Interaction of landslide spatial patterns and river canyon landforms: Insights into the Three Parallel Rivers Area, southeastern Tibetan Plateau

The interaction and mechanism of landslide spatial patterns and river canyon landforms are significant for understanding geomorphic evolution in intensive tectonic alpine environments. This study focuses on the Three Parallel Rivers Area (TPRA) in the southeastern Tibetan Plateau encompassing three parallel rivers (the Nujiang, Lancang, and Jinsha Rivers), to examine the synergistic evolution of geomorphic features and landslides. The analysis revealed a pattern of landslide aggregation in the river valley characterized by the sequence Nujiang > Lancang > Jinsha Rivers. This pattern aligns closely with the distribution of geomorphic indices (local relief, surface erosion index, and threshold slope gradient) in the valleys. As local relief, normalized surface erosion index and normalized threshold slope gradient increase, the mean values of normalized landslide area density (NLAD) rise from around 0.11 to 0.39, 0.16 to 0.48, and 0.10 to 0.21, respectively. Concurrently, the mean values of normalized frequency of landslide dams (NFLD) increase from around 0.05 to 0.24, 0.12 to 0.22, and 0.02 to 0.17, respectively. Additionally, knickpoints could induce upstream suppression and downstream promotion of landslides showcasing the feedback of landslides on the valley landscape. Our findings indicate that the landform formation process in the southeastern Tibetan Plateau orogen is intricately linked to a substantial landsliding response and the observed mass movements vividly mirror the landform formation pattern. These results hold potential implications for understanding the dynamic equilibrium between uplift and surface erosion in the region. This study enhances our understanding of the interaction and mechanisms of landslides and valley landforms.

India Indenting Eurasia: A Brief Review and New Data from the Yongping Basin on the SE Tibetan Plateau

Successive indentations of Eurasia by India have led to the Tibet-Himalaya E–W orthogonal collision belt and the SE Tibetan Plateau N–S oblique collision belt along the frontal and eastern edges of the indenter, respectively. The belts exhibit distinctive lithospheric structures and tectonic evolutions. A comprehensive compilation of available geological and geophysical data reveals two sudden tectonic transitions in the early Eocene and the earliest Miocene, respectively, of the tectonic evolution of the orthogonal belt. Synthesizing geological and geochronological data helps us to suggest a NEE–SWW trending, ~450 km-long, ~250 km-wide magmatic zone in SE Tibet, which separates the oblique collision belt (eastern and SE Tibet) into three segments of distinctive seismic structures including the mantle and crust anisotropies. The newly identified Yongping basin is located in the central part of the magmatic zone. Geochronological and thermochronological data demonstrate that (1) this basin and the magmatic zone started to form at ~48 Ma likely due to NNW–SSE lithosphere stretching according to the spatial coincidence of the concentrated mantle-sourced igneous rocks on the surface with the seismic anomalies at depth; and (2) its fills was shortened in the E–W direction since ~23 Ma. These two dates correspond to the onset of the first and second tectonic transitions of the orthogonal collision belt. As such, both the orthogonal and oblique belts share a single time framework of their tectonic evolution. By synthesizing geological and geophysical data of both collision belts, the indenting process can be divided into three stages separated by two tectonic transitions. Continent–continent collision as a piston took place exclusively during the second stage. During the other two stages, the India lithosphere underthrust beneath Eurasia.

Applicability of Geomorphic Index for the Potential Slope Instability in the Three River Region, Eastern Tibetan Plateau

Geomorphic indices (e.g., the normalized channel steepness index (Ksn) and the stream length-gradient index (SL)) highlight changes in fluvial shapes and gradients. However, the application of these indices was seldom used to identify potential landslide zones. In this study, we used the Ksn and SL indices to detect the significant variations in the stream power along river reaches, which are anomalies associated with landslides, in the Zengqu River watershed, the upper reaches of the Jinsha River. Most of the landslide anomalies originate along the trunk and surrounding tributaries below the knickpoint of the mainstream. This suggests an erosional wave is migrating upstream throughout the drainage area. The fluvial incision may generate over-steepened hillslopes, which could fail in the future. In addition, the divide asymmetry index (DAI) predicts the direction of the divide as the headwaters migrate toward lower relief, higher elevation surfaces. Landslides are expected to occur as the unstable divide migrates. The proposed methodology can benefit the detection and characterization of potential landslide zones. It should improve hazard and risk analysis and the identification of drainage network areas associated with landslides.

Cenozoic topography, monsoons and biodiversity conservation within the Tibetan Region: An evolving story

The biodiversity of the Himalaya, Hengduan Mountains and Tibet, here collectively termed the Tibetan Region, is exceptional in a global context. To contextualize and understand the origins of this biotic richness, and its conservation value, we examine recent fossil finds and review progress in understanding the orogeny of the Tibetan Region. We examine the deep-time origins of monsoons affecting Asia, climate variation over different timescales, and the establishment of environmental niche heterogeneity linked to topographic development. The origins of the modern biodiversity were established in the Eocene, concurrent with the formation of pronounced topographic relief across the Tibetan Region. High (>4 km) mountains to the north and south of what is now the Tibetan Plateau bounded a Paleogene central lowland (<2.5 km) hosting moist subtropical vegetation influenced by an intensifying monsoon. In mid Miocene times, before the Himalaya reached their current elevation, sediment infilling and compressional tectonics raised the floor of the central valley to above 3000 m, but central Tibet was still moist enough, and low enough, to host a warm temperate angiosperm-dominated woodland. After 15 Ma, global cooling, the further rise of central Tibet, and the rain shadow cast by the growing Himalaya, progressively led to more open, herb-rich vegetation as the modern high plateau formed with its cool, dry climate. In the moist monsoonal Hengduan Mountains, high and spatially extensive since the Eocene but subsequently deeply dissected by river incision, Neogene cooling depressed the tree line, compressed altitudinal zonation, and created strong environmental heterogeneity. This served as a cradle for the then newly-evolving alpine biota and favoured diversity within more thermophilic vegetation at lower elevations. This diversity has survived through a combination of minimal Quaternary glaciation, and complex relief-related environmental niche heterogeneity. The great antiquity and diversity of the Tibetan Region biota argues for its conservation, and the importance of that biota is demonstrated through our insights into its long temporal gestation provided by fossil archives and information written in surviving genomes. These data sources are worthy of conservation in their own right, but for the living biotic inventory we need to ask what it is we want to conserve. Is it 1) individual taxa for their intrinsic properties, 2) their services in functioning ecosystems, or 3) their capacity to generate future new biodiversity? If 2 or 3 are our goal then landscape conservation at scale is required, and not just seed banks or botanical/zoological gardens.

Regional Recognition and Classification of Active Loess Landslides Using Two-Dimensional Deformation Derived from Sentinel-1 Interferometric Radar Data

Identification and classification of landslides is a preliminary and crucial work for landslide risk assessment and hazard mitigation. The exploitation of surface deformation velocity derived from satellite synthetic aperture radar interferometry (InSAR) is a consolidated and suitable procedure for the recognition of active landslides over wide areas. However, the calculated displacement velocity from InSAR is one-dimensional motion along the satellite line of sight (LOS), representing a major hurdle for landslide type and failure mechanism classification. In this paper, different velocity datasets derived from both ascending and descending Sentinel-1 data are employed to analyze the surface ground movement of the Huangshui region (Northwestern China). With global warming, precipitation in the Huangshui region, geologically belonging to the loess basin in the eastern edge of Qing-Tibet Plateau, has been increasing, often triggering a large number of landslides, posing a potential threat to local citizens and natural and anthropic environments. After processing both SAR data geometries, the surface motion was decomposed to obtain the two-dimensional displacements (vertical and horizontal E–W). Thus, a classification criterion of the loess landslide types and failure mode is proposed, according to the analysis of deformation direction, velocities, texture, and topographic characteristics. With the support of high-resolution images acquired by remote sensing and unmanned aerial vehicle (UAV), 14 translational slides, seven rotational slides, and 10 loess flows were recognized in the study area. The derived results may provide solid support for stakeholders to comprehend the hazard of unstable slopes and to undertake specific precautions for moderate and slow slope movements.

Birth of the Yangtze River: age and tectonic-geomorphic implications

Large river systems are an integral and essential component of Earth dynamics. The development of large river systems in Asia is closely linked to the evolving topography driven by both near-field and far-field effects of the interplay among Indian, Eurasian and Pacific plates. Plate tectonics together with climatic changes during the Cenozoic is therefore believed to have determined the evolution of Asian large rivers, yet the age of the Yangtze, the largest in Asia, has been strongly debated over a century, with estimates ranging from 40–45 Ma to a more recent initiation postdating 750 ka. In this paper, I attempt to review the competing views about the age of the Yangtze, and evaluate the estimated pre-Miocene birth of the river based on the provenance of the fluvial sediments from the lower reaches. I further present new geological evidence from the upper stream in southeastern Tibetan Plateau to show the existence of a possible southward paleo-Jinshajiang during the Paleogene, and exploit when and how it might deviated eastward to give birth to the modern Yangtze River. I propose that the present Yangtze River system formed in response to the continental-scale gradient driven by uplifting Tibetan Plateau and regional extension throughout eastern China, synchronous with surface uplift in southeastern Tibet and strengthening of Asian summer monsoon.

Mesozoic tectonic and topographic evolution of Central Asia and Tibet: a preliminary synthesis

During the Late Palaeozoic–Mesozoic, Central Asia and Tibet were affected by several geodynamic episodes that induced either large-scale compression or widespread extension. The Late Palaeozoic final amalgamation of the Central Asian Orogenic Belt, the accretion of the Cimmerian blocks, the closure of the Mongol–Okhotsk Ocean and the accretion of the Neocimmerian blocks set the structural pattern of the continent. This Mesozoic tectonic heritage plays a first-order role in the localization and evolution of the Tertiary deformation of the continent. Similarly, large-scale Mesozoic topographic features are still preserved in Central Asia, where they form a non-negligible part of the present-day topography. This work aims at providing an overview of the major tectonic events that affected Central Asia and Tibet during the Late Palaeozoic and Mesozoic periods. The general topographic evolution of the continent is also described together with the accompanying climatic changes through time.

Impact of Geography and Climate on the Genetic Differentiation of the Subtropical Pine Pinus yunnanensis

Southwest China is a biodiversity hotspot characterized by complex topography, heterogeneous regional climates and rich flora. The processes and driving factors underlying this hotspot remain to be explicitly tested across taxa to gain a general understanding of the evolution of biodiversity and speciation in the region. In this study, we examined the role played by historically neutral processes, geography and environment in producing the current genetic diversity of the subtropical pine Pinus yunnanensis. We used genetic and ecological methods to investigate the patterns of genetic differentiation and ecological niche divergence across the distribution range of this species. We found both continuous genetic differentiation over the majority of its range, and discrete isolated local clusters. The discrete differentiation between two genetic groups in the west and east peripheries is consistent with niche divergence and geographical isolation of these groups. In the central area of the species' range, population structure was shaped mainly by neutral processes and geography rather than by ecological selection. These results show that geographical and environmental factors together created stronger and more discrete genetic differentiation than isolation by distance alone, and illustrate the importance of ecological factors in forming or maintaining genetic divergence across a complex landscape. Our findings differ from other phylogenetic studies that identified the historical drainage system in the region as the primary factor shaping population structure, and highlight the heterogeneous contributions that geography and environment have made to genetic diversity among taxa in southwest China.