Mention Dokdo to any Korean and you’ll immediately enter contested political territory. The islets — called Takeshima by Japan, which also claims sovereignty — are the subject of one of the most emotionally charged territorial disputes in East Asia. But beneath the politics lies genuinely fascinating geology: Dokdo and the nearby island of Ulleungdo are the exposed summits of ancient seamounts, volcanic structures rising thousands of meters from the floor of the East Sea (Sea of Japan). Their geological story is as compelling as their political one.
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The Geological Formation
Ulleungdo and Dokdo are not related to the Korean Peninsula’s continental geology. They are oceanic island volcanoes — formed by magma intruding through the oceanic crust of the East Sea basin, independent of any continental plate boundary process.
Ulleungdo formed through multiple phases of volcanic activity. Radiometric dating of its rocks indicates the most recent major volcanic episode occurred approximately 10,000 years ago — geologically very recent. The island’s distinctive calderas, trachytic rock formations, and steep cliffs are characteristic of phonolitic volcanic systems. The Korea Meteorological Administration monitors Ulleungdo for signs of volcanic activity, and it is classified as a potentially active volcano, though no eruption has occurred in recorded history.
Dokdo sits approximately 87 km from Ulleungdo. The two islets visible above water — East Islet and West Islet — represent just the tips of a massive seamount structure. The seamount rises approximately 2,000 meters from the seafloor; the visible portion is just the final 169 meters. Geological analysis by the Korea Ocean Research Institute indicates the seamount formed between 4.6 and 2.5 million years ago through repeated volcanic episodes.
Why Dokdo Is Geologically Important
Dokdo’s seafloor environment hosts one of the most biodiverse ecosystems in the East Sea. The volcanic substrate, combined with nutrient-rich cold currents, creates exceptional conditions for marine biodiversity. Korean fishermen have harvested squid, abalone, and sea cucumber in surrounding waters for centuries — these resources were a primary practical driver of both historical Korean use and modern sovereignty claims.
The continental shelf extending from Dokdo is also believed to hold significant natural gas hydrate (methane hydrate) deposits. While commercial extraction of methane hydrates remains technically challenging globally, the potential resource value adds an economic dimension to the sovereignty question.
Ulleungdo as a Geological Museum
Ulleungdo, inhabited by approximately 10,000 people, is increasingly recognized internationally as a significant geological site. Its rock exposures document the volcanic history of the East Sea basin in unusually accessible form. Korean geoscientists have proposed Ulleungdo for UNESCO Global Geopark designation, which would protect its geological heritage while developing geotourism infrastructure.
The island’s distinctive ecology — shaped by its volcanic isolation — includes numerous endemic plant species found nowhere else. Its Nari Basin, a collapsed caldera now filled with agricultural land, is one of the most visually dramatic examples of caldera formation in the region.
The Sovereignty Question (Briefly)
The territorial dispute over Dokdo centers on historical administrative records and the interpretation of 19th-century treaties. Korea points to Joseon-era records documenting administrative control. Japan points to a 1905 incorporation into Shimane Prefecture. Both countries maintain what international law scholars would call “non-frivolous” historical claims. South Korea has administered Dokdo continuously since 1954, with a permanent police garrison on the islets.
This article is not the place to resolve the sovereignty question — scholars and diplomats have not done so in 70 years. What is less contested: these are remarkable pieces of geology rising from the East Sea floor, representing millions of years of volcanic history, and their ecological and geological value is worth appreciating independent of their political significance.
Sources: Korea Ocean Research Institute geological surveys; Korea Meteorological Administration volcanic monitoring data; Korean national geopark documentation; radiometric dating studies published in Journal of Volcanology and Geothermal Research.
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