Avalanche: Main Days 12/17/2011

Observer Name: 
Matt Hart
Observation Date: 
12/17/2011
Occurrence Date: 
12/17/2011
Occurrence Time: 
1:00pm
Region: 
Salt Lake
Location Name: 
Main Days
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Location

40° 36' 17.622" N, 111° 38' 34.5768" W
Avalanche Characteristics
Elevation: 
10400'
and below
Aspect: 
North
Slope Angle: 
35
Trigger: 
Skier
Trigger: additional info: 
Intentionally Triggered
Avalanche Type: 
Soft Slab
Weak Layer: 
Surface Hoar
Depth (avg): 
8"
Width: 
30'
Vertical: 
200'
General Comments

I found that yellow dotted pocket of moderate avy danger today.

We were on a ridge just above a convex slope with two previously skied gullies on either side at 10,400ft in elevation.  Previous skiers had caused sluff slides of the top 4” that laid on top of a sun crust.  It looked boney.  Our first skier skied the gully to the left and hit a big rock.  I decided to ski cut the top of the convex on my way over to ski the right gully.  A previous skier had hit rocks and ski cut the same convex before me (we could see his track) while apparently changing his mind on which gully to ski.  I was actually ski cutting above his track and sort of bouncing to put a bit of extra weight on it when the top 8 inches broke 30 feet wide on the convex and ran down 200 feet through the trees below and uncovering rocks.  I happened to catch most of it on video.

Having a look at the crown I found: 3" of fist density on top of a 1/2" crust that gave way to 4 finger density for about 4 more inches until the weak layer of small to medium fragile facet snow on which it ran (updated thanks Brett! - see updated photos below).

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Video 1: 
General Comments 2

Forecaster Note:  I visited this avalanche on Dec 19.  The "buried hoar flakes" that Matt referred to were small to medium sized buried facets.  I was not able to identify any surface hoar in the crown or flank.  I've attached a couple of photos below of the grains that acted as the weak layer.  Kobernik

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