What info comes from digging?

Snowpack tests (not stability tests)

Snowpack tests can help us to delineate how each individual layer interacts within the greater snowpack. They are helpful in determining strength and structure. Though, snowpack tests do not come without limitations.

Craftsmanship: It is critical that all snowpack tests (even quick/ hasty tests) are done with the highest standard of craftsmanship. This ensures replicable results and eliminates false positives.

Parameters: Each test has certain parameters for accurate results. Certain tests are designed to test for sheer (shovel shear test), some test for compression (compression test, deep tap), and some test for propensity for propagation (Extended column test, propagation saw test). Knowing the parameters for each test will help yield the most accurate results.

Results: Not every result should be treated equally. Make sure to check your work (did you cut all sides of the column, was the column even throughout). Once you have determined that the craftsmanship was up to standard, then it is time to replicate the data. Make sure to run another test to see if the results stand up.

Tool Box: Once you have determined something like weak layer identification, then it is important to continue on in the toolbox to test for shear strength, fracture initiation (compressive strength), and propensity for propagation. Make sure you are using the appropriate tools and applying them to the appropriate problems given distribution and character of the problem.

Common Small Column Tests

Compression Test

This is one of the more popular snowpack tests. It indicates the compressive strength of a certain column of snow. It is typically reliable and quantifiable when performed by the same tester multiple times. The most common problem is that testers forget to measure the column 30cm x 30cm throughout the vertical extent of the column, thus, they can end up with a leaning tower, or a topsy- turvy column that is destined to yield inaccurate results.

This test is accurate up to 1m, but starts to see varying results at about 80cm due to the height of the column and subsequent impact on the ability to accurately conduct this test. This test correlates well with the extended column test (ECT) which can provide information on a fracture's propensity for propagation through the snowpack.

To Perform

1. Isolate a 30x30cm column up to 120cm in depth

2. If the column fractures upon isolation or the insertion of the shovel blade, check your craftsmanship and record as CTV and associated fracture characteristics

3. Tap from your wrist for 10 taps, record any fractures as CTE (easy) and associated fracture characteristics

4. Tap from your elbow for 10 taps, record any fractures at CTM (medium) and associate fracture characteristics

5. Tap from your shoulder for 10 taps, record any fractures as CTH (hard) and associate fracture characteristics

6. No fractures? Record result as CTN

7. Replicate your results

Fracture Characteristics

The character of the fracture of the column is can be more informative than the number of taps required to initiate it. Observe if the column fractures completely on a tap or if multiple taps are required. Examine both sides of the broken column and assign a fracture character according to the following descriptions.

Page 62 of the AIARE Fieldbook provides a quick reference of this information for you to use in the field.

Interpretation of Results:

• CTV, CTE, CTM, and CTH indicates that fracture initiation is possible, especially when paired with sudden planar and sudden collapse fracture character

• CTN indicates unlikely fracture initiation

• After replicating results, continue on to a large column test if you have results other than CTN, especially if you have "sudden" fracture characteristics (Sudden Planner (SP) or Sudden Collapse (SC).

Deep Tap Test

This test is typically reserved for areas deeper than a compression test can result or areas with a very hard slab overriding. Generally speaking, that would be a persistent problem. The deep tap test typically correlates well with the propagation saw test (PST) as a next step in the tool box because the problem is too deep within the snowpack to send compressive force via a shovel blade (without really hurting your hand!)

To Perform

1. Isolate a 30x30cm column 10cm below a targeted weak layer, remove all but 15cm of snow above the targeted weak layer.

2. If the column fractures upon isolation or the insertion of the shovel blade, check your craftsmanship and record as DTV and associate fracture characteristics

3. Tap from your wrist for 10 taps, record any fractures as DTE and associate fracture characteristics

4. Tap from your elbow for 10 taps, record any fractures at DTM and associate fracture characteristics

5. Tap from your shoulder for 10 taps, record any fractures as DTH and associate fracture characteristics

6. No fractures? Record result as DTN

7. Replicate your results

Interpretation of Results

• CTV, CTE, CTM, and CTH indicates that fracture initiation is possible, especially when paired with sudden planar and sudden collapse fracture character

• DTN indicates unlikely fracture initiation

• After replicating results, continue on to a large column test if you have results other than CTN, especially if you have "sudden" fracture characteristics (Sudden Planner (SP) or Sudden Collapse (SC).

Shovel Shear

This test helps to find and identify weak layers. The problem with this test is that it is very subjective and can be incorrectly leveraged to create layers that do not exist. Evenly pulling, and not prying is key to useful results. The smooth, straight shears are what you are looking for in this test, and how hard it was to pull the shovel towards you (easy, moderate or hard). Again, those results are subjective to the strength of the tester.

To perform:

1. Isolate about 1-2 feet down and the width of your shovel blade

2. Insert shovel blade and pull with even force towards you

3. Record any smooth shears and the appropriate force used as STE, STM, STH

4. Replicate for best results

Interpretation of Results:

• Shovel shear results are typically recorded more for personal data and weak layer ID due to their subjectivity.

• If the shear is very clean, examine closer for potential surface hoar

Common Large Column Tests

Extended Column Test

This test is primarily identifying the propensity for propagation within a weak layer. It excels in layers that are less than 70cm in height with 4f-1f snow overriding a weak layer. The test itself helps to determine how the weak layer is connected across a slope. It is best to try and find the side of the column that is thinner in an effort to put force into the weak layer. Think that even from the shoulder you will put more force as you travel across the slope with your weight.

To perform:

1. Isolate a column that is 30 cm upslope by 90cm across slope. You can measure up to 1m in depth. Make sure that you have isolated below the layer of concern.

2. If a fracture propagates across the entire column during isolate, record ECTPV

3. If a fracture initiates and propagates across the entire column, record # of taps as ECTP#

4. If the fracture initiates but does not cross the complete column, record # of taps as ECTN#

5. No fractures occur during the test, record ECTX

6. Replicate results

Interpretation of Results:

• ECTPV and ECTP indicate positive results for propensity for propagation of the weak layer if the weak layer is initiated from compressive forces.

• ECTN indicates a negative result, there is not enough connection between the weak layer. Though, this does not mean that as the slab stiffens or as the weak layer further facets that it could not become problematic.

• ECTX indicates a negative result. It is indicative that the weak layer in question is either not connected, spatially variable, or non existent.

• The fewer number of taps to the shovel blade, the more sensitive the weak layer is.

Propagation Saw Test

This test is designed to check for propensity of propagation once a fracture has been initiated (your saw blade). You must be able to properly identify the weak layer in order for this test to work. It is also imperative that the saw blade drags in the weak layer at a speed of 20cm/1 second use the blunt edge of your saw blade. A common mistake is for the blade to “jump” out of the weak layer- rendering the test useless. Another mistake is for the tester to continue moving the saw through the weak layer after it has propagated. Always stop the saw as soon as propagation starts. This test answers the question: If there is fracture initiation within the weak layer, how will the weak layer react (or what is its propensity for propagation)?

To Perform:

1. Isolate a column 30cm across slope by 100cm upslope (unless the LOC is greater than 1m in depth, then isolate to that depth (ie. Weak layer is buried 150cm down, then isolate 150cm upslope))

2. Draw the blunt edge of the saw upwards within the weak layer until the onset of propagation or until the entire column has been cut.

3. If propagation arrests somewhere within the weak layer before reaching the end of the column, record the result as PST x/y (ARR) down z on yy/mm/dd

4. If propagation ends at a fracture through the overlying slab, record the result as PST x/y (SF) down z on yy/mm/dd

5. If propagation continues uninterrupted to the end of the column, record result as PST x/y (END) down z on yy/mm/dd

6. Always check craftsmanship to make sure the column was fully isolated

Interpretation of Results:

• SF and ARR don't indicate propensity for propagation

• END results indicate propagation when the cut length is less than 50% of the column

• This test is great for trending PWLs, as you can watch cut lengths increase or decrease based off sensitivity of the weak layer