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These dunes are interpreted to be longitudinal dunes whose crests are oriented parallel to the dominant wind direction, which generally indicates west-to-east wind flow. The sand is likely composed of hydrocarbon particles, possibly with some water ice mixed in. [ 77 ]
Dune collisions [5] [6] and changes in wind direction spawn new barchans from the horns of the old ones and govern the size distribution of a given field. [7] As barchan dunes migrate, smaller dunes outpace larger dunes, catching-up the rear of the larger dune and eventually appear to punch through the large dune to appear on the other side.
Transverse dunes occur in areas dominated by a single direction of the prevailing wind. In areas where sand is not abundant, transverse dunes take the form of barchans or crescent dunes. These are not common, but they are highly recognizable, with a distinctive crescent shape with the tips of the crescent directed downwind.
They are oriented perpendicular to the wind in order to be most effective. [30] In regions with minimal vegetation, such as coastal and desert areas, transverse sand dunes orient themselves perpendicular to the prevailing wind direction, while longitudinal dunes orient themselves parallel to the prevailing winds. [31]
Barchans or crescent dunes are produced by wind acting on desert sand; the two horns of the crescent and the slip face point downwind. Sand blows over the upwind face, which stands at about 15 degrees from the horizontal, and falls onto the slip face, where it accumulates up to the angle of repose of the sand, which is about 35 degrees.
The dunes are believed to be remnants of a massive lake, Laka Alamosa, that dried up roughly 440,000 years ago, according to the park’s website.Over time, the park says wind, water and sediment ...
Dunes: A dune is a large pile of wind-blown material, typically sand or snow. As the pile accumulates, its larger surface area increases the rate of deposition in a positive feedback loop until the dune collapses under its own weight. This process causes dunes to move in the direction of the wind over time. [6] [7] Death Valley Mesquite Flats ...
Many inland eolian dunes are present in North America, including vegetated (stabilized) eolian dunes of the U.S. Atlantic Coastal Plain, dunes of Laurentian Great Lakes region, dunes of the Central and Southern Great Plains, the Nebraska Sand Hills, White Sands (New Mexico), Great Sand Dunes (Colorado), dunes of the southern Colorado Plateau, and dune fields of the Southwest Deserts.