• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.22 no.3
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• pp.88-102
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• 2017

Long-term changes in bathymetry and grain size of surface sediments were investigated for understanding depositional sedimentary environments in the channelized Yeongsan River Estuary, Korea. The results revealed that an average depth of the estuary had decreased up to 2.1 m from 1982 to 2006, while it had increased to 0.3 m from 2006 to 2012. The rapid decrease of the water depth from 1982 to 2006 was due to the vast deposition of mud caused by the change of water course and flow velocity after the estuary was dammed. Meanwhile the increase of the water depth from 2006 to 2012 may be associated with multiple erosional processes, including a dredging at the southern part of the estuary and other erosions from the dike sluice expansion work. Considering the water-depth change and tidal-level variation in the study area, an depositional rate in the estuary is estimated to be 8~9 cm/yr for the last 2 decades (1982~2006). The sediments of Yeongsan River Estuary are largely composed of silt-clay mixtures: overall, silt is distributed mainly in the shallow area of the estuary edge, while clay is confined to the deep area of the estuary center. Mean grain size of the sediments is 6.0 Ø on average in 1997, 7.8 Ø on average in 2005 and 7.7 Ø on average in 2012, respectively, suggesting that the sediments became finer due to the increase of silt and clay contents in 1997~2005. Furthermore, several lines of evidences, including the comparison between the amounts of the sediment influx discharged from the Yeongsan River and the sediments in the estuary, and the changes in distribution pattern of silt and clay contents implying that they moved from offshore to estuary dike, indicate that the mud sediments are originated mainly from the offshore, not from the river.

• Economic and Environmental Geology
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• v.54 no.1
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• pp.49-60
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• 2021

The Geumhwa Au-Ag deposit is located within the Cretaceous Gyeongsang basin. Mineral paragenesis can be divided into two stages (stage I and II) by major tectonic fracturing. Stage II is economically barren. Stage I, at which the precipitation of major ore minerals occurred, is further divided into three substages(early, middle and late) with paragenetic time based on minor fractures and discernible mineral assemblages: early substage, marked by deposition of pyrite with minor wolframite; middle substage, characterized by introduction of electrum and base-metal sulfides with Cu-As and/or Cu-Sb sulfosalts; late substage, marked by hematite and Bi-sulfosalts with secondary minerals. Changes in vein mineralogy reflect decreases in temperature and sulfur fugacity with a concomitant increase in oxygen fugacity. Fluid inclusion data indicate progressive decreases in temperature and salinity within each substage with increasing paragenetic time. During the early portion of stage I, high-temperature (≥410℃), high-salinity fluids (up to ≈44 equiv. wt. % NaCl) formed by condensation during decompression of a magmatic vapor phase. During waning of early substage, high-temperature, high-salinity fluids gave way to progressively cooler, more dilute fluids associated with main Au-Ag mineralization (middle) and finally to ≈180℃ and ≥0.7 equiv. wt. % NaCl fluids associated with hematite and sulfosalts (± secondary) mineralization (late substage). These trends are interpreted to indicate progressive mixing of high- and medium to low-salinity hydrothermal fluids with cooler, more dilute, oxidizing meteoric waters. The Geumhwa Au-Ag deposit may represent a vein-type system transitional between porphyry-type and epithermal-type.

• Economic and Environmental Geology
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• v.55 no.1
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• pp.63-76
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• 2022

Dacitic tuffs, 97 to 118 m thick, were recovered from the lower part of the subsurface Seongdongri Formation, Janggi Basin, which was drilled to assess the potential for underground storage of carbon dioxide. The tuffs are divided into four depositional units(Unit 1 to 4) based on internal structures and particle componentry. Unit 1 and Units 3/4 are ignimbrites that accumulated in subaerial and subaqueous settings, respectively, whereas Unit 2 is braided-stream deposits that accumulated during a volcanic quiescence, and no dacitic tuff is observed. A series of analysis shows that mordenite and clinoptilolite mainly fill the vesicles of glass shards, suggesting their formation by replacement and dissolution of volcanic glass and precipitation from interstitial water during burial and diagenesis. Glass-replaced clinoptilolite has higher Si/Al ratios and Na contents than the vesicle-filling clinoptilolite in Units 3. However, the composition of clinoptilolite becomes identical in Unit 4, irrespective of the occurrence and location. This suggests that the Si/Al ratio and pH in the interstitial water increased with time because of the replacement and leaching of volcanic glass, and that the composition of interstitial water was different between the eastern and western parts of the basin during the formation of the clinoptilolite in Units 1 and 3. It is also inferred that the formation of the two zeolite minerals was sequential according to the depositional units, i.e., the clinoptilolite formed after the growth of mordenite. To summarize, during a volcanic quiescence after the deposition of Unit 1, pH was higher in the western part of the basin because of eastward tilting of the basin floor, and the zeolite ceased to grow because of the closure of the pore space as a result of the growth of smectite. On the other hand, clinoptilolite could grow in the eastern part of the basin in an open system affected by groundwater, where braided stream was developed. Afterwards, Units 3 and 4 were submerged under water because of the basin subsidence, and the alkali content of the interstitial water increased gradually, eventually becoming identical in the eastern and western parts of the basin. This study thus shows that volcanic deposits of similar composition can have variable distribution of zeolite mineral depending on the drainage and depositional environment of basins.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.6
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• pp.552-561
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• 2023

The seafloor topography of Gomso Bay on the west coast of Korea was investigated using subtidal bathymetry and tidal-flat altimetry. Gomso Bay consists of 80% tidal flats and 20% subtidal zone, and is divided into an outer bay and an inner bay by the Jujincheon esturary channel. The outer bay tidal flat, has few tidal channels, has a concave topographic profile, and is characterized by the development of chenier and intertidal sand bars, giving it the appearance of gently sloping, dissipative beaches. The inner bay tidal flat has wide upper and middle tidal flats with a well-developed tidal channel system without cheniers. Moreover, the topographical cross-section between these tidal channels is convex upward, and shows the characteristics of a depositional environment greatly influenced by tidal channels and tidal action. An analysis of the horizontal movement of the tidal flat environment over the past 37 years investigating changes in the iso-depth lines in the Gomso-Bay tidal flat between 1981 and 2018 revealed that the Gomso-Bay tidal flat retreated gradually landward. As a result of analyzing the erosion and sedimentation characteristics of Gomso Bay, assuming that most of the water depth changes were due to changes in the elevation of the sea floor and sea level, an average of 1 cm (0 mm/y) of sediment was eroded in the outer bay over the past 37 years (1981-2018), In the inner bay, an average of 50 cm (14 mm/y) was deposited. Notably, the high tidal flats of the outer bay were largely eroded. Monitoring photographs of the coast showed that most of the erosion of the high tidal flats in the outer bay occurred in a short period around 1999 (probably 1997-2002), and that the erosion resulted from the erosion of sand dunes and high-tide beaches caused by temporarily greatly raised high tide levels and storms.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.5 no.2
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• pp.105-118
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• 2000

Anchored measurements (12.5 hr) of suspended sediment concentration and other hydrodynamic parameters were carried out at two stations located at the entrance to Hampyung Bay in summer (August 1999). Tidal variations in water temperature and salinity were in the range of 26.0-27.9$^{\circ}C$ and 30.9-31.5, respectively, indicating exchange offshore and offshore water mass. Active tidal mixing processes at the entrance appear to destroy the otherwise vertical stratification in temperature and salinity in spite of strong solar heating in summer. On the contrary, suspended sediment concentrations show a marked stratification with increasing concentrations toward bottom layer. Clastic particles in suspended sediments consist mostly of very fine to fine silt (4-16 ${\mu}$m) with a poorly-sorted value of 14.7-25.9 ${\mu}$m. However, at slack time with less turbulent energy, flocs larger than 40 ${\mu}$m are formed by cohesion and inter-collision of particles, resulting in a higher settling velocity. Strong ebb-dominated and weak flood dominated tidal currents, in the southwestern and the northeastern part, respectively, result in a seaward residual flow of -10${\sim}$-20 cm $s^{-1}$ at station H1 and a bayward residual flow less than 5.0 cm $s^{-1}$ at station H2. However, mean concentration of suspended sediments at station H1 is higher at flood (95.0-144.1 mg $1^{-1}$) than in ebb (75.8-120.9 mg $1^{-1}$). On the contrary, at the station H2, the trend is reversed with higher concentration at the ebb (84.7-158.4 mg $1^{-1}$) than that at the flood (53.0-107.9 mg $1^{-1}$). As a result, seaward net suspended sediment fluxes ($f_{s}$) are calculated to be -1.7 ${\sim}$-$15.610^{3}$ kg $m^{-2}$ $s^{-1}$ through the whole water column. However, the stations H1 and H2 show definitely different values of the flux with higher ones in the former than in the latter. Alternatively, depth-integrated net suspended sediment loads ($\c{Q}_{s}$) for one tidal cycle are also toward the offshore with ranges of 0.37${\times}$$10^{3}$ kg $m^{-1}$ and 0.21${\times}$$10^{3}$ kg $m^{-1}$, at station H1 and H2, respectively. This seaward transport of suspended sediment in summer suggests that summer-time erosion in the Hampyung muddy tidal flats is a rather exceptional phenomenon compared to the general deposition reported for many other tidal flats on the west coast of Korea.

• Water for future
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• v.9 no.1
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• pp.38-42
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• 1976

Because of differences in thoughts and ideology, our country, Korea has been deprived of national unity for some thirty years of time and tide. To achieve peaceful unification, the cultivation of national strength is of paramount importance. This national strength is also essential if Korea is to take rightful place in the international societies and to have the confidence of these societies. However, national strength can never be achieved in a short time. The fundamental elements in economic development that are directly conducive to the cultivation of national strength can be said to lie in -a stable political system, -exertion of powerful leadership, -cultivation of a spirit of diligence, self-help and cooperation, -modernization of human brain power, and -establishment of a scientific and well planned economic policy and strong enforcement of this policy. Our country, Korea, has attained brilliant economic development in the past 15 years under the strong leadership of president Park Chung Hee. However, there are still many problems to be solved. A few of them are: -housing and home problems, -increasing demand for employment, -increasing demand for staple food and -the need to improve international balance of payment. Solution of the above mentioned problems requires step by step scientific development of each sector and region of our contry. As a spearhead project in regional development, the Saemaul Campaign or new village movement can be cited. The campaign is now spreading throughout the country like a grass fire. However, such campaigns need considerable encouragement and support and the means for the desired development must be provided if the regional and sectoral development program is to sucdceed. The construction of large multipurpose dams in major river basin plays significant role in all aspects of national, regional and sectoral development. It ensures that the water resource, for which there is no substitute, is retained and utilized for irrigation of agricultural areas, production of power for industry, provision of water for domestic and industrial uses and control of river water. Water is the very essence of life and we must conserve and utilize what we have for the betterment of our peoples and their heir. The regional and social impact of construction of a large dam is enormous. It is intended to, and does, dras tically improve the "without-project" socio-economic conditions. A good example of this is the Soyanggang multipurpose dam. This project will significantly contribute to our national strength by utilizing the stored water for the benefit of human life and relief of flood and drought damages. Annual average precipitation in Korea is 1160mm, a comparatively abundant amount. The catchment areas of the Han River, Keum River, and Youngsan River are $62,755\textrm{km}^2$, accounting for 64% of the national total. Approximately 62% of the national population inhabits in this area, and 67% of the national gross product comes from the area. The annual population growth rate of the country is currently estimated at 1.7%, and every year the population growth in urban area increases at a rising rate. The population of Seoul, Pusan, and Taegu, the three major cities in Korea, is equal to one third of our national total. According to the census conducted on October 1, 1975, the population in the urban areas has increased by 384,000, whereas that in rural areas has decreased by 59,000,000 in the past five years. The composition of population between urban and rural areas varied from 41%~59% in 1959 to 48%~52% in 1975. To mitigate this treand towards concentration of population in urban areas, employment opportunities must be provided in regional and rural areas. However, heavy and chemical industries, which mitigate production and employment problems at the same time, must have abundant water and energy. Also increase in staple food production cannot be attained without water. At this point in time, when water demand is rapidly growing, it is essential for the country to provide as much a reservoir capacity as possible to capture the monsoon rainfall, which concentarated in the rainy seaon from June to Septesmber, and conserve the water for year round use. The floods, which at one time we called "the devil" have now become a source of immense benefit to Korea. Let me explain the topographic condition in Korea. In northern and eastern areas we have high mountains and rugged country. Our rivers originate in these mountains and flow in a general southerly or westerly direction throught ancient plains. These plains were formed by progressive deposition of sediments from the mountains and provide our country with large areas of fertile land, emminently suited to settlement and irrigated agricultural development. It is, therefore, quite natural that these areas should become the polar point for our regional development program. Hower, we are fortunate in that we have an additional area or areas, which can be used for agricultural production and settlement of our peoples, particularly those peoples who may be displaced by the formation of our reservoirs. I am speaking of the tidelands along the western and southern coasts. The other day the Ministry of Agriculture and Fishery informed the public of a tideland reclamation of which 400,000 hectares will be used for growing rice as part of our national food self-sufficiency programme. Now, again, we arrive at the need for water, as without it we cannot realize this ambitious programme. And again we need those dams to provide it. As I mentioned before, dams not only provide us with essential water for agriculture, domestic and industrial use, but provide us with electrical energy, as it is generally extremely economical to use the water being release for the former purposes to drive turbines and generators. At the present time we have 13 hydro-electric power plants with an installed capacity of 711,000 kilowatts equal to 16% of our national total. There are about 110 potential dams ites in the country, which could yield about 2,300,000 kilowatts of hydro-electric power. There are about 54 sites suitable for pumped storage which could produce a further 38,600,000 kilowatts of power. All available if we carefully develop our water resources. To summarize, water resource development is essential to the regional development program and the welfare of our people, it must proceed hand-in-hand with other aspects of regional development such as land impovement, high way extension, development of our forests, erosion control, and develop ment of heavy and chemical industries. Through the successful implementation of such an integrated regional development program, we can look forward to a period of national strength, and due recognition of our country by the worlds societies.

• Economic and Environmental Geology
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• v.50 no.4
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• pp.287-302
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• 2017

The carbonate rocks of the Daegi Formation are composed of the limestone at the upper and lower zones, and the dolomite at the middle zone, in which the upper zone has higher CaO content than others. The colors of carbonate rock in the Daegi Formation can be divided into five types; white, light brown, light gray, gray, and dark gray. The white to light gray colored rocks correspond to the high purity limestone with 53.15 ~ 55.64 wt. % CaO, and the light brown colored rocks contain 20.71 ~ 21.67 wt. % MgO. The bleaching of carbonate rocks are not related to CaO composition of the rocks, as light gray rocks tend to be higher in CaO content than those of the white rocks at the lower zone. The pelitic components are also occasionally increased in white limestone than light grey one. $Al_2O_3$ is one of the most difficult content to remove during hydrothermal processes, so the interpretation that the limestone is purified together with hydrothemral bleaching, has little merit. The wide range (over 16 ‰) of ${\delta}^{18}O_{SMOW}$, smaller variation (within 2 ‰) of ${\delta}^{13}C_{PDB}$ are apparent in both the upper and lower zones, which indicate the Daegi Formation had been affected overall by hydrothermal fluids. The K-Ar isotopic age of hydrothermal alteration in the GMI limestone mine is $85.1{\pm}1.7Ma$. Gradual change from grey through light grey to white limestone is accompaned by lower oxygen stable isotope values, which is major evidence that the hydrothermal effect is the main process of the bleaching. Although the Daegi Formation has suffered from hydrothermal activity and increase in whiteness, there is no clear evidence demonstrating the relationship between bleaching and high purity of limestone. The purification of limestone has nothing to do with the hydrothermal activity in this area. Instead, it should be considered that the change of sedimentary environment related to see-level fluctuation which can prevent deposition of pelitic components especially $Al_2O_3$ contrbuted to the formation of the high purity limestone in the upper zone of the Daegi Formation. Considering the evidences such as increase in CaO content of limestone by depth, gradual change from calcite to dolomite at the lower zones, and occurring the high purity limestone at the upper zone, the interpretation of sequence stratigraphic aspect to the formation of the high purity Daegi limestone appears to be more suitable than that of hydrothermal alteration origin.