A desert is a flat region of low dry sand which is formed by the slow flow of water or wind. Dunes usually occur in open spaces of low surface elevation surrounded by high cliffs. Dunes normally occur in a range of shapes from irregular to regular. The largest deserts, including the Sahara Desert, are usually found along flat ridges where the terrain becomes less steep as it moves towards the sea.
Sand dunes may also be called "slip surfaces" because they have a smooth flat underside and a gradually increasing slope (owing to the accumulation of sand). When seen from any direction, a flat sand surface appears as a curve rather than a straight edge. Dunes are typically found in areas where there is either a steep or sloping mountain side facing the wind and the prevailing winds blow from the east or the west. These conditions give rise to the occurrence of dune fields which can be used as an observation platform for studying the climate and other physical features of the area.
A dune consists of a flat area of often craggy terrain where the slope is not more than about 15 degrees, and the tide is usually washing in. Usually a thin wavy line is present to indicate the point of the dune, but a trench or a break in the soil around the dune may indicate the presence of fissures or gaps. Dune fields may be made from a wide variety of materials such as clay, sand, gravel, lichen or mosses. Usually, all these elements are tightly mixed together, though occasionally they may be different compositions.
Dune fields have their names derived from the type of soil they are found on or are likely to be found on (e.g., clay, sand). The dune field may also be named after the area in which it is found, i.e., "the Whittaker dune field". Most localities of dune fields are named by local people, but sometimes the county or state is known for the location. Dune fields are generally found in flat areas that receive little or no rainfall and are unlikely to hold vegetation. These fields are called flat and often have no vegetation in them, thus making them ideal places to carry out field research.
A dune can either be man-made or natural. Man-made dunes are those created by man for the sole purpose of living and working in close proximity to them. These usually have a face with a steep gradient, which marks its beginning and terminates. Such dunes are artificial because they need to withstand changing weather conditions and the pressure that is exerted on them due to the weight of the soil on them. Such surfaces are usually flat, and when they do not have vegetation on them, they are usually man-made.
Natural dune fields are those that are formed naturally by the deposition of clay, sand and silt over a period of time. They are generally flat, although some can have varying degrees of slope. Such natural surfaces are usually free from any plants and are suitable for field studies due to their flat nature. Since they are usually hard to study, they are usually found in places where there is little or no vegetation.