Avalanche: Turnagain

Location: Sunburst/Magnum

Route & General Observations

Conducted a short road observation before going into the field today. We wanted to see if any new avalanches had appeared overnight.

We toured up to the valley between Sunburst and Magnum as we wanted to get a better idea of what caused a large avalanche triggered sometime between 1:00 and 5:00 pm yesterday. Although, due to the hazardous nature of walking under an avalanche path with some overhead exposure, we decided to forgo a full crown profile and investigation. We decided to dig a pit at a similar elevation and aspect as the avalanche, hoping that we could dig down to a weak layer that may have instigated a large and widespread failure.

The parking lots looked much better today. The plows were able to clear out the Sunburst, Seattle ridge, and Corn biscuit lots. WooHoo!

Avalanche Details
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Trigger NaturalRemote Trigger Unknown
Avalanche Type Hard SlabAspect Northwest
Elevation 2200ftSlope Angleunknown
Crown Depth4ftWidth 500ft
Vertical Run 1000ft  
Avalanche Details

Based on photos from multiple people driving through Turnagain Pass yesterday we know this avalanche released during a warming event Thursday yesterday afternoon March 23. There were shooting cracks all across the slope adjacent to and below where the avalanche release, indicating widespread propagation on a persistent weak layer. The middle part of the slab stepped down to a slightly deeper layer. There was a sympathetic avalanche release on the north facing gully wall of the creek between Sunburst and Magnum that ran for over half a mile down the gully. All the sections that were steep enough to avalanche released 3-4' deep. The crown depth of the main avalanche ranged from 3-6'+ with an average of 4'. We estimate that this was a D 3.5.

Red Flags
Red flags are simple visual clues that are a sign of potential avalanche danger. Please record any sign of red flags below.
Obvious signs of instability
Recent Avalanches?Yes
Collapsing (Whumphing)?No
Cracking (Shooting cracks)?No
Observer Comments

Recent avalanche, cracks all over the surface from the Magnum avalanche to the Gully avalanches.

Weather & Snow Characteristics
Please provide details to help us determine the weather and snowpack during the time this observation took place.

Switching between broken clouds and overcast. Parking lot temps. were around 32-35 degrees. Gusting moderate winds transporting snow and no precip.

Snow surface

Crust at lower elevations that at the end of the day was beginning to warm up. The crust softened at about 1500' but there was still some denser snow on the surface due to wind or warming up to our high point at 2500'.


We dug across from the slide on Magnum on a representative NW aspect and 2200' elevation in order to identify a potential weak layer below the total storm snow. We dug about 4' (130 cm) down and found a layer of 1 mm buried facets that we believe are the culprit for the avalanche across the gully. We believe this layer formed on the surface during the long dry spell in early march and was buried on March 14 (Pi Day). This layer was also responsible for a very large avalanche in Summit Lake this week but that was on a southern aspect where the old snow surface has an icy crust. On top of the facets is a 4' thick right side up slab of settled storm snow from the last week that we didn't notice any instabilities within (ECTN). We did not have any results in our stability tests on the Pi day facets, but there was a notable collapse and the block slid off the column easily when we lightly pried it with a shovel. With a weak layer this deep it is very hard to assess with stability tests, and the recent avalanche activity combined with a poor snowpack structure is all the evidence we need that this layer is unstable right now.

Photos & Video
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