Monte Halla

The massive Halla shield volcano forms much of the 40 x 80 km Cheju (Jeju) Island, which lies 90 km S 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 edifice was constructed. A 400-m-wide crater truncates the summit. About 360 late-Pleistocene and Holocene basaltic cones across the flanks 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 or offshore are Pleistocene-to-Holocene tuff rings and tuff cones; lava domes also occur. The latest two eruptions took place during the 11th century.