Full Burial Avalanche on Castle/Basin Peak

2019-12-9 Avalanche Incident Update on Tuesday December 10:

SAC Forecasters went out on Dec 10 to investigate the avalanche incident that occurred on Monday Dec 9 in the Castle Peak/Basin Peak area. The area had numerous tracks and the slope that avalanched was triggered by the 9th and final snowboarder descending the area. The slope was just over 600' long and consisted of lower angle terrain on the upper slope descending into a steep convex rollover with rocky terrain with few trees below. We considered this complex terrain with many trigger points and multiple starting zones.

As the final rider was descending the slope, the rider triggered the avalanche that propagated first to adjacent terrain and then ultimately above and behind the rider. The rider was caught and carried 200' downslope. The individual was buried face down, 1 to 2' deep. The travel partners responded quickly from below and were able to successfully get to the buried individual dug out in 4 minutes. The rider was unconscious when first uncovered, but quickly became awake and oriented.

The avalanche ran about 300' and was about 200' wide. The crown line was in the 1 to 2' height range. Snow depth in this area varied greatly from as much as 8' down to 1.5' in steep rocky areas. Decomposing buried surface hoar was found in the crown as the weak layer on top of the bed surface and thought to be the primary reason for failure of this storm slab.  Propagation across the slope and remote triggering are very consistent with buried surface hoar. No other signs of instability were observed in this immediate area. On the north side of Castle Peak, there were similar natural avalanches that were mid slope on convexities that are thought to have failed near the end of the recent storm also on buried surface hoar.  See attached snowpit for more detailed information.        

Preliminary Report on Monday December 9:

Reports came in today of a human triggered avalanche on the North side of Castle Peak.  The following details were relayed from another party in the area.  The avalanche was remotely triggered and was 200' wide.  Crown was 1 to 2' deep.  The avalanche occurred on a mid slope convex rollover at 8300'.  Many tracks were already in the area at the time of the avalanche.  Victim was fully buried for 4 minutes and was successfully rescued by his group.

We will update this report as more information is available.