You might think I'm posting this just because of the awesome title above, but in fact it's for a video that's even better. I know!
Here's the scoop: after WWII, the US government found they had some extra sodium no one wanted, so they disposed of it.
In a lake. Full of water. And by the way, it was ten tons of pure sodium.
So yeah, you wanna see this newsreel footage from the event:
[UPDATE: By a funny coincidence, I just found out that io9 posted a similar article with 10 videos featuring explosive chemical reactions!]
Sodium is highly reactive. It's way over on the left side of the periodic table, which means it really wants to give an extra electron to any receptive atom or molecule that happens by. Water will happily accept that electron, but at a cost: the reaction creates sodium hydroxide (NaOH) and hydrogen gas (H2). It also generates a lot of extra energy in the form of heat. A lot. And there's hydrogen around. Remember the Hindenburg?
So yeah. Heat + hydrogen = BANG. Especially when you're dumping that much sodium into a lake! The explosions generated by this were impressive, to say the least.
In high school we did something like this, though on a very small scale. Our teacher took a tiny bit of sodium and put it in a glass with water in it. Sodium is very light, and floats. It reacted with the water, but far more slowly than in this video, rolling around on the surface. As it did, it released the hydrogen, which is lighter than air (and also warm from the reaction) so it rose. The heat ignited it, and so as the ball of shiny metal sodium rolled around on the water's surface, a tiny blue vertical flame followed it around. It was one of the coolest things I had ever seen, and probably made my nerdy adulthood that much more inevitable.
Oh, and all that surplus WWII sodium? While that would destroy the ecology of a lake, in this case it was already a heavily alkaline lake with no fish in it. While I wouldn't say this was a great thing to do, at least they thought to minimize the impact. But cripes: don't try this at home.
Tip o' the vent hood to Corante.