How to measure slope STEEPNESS and why it's important for skiers and snowboarders.Sep 18, 2023
Written by ISTD ski instructor George Treble. If you are interested in off-piste skills and avalanche safety info, join the Off-Piste Alpine Club here
Avalanches are very sensitive to slope steepness, so learning how to measure it accurately and precisely is a very useful skill for off-piste skiers & snowboarders.
This blog details 7 ways that we can measure slope steepness, and I'll try to be as concise as possible.
Let's have a look at this graph which plots human triggered avalanches against slope steepness in Switzerland. We can see that most human triggered avalanches start on slopes between 30-45 degrees, and are most common around the 39 degree mark.
Be aware that these figures can vary a bit for different parts of the world (for example continental vs coastal mountain ranges) but the general bell curve pattern is quite consistent.
The point is, by knowing how steep the terrain is, we get a decent clue about to the avalanche likelihood.
Avalanche likelihood picks up significantly when crossing the 30 degree mark.
On extremely steep terrain, above 40-45 degrees, the instance of significant human triggered avalanches decreases because more frequent smaller avalanches prevent the build up necessary for bigger ones. However, smaller avalanches have bigger consequences on these very steep slopes, so it doesn't get any safer.
When it comes to off-piste skiing and snowboarding, our most important decisions are made before we leave the house.
So we can check terrain steepness on maps before we even go anywhere near that terrain.
You can look at contour lines on paper maps to denote slope steepness; the closer together the contour lines, the steeper the terrain.
You can use tools like this BCA card translate contour spacing into slope steepness:
Fortunately, there are some far more user friendly ways to do it.
You can head to a 3D mapping software like FATMAP and apply filters which colour slopes of different gradients. You can choose 5 degree increments or graduated colours. Nice and simple.
When you are out in the field, you can use tricks with ski poles to measure slope steepness, such as the Triangle Trick which identifies 30 degree slopes. Check out the video tutorial to see how to do it.
Another trick with ski poles it to make 1/2 & 1/4 markers on your poles and to hold them at right angles to measure the slope. Once again, check the video for more info.
The thing about these two tricks using ski poles is that they only tell us about the steepness of the tiny bit of slope between the poles.
It's much often more useful to average out larger sections of the slope.
The good news is, there are lots of apps which allow you to use your smartphone to measure slope steepness.
You can align your phone or camera with the slope and work out an average gradient of, say, 10-30 metres of the slope. Try the WHITE RISK app for their inclinometer.
Sometimes it's better to keep your phone in a warm pocket and use something else like an inclinometer on a compass. You can align the straight edge of the compass with the slope angle and look in the mirror to see where the little red arrow is pointing.
But to be honest, taking gloves off and faffing around with a compass inclinometer isn't ideal either.
In my opinion, the best way to measure slope steepness whilst in the field is with a dedicated slope meter. Keep it in a your backpack hip pocket on the waist strap, keep your phone away in a warm pocket and use the thing to measure steepness (and aspect) accurately & precisely.
Having said that, this only allows you to measure slope steepness of slopes that you are close to. I often whip out my phone, open FATMAP and check slope steepeness of more distant slopes if I am wondering whether they are an option.
So there's 7 ways to objectively measure slope steepness for off-piste skiers and snowboarders.
Building up a keen eye for this is a valuable skill set for anyone who wants to understand more about avalanche terrain. Hope it helps!
If you're interested in this sort of stuff and would like to get prepared for powder, check out further tutorials on www.alpinetutorials.com/mountainsafety.
You can also join the Off-Piste Alpine Club 23/24 for free now here.