FROM THE MEDICINE BOW NORDIC SKI PATROL: 12/13/09 -
The avalanche danger for the Front Range Zone is HIGH on N-NE-E-SE aspects near and above treeline. Elsewhere, it is CONSIDERABLE. Human-triggered slides remain probable to likely for Tuesday
Snow pit summary:
Location: Just down from the ridge on a northwest facing slope in the trees at the Old Libby Creek Ski Area.
Elevation: approximately 9600 ft.
Snow pack: approx. 3ft. total depth,
1) top 6-8 inches of very new snow that was light and fluffy
2) next 6-8 inches (going down) of consolidated fine-grained new-ish snow
Note: contrast in consolidation created potential failure plane between layer 1 and 2
3) next ~12 in. of large (0.5 cm. max.) "sugar" size grains, very light, lots of air space, very loose
Note: It is highly likely that layer 3 is what is compacting and creating the "whumpfing" sound.
4) bottom foot of consolidated sugar grains appearing to be fairly stable
No uniform stress tests were performed.
We decided to spread out and descend within the trees. Upon descent it was found that shooting cracks and whumpfing were ubiquitous features of the snow pack. Slabs were prone to break, and slide a few inches. Though nothing moved very much, it was decided to abandon the decent and return to the ridge. A shallower (sorry, no quantitative values) slope with about 4 inches of snow was chosen for descent. My skis have the core shots to prove it.
Almost every open area we passed through that day made the whumpfing sound. I heard more whumpfing that day than in all my previous experiences combined. I'm tempted to call the sugar crystals depth hoar, and site the -10 degree temperatures for their formation.