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Observation: Turnagain

Location: Sunburst

Date:
Observer:
Route & General Observations

Route
Taylor Creek>Taylor Pass>Sunburst Weather station

Weather
Clear skies, no precipitation, light winds out of North at 5mph, temps in the teens
Some valley fog clearing out by mid afternoon

Obvious Signs Of Instability
Recent Avalanches-NO
Shooting Cracks-NO
Collapsing-NO

Surface Observations
Stout wind slab and crust, sastrugi, above 2,500’
Surface hoar continuing to grow at all elevations, 1-5mm (see photo 2)

Snow below the Surface
Today we looked at an upper elevation starting zone (around 3,800’) with varying
snow depths by digging 4 pits across a slope (photo 1). The general trend
in all pits was high strength and low propagation potential on any weak layers
found. The well known surface hoar layer was present in all pits and was mostly
laying down flat and anchored or melted into the slab above it (photo 3). This
was the first day that we found this layer where it was showing low propagation
potential.

**Pit data below is focused on the buried surface hoar layer.**

Pit 1
Height of Snow (HS) = 200cm/7.3 feet
Buried Surface Hoar (BSH) @ 80 cm down
ECTX

Pit 2
HS=160cm/5 feet
BSH @ 85 cm down
ECTX

Pit 3
HS=85cm/3 feet
BSH @ 35 cm down
ECTN 23, 24, 25

Pit 4
HS=55cm/2 feet
BSH @ 20 cm down
ECTN 25

Other pertinent results:
Wind slab in pit 1 failed on isolation 20 cm down on facets
Pit 2 had results on a layer of mixed forms 30 cm down-ECTN 14, CT 15, CT 23
-moderate strength/low propagation potential.

This is a great illustration of how slab depths can change dramatically across a slope. The distance between Pit 2 and Pit 4 was less than 50 feet. A common term for this is ‘spatial variability’. Wind is often a driving force behind creating this pattern. Our test results changed slightly as we moved across the slope-thin slabs were easier to trigger than thick slabs. While it was easiER to trigger the thinner slabs, it was still difficult in that test scores were on the high end of the scale (>23). This points to the overall trend of it becoming more difficult to trigger an avalanche. As stated above, this was also the first day since this slab formed that we have seen low propagation potential in tests.

Photos & Video
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