Isolated storm slab instabilities and cornice collapse near Trestle Peak

We woke up this morning with more light fresh snow than we were expecting down at Donner Lake. We toured up the east ridge of Trestle Peak and experienced very minor shooting cracks in the new snow layer, but only in isolated areas with significant slope angles. In the trees, we estimated that around 8-9 inches of new snow had been deposited. The skinning up the ridge was slightly easier as the wind had likely removed some of the new snow. As we summited Trestle, we saw 1-2 foot long shooting cracks in an area known to experience wind loading. 

Before descending, we kicked at the cornices on the N, NE aspect of the peak. The first three tests easily fractured but did not entrain snow or activate any instabilities below. The fourth cornice failure was much larger than we expected and entrained a substantial amount of snow which ran more than 300 feet. It was not immediatly apparent if the cornice activated a slab below or simply had enough momentum itself to carry loose storm snow with it as it fell. The D2 slide was roughly 40+ feet wide. . We also observed old avalanche debris from the larger slide that occured in this area during the heavy rain events. The cornice collapse snow followed the same path as the old avalanche. 

While descending, we experienced isolated storm slab instabilties in steeper terrain. The slides had crowns ranging from 6-10 inches but were never more than 8 feet wide and never slid more than 10-15 feet. 

Near the train tunnel, a snowboarder in the group dropped a steep section and triggered a D1 R2 storm slab which ran roughly 25 feet. This slab had a crown height of roughly 9 inches and was 20 feet wide. The snow carried the snowboarder a couple feet and buried him to just below his waist as it slowed down. There were no injuries associated with the slide. From what we could gather, it seemed that all instabilties failed on the new snow surface. 

Throughout our entire descent, we examined the path of the large avalanche that occured during the heavy rain and snow event a little more than a week ago. Our best guess was that the slide was triggered by a large cornice collapse that entrained more heavy wet snow as it slid down Trestle. It likely gained signifcant momentum after falling off the train tunnel where it activated a deep slab (3-4 foot crown) and slid almost down to the exit of the Lake Run where we observed signifcant old avalanche debris.