Alison Clay Avalanche - Saturday Jan 14th

Post snow pack observations - snowpits, avalanche activity, signs of instability.
Redmnt245
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Joined: January 16th, 2017, 8:49 pm

Alison Clay Avalanche - Saturday Jan 14th

Postby Redmnt245 » January 16th, 2017, 9:56 pm

On Saturday, January 14th my ski partner and I entered Alison Clay near treeline (~11,400’). Visibility was limited to 200’ above. Prior to entering we saw a group of four skiers making their way down the center of Alison. We found fresh avalanche debris approx 30-40’ wide on skiers left side of main path. Visibility prevented us from seeing the starting point location or crown height. It definitely ran 300m, likely farther. We ascended further, transitioned, and then climbed up to Philomena. We dug a pit on a 35 deg NW facing slope at ~11,400 on a subridge. ECTP17 Q1 result –top 50cm failing on rain crust from prior weekend. The overall snow depth on this slope near 180cm.

My guess is the Alison slide was of similar failure mechanism to our Philomena pit. We later spoke to the party and everyone was fine but we have received conflicting reports – likely due to different perspectives. Sounds like they entered Alison near 11,600’ or 11,700’ with the first skier triggering the event. They indicated the crown was 1-3” deep of wind slab.

I have dug 3 other pits in the Alison/Philomena area recently (in the 10,500 to 11,600) – all north/northwest facing – all had 20-40cm of facets at bottom (note that prior to Saturday getting all ECTX results). On Jan 7th I probed the snowpack in upper Alison (the same NW slope as avalanche) -it was near 210cm. All tests and probing indicate the snowpack above the facets and below the recent rain crust is very stout. Of course the depth drops significantly near the ridge lines and towards the center. At the ridges it is <30cm depth. The center of Philomenia near our pit was probing ~115cm on Sunday the 14th – guessing center of Alison is similar depth.

Sunday (1-15), dug a pit at top of Dutchman (11,600’) a W-SW facing slope also had ~30cm of facets at bottom – ECTX result. While consistent sign of stability as others have reported on West slopes, be aware - early season snow faceting is not limited to Northern facing aspects.
Not surprisingly I have found faceting surrounding rocks at very shallow depths at top of Dutchman towards Alison. The snowpack drops to nothing near the ridge lines above treeline. Which means…it is possible to trigger a wind slab that steps down to facets in a shallower area, especially on those NW slopes.

Bottom line, the red flags are out. That rain crust is still present. Please continue using caution on NW facing slopes in addition to the N and NE slope concerns that have already been reported on this site.

If anyone has additional relevant info into the avalanche in Alison, especially members of the party, that would be great to share. This is a good forum for teaching/learning from others.

splitboarder
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Re: Alison Clay Avalanche - Saturday Jan 14th

Postby splitboarder » January 17th, 2017, 1:56 pm

Thanks for submitting your findings.
I think maybe you ran into our level I group on your way up, early on the Humphrey's trail?
Were your test failures just above, or just below the rain crust? Thanks!
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OutOBounds
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Joined: January 16th, 2017, 8:06 pm

Re: Alison Clay Avalanche - Saturday Jan 14th

Postby OutOBounds » January 17th, 2017, 9:03 pm

We were a group of four that entered high in Alison's around 11am in the morning after taking a run on the Dutchman. We approached Alison's from the ridge to the south at around 11,200ft, above tree line, single file, moderately spaced, and were heading toward the downslope side of a noticeable rock band. The snow pack seemed stable with no signs of whoomping or cracking. An avalanche was initiated approximately 20ft from the rock outcropping by the weight of the lead skier at a depth of approximately 3 inches, where the first ice band was located. Fracture arched in front approximately 30ft and in back approximately 50ft increasing in depth to approximately 12inches in both directions. Slide ran directly down the side of Alison's, made the corner turning to the left and joining the main shoot until it subsided on the less steep incline, approximately 800 -1000ft run. All skiers were safe.

Redmnt245
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Joined: January 16th, 2017, 8:49 pm

Re: Alison Clay Avalanche - Saturday Jan 14th

Postby Redmnt245 » January 17th, 2017, 9:29 pm

splitboarder wrote:Thanks for submitting your findings.
I think maybe you ran into our level I group on your way up, early on the Humphrey's trail?
Were your test failures just above, or just below the rain crust? Thanks!


My ski partner and I did not see anyone from when we exited Snowbowl boundary until we were to Alison Clay - definitely didn't see any classes.
Crust/ice was above fracture in failed ECT test.

Doctor Lovesnow
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Joined: January 17th, 2017, 6:56 pm

Re: Alison Clay Avalanche - Saturday Jan 14th

Postby Doctor Lovesnow » January 18th, 2017, 8:51 am

Question: Can you verify the the avalanche you reported was a slab avalanche? Also, would you call it hard or soft slab? I would love to get more details to include in the Snowpack Summary at the end of the week. You can reach me at 928-350-2299 and leave a message.

Redmnt245
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Joined: January 16th, 2017, 8:49 pm

Re: Alison Clay Avalanche - Saturday Jan 14th

Postby Redmnt245 » January 18th, 2017, 10:52 am

Clarification on avalanche crown: I reported above as 1-3" - this was a typo. It had initially been reported to me as 1-3'. That said, this is what I believe to be the most accurate report from the party members that I have discussed the event:
"probably 4-6" under the skier, and running to 12" at a protruding rock up ~30" up slope".

The descriptions I received indicated slab. The debris pile I skied over definitely looks like it was from a soft slab.

OutOBounds - can you verify the crown depth and slab nature?

raisingarizona
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Re: Alison Clay Avalanche - Saturday Jan 14th

Postby raisingarizona » January 18th, 2017, 12:00 pm

Two days ago a group and I skied Allison's. There wasn't any visual evidence of a slide but I felt it underneath the new snow for 3 or 4 turns or so where pitch of the bowl decreases just before the avalanche path. It wasn't very much, I can't imagine that the slide was very large. I'm guessing it was just the most recent snow and it didn't step down or propagate very far. I was thinking that it started up on the viewers right side in the traditional starting zone like the OP stated. It seemed to have lost all of it's energy once the grade lessened but again, I had no visuals on it, we just felt it.

I did have a small pocket collapse on me while traversing out to the starting tree (tree right in the gut that often marks the best spot to start skiing from). It felt like rain crust but there wasn't any energy in it. It was a little creepy but I wasn't too concerned about it right there at that moment.

maadjurguer
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Re: Alison Clay Avalanche - Saturday Jan 14th

Postby maadjurguer » January 19th, 2017, 5:32 pm

Redmnt245 wrote:Crust/ice was above fracture in failed ECT test.


This is consistent with what we have been seeing in the dual crust/facet sandwich formed from DEC 16 crust (lower, clear/smooth ice crust) and the DEC 24 crust (Upper, muddled, rain/melt/freeze/rime/crappy wx). The upper crust is variable in hardness depending on where you are on the mountain, but the lower crust is pretty consistent with respect to being a clear, solid, planar ice layer.

If I read your ECT description and results, it sounds like you are describing a failure between the two crusts with the failure occurring at the base of the upper crust in the facets above the ice layer....please clarify if I've gotten this wrong. If you have a pit profile, please post it up as we would all love to take a look. Thanks for your report.
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