Wanderlust World Wanderlust World In desert geography, vast expanses of wind-blown sand are called ergs (also known as sand seas). The term originates from Arabic 'arq, meaning "dune field," and describes regions where sand covers more than 125 square kilometers with dunes comprising over 20% of the surface.
Desert sand consists primarily of quartz grains (silicon dioxide), which resist weathering better than other minerals. Over millennia, wind erodes rocks into fine particles, then sorts and transports them into dune fields. The Sahara contains the world's largest ergs, including the Grand Erg Oriental and Grand Erg Occidental.
Not all deserts are sandy—only about 20% of Earth's desert surfaces are ergs. The rest comprise reg (stony plains), hamada (rocky plateaus), dry lake beds, and mountains. Erg dunes take various forms—barchan (crescent), star, linear, and transverse—shaped by prevailing wind patterns and sand supply.