Observation: Girdwood

Location: Gulch Creek

Route & General Observations

Toured to 3100′ up Gulch Creek. Low visibility all day, and snowing lightly. Got a large collapse and easy propagation in pits at 3100′ on 3mm cupped & chained facets. Highly spatially variable slab thickness observed.

Red Flags
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Obvious signs of instability
Recent Avalanches?No
Collapsing (Whumphing)?Yes
Cracking (Shooting cracks)?No
Observer Comments

Got a large collapse atop a medial moraine feature at ~3100 after taking two steps out of my skis. Dug to investigate, collapse was on 3mm cupped, chained facets on a melt-freeze crust 1-2' below a hard slab.

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

Overcast to obscured skies all day. Snowing <1"/hr to 1"/hr, total accumulation ~4" at 3000'. Wind calm to light from the west. Temperatures in the 20's.

Snow surface

2-4" of new snow on various melt-freeze crusts (at 1300' on SW aspect there were two 6" melt-freeze crusts stacked at the surface, above about 2500' there is mostly a 1-2" melt freeze crust that is partially breakable). Below the melt-freeze crust the snow is faceted.


The snowpack is highly spatially variable. Depths ranged from 30-45 cm on a southerly aspect of the moraine to 175 cm at 2000' in the gulch, to 55 cm - 120 cm at 3100' on the medial moraine feature where we got a collapse. The mid-January melt-freeze crusts were found all the way up to 3100'. Sandwiched between the crusts and a hard slab are facets. The slab depth varies from 1-3'.

We dug four pits in two locations:

Pit 1 - 2400', SW aspect, 28*slope, HS= 90cm - Stability tests all failed on a facet layer between two crusts 55cm below the surface on 2mm dry facets. CT16, CT17, CT21, ECTN24, ECTP27 (PC) The bottom 1/2 of pit had several facet layers between deteriorating m/f crusts and basal facets on the ground. See photo diagram.

Pit 2 - 2400', SW aspect, 26* slope, HS=260cm. CT30 down 35cm on facets below an old sun crust. Facets above and below the mid-January melt-freeze crust were present, ~100cm below a hard slab, but were not reactive in tests. See photo diagram.

Pit 3 - 3000', SW, 12*slope, HS=90-110cm - Dug a pit in this location immediately after experience a large collapse. Stability tests all failed on 3mm chained facets on a crust 65cm below the surface. These facets were very loose and falling out of pit wall. Test Results: CTV, CT3, CT7, ECTP3, ECTP12. See video

Pit 4 - 3000', WNW, 20*slope, HS=55-120cm. Close to Pit 3. CT14, ECTP4, PST 40/100 END down 35cm on 3mm chained facets on a crust.

Photos & Video
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