Formation and Migration of Sand Dunes: A Simulation of their Effect in the Sedimentary Environment

Author(s):

Karolina Sobczak

Keyword(s):

Sand Dunes ◽

Living Conditions ◽

Desertification Process ◽

The Subject ◽

Abstract The subject of the article is an analysis of changes in the environment and economy of oases in southern Morocco, on the basis of a case study of Mhamid. The conclusions are that water investments carried out in the Draa Valley intensified the desertification process. This is exemplified by a stronger aeolian deflation, worsening living conditions of the population, limiting of arable areas and finally, migration. Paradoxically, because of desertification, the region has a chance to develop economically because the newly created sand dunes fields stimulate development of tourism.

Inferring Airflow Across Martian Dunes From Ripple Patterns and Dynamics

Frontiers in Earth Science ◽

10.3389/feart.2021.702828 ◽

2021 ◽

Vol 9 ◽

Author(s):

D. R. Hood ◽

R. C. Ewing ◽

K. P. Roback ◽

K. Runyon ◽

J.-P. Avouac ◽

...

Keyword(s):

Fluid Dynamic ◽

Sand Dunes ◽

Simulation Models ◽

Plan View ◽

Migration Rates ◽

Eddy Simulation ◽

Optical Images ◽

Ripple Patterns ◽

Ripple Migration ◽

Large ripples form striking patterns on the slopes of martian sand dunes which can be mapped and tracked using high-resolution optical images. The ripples vary in orientation, wavelength, plan-view morphology, and rates of migration. The variations in the ripple patterns are recognized to signal the effects of the regional and local winds and feedbacks between winds and dune topography. We examine the ripple patterns and the motion of these ripples to interpret airflow dynamics around dunes in the dune field at Nili Patera. We find that coincident changes in ripple patterns and migration rates in dune wakes indicate reattachment lengths of 4–7 brink heights. This reattachment length is similar to length scales of flow reattachment for airflow over dunes measured on Earth despite the differences in aeolian environment. Furthermore, ripples on dune flanks are shown to behave according to terrestrial models for ripple development on steep slopes. Compensating for these slope effects allows them to act as indicators of dune-modified and regional wind directions. Changes in ripple patterns and migration rates also signal the response of dunes and airflow during dune collisions. Collectively, we find that differences in ripple patterns connected to changes in migration rate provide information on airflow over and around dunes. This detailed assessment of ripple measurement and ripple migration rates advances the use of ripples on martian dunes and sand sheets to infer dune- and field-scale wind dynamics. These measurements also indicate that the low density atmosphere on Mars does not significantly modify the behavior of wind-topography interactions compared to Earth. Such observations provide targets for computational fluid dynamic and large-eddy simulation models seeking to reveal complex airflows across dune fields both on Earth and on Mars.

Elongation and migration of sand dunes

Geomorphology ◽

10.1016/s0169-555x(03)00161-2 ◽

2004 ◽

Vol 57 (3-4) ◽

pp. 293-302 ◽

Cited By ~ 79

Author(s):

Haim Tsoar ◽

Dan G. Blumberg ◽

Yoav Stoler

Keyword(s):

Sand Dunes ◽

Geomorphology, Stratigraphy, Chronology and Migration of Sand Dunes in Manitoba and Saskatchewan (62g, 72k)

10.4095/106339 ◽

1968 ◽

Author(s):

P P David

Keyword(s):

Sand Dunes ◽

Plant community predicts the distribution and occurrence of thick-billed grasswren subspecies (Amytornis modestus) in a region of parapatry

Australian Journal of Zoology ◽

10.1071/zo17081 ◽

2017 ◽

Vol 65 (4) ◽

pp. 273 ◽

Author(s):

Amy Lee Slender ◽

Marina Louter ◽

Michael G. Gardner ◽

Sonia Kleindorfer

Keyword(s):

Gene Flow ◽

Plant Species ◽

Plant Community ◽

Habitat Heterogeneity ◽

Sand Dunes ◽

Secondary Contact ◽

Ecological Barriers ◽

Dominant Plant Species ◽

Habitat Differences ◽

Habitat heterogeneity can have considerable effects on gene flow and migration across a region of parapatry. Describing habitat across a region of parapatry is important for the development of eco-evolutionary theory. Two subspecies of thick-billed grasswren (Amytornis modestus) share a region of parapatry between the South Australian salt lakes, Lake Eyre and Lake Torrens. While the two subspecies remain morphologically diverged outside the region of parapatry, it is not known what factors within the region of parapatry may affect migration and gene flow. In this study, we test associations between habitat differences and subspecies distributions and discuss whether ecological barriers could play a role in mitigating gene flow between the subspecies. We compare dominant plant species (1) between the allopatric ranges of the subspecies and within their region of parapatry, and (2) in relation to presence or absence of grasswrens within their region of parapatry. We found that the dominant plant species differed between grasswren subspecies in their allopatric range and in their region of parapatry, and also differed in the region of parapatry at sites with or without grasswrens. Specifically, grasswrens were absent in vegetation that is typical of sand dunes. These findings are discussed in light of evidence for secondary contact and hybridisation between A. m. indulkanna and A. m. raglessi, and susceptibility to introgression.

DUNE MIGRATION AND SAND TRANSPORT RATES IN TIDAL ESTUARIES: THE EXAMPLE OF THE RIVER ELBE

Coastal Engineering Proceedings ◽

10.9753/icce.v32.sediment.38 ◽

2011 ◽

Vol 1 (32) ◽

pp. 38

Author(s):

Anna Christina Zorndt ◽

Andreas Wurpts ◽

Torsten Schlurmann ◽

Nino Ohle ◽

Thomas Strotmann

Keyword(s):

Sand Dunes ◽

Offshore Structures ◽

Sand Transport ◽

Correlation Technique ◽

Data Set ◽

Migration Patterns ◽

River Elbe ◽

Tidal Estuaries ◽

Dune Migration ◽

Large parts of the tidal estuary of river Elbe (Germany) are characterized by regular patterns of sand dunes. They are presumed to evolve due to complex sand transport mechanisms and show multi-faceted migration patterns. Direction and magnitude of their migration are influenced by hydrodynamic boundary conditions such as river runoff and tides. Dune Migration can lead to residual sand transport rates, depending on its direction and magnitude and the dune’s characteristics. The understanding of dune migration patterns and associated sand transport is the basis of an effective sediment management as well as an important requirement for planning offshore structures. This study focuses on methods for computing migration and sand transport rates in automated ways. In a comparison and validation of different approaches, a cross-correlation technique was found to produce best results. From a unique data set of up to six annual bathymetrical multi-beam soundings between 1995 and 2010, dune characteristics and migration rates were processed and analysed autonomously. The findings show that in a long perspective, average dune migration and sand transport rates in the present study reach are directed upstream.

The Role of New-Emerging Lands on Sources of Aeolian Sand Deposits Driven by Shrinking of the Urmia Salt Lake

10.21203/rs.3.rs-1087192/v1 ◽

2021 ◽

Author(s):

Aliakbar Nazari Samani ◽

Leila Biabani ◽

Abolhassan Fathabadi ◽

Hassan Khosravi ◽

Robert James Wasson ◽

...

Keyword(s):

Salt Lake ◽

Sand Dunes ◽

Alluvial Fan ◽

Multivariate Statistical ◽

Dry Land ◽

Surface Samples ◽

Chemical Index ◽

Chemical Index Of Alteration ◽

Western Side ◽

Abstract Urmia Lake, the largest saline lake in Iran and the Middle East, is located in the northwest of Iran, has shrunk over the past decades. The reduced water level has increased the area of dry land around the lake allowing new environmental hazard such as sand dunes encroachment, particularly on the western side of the lake. There are five terrain types that could contribute sediment to the dunes, and it is the main aim of this research to identify the contributions to the dunes of each terrain type. Fifteen surface samples were collected from the five most erodible terrain types and eight samples were collected from the dunes both in downwind and upwind directions from the lake, and major element components were measured using X-ray fluorescence (XRF). According to the Besler classification, all samples are in the saline class. Also, the chemical index of alteration (CIA) values in all samples were less than 50, indicating weak weathering. Based on multivariate statistical analysis, suitable tracers were selected and were imported to the sourcing equations. Quantification of uncertainty and the creation of two new fingerprinting models for aeolian sediments based on both Bayesian and GLUE procedures were used. The highest proportion comes from the salty and puffy lands (44.2%) followed by salty polygon land (23.5%), clay-salty areas, puffy-flaky lands (7.01%), the terminus of the fine sandy alluvial fan (13.2%), and clay-salty abandoned lands (12.1%). It is concluded that if land managers use these results, they can more efficiently decrease the hazards posed by dune reactivation and migration though implementation of soil conservation on the affected lands around the dried lake.

SROVNÁVACÍ STUDIE POVRCHU KŘEMENNÝCH ZRN NA LOKALITÁCH JIŽNÍ A JIHOVÝCHODNÍ MORAVY

Geologické výzkumy na Moravě a ve Slezsku ◽

10.5817/gvms2016-1-2-29 ◽

2016 ◽

Vol 23 (1-2) ◽

Cited By ~ 2

Author(s):

Jana Šušolová ◽

Veronika Králová ◽

Roman Hadacz ◽

Peter Dundek ◽

Daniel Volařík

Keyword(s):

Sand Dunes ◽

Sedimentary Environment ◽

Small Collection ◽

Stereo Microscope ◽

Sandy Sediments ◽

South Moravia ◽

The Village ◽

Archeological Site ◽

Quartz Grains ◽

Archaeological Monument

Between 2013–2014, archeological researches at the Mikulčice site were performed. During these researches, necessity of a quartz grains surface study in the Moravian Sahara arose. There is a significant archaeological monument situated near the village of Mikulčice – a Slavic settlement, whose youngest bedrock is formed by fluvial sediments of extinct riverarms of the river Morava, and sand dunes composed of wind-blown sands of the Moravian Sahara. On these sand dunes, the most important churches and palaces of the settlement are found. The sandy sediments can reach up to 30 m thickness in the area of the Moravian Sahara.Samples of sandy sediments were taken from several locations of this site, and also from several other sites of south Moravia, which are sedimentary genetically different from the studied area. One sample of aeolian sand from the desert Rub-al Khali of Arabian Peninsula was provided for comparison.After gathering this small collection of sand grain samples, they were individually modified to the required study form and analyzed according to the demands of the method of exoscopy. At first, one hundred quartzgrains were separated from each sample of the collection using a stereo microscope. After that a detailed study and imaging with the scanning electronmicroscope (SEM) followed.The collection of sands from Mikulčice of the same genetical origin was compared to other samples of genetically known origin (fluvial, eolian...). The final comparison of all samples was performed by the method of multivariate analysis with NMDS. The results show that development of sediments at the archeological site Mikulčice most probably took place in very similar sedimentary environment. In this environment, the eolian transport and the fluvial transport with lower kinetic energy played important role.

Demonstration of Retinal Glycogen with Silver Methenamine

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100066875 ◽

1971 ◽

Vol 29 ◽

pp. 564-565

Author(s):

A. W. Sedar ◽

G. H. Bresnick

Keyword(s):

Lactic Acid ◽

Chromic Acid ◽

Periodic Acid ◽

Müller Cell ◽

External Limiting Membrane ◽

Electron Microscope Level ◽

Reactive Process ◽

Inner Limiting Membrane ◽

Muller Cell ◽

After experimetnal damage to the retina with a variety of procedures Müller cell hypertrophy and migration occurs. According to Kuwabara and others the reactive process in these injuries is evidenced by a marked increase in amount of glycogen in the Müller cells. These cells were considered originally supporting elements with fiber processes extending throughout the retina from inner limiting membrane to external limiting membrane, but are known now to have high lactic acid dehydrogenase activity and the ability to synthesize glycogen. Since the periodic acid-chromic acid-silver methenamine technique was shown to demonstrate glycogen at the electron microscope level, it was selected to react with glycogen in the fine processes of the Müller cell that ramify among the neural elements in various layers of the retina and demarcate these cells cytologically. The Rhesus monkey was chosen as an example of a well vascularized retina and the rabbit as an example of a avascular retina to explore the possibilities of the technique.

Structure and migration of planar defects in crystals observed in atomic scale

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100108568 ◽

1978 ◽

Vol 36 (1) ◽

pp. 284-285 ◽

Author(s):

H. Hashimoto ◽

Y. Sugimoto ◽

Y. Takai ◽

H. Endoh

Keyword(s):

Electron Microscope ◽

Rotation Angle ◽

Crystal Surface ◽

Electron Gun ◽

Atomic Scale ◽

Present Observation ◽

Twist Boundary ◽

Optical Magnification ◽

Zinc Crystal ◽

As was demonstrated by the present authors that atomic structure of simple crystal can be photographed by the conventional 100 kV electron microscope adjusted at “aberration free focus (AFF)” condition. In order to operate the microscope at AFF condition effectively, highly stabilized electron beams with small energy spread and small beam divergence are necessary. In the present observation, a 120 kV electron microscope with LaB6 electron gun was used. The most of the images were taken with the direct electron optical magnification of 1.3 million times and then magnified photographically.1. Twist boundary of ZnSFig. 1 is the image of wurtzite single crystal with twist boundary grown on the surface of zinc crystal by the reaction of sulphur vapour of 1540 Torr at 500°C. Crystal surface is parallel to (00.1) plane and electron beam is incident along the axis normal to the crystal surface. In the twist boundary there is a dislocation net work between two perfect crystals with a certain rotation angle.