Melting

Even though some smaller venues both produce and store the snow indoors in large garages or warehouses, most snow storage takes place outdoors in large snow piles from a few thousand m³ up to 100 000 m³. The following factors influence the storing- and melting process: 

  • Geography and weather
  • The ground surface 
  • Snow type, size and shape of the snow pile 
  • Type, thickness and age of the cover material

Research and experiences the last 20 years show that the main melting happens (in average) at the snow surface (80%), then due to rain (15%) and to heat from the ground (5%).

Geography and weather

Melting will depend on a few natural factors that are not easy to control or influence:

Both radiation (short waves) and heat (long waves) will increase the rate of melting. A cold and shady area with less sun exposure is therefore preferred.

North and east exposure is preferred, while south and west should be avoided.

High humidity and heavy rain will both increase the rate of melting, so a dry climate is positive.

Since wind will increase the rate of melting, the snow pile should be placed in a sheltered location.

Ground surface

Melting at the bottom of the snow pile will happen due to the ground heat. It is therefore important to ensure a proper surface with good drainage before building the snow pile. Ice will be formed if the drainage is poor or the snow pile too big (up to 1 meter ice per year may be formed, which is equivalent to several hundred meters of Cross-Country track if the snow pile is large). 

  • The following photos from Canmore show the ice buildup over several years – from snowpile with sawdust, the floor of the storage site after the snow has been distributed, and the ice layers per year clearly visible (all photos: Dave Rees)

Studies have been done to learn how different surfaces influence the temperature in the snow pile. At Beitostølen, Norway, the influence of asphalt, gravel, saw dust, wood chips and grass on the temperature in the snow pile was studied (see photos and examples from the 2016/17 study below).

Photo: Snøfarmen

Based on comparing the temperatures, using saw dust as a surface gave the best result.

Asphalt (blue), 5 cm saw dust (red): 

Photo: Snøfarmen

Size and shape of the snow pile

Both natural snow and man-made (artificial) snow can be used for storage, but the qualities of man-made snow are better suited for storage.   

The density of man-made snow (round crystals) are four times higher than natural snow (hexagonal crystals), and makes it more durable. The % or rate of melting is therefore lower for man-made snow.

The shape of the snow pile should be such that the ratio between the volume and surface is as large as possible. It has been shown that this creates the lowest total melting. Theoretically, although a half cylinder shape (or sphere) provides the best ratio, this exact shape is difficult to build with snow. The most practical soultion is therefore some kind of cylindar section (see below).

Photo of snow pile at Granåsen, City of Trondheim

To minimize the surface area it is important to construct and re-work the snow such that the entire surface is smooth and even (using the grooming machine or a backhoe). 

The larger the snow pile is, the less percentage of the pile will melt since a larger pile will have less of its volume exposed to weather and wind.

For Cross-Country venues it is typical to store between 10 000 – 20 000 m³ snow. This may be a suitable size for both reducing the formation of ice (due to the weight of the snow) and optimizing the ratio between volume and surface. 2000 m³ saw dust would cover a 13000 m³ large snow pile. 

Type, thickness and age of the cover material

Since the first snow storage projects (for skiing) around year 2000, venue operators and research projects have been trying to determine the best cover material.  Both natural and manufactured products have been used; materials that enable evaporation (can breathe) and materials that insulate the snow entirely (do not breath). Most common has been to use natural wood based materials that enable evaporation, for example saw dust or wood chips. It is important that the material is breathable and allow evaporation, since the evaporation process uses energy/heat and will therefore cool down the material below.  The cooling effect from the evaporation will have a big influence on the rate of melting.

As of today there are no manufactured materials (with reasonable costs) that are as effective as old fashioned saw dust, even though several types of “breathable” geotextile fabrics have been tested and compared.  The reason geotextile fabrics are anyhow used are due to their practical advantages. 

In addition to reflecting radiation from the sun, saw dust is able to absorb water, which will cause a cooling effect when evaporated later.  The thickness of the saw dust layer must be approximatelly 40 – 50 cm such that the result of the water absorption, evaporation and cooling process is optimal. 


The thickness of the sawdust influences the rate of melting in Davos (Grünewald et al., 2017)

In Norway it has been observed that new and light colored saw dust works well with approximatelly 20% snow loss. However, after about 3 years of use the sawdust is dirty and will have reduced reflection as well as reduced evaporation, and will then give 30% or more snow loss.

The geotextile fabric will last for at least 3 years, but should then be replaced due to damage from water, wind, dirt and other pollutants.