Feburary 5th 2012
Justin and I went for a flight around the Wheaton Valley and White Pass areas today get a better idea of the scale of the natural avalanche cycle that happened last Friday.
In the Wheaton Valley area we saw numerous natural slab avalanche size 2-2.5 which we suspect had released in the storm snow on unsupported ridge top wind loaded features on North aspects and cross loaded mid slope features on East and west aspects. The crowns and debris from these avalanche were easy to see suggesting the ran towards the end of the storm cycle. typically ran almost full path (up to roughly 400 vertical m) and were confined to their historical track where there it looked like they entrained a significant amount of snow as they ran. We also saw evidence of a couple of avalanches which had released in lower angle slopes near ridge top triggered by cornice failure. In one notable instance above Hodenet Lake between the Wheaton and Whatson drainages a an slab had propagated about 100m along the ridge line crossing several distance breaks in the terrain. Upon closer inspection I'm suspect cornice failure triggered a step down avalanche, likely on the underlying wind windslab on facets from earlier in the month. This hard lab has the stiffness to propagate failure over larger distances. From what we saw I think this was an annomoly but is a good reminder that in the right spot failures on deeper instabilities in the snow pack can still be triggered.
A significant avalanche cycle occurred in white In the White Pass on similar features although it was not as widespread as in the Wheaton. I suspect this was due to more supportive nature of the terrain at the pass (larger more uniform slopes with fewer likely trigger spots). Given the amount of snow hiding the debris I think the cycle likely happened earlier in the storm. That said I would still be treading cautiously around any unsupported wind loaded slopes. Deep and difficult trail breaking and shooting cracks are signs of instability to look out for.
Feburary 8th 2012.
Justin and I spent the day in the Fraser / Byrant Lake area today trying to get a handle on what was going on in the snowpack after last weeks avalanche cycle. Here's what we found.
The snow pack:
In sheltered areas at treelike the snow pack is roughly 160cm deep. The 50cm of snow that fell in the storm has settled into a 30cm thick soft slab. This is sitting on a slightly less dense layer above the wind crust from the cold snap in January. Bellow this the mid pack continues to gain strength. At the bottom of the pack: the mid December facet/crust combo sits on top of large week facets. In snow pack tests we found two weakness in the storm snow. One interface within the storm snow popped under moderate load (from the elbow). The interface below the storm snow popped under a hard load (from the shoulder). Given the softness of the slab we didn't investigate any further. Interestingly we couldn't find the rain crust I was anticipating at our weather plot (850m) where the temperature reached +2C during the storm.
On our flight earlier in the week we saw that most of the recent avalanche activity occurred on steep unsuported north aspects above treeline so we wanted to cheep up on how this previous instability was developing. We dug on a wind loaded north aspect just above treelike with a large fetch where we found a 70cm thick hard wind slab. In a compression test this slab popped under moderate loads but was un-reactive in an extended column test. I suspect this was due to the fact that the slab was hard enough that the larger column was supporting itself in the ECT. That said the moderate compression test result showes that the interface bellow this slab could potentially avalanche if triggered from the right spot (shallow / week areas)
Gaining confidence we decided to take advantage of the high cloud ceiling and get into the alpine. We climbed a north aspect taking care to avoid larger convexities and unsupported slopes and also space out appropriately when traveling through areas that looked as if the snow pack was thinner (around rocks and at the base of cliffs). We found the supportive slab made for easy and fast travel on the way in and up and "buff" skiing on the decent.
Winds were moderate to strong from the north and we observed moderate snow transport through out the day indicating a pattern of reverse loading. I suspect that a soft slab is developing on south aspects right now.
Feburary 9th 2012
Today Justin and I skied a traverse around Feather Peak with a short detour to the Cleveland ski summit. It gave us a good opportunity to travel on a variety of aspects through all the elevation bands and see a lot of terrain.
The only notable avalanche observation was a recent size 2 slab avalanche mid slope on the North face of Cleveland proper triggered by collapsing serac.
Like yesterday the wide spread supportive wind crust made for easy and fast travel. Winds were consistently moderate gusting to strong from the north throughout the day. We stuck to bigger features to avoid thin spot triggers on any of the normal wind loaded aspects. Our concerns from yesterday about reverse loading on southern aspects was confirmed. Climbing the south facing slopes back onto Feather after skiing the west glacier of Cleveland we found isolated pockets of a 30cm deep soft slab just below ridge line. Although we didn't see any of the classic signs of instability such as shooting cracks the slab was easy to detect. We were conscious of terrain traps and adjusted our route or spacing accordingly whenever we felt the trail breaking get tougher.
All in all a great day out in the mountains.
Feburary 10, 2012
Today we were in Powder Valley which we have found often remains relatively sheltered from the North winds like we have had all week.
We found the storm snow here to have settled in to wide spread soft slab, with isolated pockets of wind slab in alpine.
We dug a pit at tree line and found a similar instability in the storm snow to that which we found at Fraser earlier in the week. Again this interface popped under easy loads. The mid pack was starting to become less faceted and surgery. The most interesting observation was a failure in the facets above our December 5th rain crust now down al little over a meter. This deep instability dropped under a moderate load (tapping from the elbow) in a compression test. It was too deep to get a good result on with the extended column test but a propagation saw test indicated that this layer wants to propagate a failure when initiated (see the video on our Youtube channel - yaacactech).
Although in the past we have found this layer to be less widespread in Powder Valley that it is around the White Pass, our result today showed that where it does exists this persistent week layer isn't quite asleep yet and presents a classic low probability high consequence avalanche problem. We managed the hazard by "skiing the fat" avoiding thin spots in the snow pack where triggering a deep slab is more likely.
Temperatures were warm throughout the day, we saw one fresh sz 1 slab avalanche on a SE cross loaded feature along the highway corridor at treelike. It had been triggered by loose snow coming out of the rocks above. Winds at ridge top looked to be moderate from the South West with light snow transport.
February 17th, 2012
Eirik and I spent the day flying the forecast region, trying to get some snowpack data from harder to reach places. Poor visibility and weather didn't allow us to get everywhere planned in the White pass region, but we were able to see quite a bit.
White Pass (deep snow region)
Snowpack observations from East side of the highway in the big blue area. North Facing, 1500m elevation in the alpine. Height of snow was 255cms and seemed to be representative of similar slopes in that area. 20cms of storm snow overlied a well consolidated, supportive mid-pack composing of rounds. Probing did not reveal the Dec 5th crust at this elevation band. Compression results revealed E to Moderate results within the storm snow.
Observed a Small Natural solar cycle, on South-South East aspects, size 1-1.5 loose and soft storm slab. Suspect this activity ran on Wed PM/Thurs AM.
Powder Valley / Transitional snow region
Observed several Natural soft slab avalanches size 1-2 in the recent storm snow from steep, North to East facing terrain. The crowns ranged from 10-20cms.
*of special note, we observed numerous cornices failures in the region, likely failing during the warm temperatures and mod/strong southerly winds on wed PM/Thurs AM.*- Cornices will continue to be fragile if warm temperatures persist into the weekend, best to give them a wide 'birth' when travelling on ridge top or on slopes below them.
Wheaton Valley / Shallow Snow Region
A widespread (1F-P) hard slab/crust is supportive in the alpine. The mid-pack is made up of facets that are gaining strength (1F-P) and weaker facets can be found to ground. Typical snow distribution is scoured southerly aspects and anywhere from 80-110cms on lee aspects. Compression tests produced Moderate "pops" down 25 below a older wind slab on facets and Moderate results on the basal facets, down 85cms in this location.
Natural activity was less than regions to the south, but a few size 1-1.5 natural avalanches were observed on steep lee features.
Just a few photos of the widespread, large Surface Hoar in Powder Valley.
widespread in sheltered areas at treeline
But also large and widespread in alpine on ridgetop/summits (this photo taken at 1800m)
February 29, 2012
Just a quick note on our snowpack observations today. Observations from Fraser Weather Study Plot, 900m, sheltered location.
15cms of low density storm snow sits over a very small layer (quite broken and hard to recognize) layer of Surface Hoar, down 18cms. Likely this is the layer buried on February 21. This layer produced consistent Moderate "pop" results to compression tests. We have noticed significant stregthening of the mid-pack throughout February with relatively mild temperatures. The Dec 5th crust is still present (down 115cms) with facets above and below to ground.
We will continue to watch the Feb 21 Surface Hoar layer and subsequently other SH layers buried that are currently on the surface.
March 1st 2012.
Today we were in the Fraser Lakes area. Some good skiing to be had on the north faces where we found the old windslab to be bonding well to the mid pack.
Our major concern for the day was the Febuary 21st persistent week layer. This is showing up as a layer of surface hoar in sheltered and shaded features bellow TL and as a sun crust with overlying facets on steep south aspects. The recent north winds have loaded these south aspects with a hard wind slab on top the crust now down 40cm which we felt was primed for human triggering. We saw one example of a recently snowmobile triggered size 1 avalanche at TL and we suspect similar conditions exist on the bigger features in the alpine.
Given this concern our travel strategy today was to avoid bigger steep wind unsupported south facing slopes and to remain aware of terrain traps on smaller south facing features. Remember hard slabs are notoriously hard to predict and are often triggered from bellow where they are often thinner and less supported.
Check out out latest video on our youtube channel- Eirik
March 2nd, 2012
We traveled in the Transitional snow region today, Powder Valley and Paddy Pass. Yesterday's concern was the Feb 21 Crust and Facet combo on South Aspects in the White Pass region, where as today our primary concern was the Feb 21 surface hoar layer on North and East aspects. Our goal was to determine the load overtop of this SH layer.
We dug in an alpine, wind loaded location at 1500m, North Aspect. The pit revealed 20cms of storm snow on top of 50cms of old hard wind slab (1F-P). This hard slab sits over top of the Feb 21 surface hoar layer, down 65 cms in this location (shallower at Treeline elevations) . The surface hoar also sat on top of 5cms of facets and then hard mid pack of rounds below. This interface produced moderate and "drop" results to both compression tests and Extended Column Test, showing that propogation is likely.
The same message yesterday applies again today, were dealing with a persistent slab avalanche problem. Hard slabs are difficult to predict and surface hoar is renowned for remote triggering (meaning triggering the avalanche away from the actual start zone, could be from below or adjacent). DIscipline is the answer, avoiding large North and East facing slopes in this region.
Check out our latest youtube video regarding this problem.
March 3, 2012
Spent the day on the east side of white pass Found similar conditions to what we found on the west side earlier in the week. Deep snow and great boondocking in the meadows, more wind effected snow in the alpine. Eirik