Snowmobile triggered avalanches on Thursday, early afternoon. Both slide were
on west facing slopes. Both slides triggered after riding by the areas that
slid, and were slow moving slides.
Slide below Seattle Ridge ran about 400 feet and was about 200 wide fracture
area. It appeared to be a wind loaded slide on a very weak layer.
Other slide on the north side of bowl ran between 400 and 600 feet, fracture
line about 400 feet long. Wind loaded slope on very weak layer.
Forecaster Note:
It appears that both of these slides were triggered somewhat remotely (rider was not on the slab when it avalanched). This is indicative of buried surface hoar and a good reminder that fractures have the potential to propagate great distances in the presence of buried surface hoar.
-GP
below Seattle Ridge, Main bowl, west facing slope
Main Bowl, North side of bowl, Middle ridge line, west facing slope
Main Bowl, North side of bowl, Middle ridge line, west facing slope
Fracture line, about 12 inches deep
Main Bowl, North side of bowl, Middle ridge line, west facing slope