If you want to know something about the stability of the snow cover and would rather not test it by driving into it, you need alternatives. The basic principle of snow cover tests is similar to driving in: You hit it or otherwise provide a load and see what happens. Unlike driving in, you do this in a controlled environment so that you can actually take a look first and don't get buried right away.
The following should be said in advance: Anyone hoping for the ultimate "does or does not fit" information for a slope from a snow cover test will be disappointed. Individual stability tests do not show that the snowpack is stable, at best they show that it is not. I can use them to turn a GO decision into a STOP, not the other way around. They are no substitute for studying the situation report, paying attention to the weather and terrain, observing danger signs, or anything else.
Without being unsettled by this, you can also find the whole thing interesting regardless of a risk assessment. Digging in the snow has always been fun and as an adult, you rarely have a good excuse for it.
General
In most snow cover tests, a type of snow block is cut out and then examined, for example by applying increasing loads until a weak layer breaks. The strength of the load becomes approximately (!) quantifiable and comparable through standardized methods and notation. This gives you "quantitative" information about the load required to trigger a fracture in a weak layer.
Although the blocks or columns can be partially dug free with a shovel, a snow saw is extremely helpful and essential for many tests. Long edges and larger blocks are best cleared with the help of a cord (or a special slip block cord). You stick one or two probes into the snow at the corners of the block and then "saw" out the block with the cord (in pairs).
Some tests are primarily designed to find weak layers quickly and easily, but allow less precise conclusions to be drawn about the load required for triggering. Other tests have been specially developed to investigate the fracture behavior or fracture propagation within a weak layer. However, even with tests that primarily show the load required for fracture, the type of fracture should be taken into account: Does the entire block break or just a part? Is the fracture surface smooth and regular or rough and irregular, or something in between?
Short overview:
The following list is not exhaustive, but includes the most common tests and some variations.
ECT - Extended Column Test
The ECT is probably the most commonly used snow cover test in this country. It can be carried out relatively quickly and provides a lot of information: Weak layers are identified, the necessary load until breakage is "quantifiable" and breakage propagation is included.
Aim: Identify weak layers in the upper area of the snowpack (~1-2m). Comparable, "quantitative" statement about the stability, as well as the tendency to fracture propagation
Procedure: Cut out 90x30cm block (note: the shovel blade is usually about 30cm long). Place the blade at one end of the block. Gradually increase the load until it breaks: 10 strokes from the wrist, then 10 strokes from the elbow, then 10 strokes with the whole arm. Note: "Strikes" here does not mean hitting it with full force, but letting the hand or forearm/arm fall onto the shovel without applying extra force.
Once a break has occurred, you can remove the snow up to the fracture surface and then continue to apply load from the last blow until the end of the ECT (=30 blows). In this way, you may get further results if there are several critical weak layers.
Results are usually noted as follows:
ECTPV or ECTP0 - fracture already when the block is exposed;
ECTP#@x cm - fracture and propagation over the entire width of the block after # blows, or fracture at blow # and propagation at # +1; fracture surface x cm above the ground. The fracture occurs at the upper boundary of the weak layer, not at the lower boundary.
ECTN#@x cm - Partial fracture is triggered after # blows, no propagation at blow # or blow # +1.
ECTX or ECT31 - No fracture after 30 blows.
Additional comments on the type of fracture (smooth, regular, rough, irregular) are often found. "Regular fracture" means that the surface is evenly fractured horizontally and the fracture shows no upward or downward displacement. Rough fracture surfaces are usually (not always) found on irregular fracture surfaces, smooth ones on regular ones. A so-called "collapse" is when the weak layer collapses and the whole block "settles" at once.
Example video ECT, matching the snow profile on the top right:
ect2 from PowderGuide.com team on Vimeo.
CT - Compression Test
Aim: Identification of weak layers in the upper area of the snowpack (~1-2m). Comparable, "quantitative" statement about the stability.
Procedure: Expose 30x30cm column. Place the blade on top. Gradually increase the load until fracture occurs, as with ECT. Results are usually given as CT#@x cm, see ECT notation. Once a fracture has been produced, the snow can be removed up to the fracture surface as with ECT and the CT continued. A distinction is made between a regular fracture, in which the column slides completely on a layer, and an irregular fracture, in which the block breaks off in pieces or disintegrates, as well as various intermediate stages.
Here the different types of fracture are clearly explained.
Variations CT:
Deep Tap Test
Special variation of CT, sometimes performed to examine deep weak layers that cannot be triggered with CT. Example: At a depth of 2 meters there is a hard layer with a potential weak layer underneath. I cannot reach this layer with a normal CT (because it is deep down and "protected" by harder snow).
Aim: Investigation of deep-seated weak layers.
Procedure: Expose 30x30cm column (or use column from previous CT). Remove snow up to 15cm above the layer of interest. The snow above the layer should have a hardness of at least "1 finger". Proceed as for CT. Example video
Stuffblock test
Like CT, only a weight is dropped onto the shovel blade from ever greater heights (10cm, 20cm, 30cm etc) instead of hitting it. The original stuffblock test was developed with a 4.5kg (10lb) bag. There are different variations, some people take their own weights or use their backpack. If the test is to be comparable, at least within your own records, the packsack/backpack/whatever must of course weigh as much as possible each time.
Slide block
The slide block is a kind of giant column test and the only test where a skier actually represents the additional load, which can make the result quite impressive.
Aim: Identify weak layers, "quantitative" statement about stability.
Procedure: The "pillar" should be 2m wide (across the slope) and 1.5m long (upwards). The easiest way is to dig off the front edge and then use two probes and a cord to cut off the other edges. With this method, it is sometimes recommended (especially in the USA) to cut out a trapezoidal block instead of a rectangle (rear edge 190cm, front edge 210cm, side edges: 150cm) to ensure that the block does not get stuck on the sides. If the sides are dug out instead of cut with the cord, this is not necessary. As with CT, the type of fracture (smooth, irregular, etc.) is considered in order to draw rough conclusions about the fracture propagation.
Loading steps:
If the block already breaks during digging, RB1 is specified.
Person with skis carefully climbs onto the block from above, no further than 35cm from the edge. (RB2)
The person quickly bends their knees without bouncing (teetering). Repeat 3 times (RB3)
Jump on the spot. (RB4)
Jump again on the same spot (1 or 2 times). (RB5)
In hard snow or deep weak layers: Jump without skis (RB6)
For weak layers where a release with skis is expected: climb down another 35cm with skis. First rocking again, then jumping twice (RB6).
If none of these loading steps cause a fracture, RB7 is specified.
Propagation Saw Test
Aim: To investigate the tendency and type of fracture propagation in a specific weak layer.
Procedure: Once again, a block is selected. The weak layer of interest is identified and marked in another way (e.g. make a line with your finger). If the weak layer is less than 100 cm deep, the block should be 30 cm wide (across the slope) and 100 cm long (in the direction of the fall line). If the weak layer is deeper, the block is extended to at least the same length (i.e. if the weak layer is 180 cm deep, the block is 180 cm long). Use the snow saw to initiate a break in the weak layer by cutting along the weak layer with the blunt side of the saw. Be careful not to slip with the saw. As soon as the fracture "jumps ahead" of the saw, leave the saw in place. The earlier the break propagation starts, the less favorable. Note where the break starts. A distinction is also made between fracture propagation over the entire length of the block (to the end: "End"), the slipping block falling apart (part remains standing, part slips: "SF" - slab fracture) and a fracture that does not propagate or does not propagate to the end of the block ("AR" -self arrest).
Detailed example video with explanation.
Shovel shear test
Aim: Identify weak layers and qualitative stability statement.
How to proceed: Cut 30x30cm column free on three sides. Cut the rear edge about half a meter deep, leave the saw in to see where you have cut. Carefully slide the blade behind the column without exerting pressure on the column. Pull evenly downwards (= towards yourself) without levering. If a break occurs, you have found a weak layer. If nothing happens, remove the snow up to the saw and repeat the whole thing from here.
Variation: Hand shear test
Simplified variation of the shovel shear test: Roughly mark out a 30x30cm area with your hands, push your hands into the snow behind the block and pull downwards parallel to the slope. Some also use a kind of snow hug to achieve the same effect: Delineate a semicircle with your arms, push your arms down into the snow and pull.
Small block test
The small block test is primarily used as a building block of the so-called "systematic snowpack diagnosis", where it serves as a "simplified snow profile". The systematic snowpack diagnosis is a method developed in Germany that can provide further warning signals and information in addition to a 3x3 filter (conditions, terrain, people) and the snowcard - through a "diagnosis" or analysis of the snowpack. The advantage of the small block test over a snow profile is that it takes less time. In addition, certain statements about the type of fracture in a weak layer (regular, irregular, etc.) are possible, similar to a CT scan in which the fracture surface is examined.
Objective: Find weak layers as a basis for systematic snowpack diagnosis.
Procedure: A block of about 40x40cm is exposed on all sides to a maximum depth of 1 m (depending on the snowpack structure). Starting from the top, carefully tap the sides of the block with the shovel until a break occurs and the block slides off or breaks (see what the broken surface looks like). With careful tapping, even layers very close to the surface can be identified in this way. In the second step, the identified weak layer is analyzed (grain shape) and the information obtained is integrated into the process thinking (how did the weak layer form? how widespread is it? what does it mean for me?) For more information on systematic snowpack diagnosis, see here, here and here.
Additional note: Rivet test
The so-called rivet test is not a test in the sense of those mentioned here, but rather a method for interpreting a snow profile, which is used especially for old snow problems. You look for the 6 rivets in a profile: Weak layer is soft (fist or fist to 4 fingers), weak layer is angular (cup crystals, surface/deep rime, floating snow), crystals in weak layer are significantly larger than 1mm, grain size difference between weak layer and neighboring layer > 1mm, 2 hardness levels or more hardness difference between weak and neighboring layer, weak layer 1m or more below the surface. The more rivets, the less favorable the situation.
More video tips:
"Snow hugging" handshake variation, ECT, group slide block
Explanations of concepts of fraction propagation and PST
Descriptive, comprehensivecollection of numerous tests
No video: A mountain climbing report on various snow cover tests and their significance.
A general article on snow profiles will follow soon.
Thanks to Lukas R., Patrick N., Hans S. for helping and shoveling!
