CRITERIA FOR CHOOSING A SNOW PROFILE LOCATION

Listed here in order of importance, the following five criteria apply when selecting a suitable location for a snow profile: 

• The location of the profile should be representative, i.e. in the dangerous area named in the avalanche bulletin (unfavorable slope aspect) or in a location where information is required. 
• Of course, the location of the profile should nevertheless not be dangerous, thus it should be either on flat terrain (less than 30° slope steepness) or on a comparatively small slope or above the dangerous area. 
• The profile location should be “undisturbed”, i.e. it should not have any tracks or obstacles (e.g. rocks). 
• The depth of the snow should be below average compared to the general snow situation. Weak layers are often more pronounced in areas with less snow and are more easily triggered. 
• The slope should be uniform, i.e. the snowpack distribution should be consistent and it should not be located in undulating terrain – avalanches prefer uniform, regular slopes. 

The last two points can be checked using a probe. Often, not all criteria can be 100% fulfilled. The most important thing is that the slope is not dangerous and information can be gained from it.

PREPARATION AND WIDTH OF THE SNOW PROFILE

Use the probe to check whether the slope is uniform and the snow depth is below average. 

Then insert the probe vertically into one of the two corners of the planned profile wall, preferably into a corner that is facing the sun. Now you can begin digging the snow profile. 

If you want to carry out an ECT (extended column test), the profile needs to be at least 150 centimeters wide. For two tests – a CT (compression test) and an ECT – it should be 200 centimeters wide. 

The best place to test the profile is on the shaded part of the slope. Here, you can use the snow crystal card to observe the shapes, without them melting in the sun. 

EQUIPMENT 

To make a perfect snow profile you need a shovel and a probe, but also a saw, a crystal card, a stand magnifier, a snow thermometer and a notebook in which to record the results. 

A look at the snowpack can be more or less detailed, depending on your aim. Ideally, you would check the snowpack completely regarding grain forms, grain sizes, layer hardness and temperature and carry out a snowpack test. This will provide you with all of the important information, which you can later post online in the form of a detailed snow profile for other mountain athletes. However, this takes time. For this reason, profiles such as these are mostly carried out as part of a course or by people who are collecting profile data for avalanche bulletins and forwarding them to the relevant databases (e.g. www.lawis.at). 

Following the motto “looking at the snowpack is always better than not looking at the snowpack”, you can go ahead and carry out “just” a snowpack test. If the test reveals a weak layer, you can always take a closer look at it afterward. 

COLLECTING AND DOCUMENTING SNOW PROFILE DATA

To create a detailed snow profile, take the following steps: 

First, take a note of the general conditions, i.e. the exact time and location of the profile (GPS coordinates, date, height and slope aspect), the air temperature and the temperature at the snow surface (always in the shade, e.g. using the shovel blade as shade) as well as the wind direction, wind strength and weather (clouds, precipitation). 

Then use your fingers to check the snow hardness from top to bottom; this will enable you to quickly identify the main layers and the profile’s changes in hardness. Then examine the form and size of the grains, again from top to bottom. 

While doing so, measure the temperature every 10 centimeters. The probe in the shaded corner serves as a ruler. In between determining the grain forms, the temperature should be read and the thermometer then moved 10 centimeters down each time. 

The snow layers, with their grain forms, hardness and wetness, should be measured in centimeters from the ground. The probe in the corner of the profile serves as a ruler – probes with cm-markings are ideal for this. For example: With a snowpack depth of 136cm and a 6cm-thick surface crust layer, the description would be, e.g.: 136–130, crust, hardness: “knife”; grain form: “melt freeze crust”; grain size: 3–5mm; wetness: dry. The next layer could then be, e.g.: 130–111, hardness: “one finger”, rounded grains, 0.25–0.5mm, dry, etc.  

While one person is recording the date, the second person should note the values in a table in a notebook. Later, these values can be submitted line by line into the Austrian Avalanche Warning Services’ LAWIS database, which will create the familiar graphical image of a snow profile with changes in hardness, layer thicknesses, with information at the side about grain forms, grain sizes, etc. 

DETERMINING HARDNESS AND CHANGES IN HARDNESS

Hardness and changes in hardness are crucial. The hardness of each layer is determined using five hardness levels with intermediate levels. These are: 

• Fist = when your fist can be pushed into the layer with little resistance. 
• Four fingers = when your hand or four fingers can be pushed into the layer with little resistance. 
• One finger = when one finger can be pushed into the layer with little resistance. 
• Pencil = when a sharpened pencil can be pushed into the layer. 
• Knife = when the snow is so compact that only a knife can be pushed into the layer. 

If you are unsure whether one or four fingers can be pushed into the snow, record both hardness levels. Because a classic slab avalanche is made of a relatively hard layer of snow on top of a soft, faceted weak layer, sudden jumps of two hardness levels or more between layers should ring alarm bells. Especially if the soft layer is in the top meter of the snowpack and the slab on top covers a large area.

DETERMINING GRAIN FORMS AND SIZES

Grain forms are significantly more difficult to identify than layer hardness. Here you need some experience, a good magnifier and a crystal size aid. Faceted crystals are, for example, generally larger than 0.5mm (typical weak layer), while small, round grain forms (typical of wind-drifted snow and slabs) are always smaller than 0.5mm. The crystal card helps determine whether the grain size is between 0.25 and 0.5mm (= rounded grains) or whether the grains are larger, e.g. 1–3mm. In the latter case, these can only be faceted crystals or melt forms. Melt forms are rounded and often “stick” together; faceted crystals are similar to sugar and have straight edges. 

Significant differences in grain size are a warning sign, especially if small, compactly layered crystals (a slab) are lying on large, faceted, non-cohesive crystals (a weak layer) – the perfect prerequisites for a snow slab. 

READING AND EVALUATING A SNOW PROFILE

The greater the difference between layers, the more unfavorable the profile, e.g. hard on soft; small on large crystals; small, rounded crystals on faceted. The more layers there are within a profile, the more likely that you will find a weak layer. And if this weak layer can also be “stressed”, i.e. it can still be “reached” by a winter athlete, the situation is even more precarious. One way to measure this is by the sinking depth. Generally speaking, a compact slab with a hardness that allows for crack propagation, but is also not so hard that the winter athlete cannot sink through to the weak layer, should be classed as precarious. 

The rule for the weak layer is: the softer it is, the closer it is to the surface and the larger the crystals within it and the more precarious it is. However, the thickness of the weak layer does not matter. A common feature is that faceted weak layers are often found under or above a thin layer of ice or crusted snow and can be just a few millimeters thick, which means they are tricky to detect.  

A snowpack test will quickly identify the precarious layer. Therefore, experts often work in reverse: First they do a snowpack test (to identify the weak layer), then they take a closer look at the layer to understand how it could have formed so that they can then consider where this layer could or must be found elsewhere in the mountains. This transfer and interpretation of the results is known as “process thinking”. You try to imagine where this weak layer must have formed and where a slab will be lying on top, and use this information to predict where dangers can be expected in the mountains.

THE PERFECT LOCATION FOR A SNOW PROFILE

Each test is  only ever as good as the location of the profile!

1. The location should be relevant (unfavorable slope aspect, i.e. where dangerous areas are suspected). 

2. The location should not be dangerous, but should still be relevant. Preferably, you should stay under 30° or limit yourself to very small slopes and remain above the dangerous area. 

3. The profile location should be undisturbed, i.e. it should not have any tracks or obstacles (e.g. rocks). 

4. The depth of the snow should be below average compared to the general snow situation. Because weak layers are often more pronounced in areas with less snow, and are easier to initiate. 

5. The slope should be uniform, i.e. the snowpack distribution should be consistent and it should not be located in undulating terrain – avalanches prefer uniform, regular slopes.

CUTTING THE BLOCK 

The dimensions of the block to be cut for an ECT are: 30cm deep and 90cm wide. 

First, the front face is cut out vertically and the dimensions drawn on the surface of the snow. Now begin freeing the sides. This is best done with a snow saw. Saw vertically into the snow twice at an interval of 20 to 30cm and clear out the snow from the 20 to 30cm block using a shovel. Then do the same on the other side. The two ditches to the right and left of the freed block should be cut 20 to 30cm deeper than the block itself so that you can later saw the back of the block free. 

The back of the block can only be sawed with a long enough saw, preferably one that is relatively rigid and at least 50cm long. First you saw the back of the block from the top, then along the cutting surface down the whole height of the block from the ditches to the left and the right. Alternatively a cord or cable saw could be used to do this by running it around two probes stuck into the respective corners. In this case, the probes must be held in place by a third person while the other two do the sawing.

LOADING TEST

Once the block has been cut free, you can start with the actual testing. To do this, the shovel blade is placed on the left or right end of the block and loaded. The shovel is loaded in three stages by tapping it with the flat of your hand and later with your fist. You continue adding load until either a full or partial break forms. As you do so, the shovel blade will sink deeper and deeper into the snow. It helps if one person taps and the other observes closely if and when a crack forms. Because if you are on flat terrain a crack is easy to miss, as slabs on slopes less than 30° cannot slide. The best thing is for the observer to film the test using a cell phone. 

The first 10 “taps” are from the wrist; the way to do this is to allow the hand to “drop” from the wrist without applying any extra force – the load at this stage is very low. Then the lower arm is allowed to drop from the elbow 10 times. Finally, you allow your whole arm to drop from the shoulder 10 times and the “hit” is done with your fist.

LOADING STEPS, CRACK TYPES AND NOTATION

Once the block has been cut free, load is added to it step by step at one of the two sides. It is important to identify when and whether the crack propagates to the end of the block. A video can help you do this. 

The results are recorded and the shear surface examined and interpreted. The test result is noted as follows:

LOADING STEPS

Crack when digging / cutting #0 
Crack when tapping from the wrist #1–10 
Crack when tapping from the elbow #11–20 
Crack when tapping from the shoulder #21–30

TYPE OF CRACK

• Propagation – P – the crack propagates through the entire block at tap # or the following tap. # is the tap at which the crack forms. 

• No propagation – N – the crack forms at tap # and does not propagate throughout the entire block with the next tap (partial crack). 

• No crack – X – no flat shear surfaces form by the end of the test. 

NOTATION

The results are noted in the following way and order: 

First comes the abbreviation “ECT”, followed immediately by the type of crack (P/N/X), then the loading step (between #0 and #30) and then – after an @ – the layer in the profile in which the crack formed. 

Examples: 

• With the 5th tap, a crack forms in the layer located 36cm up in the profile, and then propagates throughout the entire block: ECTP 5@36cm 
• A crack forms in the layer located 75cm up in the profile with the 24th tap and then propagates throughout the entire block with the 25th tap: ECTP 24@75cm 
• With the 27th tap, a crack forms in the layer located 12cm up in the profile, but does not completely propagate by the end of the test (partial crack, the block only cracks under the shovel but cannot propagate): ECTN 27@12cm 
• A crack forms in the layer located 63cm up in the profile when sawing: ECTP 0@63cm 
• No large cracks at any loading step: ECTX 

SNOW PROFILE WIDTH

If a CT is the only test being done, a profile width of one meter is enough.
The dimensions for the column  that needs to be cut out for a CT are: 30cm deep and 30cm wide. 

First, the front face is cut out vertically and the dimensions drawn on the surface of the snow. Now begin freeing the sides. This is best done with a snow saw. Saw vertically into the snow at an interval of 20 to 30cm and clear out the snow from the 20 to 30cm block using a shovel. This creates a 20 to 30cm ditch to the left and  right of the column, and which should be cut around 20 to 30cm deeper than the height of the column (at least 1 meter). Finally, the back wall is cut free. 

This is done using a long enough saw (50cm). Stand in the ditch and saw the back wall of the column from top to bottom.

LOADING STEPS AND CRACK TYPES

Once the block has been cut free, load is added to it step by step, as in the ECT. It is important to discern if and when the crack will propagate. A video can help you do this. The results are recorded and the shear surface examined and interpreted. The test result is noted as follows:

LOADING STEPS

Crack when digging / cutting #0 
Crack when tapping from the wrist #1–10 
Crack when tapping from the elbow #11–20 
Crack when tapping from the shoulder #21–30 

TYPE OF CRACK

• Sudden, smooth crack (P – planar) – a smooth crack forms at tap # or with the next tap. # is the tap at which the crack forms. 

• Partial crack or irregular shear surface (R – resistant) – crack forms at tap #, but the crack surface is irregular rather than smooth or the crack only propagates through the column on several taps. 

• No crack (B) – no flat shear surfaces form by the end of the test, the block “crumbles”. 

NOTATION 

The results are noted in the following way and order: 

First comes the abbreviation “CT”, followed by the loading step (between #0 and #30) and then – after an @ – the layer in the profile in which the crack formed. A description of the crack surface is added at the end. 

Examples: 

• With the 5th tap, a sudden smooth crack forms in the layer located 36cm up in the profile: CT 5@36 P 
• A crack forms in the layer located 75cm up in the profile with the 24th tap; however, the crack is not sudden and is clearly irregular: CT 24@75 R 
• A crack forms in the layer located 63cm up in the profile when sawing: CT 0@63 P 
• No large cracks at any loading step: CT 31 or CT 30@ B