Scary thing is, I've seen other photos like this from the same spot. If you're at TR on a warm afternoon, you have a good chance of seeing this. It was pretty loud, perhaps like a 747 taking off from a mile away (kinda hard to estimate, but it shook the ground slightly).
Looks like you were probably at the Thumb? Looks familiar. Liberty Wall waited till we we done and back at the bottom looking up till it avalanched for us. Willis avalanched the whole time we were there over and over.