Korea Institute of Geoscience and Mineral Resources

Jeju Island, South Korea, is a volcanic island where the population depends entirely on groundwater for freshwater supply, and the island exhibits unique hydrogeological characteristics. This study examines groundwater recharge processes by analyzing the stable isotopes of oxygen (δ¹⁸O) and hydrogen (δ²H) in monthly precipitation and groundwater. Precipitation isotopes showed clear seasonal variability, characterized by a strong summer monsoon effect. Northern-slope precipitation was slightly more depleted in ¹ ⁸O and has lower d -excess values compared to other slopes. Groundwater in this area exhibited similarly depleted isotopic signatures, suggesting that high-elevation recharge moves downgradient along preferential flow pathways toward coastal areas. Mixing analysis indicates that high-elevation summer rainfall is the dominant source of groundwater recharge. These findings significantly enhance the understanding of the linkages between precipitation patterns and groundwater recharge dynamics on the island. • Summer rainfall is the primary source of recharge. • Isotope mixing analysis indicates high-altitude summer rainfall as the main source. • Low δ¹ ⁸O in northern-slope indicates rapid flow of high-altitude recharge. • Long-term isotope monitoring is vital for sustainable water management.

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.

The growing reliance on nuclear energy to attain carbon neutrality underscores the critical necessity for advanced environmental radioactivity monitoring. Currently, determining 137Cs levels in marine environments typically exceeds four days, creating a pressing need for efficient, high-throughput pretreatment systems for rapid analysis. In this study, we developed a membrane-capacitive deionization (MCDI) cell specifically designed for the electrochemical enrichment of Cs, utilizing nickel hexacyanoferrate (NiHCF) as the electrode material due to its high selectivity and redox characteristics. NiHCF electrodes were fabricated via electrospraying and casting methods, followed by comprehensive characterization using SEM, BET/BJH, TGA, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The results demonstrated that electrosprayed coatings achieved significantly higher adsorption/desorption efficiency than cast coatings, a superiority attributed to their highly porous structure which facilitates interfacial electrochemical reactions. To address the challenge of ion interference in seawater - where competing cations cause rapid electrode saturation and hinder Cs migration - a pulsed voltage application method was introduced. This approach periodically refreshes the electrode surface, increasing the frequency and duration of Cs migration and subsequently enhancing adsorption efficiency by up to 90%. Furthermore, the performance was validated using a large-scale MCDI cell. These findings suggest that this technology is a promising pretreatment method for the rapid analysis of 137Cs in real seawater, contributing significantly to the advancement of environmental radioactivity monitoring.

Infrasound has been widely applied to the remote monitoring of explosive volcanic eruptions. Although no active volcanoes are currently present within South Korea, explosive activity in neighboring regions can still generate transboundary hazards that require effective remote monitoring. In this context, we present a quantitative assessment of volcanic eruption detectability using the Korea Infrasound Network (KIN).The KIN has been operated for more than two decades and was originally established to monitor local and regional acoustic sources and to discriminate between natural and anthropogenic signals. The network consists of Chaparral M2 infrasound sensors, each of which has a flat response from 0.1 to 200 Hz. Since 2011, eight infrasound arrays with apertures ranging from 0.15 to 1.68 km have been fully operational. We evaluate the detectability of eruptions with VEI ≥ 3 that have occurred since 2011, examining detection characteristics as a function of distance, azimuth, and atmospheric propagation conditions. Detection was performed using the Progressive Multi-Channel Correlation (PMCC) algorithm to identify coherent infrasound signals.Many eruption signals recorded by the KIN extend into frequencies below the nominal flat-response bandwidth and are often obscured by persistent microbarom noise. Despite these limitations, volcanic eruptions were conditionally detected depending on eruption size and atmospheric propagation conditions. The analyzed cases include the 2022 Hunga Tonga–Hunga Haʻapai eruption (VEI 5), the 2020 Taal and 2021 Fukutoku-Oka-no-Ba eruptions (VEI 4), and several VEI 3 eruptions such as Asosan, Kirishimayama, and Raikoke.Our results indicate that automated eruption detection using KIN is feasible, particularly at the TJIAR array in central South Korea. A long-term PMCC detection catalog spanning approximately 15 years (since 2011) was compiled for TJIAR and compared with independent eruption records from the Tokyo Volcano Ash Advisory Center and the Global Volcanism Program to assess detection reliability. This study represents the first long-term assessment of volcanic infrasound detectability based on the KIN. In addition, low-frequency infrasound sensors (MB3d) with an extended dynamic range were collocated at one of the KIN arrays in 2025 to improve low-frequency detectability. Ongoing work focuses on assessing improvements in eruption detectability through comparisons between legacy and upgraded sensor configurations, with implications for the development of an infrasound-based automated eruption detection and long-term monitoring of explosive volcanic eruptions in East Asia.

Weak, sustained infrasound waves associated with natural and environmental sources (e.g., waterfalls, avalanches, dams, and debris flows) can be detected by remote infrasound arrays. Large-volume water flows at waterfalls and dams convert the mechanical energy of flowing water into various forms of energy, including acoustic energy in the infrasound range. Under certain circumstances, infrasound observations of sudden and otherwise unexpected large-scale water flow events can be used for early disaster warning, thereby contributing to disaster mitigation. Beyond early warning, this study investigates whether remote infrasound observations can be used to quantify the intensity of water release (discharge rates) at dams. To establish a relationship between infrasound energy and water discharge at a reference distance of 1 km, data were obtained from controlled water-release events at a dam in South Korea. Since water-release signals observed at regional distances are generally noise-like and exhibit low signal-to-noise ratios, two infrasound detection algorithms, based on the correlation (PMCC) and the maximum likelihood (MCML), were applied, and their detection results were compared to evaluate the performance of each method. Based on the detected infrasound signals at a distance of 15 km from the dam, discharge rates were estimated using the derived empirical relationship. The estimated discharge rates show promising agreement with the actual discharge rates, demonstrating the feasibility of this approach. Overall, our results indicate that infrasound monitoring has practical potential not only for early warning but also for quantifying hazardous water discharge, thereby enhancing disaster monitoring and response capabilities.

The Hantan River basin (central–northern Korean Peninsula) is characterized by a Quaternary volcanic–fluvial landscape in which basaltic lava flows repeatedly overlie unconsolidated fluvial deposits. Beneath these lava flows, the Baeguiri Formation consists of channelized fluvial conglomerates and sands with associated overbank silts and clays, unconformably overlying Devonian basement units. While the emplacement ages of overlying basalts are relatively well constrained by K–Ar and 40Ar/39Ar dating, the depositional and burial timing of the underlying fluvial conglomerates remains poorly constrained and controversial. Previous age estimates for the Baeguiri Formation, derived indirectly from basalt contact ages, fission-track, and TL/OSL methods, provide only partial constraints and may be affected by inheritance, post-depositional reworking, and uncertainty in the time lag between sediment deposition and lava burial.To directly date the burial of the fluvial conglomerates and to assess potential temporal heterogeneity among key outcrops, we apply cosmogenic radionuclide (CRN) burial dating using paired 10Be and 26Al measurements on quartz-bearing gravel from conglomeratic units of the Baeguiri Formation at four representative sites in the Hantan River system: Eundaeri (Chatan Stream tributary), Baeguigyo Bridge, Jangjingyo Bridge, and Hantangang Dam along the mainstem Hantan River. At all sites, the conglomerates are fully covered by multi-meter-thick basalt flows, locally associated with pillow lavas and slabby flow-top structures, indicating rapid burial and long-term attenuation of cosmic-ray exposure. Burial ages are calculated using isochron approaches to account for variable pre-burial exposure histories and possible partial reworking within fluvial deposits.The resulting burial ages provide direct chronological constraints on the timing of isolation of the Baeguiri Formation from surface processes, allowing us to (1) Test whether burial of the fluvial conglomerates by basalt flows was synchronous across different outcrops, (2) Quantify spatial and temporal heterogeneity in sedimentation–burial events within the Baeguiri Formation, and (3) Evaluate implications for refining stratigraphic relationships between fluvial deposits and multi-stage basalt emplacement in the Hantan River volcanic–fluvial succession. This study highlights the effectiveness of CRN burial dating for directly constraining the age of basalt-buried fluvial conglomerates in complex Quaternary volcanic plateaus.

We present an evaluation of the grain bulk modulus of rocks through experimental and theoretical methods. Unjacketed tests were performed on three rock types—Berea sandstone, Idaho sandstone, and Hwangdeung granite—to measure grain-scale compressibility. Theoretical estimates were obtained using mineral composition data and the Voigt–Reuss–Hill averaging method. To examine the role of pore structure, X-ray computed tomography (CT) was employed to visualize and quantify pore geometry, including isolated pores. Experimental results indicated material-dependent variation in grain bulk modulus not directly correlated with conventional mechanical properties. The theoretical values, as represented by the Hill average, were consistently higher than the experimental measurements, with overestimations of 7.2% for Berea sandstone, 37.3% for Idaho sandstone, and 31.7% for Hwangdeung granite. X-ray CT analysis confirmed that isolated pores contribute to additional volumetric deformation, which is unaccounted for in volume fraction-based models. A correlation between theoretical estimates and experimental values was derived to improve the applicability of the model. Conclusively, we present a systematic methodology for accurately evaluating grain bulk modulus by integrating experimental and theoretical approaches, offering foundational data and insight critical for geomechanical modeling in deep subsurface applications such as radioactive waste disposal or underground liquid hydrogen storage.