Why Does Ice Float

Most things sink when they turn solid, but ice floats on water. This is because water is special. When water freezes, its molecules spread apart and form a crystal pattern. This makes ice take up more space than the same amount of liquid water. Since ice is less dense, it floats.

Water's Special Trick

Most liquids get denser as they cool. Water does too, but only until it reaches about 39 degrees Fahrenheit. Below that, water starts expanding as its molecules arrange into a crystal shape. By the time it freezes at 32 degrees, ice takes up about 9 percent more space than the same water in liquid form.

Why This Matters

Floating ice is very important for life on Earth. In winter, ice forms on the surface of lakes and ponds. It acts like a blanket, keeping the water below from freezing solid. Fish and other creatures survive the winter in the liquid water under the ice. If ice sank, lakes could freeze from the bottom up and kill everything inside.

Fun Facts

• About 90 percent of an iceberg is hidden below the water surface.
• Water is one of only a few substances that are less dense as a solid than as a liquid.
• A frozen water pipe can burst because the expanding ice pushes outward with enormous force.

Did You Know?

If ice sank instead of floating, Earth's oceans might have frozen solid billions of years ago. Life as we know it might never have developed! Floating ice is one reason our planet can support life.