Avalanche in CLOSED Area - Mt. Rose Chutes

Location Name: 
Mt. Rose Chutes - CLOSED AREA
Region: 
Mount Rose Area
Date and time of avalanche (best estimate if unknown): 
Sat, 12/10/2016 - 10:18
Location Map: 
United States
39° 19' 10.182" N, 119° 52' 58.7424" W
US


Red Flags: 
Recent avalanche activity
Whumphing noises, shooting cracks, or collapsing
Recent loading by new snow, wind, or rain
Obvious avalanche path
Terrain Trap

Observation made by: Forecaster
Avalanche Observations
Avalanche Type: 
Dry
Slab
Slope: 
40degrees
Trigger type: 
Skier
Crown Height: 
4 ft
Aspect: 
North
Weak Layer: 
Old Snow
Avalanche Width: 
350ft.
Terrain: 
Near Treeline
Elevation: 
9 200ft.
Bed Surface: 
Old Snow
Avalanche Length: 
1 000ft.
Number of similar avalanches: 
3
Number of people caught: 
1
Number of full burials: 
1
More detailed information about the avalanche: 

Two skiers hiked/traversed into CLOSED uncontrolled terrain at Mt. Rose. This terrain had NOT BEEN OPENED, HAD NOT BEEN SKIED, and HAD NOT BEEN CONTROLLED this winter. It is more analogous to a backcountry snowpack. They decided to drop into a steep wind-loaded slope. The first skier triggered a large avalanche that swept him downslope and buried him 600-1000 ft. below in debris that averaged 5 ft deep and reached up to 10 ft. deep in some areas. The second skier immediately called 911 and the search for his partner continued for the rest of the day. As of 7:30pm on 12/10 the skier had not been found. The search will resume in the morning.

The avalanche that this skier triggered likely started as a wind slab and stepped down creating a larager avalanche that failed on a persistent weak layer of facets near the base of the snowpack. The slab was a mix of 1F (1-finger) and 4F (4-finger) hardness snow sitting on top of F (fist) hard facets. This avalanche started on a 40-45 degree slope and pulled out adjacent slopes that reached up to 50 degrees in steepness. The slopes that released were mostly N aspects with some NE aspects on the skier's left of the paths. The initial avalanche was likely 350-550 ft in width and connected multiple start zones. It was at least a D3 on the destructive size scale. The crown measured between 3 and 5 ft. in depth.

Later in the day after continued wind loading and snow accumulation, explosive control work triggered additional similar avalanches that started as wind slabs and stepped down to the old persistent weak layer. Ski cuts on small wind loaded test slopes caused shooting cracks and wind slab failures up to 16 inches deep. 

UPDATE 12/11/16

Searchers located the buried skier around mid-day today. Avalanche dog teams from Mt. Rose, Sugarbowl, Squaw Valley, Alpine Meadows, and Placer County narrowed the search area down to a large pile of debris where two of the avalanche paths came together. Washoe County Search and Rescue Team Members then probed this area and located the buried skier. He was buried under 220-260 cm of avalanche debris. This debris was from the slide he triggered as well as subsequent avalanches released during control work to create a safe area for searchers to operate in. 

Photo 8: The confluence of debris where the skier was found. The person is standing next to the burial location.

Photo 9: Standing in the hole where the skier was buried. He was buried prone in the area at my feet. 

Snowpit data collected near the crown of the avalanche on 12/11 showed that the new snow represents a great slab layer and that the facet layer near the base of the snowpack that failed during these avalanches remain weak. Tests indicated that human triggering of these layers remained a possibility today. See attached snowpit and video. This snowpit came from the following coordinates: 39.31922, -119.88236. More info about observations from 12/11 can be found here.  Note: the elevation on the snowpit should read 9240 ft. 

All photos except photo #7 taken by Tahoe National Forest Sierra Avalanche Center Forecasters.

Photos 1-3: The crown in the upper slide path on a N aspect with some NNE. This has both crowns from the initial skier triggered slide and the explosive triggered slides in the afternoon. 

Photos 4-6: Crown from an adjacent  and lower path (around 8900-9000 ft) path that pulled during explosive control work in the afternoon. Skier triggered cracking occurred on a small test slope near this avalanche path in the afternoon just before the explosives triggered this slide.

Photo 7: Looking uphill from the debris. Photo by Andrew Pinkham

Snowpit or crown profile photo or graph: 
Avalanche Photos: 
Weather Observations
Blowing Snow: 
Yes
Cloud Cover: 
100% of the sky covered by clouds
Air temperature: 
Below Freezing
Wind Speed: 
Gale Force
Precipitation: 
Snow
Air temperature trend: 
Warming
Wind Direction: 
Southwest
Accumulation rate: 
Greater than 1 in. per hour
More detailed information about the weather: 

Snow levels stayed lower than 8500 ft in this area till the end of the day when they climbed to between 8400 and 8600 ft. Snowfall rates this during the morning likely exceeded 3 inches per hour for some period of time and strong SW winds persisted all day.