Here's another video that captures these new cavern dynamite explosion effects pretty good. It's at the 2:00 minute mark of this video...
Now I'm the first to be Preachy McPreacher about judging things from amateur YouTube videos, but I have to say that I'm really impressed with this from what we've seen on YouTube. I can't wait to ride this for myself next week! Real life is ALWAYS better than YouTube.
But I think this whole effect is created by a combination of techniques; digital mapping projection, LED lighting, HD projections onto the smoke, the smoke blasts themselves, crystal clear audio, and some basic moving props throughout that scene (swinging lanterns, shaking dynamite crates, etc.) The sum of all those parts looks very, very impressive. Bravo Disneyland!