January 11, 2017


Eagle River: South Fork

Hiked up South Fork Eagle River trail to Rendevous Ridge trail. Did pit observation on toe of slope at treeline south of trail intersection. Snowpack is thin and variable (5-40cm) over entire valley. Not enough to ski, just enough blown into pocketed and gullied terrain to dig. Most of snowpack in area is variations of weak layers of faceted snow, with pockets of thin ~10-30 cm windslab on top in isolated catchment areas.

Thickest sections of windslab cracked and fractured in table size sections underfoot. Otherwise full boot penetration to ground in most of snowpack.


Clear, calm wind, no precip, no recent precip, 25 degrees F

Surface conditions:

Old, mostly faceted snow with pockets of windslab.


Dug test pit in 20x20m windslab pocket:
2600ft, N aspect, 29 degree slope
HS = 38cm (range ~30-45cm)

16 cm of windslab sitting on top of multiple layers of faceted grains, decomposing melt-freeze crusts, buried surface hoar, and an 11cm depth hoar layer.

Stratigraphy (layers):
0-11 cm: depth hoar and 2-3mm facet chains, F
11-13 cm: faceting melt forms, 1F
13-16 cm: 1.5mm facets, 4F
16-17 cm: 3mm faceting melt-forms, P
17-33 cm: faceting wind slab (.5mm grains), 1F, decreasing to 1F- and 4F in spots

Test results:
CTV Q3 on 11 cm depth hoar
ECTP11 Q3 on 11 cm depth hoar

PST 27/100, down 22cm ARR
PST 79/100, down 17cm ARR

Observed another weak layer upon removal of slab in test: Q1 shear and evidence of buried surface hoar not noticed in all of pit layering (spotty 4F weak layer at bottom of slab – see photo)

There is a stiff windslab present over a very weak basal layer, and faceted midpack in isolated catchment areas (gullies and NE-NW facing leeward rollovers). Collapse potential of the slab on the weak layers is very easy to moderate. Propagation potential appears significant from pit tests but shear quality and sparse occurrence of these slabs, and high variability in the snowpack layering and strength, may keep this from being a widespread problem. Keep in mind that these pockets of reactive slab are present when we receive more snow.