11th Annual Utah Snow & Avalanche Workshop Open and Motorized Sessions Oct. 27th.
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Observer Name: 
Kobernik/Kendall
Observation Date: 
Wednesday, March 4, 2015
Avalanche Date: 
Wednesday, March 4, 2015
Location Name or Route: 
Upper Spring City Canyon
Elevation: 
10300
Aspect: 
Northeast
Slope Angle: 
39
Trigger: 
Skier
Trigger: additional info: 
Remotely Triggered
Avalanche Type: 
Soft Slab
Avalanche Problem: 
Persistent Weak Layer
Weak Layer: 
Facets
Depth: 
2.5'
Width: 
250
Vertical: 
500
Comments: 

General observations included here as well as avalanche info.

Two feet plus of new snow on the Manti Skyline out of this recent storm.  We hadn't been down for a number of weeks now so we needed to approach things cautiously to see what was going on with the new snow.  It was very deep and almost too deep to travel.  There was way too much snow to get into some of our favorite bowls right off the get-go so we started out on low angled west facing terrain, not steep enough to slide.

Comments: 

We didn't note anything too significant within the new snow but did experience one collapse while ascending near the top.  It was a buried layer of facets associated with a heat crust.  Kind of odd to have a collapse on a west face like that.  There was an avalanche on the north facing portion of the bowl which ran during the southerly storm flow on Monday.  We decided that it would be safe to walk up the bed surface and we could figure out what the weak layer was that caused the slide.  This would be very important information for us as to how we would decide stability on the more northerly slopes we wanted to get into over the next couple of days.  Upon getting to the bed surface, we noted about 12" of new snow which was on top of the debris.  This put the time of the avalanche before the cold front passed on Tuesday.  The avalanche was 12 to 14" deep and we quickly determined the weak layer was facets.  At that point, all bets were off with any ideas of skiing some of our favorite big northerly facing bowls.  If the weakness had been within the new snow, we would've waited another day and then got into the bigger terrain.

Comments: 

After we were done looking at the crown and were getting ready to descend the bed surface, I went over to the west flank to have a quick look.  I poked my pole in to the flank where it hadn't avalanched and noted to my partner Lara how weak the snow was down deep.  I picked up one of my skis and half-ass kicked into the flank and got a large collapse.  The adjacent slope cracked out and slid about 30 feet farther into the flank.

Comments: 

All of the upper bowl had slid during the the pre Xmas natural avalanche cycle leaving only about 18" of snow on the ground.  It never really snowed again until now.  The slopes are very steep, 40 degrees or more and face north.  This is the perfect set up for faceting despite the very warm temperatures we experienced in January and February.

This is a dangerous set up for the unaware.  You can easily ride east, south and west facing slopes without worry.  Some north facing slopes that didn't slide during December may not avalanche either.  Some north facing slopes that see regular sled traffic may not slide either.  But it wouldn't be hard for someone to travel for most of the day and then get onto one of these northerly facing slopes which harbor a weak shallow snowpack due to avalanching in December.  "Booby traps" is a good analogy.

Coordinates: 
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