How does slope maintenance work ?
And what does it do ?
The slope should be nice and smooth, firm but not icy. A lot of know-how, even more experience, and perfect interaction between snow master and snow groomer operator are necessary to ensure the best slope quality and durability of the valuable raw material snow. A whole fleet of these high-performance machines is on the road in the ski resorts in the evening hours.
Solid slopes: The sintering
The term ‘sintering’ refers to a process used in metalworking. Applied to snow, this means that smaller ice particles combine to form larger units. In the process, dislocations in the crystal structure – which arose when snowflakes collided – disappear. Processes take place in which the ice crystals fuse together, in other words, they sinter together.
Put simply: the individual snow crystals become rounder over time because their surface area decreases. As soon as the snow has settled, the flakes are still touching each other quite loosely. Soon, the snow settles slightly under its own weight. The crystals that are touching each other recombine, releasing interfacial energy into the surrounding environment. The snow solidifies and cools slightly in the process.
A slope must rest for eight hours
The closer the temperature is to zero degrees, the more likely the snow is to sinter. At very low temperatures, the process runs less well. In addition, shape, size and size distribution influence the sintering process. Natural snow sintered differently than coarse-grained, technically produced snow. Medium to small grains down to dust grain size are optimal. This is because they can "grow together" at many points. However, this process takes time. To become solid, a slope needs about eight hours of sintering time.
This is necessary because otherwise the snowpack is not resistant enough and cannot withstand the stresses of skiers, temperature and weather conditions in the best possible way. The "resting" of the slopes is necessary after every slope preparation.
Push, loosen, compact
A snow grooner ensures that the snow retains the consistency that allows it to compact quickly and effectively. High-performance snow grooners use their plough to evenly push the snow – which skiers have carried down the slope during the day – back up the slope. The track itself has a certain compacting effect.
However, the tiller is particularly important. It cuts up to ten centimetres deep into the snow and transforms lumps of ice and even icy patches back into fine-grained snow.
Finally, levelling boards press the snow down again to create a beautiful, smooth run that can then sinter well. Speed, tilling depth and contact pressure must be perfectly coordinated.
The right time to prepare
The best time to prepare is just before freezing. If grooming is done too early, the water will reach the surface. The slope becomes icy. If the snow is not groomed until it is already frozen through, the grains will be too coarse. The snow can sinter poorly. Usually, the piste rollers are active in the evening hours. If there is fresh snow, they usually groom again in the morning hours. Between daytime operations and floodlighting as well.
Three points need to be considered to decide when to groom: whether the snow is dry or wet, whether it will cool or warm in the next few hours, and whether there will be more precipitation in the next few hours. The best time is in the evening. If the air cools overnight, grooming must be done as early as possible. If warming is imminent, it may make sense to wait. This is because soft snow is easier to work with than very firm snow.
Even the best preparation has limits
It’s tricky when snow has fallen during the night. Even with careful judgement, this can lead to unsatisfactory results. As the curing time cannot be met before the start of daytime operations, the slope isn’t firm enough. If it weren’t groomed, skiers would have to navigate through loose fresh snow, which makes the slopes slow and difficult to ski on.
In such situations, the experience of the snowcat operators is particularly important.
Grooming achieves very little on very soft, wet snow if there is no sign of it cooling down. This is because it is then virtually impossible for the snow to compact. After just half a day, the slopes are already heavily worn.
In such situations, the decision is therefore made not to groom the slopes, so as not to loosen the snow any further. If they were groomed, the impact of skiers would take an even greater toll on the snow than if it were left ungroomed.
Slope grooming is a science of sorts. The snowcat operators in the ski resorts are experienced experts who apply a great deal of know-how to their work and strive to achieve the best possible result for guests in every situation.