Geography
How Periglacial Patterned Ground Forms in High Latitudes
Quick fact
Patterned ground can also form on Mars, where periglacial processes have created polygonal ground in the absence of liquid water.
Why this is interesting
Have you ever seen the ground look like a giant honeycomb or a mosaic of stone circles? In the high Arctic, the barren soil is mysteriously arranged into perfect patterns—who built them?
Read the full explanation
Understanding How Periglacial Patterned Ground Forms in High Latitudes
In high-latitude regions like the Arctic, the ground undergoes repeated freezing and thawing. Each winter, the soil freezes from the top down. Because water expands when it freezes, the freezing front pushes soil particles upward. In spring, the thawed soil collapses, but because fine particles settle lower than coarse ones, the mixture gradually sorts itself. Over thousands of cycles, this produces distinct stone circles, polygons, or stripes. Imagine a gentle sifting machine that separates pebbles from sand—except it operates through the relentless power of ice. The type of pattern that forms depends on the slope: flat ground produces circles or polygons, while slopes produce stripes aligned downhill.
A deeper explanation
The driving mechanism behind patterned ground is frost heave combined with ice lens growth. When soil freezes, water migrates toward the freezing front and forms lenses of pure ice. These lenses grow, lifting the ground above them. Because fine-grained soil has higher capillary action than coarse gravel, it draws more water, causing differential frost heave. Over many freeze-thaw cycles, this differential heave pushes stones outward and upward, while fine particles accumulate in the center. This process, called frost sorting, creates the borders of stones that enclose finer soil. On slopes, gravity biases the direction of heave and frost creep, stretching the polygons into stripes. This pattern formation is a powerful example of how seemingly chaotic natural processes can produce ordered structures over time. Understanding it helps scientists interpret ancient periglacial landscapes and assess how current climate change may affect permafrost regions.