[Blue Thunder]

Although I understand it completely, I am not worthy of articulating it like this. An excellent explanation of how ice forms......we are getting close to that magic 39 as we speak.

"For water to freeze and change into ice, it must be cooled to its freezing point, which implies heat loss. That heat loss occurs when the ambient temperature of the air is lower than the temperature of the water.
The freezing point of fresh water is 32°F; however, its maximum density is reached at 39°f. From an ecological perspective, the latter point is extremely important, since the deeper water which is located under the ice – except in some small lakes or ponds - does not freeze, which means that the creatures living there can survive winter under the ice. Let us take the example of a lake whose temperature decreases to 39°F in the late fall. Since density (the weight of the water per unit of volume) increases with the decrease in temperature, the entire lake – from the surface to its bottom – will reach 39°F after a certain length of time. When it cools, the thin layer close to the surface of the lake becomes denser, therefore heavier, and sinks toward the bottom of the lake, and is replaced on top by “warmer” water which rises to the surface.
If the temperature continues to drop and dips below 39°F, the layer close to the surface becomes less dense when approaching the freezing point; it then increases in volume instead of shrinking, and becomes “lighter” than the water below it at 39°F. Therefore, that cooler layer will float on the surface and will continue to cool until ice is formed. Ice (a solid) is lighter than water (a liquid) due to its larger volume, and that is why it floats. The water located under the ice below remains at 39°F, except for the layer just below the ice’s surface. That layer will approach the freezing point of 32°F. As it reaches that temperature, it turns into ice as well, making the layer of ice on the surface even thicker. The colder it gets, the thicker and the more solid the layer of ice becomes.
If water behaved like other physical bodies, it would increase in density as it cools. If that were true, rivers, streams and lakes would be frozen from the surface right down to the bottom. In the summer, only the top layer would melt, while the deeper water could remain frozen throughout the year. In such conditions, it is obvious that aquatic life in our rivers and lakes would be impossible."

BT