Yarlung Tsangpo Research Articles

Reconstructing post-mid Pleistocene glacial-dammed paleolakes in the Tsangpo Gorge, southeastern Tibetan Plateau

The paleolakes of the Yarlung Tsangpo Gorge area of the southeastern Tibetan Plateau provide an important basis for testing the hypothesis that glacial dams have effectively prevented the Yarlung Tsangpo River from cutting into the edge of the Plateau. However, sedimentological evidence for the recurrence of these paleolakes during the Quaternary remains inadequate. During this research we conducted extensive geological surveys, and sedimentary and geochronological analyses, of the river terraces and valley sediments upstream of the Yarlung Tsangpo Gorge. Three fluvial-lacustrine terraces formed since the last glacial period were identified from analyses of 17 sedimentary sites, with the following depositional ages, from new to old: 0.6–0.4 ka (T1), 9–5 ka (T2) and ≥50–20 ka (T3), respectively. The sediments of T1 and T2 are <30 m thick with an overall pattern of reversely-graded sequences, each reflecting a dammed paleolake event (named Paleolake I and Paleolake II). The sediments in T3 are the thickest (>265 m), with the highest preserved terraces in the river valley. More than five depositional cycles of fluvial and lacustrine phases in this terrace reflect many sporadic damming events during the last glacial period (representing Paleolake III). Additionally, the earliest phase of sedimentation of the dammed lakes revealed by analyses of drill cores in the valley fill may have begun in the Mid Pleistocene. The sedimentary sequences of these paleolakes revealed that frequent glacial-damming events have occurred in response to climate change since the Mid Pleistocene, supporting the theory that glacial dams and outburst floods have played an influential role in the geomorphological evolution of the margins of the Tibetan Plateau.

Holocene extreme palaeofloods recorded by slackwater deposits along the Jiacha Gorge of the Yarlung Tsangpo River valley, southern Tibetan Plateau

Natural archives of past larger floods provide insights for assessment of future extreme flood events and climate variability in High Asian rivers. However, the sedimentary characteristics and ages of palaeoflood slackwater deposits (SWDs) still remain unclear in the Yarlung Tsangpo River (YTR), the largest river around the Tibetan Plateau. In this study, three palaeoflood SWD benches along the Jiacha Gorge were systemically analyzed. The SWDs are characterized by very fine and fine sand with parallel-bedding climbing ripples. High-resolution grain-size variation from bottom to end-point part of SWD layers, as well as the C–M technique and hydrodynamic model indicates a past suspension sand deposition (as graded and uniform beds) in shallow water and at lower velocity during high flood discharges. Geochemical data and heavy-mineral analysis suggest the SWDs to have experienced only a weak weathering process, and identify the assemblage to be derived from local felsic bedrocks in the Lhasa Terrane. At least two periods of palaeoflood events, 6.3–4.7 and 3.7–3.0 ka, were identified by using the optically stimulated luminescence (OSL) dating. The minimum palaeoflood discharges were estimated to be 31,600 m3/s in the one-dimensional model, varying from 28,500 m3/s to 45,000 m3/s within a 25% variation in roughness values. The palaeoflood chronology and magnitude documented herein are obviously different from earlier work in the area, do not supporting to establish a direct linkage with palaeo-lakes and outburst floods along the middle YTR valley. These extreme palaeoflood records exhibit good consistency with strengthened monsoon and glacier meltwater during the Middle and Late Holocene in the southern Tibetan Plateau.

Chemical weathering rates and controlling mechanisms of glacial catchments within different climate regimes in the Tibetan Plateau.

Continental weathering plays an important role in regulating atmospheric CO2 levels. Chemical weathering in glacial areas has become an intensely focused topic in the background of global change compared with other terrestrial weathering systems. However, research on the weathering of the glacial areas in the Yarlung Tsangpo River Basin (YTRB) is still limited. In this article, the major ions of the Chaiqu and Niangqu catchments in the YTRB have been investigated to illustrate the chemical weathering rates and mechanisms of the glacier areas in the YTRB. Ca2+ and HCO dominate the major ions of the Chaiqu and Niangqu rivers, accounting for about 71.3% and 69.2% of the TZ+ of the Chaiqu (the total cations, TZ+ = Na+ + K+ + Ca2+ + Mg2+, in µeq/L), and about 64.2% and 62.6% of the TZ+ of the Niangqu. A Monte Carlo model with six end-members is applied to quantitatively partition the dissolved load sources of the catchments. The results show that the dissolved loads of the Chaiqu and Niangqu rivers are mainly derived from carbonate weathering (accounting for about 62.9% and 79.7% of the TZ+, respectively), followed by silicate weathering (about 25.8% and 7.9% of the TZ+, respectively). The contributions of precipitation and evaporite to the Chaiqu rivers are about 5.0% and 6.2%, and those to the Niangqu rivers are about 6.3% and 6.2%. The model also calculated the proportion of sulfuric acid weathering in the Chaiqu and Niangqu catchments, which account for about 21.1% and 32.3% of the TZ+, respectively. Based on the results calculated by the model, the carbonate and silicate weathering rates in the Chaiqu catchment are about 7.9 and 1.8 ton km-2 a-1, and in the Niangqu catchment, the rates are about 13.7 and 1.5 ton km-2 a-1. The associated CO2 consumption in the Chaiqu catchment is about 4.3 and 4.4 × 104 mol km-2 a-1, and about 4.3 and 1.3 × 104 mol km-2 a-1 in the Niangqu catchment. The chemical weathering rates of the glacier areas in the YTRB show an increasing trend from upstream to downstream. Studying the weathering rates of glacier catchments in the Tibetan Plateau (TP) reveals that the chemical weathering rates of the temperate glacier catchments are higher than those of the cold glacier catchments and that lithology and runoff are important factors in controlling the chemical weathering of glacier catchments in the TP. The chemical weathering mechanisms of glacier areas in the YTRB were explored through statistical methods, and we found that elevation-dependent climate is the primary control. Lithology and glacial landforms rank second and third, respectively. Our results suggest that, above a certain altitude, climate change caused by tectonic uplift may inhibit chemical weathering. There is a more complex interaction between tectonic uplift, climate, and chemical weathering.

Brief communication: Rapid ∼ 335 × 106 m3 bed erosion after detachment of the Sedongpu Glacier (Tibet)

Abstract. Following the 130 ± 5 × 106 m3 detachment of the Sedongpu Glacier, south-eastern Tibet, in October 2018, the Sedongpu Valley, which drains into the Yarlung Tsangpo (Brahmaputra) River, underwent rapid large-volume landscape changes. Between December 2018 and 2022 and in particular during summer 2021, an enormous volume of in total ∼ 335 ± 5 × 106 m3 was eroded from the former glacier bed, forming a new canyon of up to 300 m depth, 1 km width, and almost 4 km length. The 2021 erosion peak happened through massive but still gradual retrogressive erosion into the former glacier bed. Several rock–ice avalanches of in total ∼ 150 ± 5 × 106 m3 added to the total rock, sediment, and ice volume of over 600 × 106 m3 (0.6 km3) that has been exported from the basin since around 2017. The recent erosion volumes at Sedongpu are by order of magnitude equivalent to the average annual denudation volume of the entire Brahmaputra basin upstream of the location where the river leaves the Himalayas. This high-magnitude low-frequency event illustrates the potential for rapid post-glacial landscape evolution and associated hazards that has rarely been observed and considered at such high intensity so far.

Petrogenesis and tectonic environment of the Middle Permian Luerma igneous complex in the southern Lhasa subterrane, Tibet: Evidence from geochemistry; Rb–Sr, Sm–Nd, and Lu–Hf isotopes; and zircon U–Pb geochronology

Due to the lack of corresponding magmatic records, the timing of the opening of the Yarlung–Tsangpo Neo‐Tethyan Ocean remains controversial. The Middle Permian Luerma igneous complex, which is situated in the western Gangdese magmatic belt of the southern Lhasa subterrane, western Tibet, can be divided into four or more rock types, including foid gabbro, amphibole gabbro, monzogabbro, and pyroxene‐bearing monzodiorite. Through zircon U–Pb dating using laser ablation–inductively coupled plasma–mass spectrometry, the age of the Luerma igneous complex is determined to be ~261 Ma. The complex is rich in titanium, iron, magnesium, and total alkalis, with medium to high levels of calcium, potassium and aluminium, as well as low levels of silicon. Therefore, it is classified as a shoshonite–latite rock series. The complex is relatively enriched in light rare earth elements and high‐field‐strength elements, without obvious Eu and Ce anomalies. These rocks exhibit relatively low (87Sr/86Sr)i values, high εNd(t) values, and high εHf(t) values. The geochemical and isotopic characteristics indicate that the magmas are derived from partial melting of the upper mantle in an intraplate tectonic environment. The new data presented here provide supplementary evidence for the initial rifting of the Lhasa terrane from the northern margin of Gondwana during the Middle Permian. These data also confirm that the opening of the Yarlung–Tsangpo Neo‐Tethyan Ocean occurred in the Middle Permian.

Upland river planform morphodynamics and associated riverbank erosion: Insights from channel migration of the upper Yarlung Tsangpo river

River meandering and lateral migration, caused by riverbank erosion, is a major global threat to soil, sediment, lands, and habitats. However, compared to the densely populated lowland floodplains, the upland channel morphodynamics of free-flowing rivers in a complex high-elevation alluvial setting have received less attention. In this study, we quantitatively investigated channel morphodynamics and associated frozen bank migration in the upper Yarlung Tsangpo River in the Himalayan headwater basin from the 1980s to the 2010s. By combining remote sensing analysis with field investigations, we found mean migration rates of 244 gravel-bed river bends ranging from 1.63 m/yr in the 1980s to 2.76 m/yr in the 2010s, with a maximum rate of 18.61 m/yr. The highest migration rates were associated with bends that had a width-normalised curvature radius between 3.0 and 5.0 and a sinuosity between 1.2 and 1.5. A ∼69% increase in river-bend migration and 30% more frequent bend cutoffs coincided nicely with the rapid expansion of glacial lakes due to a ∼1 °C increase in mean annual air temperature over the past four decades. Positive correlations were observed between channel migration rate and temperature, mean glacial lake area, and runoff. These results highlight the importance of the unique channel morphodynamics and the intense lateral movements of upland rivers. The close link between these dynamics and climate change suggests that a warmer world may significantly influence bank erosion and associated ecosystem processes of upland alluvial systems, which are essential for comprehending frozen channel dynamics and developing strategies for habitat protection in uplands worldwide.

Uncovering the Dominant Contribution of Untreated Domestic Wastewater to Antimicrobials in the Lower Reach of the Lhasa River on the Tibetan Plateau

A major tributary of the Yarlung Tsangpo River on the Tibetan Plateau, the Lhasa River, flows through Lhasa, one of the world’s highest-altitude cities. Along with the fast urbanization and booming tourism industry in Lhasa, pollution of its aquatic environment receives growing concerns. This study quantified the spatiotemporal distributions and potential ecological risk of common antimicrobials in the lower reach of the Lhasa River for the first time and found untreated domestic wastewater to be a key source of pollution. Thirty-four antimicrobials were detected, with concentrations spanning 4 orders of magnitude (0.01–629 ng/L). Spatial variations of antimicrobials were observed, with tetracyclines and macrolides dominated at the upstream and downstream sites of Lhasa city, respectively, due to varying source inputs and different attenuation of antimicrobials. Although only a few antimicrobials pose medium–high ecological risk individually, the simultaneous occurrence of multiple antimicrobials may result in significant ecological toxicity. While the treated wastewater effluent and agricultural runoff combined contributed to 14.2 and 23.5% of the total antimicrobials in the Lhasa River during wet and dry seasons, respectively, the untreated domestic wastewater discharge accounted for the rest. These findings indicate the urgent need for improving the collection system and treatment technology of domestic wastewater in Lhasa.

Upper Mantle Velocity Structure Beneath the Yarlung–Tsangpo Suture Revealed by Teleseismic P-Wave Tomography

We applied teleseismic tomography to investigate the 3D P-wave velocity (Vp) structure of the crust and upper mantle at depths of 50–400 km beneath the Yarlung–Tsangpo suture (YTS), by using 6164 P-wave relative travel-time residuals collected from 495 teleseismic events recorded at 20 three-component broadband seismograms. A modified multi-channel cross-correlation method was adopted to automatically calculate the relative arrival-time residuals of all teleseismic events, which significantly improved the efficiency and precision of the arrival-time data collection. Our results show that alternating low- and high-Vp anomalies are visible beneath the Himalayan and Lhasa blocks across the YTS, indicating that strong lateral heterogeneities exist beneath the study region. A significant high-Vp zone is visible beneath the southern edge of the Lhasa block at 50–100 km depths close to the YTS, which might indicate the rigid Tibetan lithosphere basement. There exists a prominent low-Vp zone beneath the Himalayan block to the south of the YTS extending to ~150 km depth, which might be associated with the fragmentation of the underthrusting Indian continental lithosphere (ICL) and induce localized upwelling of asthenospheric materials from the upper mantle. In addition, significant low-Vp anomalies were observed beneath the Yadong–Gulu rift and the Cona–Sangri rift extending to ~300 km depth, indicating that the tearing of the subducted ICL might provide pathways for the localized asthenospheric materials upwelling, which contributes to the widespread distribution of north–south trending rifts and geothermal activities in southern Tibet.

Petrogenesis of the Qiongduojiang Gabbro in Tethys Himalaya and Its Metallogenetic Implication

With the northward subduction and final closure of the Neo-Tethyan oceanic crust, the Indian and Eurasian plates finally collided together and underwent a strong collision orogenic event, resulting in large-scale crust–mantle magmatic interactions. In order to clarify the controversies about tectono-magmatic activities after the Indian–Eurasian continental collision, we report the newly dated Eocene Qiongduojiang gabbro explored in the Tethyan–Himalaya belt, southern Tibet. LA-ICP-MS zircon U-Pb dating shows that the crystallization age of the Qiongduojiang gabbro is 46.1 ± 1.7 Ma. The whole-rock major and trace elements, as well as Rb-Sr, Sm-Nd, and Pb isotopic data results, show that the Qiongduojiang gabbro is apparently depleted in Nd isotopes, is enriched in Pb isotopes, and has maintained a consistent 87Sr/86Sr(t) value. This paper argues that the E-MORB-like Qiongduojiang gabbro originated from asthenosphere upwelling caused by slab breakoff of the Neo-Tethyan oceanic plate. This event caused large-scale magmatic activities, a magmatic mixing process between ancient crust and deep mantle, and wild distribution of Eocene Gangdese plutons along the Yarlung–Tsangpo Suture Zone, and it rendered the subduction-modified Tibetan lithosphere fertile from the Gangdese porphyry Cu deposits.

Water erosion changes on the Qinghai-Tibet Plateau and its response to climate variability and human activities during 1982–2015

Climate variability and human activities cause changes in precipitation and underlying surface conditions, which are the main driving forces of changes in water erosion, especially in the Qinghai-Tibet Plateau (QTP). In this paper, the water erosion on the QTP from 1982 to 2015 was quantified by the Revised Universal Soil Loss Equation (RUSLE), and the response of water erosion changes to climate variability and human activities was investigated. The results indicated that the distribution of water erosion gradually decreased from south to north during 1982–2015. Areas of severe erosion were mainly distributed along the Yarlung Tsangpo River and in the western Hengduan Mountains. The years of the abrupt change in water erosion were 1989 and 2006. Compared to 1982–1989, the amount of water erosion was mitigated in both 1990–2006 and 2007–2015, with a 19.5% and 6.2% decrease, respectively. The contribution of human activities to the decrease in water erosion was 25.4% and 16.7% for each of these periods, respectively, and the contribution of climate variability to the increase in water erosion was 5.9% and 10.5%. However, water erosion increased by 16.5% from 2007 to 2015 compared to 1990–2006. The contribution of climate variability was 4.9% and the contribution of human activities 8.4%. The increase in water erosion due to human activities may be attributed to the construction of the Qinghai-Tibet Railway and associated human activities. It is therefore important to draw attention to the influence of human activities on the QTP on erosion, to prevent potential future risks. This study is the first attempt to research the relative contributions of variation in climate and human activities to changes in water erosion on the QTP. It would be beneficial for carrying out ecological environmental protection work on the QTP.

Feasibility and Potential Study of Yarlung Tsangpo River Power Generation Based on Optimization Model

The Yarlung Zangbo River is not only the longest plateau river in China, but also one of the highest rivers in the world. This paper studies ecology, geology, investment and benefits respectively. Based on the data of the elevation, drop and fish abundance of the Yarlung Zangbo River, combined with its geographical location, a multi-objective optimization model is established. To analyzes the number of hydropower stations built on the Yarlung Zangbo River from the perspective of maximum energy utilization, this paper use the dynamic programming method to find the maximum output energy of each hydropower station. The conclusion is that the total output of 16 hydropower stations is 51358600KW, which reaches a high level. It is estimated that the potential power generation capacity of the Yarlung Zangbo River is about 55 million KW.

Automatic Monitoring Alarm Method of Dammed Lake Based on Hybrid Segmentation Algorithm

Mountainous regions are prone to dammed lake disasters due to their rough topography, scant vegetation, and high summer rainfall. By measuring water level variation, monitoring systems can detect dammed lake events when mudslides block rivers or boost water level. Therefore, an automatic monitoring alarm method based on a hybrid segmentation algorithm is proposed. The algorithm uses the k-means clustering algorithm to segment the picture scene in the RGB color space and the region growing algorithm on the image green channel to select the river target from the segmented scene. The pixel water level variation is used to trigger an alarm for the dammed lake event after the water level has been retrieved. In the Yarlung Tsangpo River basin of the Tibet Autonomous Region of China, the proposed automatic lake monitoring system was installed. We pick up data from April to November 2021, during which the river experienced low, high, and low water levels. Unlike conventional region growing algorithms, the algorithm does not rely on engineering knowledge to pick seed point parameters. Using our method, the accuracy rate is 89.29% and the miss rate is 11.76%, which is 29.12% higher and 17.65% lower than the traditional region growing algorithm, respectively. The monitoring results indicate that the proposed method is a highly adaptable and accurate unmanned dammed lake monitoring system.

Landscape determinants of genetic structure for Schizopygopsis younghusbandi in the Yarlung Tsangpo River drainage, Tibetan Plateau

Unraveling the drivers that shape landscape genetics could help better understand the relationship between genetic structure and environmental factors and provide a scientific basis for wildlife conservation and habitat management. In this study, a typical coldwater fish on the Tibetan Plateau, Schizopygopsis younghusbandi, was selected to explore its spatial genetic structure and the determinant factors using mitochondrial cytochrome b gene as the molecular marker. The results showed a total of 80 haplotypes and 90 variable sites among 663 individuals from 25 geographical populations, with haplotype diversities (Hd) ranging from 0.636 to 0.936 and nucleotide diversities (Pi) ranging from 0.00160 to 0.00450. Significant positive correlations were observed between Hd and spatial factors (longitude and elevation) as well as the majority of single or combined bioclimatic factors. The correlations between Pi and these factors were inconclusive, revealing that Hd was more sensitive than Pi to population dynamic fluctuations. The phenomenon of greater genetic diversity in higher, colder and drier areas was consistent with the central-marginal hypothesis for this highland-origin species. The majority of genetic differentiation indices Fst indicated moderate differentiation, showing genetic heterogeneity among geographical populations. Fst was positively correlated with variations of elevation and the first principal component of bioclimatic factors, showing a weakly positive relationship with river-network distance, which demonstrated that the Isolation-by-Environment model could explain this genetic structure. In conclusion, as a highly specialized coldwater fish, S. younghusbandi retained higher genetic diversity in higher, colder and drier areas, and population differentiation was mostly related to differences of local bioclimate. For future conservation, we advocate that different geographical populations be treated as separate conservation units, with close attention paid to marginal populations, which are more vulnerable to external disturbances and exhibited less genetic variation.

Fluvial‐Aeolian Interaction and Compositional Variability in the River‐Fed Yarlung Tsangpo Dune System (Southern Tibet)

AbstractRiver‐fed dune fields characterized by relatively low quartz content are much more common on Earth than generally assumed, and the aeolian dune field system in the Yarlung Tsangpo (Upper Brahmaputra) river catchment is considered a typical example. As one of the highest‐altitude fluvial‐aeolian systems on Earth, the dune fields in different wide tracts of the Yarlung Tsangpo valley, made of sand entirely blown from the adjacent river bed, provides an excellent natural laboratory in which to investigate the diverse factors controlling textural and compositional changes induced by aeolian processes. To this aim, the textural (grain‐size, roundness) and compositional (petrography, heavy minerals) properties of multiple size classes of fluvial and aeolian sands were quantified. The results show that sediment composition is markedly controlled by grain size, with greater intrasample than intersample variability. Grain‐size controlled compositional differences cannot be exclusively ascribed to hydraulic‐sorting effects. Independent of their density or shape, quartz, sedimentary rock fragments, zircon, apatite, and epidote grains are observed to be on average smaller than feldspars, volcanic rock fragments, and pyroxenes. This indicates that the original size of minerals in source rocks also played a significant role, limiting their availability in finer (e.g., garnet) or coarser (e.g., apatite) classes. In the river‐fed dune system, the lower content of phyllosilicates and higher grain roundness could represent useful criteria to distinguish aeolian from fluvial sand. The efficient aeolian abrasion of river‐fed sediments on the Tibetan Plateau may be an effective mechanism for the production of dust deposited as vast loess covers during the Quaternary.

Early Cretaceous monsoonal upwelling along the northern margin of the Gondwana continent: Evidence from radiolarian cherts

Radiolarian-bearing cherts are widely exposed in the volcanic-sedimentary sequences associated with the Purang ophiolitic mélange in the western segment of the Yarlung Tsangpo suture zone. Highly diverse and well preserved Lower Cretaceous (Valanginian–Hauterivian) radiolarian assemblages that correlate to the Cecrops septemporatus Zone occur in bedded cherts in the Peiersanggangmu section of the southern Purang ophiolitic mélange. Fifty-five species belonging to 38 genera, including characteristic species: Archaeodictyomitra apiarium (Rüst), Cecrops septemporatus (Parona), Hemicryptocapsa capita Tan, Pseudodictyomitra carpatica (Lozyniak), and Svinitzium pseudopuga Dumitrica, have been recognized.Geochemistry of the cherts reveals high SiO2 contents (average: 92.23 wt%), Al/(Al + Fe + Mn) ratios, and low LaN/CeN ratios. Post Archean Australian Shale (PAAS) normalized rare earth element (REE) abundance patterns exhibit moderately positive Ce anomalies (mean Ce/Ce* =1.35) with relative enrichment in light rare earth elements (LREEs). These features are indicative of deposition in an oceanic basin close to a continental margin environment. Lithological characteristics and geochemical results suggest that the paleogeographical location for these radiolarian-bearing bedded cherts closely matches northern regions of the Indian continent, where existed enhanced upwelling activity and surface mixing resulting from monsoon activities.

Hydrogeochemical characteristics and recharge sources identification based on isotopic tracing of alpine rivers in the Tibetan Plateau

Alpine rivers originating from the Tibetan Plateau (TP) contain large amounts of water resources with high environmental sensitivity and eco-fragility. To clarify the variability and controlling factors of hydrochemistry on the headwater of the Yarlung Tsangpo River (YTR), the large river basin with the highest altitude in the world, water samples from the Chaiqu watershed were collected in 2018, and major ions, δ2H and δ18O of river water were analyzed. The values of δ2H (mean: −141.4‰) and δ18O (mean: −18.6‰) were lower than those in most Tibetan rivers, which followed the relationship: δ2H = 4.79*δ18O-52.2. Most river deuterium excess (d-excess) values were lower than 10‰ and positively correlated with altitude controlled by regional evaporation. The SO42− in the upstream, the HCO3− in the downstream, and the Ca2+ and Mg2+ were the controlling ions (accounting for >50% of the total anions/cations) in the Chaiqu watershed. Stoichiometry and principal component analysis (PCA) results revealed that sulfuric acid stimulated the weathering of carbonates and silicates to produce riverine solutes. This study promotes understanding water source dynamics to inform water quality and environmental management in alpine regions.

Late Holocene change in South Asian monsoons and their influences on human activities in the southern Tibetan Plateau

Prominent and well studied is the South Asian summer monsoon (SASM), but much less is known about changes in South Asian winter monsoon (SAWM). In this study, we analyzed a 3.0-m aeolian sedimentary sequence from the Yarlung Tsangpo Valley in the southern Tibetan Plateau. To establish the sequence chronology, fourteen sediment samples are dated using quartz optically stimulated luminescence dating technique, and five charcoal samples are dated using accelerator mass spectrometry 14C. The frequency-dependent susceptibility in the percentage and redness are used to reflect the SASM, and the recently proposed sorting coefficient of grain size data was used to reflect the SAWM for the past ∼4.5 kyr. Our results suggest an obvious anti-phase relationship between the SASM and SAWM during the late Holocene, and the SASM (SAWM) strengthened (weakened) significantly at ∼2 ka and was the strongest (weakest) at ∼1.3 ka. Such inverse monsoonal behavior may be attributed to the migration of Intertropical Convergence Zone. Moreover, a strong SASM and a weak SAWM could have facilitated human activities in the southern Tibetan Plateau after ∼1.3 ka, resulting in the significantly enhanced dust activity in Yarlung Tsangpo Valley.

Early Holocene dust activity variation in the southern Tibetan Plateau and its response to solar irradiance

The Tibetan Plateau (TP) is an important source for long-range-transported Asian dust, however, the past variation of dust activity in the TP is poorly understood. In this study, we analyzed a ∼ 4.8-m aeolian loess-sand sequence from the Yarlung Tsangpo Valley in the southern TP. A closely spaced sampling strategy was used for optically stimulated luminescence (OSL) dating. With single-aliquot regenerative-dose (SAR) OSL and post-infrared (post-IR) OSL protocols, the medium-grained (38–63 μm) quartz fraction was selected to establish a detailed chronology. The two most popular OSL readers (Lexsyg and Risø) were applied to all samples for equivalent dose measurement, and the corresponding comparison shows very good reproducibility of ages derived from the two independent reader systems. A total of 23 luminescence ages were obtained ranging from 6.7 ± 0.3 ka to 11.6 ± 0.7 ka in stratigraphical order. Aeolian sands accumulated during cold-dry Younger Dryas period, and the overlying loess deposited during Early Holocene. Frequency-dependent susceptibility is used to infer pedogenesis intensity or vegetation cover, and coarse grain size fraction is used to reflect the dust activity frequency during Early Holocene. The reconstructed variation of dust activity frequency in the southern TP shows strong cyclicity of ∼ 1 ka, ∼ 0.7 ka and ∼ 0.5 ka with confidence level of >95%, probably indicating that the regional dust activities on centennial and millennium scales are closely related to the changes of the North-Atlantic Oscillation (NAO) phase as response to solar irradiance forcing.

Large‐scale modelling of highly braided and laterally confined reach of a sand‐bed river

AbstractMorphological processes in sand‐bed braided rivers are highly complicated and dynamic, and it is challenging to fully comprehend and predict them quantitatively or even qualitatively. In this paper, we report the application of a physics‐based model with a single sediment fraction (D50 = 0.23 mm), based on field data, to simulate the morphodynamic processes of a large‐scale braided system in a wide valley of the middle Yarlung Tsangpo River in China. The model is capable of reproducing the evolution of large braided patterns at both microscopic and macroscopic scales, and simulating the formation of a high‐intensity braided reach from an initial lateral flat bed under lateral valley confinement. A narrow strip zone of braided corridor presents long‐term concentrated anabranches in the wide valley reach. Moreover, sensitivity analyses suggest that physics‐based modelling can simulate the multi‐thread river pattern even with relatively coarse grids and a large morphological acceleration factor. The model results show that active riverbed movement occurs and additional chutes are encouraged during flooding, while rising water level makes subchannels merge so that the statistical braiding index decreases. Conversely, only about 40% of the total channels are active in transporting sediment at low‐discharge stages, resulting in a local and slow bed scouring. The planimetric confinement of width variations and valley curvatures acts as a primary control on the local braided corridor and the forced bar assemblages. Width variations restrict the section‐average stream power for a given discharge event, while valley curvatures regulate velocity distribution through several control points. Moreover, the activities of riparian vegetation and sandstorm can interfere with the ability of rivers to braid in the corridor area, which requires much more attention in the follow‐up research.

Insights into landslide development and susceptibility in extremely complex alpine geoenvironments along the western Sichuan–Tibet Engineering Corridor, China

The Sichuan–Tibet Engineering Corridor (STEC), which provides the key function of transportation between the plain and plateau regions, is subjected to widely distributed landslides in the southeastern margins of the Tibetan Plateau. This study investigated the landslides in terms of geomorphological and geological analyses and susceptibility assessment along the western STEC between Changdu and Nyingchi Cities, which is characterized by extremely complex geoenvironments across three major river catchments. The results suggested the spatial feature that the landslides preferentially occurred in river valley regions with high elevation and distinctive local relief. Soft rock types of shale, siltstone, schist and gneiss controlled most landslide areas, while faults and rivers strongly dominated landslide formation. Landslide susceptibility results performed by the support vector machine (SVM), k-nearest neighbor (KNN), and multilayer perception (MLP) models were highly dependent on various sample sets, revealing different hazard-formation backgrounds among the Lancang, Nu, and Yarlung Tsangpo (YLTP) river catchments. A comparative analysis demonstrated the most robust model, the SVM, indicating that lithology, elevation, local relief, slope, and distance to faults were the most significant factors causing landslides. In summary, the investigations signified that the development of landslides along the STEC was macroscopically controlled by regional and vertical zonation of the tectonic geomorphology driven by regional uplift, and was locally dominated by lithology and suture zones. Eventually, further surface erosion and earthquakes dynamically offered inducements for landslide initiation. This study strengthens the understanding of landslide development and susceptibility in response to landscape evolution in southeastern Tibet, and provides a conceptual model for disaster prevention and mitigation in similar high-relief plateau margin regions.