Natural wind slab avalanche with wide propagation on Silver Peak

We toured into Silver Peak today on a route plan that kept us in sub 30 degree terrain and moved us through areas where we had intimate knowledge of both the current snowpack and the terrain. We avoided exposure to avalanche terrain, both overhead and on adjacent slopes.

Departing the trailhead on Hwy 89 at 0900 it was snowing S2 and there was over a foot of new snow. It was immediately apparent that the new snow was denser than the recent storm snow from this past weekend creating an "upside-down" storm slab structure. As we ascended into higher terrain with more wind exposure this upside-down layering was even more pronounced. There was a notable lull in snowfall intensity from 1000 to 1330, after which snowfall rates increased to S2-S5.

We stopped twice on our approach to dig test pits on the middle portion of the NE side of Silver Peak to assess the Jan 24 buried surface hoar layer and faceting below the rain crust buried on Jan 22. Our tests scored 1 x ECTP-12 in pit #1 and 1 x CT-9 SC in pit #2, both on buried surface hoar. From both pits we also had numerous ECTN scores on surface hoar (4) and on the rain crust (4), split evenly between the two snowpits.

Once we gained the East Ridge, we were able to see across to steeper terrain on the next ridge to the south. There we saw an avalanche crown with wide propagation in a wind loaded area. The avalanche start zone was open and likely held the Jan 24 surface hoar layer as I had seen widespread surface hoar all the way up to the ridgetops in this area on Jan 23. The propagation was much wider than is typical for a basic wind slab avalanche. We also saw a second, much narrower avalanche crown of similar depth adjacent to this one. Both avalanches appeared to have occurred early in the storm as there was significant new snow covering the debris.

We continued on our route plan using the intended sub 30 degree slopes to exit the area, all the while avoiding overhead exposure to nearby avalanche terrain.