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Wednesday
Feb172010

Snow has Energy?

I've heard friends say "the snow didn't have any energy," or "the new snow was humming with elastic energy." I've been wondering, how can snow have energy? Maybe when it's avalanching, but how about when it's just sitting there?

Cathy and Jeff Conaway described energy to me in terms of potential energy that accumulates in a column of snow before the snow settles or the weak layer disipates. Kinetic energy is released when the weak layer is triggered into an avalanche or it consolidates. Sounds like you need a Ph.D in geomagitianism to know if the slope will avalanche or not.

Okay, what really is energy? I need a non-physics answer. 

I consulted Tremper's Staying Alive in Avalanche Terrain. He writes "Researchers believe that shear quality does a good job of determining energy in the snowpack...High quality shears break on a clean, planar surface and pop out with 'energy' like they're spring-loaded. Canadians describe them as 'pops and drops,' meaning they pop out with energy or they collapse." Oh, that makes sense. That's why we emphasize shear quality in stability tests.

Energy is also used to describe avalanche release as one of the three slices of the snowpack stability wheel: 1) Strength from stability test results, such as the rutshblock or compression test, 2) Energy measured as the shear quality of the failure plane, and 3) Structure of the snow layering measured by yellow flags or lemons. While stability tests and shear quality show us how likely the weak layer is to fail at that spot (the pit location), yellow flags help determine if the failure will spread and cause an avalanche.

My question becomes: must we conduct a compression test and measure shear quality to determine snowpack energy? Not necessarily, I think. Some snowpack has energy that is obvious through red flags: whoomphing, shooting cracks and hollow sounds. You can also feel energy in the snowpack through your skiis, such as punchy conditions from new snow over depth hoar for or a skittery, buried crust.

Problematic energy is the type you can't observe through a keen backcountry snow sense. This is the energy you can't see, feel or hear. An example is that lingering depth hoar layer that shows up as a CT25 Q1 at 45 cm in the compression test. As Henry Munter from Chugach Powder Guides put it, "I guess I just don't see how anyone could, see, feel, intuit, or otherwise sense the energy stored in deep slab instabilities without getting some gloves and eyeballs into a pit..."

I'm now thinking there is 'observed energy' and 'measured energy.' What do you think? If you've read this far then you better send me an email!

Reader Comments (2)

This may be totally off, but I can't help but think that maybe this 'energy' is actually manifested and most easily observed in the way the snow structure is held together. As snow packs together, what is it that is actually doing the holding? In most cases, it is simply piling together due to gravity, but what, in the case of snow bridges, cornices, etc is keeping it together? I can't help but imagine from my physics background that maybe the electrical forces between snow crystals helps with the bonding. Maybe it's the static electricity holding the snow pack together that is this 'energy'. I can easily imagine that it is when some other forces overpowers these bonds that snow collapses, cracks, or falls. For example, a cornice is curled under, hanging precariously, held together by this 'energy' of static bonds, and a slight jolt is all it takes to break it lose, or a replacement of weight distribution, such as extra loading by fresh snow, or melting by the sun, which redistributes some of the weight to the bottom of the curl, increasing the moment forces on the attachment point.

Again, this is simply my hypothesis. I don't know if any papers exist on this already, or anything. Just came up with it in my head.

Thanks,

-Blaine

May 7, 2010 | Unregistered CommenterBlaine

Hi Blaine,

I think you're right about electric forces in snow. I remember Scott Schmidt at MSU in 1993 talking about his research on electrostatics in blowing snow. He created different cornices by cranking up or down the charge between two plates that the snow blew through. His big idea was burying high tension lines next to freeways in Wyoming to launch the snow over the road.

Interesting!

Joe

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