## Ice Formation Demystified | Ponds & Lakes Q&A

Ice Formation Demystified

Ice is cool. It’s fun to play on. And, to some, it’s a mystery. How in the world does ice form on your pond? Why does it expand when it freezes? Why does it float? And how is it possible that ice can actually support the weight of a vehicle?

Don’t glaze over just yet. Unlike lessons from those boring middle school science classes, this explanation will be simple—and as interesting as possible.

Lesson #1: Cold Water is Heavy Stuff

When the air temperature cools, the water on the surface of your lake or pond loses its heat and becomes heavier. This cold, heavy water sinks to the bottom while the warmer water from the bottom rises to the top and cools. The cycling process continues until the overall water temperature reaches 39 degrees Fahrenheit (or about 4 degrees Celsius). Before long, the water on top cools enough to freeze.

Lesson #2: Water Crystals Need Their Space

As the water in your pond freezes, the liquid molecules transform into solid ice crystals—and those things expand and space themselves out when they form, which is why ice takes up more room than liquid. Think of how freezing water can cause a pipe to burst when temperatures dip below freezing, or how expanding ice can crack a rock in two.

Lesson #3: Ice Floats

The spaced-out ice crystals are also less dense than liquid, which is why ice floats. As mentioned in Lesson #1, cold water is heavier than warmer water—but ice is lighter than them both. Confusing? Consider the ice cubes in your glass of lemonade: The crystallized water molecules float on the surface, the lemonade that’s cooled by the ice becomes more dense and sinks to the bottom, and the warmest liquid in the glass rises to the top where it’s cooled by the cubes.

Lesson #4: It’s Strong Stuff

When given enough time to form, the ice layer formed by this crystallized frozen water thickens—and becomes strong enough to support critters, humans and even vehicles! An inch of ice can hold a small animal without cracking, 3 inches of ice can bear the weight of an average person, and 6 to 8 inches of ice can host a hockey team or even a snowmobile. Once the ice layer grows to 8 to 12 inches, it can support a slow-moving vehicle—but we don’t recommend it!

Pond Talk: What burning questions do you have about ice formation and safety?