Avalanche at Perfect North in Indiana

Pretty much! Basically, an avalanche happens when the force that the underlying snow layer or terrain puts on the top layer of snow (in the form of friction), is overcome by the force gravity and the weight of the snow (that is pressing down) puts on it. When the hills surface cannot hold the snow anymore, it slides down.

In this case, grass that had been laid down the hill, and soaked through with lots of water from melting snow, was not enough to hold up the huge layer of dense, heavy, spring/man made snow, so it slid down the hill.

Others cases can be different, sometimes snow layers can slide on top of each other. Things such as spring pollen, atmospheric dust, ice crust, different densities, different snow crystal structures, temperature changes, and a billion other things can affect avalanche risks. Generally, the only avalanches triggered by skier or boarders, and not melting snow or a really steep slope (or any of the factors listed before), are ones where a layer or layers of light/heavy snow slide off of a heavy/light base layer. (Note: The densities have to contrast each other, because light snow tends to cohere to the light snow, and vice versa, leaving the light and heavy snow separated).

But in the end, yes, it is basically a big layer of snow sliding off of a slippery base.

 
Yeah that is what freaks me out.

I'm super sorry to hear that man, SIP to your buddies - hopefully they at least went doing something they loved.

The mountains terrify me TBH. I know that they're an unpredictable bitch and its something you simply can't mess with.

 
So if we went with our first analogy... the skier would be like walking by said guy on the slip 'n' slide and giving him just ever so slight a nudge?

Maybe it would have held indefinitely if no external force was applied, but the tiniest bit of nudge is the proverbial 'straw that broke the camels back' and blammo massive slide?

Funny enough, talking about a fat man on a slip 'n' slide seems to be the most clarity I've ever had towards avalanches.
 
getting hit in the run out zones from natural activity above and/or remote triggering something above you while crossing a path is really, really shitty.

That group of kids who died at Rogers Pass in 2003 got hit by a natural avalanche that came down the valley and took them all out. The valley they were travelling in is very dangerous when there is a chance of natural avalanches because you are almost consistently in the run out zones, and something that starts out of view, 2000M above you could come down and wipe you out at any moment. In the same month, Craig Kelly died in an avalanche that took out a lot of people as well. Those two avalanches alone made 2003 one of the highest skier avalanche fatality years in recorded history for Canada.

There was another incident back in early January, 1998 in Kokanee Glacier Park (just outside of Nelson) where a group of skiers was crossing a big bowl along a flat bench, spaced out, doing everything 'by the book', but they managed to remote trigger an avalanche hundreds of meters above them that propagated across the whole bowl and took them all out. There's a book about it, and it does a pretty good job at talking avalanches and human behaviour without confusing someone without a lot of avalanche knowledge. It's called 'In the Path of an Avalanche' by Vivian Bowers. The incident happened a just shy of a year before Michel Trudeau got taken out in an avalanche in the same park in November 1998.

I mention these because of how high profile they are. There was a lot learned from the incidents, a lot of information about what went wrong, and they helped shape how we approach avalanche terrain in BC today. They would be good cases to look into if you are interested in learning more about avalanches without actually getting too deep into the actual snow science.

 
I may have exceptional data processing ability, but I shit you not I am a park rat that doesn't know the first god damn thing about avalanches.

Our current 'fat man' analogy is honestly the most clear its ever been.
 
Two things:

1) Its now funny to me when older people say "I don't do park because its dangerous." This is purely laughable in the face of the dangers that 'getting the goods' faces.

2) I shall do my best to learn more. Of course, I'd like to learn lots about snow science before I venture out there. Didn't GI Joe teach us that knowing was half the battle?

 
more of a glide slide than a soft or hard slab avvyplayin w/ gi joe dolls

aint gonna teach ya 1/2 of mannin up and joinin the service would

but different stokes
 
Usually spells instant death. It's one thing to get swept up in something while you are skiing. When a slide comes down and hits you from above, it's like getting hit by a car going 60. Can you imagine trekking across a flat area and seeing a slide break loose above you. You can see it coming the whole way and there is nothing you can do about it. That's kind of what happened to my buddy Howard, and gave me nightmares for months afterward. He was in a gully, so he couldn't see it coming, but he could hear it. The ME told us that the impact killed him instantly. He may have just been being kind, and not wanting us to know that he suffocated. He basically wasn't moving and the slide was hauling ass, so it could be true that the impact did the job. Such an uplifting thread this has turned into.
 
That one was really bad for the snowboarding world. Also Jeff Anderson died in japan only a month later.

2 of my favorite riders gone like that. RIP

Craigs been the background on my computer for the last 6 or 7 years. Put it up one day and never saw reason to change it.
 
What are you talking about? Thats at least a category 3 wet slab avalanche. Plus its all super dense man made snow.

It lucky it didn't trigger while someone was grooming up that damn thing.

Its official, conditions are sketch everywhere.
 
Yes, the slight nudge would be enough to get the slide going (assuming there are sketchy unstable conditions). Or, imagine there are two fat guys, one that we already know is at the top of the slip and slide, just waiting to slide, and one on flat ground above it that won't slide. The fat guy that will slide, is holding onto the hands of the guy that won't (like how cohesion holds one layer together), and that's what is keeping him from breaking off and sliding. Now the skier comes across and breaks their connection (just like how a skier could cut a layer horizontally, breaking the cohesion that is holding it together) causing the guy to slide down because nothing is holding him up. -- Instead of the skier nudging the slab (fat dude) down and making it move, all he did was break what is keeping the slide up, and gravity and the weight of the snow did the pushing.

It might have, but there are always the other external forces (gravity, friction between layers, weight of layers on top, cohesion of the snow pack holding each layer together, etc) that have potential to trigger one or make it easier for a skier to trigger.

 
Moral of this story:

If two fat guys are holding hands and one of them is sitting on a slip and slide; for the love of god, leave them alone.
 
If I had to guess I would say that things got warm and developed conditions similar to a glide avalanche: http://www.fsavalanche.org/encyclopedia/glide.htm . I've seen these early and late in the season in the tetons. They often happen at the ground layer and will crawl slowly for days until eventually releasing in a wet slide.

Its possible that this progressed a similar fashion but instead of creeping for days, progressed into a wet slide overnight. The slick grass underneath wouldn't provide any anchors and once the slab gained a little momentum it would progress quickly.

Again, thats just a guess. I'm not an expert on midwest man made avalanches.
 
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