Snow Pits

This information is simply for research purposes and does not replace the knowledge you will gain by taking an actual Avalanche Safety Course.  It is highly recommended that everybody take an avalanche safety course before heading into the backcountry. You can find courses near you on the AIARE Website or by Googling “avalanche level 1 class”. 

Many people who travel in the backcountry simply rely on the avalanche forecast to tell them if it’s safe to go out. That said, just because the avalanche forecast says it is safe, there is still a chance of avalanches occurring. Alternatively, what if you are in a region that doesn’t have an avalanche forecast? When we were down in Chile, there was no app you could download that would tell you the avalanche danger or what avalanches are going off where.

 So, what do you do in a situation where you are uncertain about the snow pack?

While there are many things you can do, digging a snow pit is a great way to analyze the snow composition you will be skiing on. 

Where Do I Dig a Pit?

If you think about it, would you dig a pit on an aspect that you won’t be skiing to make observations about where you will be skiing? There are constant variations in the snow pack when it comes to different aspects due to weather, tree cover, slope, etc. 

The best place to dig a snow pit is on the aspect you will be skiing, allowing you to apply your observations to how you decide to ski down. Also, make sure you are in a safe spot to be digging for a while. You don’t want to look up and have avalanche terrain above you when digging your pit. 

Dig Your Pit

When digging a snow pit, you want it to be about 120 cm wide and around 120 cm deep (4 feet x 4 feet). While this can take a while, you want your pit to be big enough to perform multiple tests and deep enough to see multiple layers of snow. Snow packs can have persistent weak layers that are very deep and have the potential to break so it’s best to observe behavior at least 4 feet from the top.

You want to smooth out the walls of your pit as much as you can, simply so that you can see the layers in the snow pack easily. 

Initial Observation

Once you have your pit dug, observe the layers of the snow. A great way to do this is by poking the snow all the way down. Start off with your hand in a fist and push it into the snow all the way down observing the hardness of the snow. Once you do this, take two fingers and poke the wall of your pit all the way down to see if you can find any weak layers where your fingers break through. Next, take one finger and do the same.

This will give you a good idea of where the potential weak layers are when moving onto your next couple tests. 

The Compression Test

To perform this test, you will need a snow saw and a METAL avalanche shovel which you can get from Backcountry Access. 

  1. From inside your pit, cut out a column of snow that is 30 cm by 30 cm. This will have three cuts. Two going into the wall of your pit and one behind connecting the two original cuts. 
  2. Cut a wedge out of the snow next to your column on each side so that the column is isolated from any snow touching it. 
  3. Brush off any loose snow on top of the column. 
  4. Place shovel face down on the top of the column.
  5. Perform 10 taps on the shovel from your wrist (hand)
  6. Perform 10 taps on the shovel from your elbow (lower arm)
  7. Perform 10 taps on the shovel from your shoulder (entire arm)

If there is a weak layer in there, you will see it fracture with one of these tests and a slab of snow will be separated from the rest of the snow pack. This is a weak layer in the snow pack that you will potentially be skiing so you have to take this into consideration and decide if it is safe to ski that slope or not. There is a three letter system for writing down your observations with the compression test. 

Three Letter Code: CTV CTE CTM CTH CTN
Description: Fractures when cutting or placing shovel on top of column Fractures with ten taps from wrist Fractures with ten taps from elbow Fractures with ten taps from shoulder Does not fracture

If you have a field observation book, this is the code you can use to put your test results in your notes for the day.

Extended Column Test

This test is the same procedure as the compression test but the column you cut is 30 cm deep and 90 cm wide. The point of this test is to test weak layers ( like the column test ) and test propagation. Once your 30cm x 90cm column is cut and isolated, you will put your shovel on one side of the column and do the same taps as the compression test: 

  1. 10 from the wrist
  2. 10 from the elbow
  3. 10 from the shoulder

Here is a great example of an extended column test: 

While there are other tests you can do, these are the ones I have found to be most informative. They tell you where the weak layer is, how much force it will take to break it, and if it will propagate. 

If you are looking to sign up for a professional avalanche class, check out these resources where you can find one near you: 

To refresh yourself on more avalanche safety, check out four more avalanche safety articles here!

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