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Are We Setting The Stage For a Major Avalanche Cycle? #2113
Back To Discussion List Written: 2008.12.20 by: Frank W. Baumann

It has been bitterly cold for days now in places like southwestern B.C., but there is still not a lot of snow present. For example, Whistler is reporting a 64 cm snow base at 1650 m elevation, and a current temperature of -20C. Near surface faceting, a very common process that produces weak layers in the snowpack, occurs when there is greater than a 0.1C/cm temperature gradient in the snowpack; the higher the gradient, and the longer it is active, the more pronounced will faceting be. So right now at Whistler, the temperature gradient is more than 0.3C/cm; or three times what is required for faceting to proceed- and it has been that way for many days now! Now faceting proceeds most rapidly in loose, low density snow- so areas where a hard crust is present may not be faceting as much as less wind-affected areas. But be warned: when the next big snowfall comes, especially if it is not proceeded by high winds (that tend to destroy facets exposed on the snow surface), there WILL BE a major avalanche sliding cycle; the more snow that falls, the worse will be the hazard. For more details, see this related article on Bivouac regarding avalanche formation and snow metamorphism. And, of course, as always, check the CAA Avalanche bulletin- but make sure you also read the text-portion where critical information on faceting and persistent weak layers is usually described.


Comments

#1154 - 2009.01.24 Frank W. Baumann - Before you think it's safe to go back into the mountains.....
After extensive, possibly unprecedented, avalanche control work, the Peak and Symphony chairs at Whistler are finally supposed to open this weekend.

This means that the Pro Patrol is confident that they have either artificially triggered avalanches on all slopes within the ski area boundary that could potentially slide, or that any remaining snow overlying the weak facet layer has enough bridging strength, and is therefore unlikely to slide.

In other words, the forecasters are confident that the avalanche Hazard (the probably of either triggering an avalanche or having them occur) is now only Moderate. The Whistler Ski Patrol is one of the best in the business and have a perfect track-record- there have been no avalanche deaths within the ski area boundaries since the mountain opened in 1965- so I am confident they are right. I certainly would have no hesitation about skiing within the controlled ski area, and telling my kids to board at 'er!

However, if an avalanche does occur, it is still likely to run on the facet layer and therefore involve a full-depth release; that is, be big and life-threatening- which is why the Consequence (the impact that an avalanche would have if it released) is best described as being High on a typical in-bounds, steeper, longer slope frequented by skiers or boarders.

So given a Moderate hazard and a High consequence, the Risk (Hazard x Consequence) would be Considerable.

This is a very important distinction to make: winter recreationists should always focus on risk management, rather than hazard management. This is explained in more detail in this article available on Bivouac: snow avalanche risk management.

HOWEVER, there is one important caveat in all of this: the avalanche hazard at Whistler is only Moderate because of all the avalanche control that has been done; that is, because the Whistler Pro Patrol is doing its usual exemplary job of managing avalanche hazard.

In the backcountry, there has been no bombing, and so there is a much greater probability of triggering an avalanche; that is, I would suggest that the Hazard is in fact higher- and likely much higher because of the continuing presence of that weak facet layer- especially, as Scott correctly notes, in areas of shallow snow. If that is not the case, then the Whistler Ski Patrol has just wasted an awful lot of money on unnecessary avalanche control (bombing)- not likely, given some of the amazing slides that have occurred with only small hand charges!

Bottom Line: given this winter's very unusual snowpack, I would continue to be extremely cautious when going into the backcountry- especially if I'm on a snowmobile testing the bridging strength of an awful lot of terrain in a typical day! Since there is a direct relationship between slope angle and avalanche occurrence, the easiest way to reduce the hazard is to stay on lower-angled slopes.

#1153 - 2009.01.24 Wilf LeBlanc - the forecast
Here is what it said (south coast):

"Although the probability of triggering the deep persistent weak layer (PWL) is declining, the consequences of triggering remain high".

At some point, depending on what is overlaying this PWL, it becomes harder for a human to become an effective trigger. Of course it is still there, and still possible, but it is harder to get it moving.

Frank, I think you are keying on the consequences (which ARE bad) rather than on the probability of actually triggering a full depth release (which is lower now than it was). Obviously this PWL will probably hang around all year and the risk of a small slide turning into a massive one will likely always be there. As the cornices get bigger you probably don't want to be lingering underneath them (although most avalanche fatalities are triggered by someone in the party, the percentage isn't that high).

#1152 - 2009.01.24 Scott Nelson - Moderate means avalanches are possible.
Frank, you said it several times in your post - Human triggered avalanches are possible. That's the definition of moderate avalanche hazard. From reading the bulletin it seems it would be very wise to avoid shallow rocky areas right now because of the potential of triggering a large, deep avalanche (like the surf's up slide on blackcomb last year).

#1151 - 2009.01.23 Frank W. Baumann - Avalanches can still be easily triggered- so why is the Danger Rating only Moderate?
The avalanche forecasts rate the hazard in SW B.C. as being Moderate (Natural avalanches unlikely. Human triggered avalanches possible).

But the forecast also warns that the Dec 6 facet layer really hasn't changed, and so the possibility of triggering large, full depth avalanches is still very real.

Personally, as long as that facet layer is still there, I will continue to ski cautiously, as if the avalanche danger rating is still HIGH. This is because I think it's important to place a much greater emphasis on the possibility of TRIGGERING an avalanche, rather than just worrying about the FREQUENCY of avalanche activity.

#1144 - 2009.01.19 Frank W. Baumann - The January 11, 2009 Fatal Avalanche near Chetwyn.
This involved a snowmobiler who was wearing an ABS Airbag- but was not able to deploy it before he was buried and killed. Four other snowmobilers in the party of 14 were also completely buried- so the death toll could have been much higher. One obvious question here is why so many snowmobilers were in the slide path at the same time.

#1143 - 2009.01.19 Frank W. Baumann - Another death Saturday- now 16 in Canada this season.
Sadly, another snowmobiler was killed near Tumbler Ridge on Saturday, January 17 by a slide apparently started while the group was high marking. High marking (going straight up a steep slope, and then suddenly hooking around and going back downhill) is particularly dangerous during times of high avalanche hazard because it takes a rider into the steep, starting zone of a potential slide path, and then creates a sudden, large disturbance by placing a relatively large load on the snow- which can then trigger a slide.

Once a slide starts, it can rapidly propagate (especially if the snow is dense) and involve a much larger mass of snow.

But never mind the physics- an accident like this, in my experience, brings immeasurable suffering to the next of kin of the victim. This is what is so often forgotten in the headlines- the immense human cost of such tragedies that makes any efforts to prevent these accidents worthwhile and should be a sobering reminder to all of us to be careful- and think more about the impact on loved ones that an accident has.

#1142 - 2009.01.18 Steve Grant - Someone playing Russian roulette
Yesterday, rather than break trail on the flatter area below the steep east face of Columnar Peak at Diamond Head, a solo skier broke their traverse track halfway up the steeper higher portion of the face. There's absolutely no reason to do this, let alone in these avalanche conditions. On their way back, they cut a higher line to get some turns down the face. Amazing.

#1141 - 2009.01.18 Frank W. Baumann - Be wary like a long tailed cat in a room full of rocking chairs
I was skiing in the Whistler-Blackcomb area yesterday and wanted to pass on a few comments. The pro patrol (some with over 35 years of experience) is still extremely worried about avalanches- much of the high alpine is still closed, they have "hard" ski area boundary signs ("Closed- passes revoked") everywhere, and full time guards are posted at key locations to make sure people respect the closures. This is somewhat reactive since it only occurred after two people ventured into avalanche areas from the ski areas and were killed. However, despite these extraordinary measures, some people are still determined to sneak into closed areas, or are skiing the steepest lines they can find within the ski area. Personally, I am very wary- under these very dangerous avalanche conditions, just because avalanche control (bombing) has been done and an area is accessible is not enough reason to ski it. There have been too many post-control avalanches this year, so why take a chance? So I personally am staying off any steeper slopes (>30) right now, especially those big north-facing bowls, wearing my transceiver even if skiing in-bounds, and generally adopting a European-type approach and staying mainly on marked runs (piste skiing). If you're going into the backcountry, you need to be even more wary- I suggest staying off any 25 or steeper slopes (don't guess- carry a clinometer!!), and out of any area of previous avalanche activity, and beyond a 25 runout angle as measured from the top of a potential starting zone. It is guaranteed that more people will still die this year in avalanches- please don't be one of them.

#1140 - 2009.01.17 Frank W. Baumann - Another death Friday- now 15 total in Canada
Another snowmobiler was killed in an avalanche Friday, January 16. At Whistler, none of the alpine areas are open because 35 year veterans of the pro patrol are just too concerned about pockets of remaining unstable snow- and these people are the best in the business! A massive avalanche came out of Whistler Bowl earlier this week- triggered by just a small hand charge!

#1139 - 2009.01.09 Frank W. Baumann - Avalanche Awareness Day at Red Heather
BC Park Rangers in the Diamond Head area of Garibaldi Park above Squamish will be conducting an avalanche awareness session this Saturday and Sunday, January 10 and 11 at Red Heather shelter. No time is given.

#1134 - 2009.01.03 Frank W. Baumann - HIGH (revised) Avalanche Danger Sunday and Monday in SW B.C.!
A major storm and rising temperatures will increase the avalanche danger to HIGH on Sunday and Monday. Note that HIGH or EXTREME hazard means that not only is there more frequent avalanche activity- but there is a greatly increased probability that YOU will trigger an avalanche. This is an important distinction to note: being hit by an avalanche means you have to be in its path just as it releases to be affected- Russian Roulette. But when conditions are such that you will trigger an avalanche, there is essentially a 100% chance that you will be in the slide when it releases.

And remember- every new storm places more and more load on that weak Dec 6 facet layer at the bottom of the snowpack.

#1132 - 2009.01.01 Frank W. Baumann - A skier and a snowboarder have been killed in separate avalanches at Whistler!
As more and more snow accumulates on the early season facet layer, there will be more slides, and the potential for even more avalanche deaths. One of the fatalities was on Dec 31, 2008 in Ruby Bowl on Blackcomb (closed and marked as having a HIGH avalanche danger); and the other occurred today (Jan 1, 2009) on Harvey's Run at Whistler; again, a closed run.

This is a year when it is extremely important to be extra cautious! Please make a point of discussing this situation with all of your winter recreation friends- if they don't have extensive avalanche training and experience, they are better to stay in-bounds at ski areas and out of the backcountry.

#1129 - 2008.12.26 Frank W. Baumann - Avalanche Incident, Dec 24- Mt. Seymour
http://www.ctvbc.ctv.ca/servlet/an/local/CTVNews/20081226/BC_lucky_escape_skiers

B.C. couple lucky to survive avalanche drama
Updated: Thu Dec. 25 2008 23:19:35

ctvbc.ca

Two B.C. skiers are lucky to be alive after straying off track in the Mount Seymour area north of Vancouver. The couple had to dig themselves out from under an avalanche before making it back to safety on Thursday evening, along with another man who had got lost on the same mountain.

The couple, and one other lost person, were rescued by North Shore Rescue.

#1127 - 2008.12.24 Frank W. Baumann - SW BC Avalanche Danger Increasing
Heavy snow is falling in the Lower Mainland, and the avalanche bulletin is predicting that the avalanche danger in alpine areas in Sea to Sky country will rise to Considerable by Thursday and HIGH by Saturday. Given the conditions, I would strongly suggest that parents should remind their kids to stay within the ski area boundaries over the next few days. If you're an experienced winter recreationist, you need to make sure you are extra-careful in deciphering the rather complex snowpack structure that is presenting itself right now.

#1122 - 2008.12.22 Jason Holliday - But for the rest of the season...
True the best riding is on the smooth slopes (permanent snowfields etc) and these will be avalanche prone for a while due to this layer, but once things fill in elsewhere I'm less concerned that this layer will be a 'lurker' most places expect the permanent snow, meadows etc. Still, need to watch it to be sure.

#1121 - 2008.12.22 Scott Nelson - Smooth slopes make the best riding
Slopes with smooth ground cover makes the best riding right now, so you may have to choose between fun and avalanche safety.

#1119 - 2008.12.21 Frank W. Baumann - Where the problem lies....
I agree- ground anchors have to be covered before there is a more serious avalanche problem- usually, this requires at least a metre of snow. However, the so-called "surface roughness depth" is far less if the new snow is on a glacier, summer firn, or uniform alpine meadow slope. So you need to consider four important things at this time of year: how smooth or rough is the underlying surface on which the early snow is resting, how deep is the snow, is the early winter snow faceted and therefore weak; and is there (or could there be) a cohesive slab resting on the weak layer. Remember always- the avalanche is like a terrorist-it only needs to be right once!!

#1117 - 2008.12.21 Jason Holliday - lots of anchors around still
I agree that this faceting may be a problem (saw it first hand yesterday), but there is so little snow in most places that the pre-storm snowpack it is still penetrated by many anchors, even in the alpine (with the exception of the north shore which seems to have by far the most snow of any area on the south coast). I have no doubt that there will be some slides in wind loaded terrain but am thinking this won't be nearly as widespread as if it were a normal year (and the faceting was happening on top of a 2 or 3 metre snowpack).

#1115 - 2008.12.20 Frank W. Baumann - Be very careful out there!
Avalanche observers are becoming increasingly concerned about the potential for very large avalanches over the next week or two if significant amounts of snow are deposited on the thick unit of near surface facets that has now formed in many areas of the Province.

The North Shore mountains above Vancouver and mountains in the Sechelt Peninsula will be the first to be affected- the Environment Canada Alpine forecast for Mt. Seymour is calling for up to 25 cm of snow over the next day, and winds of up to 50 km/h. All of this snow will be deposited on a pronounced facet layer that is present in the upper portion of the snowpack. This is a very unusual and very dangerous facet layer that is not often seen in southwestern B.C.

If you're planning on touring- go Christmas shopping instead. If your kids are up skiing, make absolutely sure they don't wander out of bounds. And if you're a ski patroller- get those probe packs dusted off.