood.

Specific weight - it is to be understood the weight of one cubic meter of snow in kilograms. The weight become higher with hardness and wet of snow.

Powder snow               10-50 kgs/m³

Blown snow              100-200 kgs/m³

Hard dry                     200-400 kgs/m³

Hard light                    400-600 kgs/m³

Corned snow             300-800 kgs/m³

Ice                               800-900 kgs/m³

Water                               1000 kgs/m³

You can calculate from these values that a board made from blown snow at dimensions: width 10 m, length 10 m and height 10 cm has the volume of 10m³ and weight of 1-2 tonnes. You can see that the danger of small boards you cannot underestimate! These data are important also for calculation of shock-pressure of avalanche. The plasticity of snow covering is the bigger, the more free the snow is and its temperature is higher. With the plasticity arising, it occurs to balancing of internal tension of snow covering.

Text: P.V.

Photo and info: laviny.sk/snowecrystal.com

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