Why don't you just use particles, and have the x, and y randomizer set to screen width, and screen height?
I guess it would depend on what you'd want to do with the explosions. If you wanted them to, say, interact with other objects in the game, particles wouldn't cut it. Also, I don't believe particles can have animations.
This is probably more efficient. Still, add the scroll offset as Stargoat (lol) said.