Snow Science Thread

[Van Epps]

Sounds to me like depth hoar developes when the ground temp is warmer than the average air temp at the time of the first significant snowfall?? Is this correct?

If yes, this would seem to mean an early snow that does not melt off could be cause for a dangerous early season?!

 

[mtnpull]

Sounds to me like depth hoar developes when the ground temp is warmer than the average air temp at the time of the first significant snowfall?? Is this correct?

If yes, this would seem to mean an early snow that does not melt off could be cause for a dangerous early season?!

That is correct. It is many times an early season problem, but because of it's inability to bond well with other layers it can be persistent even for months. Definitely a layer to pay attention to.

 

[mtnpull]

Ok, let's talk about a wind slab or a wind event.

What is it?

How is it formed?

Is it a strong or a weak layer?

What are some concerns associated with it?

 

[mtnpull]

Wow, no responses! Come on guys....flex those brain muscles and play along here. Not only is it important, but I think it is pretty fascinating.

 

[PhantomCat]

A wind slab is created when the snow is scoured by winds and creates a slab due to the consolidation in the snow pack. Wind slab is created due to wind loading on the adjacent side of the aspect the wind is blowing from. ( meaning if the wind is blowing over a ridge from the east it will be loading the west side with a pillow of snow and then creating a slab due to the wind. You want to be careful due to the amount of snow that is being deposited and that is called wind loading which can create a tension in the snow pack and you or your buddy is the trigger to set it loose !

It is a weak layer due to wind loading and creating an unstable layer that might be triggered by a snowmobiler or a skier on a decent or a turn out !

 

[Wish]

Wind erodes and deposits snow to the back side of the peak, causing a weak layer on that backside.
I thought this animation described it a lot better than I can!
http://www.avalanche.org/~uac/encyclopedia/wind_slab.htm

By the way, great thread!!

 

[mtnpull]

Great responses guys. The wind can deposit snow much faster than it can fall from the sky in many instances. We are used to seeing wind loading up high next to the ridge top, but during really strong wind storms it can load the slope much further down than usual. Additionally with really strong wind it can compact and make a really, really dense layer of snow. This dense layer is actually really, really strong. Strong enough to support a rider to get well out onto the slope giving a false sense of security. Where the problem usually lies is when it is lying on a weak layer and the weak layer it is lying on fails. Additionally wind slabs come down off the mountain in big chunks of hard dense snow that can really beat you up if you're caught in it.

 

[snengineer]

Wind slabs suck!

 

[mtnpull]

How would you recognize a wind slab?

What is the difference between eroded snow and deposited snow and where will you find each?

 

[xrated]

Wind erodes and deposits snow to the back side of the peak, causing a weak layer on that backside.
I thought this animation described it a lot better than I can!
http://www.avalanche.org/~uac/encyclopedia/wind_slab.htm

By the way, great thread!!

great link....looks like tons of info to look at there.

 

[mtnpull]

great link....looks like tons of info to look at there.

It definitely is. Very helpful and informative. That is the purpose of this thread....to get people thinking about snow and it's mechanics. Get people searching for more knowledge and information. Finding the tools and resources that will keep them and their friends and family out of trouble and on TOP of the greatest snow on earth.

A couple more questions.

What is a soft slab avalanche?

How about a hard slab avalanche?

What are some differences between the two.

How do they form?

 

[PhantomCat]

Soft slab avy is composed mostly of new snow. Usually is not as deep as a Hard slab, and tends to break at your feet.

Hard slab avy is composed of either old, hard layers of snow or wind slabs and tends to break above you.

They form due to a consolidation of a layer of snow, weather and aspect.

A soft slab will break up more as it lets loose and goes down hill. A hard slab will have bigger chunks and will be more compressed.

 

[mtnpull]

Nice post phantom.....textbook!

Hard slabs can be more difficult to escape as well due to the fact that they tend to break above you.

 

[CatWoman]

He's kind of a snow *geek*!

 

[PhantomCat]

He's kind of a snow *geek*!

Wouldn't that make you a snow geeks wife ?


Thanks mntpull...this is a great topic and very informative. I commend you on starting this thread. As CatWoman stated, I do have some snow geek in me..it fascinates me..plus I love playing in it, and we all know that if you play you have to pay...why not do it safer and live to ride another day

 

[Wheel House Motorsports]

Well, just some info on the snow around the SW montana area, if i go back up again ill give a new report on how things bonded, but we had about 1' of sugar with 1/4" ice layer, then we got about 2' of snow, started wet, got lighter, very well could have bonded to the icy layer as the eary stuff was wet, just worried about a season of snow sitting on 1' of sugar then ice... I always enjoy playing in the snow/learning/talking about it, ill take some pics of it if i go out again.. I just hope we dont get the horrible perma bad layer like last year, might be warm enough this week for the base layers to join nicely making it a least a good base.

 

[mtnpull]

Well, just some info on the snow around the SW montana area, if i go back up again ill give a new report on how things bonded, but we had about 1' of sugar with 1/4" ice layer, then we got about 2' of snow, started wet, got lighter, very well could have bonded to the icy layer as the eary stuff was wet, just worried about a season of snow sitting on 1' of sugar then ice... I always enjoy playing in the snow/learning/talking about it, ill take some pics of it if i go out again.. I just hope we dont get the horrible perma bad layer like last year, might be warm enough this week for the base layers to join nicely making it a least a good base.

You could dig a pit and do some stress tests to see how well it bonded, if it bonds at all.

 

[Wade]

One thing I've always found interesting is that powder snow can fall as 19:1 ratio of air to water. Meaning a cubic meter of snow would only weigh 110 pounds.

As the snow settles, it weights 440 pounds / cubic meter.

Wind packed snow is around 880 pounds / cubic meter.

Wet snow can be 1800 pounds / cubic meter.

Glacier Ice can approach 2000 pounds / cubic meter.

What is interesting about this is snow can pile up at the run out at up to 1300 pounds / cubic meter, and bond together at that. It's no wonder you can't move.

 

[mtnpull]

One thing I've always found interesting is that powder snow can fall as 19:1 ratio of air to water. Meaning a cubic meter of snow would only weigh 110 pounds.

As the snow settles, it weights 440 pounds / cubic meter.

Wind packed snow is around 880 pounds / cubic meter.

Wet snow can be 1800 pounds / cubic meter.

Glacier Ice can approach 2000 pounds / cubic meter.

What is interesting about this is snow can pile up at the run out at up to 1300 pounds / cubic meter, and bond together at that. It's no wonder you can't move.

Great point. Many times as the snow moves down the mountain it, in a sense, heats up, bangs against each other and when it comes to a rest it sets up hard....almost like concrete, and like you said, no wonder you can't move.

 

[mtnpull]

Ok, back to what is important.

While we are talking about different types of slabs, what is a deep slab avalanche?