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Avalanche: Ant Knolls

Observer Name
Miller
Observation Date
Tuesday, February 8, 2011
Avalanche Date
Tuesday, February 8, 2011
Region
Provo » American Fork » Ant Knolls
Location Name or Route
Snake Creek/Ant Knoll Vicinity
Elevation
9,500'
Aspect
East
Slope Angle
36°
Trigger
Snowmobiler
Trigger: additional info
Unintentionally Triggered
Avalanche Type
Soft Slab
Depth
2'
Width
200'
Vertical
500'
Comments

After a friend and I had climbed this hill about ten different times my friend placed a track about ten feet above our last highmark. He sidehilled across the slope and was just about to turn downhill when the avalanche broke loose. At that moment my friend made a quick last minute decision and turned his sled uphill and got stuck right where the crown broke. The crown face was between 2' and 3' and it appeared to be a pillow of wind loaded snow that ran on the rain crust. In the picture you can see previous tracks we placed on left side of the field. The track going through the middle of the debris pile is from my friend descending after he dug his sled out.

We also observed another slide later in the day. Earlier I drop off a cornice into a chute of sorts with nothing more than some loose snow sluffing. Later we traveled along that ridge and as we passed the same place I went off earlier a piece of cornice broke off and triggered an avalanche. The aspect was very similiar to the one I reported, but maybe a little smaller of a slide. Here are the coordinates I got off google maps, I am not sure the format 40.548961-111.568394 (it is west and slightly north of the slide I reported) Thanks to you and all the of the forecaster, you all do a great job. I read the report just about everyday and try to pick my routes or the hills we may climb accordingly.

Comments

Forecaster Comments:

Kobernik

This was a significant avalanche. Mr Miller's assessment was correct in my opinion. It was a recent windload which failed just above the January rain crust. There was no significant weakness directly above the crust. It was difficult to get this weakness to fail in shear tests. The rapid addition of weight from the wind transported snow seemed to be the biggest factor. I suspect that if this slope were left alone for another 24 hours to give the fresh wind load a little more time to settle it probably wouldn't have avalanched.

I tip my hat to these guys for checking out the crown and trying to figure out what was going on with the layering. Our sled community is becoming more savvy as the years go on and it's great to see!!

Comments

There was one portion of the slide that did break through the January rain crust which was quite stout and about 1 inch thick. This was on the lookers right side of the slide where the avalanche fractured in the trees. Faceted snow below the crust was the weakness. You can see the facets and the crust a few inches above the bed surface in this photo. The facets were not particularly alarming and it was difficult to reproduce shears with tests here. This portion of the slope was 48 degrees in steepness.

Comments

Here is the other pocket that Mr Miller reported. It was on the north aspect of the main Ant Knolls. I did not climb down in to check it out. The stout crust not too far under the surface was too intimidating for me to get on this very steep terrain.

Coordinates