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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.
Dunes can likely be found in any environment where there is a substantial atmosphere, winds, and dust to be blown. Dunes are common on Mars and in the equatorial regions of Titan. Titan's dunes include large expanses with modal lengths of about 20–30 km. The regions are not topographically confined, resembling sand seas.
Various landforms are found in tropical deserts due to different kinds of eolian process. ... barchans, star dunes, shadow dunes, linear dunes and longitudinal dunes. [6]
Dunes take three general forms. Linear dunes, also called longitudinal dunes or seifs, are aligned in the direction of the prevailing winds. Transverse dunes, which include crescent dunes (barchans), are aligned perpendicular to the prevailing winds. More complex dunes, such as star dunes, form where the directions of the winds are highly variable.
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.
Around some sand dunes, researchers found 12 long-tailed lizards, the study said. They took a closer look and realized the animals were in fact a new species: Eremias pseudofasciata, or the false ...
They form through the lateral coalition of individual barchans and indicate increasing sand supply. Where sand is abundant, transverse dunes occur; they are commonly defined as long barchaoid ridges with fairly straight segments that are perpendicular to the wind direction. [17] The majority of dunes in Olympia Undae are transverse dunes.
On a nearby sand dune, researchers found 10 lizards with a unique pattern, the study said. They took a closer look and realized they’d captured a new species: Eremias graphica, or the ...