23-24

Recent Natural Wet slides in Bridgers

Date

Thu, 02/01/2024 - 12:50

I drove up Bridger canyon this afternoon and stopped in a few spots to glass the range for recent avalanches. There were many recent wet avalanches, both wet loose that gouged through the snowpack and wet slabs about one foot deep and 50-100' wide. Many size D2, some smaller. Happened sometime between Monday and today (1-3 days old, maybe some this morning). The main spots for recent wet avalanches were on Bridger Peak and south of the Throne. Mainly on sustained steep terrain with rocky outcrops and east-south facing. There was one wet slab on a northeast facing, mid-elevation slope near the Throne. South facing terrain near Fairy Lake had some wet loose activity. I attached a photo of the wet slab activity on Bridger Peak and south of the Throne.

I also saw a wide crown in Frazier Basin and a similarly wide crown in another bowl to the north (300-400' wide). Photos attached. I am not sure if these occurred recently with the above freezing temperatures or if they are older. they do not appear wet like the others, but I could not see the debris and was generally far away. Also they are in higher terrain favored for cooling effects. But, they easily could have occurred over the recent hot days, potentially triggered by cornice fall?

Region

Bridger Range

Location (from list)

BRIDGER RANGE

Observer Name

Alex Marienthal

Not as Wet in Taylor Fork, but Still Unstable

Date

Thu, 02/01/2024 - 12:15

Activity

Snowmobiling

We rode into Taylor Fork today towards the Beaver Creek wilderness boundary. We saw multiple natural avalanches that happened during the last week, some newer than others and ranging in size (some in gullies others 50-75' wide). Many of these avalanches were old enough to be unrelated to the recent warming. However, at the wilderness boundary on an east-facing slope, we saw one natural wet slab avalanche and several smaller wet loose avalanches that likely happened yesterday during the warm sunny weather.

We felt a large collapse while approaching our snowpit location on an east-facing slope at 9300'. The pit was mostly faceted snow capped by a small cohesive slab and crust. We got an ECTP2, which is a very unstable result. We continued riding and after parking felt another collapse just 20' from our snowmobiles. We dug on a southwest-facing slope at 8800' and again had poor stability test results of ECTP6. Facets near the ground were moist but our stability tests were failing on dry facets above.

Clouds began rolling in around 11 AM, and a strong southwest wind remained throughout the day. Almost all slopes had a crust on them and temperatures remained cold enough that they did not soften.

Region

Southern Madison

Location (from list)

Taylor Fork

Observer Name

Zach Peterson

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Sketchy in the Tobacco Roots

Date

Wed, 01/31/2024 - 10:00

Activity

Skiing

Toured up to the south side of Bell Lake near treeline. Found sugary facets with the smallest sun crust on top, but generally less heat impact than in other areas. The snow above treeline was cold and preserved into a large slab.

I heard two large whumpfs once I got into a clearing around the treeline.

Three large old naturals were spotted on east faces.

Dug a pit on a NE facing slope at around 9,207ft. The surface did not appear to be loaded relative to the rest of the area, but wind impact was noted, 140cm deep snowpack. CT11Q2 50 cm up, ECTP19 60 cm up. The structure was condescended basal ice with a layer of depth hoar that increased in softness as the distance from the bottom increased. Between 40-50cm was a reactive layer of fist facets, and between 50-55cm was a pencil/knife crust, with another layer of fist facets above. The slab was a 1F hard slab that was consistent in structure from 60cm to the top of the snowpack. The slab seemed to be formed by multiple wind events as there where multiple slabs stacked up with no weak layer in between.

Region

Out of Advisory Area

Location (from list)

Bell Lake

Observer Name

Jay Alford

GNFAC Avalanche Forecast for Thu Feb 1, 2024

Snowpack and Avalanche Discussion

Wet avalanches are our primary concern today. This is the 4th day in a row with no freeze or a light freeze in the mountains around Bozeman and Big Sky. Ian rode into Buck Ridge yesterday and saw wet slab avalanches, some big, on Cedar Mountain, and lots of wet loose rollerballs (<a href="https://www.mtavalanche.com/node/30427"><span… and photos</a>, <a href="https://youtube.com/shorts/n0SqMbdQaoI?feature=share"><span…;). His stability test scores were shockingly low and he got a large collapse when he stepped out of his snowpit. The thin, exceptionally weak snowpack, is susceptible to wet slab avalanches on sunny slopes. We don’t have a lot of experience with wet slides on a thin snowpack this early in the winter, but we recognize it is dangerous. Thus, the wet snow avalanche danger could reach HIGH today.

If you are hunting for dry snow on upper elevation shady slopes, you’ll have to pass through zones that are wet. If you persevere, you will need to contend with a snowpack that has a poor structure and remains unstable on some slopes. Weak, sugary snow the bottom half of the snowpack is capped by a 1.5 to 2 foot thick slab of snow. Ian was in the Fairy Lake area in the Bridger Range on Tuesday and navigated the wet and dry snowpack. He found it possible to trigger an avalanche at the interface between the slab and sugary facets (<a href="https://youtube.com/shorts/GsL_adXQYr8?feature=share"><span…;). This story is the same throughout our northern ranges and the dry snow avalanche danger is rated MODERATE.

Around West Yellowstone, Island Park and Cooke City the surface snow got moist and a few wet avalanches from Tuesday were noted in Cooke City (<a href="https://www.mtavalanche.com/node/30437"><span…;). A dry snow avalanche on Daisy Pass Tuesday afternoon was likely triggered at the interface between a dense wind slab and loose, sugary facets underneath (<a href="https://www.mtavalanche.com/node/30425"><span…;). This recipe of weak, unstable facets avalanching both naturally and with human triggers is everywhere in the southern mountains. I spent Sunday through Tuesday in Cooke City and found instability and an identical snow structure at the avalanche near Round Lake that <a href="https://youtu.be/cn0lR8XMzl4">… buried a rider</a>, at a large avalanche on <a href="https://youtu.be/BPzHM3837QY">… Mountain</a>, the 2 smaller natural slides on <a href="https://youtu.be/uKY34ndFmpw">… Ridge</a>, and up <a href="https://youtu.be/ZTr2QiFzbcM">… Creek</a>. Dave found the same thing in Island Park (<a href="https://youtube.com/shorts/p7JX_bhkjUA?feature=share"><span…;), and we know the mountains in between are similar. Triggering avalanches is likely, even from hundreds of feet away. On Monday, ice climbers hiking near Pilot Peak had a whumpf which triggered a large slide 150 feet distant (<a href="http://www.mtavalanche.com/node/30408">…;).

The snowpack remains unstable long after receiving a load of new snow. Recent avalanche activity, collapsing, and wet snow on sunny slopes are evidence to approach avalanche terrain very carefully. For today, the avalanche danger is CONSIDERABLE on all slopes.