Avalanche: Turnagain

Location: Johnson Pass area

Date:
Observer:
Route & General Observations

Rode up the Johnson Pass trail into the Groundhog drainage. High point of 3,800′.

Avalanche Details
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Trigger SnowmachinerAvalanche Type Unknown
Aspect NortheastElevation 3800ft
Slope AngleunknownCrown Depthunknown
WidthunknownVertical Rununknown
Avalanche Details

A few small snowmachine triggered wind slab avalanches occurred in the high elevation wind loaded terrain. There were also a few natural recent wind slab avalanches. Only one, the natural wind slab pictured below, would have been large enough to bury a person.

Red Flags
Red flags are simple visual clues that are a sign of potential avalanche danger. Please record any sign of red flags below.
Obvious signs of instability
Recent Avalanches?Yes
Collapsing (Whumphing)?No
Cracking (Shooting cracks)?Yes
Observer Comments

Strong NW winds with active wind loading, recent small wind slab avalanches and cracking in the snow around our machines were the obvious signs of instability seen today. It seemed one had to get on quite a steep slope to get a wind slab to move or to crack.

Weather & Snow Characteristics
Please provide details to help us determine the weather and snowpack during the time this observation took place.
Weather

Mostly sunny skies and temps in the 20'sF.
The NW winds were blowing snow off peaks and ridges in the mid and high elevations. Winds were getting into drainages and grown blizzard conditions were seen as low as 2,500'.

Snow surface

Wind effect everywhere above 2,000': wind crusts and slabs, sastrugi, scoured areas, and some relatively soft wind blown snow could be found in the most sheltered areas. Also, below 2,000' and in the bottom of the Johnson Pass drainage soft snow could be found unaffected by the winds.

Snowpack

Other than the obvious wind slab problem, we dug a couple pits looking for the buried weak layers.
Pit 1: 3,600', SE aspect, snow depth 10 feet.
This was in a somewhat sheltered area with no recent wind slab and chosen in order to assess any old persistent weak layers.
ECTP 14 on small facets/decomposing particles 15" down
Soft surface snow transitioning to pencil hard snow by 2' down.

Pit 2: 1,500' N facing and sheltered location, no wind effect.
CTX, no instability found in top 2.5 feet. Found the 1/23 crust 2' down, no weakness found surrounding crust.
Soft surface snow transitioning to 1finger hard snow above and below crust.

Take home, wind slabs main concern. Kept off big terrain due to this as well as possibility of triggering a larger slab knowing faceted snow sits in the top couple feet of the pack.

Photos & Video
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