Subsurface structures of solution dolines inferred from electrical resistivity tomography: A hypothesis on the evolutionary process of solution dolines at the Akiyoshi-dai Plateau, southwest Japan

Abstract

The evolution of solution dolines is regulated by carbonate dissolution mediated by water and CO2. The subsurface structure influences the evolutionary pattern of the dolines. Despite the significant effects of enlarged joints or shafts on the development of solution dolines, a few studies have identified the subsurface structures of multiple solution dolines. To this end, we utilized 2-D electrical resistivity tomography (ERT) at 15 dolines and an outcrop in the Akiyoshi-dai Plateau, Japan, which is composed of massive and fractured limestone lithology. The results of ERT exhibited the following: (i) a similar range for electrical resistivity in parallel to the topographic relief; (ii) an increase in resistivity with depth, and; (iii) a low resistivity zone characterized by <400 Ωm, at shallow areas. Some electrical resistivity distributions exhibited high resistivity zones that were vertically split by low or intermediate resistivity zones. Our results and interpretation revealed that the main shafts, which play a substantial role in the evolution of solution dolines, can be formed around the doline bottoms rather than in their central sectors. We propose a hypothesis that can better account for the subsurface structures and the development of dolines in Akiyoshi-dai. Our hypothesis suggests that the role of main shafts in the evolution of solution dolines can be superseded by another influential joint system with a potential shaft during their evolution, resulting in the ubiquity of main shafts beneath the doline bottoms. This hypothesis would further our understanding of the intricate role of shafts in the evolution of karst systems involving solution dolines.