GETTING MORE OUT OF SNOWPITS
A Breakdown of Snowpits for Recreational Skiers
Avalanche professionals speak a complex lingo, slinging around terms like ECTP12, ECTX, PST 20/100 (END), CT13, lemons, yellow flags, thin grey lines, energy, facets, rounds, depth hoar, temperature gradients, and persistent weak layers. For the average backcountry skier, you may not need to understand the micro-physics of snow metamorphosis to answer the main question: is the slope safe to ski? Here’s a simple, effective scheme for determining that.
WHAT ARE YOU LOOKING FOR?
More important than snowpits are red flags, or bullseye clues you can see without ever taking your shovel out of your pack. Pay attention to what’s been going on around you. You just need to pay attention to the snow-covered world around you. When you do finally pull out your shovel, dig your snowpit with a theory in mind. Execution of the pit will simply test that theory.
First, assess what the primary and possibly secondary avalanche problems are. What are the snowpit cues I should look for in regards to each specific problem? For instance, if the problem is a persistent slab sitting on surface hoar, I look for both the buried weak layer and the existence of a slab on top of it. The local avalanche information center will often tell you how deep, and on what aspects and elevations, to look for such a layer. If the problem is storm snow, I test the interfaces between the new snow and old snow surface. If I find what I expected to see, if I verify my theory, I feel very confident in what is going on in the snow and feel less reliance on snowpit info. If I see something different from what I expect, I need to ask if my theory was wrong. Did I miss something, or misinterpret something? Did I dig in a spot that isn’t representative of the bigger picture?
DEVELOP A SYSTEM
I can’t begin to tell you how many thousands of pits I’ve dug, in countless mountain ranges and snowpacks. Over time, I settled into a system that works for me, to quickly and concisely gather the information I need.
For decision-making purposes, analytical tools like thermometers and pocket microscopes aren’t very useful. I’ve yet to find a temperature profile that affected my real-time decision making. Ditch the thermometer unless you have a scholarly interest in what’s been happening all season. You may need a magnifier to classify snow crystals, but for decision making, I’m far more interested in whether a layer will fail and propagate than in what to call it. The critical tools are a good shovel, snow saw, ECT (extended column test) cord and avalanche probe. I also carry a Lexan crystal card and small 17.5X hand lens. Everything else is a luxury and not necessary for a day of skiing in the backcountry.
Dig once. Make your pit deep and wide enough for all the observations and tests you want to perform. I dig about 125-150 cm down (unless the layer I’m worried about is deeper!) and approximately 120 cm wide. This is a chance to practice my strategic shoveling (which happens to be a very efficient way to excavate your pit initially). I perform a few quick tests and move on. I try to spend 10-15 minutes max (often less) in snow pits. I would much rather have a lot of focused data from various sources than know the name of each snow crystal in one spot.
I start on the right side and work to my left – no reason other than habit, consistency and practice. First I look at the layers, and identify a few simple structural issues in the snowpack. I remember these three key things with the acronym PHD:
P – Persistent Weak Layer: Look for those problematic layers that can haunt us for days or weeks.
H – Hand Hardness Difference: Do I have a slab (strong snow) sitting on a weak layer?
D – Depth of Layer Interface: If the weak layer is one meter or less below the surface, there is a higher likelihood of human triggering.
Once I’ve identified my primary layers and structure, I begin with a shovel shear test (ST). To be clear, the ST is NOT a stability test, it is simply a way to look for minute layers or hard-to-find interfaces other tests may not reveal. It also makes the next step quick and easy. I don’t pay much attention here unless I get a surprise or very planar shear. Once my ST is done, I set up for an Extended Column Test (ECT).
The ECT is an isolated column of snow, 90 cm across the slope and 30 cm upslope. I set this test up by measuring my dimensions, inserting my probe at the back-left corner and using a small piece of 2 or 3mm cord to cut the back and left side. The test looks for two key parts of avalanche release – initiation and propagation. I am far less interested in the number of taps than I am whether it propagates or not across the entire block in one step. Propagation is a key indicator that the snowpack has slab avalanche potential. If you don’t have a ton of experience, use propagation as a cue to pick a different slope. It takes years of experience to assess avalanche potential beyond this and trying to outsmart or overthink the problem here often leads to accidents.
If I get no propagation in my ECT, I will cut my 90-cm column into 3 30×30 cm blocks and perform two compression tests on the two undisturbed blocks. Since we didn’t have propagation, I focus on “stops, pops and drops.” If the block fractures, does the slab just sit there (stops), does it pop out into the snow pit (pops), or is there a noticeable vertical displacement (drops)? The latter two are big red flags for avalanche potential.
Just like that, I’m done. I quickly fill in my pit and move on. But — if I find an unexpected failure or propagation, that demands further investigation. I want to figure out if I found something confined to this spot or if I missed something more important.
INTERPRETATION OF RESULTS
So how do I interpret this info? Let’s start with the simple stuff. If I perform an ECT that propagates across the column, this is a massive red flag, and for most people should indicate choosing other terrain. Trying to outsmart this test result could lead to terrible consequences. This test tells me that not only is it possible to cause a failure in the snowpack, but propagation leading to an avalanche is likely. Your best bet here is to change aspects or back off your slope angles and ski below 30 degrees.
If I get propagation, I investigate my PHD structural problems, which indicate a path of least resistance for a failure to propagate. If I have both PHD and propagation, then it’s really a no brainer and I’m moving on from that slope or ski line. Without propagation, I need to make sure this test is sound and representative of what’s going on around me. If results are consistent, then I can ski.
Snow pits are an affirmation of what I do or don’t know, not an affirmation that it’s okay to drop the rope.
Here are a few final thoughts about snowpits. Your snowpit location should be:
1. Representative: Make sure your pit represents the slope you are assessing. Aspect and elevation should be as close as possible. Slope angle can also be important, but less so than the other two.
2. Safe: Getting caught in an avalanche while digging a pit tells you all you need to know and everything you didn’t know about the slope. If it doesn’t kill you, you’ll look like a fool.
3. Polite: Don’t dig in the middle of a line someone may want to ski and don’t forget to fill in the pit when done.
4. Weigh weak tests more than strong ones. A snowpit has never been the deciding factor for me to drop the line. That decision is a culmination of season history, current weather and verification through snowpits. But, many weak snowpits have turned me around.
5. Don’t ignore the “get out of jail free cards”. Nearby recent avalanches, collapsing and cracking are Mother Nature’s way of growling to say she’s dangerous. Respect her and come back another day.
Becoming proficient at snowpits requires good instruction (take a course!) and years of practice. The pit is a useful tool when applied and assessed properly and objectively, and a potentially deceptive piece of information when not. I haven’t skied a line or bagged a peak worth dying for and don’t expect to. When conditions aren’t right, just remember that the mountains will be there for another day.
Learn more about backcountry safety with one of these articles:
- Terrain Management and Avalanche Hazard
- Avalanche Safety Checklist
- Changing Snow Conditions
- Avalanche Rescue Technique
Article by Jake Hutchinson
Jake has spent more than 25 years working as an avalanche professional. He is currently a lead instructor for the American Avalanche Institute, an avalanche dog handler and trainer and an avalanche safety consultant to the resort and rescue communities. Off the snow, Hutchinson is a Certified Instructor and former Head of Instructor and Seminar Development for Gym Jones in Salt Lake City. He is currently involved in private personal training with an emphasis on high level functional fitness for mountain and military athletes.