Thursday crust could be easily felt with a probe or during trail breaking - but it did not affect downhill riding at all. Reports from friends that skied Pilot and Freeman were very disconcerting; bruised knees (ouch!) during tele turning, and in Mike's words - "plates were flying up as we bashed through it skiing downhill".
Considering the strong wind events and good amounts of snow deposited during the week, in addition to changes in temperature during the storm, higher density snow in top of lighter cooler snow and variable snowpack, it made sense to perform several "SnowPit +" (it sounds better than hasty pit) at various locations during the day.
Three test pits were done at Pilot Peak with the following results:
- East aspect at 6900 feet, 30 degree incline- CTMQ2 (with sudden collapse) and CTMQ3 at 50 cm on a 4-5 mm weak layer of stellars and light precipitation snow crystals. Canadian extended column (undercutting WL with saw blunt side) did not propagate fracture.
- NEE aspect at 7200 feet, 32 degree incline - CTMQ3 at 50 cm
- NE Aspect at 7000 feet, 30 degree incline - CTMQ3 at 50 cm
The new snow in top of the crust did not show clean planar shears in our test, perhaps due low cohesiveness and bonding of crystals resulting from the relatively warm temperatures.
None of the pit sites appeared to be affected by windloading. We only examined the top meter of the snowpack, but each of the pit profiles were pleasently consistent on the layering thickness and structure. The top meter snow profile for site 1 is included below:
A quick view into the structure suggest the following "Lemons" (or elements present in most historical slab avalanches):
- Weak Layer within the top meter.
- Weak Layer thickness less than 10 cm.
- Hardness difference across Weak Layer of one step. Notice that the pit data documented a hardness from F+ to 4F, hence it can be argued that the hardness difference is less than one step. But considering the subjective nature of hardness estimation, it is prudent to treat it as a full step.
No persistent grain type or differences larger than 1 mm in snow grain size were detected in the top meter of the pack. Also, it should be noted that as the day progressed the compression tests were showing more irregular and "broken-up" shear planes. A suggestion of weak layer metamorphism at the 50 cm depth.
So, how do we make sense of all of this information? There are four categories that should be consider during a snow stability assestment; snowpack strength, fracture initiation, fracture propagation, and snowpack structure.
- The snowpack strength is Moderate based on the CTM results. Keep in mind that snowpack strength is sensitive to spatial variation. Rock bands or weak spots (for example snowpack thining due to wind) will have an impact on the strenght and stability tests such as compresion tests.
- Fracture initiation is Low based on the Q3 results. Studies suggest that this parameter has less sensitivity to spatial effects.
- The Extended Column test and observations of the pack during trail breaking points to Low Energy available for Fracture propagation.
- A review of the snowpack structure results in 3 Lemons.
The good news is that the slopes evaluated did not appear to have energy available for fracture initiation and propagation. The NOT so good news is that the strength is moderate and there are 3 Lemons. We acted on this information by not skiing slopes that reduced strength or exacerbated the effects of structural weaknesses. This was easy since the area we skied lacks slopes steeper than 32 degrees, there are no rock bands, and no obvious wind loading effects/features.
Temperatures during the day fluctuated between 28-30 deg-F. It was nice that the predicted hi of 34 deg-F never materialized due to overcast and obscured skies later in the day. Did you noticed the formation of a very thin layer of surface hoar in open slopes with N and NE aspects above the 6500 feet level? We need to keep an eye on that layer.
We had a fantastic day of skiing, but my 14 year old "knuckle dragger split boarder" son was almost KILLED by a falling diseased/dead tree. Suddenly without any warning a two feet diameter tree started to squeak and came down - he had the presence of mind to step back several feet saving his own life! He was VERY glad about not bringing his Ipod.Some of you that used the track I put in at Pilot's North side will have notice that this BIG tree was blocking the trail at the 6600 feet elevation. The wind was light at the ridgetop, and calm everywhere else in the hill - the trees are just overloaded with snow. PLEASE - BE CAREFUL! I do not know about you, but from now on I will keep my uphill track away from sick-dead trees overloaded with snow.
I have to say that although Mores Creek Summit area has surely changed - there were lots of NEW faces yesterday - I am VERY glad that MANY will enjoy the beauty of this area - and collectively treasure this Idaho gem.
Hey Carl and Irene - I was glad to see you yesterday. It has been a couple of years since I have seen you. Hope to see you more often in the backcountry.
Finally - WE NEED MANY OF YOU to step in and contribute to this blog. I will be gone for a week (Jackson Hole), thus I will not be able to provide updates for a week.
Pray for more snow - especially cold smoke!
Chago
