Ancient Lava Dome Comparable to Sanbangsan Discovered Beneath Jeju's Deode Oreum

Traces of an ancient lava dome comparable in scale to Sanbangsan have been discovered beneath Deode Oreum in Seogwipo, Jeju.

The Hallasan Research Institute under the Jeju World Heritage Office confirmed the existence of a massive trachyte lava dome during a deep-bore drilling survey near Deode Oreum in Sangye-dong, Seogwipo.

The research team conducted the survey at a borehole located approximately 200 meters northeast of the summit of Deode Oreum.

As a result, they confirmed that trachyte, the same rock that forms Deode Oreum, is continuously distributed in a 221-meter section from 109 meters underground to the current drilling depth of 330 meters.

By synthesizing the drilling data with the topography of Deode Oreum, the researchers estimated that this lava dome extends from at least 132 meters below sea level to its summit at 228.4 meters above sea level.

The total scale is analyzed to be at least 360 meters.

Deode Oreum, which currently stands at a height of 48 meters, has a relative elevation of 48 meters and an altitude of 228.4 meters.


It has been suggested that while it was once a massive lava dome comparable to Sanbangsan—which has a relative elevation of 345 meters and an altitude of 395 meters—it may have been covered by lava flows over a long period, resulting in its current appearance.

Relative elevation refers to the height difference between the summit of a mountain or oreum and the surrounding ground level.

Altitude refers to the height above mean sea level.

The lower boundary of the trachyte body has not yet been identified even at a depth of 330 meters.

The research team stated that the actual scale of the volcanic body could be even larger.

The World Heritage Office plans to conduct precise analysis and dating of the rock samples.

Through this, they intend to clarify the formation relationship between trachyte volcanic bodies in southwestern Jeju, such as Deode Oreum and Sanbangsan.

The research team stated, "Through this survey, we have confirmed for the first time that a massive trachyte volcanic body is hidden beneath Deode Oreum, which appears to be just a small oreum on the surface."

They added, "This is an important achievement that shows the history of volcanic activity in Jeju is much more complex and three-dimensional than what is visible on the surface today."

The researchers also noted, "Drill cores are valuable research assets that record volcanic activity beneath Jeju's soil, and once lost, they are difficult to reacquire."

They evaluated the findings by saying, "This survey result demonstrates how important drilling data is in uncovering the history of Jeju's volcanic activity."

A borehole survey is an investigation that involves drilling deep into the ground to directly examine underground rocks and strata.

The Hallasan Research Institute of the Jeju World Heritage Office has been conducting a research project titled "Construction of a Geological Map of All of Jeju" from 2025 to 2028.

This year, they are documenting drill cores obtained from 13 deep boreholes within Jeju Island that were excavated for groundwater development and observation.

They are also conducting the collection and analysis of rock samples for each lava layer.

(Photo courtesy of Jeju Special Self-Governing Province, Yonhap News)
※ Please note: This article was translated by AI and may contain errors.