Week 5: Volcanoes

 South Korea’s Volcanoes

 

South Korea has two potentially active volcanoes. The first is Ulleungdo, a 10-km wide island in the Sea of Japan, which is the tip of a submarine volcano that last erupted 5,000 years ago. Despite its beauty, with around 10,000 residents, living on such a volcano poses risks. It has a 3 km wide caldera formed by a significant eruption 10,000 years ago.


The second volcano, much larger and more prominent, is Jeju Island, located off the southern coast. Measuring 80 by 40 km, Jeju is a popular holiday destination, especially for honeymooners, and is surrounded by roughly 100 meter deep waters. At its center is Hallasan (or Mount Halla), a mountain that rises to 1,950 meters and features a crater 400 meters wide and 100 meters deep, with a seasonal crater lake called Baengnokdam. This volcano encompasses the entire island, with its mountainous terrain adding to its allure.

 

Jeju Island has experienced many eruptions, but often not at Hallasan, which forms a basaltic lava plateau. Hallasan has followed the elongated shape of the island and has a wide ridge extending east. The island features some cinder cones, typically between 150 and 200 meters high, along with a few lava domes on the coast, though most eruptions occurred on land.


Jeju Island is an unusual location for a major volcano. It lies on a stable continental plate, far from Pacific subduction arcs, with no signs of a hot spot. While magma is generated and able to reach the surface, its origins remain a mystery. It’s a volcano without a clear cause.


Jeju Lava Tubes


Jeju Island is also well-known for its lava tunnels, which were formed within the gently sloping lava beds typical of the second phase of volcanic activity. There are over 50 such tunnels on the island, with the most notable being the Manjanggul tube. This tunnel is nearly 9 kilometers long and reaches heights of up to 30 meters in certain areas. It is classified as a double-story tunnel, and a remarkable feature is the frozen lava column that stands 7 meters tall. This column marks the point where lava transitioned from the upper tunnel to the lower one.


The Manjanggul tube exhibits features similar to those found in typical caves, including lava stalactites and stalagmites, lava columns, flowstone, helictites, and blisters. Additionally, it contains cave corals, benches, lava rafts, bridges, shelves, and striations, further illustrating the unique geological processes at play.

 Photo: Manjanggul Tubes, Jeju Island, SK






Mitigation Efforts:


Think Hazard classifies South Korea’s volcanic hazard as high, indicating the area is within 50 km of a volcano with a history of damaging eruptions in the past 2,000 years. Therefore, the potential impact of a volcanic eruption should be considered during project design, implementation, and maintenance.

I conducted a thorough search but came across limited information regarding South Korea's volcanic mitigation efforts. As a result, I compiled a list of recommended measures to enhance their strategies. It is crucial for South Korea to implement robust safety protocols, particularly on Jeju Island, ensuring that residents and visitors are well-prepared for any potential volcanic events should be a top priority.

  •  Early Warning Action: Develop a plan to respond to volcanic early warnings.
  • Impact Assessment: Evaluate the potential effects of volcanic hazards, such as ballistic projectiles, lava flows, lahars, and pyroclastic flows, on the project.
  • Regulations: Consult local authorities for compliance with land use planning regulations related to volcanic hazards and existing warning and evacuation plans.
  • Technical Expertise: Hire a qualified volcanologist to analyze volcanic hazards in detail and collaborate with local volcano observatories.
  • Impact from Ashfall and Gases:  Assess the potential impacts of volcanic ashfall and gases, which can extend hundreds or thousands of kilometers from the volcano.

Sources:

https://www.volcanocafe.org/korean-volcanics-the-magic-of-jeju-island/

https://www.kma.go.kr/eng/weather/current_state/volcano.jsp

https://thinkhazard.org/en/report/202-republic-of-korea/VA




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