Another 'Sanbangsan' Beneath Jeju: Evidence of Massive Lava Dome Discovered for the First Time

Deep Borehole Investigation Beneath Deodeoreum, Sanggye-dong
Ancient Volcanic Body at Least 360 Meters in Scale
Dating of Formation Expected by Year End

The World Heritage Headquarters of Jeju Special Self-Governing Province has discovered evidence of a massive ancient trachytic lava dome, measuring at least 360 meters beneath the surface, through deep drilling near Deodeoreum in Sanggye-dong, Seogwipo City. Based on this finding, the institute has launched a detailed analysis of the drilling cores and radiometric dating to unveil the three-dimensional secrets of Jeju's volcanic history.

A geological schematic diagram visualizing the developmental structure of a massive rhyolitic lava dome hidden underground in Sangye-dong, Seogwipo City, along with analysis data by drilling points. Provided by the Jeju Special Self-Governing Province World Heritage Headquarters.

According to the Hallasan Research Department of the World Heritage Headquarters on July 16, this discovery was made during the precise analysis of drilling cores obtained from 13 deep-borehole locations across Jeju. The work is part of the 'Jeju Regional Geological Mapping Project,' which is being carried out until 2028.

The research team found that at the drilling point located approximately 200 meters northeast of Deodeoreum, at an elevation of 198 meters, there was continuous distribution of trachyte—the same rock that constitutes Deodeoreum—from a depth of 109 meters underground to the current lowest borehole depth of 330 meters, spanning about 221 meters.

Comprehensive analysis of the drilling data and surface geological structures suggests that the underground volcanic body extends from at least 132 meters below sea level up to the summit of Deodeoreum at 228.4 meters above sea level, indicating a total vertical scale of at least 360 meters.

This is comparable in grandeur to Sanbangsan—a representative trachytic volcanic body in southwestern Jeju, which stands 395 meters tall with a relative height of 345 meters. These findings allow for a precise academic inference that Deodeoreum, which today is a modest oreum with only a 48-meter relative height, was once a massive lava dome similar to Sanbangsan. Over the ages, surrounding lava flows covered it, resulting in its current topography.

Furthermore, since the lower boundary of the trachytic rock mass has not yet been confirmed even at a depth of 330 meters—where drilling is still underway—the actual size of the lava dome could be even deeper and larger.

The initial discovery of this massive underground lava dome is regarded as a unique academic achievement, demonstrating that there is a far more complex and multi-layered volcanic history beneath Jeju's visible topographical features.

Kim Hyungeun, head of the World Heritage Headquarters, stated, "The drilling cores serve as invaluable research assets, recording the volcanic activity beneath the surface of Jeju. We will continue to secure and archive underground drilling data, transparently share the analyzed physical samples with relevant researchers and institutions, and strive to clarify Jeju's volcanic geological value."

This content was produced with the assistance of AI translation services.