I was hiking up the Upper Yosemite Fall trail when I heard a loud 'crack' and 'whoosh'.
After getting away from the trail edge, I did what anyone would do when they think an avalanche might be coming...I grabbed my FZ50! 8^)
Fortunately it didn't cover the trail.
It's hard to describe the sound of one of these, but it's not something one shrugs off, to say the least.