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Author Topic: March 6, 2004, Heather Ridge/Moonlight Bowl  (Read 8418 times)
Sam Avaiusini
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March 6, 2004, Heather Ridge/Moonlight Bowl
« on: 03/08/04, 04:02 AM »

Phil, Greg, Silas, Scott, Lori and I went to Heather ridge on Saturday and actually had the place to ourselves.  We primarily skied Moonlight Bowl and got about 4,000 vert after several laps.  Over the course of the day there was a LOT of collapsing in the snowpack!  "Whoomphs" every 30 minutes or so on the upper slopes.  I remotely triggered a slide from about 200 feet away on one of the skins uphill.  We speculate that my movements caused one of those Whoomphs which we all heard and then a second later, it triggered a slab that ran about 500vf. 75 feet wide with a 2-3 foot crown.  That slide in turn caused a second slide right below the debris field of the first one.  The 2nd slide had about a 20-24 inch crown, but was on a shallower angle and didn't run more than a 200 feet or so.  The Domino Effect!  

Fortunately, this was all on an adjacent slope!  My lead on the skin up brought us to a minor rib where I was going to zig-zag away from the slope in question.  

It was crazy how my movements (on a slope that I felt good about skinning up and would have skied) transmitted so far through the snow pack.
Definitely a learning experience.

We all agreed that this was the sketchiest day any of us had experienced it the backcountry so far this season.

*From Chapter 6, Stability, in "Staying Alive in Avalanche Terrain" by Bruce Tremper:

"Collapsing snow (sometimes mistakenly called settlement) is when the snowpack collapses under you with a loud WHOOMPH.  (Actually, whoomph has been adopted by the Canadians as a technical term to describe collapsing snow.)  Whoomphsing is the sound of Mother Nature screaming in your ear that the snowpack is unstable and if you got a similar collapse on a slope that was steep enough to slide, it wouldn't hesitate to do so.  Collapsing snow occurs when your weight is enough to catastrophically collapse a buried weak layer, which is most commonly depth hoar or surface hoar.  You can easily bring avalanches down from above in collapsing snow conditions.  When the weak layer is already holding up the weight of a significant amount of snow and just the wimpy addition of your weight can collapse all the snow in sometimes a very large area and cause it to propagate long distances, then it's big-time scary out there!"
« Last Edit: 03/08/04, 04:04 AM by savaiusini » Logged

Sam Avaiusini
Gregg_C
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Re: March 6, 2004, Heather Ridge/Moonlight Bowl
« Reply #1 on: 03/08/04, 04:45 AM »

Great information.  I don't think the snowpack was quite as bad up at the Baker backcountry (Sat).  My stepson and I heard a few whoomps on some wind loaded areas heading up to the saddle.  We stuck to the trees heading south from Hermann Saddle and found fairly good skiing.  Tim and friends dug a pit and skied the Core shoot gully.   There was quite a bit of new snow but it was definately safe to ski on the south facing slopes in the trees.  Yesterday's warm temp and snowfall/rain hopefully precipitated a good avy cycle.
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fooman
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Re: March 6, 2004, Heather Ridge/Moonlight Bowl
« Reply #2 on: 03/08/04, 05:21 AM »


Huh, that's interesting.

So you were skinning up on a day that was already forecast to be dicey, experienced frequent whoomps and a sizeable slide triggered by your presence but still got in 4000 feet?

You said yourself it was the sketchiest day you'd seen this season.

Where do you draw the line?  Whoomping is definitely when I turn back after having a similar experience but without enough volume to be really dangerous.

Would you have been surprised if you had been caught?

I guess everybody has their own comfort levels, but jeez, that just seems a bit crazy.  What kind of conversations were going on in your group?
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juan
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Re: March 6, 2004, Heather Ridge/Moonlight Bowl
« Reply #3 on: 03/08/04, 05:29 AM »

there are definitely some lower angle lines in moonlight bowl.  my main concern would be on some of the steeper sections directly below the ridge...these are more or less unavoidable if you ski off the top.  i ski there often, and based on what i was seeing in the trees there on friday, i would have avoided moonlight bowl altogether probably.  glad you guys had a good day though and it all worked out.  
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Sam Avaiusini
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Re: March 6, 2004, Heather Ridge/Moonlight Bowl
« Reply #4 on: 03/08/04, 06:05 AM »

Juan:
You are correct in your assumption.  The upper portion of the bowl, below the ridge (in a slight depression) is where the slide occurred.  Phil and Greg both took photos, maybe they can post one here...
Other than the one attempt to climb back to the ridge, we made all our turns on the lower angle gladed stuff and felt pretty good about that.

Fooman:
Our choice to ski there was a calculated risk and we were pretty aware of the conditions as well as the avy forecast.  Over the course of the day we dug probably 4 pits and nothing seemed too unusual for around here really.  Comfort zones for sure.  Kinda the whole lemons into lemonade idea. Cool
« Last Edit: 03/08/04, 06:06 AM by savaiusini » Logged

Sam Avaiusini
philfort
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Re: March 6, 2004, Heather Ridge/Moonlight Bowl
« Reply #5 on: 03/08/04, 06:09 AM »

We skied the south slope, then into moonlight bowl and skied the far skiers right of the bowl, that starts in the trees (not quite yet in the full open, but fairly steep at the start).  Then we did the run with the slide, and then two more runs from where the trees start to get denser and the slope flattens to 20 degrees or so (about 400-500ft below the ridge top) down to near the PCT.

The conversations in our group were interesting, and there was definite disagreement on assumption of risk.  There was even an attempt to dismiss the whoomphing as pressure waves from the avy control that was going on at stevens.

On the run with the slide, we were skinning up aiming for the rib on the skier's left of the bowl, and headed up the right trending "bench-ish" area (skinner's right-trending) towards it... I was breaking trail and there is a slight knoll here that I thought would be a relatively safe place to get to on the bench.  From there we planned to ski down the rib.  Just before getting there, 3 of the others decided to continue skinning to the ridge top.  I tend to get persuaded by others who I perceive to have more experience, but this time I was pretty adamant about not going up any higher, and continued to the knoll with the other 2 (who were probably the least experienced, avalanche-wise, in our group).

As we were stopped and getting ready to go down, is when the others triggered the slide.

In retrospect, I doubt we even should have headed to the knoll traversing beneath the steep upper slopes - in those conditions I imagine we could bring something down on us even if the slope we were on wasn't steep enough to fracture and slide.
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gregm
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Re: March 6, 2004, Heather Ridge/Moonlight Bowl
« Reply #6 on: 03/08/04, 07:49 AM »

most of my close calls with avalanches can be traced to faulty decision making.  this time i think it was because i had dug a pit that i was overconfident about the slopes stability, as i couldn't see anything in the layers or consistency of the snow to scare me.  while it might be convenient to say i was "skinning under the influence of avaiusini" i have to admit i was the author of the ski area avy control bomb theory.  i guess that kind of settlement is something we normally don't see around here so it's definately a learning experience.  

"beware the whoomphing noise!"  [spoken in the same tone of voice one might say "beware the jabberwocky"].  
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ski_photomatt
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Re: March 6, 2004, Heather Ridge/Moonlight Bowl
« Reply #7 on: 03/08/04, 07:52 AM »

Where exactly is Moonlight Bowl?  Is this the sparsely treed bowl just east of the pass and above the highway across from Yodelin?  The lower reaches above the flat PCT are cloaked with slide alder and dense forest?

What was the weather like?  If this is the bowl I am thinking of, that area will tend to get heated in the slightest sunbreak of which there were a few Saturday near Snoqualmie Pass.  I'm wondering if slight daytime heating consolidated the new snow into a more cohesive slab and helped contribute to the instability.
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Sam Avaiusini
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Re: March 6, 2004, Heather Ridge/Moonlight Bowl
« Reply #8 on: 03/08/04, 08:02 AM »

Matt:
Yes, you are thinking of the correct place.
As far as solar heating affecting stability...that's highly likely.  We did have a few sunbreaks on and off throughout the day.

This has all been very good discussion.

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Sam Avaiusini
Jim Oker
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Re: March 6, 2004, Heather Ridge/Moonlight Bowl
« Reply #9 on: 03/08/04, 09:57 AM »

Thanks for sharing your thought processes openly, guys! This is good reading material.

I'm reminded of comments I heard many years back in Avy Level I training about group dynamics (e.g. make your own calls, pay attention to the worriers in the group, that sort of stuff), as well as about paying attention to all the factors (including whoomphing in particular - something they mentioned much more strongly in my CO class than in the one I took with Gary Brill not far from where you guys were), and not letting one seemingly safe measure eclipse another worrisome factor. But they also talked about the fact that as people get a decent chunk of experience to combine with their knowledge, they tend to be right at the highest risk point, as they can say "well, it looked kind of like this that other time and we were fine..." and you kind of keep nibbling at the risk boundary. Your story is a good reminder to me of all that, and I thank you for that fact.
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markharf
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Re: March 6, 2004, Heather Ridge/Moonlight Bowl
« Reply #10 on: 03/08/04, 10:21 AM »

Yes, an interesting, informative discussion, particularly in combination with a few more technical issues addressed at http://www.telemarktalk.com/phpBB/viewtopic.php?t=17398.  Thanks Phil, Sam, Greg.
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Don_B
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Re: March 6, 2004, Heather Ridge/Moonlight Bowl
« Reply #11 on: 03/08/04, 02:36 PM »

So now you know why you had it all to yourselves.

This is making my $47 tab at the lifts across Hwy 2 seem more worthwhile. I was really tempted to head up and over there, but...

Stevens Pass had it's own "whoomps" but they were from this huge Car Toys tractor trailer full of subwoofers.  Not exactly a wilderness experience, but a beautiful day with great powder in the trees and windpacked on the open.
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gregm
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Re: March 6, 2004, Heather Ridge/Moonlight Bowl
« Reply #12 on: 03/08/04, 05:30 PM »

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ron j
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Re: March 6, 2004, Heather Ridge/Moonlight Bowl
« Reply #13 on: 03/09/04, 01:00 AM »

That's a great picture, Greg.
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"When I stop having fun I'm turnin' around"
"Prediction is very difficult, especially if it's about the future." - Niels Bohr
"If a given person makes it a priority not to die in an avalanche, he or she stands a very good chance of living a long, happy life in the mountains." - Jill Fredston
Sam Avaiusini
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Re: March 6, 2004, Heather Ridge/Moonlight Bowl
« Reply #14 on: 03/09/04, 04:00 AM »

Quote

Stevens Pass had it's own "whoomps" but they were from this huge Car Toys tractor trailer full of subwoofers.  


New theory:  Subwoofer induced slope instability? Cool

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Sam Avaiusini
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