Freezing Lakes

Lakes tend to freeze from the top down. This is because water’s density is greater than that of ice, so the particles of water that approach the freezing point first float to the top of the water as they freeze. In this phenomena you will learn about how lakes freeze in the winter and what density is. Without having our lakes hitting maximum density, lakes would never freeze in the winter.

• Why do lakes freeze from the top?

• During November or December, as the air temperature and the water at the lake surface becomes colder than 39 degrees Fahrenheit, what do you think happens to the water?
• Why do you think shallow lakes usually freeze faster before deeper lakes?
• What do you think is more dense, water or ice? Explain why.

Students could:

• Watch a video that shows how ice is formed.
• Read “Freezing and Melting” by Robin Nelson.
• Work through an activity about how ice forms. 

• Lesson:Encyclopedia Britannica | Why Does Water Freeze from the Top Down? | This article explains the science of why water freezes from the top down.
• The STEM Laboratory | Oil and Ice Density Activity: This activity explains how density works.
• PBS LearningMedia | Backroads of Montana: Ice Formation: Follow along the backroads of Montana as we explore the process of ice formation on the Clark Fork River. Each winter as the temperatures drop, unique ice formations form. Explore border ice, frazil ice, and anchor ice in this episode.