Volcanic Activity of the Volcanoes in the Hallasan Natural Reserve, Jeju Island, Korea

This study reports the Ar-Ar dating results for the volcanic rocks from small volcanoes(oreum) of the Hallasan Nature Reserve. According to the age of 40Ar/39Ar, the volcanic activity of the Hallasan Natural Reserve was started from about 192 ka ago. The basaltic trachyandesite and trachyte located in the Y valley near the Eorimok in the western part of the Hallasan Natural Reserve represent an age of about 191 similar to 192 ka, showing the oldest record of volcanic activity in the Hallasan Natural Reserve. In the Hallasan Natural Reserve, the small volcanoes older than 100 ka are Y Valley in Eorimok area (192 +/- 5 and 191 +/- 5 ka), Dongsu-Ak (184 +/- 19 ka), Mansedongsan (153 +/- 5 ka), Janggumok-Orum (135 +/- 6 ka), Eoseungsaengak (123 +/- 9 ka), Samgagbong (105 +/- 2 ka). And the small volcanoes younger than 100 ka are Witbangae-Oreum, Seongneol-Oreum, Muljangol, Yeongsil, Bori-Ak, Witsenueun-Oreum, Witsejokeun-Oreum, Heugbuleun-Oreum, Bangae-Oreum, Albangae-Oreum, Witsebuleun-Oreum, Baengnokdam, Nongo-Ak. According to the eruption of trachytes, the Hallasan Natural Reserve can be interpreted as having about 8 volcanic activities. Among them, 4 volcanic activities are related with the formation of trachyte dome, such as Wanggwanneung, Samgakbong, Yeongsil, and Baengnokdam, and 4 volcanic activities are related with flow or dyke of trachyte. The volcanic activity at the Hallasan Natural Reserve was started from northwest area, to in the southern area, and in the eastern area, and finally volcanic activity related to the formation of Baengnokdam.

Automated summary

This study reports the Ar-Ar dating results for the volcanic rocks from small volcanoes in the Hallasan Nature Reserve on Jeju Island, indicating volcanic activity started around 192 ka ago. The research found the oldest record of volcanic activity in the area, as well as approximately 8 volcanic activities with some related to trachyte dome formation and others related to trachyte flow or dyke. The volcanic activity in the Hallasan Natural Reserve started in the northwest area, moved southwards and eastwards, culminating in the volcanic activity related to the formation of Baengnokdam.