Thermokarst lakes on the Tibetan Plateau thaw permafrost and form through-taliks beneath them

Why it matters

Through-taliks open pathways for groundwater, which the authors link to faster permafrost thaw, water loss and risk to nearby infrastructure. Measured permafrost thickness and talik shapes can serve as constraints for models that predict how lakes and permafrost change under warming. The study also shows that surveying and temperature data together can map thick permafrost where drilling alone cannot.

What they did

The team surveyed five electrical resistivity tomography transects in August 2022 in the Beiluhe basin, around three thermokarst lakes. The method infers frozen versus thawed ground from how well it conducts current. They checked the results against ground temperature records from boreholes at lakes BLH–A and BLH–B. They also used the temperature gradient to estimate where permafrost ends at depth.

Key findings

• The maximum lower limit of less-disturbed permafrost was 84–100 m deep.
• The active layer, which thaws each summer, was 0.9–4.0 m thick.
• Permafrost below lakes BLH–A, B and C had thawed completely, forming three through-taliks.
• Permafrost thinned near the lakes. Warm groundwater under and above the permafrost eroded its base and top, and the authors call this the main mechanism.
• Air temperature at the three nearby stations rose over the record, and ground temperatures around lake BLH–A warmed from 2006 to 2016.

Limitations

• Only five transects were measured, in one season (August), with no cold-season or long-term surveys.
• No new drilling or temperature measurements were made, and the temperature records used were older and had gaps.
• No single resistivity threshold cleanly separates frozen from thawed ground, because resistivity also depends on ice, water and rock type, which adds uncertainty.

Glossary

• Thermokarst lake: A lake formed when ground ice melts and the land surface sinks.
• Through-talik: A fully thawed zone that cuts through the whole permafrost layer.
• Electrical resistivity tomography (ERT): A survey method that sends current into the ground to map how strongly it resists current, which differs between frozen and thawed ground.
• Active layer: The top layer of ground above permafrost that thaws each summer and freezes each winter.