Ice Circles: The Perfect Rotating Ice Discs in Rivers

Physics or Magic? The science behind the frozen discs that defy imagination

Adorning the frozen surfaces of rivers in regions like Scandinavia, Canada, or Russia, ice circles look like huge, white vinyl records spinning silently in the water. With diameters ranging from a few centimeters to over 15 meters, these discs are so geometrically perfect that they often inspire awe in lucky observers. Although they appear man-made, ice circles are the result of a delicate balance between hydrodynamics, temperature, and continuous water movement.

1. The Classic Theory: The Eddy "Trap"

For decades, scientists believed that ice circles form exclusively due to river currents. This process resembles how a piece of wood is shaped on a lathe.

• Creating the Eddy: When a piece of ice becomes trapped in an "eddy"—a point where the river current forms a circle due to an obstacle or bend—it begins to rotate slowly.
• The Sculpting: As the piece of ice rotates, it rubs against the surrounding stationary ice or riverbanks. This continuous friction "smooths" its corners, gradually transforming it into a perfect circle.
• Maintenance: As the ice rotates, the cold water passing beneath it freezes uniformly at the edges, maintaining the circular shape as the disc grows in size.

2. The New Discovery: Rotation Due to Temperature

In 2016, a team of researchers from the University of Liège overturned the idea that only river current can cause rotation. They discovered that an ice circle can rotate even in completely still water.

The Physics of Density: Water is densest at 4°C. As ice melts slightly from below, it cools the water directly beneath the disc. This cold water sinks, creating a vertical current. Due to the Coriolis force or small irregularities, this sinking water begins to swirl, creating a vortex that pulls the ice disc into rotation. This explains why we find ice circles in lakes with no apparent currents.

3. The Giant Disc Phenomenon in Maine

One of the most famous examples occurred in 2019 in Westbrook, Maine, USA. A giant ice circle with a diameter of 90 meters formed in the Presumpscot River.

This disc went viral globally, rotating counterclockwise and becoming a "stop" for hundreds of birds using it as a floating island. Its enormous mass and absolute circularity proved that nature can create structures resembling mechanical parts on a city scale.

4. Why Are the Edges So Smooth?

The secret to the smooth surface lies in friction and thawing.

• Friction: Like a grinding wheel, rotation forces the ice to "wear down" at protruding points.
• Thermal Sculpting: The water moving around the disc's edges is slightly warmer than the ice itself. This movement uniformly melts the perimeter, ensuring no sharp corners form.

5. "Fairy Circles" and Folklore

Before science provided answers, ice circles were considered magical signs. In many northern traditions, people believed they were dance floors for fairies or water spirits. The eerie silence accompanying their rotation in a frozen landscape absolutely justifies these myths. Even today, seeing an ice circle evokes a sense of tranquility and "order" amid a river's chaotic environment.

6. Where and When to Look for Them?

Ice circles are ephemeral. To see them, you need:

1. Sub-zero temperatures: For several consecutive days to form stable ice.
2. Calm Flow: Rivers with slow flow or lakes with thermal differences.
3. Morning Hours: Before the sun begins melting the disc's fragile edges.

The Geometry of Winter

Ice circles are proof that nature loves shapes and rules, even in the cold. They are a combination of chance and physics, where a broken piece of ice transforms into a perfect geometric shape. They remind us that beneath the surface of frozen water, forces work tirelessly, "sculpting" our world in ways we are only beginning to fully understand.

Next time you find yourself near a frozen river, take a look at its curves. You might see one of nature's "discs" performing its eternal, slow dance.