Thermokarst
Thermokarst is the process and landscape pattern that develops when ice-rich permafrost thaws, causing the ground to collapse, slump, pond, or form irregular terrain.
What thermokarst is
Thermokarst is both a process and a type of terrain. It happens where ice-rich permafrost or massive ground ice thaws, removing hidden support from the soil and causing the surface to sink, slump, crack, pond, or become uneven.
Why the name says karst
The word borrows from karst landscapes, where limestone dissolution creates pits and irregular terrain. Thermokarst can look similarly pitted or collapsed, but it is not caused by dissolving limestone. It is caused by thawing ground ice.
How it forms
A disturbance or warmer climate can deepen thaw in the active layer above permafrost. When buried ice wedges, lenses, or ice-rich sediments melt, the ground loses volume. Water may collect in depressions, and that water can absorb heat, accelerating further thaw nearby.
Thermokarst lakes
Thermokarst lakes form when thaw depressions fill with water. Some expand as lake water transfers heat into surrounding frozen ground. Others drain when erosion cuts an outlet or when thaw changes local drainage. Drained lake basins can later refreeze or develop new soils, wetlands, and vegetation.
Abrupt thaw
Thermokarst is often discussed as abrupt thaw because changes can happen over meters and years rather than only centimeters and decades. Retrogressive thaw slumps, collapsing bluffs, and rapidly expanding lakes can transform small areas much faster than gradual top-down warming alone.
Carbon and methane
Thaw can expose old organic matter that had been frozen in permafrost. In oxygen-rich soils, microbes can release carbon dioxide. In waterlogged thermokarst lakes and wetlands, low-oxygen conditions can favor methane. The balance depends on temperature, water, sediment, plants, microbes, and time.
Infrastructure and ecosystems
Thermokarst can damage roads, runways, pipelines, buildings, and traditional travel routes by making ground unstable or wet. It can also reroute streams, drain lakes, create new ponds, change habitat, alter water chemistry, and reshape Arctic and subarctic ecosystems.
Why it matters
Thermokarst matters because it is a visible, fast-moving form of permafrost change. It links climate warming, ground ice, hydrology, carbon release, wildlife habitat, northern communities, and infrastructure risk in one landscape process.