Ice 'n Water

When things get cold they condense. Cold air, for instance, settles in the valleys. Jump in a lake some summer day and as you get deeper you will feel the water get cooler.

I remember the 'ol swimming hole in Red Bluff, California where I used to go swimming with my cousins. We would jump off a rock about 10 feet above the water and as we plunged into the water about 8 feet down it was flat cold and the surface temperature of the water was probably pushing 80 degrees.

The rise and fall of hot air balloons is another example of cold descending (and heat rising). How 'bout your refrigerator. When you open your refrigerator you will feel the cold air fall from the fridge and actually blow across your feet... well, it feels like it's blowing to me. In any case the phenomena is all around us. All you have to do is look.

So with this in mind let me ask, why doesn't a lake freeze from the bottom up? Why does the lake as well as the dogs water bowl get a crust of ice across the top? Heck, sometimes the ice on top of the body of water acutally gets to be very, very thick but from the surface down, not the bottom up.

OK, there are exceptions like when you make ice cubes or the body of water gets so cold that the whole thing freezes. But if you watch ice cubes form they get a crust of ice on the top FIRST. Most lakes don't freeze solid and you will find that they don't have a hint of ice at the bottom compared to possibly feet of ice at the top. Go ahead, jump in a lake this winter and check it out.

Why does it freeze from the top down? Water is a strange beast. In fact, from what I've read, water is the only compound that stops getting dense as it cools beyond 37 degrees. Yep, that's the trick. Water gets denser until it reaches 37 degrees and then it starts to expand.

What this translates to is water at the bottom of the lake being warmer than water at the surface. To explain let us imagine a cubic foot of water. This particular water is at the surface of the lake as a winter storm approaches. It gets cold and the water gets cold and the colder it gets it slowly sinks because it is getting more dense than warmer water. Finally this cubic foot of water gets to 37 degrees. It is on the bottom of the lake. It starts to get colder and as it gets colder it starts to rise because water is as dense as it will ever be at 37 degrees, colder than that it starts to expand. It continues to get colder so it continues to expand so it continues to rise. Finally it freezes... it is still expanding even after being frozen!

So what we have is floating ice like in a glass of ice water. At the bottom of the lake is 37 degree water and at the top of the lake is freezing water or ice.

This is why some boaters put bubblers under their boats to keep them from getting stuck or crushed in the ice. The bubbles cause a current that flows the warmer water at the bottom to the surface keeping the ice from forming.

I have to say, until I researched this I thought it was the bubbles that kept the ice from forming.

I realize there are many people that really could not care less about this subject. If you are one of those and still hung in and read this you are indeed special... I would never have made it. For the rest of you who find this interesting, I hope you got something out of this.

Myself, I think this is fascinating. Imagine how different our world would be if water/ice didn't have these properties and only H₂O does this (or so I read).

See you in the funny papers.....