Observation: Turnagain

Field Observations
December 23, 2014

Route
Seattle Ridge to Main Bowl

Weather
Temps: 16 – 28
Winds: Calm
No precipitation, Clear skies

Obvious Signs Of Instability
Recent Avalanches-NO – Glide crack opening on lower Northeast shoulder of Big Chief at about 2000′
Shooting Cracks-NO
Collapsing – NO

Surface Obs
1000′ – 2” low density snow on 2″ crust on ground.
1500 – 2000′ – 3-4″ low density snow on 4 – 16″ old snow from Dec.14-17 storm
2000 – 3000′ 3 -4″ low density snow on 16 – 20” old snow from Dec.14-17 storm

Snow Below the Surface
A few inches of low density snow fell on Dec.21 and is sitting on the old snow from Dec.14 -17 storm.
Over the last week this old storm snow (1 – 3′) has become a cohesive slab and is sitting on a layer of
buried surface hoar. This surface hoar has been documented throughout Turnagain Pass and Summit Lake
above 2000′ and is gradually becoming less reactive in our test pits as we get further away from the storm
event. At mid elevations (2000-2700′) this slab has varying layers of melt forms and rounds. At 2250′
these melt forms are still moist. This layers gradually goes away with altitude and only a thin (2mm) crust
was found just below 2700′, but not found 50ft above.

Pit @ 2250′ – Aspect: E, slope 23*, HS: 95cm, A 20cm varying layer of moist melt forms was found within the
Dec. 14-17 storm slab (50mm) ECTX (See pit profile and picture)

Pit @ 2700′ – Aspect: E, slope: 25*, HS:120cm, An inconsistent 2-3mm melt/freeze crust was found in the
Dec 14-17 storm slab (55cm), No obvious weak layer was found, ECTX

Pit @ 2750′ – Aspect: E, slope: 28*, HS:120cm, weak layer: 5mm buried surface hoar 55cm from surface,
ECTP 21 SC (55cm from surface)

Today is the one week mark since we received 1-3′ of snow on a layer of surface hoar. We have found this
weak layer on all aspects above 2000′ throughout Turnagain Pass. It appears to be adjusting to its new
load and is gradually becoming less reactive in our test pits. We had some conflicting test results in our
pits at 2700’/2750′. One pit resulted in the isolated slab propagating with moderate force and the another pit (only
150′ away) had no results, and the buried surface hoar layer was not found. AT 2250′ we did not have any
results in our test pit, but did find the buried surface hoar forming bonds with the melt/freeze layer below
it. These results are helpful, however test pits are only tiny slices of information and not a reason to base a
“go” decision upon. We suspect this layer is still reactive on steep slopes and could be triggered in
thin parts of the snow pack.