Mention Dokdo to any Korean and you’ll enter a contested political area. Japan calls these islets Takeshima and also claims them. They are the subject of one of the most emotionally charged land disputes in East Asia. But beneath the politics lies fascinating geology. Dokdo and the nearby island of Ulleungdo are the exposed tops of ancient seamounts. These are 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 connected to the Korean Peninsula’s continental geology. They are oceanic island volcanoes. They formed when magma pushed through the oceanic crust of the East Sea basin. This happened independent of any continental plate boundary process.
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Ulleungdo formed through multiple phases of volcanic activity. Rock dating shows the most recent major volcanic episode occurred approximately 10,000 years ago. This is very recent in geological time. 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. It is classified as a potentially active volcano. However, no eruption has occurred in recorded history.
Dokdo sits approximately 87 km from Ulleungdo. The two islets visible above water are East Islet and West Islet. They 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. It formed 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. [3]
The continental shelf extending from Dokdo is also believed to hold significant natural gas hydrate (methane hydrate) deposits. Commercial extraction of methane hydrates remains technically challenging globally. However, the potential resource value adds an economic dimension to the sovereignty question. [2]
Ulleungdo as a Geological Museum
Ulleungdo is inhabited by approximately 10,000 people. It 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. This would protect its geological heritage while developing geotourism infrastructure.
The island’s distinctive ecology is shaped by its volcanic isolation. It includes numerous endemic plant species found nowhere else. Its Nari Basin is a collapsed caldera now filled with agricultural land. It 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. It maintains 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. They represent millions of years of volcanic history. 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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Last updated: 2026-05-11
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References
- Kim, J.-S., et al. (2015). Petrological and geochemical constraints on the origin and evolution of igneous rocks on Ulleung Island, Korea. Lithos. Link
- Kang, P.-J., et al. (2006). Geology and petrochemical characteristics of Cenozoic alkali basaltic rocks in Ulleung Island, Korea. Journal of the Geological Society of Korea. Link
- Lee, J.-I., et al. (2007). K-Ar ages for the Ulleung and Dokdo Igneous Rocks, East Sea. Journal of Petrology. Link
- Ryoo, C.-R., et al. (2006). Petrogenesis of Quaternary basanites from Ulleung Island, Korea. Journal of Asian Earth Sciences. Link
- Chough, S. K., et al. (2000). Marine geology of Korean seas. Elsevier. Link
- Park, J.-B., et al. (2009). Geochemical characteristics of Dokdo volcanic rocks. Economic and Environmental Geology. Link
Ulleungdo’s Unique Flora and Endemic Species
Ulleungdo’s volcanic isolation has produced one of the most distinctive endemic floras in East Asia. Because the island has never been connected to the Korean Peninsula by a land bridge, species arriving by wind, ocean current, or bird dispersal evolved in effective isolation for millions of years. The National Institute of Biological Resources has catalogued approximately 650 plant species on Ulleungdo, of which roughly 36 are endemic — found nowhere else on Earth. Notable examples include Ulleung minamiasarum and the Ulleung thistle (Cirsium quelpaertense var. ullungense).
The island’s topography amplifies this biodiversity. Nari Basin, the only flat caldera plain on the island, sits at an elevation of approximately 250 meters and acts as a distinct microhabitat. Annual precipitation on Ulleungdo exceeds 1,800 mm, roughly double the Korean Peninsula average, creating humid conditions that support dense forests of Japanese cedar, alder, and endemic broadleaf species. Snowfall regularly exceeds 2 meters in winter months, an anomaly for an island at this latitude, driven by orographic lift as moist East Sea air masses rise over the island’s 984-meter peak, Seonginbong.
Wildlife diversity mirrors plant diversity. The Ulleung nettle tree cricket is one of several invertebrate species confirmed as island endemics. Marine surveys conducted by the National Institute of Fisheries Science between 2015 and 2020 recorded over 300 fish species in surrounding waters. The cold Liman Current and warm Tsushima Current converge near the island, generating the thermal layering that supports this productivity. UNESCO is currently evaluating Ulleungdo as a potential addition to its Global Geoparks Network, a designation already held by Jeju Island since 2010.
The Seamount Ecosystem Below Dokdo’s Waterline
The most ecologically significant parts of the Dokdo structure are entirely submerged. The seamount’s flanks between 50 and 200 meters depth support dense cold-water coral communities. A 2018 survey by the Korea Institute of Ocean Science and Technology (KIOST) documented 130 benthic invertebrate species across the seamount’s upper slopes, including commercially valuable red snow crab (Chionoecetes japonicus) at densities substantially higher than adjacent flat seafloor habitats. Seamount structures worldwide are known to concentrate biomass by disrupting deep ocean currents and forcing nutrient-rich water upward — a process called seamount-induced upwelling.
Dokdo’s position at the convergence zone of two major current systems intensifies this effect. The nutrient load delivered to the photic zone during upwelling events supports phytoplankton blooms that, in turn, sustain the squid fisheries Korean vessels have worked for at least 500 years, based on Joseon Dynasty records from the 1500s referencing fishing activities in the area. Annual squid catches in Dokdo-adjacent waters were estimated at approximately 60,000 metric tons per year during peak seasons in the 1990s, though overfishing has reduced those figures significantly since.
Natural gas hydrate deposits on the surrounding continental shelf add another scientific dimension. Methane hydrates — ice-like structures trapping natural gas in crystalline form — are estimated by the Korea Institute of Geoscience and Mineral Resources (KIGAM) to hold reserves in the Ulleung Basin equivalent to roughly 600 million tons of oil equivalent. While commercial extraction technology remains immature globally, the Ulleung Basin deposits are among the highest-concentration methane hydrate accumulations yet measured in the northwestern Pacific.
How Volcanic Age Affects the Sovereignty Argument
Geological dating has become an unexpected element in the legal and historical dispute over Dokdo. Japan’s position relies partly on the argument that the islets were uninhabited and unclaimed when Japan formally incorporated them into Shimane Prefecture in February 1905. Korean scholars counter that historical records, including the Annals of the Joseon Dynasty and a 1900 imperial ordinance by Emperor Gojong explicitly referencing Dokdo as Korean territory, predate Japan’s incorporation claim by centuries.
The geological timeline matters in a specific legal sense. Under the United Nations Convention on the Law of the Sea (UNCLOS), Article 121 distinguishes between islands — which generate a full 200-nautical-mile Exclusive Economic Zone — and rocks incapable of sustaining human habitation or independent economic life, which generate only a 12-nautical-mile territorial sea. Korea maintains a small coast guard detachment and a lighthouse on Dokdo, arguing the islets qualify as habitable islands. Japan contests this classification. The ruling would determine control over an EEZ covering approximately 167,000 square kilometers of resource-rich East Sea waters.
Geological surveys establishing the seamount’s age, structure, and resource base thus feed directly into legal arguments about economic viability and historic use. The Korea Hydrographic and Oceanographic Agency has published detailed bathymetric maps of the Dokdo seamount, providing the scientific foundation for Korea’s resource and territorial claims in any future international adjudication.
References
- Kwon, S.T., et al. Geochronology and geochemistry of volcanic rocks from Dokdo and Ulleungdo, East Sea, Korea. Journal of the Geological Society of Korea, 2007. Available through Korean geological survey archives.
- Korea Institute of Geoscience and Mineral Resources (KIGAM). Gas Hydrate Occurrence and Resource Assessment in the Ulleung Basin. KIGAM Research Report, 2012. https://www.kigam.re.kr
- Kim, H.J., et al. Seamount ecosystems and benthic biodiversity surveys of the Dokdo seamount structure. Ocean Science Journal, Korea Institute of Ocean Science and Technology, 2018. https://www.kiost.ac.kr
