Sawtooth Avalanche Center

Pro Field Report

Basic Information

Observation Details

Observation Date:
February 5, 2020
Submitted:
February 5, 2020
Observer:
SAC - Martin Stefan
Zone or Region:
Galena Summit and Eastern Mtns
Location:
South of Gladiator ck

Signs of Unstable Snow

Recent Avalanches? 
Yes
Cracking? 
Isolated
Collapsing? 
None Experienced
Fresh drifts cracked in a 30'+ radius around me on S side of ridge from 9000' upwards, one D1.5 avalanche had just released in the soft wind slab and I kicked a few D1s.

Snow Stability

Stability Rating: 
Poor
Confidence in Rating: 
High
Stability Trend: 
Improving

Bottom Line

Went to investigate crown on avalanche from S side of Gladiator. It failed on a layer of facets buried under a stiff wind slab that most likely got overloaded during the wind event on Monday 2/3.

On the way up the ridge line, I spotted a fresh D1.5 avalanche down the south face of the ridge line and fresh wind drifts on leeward slopes were reactive and easy to trigger. Wind has now blown both from NE and NW with a bit of snowfall thrown into the mix, making wind loading patterns more complex to deal with.

Media/Attachments

Thick portion of the crown of an avalanche that occurred south of Gladiator Ck. The avalanche failed on a persistent weak layer near the base of the snowpack during Monday's wind event.

Advanced Information

Weather Summary

Cloud Cover:
Overcast
Wind:
Moderate , NW

Breezy up high, mostly overcast and S-1 to S1 all day. Lots of wind transport at higher elevations, loading S-SE faces. Hard to gauge accumulation up high due to wind, down at hwy level 2-3" by 3pm.

Avalanche Observations

 #  Date Location Size Type Bed Sfc Depth Trigger Comments Photo
1 S of Gladiator Ck
S 9600'
D1.5 SS S-New Snow 20cm N-Natural Crown depth tapers from 10 to 40 cm, looked like it slid the full path but low confidence due to bad visibility. Judging by the rate of wind loading and how crisp the crown was, I don't think it was more than a couple of hours old.
Small avalanche in fresh, soft wind slab most likely failed sometimes around or before noon 2/5 due to ongoing wind loading.
1 Start zone S of Gladiator ck, west of earlier slide
SW 10000'
HS O-Old Snow 15cm (?) N-Natural The other half of the starting zone I went to investigate had slid sometime between yesterday afternoon and noon today, the area circled in the picture (taken yesterday). Slab was probably very thin and visibility was hit and miss, but I am fairly confident the northern half of the starting zone was gauged down to the same bed surface as the original slid, first observed on Monday.
The area in the circle avalanched sometime between yesterday afternoon and 2pm today. Probably a very thin slab, 4-6", failed on a thin layer of facets on a hard alpine surface

Snowpack Observations

Crown of original avalanche between 1,5m and 50cm, P-K hard. Failure layer is a 3cm thick layer of small facets, 4f hard, sandwiched between the hard slab and a K hard bed surface. The weak layer is continous along the whole crown, and my guess is that it got overloaded by wind drifted snow where the slab is thinner and propagated across, as opposed to being triggered by a cornice drop where the crown was thickest, but confidence not very high on that guess.

Crown in the first of the lower pockets on lookers right that got ripped out was thinner, around 30cm tapering down to under 20cm, HS approx 90cm. No results on ECT, PST55/100end

In the track 10-15m below crown HS around 20cm with rocks poking through in places. Mostly K hard wind crust around 10cm thick with well developed, stirated and sometimes chained DH below.

Lots of wind loading along ridge created touchy soft slabs, below approx 8600' a zipper crust could be felt under the new snow when nibbling on S side of ridge.

Crown profile where the slab was ripped out on lookers right.
Crown profile where the crown was at its thinnest on lookers left.

Avalanche Problems

Problem Location Distribution Sensitivity Size Comments
Wind Slab
Isolated
Specific
Widespread
Unreactive
Stubborn
Reactive
Touchy
D1
D1.5
D2
D2.5
D3
D3.5
D4
D4.5
D5
Layer Depth/Date: 10-50cm, 2/5 and 2/3
Comments: Wind from both NW and previously NE makes loading patterns complex.
Persistent Slab
Isolated
Specific
Widespread
Unknown
D1
D1.5
D2
D2.5
D3
D3.5
D4
D4.5
D5
Layer Depth/Date: 20-100cm, weak snow near the ground or mid-pack
Comments: It is clear that these layers are still in the mix, especially if loaded by fresh wind slabs. I did not perform any tests today, but the one fresh slide on an S aspect did not look like it stepped down. On the other hand, the thin snow on the lookers left of the starting zone seemed to have failed recently on persistent grains.

Terrain Use

I avoided avalanche terrain including overhead hazard except for the bed surface in close proximity to crowns.