By: Jeremy Parker (beyond_gravity) Here in Alberta, there have been 18 avalanche deaths. 16 of them were not properly equipped with either the hardwear or the knowledge. This article is to increase your knowledge so you can make better choices.
The avalanche triangle is the basis of avalanche hazard. When all three points of the triangle are present, there is Avalanche Hazard. The 3 points of the triangle are…
1)Avalanche Terrain- It is pretty obvious when you are in avalanche terrain below the tree line, there is simply a track where no trees are. When you are in the alpine envirinment, however, it can be more difficult to see avalanche terrain. Avalanches normally start on slope angles of 30-45º. Anything less then 30º is not steep enough for regular avalanches, however they can still occur. Remember, just because your on a 20º slope does not mean you are safe, you could in fact be in an avalanche run out zone! Slope angles of over 45º decrease the chance because snow generally slides down by itself as it falls, but again avalanches are still possible.
2)Unstable Snow- If the snow is unstable, you can get into trouble! I’ll go into more depth later on.
3)People- No people, no hazard. This is the variable for avalanche hazard that you control. If you are in Avalanche Terrain, and there is Unstable snow you must eliminate the people factor. Remember, you never want all 3 corners of the Triangle present.
Types of Avalanches
There are two kinds of snow avalanches, they are…
A) Point Release- this is when a small snowball, or rock falls down and gradually grows bigger. Point Release avalanches are what you see in your favorite ski or snowboard film that JP Walker is outrunning while doing a mute 1080. Point Release avalanches are not very dangerous, but can knock/push you over, so watch out for them if you are traversing along a cliff side!
B) Slab Avalanche- A slab avalanche is when large chunks of snow break loose and slide as plates. Slab avalanches are much more dangerous. They are caused when a weak layer of snow collapses. When the layer collapses, the cohesive snow on top breaks apart and slides down. Slab avalanches can go from small slides when you will only fall over, to huge slides that can burry small towns in the Swiss Alps.
Class One- normally a point release. Can knock over, but cannot bury a person
Class Two- Can bury a person
Class Three-Can bury a car
Class Four- Can bury a house
Class Five- Can bury a small town (yes, it has happened)
The snow is a large factor in avalanche hazard; it’s also the hardest variable to analyze. The main thing you will want to look at is the type of snow crystals there are. There are generally two kinds of crystal, rounded and faceted. Rounded crystals are self-explanitory. They are strong. Faceted crystals are jagged and weak. When snow falls, it’s always rounded. Faceting happens when the crystals melt then freeze. Faceted crystals are the ones that look like sugar when you dig your pit. The faceted layer is the one that is going to collapse if something is going to happen. When a layer collapses, it is called Whumphing. This is because when it collapses, it makes a Whumph, thus the name.
Avalanches generally happen on angles of 30-45º. You can measure a slopes angle with either a clinometer or a compass.
There are two sides of a slope, the lee side and the windward side. The windward side is the side that the wind is blowing on, as the lee side is the side it’s not. You can normally tell the lee side from the windward side by looking for cornices. Cornices are huge amounts of snow that overhang on a ridge. Like in Vertical Limit when that guy is sliding down the slope then sticks his axe in at the last possible moment? That is a cornice. Cornices overhang on the lee side. The lee side will also have much more snow. When snow blows from the windward side, the wind picks it up and drops it on the lee side. This large deposit of snow is called the “pillow”. The pillow is a bad place to build your jump so you can rip you latest 900 floppy flip.
There are also Concave and Convex slopes. Convex slopes are like the outside of a bowl, as concave slopes are like the inside of a bowl. Convex slopes are most likely to collapse in the middle of the arc where all the tension of the snow below is. On a concave slope, there is the most stress at the bottom, where all the snow is being held. Be careful on concave slopes, since the most dangerous spot is at the bottom! [page] Tests
The Snow pit
The snow pit is the place where you look at the snowpack. Before digging your pit, probe around the area you plan to dig. There’s nothing worse then spending 20 mins digging then finding there is a big boulder in the middle of the pit. Once I have a pit dug up, I go across the uphill wall with my shovel and make it straight and vertical. I then take a look at all the layers and make a line in the snow in-between each layer. An easy way to do this is to just run your figure down in the snow vertically, every time there is a change in resistance, that’s a different layer. Once I get all the layers marked out, I give each a resistance rating. The ratings are Fist, 4 fingers, 1 finger, pencil, and then knife. The idea is you want to see what will go into the layer horizontally without forcing it.
Shovel Shear Test
For this, get your snow saw and cut out a section of snow about the size of your shovel blade. Now, stick your shovel vertically behind the snow block and pull it out. DO NOT lever it as you will not get an accurate result. Where the snow slides off is your weak layer.
For this test cut out a section like the Shovel Shear Test, expect for the size of a skier. Now, you want a skier to slowly move out on it until it collapces. The ratings go as following.
1.)A single ski on, ½ the weight of the skier-Eekk!!
2.)Both skis on, full skiers weight- I wouldn’t
3.)A single jump- Hmm…I still wouldn’t
5.)Three Jumps-Most Likely
6.)More then 3 jumps- BOO YA! Lets Rip!
Well there you have it. This is just the basics! Remember to always wear your Transceivers, Probes and shovels despite the conditions. Make sure you check conditions everyday, what was safe yesterday may not be safe today. I also dig a snow pit at different altitudes as the snow will not be the safe in the alpine as it is at the treeline.
Have Fun and stay safe!