Shot from Graysill Mountain, looking north toward Grizzly Peak (upper right)
Here are a few thoughts on a natural avalanche which ran Jan 25 or 26 in the cat terrain: I shot this from half a mile away but there is a lot to take away from it; even at such a remote distance.
For starters you may recognize this area, as the Colorado Trail runs through the lower track of the slide and along tree line. This is the high point between Bolam Pass and Graysill Creek.
The face is a southeast aspect, with a large flat area to its northwest, which provides a generous fetch point for snow transport. As January's final storm cycle moved out we saw considerable winds out of the north and northwest which deposited a hefty load onto the slope. This is also shown in the wind stripped bare spots of the western faces.
The wind added more stress to an already substantial storm total but the final straw that made this run was sun in the first days after the storm cleared. The sun is significant for two reasons. It directly warmed and weakened the snow causing the failure and it was also the source of the melt freeze crust which more than likely was the interface the avalanche slid on.
I would also note that this slide, which ran very wide in relation to the size of the slope, was able to run naturally on an angle roughly 30-34 degrees. Yes that is prime avalanche terrain but it could be thought of as slightly low angle for a natural to run so big. Soooo there ya go- a lot to take in from a single picture.