Internal Permafrost Structure of Geomorphologically Distinct Palsas in Northern Sweden Revealed by Quasi‐3D ERT

Permafrost in northern peatlands occurs within individual palsas or extensive peat plateaus and controls local carbon storage. These permafrost landforms are complex, and their internal structure remains poorly understood. We used quasi‐3D electrical resistivity tomography (ERT) measurements, supported by UAV‐LiDAR topography, frost probing, and borehole drilling, to map the internal structure of two geomorphologically distinct palsas (dome‐shaped and plateau‐shaped) within Sweden's largest coherent palsa complex, Vissátvuopmi. The results suggest that the 5 m tall dome‐shaped palsa contains permafrost up to 20‐m‐thick beneath elevated areas, whereas permafrost is thin or absent in the surrounding lower‐relief areas on the palsa. In contrast, the plateau‐shaped palsa seems to contain widespread boulders, with the top of this material identified at depths between 3.8 and 5.5 m below the surface, creating large resistivity anomalies and likely limiting frost heave. The permafrost base is difficult to delineate in the plateau‐shaped palsa because of the complex subsurface and limited depth sensitivity. Together, these results support the idea that palsas in deposits lacking boulders can heave into taller domes, whereas boulder‐rich substrates experience less frost heave and produce flatter plateau forms. This strong control of subsurface composition on permafrost structure highlights the need for detailed baseline knowledge, which is important for predicting palsa responses to future climate warming.