• Journal of Korea Water Resources Association
• /
• v.52 no.7
• /
• pp.493-503
• /
• 2019

This study presents a new method of estimating the size distribution of river bed gravel through image processing. The analysis was done in two steps; first the individual grain images were analyzed and then the grain particle segmentation of river-bed images were processed. In the first part of the analysis, the relationships (long axes, intermediate axes and projective areas) between grain features from images and those measured were compared. For this analysis, 240 gravel particles were collected at three river stations. All particles were measured with vernier calipers and weighed with scales. The measured data showed that river gravel had shape factors of 0.514~0.585. It was found that the weight of gravel had a stronger correlation with the projective areas than the long or intermediate axes. Using these results, we were able to establish an area-weight formula. In the second step, we calculated the projective areas of the river-bed gravels by detecting their edge lines using the ImageJ program. The projective areas of the gravels were converted to the grain-size distribution using the formula previously established. The proposed method was applied to 3 small- and medium- sized rivers in Korea. Comparisons of the analyzed size distributions with those measured showed that the proposed method could estimate the median diameter within a fair error range. However, the estimated distributions showed a slight deviation from the observed value, which is something that needs improvement in the future.

• Journal of the Korean earth science society
• /
• v.40 no.1
• /
• pp.37-45
• /
• 2019

In spite of continued nourishments, Haeundae Beach in Busan has been suffering from erosion, this being caused by the increased wave energy due to global warming and intermittent typhoon reported by previous works. In the meantime, the typhoon Chaba hit Basan in October 2016. In order to investigate the effects of the typhoon in beach erosion and how fast the beach recovered after the typhoon, repeated beach profiling using a VRS-GPS system was carried out, and the grain size analyses for surface sediments sampled on the beach were conducted. Immediately after the typhoon invasion, Haeundae beach was eroded by 1.4 m in average height. The mean high tide lines were retreated back by 12 m, and beach slope became gentler from $3.8^{\circ}$ to $1.7^{\circ}$. The mean grain sizes of surface sediments became coarser from $1.6{\Phi}$ to $1.2{\Phi}$ after two months, and the sorting well sorted. After two months of typhoon landfall, the mean high tide lines have recovered by 85%, and the beach topography almost recovered. This suggests that the impact of typhoons on Haeundae beach erosion is negligible, and the relaxation time is shorter than that of other beaches.

• The Journal of the Petrological Society of Korea
• /
• v.8 no.1
• /
• pp.24-33
• /
• 1999

Differential Strain Analysis (DSA) was performed to examine the characteristics of microcracks for the granites from two sites, Noeunri and Gunggiri. The results of the DSA are taken every 5 MPa for the first 50 MPa, then every 10 MPa to a pressure of 100 MPa, and then every 15 MPa to a pressure of 250 MPa. Differential strain was measured on core samples in three horizontal directions, using $45^{\circ}$ rosette strain gages, and one vertical direction. The gradients of cumulative crack strain curves in one vertical direction and three horizontal directions differed from one another, indicating anisotropic crack development in the sample. The magnitude of vertical cumulative crack strain was the highest, indicating that the microcracks from the studied rock are generally developed in horizontal direction. Under the pressure of 240 Mpa, vertical cumulative crack strains for samples N-1, N-2, G-1, and G-2 were $74{\times}l0^{-6}~820{\times}l0^{-6},\; 190{\times}l0^{-6}~460{\times}l0^{-6},\; 329{\times}l0^{-6}~836{\times}l0^{-6},\; 833{\times}10^{-6}~1,592{\times}l0^{-6}$, respectively. Under the pressure of 25O MPa, volumetric crack strains for Gunggiri and Noeunri ranged from $1,804{\times}10^{-6}\; to\; 3,936{\times}10^{-6}\; and \;from,\; 1, 125{\times}10^{-6}\; to\; 1,457{\times}10^{-6}$, respectively. Therefore, the amount of microcrackes produced were more distributed in Gunggiri than Noeunri. The ratio of a maximum crack strain to a minimum crack strain was calculated to find the orientations between microcracks and the rift plane of the granites. Generally, the ratio has very high values ranging from 2.42 to 3.43, which suggests most microcracks to be intragranular cracks with the regular orientations. These results indicate that the preferred orientations of microcracks in the granites were almost parallel to the rift plane of the granites.

• The Journal of the Petrological Society of Korea
• /
• v.11 no.3_4
• /
• pp.259-270
• /
• 2002

A small granodiorite-quartz monzonitic stock containing sericitic and propylitic alteration assemblages hosts a Cu-W breccia-pipe deposit in the southeastern Cyeongsang basin. The mineralized breccia-pipe contains angular to subangular brecciated fragments of granitic rocks showing clast-supported textures. An assemblage of quartz, tourmalines, sulfide minerals (mainly chalcopyrite, arsenopyrite and pyrrhotite) and calcite was precipitated as a hydrothermal cement between the brecciated fragments. A tourmaline aureole surrounds the breccia pipe. Extensive tourmalinization of the granitic rocks near and within the pipe and no tourmalinization in the sedimentary and volcanic rocks. The tourmalines are marked by Fe-rich, black charcoal-like schorl (80 mol% schorl relative) nearer the schorl-dravite solid solution. The chemical changes in the hydrothermal fluid are reflected by variations in compositional Boning from cores to rims. They generally contain cores with low values of Fe/(Fe+Mg) and high values of Na/(Na+ca) relative to rims. This is because of an increase Fe and Ca contents toward rims. The main trend of these variations is a combination of the exchange vectors Ca(Fe, Mg) $(NaAl)_{- }$ $_1$ and $Fe^{3}^{+}$ $Al_{[-10]}$ $_1$ It is thought that boiling causes the loss of $H_2$ into the vapor phase resulting in the oxidation of Fe in the aqueous phase. pH of the melt would be one of important controlling factors for the tourmaline stability. The tourmalines could be precipitated when the system evolved to the acidic hydrothermal regime as most hydrothermal brines and acidic gases exsolved from the magma. The Ilgwang tourmaline crystallization is products of hypogene orthomagmatic hydrothermal processes that were strongly pipe-controlled.

• Journal of the Korean earth science society
• /
• v.41 no.1
• /
• pp.19-30
• /
• 2020

To understand the impact of typhoons on Gamji gravel beach Taejongdae in Busan, we carried out beach profiling using a VRS-GPS system and a Drone photogrammetry for the typhoons 'Kong-rey' invaded in October 2018 and 'Danas' in July 2019. In addition, grain sizes are analyzed to investigate the overall distribution pattern of gravels on the beach, and the beach topography is surveyed periodically to confirm the recovery rate of the beach. Grain-size analysis reveals that mean gravel sizes, in general, become finer from -6.2Φ to -5.4Φ towards the east in the seashore line direction. Variation in mean sizes is obviously observed in the cross-shore direction. Gravels in the swash zone are relatively fine about -4.5Φ in size and equant in shape, whereas the coarse and oblate gravels ranged from -5Φ to -6Φ are found in the berm. Gamji gravel beach particularly has two lines of berms: a lower berm situated facing beach and an upper berm about 10 m landward. After the typhoon Kong-rey passed by, about 1.4 m of severe erosion in upper berm occurred, and the berm eventually disappeared. On the backshore of the upper berm about 50 cm of erosion took place so that the elevation became lower. However, tangible erosion was not observed in the lower berm. When typhoon Danas hit, rated as mild storm, both upper and lower berm were eroded out. However, about 50 cm of deposition occurred only in the backshore. Only three days later, the new lower berm was formed, meaning that sedimentation rate must be high. This result indicates that Gamji gravel beach is recovered very fast from erosion caused by the typhoons when it is under the fair-weather condition even though beach morphology changes dramatically in a short period of time. Gravel beach is estimated to be or evaluated very resilient to typhoon erosion.

• Parasites, Hosts and Diseases
• /
• v.23 no.2
• /
• pp.203-213
• /
• 1985

The in situ posture of anterior body of Metagonimus yokogawai was observed in experimental metagonimiasis of dog. The metacercariae were collected from naturally infected sweetfish by peptic digestion; a total of 8 dogs was orally infected with 10,000 metacercariae respectively. Two dogs were killed on 3 days, 9 days, 4 weeks and 10 weeks after the infection. The postures of worms in histological section of small intestine and of whole worms collected from the fixed intestinal mucosa were examined by light and scanning electron microscope. The results were summarized as follows: 1. The recovery rates of worms were 42.6% on 3 days, 55.0% on 9 days, 33.2% on 4 weeks and 9. 8% on 10 weeks after the infection respectively. 2. In histological sections of small intestine, most of worms were found at intervillous spaces as ovoid sections of posterior body. However, many worms, especially in 3 day-old worms, revealed protruded anterior body in glandular lumens of crypt. Some sections of anterior body were bifurcated or sacculated. 3. The worms collected from fixed intestinal mucosa under dissecting microscope exhibited a variety of postures. Many worms showed flat shapes with a concavity or curvatures. However, in many worms, the anterior body made a single or multiple protrusions. 4. By SEM observation of protruded anterior body, a longitudinal groove was found. 5. The frequency of worms with protruded anterior body decreased in 9 days, 4 weeks and 10 weeks than in 3 day-old worms. The above findings indicated that the anterior body of juvenile and adult M. yokogawai protruded to lumens of glandular crypt by folding their lateral portions to make a reversible tubelike structure. Frequent multiple protrusions were considered to be made to adapt the microniche of glandular crypts of dog intestine.

• Journal of the Korean earth science society
• /
• v.41 no.6
• /
• pp.588-598
• /
• 2020

The seafloor geology of Ieodo, a submerged volcanic island, has been poorly understood, although this place has gained considerable attention for ocean and climate studies. The main purpose of the study is to understand and elucidate types, distribution patterns and provenance of the surficial sediments in and around the Ieodo area. For this purpose, 25 seafloor sediments were collected using a box-corer, these having been analyzed for grain sizes. XRD (X-ray Diffraction) analysis of fine-grained sediments was conducted for characterizing clay minerals. The peak of Ieodo exists in the northern region, while in the southern area, shore platforms occur. The extensive platform in the south results from severe erosion by strong waves. However, the northern peak still survived from differential weathering. Grain size analyses indicated that gravels and gravelly sands with skeletons and shells were distributed predominantly on the volcanic apron and shore platform. Muddy sediments were found along the Ieodo and the adjacent deeper seafloor. Based on the analysis of clay mineral composition, illites were the most abundant in fine muds, followed by chlorites and kaolinites. The ratio plots of clay minerals for the provenance discrimination suggested that the Ieodo muds were likely to be derived from the Yangtze River (Changjiang River). As a consequence, gravels and gravelly sands with bioclastics may be supplied from the Ieodo volcanic apron by erosion processes. Wave activities might play a major role in transportation and sedimentation. In contrast, fine muds were assumed to be derived from the inflow of the Yangtze River, particularly in summer. Deposition in the Ieodo area is, therefore, probably controlled by the inflow from the Changjiang Dilute Water and summer typhoons from the south.

• Journal of the Korean earth science society
• /
• v.43 no.5
• /
• pp.618-638
• /
• 2022

The Middle Jurassic granite dike swarm intruding into the Paleoproterozoic banded gneiss is pervasively observed in Ueumdo, Hwaseong City, mid-western Gyeonggi Massif. Based on their cross-cutting relationships in a representative outcrop, there are four dikes (UE-A, UE-C, UE-D, UE-E), and depending on the direction, there are three granite dike groups, which are NW- (UE-A dike), NW to WNW- (UE-C dike), and NE-trending (UE-D and UE-E dikes). These granite dikes are massive, medium-to coarse-grained biotite granites, and their relative ages observed in outcrops are in the order of UE-A, UE-D (=UE-E), and UE-C. The geometric analysis of the dikes indicates that the UE-A and UE-C dikes intrude under approximately NE-SW trending horizontal minimum stress fields. The UE-A dike, which showed a relatively low average SiO2 content by major element analysis, is a product of early magma differentiation compared to other dikes; therefore, it is consistent with the relative age of each dike. The ²⁰⁶Pb/²³⁸U weighted mean ages for each dike obtained from SHRIMP zircon U-Pb dating were calculated to be 167 Ma (UE-A), 164 Ma (UE-C), 167 Ma (UE-D), and 167 Ma (UE-E), respectively. The samples of the UE-A, UE-D, and UE-E dikes showed very similar ages. The UE-C dike shows the youngest age, which is consistent with the results of the relative age in the outcrops and major element analysis. Therefore, the granite dikes intruded into the Middle Jurassic (approximately 167 and 164 Ma), coinciding with those of the Gyeonggi Massif, where the Middle Jurassic plutons are geographically widely distributed. This result indicates that the wide occurrence of the Middle Jurassic plutons on the Gyeonggi Massif was formed as a result of igneous activity moving in the northwest direction with the shallower subduction angle of the subducting oceanic plate during the Jurassic.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.29 no.1
• /
• pp.14-27
• /
• 2024

Unlike the shelf sand ridges moribund in motion, nearshore sand ridges are highly mobile, sensitive to changes in ocean environments, thereby becoming of particular interest with respect to morphological changes. About 5 km off the Daesan port, the Jangan Sand Ridge has been undergoing severe subsea morphological change over the past two decades. Understanding the nature of sand ridges is critical to elucidate the causes of morphological changes. In this context, this study aims at understanding the characteristics and distribution patterns of surface sediments of the ridge and its vicinity. For this purpose, 227 sediment samples were acquired using a grab-sampler, the grain sizes being analysed by the sieve-pipette method. In addition, comparison of grain sizes in sediments between 1997 and 2021 was made in order to investigate the 25-years change in sediment composition. Surface sediments along the ridge axis are fine to medium sands with 2-3 phi in mean grain size, whereas, in the trough of ridge, the sediments are composed of gravels and muddy sandy gravels with mean sizes of -2 to -6 phi. Sediments in the crest of the ridge are well-sorted with normal distribution, on the other hand, the basal sediments are poorly-sorted and positively skewed. Along the ridge crest, the sediments are negatively skewed. From 1997 to 2021, the ridge sediments became largely coarser about 0.5 phi. Such coarsening trend in mean grain size can be explained either by elimination of fine sediments during high waves in winter or elimination of fines suspended during sand mining activities in the past. Spatial distribution pattern of surface sediments shows that ca. 30 m thick of the sand ridge itself overlies the thin relict gravels. The strong asymmetry of sand ridge, the exposure of ridge base, and reworked gravel lags suggest that Jangan sand ridge is probably sediment-deficit and hence erosive in nature at present.

• Journal of the Korean earth science society
• /
• v.45 no.3
• /
• pp.203-213
• /
• 2024

This study aimed to investigate the seasonal patterns of multiple bar formation in summer and flattening in winter on the macrotidal Sinduri beach in Taean, and to understand the processes their formation and subsequent flattening. Beach profiling has been conducted regularly over the last four years using a VRS-GPS system. Surface sediment samples were collected seasonally along the transectline, and grain size analyses were performed. Tidal current data were acquired using a TIDOS current observation system during both winter and summer. The Sinduri macrotidal beach consists of two geomorphic units: an upper high-gradient beach face and a lower gentler sloped intertidal zone. High berms and beach cusps did not develop on this beach face. The approximately 400-m-wide intertidal zone comprises distinct 2-5 lines of multiple bars. Mean grain sizes of sand bars range from 2.0 to 2.75 phi, corresponding to fine sands. Mean sizes show shoreward coarsening trend. Regular beach-profiling survey revealed that the summer profile has a multi-barred morphology with a maximum of five bar lines, whereas, the winter profile has a non-barred, flat morphology. The non-barred winter profiles likely result from flattening by scour-and-fill processes during winter. The growth of multiple bars in summer is interpreted to be formed by a break-point mechanism associated with moderate waves and the translation of tide levels, rather than the standing wave hypothesis, which is stationary at high tide. The break-point hypothesis for multi-bars is supported by the presence of the largest bar at mean sea-level, shorter bar spacing toward the shore, irregular bar spacing, strong asymmetry of bars, and the 10-30 m shoreward migration of multi-bars.