Dunes


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Dunes

 

sand reliefs formed by the wind.

Usually the term “dunes” is applied to all sand build-ups regardless of zonal and climatic conditions; in the USSR the term refers only to forms of nondesert sand relief: on the shores of seas and lakes, on river terraces, in morainic aprons, and so forth. In contrast to the barchans developed in deserts, dunes (in this sense) have a convex form on the steep side, not on the sloping side, and the “tails” are located behind the dunes, on the windward side. The sloping side faces upwind and has an angle of inclination of 8°-20°; the downwind side approaches the angle of repose of dry (32°-33°) or moist sand (up to 40°). Dunes range from 5 to 30 m high and more [on the Courland Spit in the Baltic Sea (in Lithuania) a dune 58 m high is known; in Les Landes, on the coast of the Bay of Biscay (in France) there is one 97 m high]. Dunes may shift in the direction of the prevailing wind at a speed of 10 m a year, depending on the weight of the sand and the wind velocity.

The evolution of nondesert dunes, with a prevailing wind direction, is expressed in the gradual transition from coastal or riverside dune banks, which as a rule are transverse to the wind, into staple-shaped, parabolic, and hairpin-shaped forms. Under seasonal winds directed at angles of less than 90°, spear-shaped dunes form. In areas with convective or interfering wind patterns, rounded, ridge-like dunes develop, with a scattering from the center toward the periphery. Moreover, with time simple shapes turn into complex ones. The movement of denuded dunes, which cause great harm to the economy, is being combatted by the planting of wooded vegetation (mostly pines).

B. A. FEDOROVICH

References in periodicals archive ?
As the storm moves north, those large waves are expected to erode and in some cases overwash sandy beaches and dunes that serve as protection for coastal communities.
Crescent-shaped dunes are the most common type on both Earth and Mars, according to the (https://pubs.
I--like most beach-goers--am conditioned to stay off the dunes, which are home to many plants and animals and protect the coast from storms.
The pursuit of national park status for the dunes first materialized in the 1920s out of concern about onsite gold mining operations in the area.
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A TEENAGER had to be airlifted to hospital with spinal injuries after jumping from a 10ft sand dune.
The document goes on to say that "There is evidence that the dunes have begun to re-establish through natural processes.
You finally reach the highest sand dunes in the area, and the only thought that crosses your mind is how the hell do these Bedouins know directions in this desert?
The research has found that the newly-created dunes pointed in directions dictated by two prevailing winds, which prevailed in the desert at different times of the year and the final orientation of each dune was a compromise between the two wind directions, their durations and their relative strengths.
Essentially very secluded and private, Dune Star Camp is yet within walking distance form the established Namib Desert Lodge.
The beaches and dunes in coastal areas become more vulnerable to damage during severe storms.
It's unclear why barchan dunes exist at all," says Pieter Vermeesch, a geologist at University College London.