"The massive Halla shield volcano forms much of the 40 x 80 km Cheju (Jeju) Island, which lies 90 km south of the Korean Peninsula. Eruptions during the Pliocene and Pleistocene built a lava plateau above the roughly 100-m-deep continental shelf on which the basaltic-to-trachytic Halla shield volcano was constructed. A 400-m-wide crater truncates the 1950-m-high summit. About 360 late-Pleistocene and Holocene basaltic parasitic cones dotting the flanks of the low-angle volcano were erupted primarily along the long axis of the ENE-WSW-trending island. Most of these are scoria cones, but about 20 along the coast of the island or offshore are Pleistocene-to-Holocene tuff rings and tuff cones, and lava domes also occur. Flank eruptions continued into historical time, with the final two taking place during the 11th century."  -Smithsonian Volcano Archive
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