While speaking to Henry tonite he mentioned that he has an article in the Telegraph entitled “how to avoid avalanches”.

http://www.telegraph.co.uk/travel/snowandski/6980399/Ski-safety-how-to-avoid-avalanches.html

Henry’s key points are:

i. Learn about slope angles
ii. Look for signs of recent avalanche activity
iii. Watch out for wind-loaded slopes
iv. Study the avalanche bulletin before you go
v. Go one at a time where there is any possibility of danger
vi. Keep your tracks close together
vii. Look out for convexities
viii. Look out for what is below you
viii. Make sure you have the right equipment
ix. Know how your equipment works
x. Be comfortable with the people you are going with
xi. Keep your group size to between three and five people
xii. Keep thinking about what you are doing

Read the article for more details (link above) but before you do think about each point in turn and note (or even post here) your thoughts about what they mean. I was recently reminded about vii. when skiing over the top of a small rollover the slope broke away behind.

There was an interesting article in the ANENA publication Neige and Avalanches this month. The article discussed an avalanche in one of the Isola 2000 couloirs last season. There had been heavy snow accompanied by northerly winds. The top of the couloir had been stripped bare which witnessed the strong winds and the slopes on the other side of the hill were wind loaded. The skiers thought the couloir would be safe as it faced into the wind (although one skier had a “seat of the pants” instinct that the couloir was not safe:

point xiii. trust your or your buddies instincts, if someone has a bad feeling reappraise the route choice

of course in the mountains things are never as simple. The couloir was relative open and the north wind has cross loaded the left bank (again think of what Henry says, the couloir had deeper, better powder in the left side, why?). The slab broke where the couloir made a slight turn and the slope no longer had any support underneath (convex, then cliff) again Henry’s point viii.

More from Henry here: http://www.henrysavalanchetalk.com/

Slope Angles

They say 35 degrees is the critical angle for avalanches, you need a certain amount of angle to overcome friction with the sliding plane. Then again in the Munter method any slope with a 39 degree angle seems to be critical, presumably this is a trigger point which then sets the rest of the slope going?

This graph seems to agree with Munter

but I’ve triggered small slides on slopes less than 25 degrees, they key thing seems to be that in those cases there was an icy rain crust so maybe there is less friction?

I also heard you always need a weak layer that collapses (even if it is only very thin) to get slab release, a skier isn’t heavy enough alone to trigger a whole slab.

Jake from Planetfear should have read your article Henry

So why did I get avalanched in the Lakes? A simple lack of respect for the prevailing conditions. And now I have lost my skis, poles, goggles and hat, the avalanche snapped the waist and chest buckles on my rucksack, I have a dented pride and a knackered back. I have the necessary knowledge and experience to have prevented this and am disappointed in my own decision making process.

http://www.planetfear.com/blog.php?id=209

Bubb - 15 January 2010 10:32 AM

Slope Angles
They say 35 degrees is the critical angle for avalanches, you need a certain amount of angle to overcome friction with the sliding plane. Then again in the Munter method any slope with a 39 degree angle seems to be critical, presumably this is a trigger point which then sets the rest of the slope going?

but I’ve triggered small slides on slopes less than 25 degrees, they key thing seems to be that in those cases there was an icy rain crust so maybe there is less friction?

I also heard you always need a weak layer that collapses (even if it is only very thin) to get slab release, a skier isn’t heavy enough alone to trigger a whole slab.

The critical angle depends on the character of the snow, which varies locally, but much more regionally. In cold, recrystallized continental snowpacks like Colorado’s, for instance, snow won’t even stick to anything steeper than about 45-degrees, & the shallow snow pack is generally getting weaker all the time with many wind-affected layers which can act as sliding surfaces or weaknesses. By contrast, in warmer maritime climates snow will stick to much steeper slopes. And since the air temperature is relatively warm near the ocean & the pack deeper, layers tend to break down fairly quickly, leading to higher stability. In many places, like parts of Utah & the Alps, the snow pack starts out brittle & gets stronger as the season progresses & the pack deepens. Anywhere you go, soggy wet snow slides can happen on angles as low as 10-degrees. Local knowledge of your area is a good thing.

A lot of people get into trouble predicting slope stability with a slope-meter & their local avalanche forecast. Slope angles are a guideline to suggest where the biggest problems lie, not a precise prognostication. These slope angle bulls-eyes are just statistics. Who cares whether one gets caught on a 35 or a 39-degree slope? If it’s steep enough & you have reason to suspect instability then stay away that day--don’t diddle the numbers to let you ski a steep slope when you know in your gut you shouldn’t. One of the worst recent developments in skiing is the transference of psycho ski resort powder frenzy to the backcountry, & the abject unwillingness to let things settle for a couple days after a storm.

Hi Folks,

I’ve been trying to ramp up my knowledge recently on avalanches and ski safety, mostly through info posted here & through some books & DVDs that I’ve purchased. One issue that I’ve come across that hasn’t been explained fully is this:

In avalanche prone areas occasionally you can hear what’s described as a ‘whoomph’ noise, & if you do, you’re supposed to scarper fairly prompto. Can someone tell me:
- Is this the sound of a slide going? or is it just the sound of a slab unsettling or what?

- Also this sound is supposed to resemble the sound of a rider pulling a turn in nice powder, how can you tell the difference?

Safe skiing to all.
D

Daithi - 05 February 2010 07:06 PM

Hi Folks,

In avalanche prone areas occasionally you can hear what’s described as a ‘whoomph’ noise, & if you do, you’re supposed to scarper fairly prompto. Can someone tell me:
- Is this the sound of a slide going? or is it just the sound of a slab unsettling or what?

- Also this sound is supposed to resemble the sound of a rider pulling a turn in nice powder, how can you tell the difference?
D

Usually you hear the whoomph on the skin up, in a flat meadow for instance. You often will also feel the snow drop a little as the weak layer fails & drops the snow above. I don’t know about “the sound of a rider pulling a turn”...whoomphing sounds kind of like distant canon fire, or a belly-flop into a feather bed. If you are just riding lifts & skiing off-piste rather than skinning, you may never hear this & will have to use other clues to instability...like fresh avalanches from natural triggers or ski area explosive control, for instance.

Whoomphing is a clue that there is a buried weak layer(s)--often surface hoar under the latest snowfall, or depth hoar near the ground--& that you should think very carefully about its distribution before getting onto steeper slopes. If you are already on a steep slope when this happens, there won’t be time to run--that’s the sound of the slab breaking free & starting off downhill, although when it happens on a steep slope, it usually sounds more like a muffled pop to me as the crown separates.

Test slopes are a good place to learn these things. Find a steep, very short hill with an open runout rather than a narrow gully at the bottom: wind-loaded rolls, or mountain road cutbanks are good during or right after a storm. Jump or make ski cuts from the top to trigger avalanches. Stay away from large fresh cornices until you have a better feel for how big is too big & how far back they can sometimes break. Bring a friend with a shovel--even very small slopes have killed people.

Thanks FF,

Useful info & interesting too. I hope I never have the ‘pleasure’ of hearing a ‘Whoomph’ in the backcountry.
D

BTW your point about ‘even very small slopes have killed people’, is one that is often lost on people relatively new to off piste. Also people seem to think just cos you’re near a piste then you are totally safe, again not necessarily true. This was evidenced in that unfortunate death in the White Out in Le Tour at Christmas, people can die in relatively small gullies just by the piste.

This point was brought home to me a few years back in Chamonix. I was relatively new to the joys of off piste& I was skiing with a very experinced and good off piste skier. We had been doing several GM itineries, and Pendant La Combe & so on for a couple of days, when we got a real white out day. For those who know them we were skiing the 4 little off piste gullys underneath the chairs above the Plan Joran Restaurant. My ski buddy stopped me going into one particular gully full of lovely fresh powder, and asked me had I a fall back plan if the cornice came down, i.e. did I know which way I’d try to bail out & so on? I remember feeling awkward & saying something foolish along the lines that the ledge is only 12-15 feet high and its unlikely to come down & even if it did that surely it wouldn’t cause any damage. His response was ‘So, it can still kill you’, and ‘always assess each gully you are entering & have a plan for your way out if you feel it going’. I haven’t forgotten that advice yet anyway

The article makes lots of important points.

My two problems with it are:

* It gives no hint of how complicated it can get to apply some of those principles out in real skiing situations.

* thus little hint of the critical importance of taking a multi-day on-snow course in avalanche safety, and then going on several tours with very experienced partners to get a feel for how the game really works in real skiing situations.

I wish reading the article by Henry S had made a more urgent case for spending time on-snow with Henry S.
____________________________

I disagree about a specific point:
“group size between three and five people ...
If there are more than five of you, the group can become fragmented”

This contradicts thinking of some of the best American avalanche experts and backcountry skiers about the “human factors” risk—the danger of “herding” or “groupthink” resulting in bad decision-making by parties of five or more. This thinking says that five is often already too large a group (without a professional guide) for sound decision-making about avalanche risk, and that intentional (perhaps also unintentional?) splitting of an unguided group of 5 or more could be a _good_ thing in that regard.
e.g. Bruce Tremper p261: “Two is the perfect number ... I almost always keep my groups at four or less ...”
e.g. Andrew Maclean in a magazine report about an avalanche accident, identifying the large party size of 5 as a contributing factor.

Ken