نتایج جستجو برای: cross sand dunes
تعداد نتایج: 518686 فیلتر نتایج به سال:
S U M M A R Y The current research presents ground penetrating radar images up to 30m in depth of two large desert dunes in California, USA— a barchanoid ridge in the Dumont field and a linear dune in the Eureka expanse. The radar images show a complicated structure of internal layering with ascending cross-strata, cross-bedding and bounding surfaces cutting through layers. Additional research ...
In the present work, we use dune modeling in order to investigate the evolution of transverse dunes in the presence of vegetation. The vegetation is allowed to grow up to a maximum height Hmax with a growth rate R that oscillates in time. We find that the presence of the vegetation establishes a maximum height for the transverse dunes. If the transverse dune is larger than this maximum size, th...
The most recent Cassini RADAR images of Titan show widespread regions (up to 1500 kilometers by 200 kilometers) of near-parallel radar-dark linear features that appear to be seas of longitudinal dunes similar to those seen in the Namib desert on Earth. The Ku-band (2.17-centimeter wavelength) images show approximately 100-meter ridges consistent with duneforms and reveal flow interactions with ...
Sand-moving winds blowing from a constant direction in an area of high sand availability form transverse dunes, which have a fixed profile in the direction orthogonal to the wind. Here we show, by means of a linear stability analysis, that transverse dunes are intrinsically unstable. Any along-axis perturbation on a transverse dune amplify in the course of dune migration due to the combined eff...
Sand fields develop different patterns, such as sandbars, sand ridges, sand ripples, sand dunes, and river dunes. These vary in shape from crescent to ridge-like patterns. They are formed in areas such as deserts, lakes and seashores, where winds or fluid flows are strong and tend to blow from one direction or oscillate. There is a great deal of order in these patterns: perhaps a simple model c...
Bounding surfaces and interdune deposits provide keys for detailed interpretations of the development, shape, type, wavelength and angle of climb of aeolian bedforms, as well as overall sand sea conditions. Current alternate interpretations of bounding surfaces require very different, but testable models for sand sea deposition. Two perpendicular traverses of Jurassic Entrada Sandstone, Utah, r...
this study aimed to evaluate the potential of image ratioing techniques to detect and map the extent and particle composition of sand dunes in the erg of gavkhouni in isfahan province. the 6/4 ratio index and also a new index called sadi which was calculated using landsat band 3, 6 and 7 were applied to a georeferenced landsat tm image. to evaluate the performance of ratio techniques, the extra...
Introduction: The shapes produced on terrestrial surfaces that are continually subject to aeolian processes range in size from tiny ripples to giant draa [1]. The physical mechanism of the formation of ripples, the smallest of aeolian bedforms, is intimately related to saltation and reptation processes. Sand and granule ripples are typically tens of reptation path lengths wide and do not alter ...
Located just north of the Arctic Circle, the Great Kobuk Sand Dunes (GKSD) are an inland dune field that is closely surrounded by boreal forest. The history of the GKSD tells us about changes in aridity, a climatic parameter whose history is poorly understood at high latitudes. Vegetated dunes in several states of geomorphic preservation surround the active dune field today, evidencing a comple...
Germination cues reflect the conditions under which a species is likely to succeed in recruitment. Therefore, knowledge of the seed germination characteristics of key plant species in desertified areas is essential for restoration. The aims of this study were to evaluate the seed germination responses of seven native species, and to explore the implications for vegetation restoration. Seeds of ...
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