Unnerving Times

Location Name: 
Avalanche Incident: Spruces area (Skier)
Observation date: 
Sunday, January 31, 2021 - 13:00

Is this an Avalanche Observation: 
Yes
Observation made by: Public

Tabs

Quick Observation

Spent the day touring outside of the ski area

  • First run, we skied some low angle (less than 30 degree) SSE facing from 6400-6000. No signs of instability. conditions were about 3 inches of dry unconsolidated snow on top of a breakable sun crust from thursday.
  • Second run, we skiied steeper (up to 35 degree) N facing from 6400-5800. Prior to skiing the slope, we observed a small D1.5 storm slab that appeared to have been skier triggered on 1/30. This slope appeared to be windloaded from the relatively bald ridge directly above it. We chose to proceed with caution.
  • The first 4 skiers of our party descended just to the left of the slide as well as on the bedsurface without incident. The last skier in our party traversed a little further skiers left before descending and triggered a D2 storm slab on descent. The slope propgated above and on both sides of the skier, but they were able to quickly ski through and out to the flank of the slide and avoided being carried and burried.
  • The crown was approximatley 8 inches and the slide ran on a surface hoar/facet layer that is a an inch or two above the 1/13 crust.

 

  • After this incident we started working back towards the ski area.
  • We observed some shooting cracks on an east facing slope around 6000' while ascending out of the basin. We also bumped into another party that mentioned another storm slab that was triggered yesterday on east facing terrain nearby.
  • For our third and final run we descended NW and N facing from 6300-5000'. Up high we mostly avoided slopes steeper than 30 degree and found quality skiing without instabilities. At about 5400', we carefully skied a short section of unavoidable steep terrain. We observed some cracking on open slopes and we also triggered a D1 storm slab that ran on top of the 1/13 crust layer. The storm slab was about 6-8 inches at this elevation and the 1/13 crust was much more robust than at upper elevations.

 

  • We felt that our terrain choices were not overly aggressive today and yet we still triggered a slide that involved enough snow to burry and/or injure a skier. Lesson learned was the significance of red flags. In our case, it was recent avalanche activity on our slope. We acknowledged it and everyone in our group agreed to move forward with caution, but in our particular situation the other four skiers at the bottom did not have good visual of the last skier while they were descending.
  • I think we failed to factor in the visability issue for the worst case scenario of the last skier causing a slide. We were using radios, which made us overlook this problem.
  • The skier involved thought that they were making a conservative choice by traversing further left, because the ridgeline above this part of the slope was much more heavily forested, protecting the slope from windloading compared to where the D1.5 from yesteday had failed. Unfortunately it was not a wind slab issue, rather a persistent weak layer underneath the storm slab.

 

  • I have attached some photos and a map to show the activity today. FP= Top of Flower Point, Blue slide = D2 storm slab from today. Purple Slide = D1.5 storm slab from yesterday. Orange Caution marker near 6365' is a storm slab that another party metioned to us late in the day. Orange Caution marker down lower in Canyon Creek is approximate location of D1 storm slab that we triggered late in the day.
Snowpack, Avalanche, Weather Images: 
Travel Details
Region: 
Whitefish Range - Southern (south of Coal Creek)
Activity: 
Skiing
Snowboarding
Snowpack Details
Snowpack and Weather Details: 
Hide Terrain
Elevation of observation: 
3500-5000 ft
5000-6500 ft
Aspect(s) of observation: 
N
NE
E
SE
S
NW
Red Flags: 
Avalanches from the past 2 days
Shooting cracks
Persistent Weak Layers: 
Surface Hoar
Facets or Faceted Crust
Buried
Blowing Snow: 
None
Wind Speed: 
Calm (No air motion)
Air temperature: 
Below Freezing
Sky Cover: 
Partly Cloudy (SCT)
Highest Precipitation Rate: 
Very Light Snowfall (S-1)
Avalanche Details
Avalanche Details: 
Date and Time of Avalanche: 
Sunday, January 31, 2021 - 12:30
Number of avalanches: 
2
Avalanche Type: 
Soft Slab
Failure Plane/Weak Layer: 
New/old snow interface
More information or comments about the avalanche: 

Information about this incident in the "Quick Observation" Tab

Hide Trigger
Trigger: 
skier
Trigger Modifier: 
Accidentally Triggered
Hide Terrain
Start Zone Slope Angle: 
35
Aspect: 
North
Starting Elevation: 
6300
Hide Size
Destructive Size: 
D2 Could bury, injure, or kill a person.
Relative Size: 
R2 Small
Crown Height: 
Less than 1 ft
Avalanche Length (Vertical Run): 
375ft.
Avalanche Width (Average width): 
60ft.
Hide People Involved
Number of people caught: 
1
Number of partial burials: 
0
Number of full burials: 
0
Avalanche Location: