Thermokarst

Thermokarst refers to landforms and surface processes caused by thawing of ice-rich permafrost. As ground ice melts, the soil subsides, producing uneven topography and irregular surface features. The term combines thermo (heat) and karst (collapse) to describe karst-like subsidence due to melting ground ice. Thermokarst landscapes occur wherever permafrost contains substantial ground ice and are common in cold regions, especially where warming thins permafrost.

The main driver is thaw of ground ice in permafrost due to warming, moisture changes, or heat transfer from the soil. Melting ice reduces support, creating subsidence pits, troughs, and irregular terrain. Ice wedges and lenses form networks of cracks and pits. Changes in drainage after subsidence can further modify hydrology, promoting ponds and lakes in subsiding areas.

Typical features include thaw lakes, kettle holes, polygonal patterned ground, hummocky ground, and wide troughs. Thermokarst lakes can expand and merge as permafrost degrades. Repeated cycles of thaw and collapse create terraces, valleys, and drained basins. Ecological impacts include altered hydrology, vegetation shifts, and increased methane release from decomposing organic matter.

Thermokarst is common in circumpolar permafrost regions, including Alaska, northern Canada, Siberia, Greenland, and high-elevation areas such as the Tibetan Plateau. It is influenced by climate warming and regional hydrology and is studied for permafrost stability, landscape evolution, and climate feedbacks. In addition to natural processes, thermokarst can jeopardize infrastructure by causing ground subsidence under roads, buildings, and pipelines.

Researchers study thermokarst with satellite imagery, aerial photography, LiDAR, and in situ drilling to map permafrost conditions, measure subsidence, and model future landscape change.