For those with high-speed connections here is a video of a lump of sodium bouncing around in a lake:
http://www.theodoregray.com/PeriodicTable/Stories/011.2/Videos/SodiumLake01.MOV
Here s the link to the site the movie comes from, explaining how the sodium lept three or for times about forty feet in the air after each contact with H2O (mid-page, but the whole range of experiments is funny/terrifying too):
http://www.theodoregray.com/PeriodicTable/Stories/011.2/
Enjoy!
Ori