Let's try a simple experiment. First, place hot, salty water into one cup, and cold pure water into another, ensuring the hot, salty water will be lighter than the pure water by heating it up. Then cover the hot water cup with a sheet of paper, turn it upside down, place the upside down cup on the pure water cup and pull the paper out quickly. After a while, salt finger that look like velvet shanks (mushrooms) will grow out from the boundary layer. A stably stratified fluid normally does not mix easily, but when phenomenon like salt finger occur, it mixes at a rates much faster than normal. Salt finger itself is only a small scale phenomenon, but it can trigger far bigger events.2)