Geology and Volcanic Activities of Wollabong-Gunsan, the Oldest Twin Volcanoes in Jeju Island - 고기원(Gi Won Koh); 박준범(Jun Beom Park); 고창성(Chang Seong Koh); 전용문(Yongmun Jeon); 문덕철(Deok Cheol Moon); 문수형(Soo Hyoung Moon); 임재영(Jae Young Im) (지질학회지, 2021)