Spring Snow
We have seen that good ski-ing in winter depends largely on the absence of wind. A sudden thaw may also produce a disastrous result, for snow which has once been rained on and refrozen will remain covered with crust until there is a new snowfall.
The best winter snow is without rival, but spring snow is, on the whole, safer and less capricious. In normal spring weather all snow is crusted in the early morning, for the sun is powerful enough to melt snow even on northern slopes. But this spring crust, as we shall soon show, is much less troublesome than crust in winter and yields very fine ski-ing indeed. Wind, the great enemy in winter, has no effect in spring, for wind cannot affect hard crust, and if wind blows while the snow is falling a few days of strong sun will melt any wind-formed crust and produce exactly the same surface as if the snow had never been touched by wind. It should, however, be added that, in the early spring, wind, though powerless on snow which has once been melted and crusted, is a great nuisance if it blows on snow which is still powdery, as is usually the case for twenty-four hours or so after a snowfall; snow which has once been crusted by the wind has a very strong resisting power to the action of the sun; I have known south snow in March retain irritating effects of wind action after several days of strong sun that would have been sufficiently potent to melt any ordinary crust.
Spring ski-ing is, as a rule, delightful. Snow is troublesome in the intermediate stage between powder and crust. Once a crust is formed, the more often that crust is remelted and refrozen the better, as there is nothing better than old crystalline snow which has been through the mill of melting and refreezing again and again. Unless wet Föhn blows such snow will always retain its crystalline character, even when remelted by the sun, and will always yield good ski-ing. Of course in the late spring at low altitudes the sun is powerful enough thoroughly to thaw and drench the snow, and in the middle of May below 7000 feet wet snow in the middle of the day is unpleasant. But in March and April ski-ing on melted crust is wholly delightful. Incidentally the best ‘Spring snow’ is often found at the end of or in the middle of February on southern slopes.
From the beginning of March onwards all slopes, save those at very high altitudes, begin to crust over. The process is gradual on northern slopes. There is a period when the northern slopes no longer hold the dry loose powder of winter but have not yet begun to crust.
Spring powder is common on north slopes in March. It is denser than winter powder, and is not so dry. It is slightly moist on the surface, and much heavier. It yields, however, a first-class running surface, and will take any turn or swing. Its main objection is the fact that it is peculiarly liable to avalanche.
Gradually, however, Spring powder disappears, save at great heights, and all slopes are covered by crust. In the afternoon the crust is melted, and the snow is soft and wet on all slopes. At night the snow is refrozen.
The normal cycle, then, of a normal spring (say April, at altitudes between 3000 and 9000 feet) is as follows: Hard crust at dawn; crust superficially softened between sunrise and midday; soft melted snow in the afternoon; soft breakable crust as the sun loses in strength; and solid hard crust after the sunset.
First let us consider the hard crust usually found at dawn.
This differs materially from the marble crust of winter, and from any of the crusts formed by wind action. It is, as a rule, slightly softer. What is more to the point, it is rougher. The surface of normal spring crust is perforated by numberless little holes. Sometimes these holes are quite small, mere pockmarks, sometimes they are as large as half-crown pieces. It is the presence of these holes and the roughness of the crust that makes steering easy, so that control is not difficult, and linked Christianias or Stemming turns are within the power of the good runner.
Perforated crust, in fact, is a delightful running surface. It is common at low altitudes in March, at moderate altitudes in April, and is normal in the High Alps in May, June, July and even August.
Film crust is found in May and June on the glaciers, and occasionally at low altitudes in April. It forms a delightful running surface. Unlike marble and perforated crust, it is not quite homogeneous. It is composed of a hard under-surface of solid crust, covered by a very thin, soft, and transparent film of ice, which glistens in the sun like burnished silver.
This film of soft ice is shorn away as the ski begin to come round on a turn. It provides a splendid purchase, preventing effectually all side-slip, and yet not sufficiently strong to make turns difficult.
Film crust is admirable for fast straight running, because at any moment the pace can be regulated by a swift turn. There is nothing finer than a run down the glaciers in the early morning on film crust.
We have seen that the cold nights of winter produce marble crust, which is hard and slippery. Marble crust is the kind of surface which needs crampons or a chip with the axe if it is climbed on foot.
Further, marble crust, and all forms of crust produced by winter winds, yield a very unsatisfactory surface, too slippery to give good purchase.
We have seen that the milder nights of April produce perforated crust which is much rougher and gives good ski-ing, while the even warmer nights of May and June produce film crust in which Christianias and Stemming turns are easy and safe. In fact film crust gives such a wonderful grip that even Telemarks are possible.
From this we deduce the following law:
Provided the night’s frost is sufficient to produce a solid unbreakable crust, the crust will give the best ski-ing when the frost has been least severe.
In other words, “The milder the frost the better the crust.”
This rule is important. It often happens in spring that one has to start down before the sun has produced a surface melting. Again and again the first thousand feet or so of descent have been spoiled because the crust was too hard and slippery. But the lower one ran down the better the ski-ing. The hard marble crust of winter gave way to the perforated or film crust of spring. In April, in the High Alps, winter conditions often prevail at high altitudes to give way to spring conditions lower down. You start a run on marble crust and end on perforated or film crust. The lower the altitude the milder the night frost, and hence the better the crust.
But of course the hard crust of dawn is soon changed under the influence of the sun. At first the sun produces a slight surface softening which is, however, quite sufficient to make a great deal of difference. Even marble crust, if superficially softened, yields excellent running. Gradually the melting process becomes more pronounced. Sun-touched crust with a slight surface moistening—quite sufficient to make Christianias and Stemming turns a joy—yields to crust covered by an inch or two of melted snow. Such crust is known as Telemark crust—not because Christianias are not easy, but because Telemarks are very simple, whereas Telemarks are difficult, if not impossible, on hard crust.
Telemark crust is a normal stage in the passage of hard crust to melted snow. It is the practical certainty of finding Telemark crust at certain hours in spring that makes spring ski-ing in fine weather such a delight.[21]
As the sun increases in strength all trace of the underlying crust disappears. The snow is melted through and through, and becomes dangerous on steep slopes.
This wet snow is often slow, but it never sticks like the wet snow of winter. On steep slopes it gives good running—if unsafe.
Snow sticks in the intermediate stage between freezing and thawing. Thus powder snow which is beginning to thaw sticks abominably, but snow which is melted through and through does not stick. Snow which has once been thoroughly melted and then refrozen will never stick badly again. A surface of wet snow overlying powder will, of course, stick, but melting snow which rests either on hard crust or on the hard ground does not stick. It may be slow, but it does not adhere in sticky lumps to the running surface.
Thus two inches of melted snow on top of crust (Telemark crust) gives a fine running surface, and an inch or even less of wet snow on grass also gives excellent sport.
Snow that has been melted and refrozen night after night soon acquires a crystalline character. When the crust begins to melt after the sun has struck it, the melting surface is composed of numerous wet crystals, sometimes about the size of salt crystals, sometimes much larger.
This granular snow is familiar to all spring runners, and gives an excellent ski-ing surface. Occasionally towards sunset, as the wet heavy snow that is usually found in the afternoon during the wet spring begins to freeze again, you will find the snow assuming a very marked crystalline formation, which resembles the wet hypo crystals with which photographers are familiar.
In general, so long as snow retains a crystalline formation it gives good running. Salt snow or hypo snow yields excellent sport. In May at low altitudes the sun, however, is so powerful that it dissolves the crystals and reduces all the snow to one consistent heavy wet slush. Such snow does not stick—that is to say, it does not adhere to the running surface—but it is very slow. Furthermore it is dangerous, because if you run suddenly on to a patch of this very heavy snow you are liable to be pitched on to your face. Often the snow is not only melted downwards but upwards, for the ground is very warm in spring, and thaws the snow from below, so that you will often find a patch of soft heavy snow resting in the form of a shallow bridge on an empty space. The ski break down the bridge of snow, and the ski-runner pitches heavily forward. Such hollow snow is seldom found in April, but is common in May at lowish altitudes. In May the best ski-ing at low altitudes (5000-7000 feet) is obtained before 10 a.m. and after 7 p.m. In the early morning and just after sunset I have often enjoyed first-class ski-ing right down to 5000 feet and lower, well on into the middle of May.
We may therefore sum up the normal cycle of a spring day as follows:
At dawn every slope will be covered by a hard homogeneous crust. This crust will be either marble crust, in which case it will yield very difficult and unpleasant ski-ing, or perforated crust or film crust. Perforated and film crusts give excellent ski-ing even before the sun has begun to soften the crust.
When the sun begins to gain in strength the hard crust is superficially softened, and gives good running even in the case of marble crust.
A later stage is reached when the hard crust is softened to a depth of about two or three inches (Telemark crust). This again gives good running.
Either before or after midday, according to altitude and inclination, all traces of crust disappear, and all slopes at moderate altitudes are reduced to wet, heavy and more or less water-logged snow. In the early spring this stage is perhaps only reached on southern slopes. In the late spring it is reached on all slopes at low altitudes and on north slopes, save, perhaps, at very high altitudes. In general, the ski-runner should not be abroad at such hours. Towards evening the slopes begin to refreeze. There may be an interval of hypo snow—soft hypo-like crystals in which fast running and every kind of swing is perfectly safe and easy. This is soon followed by the formation of a soft breakable crust, which gradually hardens until at last the cycle is complete by the formation of a hard solid crust.
Thus in general there are two periods of a spring day when ski-ing is easy, fast and safe. The first period is when the hard crust begins to soften, and the second period is when the wet melted snow begins to freeze. The ski-ing is least pleasant and most dangerous between midday and sunset.