Volcanic mountains

[Visual History of Korea] Jeju Island’s Volcanic Lava Caves Reveal Earth’s History

[Visual History of Korea] Jeju Island’s Volcanic Lava Caves Reveal Earth’s History

Volcanologist Ahn Ung-san from the Jeju Province World Heritage Headquarters examines an undisclosed section of the Manjanggul lava tube. Photo @ Hyungwon Kang

Some of nature’s most powerful forces are volcanoes and hot, molten lava flowing from the earth’s mantle, often hundreds of miles deep underground.

Earth’s inner core is almost as hot as the surface of the sun at an estimated temperature of nearly 5,500 degrees Celsius. Hot molten lava, known as magma, occasionally erupts from the Earth’s surface. The openings where such eruptions occur are called volcanoes.

As the molten lava wraps around objects in its path, the outer surface cools into a shell of solid rock. Liquid lava continues to flow inside the lava tube tunnels or lava tubes may form under these newly created stone shells as the liquid lava eventually flows out of the lava tube and cascades to the ground lower or in the sea.

The Hawaiian Islands are known for their volcanic origins and have many of these lava tubes. In fact, Hawaiian volcanoes are still forming new land in the middle of the Pacific Ocean. On the Big Island of Hawaii and Maui there are active volcanoes, which are popular with visitors who can see the lava lakes in person.

“Very little was known about the formation of volcanic lava tubes until the 1983 Pu’u ‘o’o eruption of Kilauea Volcano in Hawaii. Most of what we know about the formation of the lava tubes and caves comes from the eruption of Pu’u ‘o’o,” said volcanologist Ahn Ung-san of the Jeju Province World Heritage Headquarters.

Daylight enters entrance #3 of the closed section of the Manjanggul lava tube. Photo @ Hyungwon Kang

The eruption of Pu’u ‘o’o lasted approximately 35 years from 1983 to 2018.

Hundreds of volcanoes, over tens of thousands of years, are responsible for forming Korea’s largest island, Jejudo. On Jeju Island, there are more than 360 volcanic cones of various shapes called Oreum.

From the air, visitors to Jeju can see Oreum all over the island, looking like small bumps on the ground. Over the past 10 years, scientists have learned more about Jeju Island’s volcanic history through modern scientific dating methods, Ahn said.

For example, recent scientific dating methods have revealed that Songaksan Oreum, which has double craters and is defined as a parasitic volcano, erupted around 3,600 to 4,000 years ago, depositing its volcanic ash on what is now known as “Jeju Fossil Site of Human and Animal Footprints” along the southwestern coastal area of ​​Seogwipo.

“The Hallasan Mountain crater was formed around 20,000 years ago, and the most recent volcanic eruption in Jeju was around 2,000 years ago,” Ahn said.

Jeju Island’s coolest place is in its volcanic lava tubes, in the Manjanggul lava tube where the temperature is around 12 degrees Celsius at this time of the year. Of the 8,928 kilometers in length and three openings of the Manjanggul lava tube, a one kilometer stretch has been opened to the public.

Manjanggul Cave is part of a larger network of lava tubes originally formed from hot molten lava flowing out of the Geomun Oreum. Jeju Volcanic Island and Lava Tubes has been designated as a UNESCO World Heritage Site.

The Geomun Oreum was recently dated to around 8,000 years old in research authored by Ahn and others using optically stimulated luminescence (OSL).

Deep, dark and winding, these lava caves have been the source of many mysteries and legends.

Among the many folk tales of Jeju Island, the story of a human sacrifice has been passed down about Gimnyeongsagul Grotto which, along with Manjanggul Grotto, has been designated Natural Monument No. 98.

Volcanologist Ahn Ung-san examines a 7.6 meter high lava column inside Manjanggul Cave. Photo @ Hyungwon Kang

Residents used to sacrifice a 15-year-old girl every year to appease a giant snake which they believed lived in the Gimnyeongsagul lava cave and would destroy local agricultural fields.

In 1513, during the Joseon period, a newly dispatched military administrator named Seo Ryun led a military expedition to rescue a young woman from the deadly ritual by slaying the gigantic snake.

On his way back to his government building, a ray of red energy shone on Seo’s back, who fell ill and died on April 10, 1515. Seo was buried with honors in his hometown of Bogaesan in South Chungcheong Province.

Scientists know that around 18,000 years ago, during the ice age, sea level was about 120 meters below what it is today.

Jeju was not an island at the time and would have been walkable from mainland Korea.

The ruins of Jeju Gosan-ri, Korea’s oldest human settlement discovered so far, are located on Jeju Island. The Stone Age ruins were discovered in 1987 and extensive archaeological excavations have found Gosan-ri style faience, a pottery made of clay mixed with plant fibers which can be considered one of the earliest examples in Korea, dating from around 6,000 to 10,000 BC.

“The people of Jeju have certainly experienced volcanic eruptions on the island. Broken pottery pieces have been located under volcanic ash deposits on Jeju Island,” Ahn said.

During the Silla period (57 BC-935 AD), the Tamna kingdom of Jeju was named one of the nine enemy states of Silla.

About 2 kilometers into Yongcheondonggul Cave, which lies along the same lava flow path as Geomun Oreum, further seaward from Manjanggul Cave, researchers have found evidence of Silla pottery and Silla metal tools, as well as animal bones.

By Hyungwon Kang ([email protected])

Korean American photojournalist and columnist Hyungwon Kang is currently documenting Korean history and culture in pictures and words for future generations. — Ed.

By Korea Herald ([email protected])