CNFAIC LogoCNFAIC Logo

Observations

Region: Anchorage Front Range
Location: SF Eagle River/Rendevous Ridge Trail intersection
Observer:
Date:

Route & General Observations

When you are waiting for a back to heal and the snow to come…it is time to go practice snowpit skills and gather snowpit observations!!

Hiked up SF 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 deposition areas.

Red Flags

Observer Comments

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

Weather

Weather

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

Snow Characteristics

Snow surface

Old, mostly faceted snow with pockets of facet-grain windslabs.

Snowpack

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

16 cm of windslab of old faceted (0.5mm) snow grains blown into a fairly strong slab (...hmm?) sitting on top of multiple layers of faceted weak layers; defragmenting melt-freeze crusts, faceted buried SH, topping an 11cm depth hoar layer.

Snowpit results:
0-11 cm: depth hoar, 2-3mm chains and individual grains, F
11-13 cm: melt-form, variable faceting crust, 1F
13-16 cm: facets, 1.5mm, 4F
16-17 cm: melt-form clusters, 3mm, P
17-33 cm: facets, 0.5mm, 1F, decreasing to 1F- and 4F in spots

Test results:
CT = CTV Q3 on 11 cm depth hoar
ECT = ECTP11 Q3 on 11 cm depth hoar layer, but observed on removal of slab another separation in slab: Q1 shear and evidence of a faceted old buried surface hoar grains not noticed in all of pit layering (spotty 4F weak layer at bottom of slab). (see photo)
PST = PST 27/100, down 22cm ARR
PST = PST 79/100, down 17cm ARR

Synopsis:
There is a stiff windslab present over very weak basal layer, and faceted midpack in very isolated pocket and deposition terrain (gullies and NE-NW facing leeward rollovers). The windslab actually looks to be packed old faceted snow grains (not rounds) but acts like a dense solid slab until it starts to break up. (The grains don't form into a snowball) 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 help this from being an overall widescale problem. But this is something to keep in mind that these pockets of reactive slab are present if that BIG storm ever happens...or at least enough snow to making skiing something of a reality!

Let it snow!!

Photos & Video

Photos



USFS SNOW AND AVALANCHE HOTLINE (907) 754-2369
If you have comments or questions regarding CNFAIC operations or winter recreation management, please email staff@chugachavalanche.org
© 2017 Chugach National Forest Avalanche Information Center. All rights reserved.
FCNFAIC
Donate
If you think a public avalanche
center is important then we urge
you to become a member & donate.


PickClickGive