I recently did a course on avalanche awareness and rescue, that taught me all about avalanche sizes, formations and human/natural causes, how to evaluate terrain and avalance conditions before embarking on a route or entering into new terrain, and also rescue strategies, reinforced by 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 after these types of courses:
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. Dad
One, I’ve got a great dad <3 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 start with the basics
Avalanches are caused by four factors: a steep slope, snow cover, a weak layer in the snow cover and a trigger.
Basically, there’s two kinds of avalanches: from new snow or from slab snow (that is, snow that has 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 more wet and heavy. These can be caused by a slight drop of snow from a ledge up above, for example, that then starts to snowball and gather more snow as it goes down.
- For slab snow, this tends to be heavier snow as the particles have formed links between themelves. This type of falls as a cohesive piece, and you can typically see a line where the snow fractured and began to fall. These are generally bigger and more destructive avalanches, as well as more difficult to predict their behavior.
Snow tells a story
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 was 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 gotta be even more. Anyways, looking at the picture you can see quite a few layers. But even more so is when you analyze the different densities of each.
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 knife and then between 4 fingers/fist. But the snow on the bottom was a totally different texture than the powdery snow up top, it was snow that due to pressure and other variables, never formed links between the individual flakes, making them hard, quite large crystals. 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 a section of this snow out, 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, tapping it 10x, then hitting it 10 times with your elbow on the end of the shovel, then hitting it harder 10x with full shoulder movements. The idea here is one to understand not only under what pressure the snow collapses/breaks and in what layer it does so but, more importantly, how it breaks.
In the slab avalanches that I mentioned above, they “give” at the weakest layer, bringing down all the snow above.
Why does the snow fall?
Avalanches happen when a new weight/stress/impact is added to the slope.
- new snowfall
- new snow added to the slope due to wind
- increase in temperature or rain
- a ledge falling from up above (ledges from from snow accumulated due to wind deposit)
- snow falling from above from rocks or trees, rocks falling from the mountain above, etc.
- skiiers, snowboarders, cross-country skiiers, etc moving too close to the ledges or adding stress to weak layers in the snow
Ok, now, how do you evaluate conditions, to know what you’re getting into?
One of the key aspects for me, is being able to evaluate 1) recent/current climate conditions that make avalanches more probable and 2) terrain that makes avalanches more probable, so that I can determine the risk factors before choosing a route, entering into a new terrain, etc. Some of the important things 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; chutes, basically anything that a person could “hit” as they are being dragged)
- Previous avalanches from recent days
- Orientation of these elements according to sun/wind orientation
The three main factors that affect the dangerousness of an avalanche are: angle of the incline, the orientation according to the wind / sun and terrain traps.
The effect of the wind and sun
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 accumulations and can often form very high ledges. This side of the mountain tends to be more dangerous.
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 they are more prone to quick heating, which in turn causes weaknesses in the snow slabs and higher frequency in 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, to summit early, etc. But, just the other day as I was showing my grandpa pictures from a mountain I went to a couple weeks ago, I now 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, I understood terrain way better than I had just a few weeks prior.
When looking for victims of an avalanche, there are various steps in the process, all of which you use 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 by having your tracker emitting signal, and, once you need to search for a victim, you switch it to “search” mode. In search mode, it 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 parrellel lines (if you’re 2+). As soon as your tracker notes a signal, there are very strategic tips for how do the “fine tracking” and identify the best estimate for location of the victim. Once this is identified, you use a probe, again, 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, identifying 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, as this impacts where you need to begin shovelling. If the victim is less than 50cm/20in under, you can dig pretty much right over them. However, if they are more than that under, you need to start digging 1.5x the depth, away from them. Which means, if they are 100cm/40in under, you need start about 1.5m/5ft away from the person, in the direcction going down the mountain.
- the majority of avalanches happen at “medium” inclines of 30-45 degrees, 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. What often happens, is a little snow falls off the steeper inclines, onto the less incline below, causing the avalanche to begin at 30-45 degrees.
- avalanches can travel up to 90kph / 56mph in a matter of seconds
- Only a few seconds after an avalanche, the snow can quickly turns into ice, freezing hard hard after all the heat it generated on the way down.
- If a victim can be rescued within 18 minutes, the survival rate is greater than 91%. This drops to below 50% as you get up to 30 minutes.
- the biggest avalanches are strong enough to destroy a village or 100 acre forest!! imagine that!!!