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A Question For the Snow Science/Avalanche Experts Here

post #1 of 9
Thread Starter 

I was watching a few video reports from the Utah Avalanche Center and started thinking....I know that can be a very dangerous thing.  Presuming the weather remains cold will the hard slabs that formed after the most recent storm cycle stick around or is it possible that with time and more snow things will become much more uniform?

post #2 of 9

I am by far no expert not even a little but I can explain my understanding as well as the information I have collected from the colorado avalanche information center.


When you say hard slab I am assuming you are referring to the type of avalanche or to the stiffening of the snow.


From what I have read in various sources is that stiffening of the snow layers is a double edged sword. It tends to lead to more stable snow due to the bonding of the snow and meaning that avalanches. However, when the avalanche is triggered on one of these stiffened snow layers the slides tend to be much larger and more deadly.


What is more important than the stiffening of a specific layer in terms of stability is that layer's bonding to the underlying layer. This is the problem we are currently experiencing in Colorado. The new snow from the last storm cycle has began stiffening and forming a cohesive layer. The underlying weak layer however, is still extremely pronounced leading to less frequently triggered slides but much larger ones. 


My explanation is pretty rudimentary here is a full description from CAIC:



Like I said I have a very basic understandign, I am sure some other members will chime in and give you all the technical info you want.

post #3 of 9
Thread Starter 

There still seems to be a lot of instability out there.  So is there any chance of the snowpack stabilizing this season or is pretty much a lost cause?

post #4 of 9

 I think it's impossible to answer your question.  There will be places were it stabilizes and others won't.  


In Aspen, I'm waiting until we get some freeze/thaw cycles and then I'll look at it again, before I ski anything steep?

post #5 of 9
Thread Starter 

OK, to be more location specific, in Utah there seems to be a pretty nasty snow down low and it doesn't appear to be improving much what does it take for it to stabilize.  If the snow goes through a freeze thaw cycle or two wouldn't that just create the same issues if it snows more on top?

post #6 of 9

Always a big issue in Colorado's (continental) snowpack, less so in Utah (intermountain), but I guess this year they are dealing with more of it.







As Canadian avalanche specialist Clair Isrealson once told me, "Depth hoar is like having your crazy aunt come for a visit. She stays forever and you just never know when she's going to snap." 

Large-grained depth hoar persists longer than any other kind of weak-layer. And as long as it does, you just tiptoe around and accumulate gray hairs. Usually the larger the grain size, the more persistent the instability. The time-honored adage among experienced avalanche professionals is: "Never trust a depth hoar snowpack." In other words, it's always guilty until proven innocent. 

Carefully watch each loading event all winter--especially the big ones. Then even after you think you've seen the last of it, percolating melt water in the spring will re-activate the depth hoar layer and produce large, wet slab avalanches. Yikes! 

The best stability tests for depth hoar listed roughly in the order of reliability: explosive tests, cornice drops, Rutschblock tests, compression tests (do lots of them in representative places), jump on test slopes and pay attention to recent avalanche activity. Weather isn't quite as reliable unless it's really obvious weather like a heavy loading event or rapid warming of a thin slab overlying depth hoar.

If you can't use active tests, use a thermometer and carefully measure the temperature gradient across the weakest layers. As soon as the temperature gradient drops below the critical level (about 1 degree centigrade per 10 centimeters) then it is gaining strength. But remember that depth hoar is quick to form but takes a long time to gain strength after the temperature gradient is removed. With no additional loading and with a weak-layer of -5 deg C or warmer, it takes several days to a week to stabilize. With cold weak layers and a lightweight overlying layer, it can take much longer.


post #7 of 9
Thread Starter 

Well that's kind of scary but pretty much what I was looking for.

post #8 of 9

It IS scary. Few have seen a year like this. When I was driving up Mon morning, the variable message signs on I-70, as you were leaving the Denver metro area and again farther up near Frisco, had a warning: Backcountry Avalanche Danger Is High!  I had never seen that before. Doesn't mean they haven't used those signs for that before, but I've driven that highway quite a bit over the past years, and not seen it.  A good idea for a holiday weekend, for sure. 

post #9 of 9

I dug a small pit a while back. There was about 1" of hard crust, breakable if you turn on it. Then there was some air, space, a couple inches. then there was frozen crystals of ice with no branches, like ice balls, and this went right down about 5 inches to the dirt. You can pick up those "sugary" crystals and sift them through your fingers. In some areas we received about 3 inches of rain which soaked to the ground I suppose. Haven't checked to see the effect of the rain.

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