When lakes/ponds freeze, how come only the top layer is frozen and there is still water underneath? Yet when you put a bowl of water in the freezer, the whole thing is one solid block of ice.


This probably has an obvious answer and something is just not clicking for me.

In: Chemistry

The freezer has a lot more heat removing capability than the weather. It circulates air all around the bowl, pulling out all the heat.

On a lake, once the ice forms, the cold air can’t really get at any of the other water. The Earth itself doesn’t freeze, even in the arctic, down to the depth of many lakes. Outside Siberia, permafrost isn’t even 200m thick. A thin layer of air forms above the water’s surface, caused by the expansion of the ice and air dissolved in the water, which further insulates the water. Finally, the pressure grows very quickly as you go down into a lake, about 1 atmosphere worth of pressure every 10m. At high pressure, water is harder to freeze because it has to expand to freeze and that is harder to do at high pressure.

In the freezer all the water freezes because it’s a small amount of water. But a lake or a pond has more heat overall since it’s so much larger, so the whole thing doesn’t get frozen.

Ice is actually quite a good insulator, meaning it’s bad at conducting heat. It takes a realllllly long time for ice to conduct heat from the water underneath it to the cold air on top.

In a freezer, you only have a small amount of water. It’s easy for the freezer to efficiently and continuously remove the heat from the water until it all turns into ice. Some lakes and ponds *do* freeze all the way, but if there’s enough water, there’s so much heat that the cold air just can’t remove it all through the layer of insulating ice before the spring thaw comes.

Plus you have natural ground heat coming up into the lake because the earth has molten iron at its core.