• The Korean Journal of Quaternary Research
• /
• v.15 no.2
• /
• pp.101-109
• /
• 2001

The landscape changes at the Mujechi moors I and II during the last twenty two years were analysed using a tree ring analysis of pine trees, a distributional pattern of pine tree, an aerial photograph interpretation and a measurement of firebreak line. The analysis of aerial photographs(taken in 1978, 1988, 1998) indicates that the area of Mujechi moors I and II have gradually decreased. The decreased rate of moor area was relatively high, i.e.,-23.9 %(1978~1988) and -16.4 %(1998~1998) at the Mujechi moor I, but a little bit low, i.e., -2.6% (1978~1988) and -12.6 % (1998~1998) at the Mujechi moor II. However, dendrochronological analysis of pine trees at moors I and II shows that the appearance rates of pine trees per $100\textrm{m}^2$ at moor I and II were 0.28 and 0.57 respectively. And the number of younger pine trees(height is under 1.5m, DBH is less than 2.5 cm) invaded into moors are numbered eleven at the moor I, and ten at the moor II. This shows that the shift of a wetlands into a land was faster at the moor II than the moor I. The construction of a firebreak line and waterway along the moors I and II areas since the December, 1995, has diverted watershed flow and prohibited the runoff flow into the moors. The analysis of GIS suggests that the decreased watershed area were about $11,413.8\textrm{m}^2$(12.1 % of whole watershed area) at the moor I and $15,969.5\textrm{m}^2$(40.4 % of whole watershed area) at the moor II. The negative impact of firebreak line on the inflow of water into the moors I and II and destruction of vegetation along the firebreak line are noticeable from the field survey.

• Economic and Environmental Geology
• /
• v.43 no.1
• /
• pp.53-66
• /
• 2010

We report petrologic characteristics including $^{40}Ar-^{39}Ar$ absolute ages of the subsurface lavas recovered from borehole cores in two islets, Marado and Gapado, off the southwestern coast of Jeju in southernmost Korea and discuss on the volcanism in the region. The lavas in Gapado are apparently divided into one unit with bright colored, aphanitic texture and sheet jointed, and another unit with dark colored and massive. The outcrops often show differentially weathered pattern due to textural difference. While, the lavas in Marado have vesicular and glomerporphyric texture, even though each lava flow unit in Marado has slight unique texture with variation of vesicularity and phenocrysts. The chemical composition of rock core samples from Gapa borehole and Mara borehole shows that the lavas from Gapado and Marado are classified into basaltic trachyandesite($SiO_2$ 52.6-53.6 wt%, $Na_2O+K_2O$ 7.3-7.5 wt%) and tholeiitic andesite($SiO_2$ 51.7-52.8 wt%, $Na_2O+K_2O$ 3.6-4.1 wt%), respectively. The measured $^{40}Ar-^{39}Ar$ plateau ages range from $824{\pm}32\;Ka$(MSL -69 m) to $758{\pm}\;Ka$(MSL 19 m) for core samples of Gapa borehole and $259{\pm}168\;Ka$(MSL -26 m) for a core sample of Mara borehole, respectively. The absolute age of Gapado basaltic trachyandesite is well correlated with that of Sanbangsan trachyte(Won et al., 1986). Meanwhile, the age of a sample in Marado has $259{\pm}168\;Ka$(MSL -26 m) with poor plateau age formation and high error range. We report the data in caution but the rock composition and absolute age of Marado tholeiitic andesite are relatively correlated with those of lava units from Duksu and Sangmo-2 boreholes, indicating the volcanism during 260-150 Ka. On the basis of interpretation of occurrences of exposed and subsurface volcanic rocks of the study area, stratigraphic relationship with adjacent borehole cores and the bathymetry chart of surrounding area, it indicates that the lavas in Gapado were formed around 800 Ka during relatively early stage of volcanic activity in Jeju Island. Meanwhile, Marado may have originated around 260-150 Ka during relatively young stage of volcanism in Jeju Island. It is inferred that the volcanisms have originated in land and these islets were individual ancient volcanoes. The apparent topography has been re-shaped by tidal erosion due to transgression.

• Korean Journal of Agricultural Science
• /
• v.13 no.2
• /
• pp.227-242
• /
• 1986

This paper describes the observed behavior in the direct shear test on decomposed granite soil having the complicate engineering properties at various different levels of factors. The objectives of this study were to investigate the characteristics of the decomposed granite soil under controlled various moisture content, dry density, strain rate and soaking which give influence to the shear strength. The results were summarized as follows; 1. The shear strength was decreased remarkably with the increasing of moisture contents of A and B soil were 5-10% and 15-20% respectively. 2. Cohesion and angle of internal friction were decreased with the increasing of moisture content and increased with the increasing of dry density. 3. The shear strength was increased with the increasing of normal stress and volume change was decreased on the whole. The shear strength was generally increased with the increasing of the strain rate. 4. As dry density increases, A-soil shows the progressive failure and the decrease of volume change while B-soil shows the initial failure and the increase of volume change. 5. The relationships between the soaked and unsoaked specimens were as follows ; ${\tau}_f=0.1009+1.026{{\tau}_f}^*$ (A-soil), ${\tau}_f=0.1586+0.8005{{\tau}_f}^*$ (B-soil) 6. Angle of internal friction of the direct shear test shows larger value than that of the triaxial compression test. All effective stress path was nearly similar.

• Journal of Korean Society of Forest Science
• /
• v.23 no.1
• /
• pp.29-33
• /
• 1974

U-Reuk, a laureate musician in the days of King Jin-Heung, Silla Dynasty, built the Eui Rim Reservoir about 1,400 years ago. This was one of the oldest man-made reservoir. The embankment of the reservoir collapsed by the clumsy artificial drainage on August 19, 1972 when the heavy rainfall of 462 mm/day caused a dangerous overflow of the reservoir. The result of the study on the mystic ancient embankment techniques are as follows: 1. Sandy loam derived from the weathering of granite which is the most widely distributed rock type in the area, was used in the embankment. Large size logs (embankment core) of 30-50 cm in diameter were buried lengthwise along the embankment. 2. The six stocks of Pinus densiflora, 3 stocks of Quercus acutissima, 1 stock of Quercus variabilis and 1 stock of Popolus maximowiczii, altogether 11 stocks are identified. Forest types in the nearby area during the days of the reservoir construction seem to be includde a considerable number of Pinus densiflora, Quercus and Populus species. 3. The angle of repose of the earth materials is taken into account during the embankment. On top of the embankment double layers of clay (20-30 cm indepth) were spread and consolidated. Layer of litter of 20-40 cm in deep covered on the clay layer of the embankment completely, and another layer of clay was consolidated over the litter. Finally, a layer of stones of 10-30 cm in diameter and clay (yellow soil layer) toped the embankment. 4. At the lower part of the embankment clay layer was thicker and became thinner as it goes upwards. At every layer, soil was consolidated and burned. When embankment was completed, it was covered evenly with heavy clay, and finally it was topped with general soil. 5. The heavy clay layer on the inner slope of the embankment showed gray phenomena and litter remained raw humus layer. The clay layer functioned as rubber in the water, and raw humus layer prevented water from seepages. Thus, the embankment was solidly built in this way. 6. The ancient embankment techniques used soils conveyed from nearby area taking the angle of repose into account. Once embankment was completed, clay and litter layers were added to have a plasticity and to withstand the water pressure. 7. It is an excellent technique that the reservoir was constructed with least labor for maximum effects while the recent embankment techniques requires a large amount of labor.

• Economic and Environmental Geology
• /
• v.42 no.5
• /
• pp.403-412
• /
• 2009

The objective of this study is to investigate the geochemical change of feldspar minerals by supercritical $CO_2$, which exists at $CO_2$ sequestration sites. High pressurized cell system (100 bar and $50^{\circ}C$) was designed to create supercritical $CO_2$ in the cell and the surface change and the dissolution of plagioclase and orthoclase were observed when the mineral surface reacted with supercritical $CO_2$ and water (or without water) for 30 days. The polished slab surface of feldspar was contacted with supercritical $CO_2$ and an artificial brine water (pH 8) in the experiments. The experiments for the reaction of feldspar with only supercritical $CO_2$ (without brine water) were also conducted. Results from the first experiment showed that the average roughness value of the plagioclase surface was 0.118 nm before the reaction, but it considerably increased to 2.493 nm after 30 days. For the orthoclase, the average roughness increased from 0.246 nm to 1.916 nm, suggesting that the dissolution of feldspar occurs in active when the feldspars contact with supercritical $CO_2$ and brine water at $CO_2$ sequestration site. The dissolution of $Ca^{2+}$ and $Na^+$ from the plagioclase occurred and a certain part of them precipitated inside of the high pressurized cell as the form of amorphous silicate mineral. For the orthoclase, $Al^{3+}$, $K^+$, and $Si^{+4}$ were dissolved in order and the kaolinite was precipitated. In the experiments without water, the change of the average roughness value and the dissolution of feldspar scarcely occurred, suggesting that the geochemical reaction of feldspars contacted with supercritical $CO_2$ at the environment without the brine water is not active.

• Korean Journal of Heritage: History & Science
• /
• v.53 no.4
• /
• pp.170-187
• /
• 2020

Dolmens bearing the burial layout and stone coffin tombs of the late Bronze Age were excavated from Samdeok-ri, Goseong, Gyeonsangnsamdo, and grave items such as red-burnished pottery, arrowheads, and stone swords were also discovered. In the case of the red-burnished pottery that was found, it retains a pigment layer with a thickness of about 50 to 160㎛, but with most of the other items, exfoliation and peeling-off of pigment layers can be observed on the surface. The raw materials of the red-burnished pottery contained moderately sorted minerals such as quartz, feldspar, and hornblende, and partly opaque iron oxide minerals were also identified. In particular, the raw materials of the red-burnished pottery from stone coffin tomb #6 were different from those of the other pottery, containing large amounts of hornblende and feldspar. The pottery's red pigment was identified as hematite and showed similar mineral content of raw materials such as fine grained quartz, feldspar, and hornblende. The firing temperature is estimated to have been approximately 900℃, based on their mineral phase. The possibility exists that the raw materials had been collected from the Samdeok-ri area, because diorite and granite diorite with dominant feldspar and hornblende have been identified within 3km of that area. During the pottery manufacturing process, it is estimated that the pigment was painted on the entire surface of the red-burnished pottery after it had been molded and then finished using the abrasion technique. In other words, the red-burnished pottery was made by the process of vessel forming - semi drying - coloring - polishing. The surface and cross-section of the pottery appears differently depending on the concentration of the pigment and the coloring method used after vessels were formed. Most of the excavated pottery features a distinct boundary between pigment and body fabric. However, in the case of pottery in which fine-grained pigments penetrate the body fabric so that layers cannot be distinguished, there is the possibility that the fine-grained pigment layer was applied at a low concentration or immediately after vessel forming. Many cracks can be seen on the surface pigments in thickly painted pottery items, and in many cases, only a small portion of the pigment layers remain due to surface exfoliation and abrasion in the burial environment. It is reported that pottery items may be more easily damaged by abrasion if coated with pigment and polished, so it is believed that the red-burnished pottery of the Samdeok-ri site suffered from weathering in the burial environment. This damage was more extensive in the potsherds that were scattered outside the tomb.