TR: San Juan Avy

[Hugh Jass]

In the interest of public education and discussion, here is a recent experience to share:

Last Friday, after a day inbounds at Silverton, two friends and I toured across the road from the Silverton base area. I don’t remember the drainage, and don’t have the topo in front of me.

According to CAIC, the avalanche danger in the Southern San Juan zone was MODERATE on N-NE aspects near and above treeline and LOW on other aspects and below treeline. Having skied similar aspects the day before inbounds at Silverton, we saw bulletproof conditions from the previous week of warm weather, with 4+” of new snow on top. We did not observe any sliding of that new snow on N-NE aspects inbounds, but on S aspects, the 4” that fell Thursday night was “sheeting” on the harder layer.

Having a healthy respect for the San Juan snowpack, but feeling reasonably good about the forecast and our observations the day before, we headed out on a bluebird day. 14 degrees at the trailhead, with high-20s in the forecast. We skinned up the ridge, and topped out one peak N of the billboard across from Silverton’s billboard.

We planned to ski a slide path N-NE aspect, generally hugging trees skier’s right, with plenty of safe zones and duckable options. We discussed safety protocol – skiing one at a time, SZ to SZ, and spotting one another. I put in 3 big ski cuts near the top, and nothing moved. We did not dig a pit, for the following reasons:
a) the CAIC forecast
b) nothing moved on ski cuts
c) pole testing yielded no suspicious layers

I’m not defending this decision at all. I am typically very conservative, and swear by the rutschblock test. Despite the obvious pow in our line, I think we were exhibiting a “spring skiing” mentality, given the CAIC forecast and recent extended warm temps. Heuristic factors, to be sure.

We skied the line, using safety protocol described above, bailing out about 200’ vert above the bottom of the drainage. Knee to mid-thigh deep pow, ranging from 35-38 degrees. It was good. We skinned back up a treed ridge parallel to our descent for another go at it. Skied down to our previous bail-out point and assessed what to do.

The slide path we were skiing steepened, with a small convexity near the bottom. It curved a bit, making the true angle and severity of that convexity difficult to determine. At the bottom, the force of slides had “cupped” out the drainage, forming an obvious terrain trap. Given these factors, we opted to traverse skier’s right, where we got into a sparse stand of 3-5’ tall trees. The idea was to get onto a slope with more anchors, and avoid the terrain trap below.

We traversed this lightly treed slope one at a time, spotting one another, regrouping in a full-size stand of trees to skier’s right (too thick to ski down through). Our third member triggered the slide, which broke about 10 horizontal feet above him. Hard slab, 3’+ crown, about 100’ across. He yelled to attract attention, chucked his poles, got his avalung hose in, and started fighting. Me and the other guy had a clear spot on him, and shouted various forms of encouragement. He hit one tree before latching on to another and hung on. The slide ran about 150 vertical feet to the drainage below. He traveled probably 50 horizontal feet and maybe 30-40 vertical before arresting.

Once we established he was OK, he skied the bed surface to the bottom. Me and the other guy gingerly traversed one at a time back skier’s left, to the bed surface, which we skied to the bottom. We assessed the slider quickly for injuries, then spaced out and made a run for the drainage exit.

The slide ran on at least a foot of sugar at the ground. We took a few quick photos, but generally got out without a lot of observation and analysis. The fracture occurred on a 30ish degree slope, but ran over a bulge which steepened to 40-45 degrees before hitting the bottom of the drainage. My general feeling is that snow conditions were worse close to the bottom of the drainage, which given its generally parabolic shape, was prone to a lot of sun reflection. I can’t say for sure, but I think the rotten layer did not extend higher up the slope.

Regardless, a few final thoughts and take-aways:
a) Our lack of pit/block test notwithstanding, I think our general observance of safety protocol was good.
b) We all traversed the same track, and it was the last and heaviest guy who triggered the collapse from above. His position in line, his weight, and the fact that he was on the narrowest skis in the group may have contributed to the removal of support, which initiated the fracture just above.
c) He would have certainly been at least partially buried, and given the slide ripped down to the ground, the probability of him experiencing some trauma from collisions with stumps, rocks, trees is high.
d) As Dawson’s blog notes yesterday, trees may not serve as anchors, but could present obstacles to collide with.
e) We had never been in this area, and our lack of knowledge drove us to the trees. If there was a better exit, we didn’t know about it.
f) The slider was wearing a BD Anarchist avalung pack. He claimed a higher level of confidence that things would work out once getting the hose in his mouth. I have the same pack. Our third now plans to buy one.

There you have it. Insight and constructive criticism is welcome. If nothing else, take from this that vigilance is always a requirement, no matter what the forecast.

[lemon boy]

thanks for the post hugh, scary indeed.

[pechelman]

damn.
excellent writeup.
glad everyone is ok.

gonna add this to the tgr torrents.

[Ermine]

The slide ran on at least a foot of sugar at the ground. We took a few quick photos, but generally got out without a lot of observation and analysis. The fracture occurred on a 30ish degree slope, but ran over a bulge which steepened to 40-45 degrees before hitting the bottom of the drainage. My general feeling is that snow conditions were worse close to the bottom of the drainage, which given its generally parabolic shape, was prone to a lot of sun reflection. I can’t say for sure, but I think the rotten layer did not extend higher up the slope.

Glad everyone's ok. Something I've noticed over the past few years of living in the hills is that the valley bottoms are colder during clear weather (due to inversions), there's less snow depth, more TG at work and more surface hoar.

[Bunion 2020]

In the interest of public education and discussion, here is a recent experience to share:

Last Friday, after a day inbounds at Silverton, two friends and I toured across the road from the Silverton base area. I don’t remember the drainage, and don’t have the topo in front of me.

According to CAIC, the avalanche danger in the Southern San Juan zone was MODERATE on N-NE aspects near and above treeline and LOW on other aspects and below treeline. Having skied similar aspects the day before inbounds at Silverton, we saw bulletproof conditions from the previous week of warm weather, with 4+” of new snow on top. We did not observe any sliding of that new snow on N-NE aspects inbounds, but on S aspects, the 4” that fell Thursday night was “sheeting” on the harder layer.

Having a healthy respect for the San Juan snowpack, but feeling reasonably good about the forecast and our observations the day before, we headed out on a bluebird day. 14 degrees at the trailhead, with high-20s in the forecast. We skinned up the ridge, and topped out one peak N of the billboard across from Silverton’s billboard.

We planned to ski a slide path N-NE aspect, generally hugging trees skier’s right, with plenty of safe zones and duckable options. We discussed safety protocol – skiing one at a time, SZ to SZ, and spotting one another. I put in 3 big ski cuts near the top, and nothing moved. We did not dig a pit, for the following reasons:
a) the CAIC forecast
b) nothing moved on ski cuts
c) pole testing yielded no suspicious layers

I’m not defending this decision at all. I am typically very conservative, and swear by the rutschblock test. Despite the obvious pow in our line, I think we were exhibiting a “spring skiing” mentality, given the CAIC forecast and recent extended warm temps. Heuristic factors, to be sure.

We skied the line, using safety protocol described above, bailing out about 200’ vert above the bottom of the drainage. Knee to mid-thigh deep pow, ranging from 35-38 degrees. It was good. We skinned back up a treed ridge parallel to our descent for another go at it. Skied down to our previous bail-out point and assessed what to do.

The slide path we were skiing steepened, with a small convexity near the bottom. It curved a bit, making the true angle and severity of that convexity difficult to determine. At the bottom, the force of slides had “cupped” out the drainage, forming an obvious terrain trap. Given these factors, we opted to traverse skier’s right, where we got into a sparse stand of 3-5’ tall trees. The idea was to get onto a slope with more anchors, and avoid the terrain trap below.

We traversed this lightly treed slope one at a time, spotting one another, regrouping in a full-size stand of trees to skier’s right (too thick to ski down through). Our third member triggered the slide, which broke about 10 horizontal feet above him. Hard slab, 3’+ crown, about 100’ across. He yelled to attract attention, chucked his poles, got his avalung hose in, and started fighting. Me and the other guy had a clear spot on him, and shouted various forms of encouragement. He hit one tree before latching on to another and hung on. The slide ran about 150 vertical feet to the drainage below. He traveled probably 50 horizontal feet and maybe 30-40 vertical before arresting.

Once we established he was OK, he skied the bed surface to the bottom. Me and the other guy gingerly traversed one at a time back skier’s left, to the bed surface, which we skied to the bottom. We assessed the slider quickly for injuries, then spaced out and made a run for the drainage exit.

The slide ran on at least a foot of sugar at the ground. We took a few quick photos, but generally got out without a lot of observation and analysis. The fracture occurred on a 30ish degree slope, but ran over a bulge which steepened to 40-45 degrees before hitting the bottom of the drainage. My general feeling is that snow conditions were worse close to the bottom of the drainage, which given its generally parabolic shape, was prone to a lot of sun reflection. I can’t say for sure, but I think the rotten layer did not extend higher up the slope.

Regardless, a few final thoughts and take-aways:
a) Our lack of pit/block test notwithstanding, I think our general observance of safety protocol was good.
b) We all traversed the same track, and it was the last and heaviest guy who triggered the collapse from above. His position in line, his weight, and the fact that he was on the narrowest skis in the group may have contributed to the removal of support, which initiated the fracture just above.
c) He would have certainly been at least partially buried, and given the slide ripped down to the ground, the probability of him experiencing some trauma from collisions with stumps, rocks, trees is high.
d) As Dawson’s blog notes yesterday, trees may not serve as anchors, but could present obstacles to collide with.
e) We had never been in this area, and our lack of knowledge drove us to the trees. If there was a better exit, we didn’t know about it.
f) The slider was wearing a BD Anarchist avalung pack. He claimed a higher level of confidence that things would work out once getting the hose in his mouth. I have the same pack. Our third now plans to buy one.

There you have it. Insight and constructive criticism is welcome. If nothing else, take from this that vigilance is always a requirement, no matter what the forecast.

I will be gentle.

Take these as positives and don't feel I am ripping on your decisions.

1. you were thinking avalanche, a good start.

2. Any stability test (Rutschblock) is valid on that slope in that spot, period.

3. Ski cuts are not an effective test for hard slab avalanches.

4. Ski cutting on hard slabs, the person doing the cutting may get themselves in too deep before the cuts become effective.

5. Extrapolating the stability of in ski avalanche conditions and applying that stability evaluation to an out of area slide path is apples and oranges.

6. The CAIC forecast is just that, a forecast.
(According to CAIC, the avalanche danger in the Southern San Juan zone was MODERATE on N-NE aspects near and above treeline and LOW on other aspects and below treeline.)
Probably more people take rides during periods of Moderate Hazard than during any other time.


(Given these factors, we opted to traverse skier’s right, where we got into a sparse stand of 3-5’ tall trees. The idea was to get onto a slope with more anchors, and avoid the terrain trap below.)

3-5' tall trees in a slide path are not anchors, they are the stunted survivors of past avalanches. Good on you for recognizing and avoiding the terrain trap.

(The slider was wearing a BD Anarchist avalung pack. He claimed a higher level of confidence that things would work out once getting the hose in his mouth. I have the same pack. Our third now plans to buy one.)

Thats nice & all, but a ride in a hard slab avalanche and that Avalung won't help for shit.

Glad you are o.k. and all. Too many dead people this year already. A former employee at my area took a 2000 footer a couple of weeks ago in a 1 1/2 foot hard slab over cliffs and through sparse trees.

All the avalungs and ABS systems in the world wouldn't have made a bit of difference.

Good post. We can all learn from out judgements.

[Hugh Jass]

Glad everyone's ok. Something I've noticed over the past few years of living in the hills is that the valley bottoms are colder during clear weather (due to inversions), there's less snow depth, more TG at work and more surface hoar.

Sounds like a winning theory to me. Snow was definitely shallower down close to the bottom, and where the slide occurred.

d) As Dawson’s blog notes yesterday, trees may not serve as anchors, but could present obstacles to collide with.

I'm interested in any insight on this. I've always been taught that a slope with anchors is preferable to a slope without. Paradigm shift? Thoughts?

[FrankZappa]

Yikes! Thanks for puttin this up Hugh.

Couple more thoughts to toss in and maybe hugh can elaborate on some of them:
z) The snowpack in CO is thin (and therefore more dangerous) and this year I think it is only about 75% of normal - so even worse.
y) I think I know which drainage you speak of and I seem to recall seeing plenty of slide activity in there before (tho all were small slides), so maybe the "local" pack you were on was even thinner than average due to previous sliding.
x) If you were on your 2nd lap I'm assuming the time was in the afternoon? - plenty of time for the sun to work on the snow - pecolation... Knowing the SJ's I bet there was some - at least around the trees.
w) Convex surfaces. Need I say more? think tension / compression on the slab.
v) I hate terrain traps, I really do. Yuk!
u) I think anchors work if the slab is hard (or at least firm) vs. wet slide that "flows" through them easier.

[couloirman]

I'm interested in any insight on this. I've always been taught that a slope with anchors is preferable to a slope without. Paradigm shift? Thoughts?

The term "anchor" when referring to trees like that, could easily be replaced by "trigger point" it seems depending on who you talk to. I personally noticed cracking at treeline on the standard MT Elbert trail yesterday going from tree to tree, and rock to rock, and thought this very same thing you're asking about. Hopefully someone more seasoned than me will chime in too.

[hutash]

As stated above 3-5' trees are not anchors, but an indication of former slide path. They also act like baseball bats when you do slide through them.

[Hugh Jass]

As stated above 3-5' trees are not anchors, but an indication of former slide path. They also act like baseball bats when you do slide through them.

Indeed. That much was recognized. My point was that the main gulley was wide open with a terrain trap below, and the thick trees far skier's right were too thick to ski through. Despite the obvious history to these smaller trees, they were considered the safest option, due to the perception that they would act as anchors to some degree.

Still waiting for new information as to whether trees are more likely to anchor or cause collateral damage. If the latter, I'll stay in the open and take my chances.

[FiveLarge]

Thanks for the post...always appreciate being able to learn from the experiences of others...and the collective disucssion. Glad it turned out as well as it did...sounds like your crew did alot of good things...and God's grace to cover things you might have done differently.

[SkiBumOfVT]

good post glad everyones alright
I love learning about avalanches there so powerful

[covert]

while trees may assist in anchoring a slab in place the influence they have on the temperature gradient also induces facet growth in the vicinity of the tree creating a "weak spot" from which a slab may be more easily triggered.

if failure occurs trees may rapidly become your worst enemies.

prospect gulch?

the snowpack stability at silverton mtn should not be compared to that in the bc even in adjacent areas subject to frequent skier pressure.

[Hugh Jass]

while trees may assist in anchoring a slab in place the influence they have on the temperature gradient also induces facet growth in the vicinity of the tree creating a "weak spot" from which a slab may be more easily triggered.

if failure occurs trees may rapidly become your worst enemies.

Exactly the insight I was looking for. Thanks.

prospect gulch?

I'm thinking Minnesota Gulch, but it could be Porcupine or Ohio too. My short-term memory is going.

[lemon boy]

I might offer that the only way to know if the trees are anchoring or weakening is to dig around a few and see what they got. Otherwise, I've always heard and gone with the rule that if the trees are too tight to ski enjoyably then they're a much better bet avy wise. If they're open enough to happily ski, all bets are off.

But...that's a heuristic that almost everyone I know is guilty of not always taking particularily to heart equating perfect and fun trees with safer.

[pechelman]

I might offer that the only way to know if the trees are anchoring or weakening is to dig around a few and see what they got. Otherwise, I've always heard and gone with the rule that if the trees are too tight to ski enjoyably then they're a much better bet avy wise. If they're open enough to happily ski, all bets are off.

Thats always a question Ive wondered, whether sometimes its just better not have any any trees or rocks at all, especially when I notice how much faster snow melts around the trunks of trees, probably due to heat conduction from the ground or from incident radiation. Then theres always the issue of wells, weird drifting, strange settlement patterns etc. Guess the only way to know for sure is to dig around each of them.

[AK Rev]

Thanks for posting your experience. I have never felt like I knew enough about avy danger and protection. I have serious plans to improve my training, knowledge and gear.

[covert]

equating perfect and fun trees with safer.

personally, i believe perfect and fun trees are more often than not "safer" however the distinction between "safer" and "safe" is critical. trees will break you into a million fucking pieces if you take a ride. assessing the consequences of failure should always be paramount.

[smitchell333]

Thx for posting - its informative to read and discuss real incidents.

It is easy to use the word mistake because there was a slide, but if there had been none would it have been a success???

I think you did a number of things right from avoiding the terrain on the 1st run to having the proper equipment and travel protocol. Also avoiding the terrain trap.

This time of year there is a transition where the top gets heavier from the warm temps but the bottom is cold, hoary, and brittle. Sometimes mid winter and spring I'm more skeptical of the at/below treeline terrain because of the massive inversion the pack demonstrates. In the winter it can be safer to ski the trees where the wind hasn't slabbed it out, but sometimes its worse than higher, deeper snowpack terrain.

And trees - I think they are trigger points. I think that rather than treed slopes having anchors for the pack the dangerous slopes have no trees b/c the avalanches wipe them out - somehow a misconception instead comes out "hey that slope slides b/c there are no trees."

[Doughnuts01]

good websites for avy info, besides caic, and that canuck website...??

[Hacksaw]

Check out www.avalanche.org

and also

www.americanavalancheassociation.org

Cheers,
Halsted