Digging snow profiles and recording them correctly requires a lot of experience, starting with the question of site selection through to determining the layers. However, reading standard recorded profiles is less complicated than it may seem at first glance. Lukas Ruetz explains it below using an example from the Sellrain. The profile discussed, like many others, can be found in the LAWIS database of the Austrian avalanche warning services and all notations correspond to those used there. Other organizations sometimes use slightly different forms, but the basics (e.g. hardness levels, signs for the grain shape) remain the same. Looking at snow profiles is of course no substitute for studying the situation report, but can provide valuable additional information and help to understand the processes within the snowpack and observe them during the winter.
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In the snow profile "Lampsenspitze, Koglalm" from January 18, 2016, the snowpack has a height of 65cm, divided into eight layers, which were worked out by hand profile (= without the aid of a pile driver or other equipment).
Layer 1: From 65cm to 53cm high, there is fresh snow that has already been slightly degraded. The branches of the fresh snow crystals break off, known as "felty snow". This layer has a hardness of 1, i.e. it can be penetrated with a fist using moderate force. It has a moisture content of 1, i.e. it is dry. The crystals are 1.5 to 2 mm in size.
Layer 2: From 53 cm to 35 cm in height, there is round-grained snow that has already been progressively degraded. This may be drift snow, where the wind has destroyed the fresh snow crystals and thus accelerated the degradation process, or former fresh snow that has already had some time to degrade from fresh snow crystals to felt to round grains. The layer has a hardness of 3, i.e. it can still be penetrated by a finger with moderate force. It has a moisture content of 1, i.e. it is dry. The crystals are about half a millimeter in size. There are four calculated rivets (automatically calculated according to differences in grain size, hardness, grain shape between the two layers, see "Rivet test").
Layer 3: From 35cm to 18cm, there is also round-grained snow that is in the process of being transformed. It is already slightly larger than the round grains of the layer above (exactly 0.5mm or slightly larger, almost no grain is smaller than 0.5mm, in contrast to the layer above) and probably already slightly glassy, no longer pure white. The layer has a hardness of two to three, is difficult to penetrate with four fingers, but very easy to penetrate with one finger. It has a moisture content of 1 and is dry. There is a rivet at the layer boundary at 35 cm.
Layer 4: From a height of 18cm to 12cm, there is angular-grained snow with a diameter of 0.5 to 1mm. Here, the crystals already have clearly visible corners and edges as a result of the build-up transformation, are clearly glassy, no longer white, making the layer very easy to distinguish from the layers above it with the naked eye due to the "color jump" from pure white or slightly glassy to strongly glassy. The layer is also dry. At the boundary at 18cm there are three rivets.
Layer 5: From 12cm to 11cm height there is a thin fusion crust, which is already strongly "eaten away" from below. This means that free water vapour crystallizes on its underside (which, incidentally, is always present in the snowpack, the process is called resublimation or deposition). During the transition from vapor to solid form, floating snow forms on the underside of the melting crust. This is why there is a circle on the left-hand side of the spectacle shape = melting form, representing the melting grains in the crust, and a V on the right-hand side = deep frost, floating snow, symbolizing the crystals that form directly on the crust. The crystals of the crust (regardless of whether they are the already formed part or the melting grains) are 1.5 to 2.5 mm in size. The layer has hardness 3 and four rivets at the transition at 12cm.
Layer 6: From 11cm to 8cm there is floating snow: Divided into hollow shapes (inverted V, already three-dimensionally built) and angular shapes (still planar platelets, no recognizable three-dimensional structure). The crystals have a size of 2 to 3 mm, are dry and the layer can easily be penetrated with a fist. It probably trickles towards you at the slightest touch. There are five rivets on the border at 11cm.
Layer 7: From 8cm to 6cm there is again a melt crust, which is also "affected" by the build-up transformation. The crystals are somewhat larger than in the crust above and it is even harder, possibly because the proportion of melt grains is even higher than the proportion of floating snow, or because the melt grains have formed a harder crust with larger "melt lumps" due to more frequent thawing and refreezing.
Layer 8: From 6cm to the bottom there is again floating snow, which consists only of hollow forms and cup crystals. Almost all crystals have a three-dimensional structure, which is why only the inverted V was given as the grain shape. They are 3 - 4mm in size and the layer is easy to penetrate with a fist.
The air temperature during the photo was -18.3°C in the shade. The snow temperature at a height of approx. 60cm -18.2°C, at a height of 35cm -9.5°C, at a height of 3cm -1.5°C. The connecting line between the measured values represents the temperature gradient: the flatter the line, the stronger the gradient.
A ECT was carried out as a stability test, the slope inclination at the profile location is 29°. The result was a fracture through the entire block (ECTP) at the 11th strike (ECTP11) at the layer boundary at 18cm (ECTP11@18cm). The fracture surface was smooth and regular.
Interpretation:
There is just enough snow at the location for a ski tour without stone skis, given the inner alpine vegetation (alpine roses) and presumed surface characteristics of mountains with siliceous parent rock (often boulder slopes) at 2170m. There was fresh snow shortly before the profile was created. The first part of it may have fallen under the influence of strong winds. There are two crusts that are most likely the result of early winter snowfall followed by periods of warm or fine weather. If you have the weather pattern for the area in mind, you can draw conclusions: In this case, the snow is from the ground up to 8cm high from mid-October, the crust formed during the warm period at the end of October, beginning of November. From 12cm to 8cm the snow is from the snowfall at the end of November. The crust on top of this comes from the good weather throughout December 2015. The snow above 12cm comes from the snowfall since New Year's Eve 2015. Above 12cm, this snow, which fell in January 2016, is beginning to build up. The process is most likely based on the currently very strong temperature gradient within the snowpack. In the stability test, we were able to cause a smooth fracture through the entire block with little additional load (11th blow). In conjunction with the additional remarks ("settling and cracking"), we can assume at this location at this time that the snowpack is susceptible to failure due to the layers built up near the ground.
If you deal with this regularly over the course of a winter, you will classify this small component (a profile says very little!) in conjunction with the situation report (not with the hazard level but with the paragraph "snowpack build-up"), profiles already dug this season and process thinking (When? Where? Why?) and sharpens its picture of the current situation: the spread of existing problems, their delimitation according to altitude range and exposure or thinks about future, possibly emerging problems.
For further reading we recommend this bergundsteigen article by Patrick Nairz (LWD Tirol).
