Now imagine the power of an A-380
It's engines are much more powerful than a 747. For that matter, the twin engines on a Boeing 777 produce about as much thrust as a 747. It's possible that thrust is even more powerful because it isn't spread out as much.
There is concern about the wake turbulence from a A-380, too. So much so that they're restricting anyone from flying within several miles behind an A-380. The issue is discussed on this thread on Airliners.net.