Geography
Why Periglacial Landscapes Form Patterned Ground and Ice Wedges
Quick fact
In some periglacial regions, ice wedges can grow for centuries, eventually forming ice masses up to 10 meters deep and several meters wide at the surface—like giant underground ice walls.
Why this is interesting
Have you ever seen a field of perfectly arranged stone circles or a honeycomb pattern carved into the frozen ground? These astonishing patterns aren't human-made—they're the natural signature of a landscape shaped by ice.
Read the full explanation
Understanding Why Periglacial Landscapes Form Patterned Ground and Ice Wedges
Imagine a muddy puddle on a cold winter morning. When it freezes, the ice expands, and if the ground is wet, frost heave can lift the soil. In periglacial regions, this happens repeatedly through the seasons. The ground is often permanently frozen deep down (permafrost), but the top layer thaws each summer and refreezes each winter. This freeze-thaw action sorts and moves sediments in a remarkable way: stones of different sizes get separated, forming patterns like circles, stripes, and polygons. Similarly, when the ground gets extremely cold, it contracts and cracks. Meltwater seeps into these cracks, freezes, and forms veins of ice. Over many cycles, these veins grow into massive ice wedges that create the classic polygonal (honeycomb) patterns on the surface.
A deeper explanation
The formation of patterned ground and ice wedges is driven by two primary mechanisms: frost heave and thermal contraction. Frost heave occurs when ice lenses grow within the soil as water migrates toward the freezing front (due to capillary action and adsorption). The growth of these ice lenses pushes soil particles upward. When thawing occurs, the ground subsides, and finer particles move down while coarser stones are dragged up and sideways. This process, called frost sorting, creates networks of stones and fine soil. The size-sorting leads to distinct patterns: in stone polygons, coarse stones ring fine centers; in stone stripes, parallel lines form on slopes. Ice wedges form from thermal contraction cracking. When air temperatures plunge, the ground contracts and fractures in polygonal patterns. Melting snow fills these cracks with water, which freezes into ice veins. Over repeated cycles, the veins expand and grow into wedges, widening the cracks. This process is self-reinforcing: the ice wedges exert pressure on surrounding ground, causing further contraction and cracking. The result is a landscape fragmented into polygonal blocks. Understanding these mechanisms is crucial for predicting how periglacial regions respond to climate change—as permafrost thaws, the ground becomes unstable, affecting infrastructure and releasing greenhouse gases.