Slope

neilm · Joined: 12 Dec 2004 Posts: 388 Location: Kodiak, AK

I've heard that 35-40 deg is the most common slope for avalanche. Do most educated Tele skiiers simply avoid a certain range 100% of the time? Most of the time? Is there some rule of thumb that people use when it comes to slope? I have been skiing slopes around 25 deg but mostly because I'm still learning to ski and I find anything more to be intimidating. As I get better I'll be tempted to ski steeper stuff.

Neil

AltaPowderDaze · Joined: 06 Dec 2004 Posts: 689 Location: Snowbird

when the slope is unstable (or an aspect is suspect) and it can slide (25 degrees +) i usually avoid it. you should look into an avy class or read a few of the books that are out there. abc's, snow sense and staying alive in avalanche terrain are all good books with the latter being the most complete.

Gary Brill · Joined: 07 Dec 2004 Posts: 1717

It's not just about the angle. It's also about the slope size and consequences, and conditions, including layering and wind and sun effects. Sometimes (many times really) a steep slope on a wind or sun-sheltered or exposed slope can be relatively safe while a somewhat lower angled slope on the opposite aspect may be unsafe.

The size of slope, depth of the potential sliding layer, and terrain traps, cliffs, etc. all influence the likely consequences. I don't ncessarily mind triggering a slab limited to a relatively shallow depth if I know I won't get buried or carried by the slab. Trees are often a good answer to this dilemma, as are smaller slopes and many times crested slopes, where the debris from a slide will spread instead of concentrate.

Ava Blanche · Posted: Thu Jan 06, 2005 8:23 pm Post subject:

This has been the subject of much previous discussion, but here is the answer to your question:

This is a graph of avalanche occurrence vs slope angle. It shows that avalanches most commonly occur on slopes of between 38 and 40°. Note that avalanches are rare on slopes of less than 25°, and above 40°, snow tends to slough off before an avalanche problem is created.

But look at this graph of slope angle vs number of avalanche accidents:

This shows that most avalanche accidents occur on slopes of between 31 and 35°.

Why the difference? To make for a problem you need to have avalanche hazard AND people in the way. So between 31 and 35° you have the combination of a high enough avalanche hazard AND a slope that people like to ski.
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snowdynamics · Joined: 12 Dec 2004 Posts: 618 Location: Wasilla, Alaska

Let's not forget slope shape:

Convex slopes have a greater propencity for failure under similiar conditions.

Carry on.....
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Snowman · Joined: 06 Dec 2004 Posts: 791 Location: Ask Heisenberg

Ava Blanche · Posted: Fri Jan 07, 2005 12:20 am Post subject:

This is off the topic of the original question, but I do think that convex slopes have an extra element of hazard, and should be skied more cautiously.

Convexities most often reflect underlying topography- a steep slope rolling over to a more gentle one. They might also be formed by wind deposition.

But convex slopes are more hazardous because, unlike a straight slope, they are in tension due to the fact that there is more snow creep below the break in slope as compared to above. If a skier crosses this area of snow that is in tension, a fracture may be precipitated, which may then run into adjacent snow.

Another problem with convex rolls is that snow above the break in slope may be less deep, and therefore is more likely to collapse under the weight of a skier.

Finally, convex slopes are locally steeper, which increases their likelihood of being start zones.

But Jim's point is a good one: if a slope is really so close to failing, should you decide, on the basis of something as relatively trivial as its shape (convex or concave), whether you ski it or not? I hardly think so.
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funhog · Posted: Fri Jan 07, 2005 12:52 am Post subject:

About the only place I know you can go and have minimal worries about Avies is Manitoba Mountain on the Kenai. Eddies has Avys and that's probably the next safest place. I don't think Manitoba has ever had any. All of its slopes are below 28 and most are between 22 and 25. I hope that's not famous last words.

Maybe some other folks have ideas but if you're in avy terrain, its best to be prepared and have knowledge besides slope angles.

Sole heeler had a thread someplace that I can't find about the basic question you asked.
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Valdez Telehead · Joined: 06 Dec 2004 Posts: 1568

"Is there some rule of thumb that people use when it comes to slope? "

Yes there is a rule and that is to accurately measure your slopes with a slope-meter. Do not guess. Stay at or under 30 degrees under most conditions except Considerable to High, at least til your snowpack evaluation skills are improved either by expereince or Level One.

Skiers can be so obsessed with steep that they forget what a pleasure and option it is to ski at 25-30. I would think over a season, I may actually spend 15% of my time above 32 degrees. Its not always possible to just ski steep (like all the ski-porn stars seem to do!!) So get steep out of your head. Its about stability, not steep.

The #1 thing to know about a slope is its correct angle. Everything else come after that input.

My alarm alway go off at 30 degrees. I become a totally different BC skier.

Snowman · Joined: 06 Dec 2004 Posts: 791 Location: Ask Heisenberg

Gary Brill · Joined: 07 Dec 2004 Posts: 1717

funhog · Posted: Fri Jan 07, 2005 9:54 am Post subject:

Gary and Jim you are too funny.

Here's an avy looking from the North side of Manitoba. this was taken last weekend.

And here's a closer view...

so instead of Oklahoma maybe we need a license plate for Wisconsin?
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Kees · Joined: 06 Dec 2004 Posts: 324 Location: Nederland

There is a rule about these slopeangles and it is called the Munter reduction formula. But you won't make much friends with that rule in America Wink

Do not forget, not only the steepness of the slope at the point where you are skiing is important, you should look at the steepest part of the entire slope, even if you don't tread that part. There are some Euro rules to that too. Depending on the avy danger more or less parts of the slope are critical to you.

I won't go in more detail. This is just to add the international flavor to this forum.

hutguy · Joined: 06 Dec 2004 Posts: 7117 Location: Breckenridge CO

wow · Posted: Fri Jan 07, 2005 3:19 pm Post subject:

Reading through this thread it seems I'm blessed to be living where I do.
I ski slopes between 30 and 35 degrees just about everyday I ski.
Seldom carry a slope meter anymore but I did for years and have most slope angles I ski memorized. I also know which are most likely to slide and under what conditions.
Familiarity? Expert halo? Don't think so as the route changes based on the snow conditions.
Munter method? It's in my head but isn't called that. It's called common sense or maybe snow sense.
I'd suggest basing the what is safe to ski and what is not on the prevailing coditions in the area you live and either a knowledge of this or study and or a mentor who has experience with the conditions would be neccesary.

Not old, but getting there. Bold, only when the snow says so.
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