Young Kwan Sohn

Gyeongsang National University | GNU · Department of Geology

Anisotropy of magnetic susceptibility (AMS) has been used as a proxy of grain fabrics and as a basis of interpretation of depositional processes and paleocurrent directions in sedimentary successions. In this paper, we present the results of the AMS analysis of over 900 core specimens from the sandy to muddy deposits intercalated between the gravel...

Understanding the roles of external controls, such as hydrology and tectonics, is crucial for interpreting the evolution of a phreatomagmatic volcano and its subsurface structure called the diatreme. The Yangpori diatreme in a Miocene terrestrial half-graben basin of Korea provides an opportunity to assess the roles of synvolcanic fault movement in...

Ilchulbong (Sunrise Peak) tuff cone is a UNESCO World Heritage site that owes its scientific importance to the outstanding coastal exposures that surround it. It is also one of the classic sites that provided the sedimentary evidence for the primary pyroclastic processes that occur during phreatomagmatic basaltic eruptions. It has been long conside...

The Miocene Eoil Basin, SE Korea, is a small half-graben basin that was rifted by both extensional and dextral strike-slip deformations during backarc opening of the East Sea (Sea of Japan). The basin was filled by fluviolacustrine sediments and abundant basaltic and dacitic volcanic deposits. The Paljori Tuff is a 2-20-m-thick, basinwide dacitic v...

Explosive volcanism results in a wide range of volcaniclastic deposits in many of Earth's subaerial and subaqueous environments. In this paper, we introduce a unique, shallow-marine volcaniclastic deposit from Jeju Island, Korea, for which the materials were transported to the water surface by pyroclastic clouds and then settled from the surface as...

Core LC42, retrieved from the Central Basin of the northwestern Ross Sea, contains three distinct sediment facies (IRD (ice-rafted debris)-poor bioturbated sandy mud, IRD-rich massive sandy mud, and laminated mud) that are interleaved with each other and deposited over the last 1 Ma. The biogenic components (biogenic opal, total organic carbon, and...

This article presents the results of research carried out at two previously unreported Eastern Desert Atbara River project (EDAR) Middle Stone Age (MSA) sites-EDAR 134 and EDAR 155. Luminescence dating results indicate human activity in this area during the Marine Isotope Stage 5 period (MIS 5), approximately 90 kya. Discussion concerning the affil...

The Suwolbong tuff ring is a basaltic monogenetic volcano in the Quaternary intraplate volcanic field of Jeju Island, Korea. The tuff ring was formerly interpreted to have had a congested magma plumbing system consisting of multiply-sourced dike complexes, based on stepped and mixed chemical trends of alkaline to sub-alkaline glassy pyroclasts. Mic...

This study examines subaqueous dunes located on the southern periphery of the flat top of Dokdo Seamount at water depths from 120 to 170 m where the present ocean currents are incapable of generating such large bedforms. To determine their origin, we conducted a comprehensive analysis of the geomorphic characteristics using high-resolution multi-be...

Since the Middle Pleistocene, the Sahara region has undergone strong environmental changes resulting from climate changes. Dry periods, constituting an ecological barrier to human presence, alternated with wet periods when the Sahara area was covered with green savanna and an extensive network of watercourses, allowing the area to be occupied by hu...

(Introduction) This article is dedicated to yet another site belonging to the agglomeration of Pleistocene sites in the Eastern Desert in Sudan known in the literature as EDAR (Eastern Desert Atbara River). The discussed site – EDAR 6 – occupies the central position within the complex of EDAR sites; it was discovered as one of the first Acheulean s...

Glaciomarine laminated muds around the Antarctic continental margin are important in the marine geological record related to ice sheet dynamics. Microscopic observation and backscattered electron imagery of Pleistocene laminated muds in the Central Basin (Ross Sea) reveal that the light laminae comprise terrigenous angular to subangular silt‐sized...

Melt inclusions readily rupture and form gas bubbles during explosive volcanic eruptions, but their role as a volcanic gas source remains enigmatic. Here, we examined a pumice texture generated by the instantaneous bursting of melt inclusions during the 946 CE Plinian eruption at Baekdusan. The burst produced non-sheared, super-vesicular (>80 vol.%...

This study reports a unique pumice texture generated by the instantaneous bursting of melt inclusions in alkali feldspars during the 946 CE Plinian eruption at Baekdusan. The burst produced super-vesicular (80−90 vol.% voids), subspherical (i.e., non-sheared), and subcentimeter-sized “bubble pockets” indicating their formation at the moment of magm...

Aggregation of ash generated by explosive volcanic eruptions controls the dispersal and residence time of ash in the atmosphere and, therefore, the hazard to aviation. Ash aggregation is particularly common in hydromagmatic volcanoes produced by explosive magma-water interactions. Nevertheless, few studies have been done on this process because of...

Two lava units of basaltic composition named the Cheongryongsa and Hakbong basalts are intercalated in the Cretaceous nonmarine backarc basinfill of Korea. The Cheongryongsa Basalt is 5 to 6 m thick and laterally extends for about 12 km. It is underlain by massive sandy mudstone and overlain erosionally by a basaltic conglomerate, suggesting lava e...

Jeju Island comprises numerous tuff rings and tuff cones and their reworked deposits in the subsurface, which formed on the ca. 120-m-deep Yellow Sea continental shelf under the fluctuating Quaternary sea levels. Tens of meter-thick and massive deposits were found by chance during groundwater drilling at three sites. These deposits are interpreted...

Dokdo is an erosional remnant of an oceanic intraplate volcano built on the backarc basin floor off the Korean peninsula. Basaltic and trachytic volcaniclastic rocks named the Dongdo and Seodo tuffs, respectively, are sandwiched between the submarine and subaerial volcanic rocks of the island. The Dongdo Tuff consists of polymictic breccia of varia...

Middle Stone Age (MSA) lithic artefacts coming from dated layers preserved in their original stratigraphic position are still rare in Northeast Africa in general and in Sudan in particular. This paper aims to present the results of technological and functional analyses of an assemblage coming from a stratigraphic context, i.e. the upper level of th...

This paper presents the results of the analysis of a late Acheulean horizon from the EDAR 135 site, which was discovered in the Eastern Desert, Sudan, in an area heavily transformed by modern mining activity. A lithic assemblage was discovered there, within a layer of gravel sediments formed by a paleostream in a humid period of the Middle Pleistoc...

Explosive volcanic eruptions can occur within days to years after an earthquake, suggesting a causal relation between them. Such paired seismic‐volcanic events in the past, which occurred on a human time scale, can only be confirmed by field relationship of eruptive products. The Southern Kusandong Tuff (SKT) is an ignimbrite in a Cretaceous backar...

Low-aspect-ratio ignimbrites, produced by the most lethal volcanic eruptions, are thin but laterally extensive and can serve as good stratigraphic markers in many sedimentary basins. They are commonly structureless, and require diverse analytical tools to reveal the related geological processes. This study aims to understand better the eruptive and...

The Holocene tuff ring of Songaksan, Jeju Island, Korea, is intercalated with wave-worked deposits at the base and in the middle parts of the tuff sequence, which are interpreted to have resulted from fair-weather wave action at the beginning of the eruption and storm wave action during a storm surge event in the middle of the eruption, respectivel...

Mt. Seoraksan, Korea, is a rugged granitic mountain where extremely steep slopes and strongly seasonal rainfall have facilitated bedrock exposure and geomorphic changes mainly by rockfalls and streamflows. Although the environment was not suitable for alluvial fan formation, a bouldery alluvial fan, 170 m long and 330 m wide, formed overnight by a...

Vesiculated tuff, containing submillimeter-size vesicles, is commonly found in Surtseyan and phreatomagmatic deposits. However, the processes and conditions of vesicle formation and preservation in granular substances have been poorly explored so far in spite of their potential importance in understanding the eruptive and depositional processes of...

This research note presents evidence for the oldest Middle Pleistocene Eastern Saharan human activity from the area referred to as the Eastern Desert Atbara River (EDAR), Sudan, which is currently threatened by gold mining. Preliminary results of multifaceted analyses indicate the activity of Homo sapiens during MIS 5 as well as Homo erectus during...

Although essential for reconstructing hominin behaviour during the Early Palaeolithic, only a handful of Acheulean sites have been dated in the Eastern Sahara region. This is due to the scarcity of sites for this time period and the lack of datable material. However, recent excavations in the Atbara region (Sudan) have provided unique opportunities...

The Bangudae Petroglyphs is Korea’s National Treasure No. 285, carved on a vertical rock face on the riverside of a mountain stream (Daegokcheon) near Ulsan. Since the construction of the Sayeon Dam in the downstream area in 1965, the petroglyphs was repeatedly flooded and submerged, raising concerns of erosion and water damage of the prehistoric r...

Late Cenozoic intraplate basaltic rocks in northeastern China have been interpreted as being derived from a mantle source composed of DMM and EM1 components. To constrain the origin of the enriched mantle component, we have now determined the geochemical compositions of basaltic rocks from the active Baekdusan volcano on the border of China and Nor...

The distinction between primary and secondary volcaniclastic deposits, which are currently defined as the “direct” products of volcanic eruptions and the “reworked” products of the former, respectively, is the first step to interpreting volcaniclastic deposits, particularly the genetic connection with active volcanism. The distinction appears strai...

Caldera fault zones, identified in many modern and ancient volcanoes, have been the subject of geological and geophysical observations and of analog and numerical modeling. However, the physicochemical processes in fault zones during a caldera collapse are still poorly understood. Here, we present field observations from a caldera fault zone in the...

The Sahara Desert episodically became a space available for hominins in the Pleistocene. Mostly, desert conditions prevailed during the interpluvial periods, which were only periodically interrupted by enhanced precipitation during pluvial or interglacial periods. Responding to Quaternary climatic changes, hominin dispersal was channeled through ve...

The need for more accurate and extensive records of storm activity is increasing because of growing population and infrastructure in coastal areas. Records of past storm activity have consequently been sought from diverse sedimentary proxies in marginal marine environments, as well as historical documents. In this paper, we introduce a unique recor...

Paleomagnetic and rock magnetic investigations were performed on a 64-cm-thick section of nonmarine unconsolidated muddy sediment from the Gosan Formation on Jeju Island, Korea. This sediment was recently dated to have been deposited between 22 and 17 kyr BP calibrated, with a sedimentation rate of 13–25 cm/kyr, based on many radiocarbon ages. Inte...

It is well known that Baekdusan (Changbaishan), an active 2744-m-high stratovolcano located on the border between North Korea and China, initiated trachytic/commenditic eruption in the Pleistocene but the petrogenetic and temporal evolutions of this alkaline magma system remain insufficiently constrained. The so-called “Millennium Eruption” (ME) in...

The Quaternary Hantangang River Volcanic Field (HRVF) in the central part of the Korean Peninsula hosts unique volcanic landforms associated with fluvial topography. The volcanic field consists of a series of basaltic lava flows, ca. 0.1 to 0.6 Ma old, which originated from two source vents in DPRK (Democratic People’s Republic of Korea; North Kore...

The Lago Sofia conglomerate in southern Chile is a deep-marine gravelly deposit, which is hundreds of meters thick and kilometers wide and extends laterally for more than 100 km, filling the foredeep trough of the Cretaceous Magallanes Basin. For understanding the depositional processes and environments of this gigantic deep-sea conglomerate, detai...

Clastic dikes are generally classified into neptunian and injected dikes. Using the magnetic fabrics (AMS: anisotropy of magnetic susceptibility), we attempt to classify the clastic dikes in the late Cretaceous Dadaepo Basin, SE Korea, and interpret their emplacement mechanisms. The neptunian dikes exhibit a typical oblate sedimentary fabric which...

The silicic volcanism of Baekdusan (Changbaishan), which is on the border between North Korea and China, was initiated in the Late Pleistocene and culminated in the 10th century with a powerful (volcanic explosivity index = 7) commendite-trachyte eruption commonly referred to as the “Millennium Eruption.” This study presents oxygen isotope data of...

The Songaksan tuff ring, Jeju Island, Korea, which erupted ca. 3.7 ka BP in a coastal setting, provides an unusual opportunity to study the processes of phreatomagmatic eruption and the formation of a diatreme because of the exceptionally well-preserved ejecta beds and well-known subsurface geology. The tuff sequence can be divided into four units...

Phreatomagmatic volcanoes and their sedimentary products can preserve high-resolution records of earth surface processes because of their high deposition rate. Songaksan, Jeju Island, Korea, is a phreatomagmatic volcano, which erupted ca. 3.7 ka BP in a coastal setting. Its tuff ring preserves a record of intertidal to supratidal facies transition...

The Dadaepo Basin is a small late Cretaceous sedimentary basin in SE Korea, located on the eastern margin of Asia. The basin is an isolated extensional basin situated between the NNE-striking Yangsan and Dongnae faults. The basin-fill sediments, named the Dadaepo Formation, consist of channelized conglomerates and sandstones intercalated with domin...

The age of the human footprints found on the bedding plane of a reworked volcaniclastic deposit on Jeju Island, Korea, has been a subject of controversies in Korea for more than a decade. Two researchers that discovered the footprints and their colleagues have argued that the footprints belong to Paleolithic 'hominids' that lived in the Late Pleist...

In granite quarry, stones are generally quarried along easily separating planes called as ‘rock cleavage’. Because orientation and characteristics of the rock cleavage are directly involved with easy quarrying, it is the most important factor on selecting a direction of digging. Using AMS (anisotropy of magnetic susceptibility), we attempt to inter...

Crustal deformation of SE Korea caused by back-arc opening of the East Sea (Sea of Japan) commenced locally in the Late Oligocene. Intense deformation occurred during the Early Miocene, accompanying extension of parallelogram-shaped pull-apart basins between NNW-striking principal displacement zones, clockwise rotation and northwestward tilting of...

New eruptions in monogenetic volcanic fields conceptually occur independently of previous ones. In some instances, however, younger volcanic structures and vents may overlap with older edifices. The genetic links between such co-located eruptions remain unclear. We mapped and analysed the stratigraphic relationships between eruptive units on the 40...

Anisotropy of magnetic susceptibility (AMS) method is a very useful technique for determining rock fabrics that have been broadly used for interpreting a variety of geological processes. In particular cases, however, inverse/intermediate magnetic fabrics that cannot provide information of real rock fabrics have been reported. In this study, AMS mea...

In order to assess the geological storage potential of CO2 in saline aquifers of the Miocene Pohang Basin, SE Korea, a synthetic analysis of structural, stratigraphic, deep drilling, and geophysical data with hydraulic features of basin-fill has been carried out. As a result, three potential storage sites along the eastern coastline of the basin, w...

The drivers behind the inception of, and the variable, pulsatory eruption rates at distributed intraplate volcanic fields are not well understood. Such broad areas of monogenetic volcanism cover vast areas of the world and are often heavily populated. Reliable models to unravel their behaviour require robust spatio-temporal frameworks within the fi...

This paper focuses on the tectonic, sedimentary, and volcanic evolution of a unique back-arc basin (Ulleung Basin) in the southwestern part of the East Sea (Sea of Japan). The basin consists of thick extended continental (or transitional) crust and an overlying sedimentary succession (4-8 km thick), with interlayered volcanic flows and sills, defin...

Ulleung Island is a Quaternary volcanic island located in the mid-western part of the East Sea (Sea of Japan) back-arc basin, which has erupted from the Pliocene until the late Holocene. This study focuses on reconstructing the latest eruptive history of the island by describing the sedimentological and stratigraphic characteristics of the most rec...

Ulleung Island is the top of a 3000 m (from sea floor) intraplate alkalic volcanic edifice in the East Sea/Sea of Japan. The emergent 950 m consist of a basaltic lava and agglomerate succession (Stage 1, 1 center dot 37-0 center dot 97 Ma), intruded and overlain by a sequence of trachytic lavas and domes, which erupted in two episodes (Stage 2, 0 c...

The Early Eocene sequence of Neyshaboor, Binalud region of Iran is predominantly composed of arenaceous deposits. Two stratigraphically important sections from the Damanjan and Taghan areas have been investigated based on field work, petrographic and geochemical analyses. Eight lithofacies were identified and have been grouped in to conglomerate, s...

Monogenetic volcanoes in a continental field environment are typically conceived of as being constructed in single eruptive episodes, often involving low-volume single magma batches of alkali basalt. Well exposed pyroclastic successions at four eruptive centres (Udo, Suwolbong, Songaksan, Ilchulbong) in the Jeju Island Volcanic Field (Korea) allow...

This study focuses on revealing the origin of deep-marine wave planation surfaces and its geomorphic and tectonic implications for the back-arc evolution based on multi-channel seismic reflection profiles acquired from the mid-western East Sea (Sea of Japan). On seismic reflection profiles, the wave-planation surfaces are recognized as continuous a...

There are many sites which deserve to be identified, managed and interpreted as geosites within the Jeju Island Geopark. Twenty-one sites have been identified for inclusion over the next 10–15 years (Fig. 7.1). An Action Plan will be developed to progressively formally incorporate these additional sites within the Jeju Island Geopark. Other geosite...

Education opportunities with and about geoparks are to provide and organize support, tools and activities to communicate scientific knowledge and environmental concepts to the visitors (e.g. through museums, interpretive and educational centers, trails, guided tours, popular literature and maps, modern communication media and so on). They also allo...

Jeju is an island, volcanic in origin, situated on the continental shelf 90 km south of the Korean Peninsula. Specifically, Jeju Island is located between 33°11′27″ and 33°33′50″ north in latitude and between 126°08′43″ and 126°58′20″ east in longitude. The island is a slightly flattened ellipse, ~ 70 km in length from south south-west to north nor...

Jeju Island, a volcanic island, is in an oceanic climatic zone and has a relatively mild weather with 15.5 °C as an average annual temperature. However, the climate of Hallasan varies according to altitude so that the geographical distribution of subtropical and arctic plants and animals is different. The land ecosystems of Jeju, reaching from the...

The history of Jeju began during the Paleolithic Age, 70,000–80,000 years ago. Jeju people from the prehistoric age mostly lived in caves. In Billemotgul (cave) there are Paleolithic artifacts, including chipped stone tools and bones of reindeer and bear which are today found to inhabit only Siberia or Alaska. Prehistoric remains in Gosan-ri, Hangy...

Jeju Island is a volcanic island situated off the southern coast of the Korean Peninsula. The island was produced by volcanic activity which occurred from about 2 million years ago until historic times. The island is 73 km long in the east-west direction and 31 km long in the north-south direction, having an area of 1,847 km2. The island has the ty...

Mt. Hallasan is the central peak of the gently sloping shield volcano of Jeju Island. It is the highest mountain in South Korea, reaching 1,950 m above sea level. Mt. Hallasan is the symbol of Jeju Island and a representative product of the Quaternary volcanism in the Korean Peninsula and adjacent seas. Mt. Hallasan boasts peculiar volcanic landsca...

The purpose of the Management Plan is to provide a framework for the care, control and management of nine geosites as the focal points of the Jeju Island Geopark. The plan supports protection of the geosites, development of geotourism and the ongoing economic development of the Jeju Island Geopark in a sustainable manner. The Plan has three main el...

The Jeju Island Geopark has a fundamental objective to play an active role in the economic development of the island through enhancement of an identity and mission to link the geological and other heritage with geotourism and public awareness and education. This will require the development with strong and effective links between: (1) the Jeju Isla...