20-21

Loose Dry Avalanches on the Throne

The Throne
Bridger Range
Code
L-N-R1-D1-I
Elevation
8000
Aspect Range
SE-NE
Latitude
45.88220
Longitude
-110.95200
Notes

Multiple small dry looses all across the throne. Sliding on a thin sun crust with overlying near surface facets buried 15-25 cms down. None stepped down to deeper layers.

Number caught
0
Number buried
0
Avalanche Type
Loose-snow avalanche
Trigger
Natural trigger
R size
1
D size
1
Bed Surface
I - Interface between new and old snow
Problem Type
Loose Dry
Slab Thickness
20.0 centimeters
Vertical Fall
500ft
Slab Width
50.00ft
Weak Layer Grain type
Near surface faceted particles
Weak Layer grain size
2.00mm
Weak Layer Hardness
F+
Slab Layer Grain Type
Decomposing and Fragmented precipitation particles
Slab Layer Grain Size
1.00mm
Slab Layer Hardness
F
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year

Divide Peak CT test on 1/23

Date
Activity
Snowboarding

Sorry about the old data but I though some Hyalite-specific observations might still be useful. We did a quick compression test near the base of Divide Peak on Saturday (location on map below should be pretty accurate). I could not see the buried surface hoar but maybe I should have looked more carefully because the compression test revealed two weak layers. We got: CT11, Q1 @ 12" below the surface, CT14, Q1 @ 15" below the surface, and the ground facets (about 36" below the surface) crumbled at CT22. More subjective observations: snow penetration while skinning was only about 6 inches and even hard turns only made 10"ish deep tracks. Nice snow, but relatively firm base.

Region
Northern Gallatin
Location (from list)
Divide Cirque
Observer Name
Alex Lussier

Northern Bridgers, West of Sixteen Mile Creek headwaters

Date
Activity
Skiing

Sorry this is late, from 1/23/21
Two pits: Immediately west of Sixteen Mile Creek headwaters on Ridge
No collapsing on the way up.

1) NNE Slope
Slope 29 degrees
Elevation 8000 feet
Depth 100 cm
Upper 15 cm - fist
upper 55 cm - 1 finger hard
lower 30 cm - 4 finger hard
ECT X

2) NNE Slope (same slope)
Slope 30 degrees
Elevation 8200 feet
Depth 137 cm
Upper 100- 137 cm - fist
upper 80 -100 cm - 1 finger hard
lower 30 - 80 cm - 3 finger hard
Lowest 0-30 cm - 4 finger hard
ECT 29
Failure on Surface Hoar at 80 cm, clean surface
Skied the slope several times

Region
Bridger Range
Location (from list)
BRIDGER RANGE
Observer Name
Jeff Riedel

GNFAC Avalanche Forecast for Tue Jan 26, 2021

Snowpack and Avalanche Discussion

<p>The mountains from the Lionhead Range through the Bridger Range received 1-3" of snow in the previous seven days and nothing in the last four. The lack of new snow provides the weak snowpack time to adjust and avalanches are becoming less likely. On Sunday, a snowmobiler triggered a wind-loaded slope in the Taylor Fork that piled debris 8 feet deep (<a href="https://mtavalanche.com/images/21/snowmobile-triggered-avalanche-sunlig…;). Yesterday, we did not see any other recent activity in the area, but we triggered a collapse and found a reactive layer of surface hoar buried 6-18" under the snow (<a href="https://www.youtube.com/watch?v=hkLoYCcemg0"><strong>video</strong></a&…;). Alex found similar conditions at Bacon Rind (<a href="https://www.youtube.com/watch?v=Sw_8eiygoSc"><strong>video</strong></a&…;). The weak depth hoar near the snowpack's base across all areas remains the most concerning weak layer. In the last week, we have reported avalanches, loud "whumphs" and unstable test results in the Madison, Gallatin, Lionhead and Bridger Ranges (<a href="https://mtavalanche.com/weather/wx-avalanche-log"><strong>weather and avalanche log</strong></a>, <a href="https://www.youtube.com/watch?v=HtHMcXwo3mw&amp;list=PLXu5151nmAvQDzKmH… video</strong></a>, <a href="https://youtu.be/fUK0nUTBSvU"><strong>Buck Ridge video</strong></a>). In the last two days and for the first time in a month, depth hoar in two of my snowpits did not propagate failure with extended column tests. This is a good sign, but keep the big picture in mind remembering that trust for this deeply buried sugary snow will be hard-earned.</p>

<p>Plan your route carefully and assess the snowpack thoroughly if you are considering entering avalanche terrain. Finding any sign of instability is a good reason to turn around and stick to low-angle terrain. Large, human-triggered avalanches remain possible and the danger is rated MODERATE.</p>

<p>Snowmobilers triggered several avalanches north of Cooke City three to four days ago on a layer of weak snow buried 12-18" deep. Yesterday, skiers recently witness a spiderweb of shooting cracks breaking on the same layer (<a href="https://mtavalanche.com/images/21/shooting-cracks-meridian-peak"><stron…;). Despite these events, stability is showing signs of improving. Currently, Doug is documenting these and other avalanches in the area (check out the <a href="https://mtavalanche.com/images/21/snomobiler-triggered-slide-near-huckl… photo</strong></a>, <a href="https://mtavalanche.com/images/21/cornice-triggered-avalanche-miller-ri… Ridge photo</strong></a>, <a href="https://mtavalanche.com/images/21/2-avalanches-sheep-mtn"><strong>Sheep Mountain photo</strong></a>). He found the suspect weak layer buried and it is adjusting to the weight on top (<a href="https://mtavalanche.com/images/21/surfae-hoar-crystalcloseup"><strong>p…;). A second weak layer of sugary snow is buried 2-3' deep on some slopes. This deeper layer is more prevalent in the thinner snowpacks around Cooke City and skiers recently triggered large collapses on this layer.</p>

<p>While tracks <em>don't equal</em> stability, riders are climbing steep slopes and are generally <em>not</em> triggering avalanches. A rider or skier can get unlucky and hit the "sweet spot" but the snowpack is less sensitive.&nbsp;Human-triggered avalanches remain possible and the danger is rated MODERATE.</p>

<p>If you get out, please send us your observations no matter how brief. You can submit them via our <a href="https://www.mtavalanche.com/node/add/snow_observation"><strong>website<…;, email (<a href="mailto:mtavalanche@gmail.com"><strong>mtavalanche@gmail.com</strong></a…;), phone (406-587-6984), or Instagram (#gnfacobs).</p>

Upcoming Avalanche Education and Events

See our education calendar for an up-to-date list of all local classes. Here are a few select upcoming events and opportunities to check out:

Yellow mule. Creek

Date
Activity
Skiing

Hi I performed some tests today at the yellow mule trail north face in a shelter tree area at 7000 ft. It was 1 pm when I got ectp12 SC 40 cms down. It fail above the 25 cm of facets at bottom of the snowpack. I did not find surface hoar hurried. Lots of woofing and cracking

Observer Name
Pedro Crespo