It sort of feels like this could happen at any point. It's terrifying.
I've gone down pretty big a handful of times on skis, but this feels way worse. You have virtually no chance of stopping yourself - if you try to use your legs to catch yourself or stop yourself on a rock, they could easily get crushed, going at that kind of speed.
It looks like the person filming this made it out OK, as they seem to be moving around fairly normally after finally coming to a stop, but, damn, this is scary stuff.
Have you ever been ice climbing? Does it feel totally safe?