Yeong Bae Seong

Quaternary glaciation of Muztag Ata and Kongur Shan: Evidence for glacier response to rapid climate changes throughout the Late Glacial and Holocene in westernmost Tibet

The glacial geology of two massifs, Muztag Ata and Kongur Shan, in western Tibet was examined to help define the timing and style of glaciation in the semiarid regions of western Tibet. Remote sensing, geomorphic mapping, and 10Be terrestrial cosmogenic nuclide (TCN) surface-exposure dating of boulders on the moraines and sediment in depth profiles show that glaciers advanced at least 12 times during at least the last two glacial cycles. Over this time, the style of glaciation changed progressively from one that produced ice caps to one that produced less extensive and more deeply entrenched valley glaciers. The timing of the two earliest glaciations is poorly defined, but they likely occurred prior to the penultimate glacial cycle (the Karasu glacial stage) and the early part of the last glacial cycle or during the penultimate glacial cycle (the Subaxh glacial stage). In contrast, the timing of later glacial advances (the Olimde glacial stage) is relatively well defined showing quasiperiodical oscillations on millennial time scales (17.1 ± 0.3 ka, 13.7 ± 0.5 ka, 11.2 ± 0.1 ka, 10.2 ± 0.3 ka, 8.4 ± 0.4 ka, 6.7 ± 0.2 ka, 4.2 ± 0.3 ka, 3.3 ± 0.6 ka, 1.4 ± 0.1 ka, and a few hundred years before the present). These data suggest that since the global Last Glacial Maximum (LGM), the glaciers in western Tibet likely responded to Northern Hemisphere climate oscillations (rapid climate changes), with minor influences from the south Asian monsoon. This study provides the first well-defined glacial geologic evidence to suggest that glaciers in western Tibet respond to rapid climate changes on millennial time scales throughout the Late Glacial and Holocene.

Expanded and Recently Increased Glacier Surging in the Karakoram

Abstract A review of published literature and satellite imagery from the late 1960s onwards has revealed 90 surge-type glaciers in the Karakoram mountains, of which 50 have not previously been described in detail. These glaciers were identified by a number of surface features indicative of surge-type behavior such as looped moraines, rapid terminus advance, strandlines and rapid changes in surface crevassing. These observations indicate that surge-type behavior is more common and widespread than previously believed on Karakoram glaciers. There is strong spatial clustering of the surge-type glaciers, and a doubling in the number of new surges in the 14 years after 1990 (26 surges) than in the 14 years before 1990 (13 surges). This is coincident with a period of increased precipitation and positive glacier mass balance in this region, and supports previous studies which have found that mass balance has an important control on the frequency of glacier surging.

Glacier velocities across the central Karakoram

Abstract Optical matching of ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) satellite image pairs is used to determine the surface velocities of major glaciers across the central Karakoram. The ASTER images were acquired in 2006 and 2007, and cover a 60×120km region over Baltoro glacier, Pakistan, and areas to the north and west. The surface velocities were compared with differential global position system (GPS) data collected on Baltoro glacier in summer 2005. The ASTER measurements reveal fine details about ice dynamics in this region. For example, glaciers are found to be active over their termini even where they are very heavily debris-covered. The characteristics of several surge-type glaciers were measured, with terminus advances of several hundred meters per year and the displacement of trunk glaciers as surge glaciers pushed into them. This study is the first synthesis of glacier velocities across this region, and provides a baseline against which both past and future changes can be compared.

Climate Change and Mountain Topographic Evolution in the Central Karakoram, Pakistan

Mountain geodynamics represent highly scale-dependent interactions involving climate, tectonic, and surface processes. The central Karakoram in Pakistan exhibit strong climate–tectonic feedbacks, although the detailed tectonic and topographic responses to climate perturbations need to be systematically explored. This study focuses on understanding climate variations in relation to glacier erosion and relief production. Field data, climate modeling, remote sensing, geomorphometry, geochronology, glaciology, and geomorphological assessment are utilized to characterize climate change and geomorphic response. Climate simulations suggest that the region has experienced significant climate change due to radiative forcing over at least the past million years due to changes in Earths orbital configuration, as well as more temporally rapid climate dynamics related to the El Niño Southern Oscillation. Paleoclimate simulations support geomorphological evidence of multiple glaciations and long-term glacier retreat. Mesoscale relief patterns clearly depict erosion zones that are spatially coincident with high peaks and rapid exhumation. These patterns depict extreme spatial and temporal variability of the influence of glacier erosion in the topographic evolution of the region. Results support the interpretation of high-magnitude glacial erosion as a significant denudational agent in the exhumation of the central Karakoram. Consequently, a strong linkage is seen to occur between global, or at least hemispheric, climate change and the topographic evolution of the Karakoram and the western Himalaya.

Cosmogenic 10Be and OSL Dating of Marine Terraces Along the Central-East Coast of Korea: Spatio-Temporal Variations in Uplift Rates

We report the abandonment age of the Jeongdongjin (JDJ) coastal terrace that lies at 65 m a.s.l. The age of the JDJ terrace surface has yet to be equivocally constrained because of its antiquity (>MIS 5), challenging the application of conventional radiocarbon and optically stimulated luminescence (OSL) dating techniques. The reliability of applied indirect age constraints on the sediments by amino-acid racemization and tephra chronology is debated. We present the first application of cosmogenic surface exposure dating to constrain the age of the old terrace in Korea. We dated four samples from the paleo shore platform surface using cosmogenic 10 Be surface exposure dating techniques. The analyses yielded exposure ages ranging from 240 to 170 kyr and likely correspond to the penultimate interglacial period (MIS 7). Sandy beach sediments overlying marine terraces at nearby Anin (~23 m a.s.l.) and Ayajin (~17 m a.s.l.) were dated by OSL. OSL dating of terrace beach sand in two separate areas yielded ages between 129-117 and 70-66 kyr, interpreted MIS 5e and MIS 5a, respectively. Combining the exposure ages and the heights of terraces corrected for paleo sea level, we obtain uplift rates of 353 for JDJ, 159 for Anin, and 238 mm/kyr for Ayajin. The results indicate spatio-temporal variations in the rate of surface uplift along the east coast of Korea during the late Quaternary. Furthermore, the west and east coasts of central Korea experienced different uplift histories during the late Quaternary, possibly resulting from the effects of different tectonic regimes.

Cosmogenic Nuclides Dating of the Earth Surface: Focusing on Korean Cases

지난 ~30년 동안 가속기질량분석기와 비활성기체질량분석기 기술의 진보와 함께, 우주선유발 동위원소도 지표면의 연대측정 분야에 광범위하게 적용되어 왔다. 우주선유발 동위원소를 이용한 세부적인 연대측정법으로는 단순노출연대측정, 수직단면연대측정, 매몰연대측정 등이 있어, 다양한 노출(또는 퇴적) 환경에 따라, ...

Role of debris flow on the change of 10Be concentration in rapidly eroding watersheds: a case study on the Seti River, central Nepal

The concentration of cosmogenic 10Be in riverine sediments has been widely used as a proxy for catchment-wide denudation rate (CWDR). One of the key assumptions of this approach is that sediments originating from sub-basins with different erosional histories are well mixed. A tragic debris flow occurred in the Seti River watershed, central Nepal, on May 5, 2012. This catastrophic debris flow was triggered by slope failure on the peak of Annapurna IV and resulted in many casualties in the lower Seti Khola. However, it provided an opportunity to test the assumption of equal mixing of sediments in an understudied rapidly eroding watershed. This study documents the CWDR of 10Be to evaluate the extent of the influence of episodic erosional processes such as debris flow on the spatio-temporal redistribution of 10Be concentrations. Our data show that the debris flow caused little change in CWDR across the debris flow event. In addition to isotopic measurement, we calculated denudation rates by using the modeled concentrations in pre- and post-landslide sediments based on the local 10Be production rate. The modeled result showed little change across the event, indicating that the debris flow in May 2012 played a minor role in sediment evacuation, despite the rapid erosion in the catchment. Our study concludes that although the 2012 event caused many casualties and severe damage, it was a low-magnitude, high frequency event.

How Rivers Get Across Mountains: Transverse Drainages

Although mountains represent a barrier to the flow of liquid water across our planet and an Earth of impenetrable mountains would have produced a very different geography, many rivers do cross mountain ranges. These transverse drainages cross mountains through one of four general mechanisms: antecedence—the river maintains its course during mountain building (orogeny); superimposition—a river erodes across buried bedrock atop erodible sediment or sedimentary rock, providing a route across what later becomes an exhumed mountain range; piracy or capture—where a steeper gradient path captures a lower gradient drainage across a low relief interfluve; and overflow—a basin fills with sediment and water, ultimately breaching the lowest sill to create a new river. This article reviews research that aids in identifying the mechanism responsible for a transverse drainage, notes a major misconception about the power of headward eroding streams that has dogged scholarship, and examines the transverse drainage at the Grand Canyon in Arizona.

Pace of Landscape Change and Pediment Development in the Northeastern Sonoran Desert, United States

Pediments of the Sonoran Desert in the United States have intrigued physical geographers and geomorphologists for nearly a century. These gently sloping bedrock landforms are a staple of the desert landscape that millions visit each year. Despite the long-lived scientific curiosity, an understanding of the processes operating on the pediment has remained elusive. In this study we revisit the extensive history of pediment research. We then apply geospatial, field, and laboratory cosmogenic 10Be nuclide dating and back-scattered electron microscopy methods to assess the pace and processes of landscape change on pediment systems abutting the Salt River in Arizona. Our study focuses on the Usery pediments linked to base-level fluctuations (river terraces) of the Salt River. Relict pediment surfaces were reconstructed with dGPS data and kriging methodologies utilized in ArcGIS—based on preserved evidence of ancient pediment surfaces. 10Be ages of Salt River terraces established a chronology of incision events, where calculating the volume between the reconstructed relict pediment and modern surface topography established minimum erosion rates (∼41 mm/ka to ∼415 mm/ka). Pediment area and length appear to have a positive correlation to erosion rate and development of planar pediment surfaces. Field and laboratory observations reveal that pediment systems adjust and stabilize at each Salt River terrace. Relief reduction across the pediment begins with pediment channel incision via headward erosion. Next, tributary drainage capture begins and collapses interfluves. Lateral stream erosion promotes planation where the porosity of decayed granite along channel banks exceeds the bedrock underneath ephemeral channels.