In the small town of Eden, N.Y., the recent appearance of mysterious circles in a frozen pond has residents baffled.

Intriguing circular formations are known to occur throughout the natural world during seasonal freeze and thaw cycles.
In areas of permafrost (like the northern Canadian tundra), the expansion of ice beneath the soil surface — a process called frost heaving — creates raised landforms called lithalsas. Lithalsas often form circular or ring-shaped patterns on the surface.

Frost heaving also creates a related landform called a pingo. Over many years, pingos can grow into small, circular hills: The tallest known pingo is the Kadleroshilik Pingo in Alaska, which reaches 178 feet in height.