The lava flows forming the Manjanggul lava tube are commonly said to have a potential source from the Geomunoreum scoria cone. We inferred the source of lava flows with the Manjanggul lava tube, based on many studies about lava tubes within lava flows of active volcano in the world. We made a lava f...
The lava flows forming the Manjanggul lava tube are commonly said to have a potential source from the Geomunoreum scoria cone. We inferred the source of lava flows with the Manjanggul lava tube, based on many studies about lava tubes within lava flows of active volcano in the world. We made a lava flow field map from lithofacies, features and latitude of lava surfaces in the northeastern part of Jeju Island, and then examined closely the distribution and mutual relation of lava tubes in each lava flow field. As result, the Geomunoreum lava tube system is divided into a series of master tubes(Utsanjeungul, Bukoreumgul, Daerimdonggul, Manjanggul, Gimnyeonggul, Yongcheon- donggul and Dangcheomuldonggul lava tube), a complicated networks of small tubes(the Bengdwigul lava tube), and a series of unitary tubes (the Gimyeongbilemotgul ~ the Gaeusaemgul lava tube) in the Geomunoreum lava flows. Particularly a canyon, 2 km in length to NNE direction from the Geomunoreum scoria cone, is interpreted to be collapse trench of lava tube roof that belongs to an upflow part of the master tube in the Geomunoreum lava tube system, according to the location and direction. Accordingly, the source of lava flows, forming the Manjanggul lava tube, is the Geomunoreum scoria cone. In this study, a detailed survey by electronic total station and the description of internal structures were carried out on the Manjanggul lava tube(from 3rd entrance to 1st entrance), which is a well preserved portion of master tube line within the Geomunoreum lava tube system located in the northeastern Jeju Island. Based on the surveying data and internal structures, we interpretate formation and growth processes of the lava tube. According to this detailed survey, the horizontally surveyed distance of the lowest level tube in the Manjanggul lava tube from 1st to 3st entrance is about 4.5 km with about 54 m of a vertical extent, 0.4o of average tube floor slope, and 0.7° of average ground slope. The linear distance of lava tube from 1st and 3st entrance is about 3.4 km and the linear average ground slope is 0.9°. Here we can recognize that the Manjanggul lava tube is located in much less slope region as compared to the longest lava tube of the world, Kazumura Cave with 42 km of main passage length, 1,108 m of a vertical extent, 1.9° of linear average ground slope and 1.5° of average ground slope over lava tube passage. This lava tube is 2 m to 23 m high and 3 m to 21 m wide but it has generally 12 m to 15 m width in large passage and 4 m to 7 m width in small passage. The depth of highest ceiling from surface is 3.4 m to 14 m and the depth of lowest level floor from surface is 14 m to 33 m, which is decreasing toward downflow. On the whole, maximum height to maximum width in the lava tube have 1.3 ratio, suggesting that the tube's height is taller than the width. And the tube floor is consistently sloped towards the downstream, while the ceiling height in the tube is extremely irregular without a consistency, ranging from 2 m to 23 m. Geometry and scale of this lava tube mentioned above is thought to be affected by thermal erosion and lava accretion(deposition) in the growth process of lava tube. There are many of internal structures to indicate such processes. Lava erosion is inferred by ① exposed clinker or paleosols in the wall of lava tube, ② asymmetric cross section of lava tube, ③ plan view showing lateral and downstream meander migration, ④ alcove or perched tube, and ⑤ skull or hourglass-shaped cross section, canyon-like passage so on. Internal structures indicating lava accretion are ① multi-level lava tube, ② lava shelf, ③ lining, ④ quartzite xenolith accreted at ceiling or wall of lava tube, and ⑤ lava injection into gaps between superposed linings so on. Interpreting the formation and growth processes of the Manjanggul lava based on its geometry and internal structures, the lava tube was formed from the continued sheet flows on a gently sloped topography. Then the outer crust of the sheet flows was first solidified and the inner fluidal lava drained out during a continuous flowing beneath the solidified crust to eventually form the initial stage of the lava tube. Later, the subsequent lava flows were continuously supplied into the tube to cause thermal erosion of the tube's floor, which gradually modified into the long-shaped tube that the height is taller than the width. Although the thermal erosions were dominant in on the floor, there occurred dominant accretions of lava on the tube-ceiling to cause irregular height of the tube. It is guessed that the main factors affecting to the degree of erosion are duration of lava flow and slope, and lava accretion such as multi-level tube is controlled by duration of steady lava level in lava tube and slope. We can summarize the formation and growth processes of the Manjanggul lava tube, based on these interpretations. First, after the initial lava tube was formed, there were subsequent lava flows that passed through the initial tube. Then the surface of flowing lava became solidified to form the floor of the upper level tube, with drains of the residual liquid lava forming the lower level tube, which constructed a multi-level lava tube. The later lava flows that continually flow into the lower level tube caused deeper erosions of the tube's floor, and thicker lava accretions on the tube's ceilings. Finally, a new lava influxing from the ground surface fell down a ceiling of the lower level tube to flow on the floor, with a lava columns constructing in the tube.
The lava flows forming the Manjanggul lava tube are commonly said to have a potential source from the Geomunoreum scoria cone. We inferred the source of lava flows with the Manjanggul lava tube, based on many studies about lava tubes within lava flows of active volcano in the world. We made a lava flow field map from lithofacies, features and latitude of lava surfaces in the northeastern part of Jeju Island, and then examined closely the distribution and mutual relation of lava tubes in each lava flow field. As result, the Geomunoreum lava tube system is divided into a series of master tubes(Utsanjeungul, Bukoreumgul, Daerimdonggul, Manjanggul, Gimnyeonggul, Yongcheon- donggul and Dangcheomuldonggul lava tube), a complicated networks of small tubes(the Bengdwigul lava tube), and a series of unitary tubes (the Gimyeongbilemotgul ~ the Gaeusaemgul lava tube) in the Geomunoreum lava flows. Particularly a canyon, 2 km in length to NNE direction from the Geomunoreum scoria cone, is interpreted to be collapse trench of lava tube roof that belongs to an upflow part of the master tube in the Geomunoreum lava tube system, according to the location and direction. Accordingly, the source of lava flows, forming the Manjanggul lava tube, is the Geomunoreum scoria cone. In this study, a detailed survey by electronic total station and the description of internal structures were carried out on the Manjanggul lava tube(from 3rd entrance to 1st entrance), which is a well preserved portion of master tube line within the Geomunoreum lava tube system located in the northeastern Jeju Island. Based on the surveying data and internal structures, we interpretate formation and growth processes of the lava tube. According to this detailed survey, the horizontally surveyed distance of the lowest level tube in the Manjanggul lava tube from 1st to 3st entrance is about 4.5 km with about 54 m of a vertical extent, 0.4o of average tube floor slope, and 0.7° of average ground slope. The linear distance of lava tube from 1st and 3st entrance is about 3.4 km and the linear average ground slope is 0.9°. Here we can recognize that the Manjanggul lava tube is located in much less slope region as compared to the longest lava tube of the world, Kazumura Cave with 42 km of main passage length, 1,108 m of a vertical extent, 1.9° of linear average ground slope and 1.5° of average ground slope over lava tube passage. This lava tube is 2 m to 23 m high and 3 m to 21 m wide but it has generally 12 m to 15 m width in large passage and 4 m to 7 m width in small passage. The depth of highest ceiling from surface is 3.4 m to 14 m and the depth of lowest level floor from surface is 14 m to 33 m, which is decreasing toward downflow. On the whole, maximum height to maximum width in the lava tube have 1.3 ratio, suggesting that the tube's height is taller than the width. And the tube floor is consistently sloped towards the downstream, while the ceiling height in the tube is extremely irregular without a consistency, ranging from 2 m to 23 m. Geometry and scale of this lava tube mentioned above is thought to be affected by thermal erosion and lava accretion(deposition) in the growth process of lava tube. There are many of internal structures to indicate such processes. Lava erosion is inferred by ① exposed clinker or paleosols in the wall of lava tube, ② asymmetric cross section of lava tube, ③ plan view showing lateral and downstream meander migration, ④ alcove or perched tube, and ⑤ skull or hourglass-shaped cross section, canyon-like passage so on. Internal structures indicating lava accretion are ① multi-level lava tube, ② lava shelf, ③ lining, ④ quartzite xenolith accreted at ceiling or wall of lava tube, and ⑤ lava injection into gaps between superposed linings so on. Interpreting the formation and growth processes of the Manjanggul lava based on its geometry and internal structures, the lava tube was formed from the continued sheet flows on a gently sloped topography. Then the outer crust of the sheet flows was first solidified and the inner fluidal lava drained out during a continuous flowing beneath the solidified crust to eventually form the initial stage of the lava tube. Later, the subsequent lava flows were continuously supplied into the tube to cause thermal erosion of the tube's floor, which gradually modified into the long-shaped tube that the height is taller than the width. Although the thermal erosions were dominant in on the floor, there occurred dominant accretions of lava on the tube-ceiling to cause irregular height of the tube. It is guessed that the main factors affecting to the degree of erosion are duration of lava flow and slope, and lava accretion such as multi-level tube is controlled by duration of steady lava level in lava tube and slope. We can summarize the formation and growth processes of the Manjanggul lava tube, based on these interpretations. First, after the initial lava tube was formed, there were subsequent lava flows that passed through the initial tube. Then the surface of flowing lava became solidified to form the floor of the upper level tube, with drains of the residual liquid lava forming the lower level tube, which constructed a multi-level lava tube. The later lava flows that continually flow into the lower level tube caused deeper erosions of the tube's floor, and thicker lava accretions on the tube's ceilings. Finally, a new lava influxing from the ground surface fell down a ceiling of the lower level tube to flow on the floor, with a lava columns constructing in the tube.
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