Grand Erg Occidental Grand Erg Occidental The Grand Erg Occidental (, al-ʿIrq al-Gharbī al-Kabīr), (also known as the Western Sand Sea) is the second largest erg in northern Algeria after the Grand Erg Oriental. It covers an area of approximately . The sand dunes in the erg are formed by the wind, and can be up to high. Certain crescent-shaped dunes, known as barchans, are actually mobile; the wind can push these dunes as much as 20 to 30 m (65-100 ft) in one year. It is a desert natural region that receives less than 50 mm (1,96 in) of rainfall per year.
Erg Erg The erg is a unit of energy and work equal to 10 joules. It originated in the centimetre–gram–second (CGS) system of units. It has the symbol "erg". The erg is not an SI unit. Its name is derived from "ergon" (ἔργον), a Greek word meaning "work" or "task". An erg is the amount of work done by a force of one dyne exerted for a distance of one centimeter. In the CGS base units, it is equal to one gram centimeter-squared per second-squared (g·cm/s). It is thus equal to 10 joules or 100 nanojoules (nJ) in SI units. An