Avalanche in the Gully Leading to Relay Peak

Location Name: 
Relay Peak
Region: 
Mount Rose Area
Date and time of avalanche (best estimate if unknown): 
Mon, 02/09/2015 - 09:00
Location Map: 
United States
39° 18' 53.28" N, 119° 56' 3.48" W
See map: Google Maps
US


Red Flags: 
Recent avalanche activity
Recent loading by new snow, wind, or rain
Terrain Trap
Observation made by: Forecaster
Avalanche Observations
Avalanche Type: 
Dry
Slab
Slope: 
38degrees
Trigger type: 
Snowmobiler
Crown Height: 
3 ft
Aspect: 
North
Weak Layer: 
Old Snow
Avalanche Width: 
200ft.
Terrain: 
Below Treeline
Elevation: 
9 320ft.
Bed Surface: 
Old Snow
Avalanche Length: 
100ft.
More detailed information about the avalanche: 

Judging by the amount of snow on the debris and bed surface of this avalanche it likely occurred this morning. It looked like a snowmobile track went into the bottom of the avalanche and came out the other side. It is possible that the this slide was triggered by that snowmobiler as he or she rode up or down the side of the gully. A likely trigger point existed near uphill side of the slide inline with the track.

This slide occurred on a N-NE facing slope and the steepness ranged from 38-42 degrees. It had several trigger points in the form of shallowly buried rocks and likely progagated uphil along the softer snow layer of rounding facets above the old rain crust. The crust served as the bed surface. The debris measured between 100 and 170 cm in depth. The crown height measured 2-3 ft.

Snowpit data adjacent to the slide showed two active weak layers. One was a graupel layer within the storm snow and the other was the rounding facets above the old crust.

Photo 1: Looking up gully at the slide and the debris pile. The 260 cm probe is inserted to the bottom of the avalanche debris. The debris measured 170 cm at this point.

Photo 2: Looking down gully at the slide with a possible trigger point marked. 

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: 
Moderate
Precipitation: 
Snow
Air temperature trend: 
Cooling
Wind Direction: 
Southwest
Accumulation rate: 
Less than 1 in. per hour
More detailed information about the weather: 

Snow showers and wind were strongest in the morning and decreased in the afternoon.