I'm not entirely sure how much going to another continent would help in this case, I went and calculated the power release of 1 cubic kilometer of rock falling down to Earth from about 5 km (Minus air resistance, but hey, how much will air stop something that big anyway?) and got a figure equivalent to 32 MT of TNT.
And that's just 1 cubic kilometer, the stuff going to be lifted up is going to be much much larger then that. A big mountain can easily be 100s of cubic kilometer, and thus if it fell from such a height could exceed 10 GT on impact. (By rough guesstimation from Mt Helens, that's the amount of energy a super volcano releases thermally, except this does it almost instantaneously, while a super volcano spreads it out over days) I don't even really want to know how much material that would pump in to the stratosphere, never mind the terrors something like that would bring if it fell in to a sea or ocean. And for all we know, that wouldn't be even close to the largest continuous piece that might fall down in more or less one piece.
This could very easily turn out to be an Extinction Level Event. (ELE) And should at the least be an extreme world wide cataclysm.
(I'm pretty sure this has been discussed before once, albeit perhaps with out an actual number put to the energy release)