...Stability Tests...

Snow Pits:
The snow pit test has many variations which all consist of digging a hole in the snow, then examining and assessing the strength of the layers and bonds within the snowpack. My favorite test is the rutschblock test because it tells me exactly what I want to know: will this snowpack support my weight?

The amount of detail you should collect depends on the question you are trying to answer. A snow scientist will record extensive information about temperatures, snow crystal types and depth of layers in an attempt to grasp the processes at work within the pack and predict it's future behavior. A recreationist, however, may spend less time, attempting only to figure out the strength of the snow at this moment.

The more you know, the better able you will be to anticipate the snow stability today, and after the influence of future weather factors.

FAQs about snow pits:

1. What do snowpits tell me?

   Generally speaking, you can answer 3 questions with a snow pit or series of snow pits:

   • Are there weak bonds and layers in the snowpack?
   • What is the strength of these layers?
   • What is their distribution across the landscape?
   
        
2. Where should I dig a pit?

   Snow pits should be dug in a safe area, on a slope that has similar characteristics to the one you want to descend, i.e. same aspect, elevation and angle. Use your avalanche probe to locate a site that isn't too rocky. The snowpit should have at least one shady wall and should not be located in a wind pillow near a ridge.

3. When should I dig a pit?

   Dig a pit whenever you don't know what the snow is doing. Some good rules of thumb include:

   • one for every 1000 ft of elevation change;
   • one for every significant aspect change while near avalanche terrain;
   • before crossing slopes of 25 degrees or steeper;
   • before crossing recognized avalanche paths.
     
     
4. How deep should I dig?

   The stress of a person's weight on the snowpack spreads out and effectively dissipates as the depth of the snow increases. Below 6 feet, a person's weight is not really very significant. Dig down at least this far, to the ground in a shallower pack, or down to snow that you know to be stable. Oddly enough, due to the increased surface area, the stress of a snowmobile on the snowpack is about the same as that of a skier--many snowmobiler-triggered avalanches happen when the sled gets augured and the driver steps off the machine.
   In cases where humans triggered slabs deeper than about 6 feet, the failure usually started in shallower snow then propogated into deeper deposits. If you suspect sensitive deep slab instability below 6 feet down, maybe you shouldn't be there.

5. What do the results mean? Is it safe to ski/board/ride it?

   Each snow pit tells you what is happening right here, right now. You need to use the other information available to you and test your theories about the snow stability by digging many pits to evaluate the big picture. If the snow is green light, no problem! If it's red light, also no problem--obviously you don't want to go there. If it's yellow light, things are harder to evaluate and you may chose to stay in mellower terrain or opt for very careful technique.
   
   Many people get frustrated at this point. The fact is, avalanche hazard evaluation is, at least in part, a question of how much risk you are willing to accept. While this seems really scary, most of us accept much higher risk when we step into our automobiles every day--and we don't even think about it or question it. Start out on less steep slopes, dig pits, look for surface clues , travel with skilled partners using good technique, and get good and comfortable before you pounce into the steep stuff.
   
   If you don't like it, stay on low angle slopes or in the ski area where it's someone else's job to worry about avalanches--that's the best place for Joe Gnarly aggression, anyway.

Ski Pole/Hand Pit Test:
Once you think you have an idea about what's going on with the snow, shove your pole down through the pack or dig a quick hole with your hand to confirm what you believe is going on. If you encounter something you didn't expect, it's time to dig another snow pit. This test is great because it's virtually effortless and can be performed 100 times a day.

Cornices:
Cornices are the "bombs of the backcountry". Much as professional avalanche control workers use explosive charges to deliver a big shock load to a suspect slope, backcountry skiers can use chunks of cornice to do the same thing.

Don't just start jumping on a huge curler unless you want your body to be part of the test. Use a length of knotted parachute cord, a ski tail or your snow saw to hack off a piece from a safe stance. If the slope doesn't avalanche when you trundle a thousand-pound snowball down it then it will probably hold your weight, too.

Try not to hit anyone on the slope below.

Ski Cutting:
Use ski cuts on small, safe test slopes, not major avalanche paths.

Make a swooping pass across the top of the suspect slope, aiming for a safe location (a ridge or a big tree at the edge of the slide path works). Keep enough speed that you don't bog down and stop. If the slope is unstable, it should avalanche behind you, not under you. Use these results to assess stability on similar, larger avalanche paths.