erg

Issaouane Erg, Algeria Linear Dunes, Namib Sand Sea

An erg (also sand sea or dune sea, or sand sheet if it lacks dunes) is a broad, flat area of desert covered with wind-swept sand with little or no vegetative cover. The word is derived from the Arabic word ʿirq (عرق), meaning 'dune field'. Strictly speaking, an erg is defined as a desert area that contains more than 125 km (48 sq mi) of aeolian or wind-blown sand and where sand covers more than 20% of the surface. Smaller areas are known as "dune fields". The largest hot desert in the world, the Sahara, covers 9 million square kilometres (3.5×10^ sq mi) and contains the largest amount of ergs, including many large ergs such as the Chech Erg and the Issaouane Erg in Algeria. Approximately 85% of all the Earth's mobile sand is found in ergs that are greater than 32,000 km (12,355 sq mi), the largest being the Rub' al Khali, the Empty Quarter of the Arabian Peninsula. Ergs are also found on other celestial bodies, such as Venus, Mars, and Saturn's moon Titan.