Detailed Observation

ObserverGareth Brown

General Observations

1/8- Cracked Ice up to 3000’/NW- N aspect/SCT/No precipitation/Calm

Shooting Cracks: No

Collapsing: No

Avalanches: Yes, our group triggered 3 separate D1.5-2 avalanches on north aspects. Crowns were around 40 cms deep (16 inches).  All three originated from convexities in the terrain around 2800′ on a ~37-39° slope angle.  Two of these were around 100 feet wide with another failing in a cross loaded gully that was closer to 300′ wide, ran 600-700 vertical feet.  Failed on 1/3 Buried Surface Hoar.  SS-AR-U-D2-O.  

On tour up found no obvious signs of instability. 12 inches of new snow overnight.   Hand shear tests produced moderate result down 1 1/2 feet but without a clean shear plane.  1/3 Buried surface hoar was present but was difficult to locate.  We directly triggered 3 separate avalanches on the descent, details above.  All of these were triggered from terrain convexities and some triggered other convexities within the path.  No one in the party was caught.  Skinned back up to lower section of crown and found the crown depth to be 40 cms and the 1/3 buried surface hoar was the weak layer,  these facets were not fully intact, they were fragmented and averaged 2mm in size.

 This instance is a great example that incremental loading of the 1/3 BSH has reached the tipping point in specific locations on specific terrain features.  Additional snowfall later this week will create deeper slabs and will make more terrain reactive to human triggers.  

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Observed Avalanche Activity