Avi Conditions and Simulations In Danville

In anticipation of the coming storm tonight, I cut the snowbanks back about 30 inches to widen the driveway and make room in the 'parking area'. In the process I noted some interesting aspects of the accumulated snow that I was digging into. Basically, I was digging a test pit, like one would do to evaluate snowpack stability. Here's what I noticed - and will probably photograph one day:

  • Snowblowing simulates windblown wind-crust. The process of shooting snow through the chute allows flakes to adhere to each other and lay down a crust made of larger, more icy flakes that pack tighter due to both the larger particles and the higher velocity. This snowblown layer overlying cold powder is only stable to the point where it breaks under its own weight. When horizontal, this is unlikely. When on a slope, will happen spontaneously - but unpredictably. I relied on this so I could undermine the windcrust with a snowshovel, and then hit it with a spade to crack it and have the slabs drop to the ground on their own.
  • After a lot of time has passed, even frozen slush will turn to sugar. Under all the snowbank is 'sugar'. Heat from the ground gets trapped under the snow and it melts the snowflakes. All that water vapor seeps upwards, collecting on flakes and turning everything into sugar. It destroys the adhesion completely, creating a unbonded layer on which the upper layers - no matter how coherent - to slide. Because my driveway is almost level, nothing moves - but when I dig out the snowbank, I'm digging into sugar.
  • The history of the snowpack is pretty interesting and reliably interpreted through digging pits and examining the walls. Never underestimate the ability of the snowpack to reveal its character through a dug pit.

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