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Cornice Bombs Away...
Location Name:
BNSF Avalanche Safety - Running Rabbit Mtn. GNP
Observation date:
Saturday, March 13, 2021 - 00:15
Is this an Avalanche Observation:
Yes
Observation made by:
Public
Tabs
Quick Observation
Long tour on the western end of the Program Area with objectives to investigate some older avalanche activity, look for any recent avalanche activity, and assess snowpack stability in this area.
Excellent views of the surrounding terrain all day. Noticed a crown on the north face of Unawah Mtn. Date of occurrence unknown, likely sometime during the last week, estimate about D2-size.
Remotely and unintentionally triggered a large cornice fall from a safe location while skinning along a ridgeline at 7400’. Cornice chunk was approx. 20’ wide by 15’ tall and was overhanging an east-facing slope. No slab released when the chunks thumped the snow slope about 200’ below.
No other recent avalanche activity observed.
Visited the crown of a large avalanche (previously reported) that ran a week ago on the west face of Running Rabbit Mtn. in a path known as I-Beam. We inspected the crown (photo) at about 7400’ and no Jan. 13th crust present at this elevation. But the failure layer of this large hard slab was the mid-Jan. facets.
Variety of snow surface conditions depending on elevation, aspect, and time of day. Most notable was a healthy crop of surface hoar found on sheltered, shaded aspects which seemed to be confined to elevations above 6000’.
Dug a pit at 6900’ on a southerly aspect near the Shed 10.7 starting zone and at a location where the mid-Jan. facets were reactive and propagating during stability tests a month ago. An extended column test resulted in ECTX. A Deep Tap test targeting the mid-Jan. facets (buried ~3’ down) resulted in DT21, Resistant Planar fracture.
Other than the falling cornice event mentioned above, no other signs of instability observed during the tour: no cracking, collapsing, or rollerball activity.
Clear skies with no precipitation all day. Calm to light westerly winds at all elevations.
Daytime highs reached the mid-40s °F on the Canyon floor and mid-30s °F at elevations above 6000’.
Snowpack, Avalanche, Weather Images:
Travel Details
Region:
Flathead Range/Glacier National Park - John F. Stevens Canyon
Activity:
Skiing
Avalanche Details
Avalanche Details:
Date and Time of Avalanche:
Friday, March 12, 2021 - 13:30
Number of avalanches:
1
Avalanche Type:
Cornice
Failure Plane/Weak Layer:
Old snow
Trigger
Trigger:
skier
Trigger Modifier:
Remotely Triggered
Terrain
Aspect:
East
Starting Elevation:
7400
Size
Destructive Size:
D2 Could bury, injure, or kill a person.
Relative Size:
R1 Very Small
Crown Height:
More than 10 ft
Avalanche Length (Vertical Run):
200ft.
Avalanche Width (Average width):
20ft.
Avalanche Location:
Javascript is required to view this map.
Date and Time of Avalanche:
Tuesday, March 9, 2021 - 13:00
Number of avalanches:
1
Avalanche Type:
Hard Slab
Failure Plane/Weak Layer:
Old snow
Trigger
Trigger:
unknown
Terrain
Aspect:
North
Starting Elevation:
above-treeline
Size
Destructive Size:
D2 Could bury, injure, or kill a person.
Relative Size:
R2 Small
Crown Height:
3 ft
Avalanche Location:
Javascript is required to view this map.
