"Snow Doughnuts"...anyone seen one?

Came across this article in the Seattle Times on snow doughnuts.

Anyone ever seen one of these?

Garth Ferber and I found one in the B.C. Coast Mountains a couple years ago. I don't recall ever seeing one before.

I've been thinking a little about snow donuts. It seems to me that they could only form two ways.

1) A snow wheel rolls down the slope and, at some point, the center falls out.

2) A small snowball starts rolling down the slope. As it rolls, it picks up snow rapidly on the underside, becoming asymmetrical. The weight of the "upper" side of the ball is enough to keep the object moving. It sort of rolls and sort of deforms (somewhat like a wave breaking) until the elevated part of the object touches down, completing the donut.

Of these two scenarios, number 2 seems improbable to me, especially considering the low angle of the slope shown in the picture above. It doesn't seem like the forces work out right in this scenario. Number 1 seems like the most probable explanation. I wonder what the truth is...   ???

Once I got knocked off my skis by a snow honey bun, sorry no pics

I found this one on the Pipeline trail near Mission Ridge last January while snowshoeing.  I'd never seen one before either!  ???

Found the hole ....  There were no trees within 10 feet of this hole in the snow.  Very strange and I thought I'd never have a chance to use this photo!

This is a fun mystery.

At this point I like Lowell's "breaking wave" idea best.  cascadianwarrior's pic shows one where the leading edge looks look a curled wave folding into itself. 

Maybe the wind blows out the loose stuff from the middle?  Maybe they form with the hole already there?  I guess we won't know for sure until someone sees it happen live and shares the recipe.  MMMMM doughnuts

TonyM: sometimes when I pee in the snow it looks kinda like that ;D

Cascadianwarrior, is that a donut or a sticky bun?    

What I mean is, does it have a hole in the middle?

I'm leaning toward my first hypothesis. The wheel does not initially have a hole in the center, but at some point the center falls out, creating a donut.

Cascadianwarrior's picture illustrates how this happens, I think. The wheel starts as a small snowball. As it rolls, it picks up more snow. When the snow conditions are right, the wheel grows not just in diameter (becoming a bigger disk) but also in thickness (the wheel's "tread" becomes wider). This can be seen clearly in Cascadianwarrior's picture. The outer edge of the wheel is not only thicker than the core, it is also more firmly packed. This happens because the wheel gets heavier as it grows, so the snow farthest from the center is packed under more weight. The inner, less consolidated core either melts or breaks away at some point.

===
Edited to add: I think some sort of heat source under the snow made the hole in TonyM's picture. Maybe a critter. I've seen holes sort of like this near marmot burrows.

I think some sort of heat source under the snow made the hole in TonyM's picture. Maybe a critter. I've seen holes sort of like this near marmot burrows.

Critter - you mean a Sasquatch?  Okay, maybe a baby Sasquatch given the hole's size.
Here's what an adult Sasquatch hole/lair looks like:
picasaweb.google.com/jshefftz/WhenSasqua...#5042150575205281634

Oh, and the snow donut story made it onto NPR Monday!  Between that and the incidents on Mt Doom, err, I mean, Mt Hood, NPR is quite the source this season for ski mountaineering coverage.

Doug, when are we going to see TR from Deutchland? :

Cascadianwarrior, is that a donut or a sticky bun?    

What I mean is, does it have a hole in the middle?

It was a true doughnut and a beauty at that! ;D  I kinda messed up on the exposure but here are a couple more pictures of said doughnut:





Also, this story is picking up momentum (just like the doughnut :).  Here's an article from today's Wenatchee World:

Snow Doughnuts

And lastly, here is the ultimate specimen from Sandpoint, ID.  They really know how to grow 'em in Idaho.  I think it's even steel belted! 

I think Lowell's first point is correct. It begins with a small snowball which often encounters friction and loses it's radial motion, which starts a sluff. Then the sluff hangs up a bit from friction, sticks to the surface snow layer, and begins, once again to rotate. The dougnut or "pinwheel" tends to pick up the amount of unstable, sticky snow available on each revolution. If the pinwheel gets big enough, or is somehow deflected it may fall over, which ordinarily will cause a loose, wet slide.

I've had fun with these on occasion. The biggest snowballs I've gotten going probably reached 5-8 feet in diameter before falling over. Some initiated avalanches of 4-8' of sliding wet (moist) snow.

In the first revolution the snow that congeals to form the core doesn't become compressed because the snowball has yet to gain much mass, but as it gets bigger with each revolution, the compression of the adhering snow layer becomes greater and greater. So, me thinks that the central core is more of a loose amalgamation than the surrounding layers that accumulate. Probably, that allows for the loosely packed center to fall out under the right circumstances.

Snow donuts seen off the Snoqualmie Middle Fork today! I saw at least 50 of them fallen over, but none standing.

Here's another to add to the collection, this one with a icing of freshies and fine surface hoar sprinkles:
http://farm1.static.flickr.com/172/462824613_effbd929a1.jpg?v=0

Found it on a west facing slope below some rocks at about 5700 in Bullion Basin.

This from the WSDOT website, I think from up by Washington Pass. Their opinion is that they form with the hole in the middle from the genesis.

It's like the "missing" WMD in Iraq: noone in the know can quite explain how what should be there ain't.... ???

The density of snow at higher elevations is less, so as the snow rolls down the slope the low density snow could simply fall out because it was more faceted and had less bonding strength to the other snow, or... as the snow honey bun (soon to be doughnut) consolidates the low density snow (having lower water content) melts out sooner leaving the hole. I would guess that the snow doughneut pic by cascadianwarrior grew a much larger hole before it dissapeared. (like the one pictured by ron j in bullion basin)

fascinating ;D

While touring around Crater Lake this March we saw many snow doughnuts 50 + that were caused by rolling rocks that packed snow around themselves until they stopped under their own weight. Once the sun heated the rocks they fell out of their cozy little snow nest leaving a snow doughnut behind. The rocks then melted into the snow and disappeared (new snow will cover the escape hole leaving behind a mystery). I wish we had a camera but .....

I hope this helps ;D

Climberdave