Public Field Report

Observation Date:

December 8, 2019

Submitted:

December 9, 2019

Zone or Region:

Banner Summit

Activity:

Skiing/Snowboarding

Location:

Copper

Did you observe any avalanches?

Yes

Avalanche Type:

Soft Slab

Size:

Size 2: Could bury, injure, or kill a person

Elevation:

Summit of Copper - approx. 8900

Aspect:

Comments:

Peeking into the North chutes off of the first summit of Copper, distinct crowns were observed with varying depths of 12-24 cm

Access to the beds layers seemed tricky so we didn't investigate further. However, cornices have began to form on windward sides above North/Northwestern slopes. It appeared that cornices have broken off in some areas possibly causing or assisting avalanches on these slopes.

None reported

It was interesting comparing the recent observations at Copper. One before the recent storm (Dec. 5th) and the latest from SAC from yesterday (Dec. 8th). If there is one word to describe our current snow pack it would be "variable". It was hard to get a general read on the snow pack working up the main ridge to the summit of Copper. Layering and crust structures differed greatly between small changes in aspect and elevation, this made us more worried about the lurking dangers in our terrain choices.

In contrast to SAC's forecast, we did not experience significant cracking or whumpfing, but this may be due to our very conservative terrain choices. Mainly keeping to the ridge, which carried little snow due to wind scour and low angle slopes (3mm) sits beneath crusts of varying thickness. New snow from the weekend storm felt uniform and well consolidated. While the rotten layer poses a significant problem we were quite interested in seeing the effects of well documented surface hoar from the previous observations at Copper.

We had some trouble finding appropriate pit areas with the thin snow pack, running into grass and debris, we may have been better suited to dig at higher elevations. Settling on a North West slope with a shallow incline of around 25 degrees around 8200 ft.

Total Snow Pack - Approx 70 cm
SH layer at 40 cm
Sept/Oct Crust at 20 cm
Rotten DH 0-20 cm

CT9 weak break at SH 40cm
CT20 at crust

ECT6 no propagation at SH 40 cm
ECTP12 full propagation at 20cm ("low energy" is that still a term?)

Where new snow has fallen in protected areas (i.e. no wind and lower elevation), consolidation and water content appear to have created a cohesive layer above previous ice crusts and new SH layers. The SH layer we encountered was very subtle and not very reactive, but still was visible in stability tests and is most likely more prevalent at higher elevations where SH size was reported to be larger.

Avalanches were observed on the northern slopes off the summit of Copper, stretching the full length of the summit itself. It did not appear that these were the same caused by cornice breaks from SAC crew traveling in the area but looked very fresh and quite scary. We carefully approached the notch between the two chutes to look at the starting zones and their significant crowns.

All in all, it seems to us the worst is yet to come. Rotten layers with poorly bonding crust interfaces will continue to be an issue for the foreseeable future, and will most likely become more reactive as the weight of the snow pack increases.