Avalanches occur when a layer of snow collapses and slides downhill. No big surprise. Looking at other avalanches facts and what are avalanches, there are different types and causes of avalanches as well as avalanche rescue best practices. I learned a ton in my course with Avalanche Canada and here are some of those insights.
During my Avalanche Skills Training 1 course, I learned all about avalanche sizes, different types of avalanches, human and natural causes of avalanches, as well as important mountain safety tips on how to evaluate terrain and avalanche conditions before embarking on a route or entering into new terrain. We also practiced avalanche rescue strategies with actual simulations. Needless to say, I no longer look at snow the same.
My first day in the classroom portion of the course, I snapped a quick pic and my dad’s response pretty much sums up how I feel, every time I take a mountain course:
Everything is more amazing upon further review and detail. You may get a certificate showing your advanced knowledge once completed – but then again maybe you will have only scratched the surface of knowledge. Make the best of it.
One, I’ve got a great dad. His way of looking at this world is no doubt a huge part of the reason that I am who I am. I’m a lucky girl. Two, the more that I learn, the more that I learn… how much I have to learn!! This year I have done quite a few courses and participated in a number of presentations, which has just sky-rocketed my appreciation and complete awe for not only the mountains but Mother Nature. Let’s keep moving forward!
Start with the basics: What are avalanches?
Avalanche fun fact #1: There are two kinds of avalanches: from new snow or from slab snow.
New snow is obviously freshly fallen snow. Slab snow is snow that has already solidified together and formed a slab.
- For new snow, it’s important to take into consideration if it’s fluffy and light or if it’s wet and heavy. Avalanches from new snow can be caused by a slight drop of snow from a ledge up above, for example, that then starts to snowball and gather momentum and more snow as it goes down.
- Slab snow tends to be heavier snow, since the particles have had time to form links between themelves. Avalanches from slab snow fall as one cohesive piece, and you can typically see a line where the snow fractured and began to fall. These types of avalanches generally bigger and more destructive, as well as more difficult to predict in behavior.
”As a mountain lover who wants to safely spend time outside, you need to be able to evaluate 1) recent/current climate conditions that make avalanches more probable and 2) terrain that makes avalanches more probable. Analyzing these factors can help you determine the risk factors before choosing a route or entering into new terrain.Chelsey Berg
What causes avalanches?
Avalanche fun fact #2: Avalanches are caused when four factors are present.
While there are human causes and natural causes of avalanches, no matter what there are four factors that need to be in place for an avalanche to occur:
- a steep slope
- a snow cover
- a weak layer in the snow cover
- a trigger
Avalanche fun fact #3: Avalanches happen when a new weight, stress, or impact is added to the slope.
Okay, let’s look at why what actually makes the snowfall in an avalanche. There are natural and human causes.
Natural causes of avalanches:
- new snowfall
- new snow added to the slope due to wind
- increase in temperature or rain
- a ledge falling from up above (ledges form from snow accumulated due to wind deposit)
- snow falling from above, like from rocks or trees
- rocks falling from the mountain above, etc.
Human causes of avalanches:
- skiiers, snowboarders, cross-country skiiers, etc that move too close to the ledges or add stress to weak layers in the snow
- Avalanche myth: Noise does not cause avalanches. So, yell away to your partner, you aren’t placing yourself in danger’s path 🙂
- Interesting avalanche fact: most people who get trapped in an avalanche were the trigger of that avalanche, or someone in their party!
There are human and natural causes to avalanches. And contrary to popular belief, noise, like screaming, isn’t one of them!
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How can you evaluate avalanche risk?
Avalanche fun fact #4: Snow tells a story and you must read it!
Normally, one looks out and sees the snow and thinks “boy, there’s a lot of snow” or “man, that’s beautiful” … but the buck stops there. Well, we cut a big piece out of the snow and, sure enough, there told the story of the whole season’s snowfalls, laced right there in-between its layers.
As we analyzed what the snow was telling us, I was so surprised to see so much snow diversity in one little piece!!!
And, we were down on a flat part of the mountain. Up higher, where there is heavier snowfall and colder/windier conditions, it’s even more. Anyways, looking at the picture you can see quite a few layers. It’s interesting to analyze the different densities of each layer.
To test snow densities you ask yourself, “what can puncture this snow? A fist? 4 fingers (together)? 1 finger,? Just a knife?”
In this one little spot, we had 5 different densities!! It started with a fist, then 4 fingers, then 1 finger, then a knife, and then again between 4 fingers/fist. The snow on the bottom was a totally different texture than the powdery snow up top. The snow at the bottom had formed into hard, quite large independent crystals. These crystals, due to pressure and other variables, had never formed “links” between the individual flakes.
In avalanche conditions, when you have this layer below or above a sheet of ice, just imagine how these crystals act like little marbles, sending the avalanche flying down the mountain!
When you cut out a section of this snow, you can do a density test to see how the specific snow layers behave under pressure. You start by placing your shovel over your snow sample and adding different amounts of pressure to see when, and how, it breaks.
You start by tapping the shovel 10x. If it doesn’t break, you hit it 10x with your elbow on the end of the shovel. If it doesn’t break, you hit it harder 10x with full shoulder movements.
Slab avalanches “give / break” at the weakest layer and bring down all the snow above.
Avalanche fun fact #5: You can evaluate terrain and predict avalanche probability.
Ok, great! Now, how do you evaluate those conditions in order to know what you’re getting into?
As a mountain lover who wants to safely spend time outside, you need to be able to evaluate 1) recent/current climate conditions that make avalanches more probable and 2) terrain that makes avalanches more probable. Analyzing these factors can help you determine the risk factors before choosing a route or entering into new terrain.
Some of the important avalanche factors to look for are:
- Ledges (concave formations, typically from wind deposits)
- Dips (convex formations)
- The bottom of cliffs
- Terrain traps
- ie: rocks! Since they are warmer than the snow, they heat the snow.
- ie: Chutes, trees, and basically anything that a person could “hit” as they are being dragged by an avalanche.
- Previous avalanches from recent days
- Orientation of these elements according to sun/wind orientation
Avalanche fun fact #6: There are 3 main factors that affect the dangerousness of an avalanche.
The top avalanche danger factors are:
- angle of the incline
- the orientation according to the wind / sun
- terrain traps
Avalanche fun fact #7: The orientation to the wind and sun plays a big role.
The orientation according to the wind means, which side of the mountain receives more wind? The side that receives more wind has less snow deposits since it gets moved around more. The side of the mountain more protected from the wind has higher snow accumulations and can often form very high ledges. This side of the mountain tends to be more dangerous and more prone to avalanches.
The orientation according to the sun means, which side receives the direct sunlight? Here in Chile, the north side receives the direct sunlight, which means that side is more prone to quick heating. This, in turn, causes weaknesses in the snow slabs and a higher probability of avalanches.
It’s interesting because I naturally always looked at these elements and known for example, not to walk near the ledges because they are not solid formations. Or not to walk too near the rocks as they have hollow patches. That summitting early is better because as the air heats up, rocks can fall, snow can get sloppy, etc.
But, just the other day as I was showing my grandpa pictures from a mountain I went to a couple weeks ago, I looked at the pictures with a whoooooole new eye! I noticed previous avalanches, I saw avalanche risk factors…. I understood “the why” behind things I’d always known as best practice, and understood the terrain way better than I had just a few weeks prior.
Avalanche fun fact #8: If a victim can be rescued within 15 minutes, the survival rate is around 90%. This drops to below 50% as you get up to 30 minutes.
Let’s talk about avalanche rescue.
When looking for victims of an avalanche, there are various steps in the process. You need 3 pieces of equipment: a tracker, a probe and a shovel.
The tracker functions like a GPS in that it sends signals out. When out on a route, you always begin with your tracker emitting signal. Should you need to search for a victim, you switch it to “search” mode.
In search mode, the tracker will look for all emitting signals within a 40 meter / 130 foot distance. In the first part of the search, you need to strategically track the avalanche deposit in zig zags (if you’re the only searcher) or in parallel lines (if you’re 2+). As soon as your tracker notes a signal, there are very strategic tips for how to do the “fine tracking” and identify the best estimate for the victim’s location.
Once you have your closest estimate for where the victim is below the snow, you use the probe. With very specific strategies, to poke through the snow until you can verify that the victim is below.
By following the specific strategies in each step, you can as quickly as possible, identify the exact position of the victim.
The probe has ruler marks on it, so you can also identify how far under the snow the victim is. This impacts where you need to begin shoveling. If the victim is less than 50cm/20in under, you can dig pretty much right over them. However, if they are further down, you need to start digging 1.5x that depth away from them.
This means, if they are 100cm/40in under, you need to start about 1.5m/5ft away from the person, in the direction going down the mountain.
There is a specific strategy to using the probe to identify where the victim is and how far under, which influences how to use the shovel to dig him or her out.
Other interesting avalanche facts:
- Where do avalanches occur? The majority of avalanches happen at “medium” inclines of 30-45 degrees!! This is because, at this incline, the mountain can support more accumulation, whereas at the steepest inclines, the snow falls more frequently and therefore has less build-up. Makes sense but you probably wouldn’t have guessed that, huh?! What often happens, is a little snow falls off the steeper inclines, onto the medium incline below, causing the avalanche to begin at 30-45 degrees.
- How fast do avalanches travel? Avalanches can get up to a speed of 90kph / 56mph in a matter of seconds!!
- What happens after an avalanche? Within only a few seconds after an avalanche, the snow quickly turns into ice, freezing hard after all the heat it generated on the way down.
- How strong are avalanches? The biggest avalanches are strong enough to destroy a village or 100 acre forest!! imagine that!!!
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