How is ice created in lakes?

The temperatures drop, and we all wonder, "When will the lakes freeze?"

My question today was, how does that actually happen?

Of course, ice is created when the water temperature reaches freezing. That is pretty obvious. We've all seen ice cubes created in the freezer. Yet, lakes don't freeze all at once, and they don't completely freeze all the way through. So how does that happen?

(See the dates the Iowa Great Lakes typically freeze here.)

It all starts with water density. As warm summer waters begin to cool, they will sink. Think of how the deeper that you go in the lake, the colder the water gets.

But once water hits 39 degrees (4 Celsius), the density actually begins to swing the other direction. At that temperature, the water begins expanding and becomes less dense as it gets even colder.

Graphic about water temperature versus densityopens IMAGE file

That means that colder water begins to come to the surface, and the warmer water sinks to the bottom.

The water on the surface will then freeze to form a layer of ice, and the ice will have the least density, making it float on top of any cold water as well.

How does it freeze?

There are two different types of lake ice that are created in different ways.

Congealation ice is created from cold conditions. Spontaneous nucleation takes place on cold, calm nights when the surface of the lake drops below freezing and ice spreads across the surface. Heterogeneous nucleation takes place when strong winds blow dust, snow or frozen rain across the surface of a cold lake and as that hits the surface of the water, it freezes.

Snow ice occurs where snow falls on congealation ice and when it cracks, the water from below rushes to the surface and meets the snow, which will then freeze.

Why doesn't the water freeze all the way to the bottom?

In deep lakes, like the Iowa Great Lakes, water pressure also plays a role in why the surface freezes but water stays liquid underneath.

The weight of the water higher in the lake presses down on the water that is deeper. The pressure allows the water near the bottom to still get cold but does not allow the same expanding and rising as the water near the surface. Because of that pressure, the water at the bottom will not turn to ice even though it is at a freezing temperature.

How lake ice melts

It seems pretty obvious how ice melts, right? It gets warm, so ice changes to its liquid form — water. However, the way that the lakes, including the Iowa Great Lakes, melt may be different than what you would think. Usually in March — the average date for ice out on East Lake Okoboji is Read More »

Read More

What is a watershed?

The augmented reality sandbox in the Dickinson County Nature Center has been a hit since it was installed. The exhibit talks about watersheds and how water moves through the landscape, but do you really understand what a watershed is? Let’s answer some questions about watersheds. What is a watershed? A watershed is an area of Read More »

Read More

Prairie plant roots help water quality

Native prairie plants make wonderful habitat for wildlife like voles, turkeys, rabbits, ground squirrels, hawks and foxes. They provide both habitat and food sources for tiny creatures such as monarch butterflies, bumblebees and milkweed beetles. They are beautiful to look at. However, they are also important in a way that we can’t see. Deep down Read More »

Read More

How fish survive in frozen lakes

The frozen Iowa Great Lakes are dotted with blue and black as ice fishermen set up their shacks, drill holes and search for life below the ice. And there is still plenty of life to be found, but how exactly do fish survive in those frigid temperatures? You can learn how ice is created on Read More »

Read More

Fish are fun!

Test your fish knowledge with our fun quiz here!

Read More

Iowa Great Lakes fun facts

We all love the lakes. That’s what makes Okoboji, Okoboji. But how much do you know about the lakes themselves? Did you know that Upper Gar Lake is the smallest lake in the Iowa Great Lakes at only 37 acres with an average depth of 3.5 feet? That is the height of the average 6-year-old! Read More »

Read More

What fish is it?

[wp_quiz id=”6531″]

Read More

Big Spirit Lake’s perfect south shore

Only two years after the Dickinson County Conservation Board was established, it took on the care of a beautiful recreation area on the south side of Big Spirit Lake. The conservation board worked on an agreement with the State Conservation Commission for 25 years of management of Orleans Beach. The area east of the spillway Read More »

Read More