Three-Dimensional Geological Model of Scoria and Clinker as Major Groundwater Flow Media in Volcanic Aquifers

The southernmost island of the Republic of Korea, Jeju Island, is composed of multi-layered lava flows formed by repeated volcanic activity and sedimentary layers deposited during quiescent periods between eruptions. Approximately 96% of the island’s total water use is supplied by groundwater, making groundwater the most critical water resource in the region. Therefore, accurate identification of the spatial distribution of aquifers and the major groundwater flow pathways is essential for sustainable groundwater management.

The objective of this study is to establish a 3D geological model for the mid-mountain area of Jeju Island and to quantitatively characterize the spatial distribution of the volcanic aquifer system and the major groundwater flow pathways. This approach enhances the understanding of groundwater recharge and flow mechanisms and provides a scientific basis for future groundwater conservation and management.

The 3D geological modeling results are summarized as follows. The basal Seogwipo Formation occurs below approximately 50 m above mean sea level and has an average thickness of about 50 m. It is overlain by basaltic lava flows with a total thickness of approximately 400 m, emplaced by at least 14 eruptions over the past 500,000 years. Intercalated sedimentary layers mainly consist of mudstone and silty sandstone and are generally less than 5 m thick. These fine-grained, silt–clay–dominated layers act as semi-confining units that retard downward infiltration of rainfall. Scoria and clinker layers occur mainly at the upper and lower boundaries of lava flows and increase in frequency from high-elevation zones to low-lying areas. In contrast to the dense basalt, these porous layers serve as major groundwater flow pathways.