Saturday, February 27, 2010

Its a Mine Field Out There

Well, this one will be short since I'm on the way out the door for some sun crust. I didn't ski on Friday due to a 'Leadership Enhancement' Course that took from 7-3, but on reading about it, it was well... explosive? The major problem we are currently facing is buried surface hoar (otherwise known as frost) which creates a beautiful reflective surface on the snow caused by sublimation (I believe thats the one...) on the surface on cold, calm, clear nights. It seems to me that you see this more commonly in Lambs and Mill Creek, but still fairly uncommon in the Wasatch. The problem is that it doesn't uniformly grow, so you end up with pockets of seriously unstable snow. From this mornings forecast:

"As forecast, yesterday was an extremely wild day. I think it set a record for the number of human triggered avalanches rep
orted to us in one day. Here is the list:

21 significant, human triggered avalanches in the backcountry

9 unintentionally triggered

7 people caught

4 partial burials including one with just his hand sticking out"


Depth Hoar is not a common problem in the Wasatch because our temperatures are more moderate than you would see in an continental snow pack (like the rockies) and so we tend to be not so good at dealing with it, as the above statistics would dictate. I would say our most common snow tests are different compression tests, like the extended column test, but unfortunately they don't really work because they only tell you the conditions of the localized are that you are testing. The slope 10 feet away could have a aspect change of 10 degrees and have a completely different level of stability. So in lies the problem. Finding an accurate 'test slope' is tricky, if not impossible.

On Thursday I was out in Days/Davenport Ridge doing some death crust skiing and ventured into the North aspect of Days do a quick extended column test and the results were, well.... terrifying? The test slope I used was 38 degrees about 98ooft on a directly North aspect. On entering the test slope some things come clearly into view as I see lightnng cracks shoot out in front of me through the snow, a sure sign of propagation. Also before of the was up on about a 26 degree slope the entire new soft slab settled... a difficult experience to explain but it sounds something like an empty dumpster being dropped from 4 feet in the air. Very disturbing. Already by the time I started doing my test I was pretty certain what the results would be. Once I had completed my construction I did the test... three taps on the shovel from the wrist.... 1 tap from the elbow and like a breaking rubber band, the whole column released on a perfectly clean sheet of depth hoar. No deformation, or residual consolidation what so ever. Its difficult to explain how unstable AND unpredictable this snow pack is at the moment, but as I was tip-toeing back to my car with fear and trembling the analogy o the mine field came to mind. Our North aspect slopes are really like mine fields... the mines are where the surface hoar is buried. So if you lucky, you could ski that 38 degree slope and never hit a mine... like the 2 tracks I observed on the NNW aspect off the top of Davenport Hill. But just as likely is hitting 20 mines as you go down and releasing all 18 inches of new snow.... on the entire slope--enough to cause serious injury or death.

I'm not a professional, and I clearly don't work for the Utah avalanche center, but I am interested in the difference between the considerable rating and the high rating as I would be inclined to place a high rating on our Northerly aspect slopes greater than 35 degrees (and a considerable on greater than 30) in the common surface hoar zones which it seems they have determined to be mostly between 8-10,000ft. This task, I might add, of determining what altitudes and aspects the surface hoar is at is very, very difficult. Many pitts need to be dug, local knowledge needs to be applied based on previous years experience, and maybe some magical upper level meteorological skills.

So if

you are going off in the BC today maybe stay off, or out from below, anything Northerly greater than about 30 degrees: its a mine filed out there.

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