I'm glad you asked. When the temperature of a body of water such as a lake reaches a certain low point, it undergoes something called a thermal inversion where suddenly, it's colder at the TOP than at the bottom. This is what allows fish to survive under the surface or a frozen pond and it is also what allows silly fourwheeling rednecks the opportunity to bust their vehicles through the ice and sink them to the bottom of the lake much farther off shore than the would EVER be able to do in the spring, even WITH a Dukes of Hazard style jump ramp and 500 yards head start.
So what does this have to do with Starbucks? I'm glad you asked. If you are a fan of their Frappuccino style frozen beverage, you may know that you can now get them"affogato style." Now, I have no clue what affogato means (but some non-pc ideas come to mind), but what it ammounts to is a shot of espresso and mocha (or caramel) dumped on top of the drink. If you let it sit long enough, after a bit, the hot mocha (or caramel) will cause a simulated thermal inversion, and go cascading down the side of the clear plastic cup so that it can pool at the bottom. It's pretty cool to watch.
This has been your moment of Science.