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Sand Dunes Return to main pageResearch on Sand Dunes in the Sibley SchoolThis work, which is sponsored by the Qatar National Research Foundation, is a collaboration with the Weill-Cornell Medical College in Qatar, the Biotechnology Centre of the Qatar Ministry of Environment, Maersk Oil in Qatar, the Ecole Polytechnique Federale de Lausanne, Tencate Geosynthetics, the Universite de Rennes, the Universite de Nantes, the Laboratoire 3SR of the Universite de Grenoble, DAMTP at the University of Cambridge, the LGPM laboratory of the Ecole Centrale de Paris, and the Faculte des Sciences de Nouakchott. So far, we have carried out measurements in the Sahara desert on barchan sand dunes in Mauritania, and in Qatar.

Our motivation is to work against desertification by stabilizing sand dune with microbiological means. The context of what we are trying to accomplish is aptly articulated by inspirational TED talks by Magnus Larsson and Allan Savory.

Visualize Michel Louge's presentation on the "Role of pore pressure gradients in geophysical flows over permeable substrates" at the Kavli Institute of Theoretical Physics in Santa Barbara during the conference on Fluid-Mediated Particle Transport in Geophysical Flowson Wednesday, December 18, 2014. The first part of the presentation concerns powders snow avalanches. The second discusses the role of the porous sand bed in desert ripples.

Latest newsA recently published open access paper documents the unique properties of inclined flows on a dissipative base, such as on the avalanche face of a sand dune.

Click on the picture above to see photos of our January 2015 campaign in Qatar.

Recent ArticlesLouge, M. Y., A. Valance, A. Ould el-Moctar, J. Xu, A. G. Hay, and R. Richer (2013), Temperature and humidity within a mobile barchan sand dune, implications for microbial survival, J. Geophys. Res. 118, doi:10.1002/2013JF002839, open access.

Although microorganisms play an important role in biological soil crusts and plant rhizospheres in deserts, it is

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unclear whether temperature and moisture deep within relatively fast-moving hyper-arid mobile dunes present a suitable habitat for microbes. To inform this question, we report measurements of temperature and humidity from probes initially sunk below the leeward avalanche face of a mobile barchan dune in the Qatar desert, emerging windward after 15 months of deep burial. Despite large diurnal variations on the surface, temperature within this dune of 5.6m height is predictable (see movie), as long as dune advection is properly considered. It evolves on smaller amplitude and longer time scale than the surface, lagging average seasonal atmospheric conditions by about two months. We contrast these deep thermal records with measurements of diurnal variations of the temperature profile just below the surface (see movie), which we calculate with a thermal model predicting the relative roles of wind-driven convective heat transfer and net radiation flux on the dune. Observations and analyses also suggest why random precipitation on the leeward face produces a more unpredictable moisture patchwork on the windward slope. By rapidly reaching sheltered depths, small quantities of rain falling on that face escape evaporation and endure within the dune until resurfacing upwind. At depths below 10cm, we show that moisture, rather than temperature, determines the viability of microbes, and we provide initial microscopic and respiration-based evidence of their presence below the windward slope.

Microbial life on a Qatar dune sand grain. Left: Fluorescence micrograph of a single sand grain showing an abundance of bacteria. Live cells stained green with Syto 9 using a technique similar to Gommeaux, et al (2010). Cells stained red/orange with propidium iodide are dead or dormant (400x magnification using a Zeiss Axio LSM

710 Fluorescence Microscope). Right: image of a similar sand grain from an FEI Quanta 200 Environmental Scanning Electron Microscope (ESEM) in low vacuum mode.



Top: Dune reconstructed from points mapped with a Leica TS02 theodolite, with estimated relative path followed by the buried RTR-53 data loggers that measured long-term record of temperature and relative humidity. (If you have access to Matlab, you can download the 3-D figure of the dune profile by cliking here). Middle: Record of temperature and humidity from the logger buried on the avalanche face in March 2010 and recovered windward in July 2012. In the paper above, we provide a model for humidity and temperature recorded by this probe. Bottom: Record from the second logger between November 2011 and March 2013.

Download our slides for the ICACM-2013 conference in Aussois, May 2013. This presentation draws attention to the role of pressure gradients in counteracting gravity in porous media such as snowpacks and desert sand ripples. Further information on this subject is provided in the following paper:

Musa, R. A., S. Takarrouht, M. Y. Louge, J. Xu, and M. E. Berberich (2014), Pore pressure in a wind-swept rippled bed below the suspension threshold, J. Geophys. Res. Earth Surf., 119, doi:10.1002/2014JF003293., open access.

Toward elucidating how a wavy porous sand bed perturbs a turbulent flow above its surface, we record pressure within a permeable material resembling the region just below desert ripples, contrasting these delicate measurements with earlier studies on similar impermeable surfaces. We run separate tests in a wind tunnel on two sinusoidal porous ripples with aspect ratio of half crest-to-trough amplitude to wavelength of 3% and 6%. For the smaller ratio, pore pressure is a function of streamwise distance with a single delayed harmonic decaying exponentially with depth and proportional to wind speed squared. The resulting pressure on the porous surface is nearly identical to that on a similar impermeable wave. Pore pressure variations at the larger aspect ratio are greater and more complicated. Consistent with the regime map of Kuzan et al. (1989), the flow separates, creating a depression at crests. Unlike flows on impermeable waves, the porous rippled bed diffuses the depression upstream, reduces surface pressure gradients, and gives rise to a slip velocity, thus affecting the turbulent boundary layer. Pressure gradients within the porous material also generate body forces rising with wind speed squared and ripple aspect ratio, partially counteracting gravity around crests, thereby facilitating the onset of erosion, particularly on ripples of high aspect ratio armored with large surface grains. By establishing how pore pressure gradients scale with ripple aspect ratio and wind speed, our measurements quantify the internal seepage flow that draws dust and humidity beneath the porous surface.

Text files contain data collected on turbulence velocity profiles and pore pressure. This ReadMe file explains how to



use these text files.

Note the typo in Fig. 7 of this article: the caption should read h0/lambda = 3%.

Flow development on the artificial rippled bed in the wind tunnel.

The graph above shows the sharp contrast between dimensionless static pressures at the surface of impermeable ripples (symbols) and the same pressure on our porous solid (lines) at 6% ripple aspect ratio. By diffusing the

depression created by flow separation behind the crest (halfway on the horizontal axis), the porous medium reduces pressure on the first half of the ripple.



The above image shows the dimensionless pore pressure gradient that we measured in our rippled bed at 3% aspect ratio. Note the contrast with the same field at 6% ratio, shown below. Where the gradient field is largest (shown in

red), ripples of large aspect ratio have a greater propensity to relieve bed weight and thus enhance surface erosion. In the paper above, we derive a geometrical criterion indicating when ripple mobilization by internal pressure gradients

prevails over aeolian erosion of surface grains. We expect that such mobilzation, which has often been ignored in Shields-like erosion threshold criteria, is important in the formation of megaripples.

For this work, Ryan Musa, Brian Mittereder, and Mike Berberich designed and built a unique setup to record pore pressure within a porous rippled plastic sheet reproducing seepage flow within desert ripples. They used CNC milling machines to create waves on the free surface. Once they demonstrated feasibility of these measurements in Cornell's Environmental Wind Tunnel, Smahane Takarrouht took an extensive data set for mean and fluctuation pore pressure by multiplexing pressure taps to a single MKS Baratron 10 mTorr differential pressure transducer with a Scanivalve in the summer 2011. In the Fall 2011, Amin Younes constructed another bed with twice the ripple amplitude.



Left: Brian Mittereder with the Okuma CNC milling machine. Right: the porous rippled bed being machined.

Left: the design team and their realization. Right: Smahane Takarrouht takes measurements in the wind tunnel on the rippled bed of 3% aspect ratio.

Amin Younes with the rippled bed of 6 mm amplitude, which he manufactured on the Architecture department CNC with the help of Frank Parish.

Field expedition blogOur latest field campaign took place in April 2014 in Qatar. Data from earlier field campaigns (March 2010, January 2011, March 2011, June 2011, November 2011, January 2012, April 2012, July 2012, and November 2012, April 2013, January and April 2014, and January 2015) are found below.

January 2015 in Qatar



In January 2015, we deployed on a large dune a ground-penetrating radar (GPR) loaned to our collaborator Nathalie Vriend of the Department of Applied Mathematics and Theoretical Physics at the University of Cambridge by Alan Hobbs at the Geophysical Equipment Facility of the UK's National Environment Research Council. Participants in this campaign included Nathalie Vriend, Matthew Arran, Anil Netravali, Anthony Hay, Thomas McKay, Anushree Acharya, Sullen Qassim, Ali Sultan, and Michel and Nadine Louge.

Composite picture of our January 2015 campaign of measurements on a large dune at 25° 00.630'N 51° 20.026'E. From left to right and top to bottom: Matthew Arran fixes a sand sample with epoxy resin to study its fine stratigraphy. Anthony Hay poses near sunset. Michel and Nadine Louge watch Anil Netravali slide down the avalanche face of the dune, making it "sing" in the process. Tom McKay of the Maersk Oil Research and Technology Centre adjusts his head gear before resuming GPR measurements. Sullen Qassim sets the GPR antenna on the dune surface. Matthew Arran and Nathalie Vriend stand beside a pit dug to inspect dune stratigraphy. Nadine Louge stands at the base of the 55m-long avalanche face after recording positions along a rope marking GPR measurement locations. Michel Louge poses infront of that face. Nadine Louge is seen through the reticle of the Leica TS02 total station holding its reflecting prism. The colored 3D graph shows a reconstruction of the dune shape from about 800 point measurements.



Nadine poses behind her namesake, which she helped to survey on January 15, 2015.

Nathalie Vriend (left) and Sullen Qassim operate the GPR.



Relative size and position of the two dunes surveyed in January 2015.

April 2014 in Qatar

In April 2014, we deployed a ground-penetrating radar menioned earlier on the smaller sand dune at 25° 00.597'N 51° 20.409'E.





From left to right and top to bottom: Eric Deitch and Anthony Hay are viewed in the cross-hairs of the Leica TS02 theodolite. Anthony Hay shows a dune core sample to Michel Louge. MatthewAran, Joshua Caplan and Nathalie Vriend operate the ground-penetrating radar (GPR). A 3D rendering of the dune and the transects of the GPR. Jin Xu descends on the avalanche face of a large dune and operates the Leica. Theis Solling and Jin Xu operate the CT-scanner at the Maersk Oil Research and Technology Centre. Anthony Hay and Rashmi Fotedar discuss dune fungal



cultures at the Biotechnology Centre of the Qatar Ministry of Environment.

April 2013 in Qatar

In April 2013, we deployed a GeoDetect® system of fiber Bragg gratings to measure strain and temperature on the avalanche face of a barchan sand dune in Qatar. The system consisted of a geotextile manufactured by TenCate Geosynthetics firmly holding two optical fibers with a total of eleven Bragg networks measuring local strain, as well as another six Bragg networks on a separate optical fiber to measure local temperature. The interrogator was made by Scaime.



From left to right and top to bottom: Olivier Artieres of TenCate Geosynthetics sets up the GeoDetect® system. Patrick Chasle prepares the geotextile on the windward slope. Olivier Artieres sets up optical fiber connections. Alexandre Valance, Michel Louge and Patrick Chasle deploy the geotextile on the leeward avalanche face. A panorama of the dune. Alexandre and Michel operate the Leica TS02 theodolite to measure sand thickness with millimetric precision. Another panorama with Patrick Chasle in front of the avalanche face. Patrick Chasle anchors and tensions the geotextile. A view of the setup with the solar panel providing long-term power to the system.



The dune outline on April 15 and 16, 2013. A 3D Matlab figure created with this program is also available by cliking on the picture above. The arrow shows the relative path of our second RH/T probe buried, which produced the record

shown below and reported in the article above. CO2 sampling was carried out at locations shown (dots). Plus signs represent locations of fiber Bragg gratings deployed on the leeward avalanche face.

Dune displacement from July 2012 (grey) to April 2013 (color).



Dune speed vs size obtained from historical images of GoogleEarth.

November 2012 in Qatar



From left to right and top to bottom: Undergraduate medical student Yanal Shaheen learns how to use the Leica theodolite from Jin Xu (left) and Sara Abdul-Majid (right). Anthony Hay shares his knowledge of sand dune

microbiology with students of the Weill-Cornell Medical College in Qatar. Michel Louge presents results at a Qatar National Research Foundation event for CoP-18 in Doha on November 29, 2012. A copy of the presentation is

available here. Jin Xu covers the capacitance and temperature probes to test the effect of covering the surface with an impermeable geotextile. At sunset, he finally packs probes and electronics after two days of continuous

measurements on the dune. Michel Louge shows instruments to be buried in the dune. The National Instruments cRIO does data acquisition automatically. The Capacitec electronics processes signals from the capacitance probe, buried on the right. The multiplexer, designed by Patrick Chasle, connects any one of 15 sensors on the capacitance probe to the single channel of the Capacitec amplifier. The temperature probe on the left was used in March 2011 to

acquire data shown in the animation below. An animation of the temperature field near the surface of the dune is available by cliking on the image below.



Another animation of the temperature experienced by the probe buried from May 2011 to July 2012 is available by clicking on the image below. This solution of the heat equation was obtained with Comsol Multiphysics subject to a surface temperature boundary condition calculated using the pdepe toolbox in Matlab from data obtained with our weather station, see explanations in this article.

July 2012 in Qatar



Top to bottom and left to right: Jin Xu operates the Leica TS02 theodolite mapping the dune surface. Sara Abdul-Majid samples a dune for microbiological analyses. Michel Louge is viewed through the Leica reticle in the searing July heat.

April 2012 in Qatar



Top to bottom and left to right: Michel Louge and Alexandre Valance interrogate the ThermoWorks RTR-53 humidity/temperature recorder buried in the dune. Alexandre Valance holds the Young rain gauge that he deployed high above his flux "saltation meter" to

avoid sand contamination. Renee Richer sets up the LiCor 8100A for CO2 flux measurements on the dune surface. Anthony Hay sets up the AMS soil gas sampling cones for CO2 analysis. Alexandre Valance stands on the dune. A group picture.

Click on this link to animate the graphs below for the entire April 13-23 duration.



Top to bottom: data from April 13 to 23 for H2O mass fraction at 15 depths. A serendipitous rainstorm occurred on April 13, 2012, causing massive changes in humidity near the surface, which took several days to dry up. Then a smaller rain fell mid-day on April 22,

causing further disruption to the humidity time-history.

Close-up of humidity time-histories on April 13 (left) and 22-23 (right) showing effects of two rain events.

On November 21, 2011, Sara Abdul Majid's presentation on this research at the Qatar Foundation's 2011 Annual Research Forum won the "Best Environment Research Program of the Year," which carries a $100,000 award encouraging us to pursue this work, see this article in the Qatar Tribune, and this one written by Susan Lang for the Cornell Chronicle. The New York Academy of Sciences also wrote a report on the conference, available by clicking on the tab "Meeting Report > Soil Science" of this web site.



Left: Sara Abdul-Majid accepts the award for Best Environment Research Program of the Year from Dr. Fathy Saoud, President of the Qatar Foundation at the QF research forum. Right: Renee Richer and Sara Abdul Majid at the QF Forum banquet, November 21, 2011.

See also the July 2011 Newsletter from Kipp & Zonen, and an article in French written by Celine Duguey for l'Espace des Sciences de Rennes.

Weather station setup, November 2011 and January 2012 in Qatar

Left: Sara Abdul-Majid and Michel Louge pose behind the weather station that they installed in November 2011. The station includes a Nomad2 Wind Data logger that acquires signals from a Young tipping bucket rain gauge, two SecondWind C3 anemometers, a SecondWind NRG 200P wind vane, and a Young combined HMP155 temperature/humidity sensor from Vaisala with radiation shield.The station is powered by a REC10-12 battery and a solar panel. Right: Michel Louge installs a fence in January 2012.

From right to left: Said Al-Hajri, one of his camels, and Michel Louge pose for a photo in January 2012. Mr. Al-Hajri supports our research by providing essential logistical support near his farm.

Pictures and data from our March 2011 campaign in Qatar



Top, left to right: Anthony Hay, Renee Richer, Sara Abdul-Majid, Michel Louge. Bottom: system tested in the lab; Renee and Sara test the LiCor; Michel and Renee raise the weather station with Nexgen anemometer and wind vane acquired with a Second Wind NOMAD 2 data logger, as well as two ThermoWorks

temperature and humidity USB gauges. Data from the capacitance instrument, the temperature probe, and the Kipp & Zonen net solar radiation detector was acquired with a National Instruments cRIO, which, together with a 20Ah LiPo battery from Tenergy, allowed us as long as 60 hours of autonomy. Matthew Blair wrote a

tutorial on developing the LabView-based software for the cRIO.

Preliminary Qatar campaign results

The movie below shows variations of diurnal sand temperature (red) and humidity (blue) below the surface at the toe of a barchan sand dune taken on March 19-21, 2011 in Qatar. The dashed red line is a numerical model of temperature time-history obtained by solving the unsteady heat equation in the sand bed with input from the measured Kipp & Zonen net radiation flux on the surface and the turbulent heat transfer flux at the surface arising from the measured wind speed. The vertical arrow indicates the direction and strength of humidity gradient at the surface. The blue line is a spline fit to the data that is used to evaluate the gradient. Note a gradual drying of the bed over the 44 hours of this field experiment.

Pictures and data from our January 2011 campaign in Mauritania



Top, from left to right below the group photos: Michel Louge inserts his 15-sensor capacitance probe made of a PCB designed using PCB Artist through the surface of a barchan dune in the Sahara desert near Akjoujt (19N 50.637' 014W 08.869') in January 2011; close-up of the PCB capacitance probe that records depth profiles of volumetric water content < 1% per mass accurately by multiplexing the sensors to single-channel capacitance processing electronics; close-up of the temperature

probe made of 15 National Semiconductor LM235 sensors deployed along the capacitance instrument. Middle: data acquisition system based on a National Instrument USB-6259 BNC acquisition board driven by an Acer Aspire ONE 532h-2588 laptop of low power consumption (< 1 amp at 14 V); the mutiplexing

electronic box shown at the upper left was built by Patrick Chasle at the Université de Rennes. Bottom, from left to right: two ThermoWorks TW-USB-2-LCD+USB data loggers recorded diurnal variations of ambient temperature and relative humidity in the turbulent boundary layer above the surface, along with two anemometers

recording wind speed and direction using a Nomad data logger; a Kipp & Zonen NR-Lite 2 recorded simultaneously irradiation from the sun minus radiosity from the sand surface. Patrick Chasle shows the 100 W solar panel, which allowed us, together with a 30 Ah Lithium Ferro Phosphate Ion rechargeable battery donated by

Dr. Chun-Chieh Chang, complete energy self-sufficiency in the field.



Anthony Hay observes live microbes with fluorescence microscopy using a Paralens kit, and explains students at the Faculte des Sciences de Nouakchott the significance of the microbiology in sand dunes.

Preliminary Mauritania January 2011 campaign results

Movies below show variations of diurnal sand temperature and humidity below the surface at the toe of a barchan sand dune taken on January 19-21, 2011.

The graph below also provides wind speed at two elevations above ground, ambient temperature and humidity, and net radiation flux on the Mauritania barchan. Kipp & Zonen, manufacturer of the radiation instrument, published a short article on our work in its July Newsletter.



Pictures from our March 2010 campaign in Mauritania

In March 2010, we carried out field experiments near Akjoujt, as well as in the Banc d'Arguin National Park of Mauritania (19N 29' 31.6"; 016W 24' 50.9"). Left: Alexandre Valance records the location of the relative humidity/temperature profile measurements. Center: Michel Louge connects instruments before carrying out

measurements. Right: Ahmed Ould el Moctar and Michel Louge enjoy breakfast after a night of measurements on a barchan sand dune.

Left: Dah Ould Ahmedou (Faculté des Sciences de Nouakchott) monitors the data acquisition system. Right: group photograph; from left to right: our tireless driver Mohameden Ould Eddi, Ahmed Ould el Moctar (Université de Nantes), Pascal Dupont (INSA de Rennes),

Alexandre Valance (Université de Rennes 1), and Michel Louge.



Earlier publications

Louge, M. Y., A. Valance, A. Ould el-Moctar, and P. Dupont (2010), Packing variations on a ripple of nearly monodisperse dry sand, J. Geophys. Res., 115, F02001, doi:10.1029/2009JF001384.

This paper reports measurements of solid volume fraction at the surface of sand ripples using our capacitance technique. By recording variations of sand elevation at the capacitance probe (see picture below), we find that sand ripples have compaction at troughs near random jammed packing (~64%) and near the minimum packing for a stable solid at crests (~54.5%). The paper discusses these results in the light of models of aeolian transport. It also describes a seepage flow of air that is driven by the Bernouilli effect as streamlines contract and expand on ripples. A short movie demonstrates that ripple crests cannot sustain much stress, as explained in the paper.

Measurements of the ripple profile with a diode laser and solid volume fraction with a capacitance probe. From left to right, Michel Louge, Alexandre Valance, Dah Ould Ahmedou, Ahmed Ould el Moctar, and Ahmedou Ould Mahfoudh, February 2006.

Louge, M. Y., A. Valance, H. Mint Babah, J.-C. Moreau-Trouvé, A. Ould el-Moctar, P. Dupont, and D. Ould Ahmedou (2010), Seepage-induced penetration of water vapor and dust beneath ripples and dunes, J. Geophys. Res., 115, F02002, doi:10.1029/2009JF001385.

This paper reports measurements of solid volume fraction and humidity in sands just below the surface of a barchan dune in the Sahara using our the same probe we had deployed in snow packs. The paper also shows that the seepage flow through the sand surface acts forces dust particles to penetrate the ripple surface through troughs and guides water vapor through crests. The suction of dust into ripple troughs, which causes it to accumulate under a protective sand surface, may explain why desert air is so clear under normal winds, while dust only resuspends during unusually high winds.

A short erratum clarification can be downloaded here. It corrects a minor parenthetical point on Darcy shear stresses on p. 4, shortly after equation (10).

(a) Channeling of moisture through crests and (b) dust penetration in troughs driven by seepage on sand ripples; for details, see Louge, et al (2009).



M. Y. Louge, A. Valance, A. Ould el-Moctar, D. Ould Ahmedou, and P. Dupont: "Model for surface packing and aeolian transport on sand ripples," Powders & Grains 2009, M. Nakagawa, ed. (2009).

This paper extends our analysis of the aeolian transport on sand ripples. It predicts the threshold shear velocity, and compares aeolian transport on Earth and Mars.

A movie shows wind transport on a small barchan. A movie requiring longer download and only playing on QuickTime (.mov extension) shows various modes of avalanching on the downwind face of barchan dunes.

Alexandre Valance (right) and Michel Louge (left) record the volume fraction on sand ripples near the route de l'Espoir in Nouakchott.

The snow probe deployed on a sand dune in Mauritania.

Group photo: from right to left: Valance, ould Ahmedou, ould el Moctar, Louge.

Water balance in barchan dunes

Current work involves the water balance in sand dunes of hyper-arid regions, see for example our simulations of water penetration through a mobile dune after modest desert rain:



Simulated water retention in a barchan sand dune 120 days after modest rain. This 3D simulation was carried out by programming Richards' equation on the Comsol Multiphysics platform.

Mobile dunes can harbor a remarkable amount of water after rain, despite hyper-arid desert conditions. Click on the picture for animation. This 2D simulation was carried out by programming Richards' equation on Comsol

Multiphysics.

Miscellaneous information

You can generate barchan dune profiles in the figure below using this Matlab program, which implements dune dimensions reported by G. Sauermann, P. Rognon, A. Poliakov, H. J. Herrmann, The shape of the barchan dunes of Southern Morocco, Geomorphology 36, 47-62 (2000).



You can do similar calculations with this Mathematica notebook.

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