Pulling this common theme into its own thread, do we have some good case studies of tracked-out slopes that slid? Conditions, etc.
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Tracked-out slopes that avalanche
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I'll have to dig a bit, and most of it will be in German, French or Italian. Let me get back to this thread.
Here's the first one: Dutch snowboarder triggers avalanche in Fiss, Austria, last March. Big item on the Dutch Website wintersport.nl
www.wintersport.nl
And some Austrian news clippings: https://www.meinbezirk.at/landeck/c...n-skiraum-in-fiss-sucheinsatz-laeuft_a5222305
Indrukwekkend getuigenverslag: flinke lawine in fiss
Schijnt skiroute bereikt te hebben. Vooralsnog vermoedelijk geen slachtoffers. Er is door een man of 80 gezocht, tevens lawine honden ingezet https://www.
And here's a great German article on the so-called 'Arlbergeffekt' (Arlberg Effect), as it is known in the avalanche safety world, apparently. Great comparison to the measures that are taken in Highland Bowl, Aspen (people treading the snow early season, basically tracking it out) vs Europe, and why they work in Aspen, but not in Europe. "Recent winters in the Alps have shown that slopes that have been tracked-out - and even those that have been blasted multiple times - do not necessarily offer protection from old snow avalanches." (page 2).
One of the things studies show is that boot packing a slope has a much more stabilizing effect than skiing the slope.
One of the things studies show is that boot packing a slope has a much more stabilizing effect than skiing the slope.
A-Basin, May 2005 (1 casualty) - https://avalanche.state.co.us/caic/acc/acc_co.php?accident=20050520
https://www.summitdaily.com/news/a-basin-exonerated-in-avalanche-death/
https://www.summitdaily.com/news/a-basin-exonerated-in-avalanche-death/
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I recall skiing repeated runs in terrain with a guide for the good part of an afternoon. At a certain point, she pulled it because the consistency of the snow had changed. Anyone going by our tracks or the sight of a group skiing a slope most of the day wouldn't have had the full picture.
Therein lies the danger, I think. If you ski into a slope that others are skiing or that has clear tracks without doing the risk assessment yourself, that's dangerous. Conditions and the snowpack can change, even throughout the day. Just following other skiers and assuming that 'if they're skiing that slope, I can too' is a bit naive. The problem is: in order to realize that, you need to be aware of the risks and your own (in)capability to assess the situation.
But back to the tracked-out slopes and why that is not necessarily a safer slope. There are quite a few studies that debunk that theory, or at least put the much-needed nuance in the discussion. A few studies are cited in the article I shared in post #4
But back to the tracked-out slopes and why that is not necessarily a safer slope. There are quite a few studies that debunk that theory, or at least put the much-needed nuance in the discussion. A few studies are cited in the article I shared in post #4
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Pic 1 from the original thread looks unusual and is most scary to me.
Pic 2 shows snow that has had sand deposited on it (from a Foehn wind possibly?) hence absorbs solar radiation faster and is around rocks which also heat faster in the sun. It's also on a higher apparent angle and maybe some convexities. Looks like a spring wet avalanche to me. So avoidable for those that pay attention.
Pic 1 looks riskier because doesn't have the same cues/clues.
Pic 2 shows snow that has had sand deposited on it (from a Foehn wind possibly?) hence absorbs solar radiation faster and is around rocks which also heat faster in the sun. It's also on a higher apparent angle and maybe some convexities. Looks like a spring wet avalanche to me. So avoidable for those that pay attention.
Pic 1 looks riskier because doesn't have the same cues/clues.
Depending on how interested you are, one of the best sources for that information would be the publications Snowy Torrents: Avalanche Accidents in the United States. I believe there are five editions published covering a number of years in each.
Some web searching on “Snowy Torrents“ brought up a free edition to get you started.
coloradogeologicalsurvey.org
Some web searching on “Snowy Torrents“ brought up a free edition to get you started.
The Snowy Torrents - Colorado Geological Survey
Here in Colorado, avalanche season is not over yet, and it’s been another deadly one with 26 fatalities so far in the US, six in the state. In that light, we thought we would re-release a publication that highlights at least one challenging aspect of Colorado snowfall — that is, the significant...
coloradogeologicalsurvey.org
Wow, thanks @Cheizz for these, could only digest the first for now. (With some knowledge of German I can *sort of* read Dutch, but the brain quickly tires and the cloud translator is ever at the ready.) Really a good discussion there, with more of the truth coming out in later posts. Also looks like some great moderation at that forum.Here's the first one: Dutch snowboarder triggers avalanche in Fiss, Austria, last March. Big item on the Dutch Website wintersport.nl
And some Austrian news clippings: https://www.meinbezirk.at/landeck/c...n-skiraum-in-fiss-sucheinsatz-laeuft_a5222305Indrukwekkend getuigenverslag: flinke lawine in fiss
Schijnt skiroute bereikt te hebben. Vooralsnog vermoedelijk geen slachtoffers. Er is door een man of 80 gezocht, tevens lawine honden ingezet https://www.
First avalanche: warming, rotting spring snow, triggered at the transition from rocks to deeper snow. A classic trigger point in any condition, and especially in warming conditions.
The poster's description of how he triggered two separate avalanches and the thought/panic process involved seems genuine, and is worth reading (throwing into the translator). This could be almost anyone skiing/riding at a resort.
Another misconception about avalanches: that they don't occur (as much) in trees. Here's a nice video that shows one example that they do.
That is a good example, and a pretty unusual capture from above and below. It looks like the fault line happened at the edge of the trees where it opened up into the meadow, and once it started inertia took over. The skier made the absolute right move getting over into the thicker trees. It would not have been a fun ride going 'pinball' down through the trees.
In Europe do you have as many issues with tree wells as we do in Western NA?
I don't think as many issues. You don't hear about them as much. But then again: fewer people ski off-piste in the trees. And in most places, trees are either very close together (not a whole lot of fun skiing in between, since snow cover is minimal), or they are larches. they lose their needles and the snow cover is quite nice and reaches right up to the tree stem, leaving fewer tree wells.
Less but not zero.
In addition to the factors @Cheizz mentioned, snowpack tends to be less where trees exist in the Alps, relative to NA. I leave to ecologists and environmental historiams to explain that (historically forests were mostly gone from the Alps from overcutting, then replanted to protect villages from all the avalanches that ensued.) I’d be curious to know how all that may have affected the modern treeline).
Whenever I come across trees that have been snapped in half by an avalanche, I tell whoever I’m with that trees are no guarantee of safety. Or if I’m alone, I just tell myself that.
Scary video, the small, slow moving mass at the start already knocked him off his feet, fortunately he was on the side and able to move further to that side. If it caught him a few seconds earlier or later, he could easily have been swept along with the main mass
Trees do prevent avalanches to happen, but the thing is, they need to be close together to have that effect. Unfortunately this means, they need to be so close together that there's no chance anyone will be skiing between those tree. There is one other aspect of trees though. When avi danger comes from wind, there's less chances it would be problematic between the trees, as trees "protect" terrain from wind, so there's less wind shifting snow around building problematic layers. So yes on one side trees can "prevent" avalanches to happen, on the other side they don't. Quite often problem is, that people think trees are safe in general. Yes they can be safe in particular situation, or no they are not any safer then terrain without tree, and can actually be way more dangerous then open slope (more chances for trauma if avi does happen). So it's about particular situation and reason for avi danger to say if trees will help and be safer place or not.
In other words, whether it comes to tracked-out slopes or trees, overgeneralizations are a risk and ever only half true. Get proper avalanche education to understand and know when things are safe to ski and when they're not.
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I'll add tree islands or rock outcroppings often help develop faceted snow crystals deep in the snowpack.
If there are trees present: Do they help prevent avalanches? OR Are the trees growing here because the avalanches avoid this area?
I think you get both effects. Trees show where the avalanches are less prevalent. AND Stands of trees help stabilize the snowpack and prevent avalanches.
I think you get both effects. Trees show where the avalanches are less prevalent. AND Stands of trees help stabilize the snowpack and prevent avalanches.
