Heat is a driving force behind many natural fluid flows -- from the surges of magma in volcanic eruptions to the rising of water vapour forming thunderstorms. This experiment from UCLA show the effect in action, and it's beguiling.
It's simple, really: the folks at the the UCLA Spinlab simply place some dye on a continuously heated plate, then watch as it rises into the water above because of the increase in temperature. It's the exact same convectional effect that causes those eruptions and thunderstorms -- just quite a lot more relaxing. [YouTube via Fuck Yeah Fluid Dynamics]