Reconstruction of paleo-channels and the spatiotemporal distribution of the Yeoncheon lava plateau, South Korea, constrained by borehole data

 Quaternary lava plateaus profoundly modify landscapes by filling the lowlands, disrupting drainage systems, controlling long-term fluvial evolution and leveling the pre-existing topography. To constrain the spatiotemporal evolution of these processes, robust geochronological data integrated with subsurface stratigraphic information are required. In this study, we aim to re-evaluate the timing and number of basaltic eruptions in the Yeoncheon lava plateau and to reconstruct the spatiotemporal evolution of the lava plateau and associated paleo-channels using field surveys, borehole stratigraphy, and high-precision ⁴⁰Ar–³⁹Ar geochronology supported by GIS-based analyses.

 A total of 19 boreholes penetrating from upper Quaternary deposits down to the underlying basement were analyzed, together with detailed field surveys of well-exposed outcrops along river corridors. Basalt samples from boreholes and outcrops were dated using ⁴⁰Ar–³⁹Ar dating methods, providing independent absolute age constraints for lava emplacement. The results indicate the presence of basalt units emplaced during two distinct eruptive periods, with weighted mean ages of 518 ± 2 ka and 168 ± 1 ka. These basalts are geochemically distinguishable and show systematic elevation-dependent distributions, with the older basalt generally occurring at elevations of ~50–55 m a.s.l. and the younger basalt distributed at ~65–70 m a.s.l.

 Based on integrated evidence from borehole stratigraphy, basalt age–elevation relationships, and comparison with GIS-based topographic data, we identify the presence of at least two paleo-channels and constrain the timing of drainage reorganization leading to establishment of the present Hantangang River. The first paleo-channel between ca. 518 and 168 ka, is inferred to have incised the older lava plateau and basement rocks prior to emplacement of the younger lava, which preferentially filled this topographic depression. The second paleo-channel formed after ca. 168 ka and is inferred to have passed through a low-lying area within the lava plateau, now known as the Eum-teo town, where surrounding basalt cliffs and the scarcity of basalt in boreholes indicate sustained headward erosion. Finally, geomorphic evidence from river terrace development indicates that subsequent drainage reorganization led to establishment of the present Hantangang River after ca. 35 ka.

 This study demonstrates that borehole-constrained chronologies significantly reduce uncertainties in volcanic stratigraphy and provide a robust temporal framework for reconstructing paleo-channels and landscape evolution in lava plateau environments. By integrating absolute dating with borehole data, this approach enables reconstruction of spatiotemporal changes in lava plateau development and associated drainage reorganization. The framework is transferable to other lava plateau systems and offers broad potential for resolving long-term environmental change in Quaternary landforms.