Forums Avy Discussion Forum Pit Locations: Representative of what?
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  • #772702
    HansGLudwig
    601 Posts

    When choosing where to dig a snowpit, textbooks and instructors say to look for safe and representative sites. ‘Representative’ meaning a slope with same angle, aspect, & elevation as the slope we want to hit; provided that location is free from the influence of trees. We consider this distance as far away from the base of any tree as that tree is tall (i.e. ≤ ∠45º from the pit site to the top of any nearby tree).
    We imagine an idealized, ‘general snowpack’ which local terrain features influence. Trees create aberrations from this general snowpack and data from sites near trees is aberrant thereby skewing our understanding of the general snowpack. This is bad for the forecaster and hazard evaluator alike. Or is it?

    Here in California’s transverse ranges—with a few exceptions—we ride in treed terrain. Further, it’s rare to find a clearing wider than surrounding trees are tall, let alone a safe one.

    If we plan to ride treed slopes, is it not at-least “O.K.” for the hazard evaluator to choose pit sites near trees? Granted, we hazard evaluators (riders) would do our best to find “wide-ish” clearings with neither branches overhead nor shrubbery underneath. It seems to make sense that treed slopes are more representative of other treed slopes than clear slopes are.
    Are sites with trees (and pockets of instability) just as likely to test false-stable as false-unstable?

    It should be noted these data are not useful for the forecaster for whom the idealized snowpack is, in the words of Austin Powers, “his bag, baby.” Treed-slope pit-data would only be useful for evaluating hazard on a particular slope, on a particular day.

    I know it’s not ideal. I’m trying to play with the cards I got dealt. Or am I spinning my wheels and pits in such places a crapshoot and waste of time?

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    #773276
    dishwasher-dave
    460 Posts

    Treed-slope pit-data would only be useful for evaluating hazard on a particular slope, on a particular day.

    All slope data is similarly limited, that’s the nature of spatial distribution (as well as temporal change). The basic answer to the challenge of digging near trees is Yes…but also to do your best…and try to make the most relevant obs you can with what you have. If you are in unrepresentative terrain, digging a pit is probably of little benefit.

    Pits are great for learning about the snow but shouldn’t really be used for making go/no go decisions. Making continuous obs throughout the course of your touring day is often far more beneficial in terms of relevant info gathering, than spending a bunch of time digging in one spot.

    #774610
    HansGLudwig
    601 Posts

    After writing this, I thought got the idea to run the question by Bruce Tremper. The guy responded in less than 24 hrs. Better than I usually do!

    Hans,

    Good question. I’m not sure I have any good answers. But you want information from the kind of terrain that you plan to ride, so digging pits in the trees seems like the right thing to do. I usually choose a clearing in the trees to dig because the trees affect the snow in many ways. You don’t often see avalanches in thick trees but you often see them in more sparse trees. So sure, keep digging pits in the trees but realize that there’s a lot of spatial variability in the trees.

    That’s my 2 cents worth,

    Bruce

    I guess in practice that means keep digging pits in the best locations you can, but dig more of them to even out spatial variability within trees.

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