Clement Narteau | Institut de Physique du Globe de Paris (original) (raw)

Papers by Clement Narteau

EGU General Assembly Conference Abstracts, Apr 1, 2013

Journal of Geophysical Research: Earth Surface, 2021

We study the morphodynamics of reversing dunes on the gravel deposits of the alluvial fan of the ... more We study the morphodynamics of reversing dunes on the gravel deposits of the alluvial fan of the Molcha river at the border between the Tibetan Plateau and the Taklamakan Desert. Independent sets of wind data show that this area of low sand availability is exposed to two prevailing winds from opposite directions and of different strengths. The predicted resultant transport direction of sand particles is westward. Nevertheless, satellite observations combined with field measurements and ground‐penetrating radar surveys reveal that isolated dunes a few meters high migrate eastward. This apparent dune migration paradox is resolved using numerical and analytical models that take into account the speed‐up effect and the continuous change in dune shape after each wind reversal. When a newly established wind hits what was before the steeper lee slope of the dune, the sand flux at the crest abruptly increases before relaxing back to a constant value as the crest migrates downwind and as the...

Water, 2019

This paper describes a large-scale experiment designed to examine if reinstating natural processe... more This paper describes a large-scale experiment designed to examine if reinstating natural processes in the coastal dune systems of Southwest France can be a relevant nature-based adaptation in chronically eroding sectors and a nature-based solution against coastal hazards, by maintaining the coastal dune ecological corridor. An experiment started in late 2017 on a 4-km-long stretch of coast at Truc Vert, where experimental notches were excavated and intensively monitored in the incipient and established foredunes. Preliminary results indicate that most of the excavated notches did not develop into blowout. Only the larger elongated notches subsequently excavated in the established foredune in 2018 showed evidence of development, acting as an effective conduit for aeolian landward transport into the dunes. All notches were found to have a statistically significant impact on vegetation dynamics downwind, even those that did not develop. The area of bare sand landward and within the elo...

Earth Surface Dynamics, 2018

The grain-size distribution of ancient alluvial systems is commonly determined from surface sampl... more The grain-size distribution of ancient alluvial systems is commonly determined from surface samples of vertically exposed sections of gravel deposits. This method relies on the hypothesis that the grain-size distribution obtained from a vertical cross section is equivalent to that of the riverbed. Such an hypothesis implies first that the sediments are uniform in size in the river bed, and second that the sampling method implemented on a vertical section leads to a grain-size distribution equivalent to the bulk one. Here, we report a field test of this hypothesis on granulometric samples collected in an active, gravel-bedded, braided stream: the Urumqi River in China. We compare data from volumetric samples of a trench excavated in an active thread and from surface counts performed on the trench vertical faces. Based on this data set, we show that the grain-size distributions obtained from all the samples are similar and that the deposit is uniform at the scale of the river active layer, a layer extending from the surface to a depth of approximately 10 times the size of the largest clasts. As a consequence, the grid-by-number method implemented vertically leads to a grain-size distribution equivalent to the one obtained by a bulk volumetric sampling. This study thus brings support to the hypothesis that vertical surface counts provide an accurate characterization of the grain-size distribution of paleo-braided rivers.

Nature communications, Jan 6, 2017

Characterising the state of stress in the brittle upper-crust is essential in mechanics of faulti... more Characterising the state of stress in the brittle upper-crust is essential in mechanics of faulting, industrial production processes, and operational earthquake forecasting. Nevertheless, unresolved questions concern the variation of pore-fluid with depth and the absolute strength on tectonically active faults. Here we show that, along the San Andreas fault system, the time-delay before the onset of the power-law aftershock decay rate (the c-value) varies by three orders of magnitude in the first 20 km below the surface. Despite the influence of the lithostatic stress, there is no continuous change in c-value with depth. Instead, two decay phases are separated by an abrupt increase at an intermediate depth range of 2-5 km. This transitional regime is the only one observed in fluid-injection-induced seismic areas. This provides strong evidence for the role of fluid and a porosity reduction mechanism at depth of few kilometres in active fault zones. Aftershock statistics can then be u...

Journal of Geophysical Research: Solid Earth, 2015

Using the unique data sets provided by satellite observations, correlated temporal variations in ... more Using the unique data sets provided by satellite observations, correlated temporal variations in gravity and magnetic fields over a large area extending from the Atlantic to the Indian Ocean have been recently reported. On a timescale of few years to a decade, both field variations may be linked to changes at the top of the core. Here we propose that in addition to the topography generated by the convection in the mantle, the core‐mantle boundary (CMB) may be in a dynamic equilibrium state, mainly controlled by a dissolution‐crystallization process of the mantle silicate rocks in the liquid alloy of the core. Due to the resulting continuous changes in CMB topography, anomalies of hundreds of nGal and tens of nT yr−2 might be produced by the corresponding mass redistribution and the secondary flow generated by the associated pressure field. Numerical modeling and both gravimetric and magnetic anomaly magnitudes suggest a rate of centimeters per year and a large range of length scales...

Encyclopedia of Planetary Landforms, 2014

• Dunes of different shapes and orientations develop and coexist under the same natural wind regi... more • Dunes of different shapes and orientations develop and coexist under the same natural wind regime depending on sand availability. • The dynamics of pattern coarsening selects dune aspect-ratio over short time. • There is a minimum size for dune elongation on a nonerodible bed, below which barchan or asymmetric barchan shapes are observed.

&lt;p&gt;Wind-blown sand dunes emerge due the linear instability of a flat sedime... more &lt;p&gt;Wind-blown sand dunes emerge due the linear instability of a flat sedimentary bed. This instability has been studied in experiments and numerical models but rarely in the field, because of the large time and length scales involved. Here we examine dune formation at the upwind margin of the White Sands Dune Field in New Mexico (USA), using 4 years of lidar topographic data to follow the spatial and temporal development of incipient dunes. Data quantify dune wavelength, growth rate, and propagation velocity and also the characteristic length scale associated with the growth process. We show that all these measurements are in quantitative agreement with predictions from linear stability analysis. This validation makes it possible to use the theory to reliably interpret dune-pattern characteristics and provide quantitative constraints on associated wind regimes and sediment properties, where direct local measurements are not available or feasible.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Reference&lt;/strong&gt;: Gadal et al., Geophys. Res. Lett. &lt;strong&gt;47&lt;/strong&gt;, e2020GL088919 (2020).&lt;/p&gt;

pen A ccess Transport capacity and saturation mechanism in a real-space cellular automaton dune m... more pen A ccess Transport capacity and saturation mechanism in a real-space cellular automaton dune model

Introduction: Dome dunes are individual sand piles with a rounded shape and no slip face. They ar... more Introduction: Dome dunes are individual sand piles with a rounded shape and no slip face. They are not only incipient or disappearing dunes, they can also reach a steady-state or a giant size (Fig. 1c) . They are frequently observed in dune systems on Earth and Mars [1,2]. Nevertheless, unlike other dune types, dome dunes cannot be classified according to the orientation and/or the sinuosity of their crestlines. Hence, they have not been the subject of intense research and there are still uncertainties about the conditions under which they develop. Mainly observed in zones of low sediment availability, dome dunes are not isolated objects. They generally occur in dome-dune fields, in which all individual structures share common morphological properties (e.g., size, shape, planar contour), as in stardune fields [3]. In addition, they often coexist either with barchan or linear dunes along the sediment transport pathways. This indicates that the shape and the spatial distribution of do...

Proceedings of the National Academy of Sciences, 2021

Significance We report a landscape-scale experiment with controlled initial and boundary conditio... more Significance We report a landscape-scale experiment with controlled initial and boundary conditions to reveal incipient dune growth under natural action of wind. We measured growth rate of dunes of different wavelengths for 42 mo in a desert plot of 7,500 m 2 . We identify an early phase in which a clear maximum growth rate occurs for a 15-m dune spacing. Successful comparison with dune instability theory allows us to quantify the size-selection mechanism leading to the emergence of periodic dune patterns, which can be directly related to flow and sand transport properties. An experiment of this type and scale is unprecedented. Its results boost confidence in the existing theory, confirming its application to a variety of planetary landscapes from repeated aerial/orbital imagery.

Sand seas on Titan may reflect the present and past climatic conditions. Understanding the morpho... more Sand seas on Titan may reflect the present and past climatic conditions. Understanding the morphodynamics and physicochemical properties of Titan’s dunes is therefore essential for a better comprehension of the climatic and geological history of the largest Saturn’s moon. We derived quantitatively surface properties (texture, composition) from the modelling of microwave backscattered signal and Monte Carlo inversion of despeckled Cassini/SAR data over the equatorial sand seas. We show that dunes and inter-dunes have significantly different physical properties. Absorption is more efficient in the dunes compared to the inter-dunes. The inter-dunes are smoother with an higher dielectric constant than the dunes. Considering the composition, the inter-dunes are in between the dunes and the bright inselbergs, suggesting the presence of a shallow layer of sediment in between the dunes. Additionally potential secondary bedforms may have been detected. Implications for dune morphodynamics, s...

Z. Dong, P. Claudin, S. Rodriguez, L. Fernandez-Cascales and S. Courrech du Pont. Université de P... more Z. Dong, P. Claudin, S. Rodriguez, L. Fernandez-Cascales and S. Courrech du Pont. Université de Paris, Institut de Physique du Globe de Paris, CNRS (F-75005 Paris, France, narteau@ipgp.fr, rodriguez@ipgp.fr), School of Geography and Tourism, Shaanxi Normal University (620 Chang'an West Avenue, Xi'an, Shaanxi 710119, China, lvping@lzb.ac.cn), 3 Key Laboratory of Desert and Desertification, Northwest Institute of EcoEnvironment and Resources, Chinese Academy of Sciences (320 West Donggang Road, 730000 Lanzhou, Gansu, China, zbdong@lzb.ac.cn), Physique et Mécanique des Milieux Hétérogènes, CNRS, ESPCI, PSL, Sorbonne Université, Université de Paris (10 rue Vauquelin, 75005 Paris, France, claudin@pmmh.espci.fr), Laboratoire Matière et Système Complexes, Université de Paris, CNRS (Bâtiment Condorcet, 10 rue Alice Domon et Léonie Duquet, 75205 Paris Cedex 13, France, sylvain.courrech@univ-paris-diderot.f r ).

Geophysical Research Letters, 2019

• Linear dunes with a finger-like shape are identified as an elementary dune type. • The longitud... more • Linear dunes with a finger-like shape are identified as an elementary dune type. • The longitudinal mass balance governs the elongation and stability of a linear dune. • Dune morphodynamics is controlled by reversing winds and by the minimum dune size at the tip.

Earth and Planetary Science Letters, 2018

Dunes provide unique information about wind regimes on planetary bodies where there is no direct ... more Dunes provide unique information about wind regimes on planetary bodies where there is no direct meteorological data. At the eastern margin of Olympia Undae on Mars, dune orientation is measured from satellite imagery and sediment cover is estimated using the high contrast between the dune material and substrate. The analysis of these data provide the first quantification of relationship between sediment availability and dune orientation. Abrupt and smooth dune reorientations are associated with inward and outward dynamics of dunes approaching and ejecting from major sedimentary bodies, respectively. These reorientation patterns along sediment transport pathways are interpreted using a new generation dune model based on the coexistence of two dune growth mechanisms. This model also permits solving of the inverse problem of predicting the wind regime from dune orientation. For bidirectional wind regimes, solutions of this inverse problem show substantial differences in the distributions of sediment flux orientation, which can be attributed to atmospheric flow variations induced by changes in albedo at the boundaries of major dune fields. Then, we conclude that relationships between sediment cover and dune orientation can be used to constrain wind regime and dune field development on Mars and other planetary surfaces.

Geophysical Research Letters, 2016

Unlike ripples, there are only few numerical studies on grain size segregation at the scale of du... more Unlike ripples, there are only few numerical studies on grain size segregation at the scale of dunes in aeolian environments. Here we use a cellular automaton model to analyze vertical sorting in granular mixtures under steady unidirectional flow conditions. We investigate the feedbacks between dune growth and the segregation mechanisms by varying the size of coarse grains and their proportion within the bed. We systematically observe the development of a horizontal layer of coarse grains at the top of which sorted bed forms may grow by amalgamation. The formation of such an armor layer controls the overall sediment transport and availability. The emergence of dunes and the transition from barchan to transverse dune fields depend only on the grain size distribution of the initial sediment layer. As confirmed by observation, this result indicates that armor layers should be present in most arid deserts, where they are likely to control dune morphodynamics.