A Cracked Landscape
Across vast lowlands of the Siberian tundra, the ground is fractured into a mosaic of geometric shapes. These patterns, known as ice-wedge polygons, are the surface result of a process happening deep within the permafrost. They typically range from 5 to 30 meters in diameter. The process begins in the extreme cold of arctic winters, when temperatures drop below -17°C. The frozen ground contracts and splits open, forming cracks. In the spring, meltwater seeps into these fissures and freezes, creating a small vein of ice.
This cycle repeats for hundreds or thousands of years. Each winter the ground re-cracks along the same lines of weakness, and each spring more water enters and freezes. The ice vein grows into a massive vertical wedge, sometimes several meters deep. The immense pressure exerted by the growing ice wedge deforms the surrounding soil, pushing it upwards to form raised rims along the cracks. This relentless process sculpts the entire area from below.
Polygons in Flux
The shape of the polygons dictates the life they support. "Low-centered" polygons, the active, growing stage, have raised rims that create a shallow, insulated basin. These centers are often waterlogged and host wetland plant communities dominated by sedges like Carex aquatilis and various mosses.
Over time, or as permafrost conditions change, these can transform into "high-centered" polygons. Here, the central area is pushed up into a dry, raised mound, while the troughs above the ice wedges become water channels. These drier mounds support a different suite of plants, including dwarf shrubs like dwarf birch (Betula nana), lichens, and grasses.
This delicate balance is now under threat. As arctic temperatures rise, the massive ice wedges that form the polygon boundaries begin to melt. This process, called thermokarst, causes the raised rims to collapse, draining the wet centers and fundamentally altering the hydrology. Studies in the Lena Delta show that a significant percentage of polygons are already in advanced stages of degradation, collapsing into ponds, slopes, and valleys. This landscape-level change releases large amounts of carbon, previously locked in the frozen soil, into the atmosphere.