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Geological mapping, electric resistivity survey, drilling of the crater-filling sediments, and geochemical analysis of rock samples were carried out in order to unravel geomorphic and geological characteristics and evolution of the Hanon volcano on the southern margin of Jeju Island. The volcano has...

Geological mapping, electric resistivity survey, drilling of the crater-filling sediments, and geochemical analysis of rock samples were carried out in order to unravel geomorphic and geological characteristics and evolution of the Hanon volcano on the southern margin of Jeju Island. The volcano has the largest crater in Jeju Island, of which the diameter or the rim-to-rim width is 1.0-1.2 km and the altitudinal contrast between the crater rim and the crater floor is up to 90 m. The crater has a nested scoria cone in the southern part and is surrounded by thin (ca. 40 m thick) and gently outward-dipping rim beds of a tuff ring. Basement rocks are exposed inside the crater wall, and lacustrine sediments as thick as 15 m are filling the topographic lows of the crater, suggesting that the crater was excavated not only below the pre-eruption surface but also below the groundwater table. It is thus interpreted that the Hanon volcano once comprised an archetypal maar or a water-filled crater, and can be classified as a tuff ring with a maar crater based on its present morphology. The AMS ¹⁴C ages of the crater-lake deposits suggest that the volcanic eruption took place ca. 34 kyr BP in an inland area about 130~150 m above the sea level. The early eruptive activity was phreatomagmatic, involving explosive interaction of rising trachyandesitic magma with groundwater and resulting in excavation of a maar-type crater and construction of a tuff ring around it. As the groundwater was exhausted, the eruption style changed gradually from phreatomagmatic to magmatic, resulting in the formation of a nested scoria cone and a ponded lava flow. After the cessation of the volcanic activity, the Hanon crater was filled by max. 15 m-thick sediments deposited in a shallow crater lake or a maar.

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