Construction, marine reworking, and stabilization of continental-shelf volcanic edifices in the Wollabong Volcanic Complex, Jeju Island, South Korea

Volcanic islands on continental shelves have complex growth histories because of repeated cycles of emergence and submergence driven by sea-level fluctuations, episodic volcanic activity, and marine erosion. The Wollabong Volcanic Complex (WVC) on Jeju Island, South Korea, is one of the oldest and best-exposed early volcanic successions on the island, preserving a local record of edifice emergence, marine reworking/partial submergence, and stabilization during the early proto-Jeju stage. The complex formed between ca. 0.92 and 0.84 Ma by magmatic and phreatomagmatic eruptions from multiple vents. Based on detailed field observations, this study reconstructs the early evolutionary history of a basaltic volcanic island in a continental-shelf environment influenced by fluctuating Quaternary sea levels. The stratigraphy of the WVC suggests three phases: (1) an initial subaerial phase during sea-level fall and lowstand, characterized by early phreatomagmatic to Strombolian eruptions, lava effusion, and a prolonged period of pedogenesis, indicating subaerial exposure of the early WVC; (2) a transitional phase during sea-level rise, marked by alternating phreatomagmatic and Surtseyan eruptions, together with lava effusion in subaerial to shallow-marine environments, during which marine erosion competed with volcanic growth and delayed the development of a stable island; and (3) a final subaerial phase during sea-level highstand, dominated by phreatomagmatic through Hawaiian to Strombolian eruptions, in which volcanic growth rates exceeded marine erosion, resulting in the construction of a stable subaerial edifice. Overall, the WVC provides a high-resolution record of volcanic-island growth on continental shelves, documenting how multiple monogenetic volcanic edifices progressively emerged and ultimately coalesced into a single volcanic island. The succession demonstrates that island evolution is governed by competition between volcanic accumulation (including magmatic output and lava capping) and marine erosion. We propose an integrated stratigraphic model for the WVC as an example of the development and stabilization of volcanic islands in shallow-marine settings.