Date of Observation: 02/25/2022
Name: Eric Murrow
Zone: Northwest Mountains
Route Description: Snowmobile out Slate River to just past Pittsburg. Ascended west and southwest terrain to Elkton Knob. Descended the same terrain.
Observed avalanche activity: Yes
Avalanches: In this terrain, there were numerous natural avalanche midstorm (partially filled bed surfaces) on west-facing below treeline terrain, generally D1.5 with one D2. We remotely triggered a steep west rollover from several hundred feet away.
Weather: Light snowfall and obscured skies in the AM gave way to mostly clear skies by 4pm. Overnight new snow accumulations around 2 inches. Westerly winds were transporting good amounts of snow above treeline and some near treeline.
Snowpack: Lots of loud collapsing on the February “drought layer” beneath the recent storm snow. Some collapses ran several hundred feet and shattered slopes less than 30 degrees. One collapse was able to connect to a small, steep rollover releasing a small avalanche 70cm deep. Westerly slopes tilted to the south had a thin melt/freeze crust capping the horrendous weak layer and northerly-tilted west slopes had the slab resting directly on the weak facets. Both structures behaved very similarly with long-running collapses. West-facing terrain below treeline is very much in the bullseye for human-triggered avalanches.
Photos:
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This avalanche was remotely triggered from the far left portion of the photo.
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A quick look at the ugly Persistent Slab problem on west-facing slopes below treeline. This site had already collapsed yet still produced an ECTP 13 result.
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The triggered avalanche on the left and a couple of small avalanches that ran midstorm on the right.
Estimated avalanche date: 02/25/2022
Number of Avalanches: 1
Location
Location: Upper Slate (Purple, Yule Pass, Paradise Divide)
Location Specific:
Start Zone Elevation: BTL: Below Tree Line
Aspect: W
Characteristics
Trigger: Skier
Trigger modifier: Remote
Type: Soft Slab
Failure Plane:
Size
Relative Size: R1 very small
Destructive Size: D1- Relatively harmless to people
Avg. crown height (inches): 27
Avg. width (feet):
Avg. vertical run (feet): 80
Involvements
# of people caught:
# of partial burials:
# of full burials:
Additional comments: Long-running collapse remotely triggered this roll over. Rest of slope shattered.
Estimated avalanche date: 02/23/2022
Number of Avalanches: 3
Location
Location: Upper Slate (Purple, Yule Pass, Paradise Divide)
Location Specific:
Start Zone Elevation: BTL: Below Tree Line
Aspect: W
Characteristics
Trigger: Natural
Trigger modifier:
Type: Soft Slab
Failure Plane: Old snow
Size
Relative Size: R1 very small
Destructive Size: D1.5
Avg. crown height (inches): 14
Avg. width (feet):
Avg. vertical run (feet): 250
Involvements
# of people caught:
# of partial burials:
# of full burials:
Additional comments: Naturals that ran midstorm with crowns around 14 inches
Estimated avalanche date: 02/23/2022
Number of Avalanches: 2
Location
Location: Upper Slate (Purple, Yule Pass, Paradise Divide)
Location Specific:
Start Zone Elevation: BTL: Below Tree Line
Aspect: W
Characteristics
Trigger: Natural
Trigger modifier:
Type: Soft Slab
Failure Plane: Old snow
Size
Relative Size: R1 very small
Destructive Size: D2 – could bury, injure, or kill a person
Avg. crown height (inches):
Avg. width (feet):
Avg. vertical run (feet): 300
Involvements
# of people caught:
# of partial burials:
# of full burials:
Additional comments: Naturals that ran towards end storm. Slightly longer vert than others and a bit more volume. Low end D2s
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