Contemporary changes in the Himalayan cryosphere are an important concern in the global climate change debate. In this context, the glaciers of the Upper Indus Basin (UIB) deserve special attention ...because of their importance for freshwater supply in the mountain valleys and the adjoining lowlands. However, detailed long-term glacier monitoring studies are rare due to the lack of historical data with adequate spatial and temporal resolution. In the case of Nanga Parbat, the ample availability of historical maps and terrestrial photographs together with satellite imagery and digital elevation models make it possible to analyse and quantify glacier changes for the period between 1856 and 2020. Using diverse multi-temporal datasets, this study reveals slight changes in ice-covered area for 63 glaciers, which decreased by 7% between 1934 and 2019. A detailed analysis of five glaciers in the Rupal Valley over the period 1856–2020 identifies diverse response patterns and highlights the importance of ice and snow avalanches, surge-type instabilities and site-specific topographic particularities for individual glacier changes. The results show high similarity with the stable glacier mass in the Karakoram. This study demonstrates the advantages of combining multiple sources and types of data in order to achieve consilience and offer robust insights.
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•Analysis of Himalayan glacier changes over a very long observation period (1856–2020).•Integration of multi-source historical and remote sensing data sets•Avalanches have a major impact on glacier dynamics of the mountain massif.•Individual glaciers show surge-type ice movement due to high relief energy.•Nanga Parbat glacier dynamics show similarity to the Karakoram Anomaly.
Rapid uplift and exhumation is hypothesized to occur within focused zones of orogenic syntaxes which may dominate sediment flux from a mountain belt. The Namche Barwa-Gyala Peri Massif (NBGPM) in the ...Himalayan Eastern syntaxis is an example of such a high sediment production zone. Here we apply detrital zircon and rutile U–Pb dating to modern river sediments sampled up- and downstream of the Nanga Parbat-Haramosh Massif (NPHM) in the Western Himalayan syntaxis. Mass balancing of these data show that the total amount of sediment contributed to the trunk Indus from NPHM is relatively small, accounting for 9–10% of the total zircons reaching the Arabian Sea, and potentially much less when source fertility is taken into account. The sediment productivity of NPHM is high but likely less than half of that seen at NBGPM (30–56 Mt/yr vs. 72–211 Mt/yr). This discrepancy may be explicable by the drier climate, less prominent syntaxial knick-zone, and weaker spatial relationship between NPHM and the Indus River compared to its eastern twin. Our revised sediment flux estimate for NPHM implies regional modern exhumation rates of ∼3–5 mm/y, lower than estimated from the core massif since 1.7 Ma.
•Nanga Parbat-Haramosh Massif is presently contributing no more than 9–10% of the sediment reaching the Indus Delta.•U–Pb rutile dating resolves ambiguity from U–Pb zircon over sediment sources.•Eastern Karakoram is single largest sediment producer in the modern Indus.•Nanga Parbat-Haramosh Massif differs from Namche Barwa because of drier climate, smaller knick-zone and contrasting geometry.
Closure of the Neotethys Ocean and high-angle continent-continent collision between India and Asia after about 55 Ma resulted in low-angle subduction of the Indian plate below the Tibetan Plateau and ...by ~30 Ma established an arcuate 2300 km long, shallow north-dipping metamorphic fold-thrust belt in the foreland. This Himalayan Metamorphic Front quickly established an Upper-Plate/Lower-Plate paired metamorphic architecture centred on the median High Himal Thrust that largely controlled subsequent evolution. The Upper-Plate is a thick slab of high-T/moderate-P high-grade migmatized metamorphic rocks, whereas the Lower-Plate is an inverted series of moderate-T/high-P schists in two crustal wedges, the broad Main Central Thrust Zone and at lowest structural levels the Footwall, below the Basal Main Central Thrust. Spatial and temporal patterns of metamorphic response in the evolving Himalayan Metamorphic Front has been characterized in a large-scale integrated structural-metamorphic study based on 8 profiles across eastern Nepal. Metamorphic response at all structural levels is established using a large dataset (n ~ 160) of internally consistent quantitative PT determinations, petrology of metapelite samples, semi-quantitative P-T paths, metamorphic mapping and metamorphic field gradients. These results are integrated with previously published metamorphic studies, structural profiles and metamorphic chronology. From these datasets the architecture and evolution of the Himalayan Metamorphic Front is constrained by rock kinematics, metamorphic field gradients showing discontinuities, and diachronous metamorphism with contrasting P-T evolutions at different structural levels. Each of the three panels constituting the Himalayan Metamorphic Front: Upper-Plate, Main Central Thrust Zone and Footwall, experienced distinctly different tectono-metamorphic histories. Crustal processes operating during metamorphism and exhumation differ between the Upper- and Lower-Plates. The Upper-Plate experienced long-lived metamorphism starting from at least 28–38 Ma and tracking low ΔP/ΔT clockwise P-T paths that culminated at ~19–27 Ma in peak high-grade condition with 27–31 °C/km thermal regimes. Protracted high-grade conditions produced significant partial melt, which facilitated gravity driven southward extrusion involving internal ductile flow processes. Southward extrusion of the Upper-Plate was accommodated by coeval reverse movement on the High Himal Thrust and top down to the north, normal reactivation of the South Tibet Detachment System between ~22–10 Ma. Transport of this thick slab to the south resulted in further prograde burial of the Lower-Plate below, culminating in peak metamorphism at the highest pressures attained in the Lower-Plate rocks. The Lower-Plate consists of at least two deeply buried (7.5–9.4 kb) crustal wedges, both of which experienced steep ΔP/ΔT hairpin clockwise P-T paths with isothermal decompression. The Main Central Thrust Zone experienced 20–26 °C/km metamorphism at ~12–22 Ma and was exhumed along the Basal Main Central Thrust after ~11 Ma. Whereas, loading by the Main Central Thrust Zone gave rise to further prograde burial of the Footwall, which experienced 16–21 °C/km metamorphism at ~4–10 Ma and was exhumed along the Main Boundary Thrust at ~3–9 Ma. In contrast to the Upper-Plate, both crustal wedges were exhumed by a process of out-wedging, which involved upthrusting along basal and internal thrusts with coeval extensional slip in the hanging walls. This three-stage foreland propagating lateral exhumation history resulted in telescoping of the Himalayan Metamorphic Front in concert with peak metamorphic events at different structural levels during main phase orogenesis, and is not the result of superimposed retrograde reactivation of the belt.
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•Evolution of orogenic front controlled by three reactivated kinematic-metamorphic discontinuities•Foreland propagating exhumation events result in extensional telescoping of the metamorphic front.•Along-orogen variation in upper-plate extrusion variably loaded different sectors of the lower-plate.•Loading precipitated cycles of burial-metamorphism-isothermal exhumation of successive footwalls•Lower-plate panels exhumed by at least two episodes of out-wedging at ~16–9 Ma and ~8–3 Ma.
Some of the highest and most localized rates of lithospheric deformation in the world are observed at the transition between adjacent plate boundary subduction segments. The initiating perturbation ...of this deformation has long been attributed to vigorous erosional processes as observed at Nanga Parbat and Namche Barwa in the Himalaya and at Mount St. Elias in Alaska. However, an erosion‐dominated mechanism ignores the 3‐D geometry of curved subducting plates. Here we present an alternative explanation for rapid exhumation at these locations based on the 3‐D thermomechanical evolution of collisions between plates with nonplanar geometries. Comparison of model predictions with existing data reproduces the defining characteristics of these mountains and offers an explanation for their spatial correlation with arc termini. These results demonstrate a “bottom‐up” tectonic rather than “top‐down” erosional initiation of feedbacks between erosion and tectonic deformation; hence, the importance of 3‐D subduction geometry.
Key Points
Three‐dimensional variations in subduction geometry can localize upper plate exhumationClimate‐tectonic coupling at orogens may be initiated by plate geometryModeled pattern and range of predicted cooling ages match observations
Regular availability of glacier and snow meltwater is essential for irrigated crop cultivation in the northwestern Himalaya. Based on a case study from the Nanga Parbat region in Gilgit-Baltistan, ...Pakistan, general patterns and site-specific particularities of irrigation networks in semiarid high mountain regions are conceptualized as continuously evolving sociohydrological interactions. These interactions are shaped by an interplay of glacio-fluvial runoff, water distribution, socioeconomic setting, institutional arrangements, external development interventions, and historical trajectories. Building on the paradigm of sociohydrology that changes in water availability coevolve with socioeconomic and land use transitions, this article explores glacier fluctuations and associated developments in meltwater-dependent crop cultivation in the Rupal Valley. The evolution of irrigation networks is analyzed using multitemporal high-resolution satellite imagery, repeat photography, and primary socioeconomic data collected in successive field surveys. Changes are historically contextualized with the help of archival material such as colonial reports and cadastral maps. This integrative study discovered the extension of cultivated areas, an increase in individual field numbers, and a reduction in average field size against the background of population increase and glacier retreat. Despite socioeconomic and environmental changes, the strong coupling of the human-water system remains intact, demonstrating a high degree of persistence of sociohydrological features over time. Adaptive strategies, however, often fail in the face of unpredictable natural processes.
Metamorphic core complexes (MCCs) are interpreted as domal structures exposing ductile deformed high-grade metamorphic rocks in the core underlying a ductile-to-brittle high-strain detachment that ...experienced tens of kilometres of normal sense displacement in response to lithospheric extension. Extension is supposedly the driving force that has governed exhumation. However, numerous core complexes, notably Himalayan, Karakoram and Pamir domes, occur in wholly compressional environments and are not related to lithospheric extension. We suggest that many MCCs previously thought to form during extension are instead related to compressional tectonics. Pressures of kyanite-and sillimanite-grade rocks in the cores of many of these domes are c. 10-14 kbar, approximating to exhumation from depths of c. 35-45 km, too great to be accounted for solely by isostatic uplift. The evolution of high-grade metamorphic rocks is driven by crustal thickening, shortening, regional Barrovian metamorphism, isoclinal folding and ductile shear in a compressional tectonic setting prior to regional extension. Extensional fabrics commonly associated with all these core complexes result from reverse flow along an orogenic channel (channel flow) following peak metamorphism beneath a passive roof stretching fault. In Naxos, low-angle normal faults associated with regional Aegean extension cut earlier formed compressional folds and metamorphic fabrics related to crustal shortening and thickening. The fact that low-angle normal faults exist in both extensional and compressional tectonic settings, and can actively slip at low angles (<30°), suggests that a re-evaluation of the Andersonian mechanical theory that requires normal faults to form and slip only at high angles (c. 60°) is needed.
We used episodic GNSS measurements to quantify the present‐day velocity field in the northwestern Himalaya from the Himalayan foreland to the Karakoram Range. We report a progressive N‐S ...compressional velocity gradient with two noticeable exceptions: in the Salt Range, where important southward velocities are recorded, and in Nanga Parbat, where an asymmetrical E‐W velocity gradient is recorded. A review of Quaternary slip along active thrusts both in and out of sequence allows us to propose a 14 mm/yr shortening rate. This constraint, together with a geometrical model of the Main Himalayan Thrust (MHT), allows us to propose estimations of the slip distributions along the active faults. The lower flat of the MHT is characterized by ductile slip, whereas the coupling increases along the crustal ramp and along the upper flat of the MHT. The basal thrust of the Potwar Plateau and Salt Range presents weak coupling, which is interpreted as the existence of a massive salt layer forming an excellent décollement. In the central part of the frontal Salt Range, the velocities suggest the existence of a southward horizontal flux in the massive salt layer. The simulations also suggest that the velocities recorded in Nanga Parbat can be explained by active westward thrusting along the fault that borders the massif to the west. Simulations suggest that the slip along this fault evolves with depth from 5 mm/yr ductile slip near the MHT to no slip along the upper part of the fault.
Key Points
Estimation of interseismic deformation using GNSS velocities
Estimation of coupling along the Main Himalayan Thrust in northwestern Himalaya
Quantification of GNSS velocities in northwestern Himalaya and Karakorum ranges
Anisotropic reflectance correction (ARC) of satellite imagery is required to remove multi-scale topographic effects in imagery. Commonly utilized ARC approaches have not effectively accounted for ...atmosphere-topographic coupling. Furthermore, it is not clear which topographic effects need to be formally accounted for. Consequently, we simulate the direct and diffuse-skylight irradiance components and formally account for multi-scale topographic effects. A sensitivity analysis was used to determine if characterization schemes can account for a collective treatment of effects, using our parameterization scheme as a basis for comparison. We found that commonly used assumptions could not account for topographic modulation in our simulations. We also found that the use of isotropic diffuse irradiance and a topographic shielding parameter also failed to characterize topographic modulation. Our results reveal that topographic effects govern irradiance variations in a synergistic way, and that issues of ARC need to be formally addressed given atmosphere-topography coupling. Collectively, our results suggest that empirical ARC methods cannot be used to effectively address topographic effects, given inadequate parameterization schemes. Characterizing and removing spectral variation from multispectral imagery will most likely require numerical modeling efforts. More research is warranted to develop/evaluate parameterization schemes that better characterize the anisotropic nature of atmosphere-topography coupling.
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This article presents a multitemporal photographic dataset from the Rupal Valley, south of Nanga Parbat in the north-western Himalaya. The historical metric photographs were taken in ...1934, 1958 and 1987 during scientific expeditions focussing on topographical mapping and glacier dynamics of the mountain massif. All photographs showing glacier aspects have been collected from archives and repeated from the same viewpoints during several surveys between 1992 and 2010. This dataset allows for a detailed visual assessment of glacier fluctuations, changes in snout positions, ice volumes, and debris cover over almost eighty years. It offers insights for a better understanding of glacier changes in this prominent Himalayan mountain region. The dataset supports a recently published article (Nüsser and Schmidt, 2021) with original archival material.
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