Brahmaputra sediment flux dominated by highly localized rapid erosion from the easternmost Himalaya

Stewart, Robert L.; Hallet, Bernard; Zeitler, Peter K.; Malloy, Margaret; Allen, Charlotte M.; Trippett, David

doi:10.1130/g24890a.1

Cited by 126 publications

(88 citation statements)

References 16 publications

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“…Particularly the eastern and western syntaxes are areas of high exhumation and erosion (1-10 mm yr −1 ) (Burbank et al, 1996;Burg et al, 1998;Finnegan et al, 2008;Stewart et al, 2008;Zeitler et al, 2001). In contrast, erosion rates on the orographically shielded Tibetan Plateau are significantly lower (< 0.03 mm yr −1 ), due to lower rainfall amounts and lower topographic relief (Lal et al, 2003).…”

Section: Introductionmentioning

confidence: 91%

Climatic and geologic controls on suspended sediment flux in the Sutlej River Valley, western Himalaya

Wulf

Bookhagen

Scherler

2012

Hydrol. Earth Syst. Sci.

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Abstract. The sediment flux through Himalayan rivers directly impacts water quality and is important for sustaining agriculture as well as maintaining drinking-water and hydropower generation. Despite the recent increase in demand for these resources, little is known about the triggers and sources of extreme sediment flux events, which lower water quality and account for extensive hydropower reservoir filling and turbine abrasion. Here, we present a comprehensive analysis of the spatiotemporal trends in suspended sediment flux based on daily data during the past decade (2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)) from four sites along the Sutlej River and from four of its main tributaries. In conjunction with satellite data depicting rainfall and snow cover, air temperature and earthquake records, and field observations, we infer climatic and geologic controls of peak suspended sediment concentration (SSC) events. Our study identifies three key findings: First, peak SSC events (≥ 99th SSC percentile) coincide frequently (57-80 %) with heavy rainstorms and account for about 30 % of the suspended sediment flux in the semi-arid to arid interior of the orogen. Second, we observe an increase of suspended sediment flux from the Tibetan Plateau to the Himalayan Front at mean annual timescales. This sediment-flux gradient suggests that averaged, modern erosion in the western Himalaya is most pronounced at frontal regions, which are characterized by high monsoonal rainfall and thick soil cover. Third, in seven of eight catchments, we find an anticlockwise hysteresis loop of annual sediment flux variations with respect to river discharge, which appears to be related to enhanced glacial sediment evacuation during late summer. Our analysis emphasizes the importance of unconsolidated sediments in the high-elevation sector that can easily be mobilized by hydrometeorological events and higher glacialmeltwater contributions. In future climate change scenarios, including continuous glacial retreat and more frequent monsoonal rainstorms across the Himalaya, we expect an increase in peak SSC events, which will decrease the water quality and impact hydropower generation.

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Section: Introductionmentioning

confidence: 91%

Climatic and geologic controls on suspended sediment flux in the Sutlej River Valley, western Himalaya

Wulf

Bookhagen

Scherler

2012

Hydrol. Earth Syst. Sci.

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“…The main increase in sediment fluxes occurs during the transit of the river through the Himalayan range and the NBGPm (locations 3 to The main trunk river of the Tsangpo-Brahmaputra catchment drains highly contrasted physiographic units with different denudation rates. The NBGPm in particular shows very active erosion processes, with steep river gradients and active landsliding that coincide with rapid exhumation (Finnegan et al, 2008;Stewart et al, 2008;Enkelmann et al, 2011;Larsen and Montgomery, 2012;Lang et al, 2015;King et al, 2016). The NBGPm separates the slowly eroding (< 0.3 mm yr −1 ), high-altitude (> 4000 m) Tibetan Plateau from the lowerlying reaches of the Tsangpo-Brahmaputra (< 2000 m) and the Indo-Gangetic floodplain (< 200 m).…”

Section: Be Concentrations Denudation Rates and Erosion Fluxesmentioning

confidence: 99%

“…The eastern Himalayan syntaxis has been proposed as a typical example of how active tectonic deformation, thermal weakening of the crust, and steep topography could be selfsustained by intense erosion and rapid exhumation of crustal material within the framework of the tectonic aneurysm model (Zeitler et al, 2001). Although the extent and nature of this coupling has recently been challenged (Bendick and Ehlers, 2014;Wang et al, 2014;King et al, 2016), there is ample evidence for superimposed rapid exhumation (Burg et al, 1998;Seward and Burg, 2008;Zeitler et al, 2014;Bracciali et al, 2016) and active erosion (Finlayson et al, 2002;Finnegan et al, 2008;Stewart et al, 2008;Enkelmann et al, 2011;Larsen and Montgomery, 2012;Lang et al, 2013) in a focused area around the Namche Barwa-Gyala Peri massif (NBGPm), where the course of the Tsangpo-Brahmaputra is marked by a sharp bend to the south-west (Fig. 1).…”

Section: Introductionmentioning

confidence: 99%

“…Difficult access to the NBGPm means that contemporary denudation rates are poorly constrained, but estimates range from ca. 5 to 17 mm yr −1 (Stewart et al, 2008;Enkelmann et al, 2011;Larsen and Montgomery, 2012). The NBGPm is thought to be responsible for up to 40 to 70 % of the sediment discharge of the entire Brahmaputra (e.g., Singh and France-Lanord, 2002;Garzanti et al, 2004), illustrating the potential for a small area of the Tsangpo-Brahmaputra to act as a major source of sediments to the entire river network.…”

Section: Introductionmentioning

confidence: 99%

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<sup>10</sup>Be systematics in the Tsangpo-Brahmaputra catchment: the cosmogenic nuclide legacy of the eastern Himalayan syntaxis

Lupker¹,

Lavé²,

France‐Lanord

et al. 2017

Earth Surf. Dynam.

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Abstract. The Tsangpo-Brahmaputra River drains the eastern part of the Himalayan range and flows from the Tibetan Plateau through the eastern Himalayan syntaxis downstream to the Indo-Gangetic floodplain and the Bay of Bengal. As such, it is a unique natural laboratory to study how denudation and sediment production processes are transferred to river detrital signals. In this study, we present a new 10 Be data set to constrain denudation rates across the catchment and to quantify the impact of rapid erosion within the syntaxis region on cosmogenic nuclide budgets and signals. The measured 10 Be denudation rates span around 2 orders of magnitude across individual catchments (ranging from 0.03 to > 4 mm yr −1 ) and sharply increase as the Tsangpo-Brahmaputra flows across the eastern Himalaya. The increase in denudation rates, however, occurs ∼ 150 km downstream of the Namche Barwa-Gyala Peri massif (NBGPm), an area which has been previously characterized by extremely high erosion and exhumation rates. We suggest that this downstream lag is mainly due to the physical abrasion of coarse-grained, low 10 Be concentration, landslide material produced within the syntaxis that dilutes the upstream high-concentration 10 Be flux from the Tibetan Plateau only after abrasion has transferred sediment to the studied sand fraction. A simple abrasion model produces typical lag distances of 50 to 150 km compatible with our observations. Abrasion effects reduce the spatial resolution over which denudation can be constrained in the eastern Himalayan syntaxis. In addition, we also highlight that denudation rate estimates are dependent on the sediment connectivity, storage, and quartz content of the upstream Tibetan Plateau part of the catchment, which tends to lead to an overestimation of downstream denudation rates. While no direct 10 Be denudation measurements were made in the syntaxis, the dilution of the upstream 10 Be signal, measured in Tsangpo-Brahmaputra sediments, provides constraints on the denudation rates in that region. These denudation estimates range from ca. 2 to 5 mm yr −1 for the entire syntaxis and ca. 4 to 28 mm yr −1 for the NBGPm, which is significantly higher than other large catchments. Overall, 10 Be concentrations measured at the outlet of the Tsangpo-Brahmaputra in Bangladesh suggest a sediment flux between 780 and 1430 Mt yr −1 equivalent to a denudation rate between 0.7 and 1.2 mm yr −1 for the entire catchment.

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“…A second explanation for the difference between the average short-and long-term exhumation rates is that rivers provide a biased sample by preferentially sampling areas that are currently undergoing anomalously high rates of crustal uplift and erosion, and the areas of rapid uplift and exhumation change from time to time (France-Lanord et al, 1993;Stewart et al, 2008). This conclusion is consistent with a study of detrital zircons from the Indus River, which showed that ~75% of the grains have He ages of <5 Ma (Campbell et al, 2005).…”

Section: Possible Controls On the Differences Between Shortand Long-tmentioning

confidence: 99%

Detrital zircon U-Pb-He double dating: A method of quantifying long- and short-term exhumation rates in collisional orogens

Wang

Campbell

Reiners

et al. 2014

Sci. China Earth Sci.

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A U-Pb-He double-dating method is applied to detrital zircons with core-rim structure from the Ganges River in order to determine average short-and long-term exhumation rates for the Himalayas. Long-term rates are calculated from the U/Pb ages of metamorphic rims of the grains that formed during the Himalayan orogeny and their crystallization temperatures, which are calculated from the Ti-in-zircon thermometer. Short-term rates are calculated from (U-Th)/He ages of the grains with appropriate closure temperatures. The results show that short-term rates for the Himalayas, which range from 0.70  0.09 to 2.67  0.40 km/Myr and average 1.75  0.59 (1) km/Myr, are higher and more varied than the long-term rates, which range from 0.84  0.16 to 1.85  0.35 km/Myr and average 1.26  0.25 (1) km/Myr. The differences between the long-term and short-term rates can be attributed to continuous exhumation of the host rocks in different mechanisms in continental collision orogen. The U/Pb ages of 44.0 ± 3.7 to 18.3 ± 0.5 Ma for the zircon rims indicate a protracted episode of ~25 Myr for regional metamorphism of the host rocks at deeper crust, whereas the (U-Th)/He ages of 42.2 ± 1.8 to 1.3 ± 0.2 Ma for the zircon grains represent a protracted period of ~40 Myr for exposure of the host rocks to shallower crustal level. In particular, the oldest (U-Th)/He ages of the zircon grains are close to the oldest U/Pb ages for the rims, indicating that some parcels of the rocks that contain zircons were rapidly exhumed from deep to shallow levels in the stage of collisional orogeny. On the other hand, some parcels of the rocks may have been carried upwards by thrust faults in the post-collisional stage. The parcels could be carried upwards by the thrust faults that steepen as they near the surface, or by transient movement faults so that areas of rapid exhumation became areas of slow exhumation and visa versa on a time scale of a few Myr in order to maintain the continuous exhumation. In this regard, the Ganges River must be preferentially sampling areas that are currently undergoing above average rates of uplift.zircon, U-Pb-He double-dating method, Himalayas, exhumation rate, collisional orogen Citation:Wang C Y, Campbell I H, Reiners P W, et al. 2014. Detrital zircon U-Pb-He double dating: A method of quantifying long-and short-term exhumation rates in collisional orogens.

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Brahmaputra sediment flux dominated by highly localized rapid erosion from the easternmost Himalaya

Cited by 126 publications

References 16 publications

Climatic and geologic controls on suspended sediment flux in the Sutlej River Valley, western Himalaya

Climatic and geologic controls on suspended sediment flux in the Sutlej River Valley, western Himalaya

<sup>10</sup>Be systematics in the Tsangpo-Brahmaputra catchment: the cosmogenic nuclide legacy of the eastern Himalayan syntaxis

Detrital zircon U-Pb-He double dating: A method of quantifying long- and short-term exhumation rates in collisional orogens

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Brahmaputra sediment flux dominated by highly localized rapid erosion from the easternmost Himalaya

Cited by 126 publications

References 16 publications

Climatic and geologic controls on suspended sediment flux in the Sutlej River Valley, western Himalaya

Climatic and geologic controls on suspended sediment flux in the Sutlej River Valley, western Himalaya

&lt;sup&gt;10&lt;/sup&gt;Be systematics in the Tsangpo-Brahmaputra catchment: the cosmogenic nuclide legacy of the eastern Himalayan syntaxis

Detrital zircon U-Pb-He double dating: A method of quantifying long- and short-term exhumation rates in collisional orogens

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<sup>10</sup>Be systematics in the Tsangpo-Brahmaputra catchment: the cosmogenic nuclide legacy of the eastern Himalayan syntaxis