Avalanche: Millville Peak 3/22/2011

Observer Name:

Dean Harris 3-22-11, Weed/Archibald 3-23-2011(photos)

Observation Date:

03/22/2011

Occurrence Date:

03/22/2011

Occurrence Time:

Morning

Region:

Millville Peak
Providence Canyon
Logan

Location Name:

Millville Peak. "Furthest bowl to the east"

Location

41° 40' 45.4476" N, 111° 43' 1.236" W

Avalanche Characteristics

Elevation:

9200'

and below

Elevation Range Maximum:

9200'

Elevation Range Minimum:

8200'

Aspect:

North

Northeast

and steeper

Slope Angle:

Alpha Angle:

Trigger:

Natural

Trigger: additional info:

Cornice Triggered

Avalanche Type:

Hard Slab

Weak Layer:

Surface Hoar

Depth (avg):

3.5'

Depth Range:

2' to

Width:

175'

Width Range:

150' to

300'

Vertical:

800'

Vertical Range:

300' to

900'

General Comments

Dean phoned in to report seeing a large fresh avalanche on the north face of Millville Peak from across the canyon on the route to the upper canyon.... We feared that we weren't done with deep slab avalanches yet this season, and this avalanche likely proves that we're not. ....The avalanche is similar to a nearby hard slab naturally failed on 2/28/2011. (see report HERE)

Josh and I were able to get up to the site and examined the avalanche on 3-23-2011...

Video 1:

General Comments 2

Interesting and complex natural avalanche including 3 threats.... A natural fresh wind slab avalanche likely triggered by cornice-fall overran a slope with a buried persistent weak layer causing a dangerous deep hard slab avalanche which propagated into adjacent slope to the east under trees... The initial foot-deep and a couple hundred foot wind slab started under a large cornice near the summit of Millville Peak and failed on graupel and small sugary or faceted grains...The avalanche stepped down 3 to 4 feet into old snow and propagated on a very thin layer made up of two dimensional frost crystals or surface hoar and small faceted grains.... The blown in crown from the upper soft wind slab avalanche..... We noticed a small natural release at the top of the avalanche path, which occurred today while we were examining the deep slab crown below....

More fresh surface hoar was evident on today's snow surface....

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