23-24

New Snow Instability

Date
Activity
Snowmobiling

We rode through White Elephant and Yale Creek to the head of Hellroaring Creek. There was 8-10” of dense new snow. Poor visibility limited The avalanche viewing. 

As we reached the upper reaches of Yale, the snowpack was 250-280cm deep. When we dropped our probes to the base of the snowpack, we found weak snow toward the bottom. CTs and ECTNs in the single digits broke below the new snow on a layer of graupel. No other upper-level instabilities were noted. The depth of the weak layers at the base of the snowpack makes them difficult to trigger but any subsequent avalanche would be catastrophic. 

Region
Island Park
Location (from list)
Centennials - Idaho
Observer Name
Dave Zinn

Signs of Avalanches on Ross Peak

Date
Activity
Skiing
Snowboarding

Deep Avalanches all over the mountain in multiple spots. One was spread across the Ross Peak approach gully and debris ran all the way to the bottom of the gully.

Region
Bridger Range
Location (from list)
Ross Peak

GNFAC Avalanche Forecast for Tue Mar 12, 2024

Snowpack and Avalanche Discussion

<p>Dangerous avalanche conditions exist in the mountains south of Bozeman through Cooke City, Big Sky, West Yellowstone, and Island Park. Today's new and wind-drifted snow will keep the snowpack on edge. Enormous avalanches breaking 5-10 feet deep and hundreds to 1000s of feet wide on deeply buried persistent weak layers are possible, and they are almost certainly unsurvivable if they wrap you up in their grasp. Smaller avalanches within the new and wind-drifted snow are likely.</p>

<p>Recent human-triggered avalanches in Cooke City resulted in partial burials on Sheep Mountain (<a href="https://www.mtavalanche.com/node/31377"><strong><span>photos</span></st…;) and multiple close calls on Scotch Bonnet Mountain (<a href="https://www.mtavalanche.com/node/31345"><strong><span>details</span></s…;, <a href="https://www.mtavalanche.com/node/31357"><strong><span>details</span></s…;, <a href="https://www.youtube.com/watch?v=9kyGpQxAs2A"><strong><span>Scotch Bonnet video</span></strong></a>) and Miller Mountain (<a href="https://www.youtube.com/watch?v=BJGckpdQQpQ&amp;list=PLXu5151nmAvSH326z…;, <a href="https://www.mtavalanche.com/images/24/big-avalanche-north-miller-mtn"><…;). Last Thursday, a rider triggered a behemoth avalanche on Henderson Mountain that broke 2000 feet wide and over 10 feet deep in places (<a href="https://www.mtavalanche.com/node/31294"><strong><span>photos, video and details</span></strong></a>). Read about and look at photos of the long list of large human-triggered and natural avalanches on the <a href="https://www.mtavalanche.com/avalanche-activity"><strong><span>avalanche activity log</span></strong></a>.</p>

<p>The frequency of avalanches in the mountains south of Bozeman through Island Park has not equaled Cooke City. However, the magnitude of the slides makes my stomach turn. Yesterday morning, groups reported a fresh avalanche on the north side of Mount Blackmore that ripped apart mature trees after breaking 8 feet deep and hundreds of feet wide <span>(</span><a href="https://www.mtavalanche.com/node/31432"><strong><span>overview video and photos</span></strong></a><span>)</span>. Three avalanches at the head of Beehive Basin broke 3-5 feet deep this weekend, one of which wiped out the skier’s skin track and piled debris 10-15 feet deep (<a href="https://youtu.be/ZaqRmvvNp9c"><strong><span>video</span></strong></a&gt;, <a href="https://www.mtavalanche.com/node/31386"><strong><span>details</span></s…;, <a href="https://www.mtavalanche.com/node/31343"><strong><span>photos and details</span></strong></a>).</p>

<p><span>Execute a conservative travel plan that largely avoids slopes over 30 degrees. If you go onto steeper slopes, select smaller pitches free of terrain traps and at the lower angle end of the spectrum, and be prepared should something go wrong. The danger is CONSIDERABLE. </span></p>

<p>Human-triggered avalanches breaking within recent and wind-drifted snow are possible in the Bridger Range. Last week, two skier-triggered avalanches on Saddle Peak initiated on wind-loaded slopes and broke 1-2’ deep and up to 200’ wide (<a href="https://www.mtavalanche.com/node/31330"><strong><span>details and photos</span></strong></a>). Skiers in the northern Bridger range noted recent natural avalanches that occurred earlier last week (<a href="https://www.mtavalanche.com/node/31418"><strong><span>Bridgers photos</span></strong></a>). Slides do not need to be large to injure or kill backcountry travelers, especially when they are in high-consequence terrain like those on Saddle Peak.</p>

<p>Assess the snowpack for instability before considering terrain steeper than 30 degrees. Choose simple, low-consequence terrain and slopes without previous wind-loading. Carry rescue gear and only expose one person at a time to steep slopes. The avalanche danger is rated MODERATE.</p>

Upcoming Avalanche Education and Events

Our education calendar is full of awareness lectures and field courses. Check it out: Events and Education Calendar.

Next weekend in Cooke City: Friday at The Antlers at 7 p.m., Free Avalanche Awareness and Current Conditions talk, and Saturday from 10 a.m.-2 p.m. at Round Lake Warming Hut, Free Rescue Practice.

Large avalanche N face Blackmore

Mt Blackmore
Northern Gallatin
Code
HS-NC-R3-D3.5-O
Elevation
9800
Aspect
N
Latitude
45.44440
Longitude
-111.00400
Notes

Large avalanche North face Mt Blackmore. Appeared to be potentially triggered by cornice fall from above. Crown propagated across majority of the bowl and was quite large in places. 

From Obs: "Cornice fall triggered a big one. Looks to be real fresh. last night or this morning    Broke across the whole bowl and up to 8 feet deep maybe more right in the middle. Broken trees in the debris, And ran out of sight."

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Hard slab avalanche
Trigger
Cornice fall
R size
3
D size
3.5
Bed Surface
O - Old snow
Problem Type
Persistent Weak Layer
Slab Thickness
96.0 inches
Vertical Fall
1000ft
Slab Width
600.00ft
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

Skiers noted a large natural avalanche on the North face of Mt Blackmore that broke overnight. The crown was around 8 feet deep. Photo: E. Roman

Northern Gallatin, 2024-03-11

Maid of Mist Basin

Date

Large avalanche in Maid of the mist basin

Observer Name
Wallace Casper