Snowmobile Triggered Avalanche on Relay Peak

Location Name: 
Relay Peak
Region: 
Mount Rose Area
Date and time of avalanche (best estimate if unknown): 
Mon, 03/14/2016 - 12:00
Location Map: 
United States
39° 19' 20.928" N, 119° 56' 36.852" W
See map: Google Maps
US


Red Flags: 
Recent loading by new snow, wind, or rain
Obvious avalanche path
Observation made by: Forecaster
Avalanche Observations
Avalanche Type: 
Dry
Slab
Slope: 
38degrees
Trigger type: 
Snowmobiler
Crown Height: 
2 ft
Aspect: 
Southeast
Weak Layer: 
Storm Snow
Avalanche Width: 
150ft.
Terrain: 
Above Treeline
Elevation: 
10 125ft.
Bed Surface: 
Storm Snow
Avalanche Length: 
300ft.
More detailed information about the avalanche: 

This avalanche was triggered during the day on March 14 by a snowmobiler on the slope. The snowmobiler was able to ride out of the avalanche unharmed. It is likely that the slide released when the snowmobiler hit one of the trigger points on the slope. This wind loaded slope wraps from E facing to SE facing lookers left to lookers right. The weak layer was a layer of softer snow on a crust and the slab was a recently formed wind slab. The fracture from this avalanche continued another 150-200 ft. away from the crown onto a lower angle slope as a very long shooting crack. 

On March 15 snowpit work at the crown of the avalanche at 1:30 pm still yeilded ECTP results indicating that fractures could still propagate along that layer on that slope (see snowpit). Tests on nearby slopes of similar loading and aspect did not yield unstable results and numerous ski cuts on test slopes and cornices dropped onto test slopes also did not produce any signs of instability during the day. In this area several parties of snowmobilers were also highmarking similar slopes and skier and boarders were riding similar slopes and no other avalanches occurred or were observed. 

Photo 1: Overview of the avalanche.

Photos 2 & 3: The crown line of the avalanche. Note the shallower section of the crown near the rocks on the left side of photo 2.

Photo 4: The extent of the shooting crack triggered by this slide showing how far the fracture propagated along the weak layer.

Photos 5 & 6: The debris from the avalanche. 

Photo 7: Overview of the area from a distance.

Snowpit or crown profile photo or graph: 
Avalanche Photos: 
Weather Observations
Blowing Snow: 
No
Cloud Cover: 
25% of the sky covered by clouds
Air temperature: 
Above Freezing
Wind Speed: 
Light
Precipitation: 
None
Air temperature trend: 
Warming
Wind Direction: 
West