Avalanches at Andesite Ridge

Location Name: Andesite Ridge Region: Donner Summit Area Observation Date & Time: Saturday, January 14, 2023 - 13:00
Location: 39.343332, -120.352625 See map: CalTopo	Is this an Avalanche Observation?: Yes Conditions Alerts: Avalanche Activity Other Signs of Instability (cracking, whumpfing, collapsing) Other Signs of Instability (cracking, whumpfing, collapsing)›Shooting Cracks Recent Loading Recent Loading›Blowing Snow Recent Loading›More Than a Foot of New Snow Recent Loading›Snowfall Rates of More Than 1 in/hr Terrain Alerts: Slopes Steeper than 30 degrees Terrain Matches the Advisory

Location Name:

Andesite Ridge

Region:

Donner Summit Area

Observation Date & Time:

Saturday, January 14, 2023 - 13:00

Location:

39.343332, -120.352625

See map: CalTopo

Is this an Avalanche Observation?:

Yes

Conditions Alerts:

Avalanche Activity
Other Signs of Instability (cracking, whumpfing, collapsing)
Other Signs of Instability (cracking, whumpfing, collapsing)›Shooting Cracks
Recent Loading
Recent Loading›Blowing Snow
Recent Loading›More Than a Foot of New Snow
Recent Loading›Snowfall Rates of More Than 1 in/hr

Terrain Alerts:

Slopes Steeper than 30 degrees

Terrain Matches the Advisory

Observation made by: Guide at Blackbird Mountain Guides

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Observation

Description of Snow, Weather, and Avalanche Conditions:

Very stormy conditions at Castle Valley and Andesite Ridge today. S5 snowfall nearly continuous from arrival at 8:00 am to 4:00 pm departure. Light SW winds and some blowing snow observed at the ridgeline. New snow over the 1/13 rain crust was 18-24" deep F to F+ hard.

Test slopes on the way up from Castle Valley showed shooting cracks and a small storm slab failure (photos 2+3). These both failed on a suble hardness change about 8" deep within the new storm snow. We also saw settlement cracks around trees just starting to form.

At the ridgetop at the pin drop location we observed a wide propagating D1.5 wind slab avalanche that had failed naturally. The crown was partially refilled suggesting it failed early today. (Photo 1). On descent we observed that the paralell ridgetop windloaded slopes toward the Andesite Ridge S Peaklet had failed naturally too.

Recent natural wind slab avalanche

test slope shooting crack

test slope avalanche

Snowpack Details

Total Snow Depth:

407cm

Persistent Weak Layers:

Not observed

Terrain Details

Terrain: elevations:

Near Treeline

Below Treeline

Terrain: aspects:

Avalanche Details

Avalanche Type:

Wind Slab

Failure Plane/Weak Layer:

New/old snow interface

Additional number of similar avalanches:

Trigger

Trigger:

Natural

Terrain

Start Zone Slope Angle:

35degrees

Aspect:

East

Starting Elevation:

near-treeline

Size

Destructive Size:

D1 Relatively harmless to people.

Relative Size:

R4 Large

Crown Height:

2 ft

Avalanche Width (Average width):

150ft.

Avalanche Length (Vertical Run):

100ft.

People Involved

Number of people caught:

Number of partial burials:

Number of full burials:

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