Thermokarst lakes disturb the permafrost structure and stimulate through-talik formation in the Qinghai–Tibet Plateau, China: A hydrogeophysical investigation

Abstract. Thermokarst lakes are widely distributed in the Qinghai–Tibet Plateau (QTP) and continuously disturb the permafrost structure. Investigating the permafrost and sublake talik structures is crucial to assessing and predicting the fate of the ecosystem and engineering under climate warming. Until recently, measurements of the permafrost distribution are often limited to seasonally frozen soil or permafrost at a few borehole locations, and the detection of deep permafrost and sublake taliks in the QTP has rarely been attempted on larger scales. Here, a synergistic application of electrical resistivity tomography, transient electromagnetic method, and borehole temperature measurement was used to investigate the permafrost and sublake talik structures in a thermokarst lake region of the QTP. The results showed that the maximum lower limit depths of the permafrost and active layer were determined to be 84–100 m and 0.9–4.0 m, respectively. Sub- and supra-permafrost water continuously erode the base and top plate of the permafrost, thereby reducing its thickness and disturbing its structure. Moreover, thermokarst lakes (unofficially named lakes BLH–A, B, and C) thaw the surrounding permafrost and form three through-taliks below them. These findings can help understand the interaction between thermokarst lakes and permafrost and optimize cryohydrogeologic models that can predict the evolution of permafrost and thermokarst lakes in similar cold regions.