The subject of Diet Coke/Mint Mentos geysers came up at lunch. If you haven't tried it yet, why not make it park of your Independence Day Celebration. 13 Mentos per pack. 13 original states. SPOOKY.
This YouTube embed demonstrates solid techique.
The following NPR segments are nice. Not a story I expected to pop-up there.
Don't Miss: Mentos Redux
An Explosive Pair: Take a Mentos, and a Diet Coke...