Caused when a user hasn't been on twitter in a while, and has lots of @replys. The user tweets masses for a short period of time, most likely in the space of a few minutes, and then goes back to their normal rate of tweeting.
Johnny - I haven't been on twitter in a while.
Carlos - Oh, well you'd better get there quickly, loads of people have been tweeting you since you came out of the closet.
Johnny - Oh, you're probably right. Ha, this is gonna be a massive tweet explosion.