This Dunes Essay example is published for educational and informational purposes only. If you need a custom essay or research paper on this topic, please use our writing services. EssayEmpire.com offers reliable custom essay writing services that can help you to receive high grades and impress your professors with the quality of each essay or research paper you hand in.
Dunes are piles of granular material that have been deposited by wind and water into hills or long ridges. Dune formation begins with a process called saltation, in which the flow of sand across the desert floor is interrupted by an obstacle that blocks the sand’s movement. It then begins to accumulate and eventually to form a hill. The heights of dunes may be shallow, or they may grow up to 500-600 feet (150-180 meters). Most dunes are sand, but white gypsum dunes are found in southern New Mexico’s Tularosa Valley at White Sands National Monument. Rarely, dunes may be composed of tephra, shell fragments, or heavy minerals such as magnetite.
Dunes are sculpted by the winds into different kinds of shapes. Transverse linear dunes are formed from moderate winds that push the lighter material to form ripples perpendicular to the direction of the wind. Strong, steady winds form longitudinal (seifs) dunes. The abrasive winds gouge deep troughs in the desert floor. Sand is then deposited in parallel lines on either side of the troughs. If there are slight wind variations, then the tops of the dunes are formed into a wavy appearance. Crescent-shaped barchan dunes are formed into an arc by a constant wind moving faster around the ends of the dune than over its windward top. The horns of the crescent are downwind. In contrast, parabolic crescent dunes have horns that face into the wind. They are held in place by vegetation, so the wind scoops out the center of the dune to form the crescent shape. Star dunes are formed when shifting winds create arms as the sands radiate outward from the stable center of the dune. Whaleback dunes are very large longitudinal dunes.
Dunes occur along ocean shores or on islands. They may also be found on the shores of large lakes, such as the dunes at the southern end of Lake Michigan. Many of the dunes in the sand seas of the Sahara and the Arabian deserts (Rub’ al-Khali or Empty Quarter) are active, “traveling” dunes. The wind pushes the sand so it moves across the desert to swallow everything that stands in its way, including towns and oases. Dunes that are fixed by vegetation are inactive. Destruction of fixed coastal dunes causes beach erosion and opens areas to flooding during storms. Some dunes give off noises as the sand in the dune shifts from place to place, and are sometimes called singing dunes. Great sand dunes occur in Australia, the Atacama Desert, Baja Mexico, and Cape Cod (Massachusetts). The ocean fog supplies the Namibian coastal desert with enough moisture to sustain 100 species in the rainless dunes. Fossilized dunes have been found in a number of places such as the Permo-Trias.
Bibliography:
- Dennis Albert, Borne of the Wind: Michigan Sand Dunes (University of Michigan Press, 2006);
- A. Bagnold, The Physics of Blowing Sand and Desert Dunes (Dover Publications, 2005);
- Bill and Karl F. Nordstrom, eds., Coastal Dunes: Form and Process (John Wylie and Sons, 1999).
See also:
ORDER HIGH QUALITY CUSTOM PAPER
Always on-time
Plagiarism-Free
100% Confidentiality
Special offer!
