• The Journal of Engineering Geology
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• v.25 no.4
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• pp.473-484
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• 2015

Geophysical exploration using electric resistivity, ground penetrating radar (GPR), and impedance high-frequency (ZHF) surveys was conducted in Gujwa-eup, Jeju City, Jeju Island, an island in the Korea Strait, to confirm the existence of new caves near known caves. The exploration revealed a number of anomaly zones, presumed to be caves; 27 sites at suitable locations and depth ranges were selected for drilling and further surveys. However, contrary to predictions, most of the anomaly zones were clinker layers or paleosols intercalated with lavas. Only five boreholes intersected caves. The clinker layers and paleosols were possibly detected as anomalies owing to their different physical properties from the other rocks. Two of the five cave-finding boreholes penetrated Yongcheon Cave; a new cave was found at the other. The two boreholes that penetrated Yongcheon Cave were drilled in areas where the cave has not been previously reported, and thus helped correct an error in the cave distribution map. The cave newly discovered in this boring exploration is 180 m long, and it is connected to the upstream part of Dangcheomul Cave (110 m). The cave contains well-developed lava helictites, lava levees, and ropy structures; carbonate speleothems such as soda straws, stalagmites, columns, and curtain shawls are also well preserved. Notably, the unique shape of the carbonate speleothems is attributed to their growth in relation to the cavern water that flowed into the cave along plant roots.

• Atmosphere
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• v.20 no.3
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• pp.261-271
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• 2010

Carbon isotopic compositions of the YC-2 stalagmite in Yongcheon Cave were analyzed to delineate paleoclimatic variations near Korean peninsula for the past historical period. The YC-2 stalagmite is about 68 mm long and annual growth laminae are distinctively identified. Because the number of growth laminae is at least 242, the stalagmite can be estimated to be at least 241 years old. At about 15 mm from the bottom, one thick brown growth lamina is observed, and this lamina was likely to have been formed when the stalagmite ceased to grow, making the hiatus. High resolution, carbon isotope data indicate past fluctuations of East Asia monsoonal intensity (intimately related to the amount of precipitation). Based on the carbon isotope trend, the stalagmite can be divided into three stages (Stages I, II and III). The highest carbon isotopic compositions of Stage I (${\delta}^{13}C$=-3.3~0.4‰, PDB) indicate that the stalagmite grew during the Little Ice Age when cold and dry climate prevailed with less vegetation. Stage II is characterized by a transitional period from cold and dry to warm and wet climate with a increasing trend of carbon isotopic compositions (${\delta}^{13}C$=-9.6~-0.6‰) and this period indicates the weakening of the Little Ice Age climate. This decreasing trend also suggests that Little Ice Age was terminated near middle 1870's around Korean peninsula. Relatively low carbon isotopic compositions during Stage III (${\delta}^{13}C$=-11.0~-8.0‰) indicates that the climate was changed to warm and wet conditions which are similar to the present.

• Journal of the Korean Applied Science and Technology
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• v.36 no.4
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• pp.1338-1348
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• 2019

The Geomunoreum Lava Tube System, declared as a UNESCO World Heritage Site, has a unique natural ecosystem. The information available about this ecosystem, which contains lava caves with secondary carbonate speleothems, is sparse. Hence, extensive research is warranted for establishing a conservation standard. We commenced microbial research on the system and have been studying the microorganisms coating the lava tube wall to acquire fundamental information for understanding the lava cave ecology of Jeju Island. Samples were collected from yellow-colored walls in six caves that are part of the system-the Bengdwi, Utsanjeon, Bukoreum, Manjang, Gimnyeong, and Yongcheon caves. This study focused on yellow walls as it is the most easily distinguished color. According to previous studies, the color of cave walls is attributed to microorganisms or their components. To determine whether the yellow mats from the Jeju lava tube walls are caused by microorganisms, we examined samples at the microscopic scale, by staining mats and analyzing bacterial isolates from glitter particles. As a result, we found that the yellow walls of lava tubes are comprised of microbial mats.