Geology and Volcanic Activities of Wollabong-Gunsan, the Oldest Twin Volcanoes in Jeju Island

Researchers have identified Wollabong-Gunsan as the oldest exposed twin volcanoes on Jeju Island, providing new insights into the volcanic history of the region. The study, published in the Journal of the Geological Society of Korea, reveals that these volcanoes formed between 920,000 and 830,000 years ago through a series of magmatic eruptions, followed by a period of dormancy and renewed activity around 530,000 years ago. The study also challenges historical records linking the Gunsan volcano to an eruption in 1007 CE. To reconstruct the volcanic history, the team conducted field geological surveys, petrographic analysis of lava flows, rock chemistry analysis, Ar-Ar dating, and re-evaluated nearby drill core stratigraphy. Notably, they discovered a previously unknown basaltic lava flow (AB-I) with an age of 917.7±23.2 ka to 915.6±11.5 ka, which had only been documented in drill cores before.

Koh, G. W., Park, J. B., Koh, C. S., Jeon, Y., Moon, D. C., Moon, S. H., & Im, J. Y. (2021). Geology and Volcanic Activities of Wollabong-Gunsan, the Oldest Twin Volcanoes in Jeju Island. Journal of the Geological Society of Korea, 57(2), 141–164. https://doi.org/10.14770/jgsk.2021.57.2.141