Snow Observations List

We toured into Hyalite Peak to investigate a large, skier-triggered avalanche that occurred on Saturday (avalanche details and photos). The avalanche broke 750' wide, ran 650' vertical and broke 3-5' deep. It failed on a layer of sugary facets buried 95 cm (3 feet) deep. This layer had not been producing avalanche in the weeks prior to this slide. We measured 8.3" of snow water equivalent contained in the slab overlying the weak layer. We tested the weak layer in the eastern most part of the crown and got an ECTP26.

Additionally, we found a very weak layer of facets and surface hoar buried 1-1.5 feet deep. This had nothing to do with the large avalanche. The party reported triggering some small wind slabs near the summit, these may have been related but we don't know for sure. This layer failed with at ECTP13 and ECTP20. We looked for it again on our exit from the basin and came up empty. It is certainly something that we will look for in the coming weeks, but the primary driver of our decision-making will remain the deeper instability for now. 

We saw 6 natural avalanches on our ride in Lionhead. They all involved snow in the last week or two. On our exit we ran into who a group that witnessed a sledder triggering this slope. It was about 3 feet deep and was clearly wind loaded. Luckily he was not caught. When folks are triggering slides we know other slopes are also unstable. Be careful out there!

From IG, “Noticed a few natural and human triggered surface slides of the new snow on the old crust layer. All of these were north of Bridger Bowl on The Ramp”

Our party experienced a sudden collapse while ascending, as we exited the trees above Olie’s Woods and began to cross a a meadow @9600’. The collapse was assumed to be at least 100’ wide, as we saw a small tree shake approx 100’ from the leader and our entire party felt the collapse. We dug a pit and got the following results:

HS 135

ECTP 17; 55cm down.

SP- Q1, Sudden Planar failure, entire block slid into pit

Failed on 2mm facets, 10 cm below an ice crust.

On Buck Ridge today (3/5/23) we found fresh, unstable drifts and buried weak layers. Recent avalanche activity is a sign that buried weak layers could be triggered and cause large avalanches, even though we didn't see unstable results in our snowpack tests.

Be cautious of steep slopes, especially if they are wind-loaded and avoid steep slopes if you suspect buried weak layers exist. Recent snow being drifted into thicker slabs is adding weight to weak layers and may cause danger to rise.

Around 4 or 5 pm today we rode out of Sheep Creek into the Miller Mountain area. When we looked at Miller there was a large avalanche that appeared to have occurred naturally (to our knowledge). It looked like the crown was 12-24'' and a few hundred feet wide. The debris looked fresh and must have occurred today. Given the depth we assumed it was windslab that had built up sometime in the last few days; however, hard to tell from so far away. We also observed another smaller natural avalanche on an exposed ridge below Miller Mtn, this looks to have been about 12in deep and probably occurred on the same layer as the larger avalanche. Both were on N or NNW facing slopes in areas with heavy wind deposition.

PST 50/100 at two layers - 115 down(crust facet combo) and 140 down (basal facet interface) 7500 ft NE aspect 15 degree slope angle. Several ECTX across region.

While skiing Shafthouse Hill I intentionally trigger a wind slab on a small slope. The slab was actively forming with the new storm snow. I triggered it by ski cutting the slab at the rollover. It broke very easily and was approximately 15cm thick.

Aspect: SE

Slope angle: 36 degrees

Elevation: 8315’

Weather conditions @ 1130, overcast and moderate snowfall, 18 degrees F, winds SSE 15-20 mph.

Single pit (aspect: 100 deg, slope angle: 18 deg), two tests:

1. CTN

2. ECTX

- Lochlan Bennett, age 13, first snowpit (with assistance from a friend)

Our party dug a quick pit while skiing Submarine Bowl on woody ridge. Our pit was E facing at 9800 ft. Total snow depth was 205cm. We got an ECTN 25 @176cm from the ground. Though we were not able to get propogation on that layer, we were reliably able to get Q1 failures on that layer with a series of column tests which failed around 15-20 taps (5-10 elbow taps). Attached is a picture of one of these failed column tests. We didn't really observe any cracking or collapsing while we skied or approached from republic creek. 

Hey GNFAC,

I dug on a SE facing aspect at the top of the Skillet in Bacon Rind today.

I found a HS of 163cm, and a 40cm slab from the last two weeks of on top of at least four notable weak layers.

I was initially optimistic about the stability, but had an easy shovel shear test, followed by an ECTP17 Q1 at 120cm up from the bottom.

Our group opted not to ski the Skillet, and found some great turns in lower angle trees nearby.

Another observation of note is a widespread layer of surface hoar that was deposited about 4 days ago, and is now covered by about 10-12 cm of snow.

Ben Zavora of Beartooth Powder Guides and the GNFAC investigated a skier triggered avalanche near Daisy Pass (3/2). It was remotely triggered (they were not on the slope) and failed on a layer of feathery surface hoar crystals that formed in early January. The slab was 4 feet thick and very dense and termed a Deep Slab Avalanche. The recent snow and wind added weight and stressed this layer to its breaking point. In January we found surface hoar on all aspects, so it's a bit scary. Remotely triggering a 4' deep hard slab avalanche is dangerous. The slope angle at and near the crown was only 31-32 degrees; very shallow. Surface hoar is known to break on less steep slopes, which can catch us off-guard.

It's time to recalibrate our thinking because deep slab avalanches are deadly, yet not very widespread. It will become a low-probability, high consequence problem.

FYI big skier triggered avalanche on the lawn mower slide path on town hill today around 3pm. One skier caught and buried to neck and later airlifted out with leg injury. Our party arrived maybe 45 min after the slide and assisted others who were there.

Yesterday, I was in the party of three that had one skier injured on the Lawn Mower, and witnessed the slide. 

Our pit results before the descent were stable (ECT-X), we made sure to dig past the problematic layer noted in the snowpit observation at town hill on 2/19. 

We began our descent leapfrogging one another to zones of safety. Myself and the third person in our party below the skier in a safe zone when he was was caught. The avalanche broke above him and came down on to him to sweep him down into the gully. Based on how he trigged it toward the far edge of the path, best guess is he found a shallower trigger point that remote triggered above. 

The two of use remaining split up so one could search above where we last saw him, and one going down the path. Got a signal and shortly spotted him buried with his head and arm out and conscious. After excavating him it was clear his leg was broken at the femur. 

Two other groups showed up on the scene some time after to help. 

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Outside of the observation above, one of the groups gave their extra jackets and we do not have contact information to return them. If possible would you be able to share that with me? 

On March 4th around 2:15 PM my partner and I observed a skier (of a separate party that was caught and carried) in a D2 R2 on the Lawnmower in the Absorkas. I believe the slide was released on a buried weak layer (We only observed the crown from a distance). The victim came to a stop approximately 1,200 ft below the start zone and was buried up to his neck. There were multiple tracks on the slope prior to the avalanche. My partner and I skied up to the separate party with the victim approximately 30 minutes after the event. 

We skied the Throne today, the windboard from thursdays wind was more widespead than we had hoped. It wasn't very well bonded, and didn't feel good, but it wouldn't move, either. I dug a pit on the north facing at the top, away from the windboard, and got no results. I tried to get down to the older weak layers and could spot them and get them to break, but I had to wrestle with it to get it to do it. Parking is still limited.

Traveling into Blackmore Basin we assessed two potential lines from below that we had already planned to potentially ski.  We gained the saddle between Blackmore and Elephant. We observed snow transport from SW winds and noted the zone we were heading to might have wind loading occurring at the top. We traversed on scoured slopes by foot over to the entrance of the line that we intended to ski. Upon our arrival we noted a convexity of wind loaded snow on the skiers left of the start zone and made note to avoid it. We transitioned to skis and made a plan for skier 1 to enter traversing to the skiers right. Once skier 1 started traversing to the right, approximately 40 feet from skier 2,  a small collapse propagated at the ski tips of skier 1 across the entire entrance. Skier 1 yelled avalanche and was able to self arrest on the bed surface/ crown. After the slide occurred, we reassessed and felt comfortable descending on the bed surface to the toe of the debris, one at a time. We decided that was enough for one day and headed back to the trailhead. In retrospect, we underestimated the size of the potential wind slab and the danger of the high consequences terrain where a slide might not bury but potentially carry and kill a skier by taking them over cliffs. 

SS-ASu-R2-D1.5-I

Vertical Fall: ~700'

Distance Traveled: ~1000'

Aspect: 15 N

Elevation of start zone: 9645'

Chunk of cornice fell off the top of Arden Peak. Notably the same aspect/elevation as the 2/27 observed natural slide on E face of Mt Bole but the cornice fall did not step down beyond the surface snow.

(NE, HS, ASu, D3, R4)

We toured into Hyalite with the intention of skiing the North East Face of Hyalite Peak. Our primary concern was wind loading on leeward slopes. Before starting the day 6" of snow was reported in the Northern Gallatin range however we only found up to three inches of new snow. Approaching the saddle we found soft snow (2-3") on a pencil-hard crust. Once reaching the summit we descended carefully onto the NE face observing a shooting crack on a pocketed soft wind-slab after performing a ski cut. Noting this we descended further staying on the ridgeline. We then found a similar snowpack to the saddle with no cracking after a few more ski cuts and decided to ski one at a time down the duration of the face. Skier 1 skied a few turns down the face when a loud wumph was heard and the whole face started sliding. Skier 1 was caught, carried, and partially buried at the tail of the slide path. Skier 2 observed skier 1 and skied down to them after the avalanche stopped. Skier 1 was then fully dug out and both skiers left the avalanche path unharmed. The slide was thought to be (D3,R4) breaking all the way to the ground and spanning at least 500' wide. 

During wolf watching this morning we noticed large areas of avalanching snow between Mammoth-Balacktail-Tower. Break face 2-3 feet. Slope was only 20%. We were very surprised to see this terrain producing avalanches.