Dunes
Landforms of wind- or water-driven sand, from crescentic barchans to towering star dunes.
A dune is a landform composed of wind- or water-driven sand, typically taking the form of a mound, ridge, or hill. An area with dunes is called a dune system or dune complex; a large dune complex is a dune field, while broad, flat regions covered with wind-swept sand or dunes with little vegetation are called ergs or sand seas. Dunes occur in different shapes and sizes, with most kinds longer on the stoss (upflow) side and having a shorter slip face on the lee side. The valley between dunes is called a dune slack.
Quick Facts
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Lore & Background
Dunes are most common in desert environments, where lack of moisture hinders vegetation growth, but they also occur along sea shores, streams in semiarid climates, areas of glacial outwash, and where poorly cemented sandstone bedrock disintegrates. Subaqueous dunes can form from water flow on sand or gravel beds of rivers, estuaries, and the sea-bed. Some coastal areas have sets of dunes parallel to the shoreline, important for protecting land against storm waves. Artificial dunes are sometimes constructed for coastal protection. Dune drift can have serious consequences; for example, the town of Eucla, Western Australia, had to be relocated in the 1890s because of dune drift.
Reader's Guide
Five basic dune types are recognized: crescentic (barchan), linear (seif), star, dome, and parabolic. Barchan dunes are crescent-shaped, wider than long, with lee-side slipfaces on the concave side, forming under unimodal winds. Transverse dunes lie across the wind direction. Seif dunes are linear with two slip faces, associated with bidirectional winds, and can be over 160 km long. Star dunes are pyramidal with slipfaces on three or more arms, growing upward rather than laterally. Dome dunes are circular to oval with no slip face; mega-domes can reach 150 m in height. Parabolic dunes are U-shaped with convex noses and elongated arms, often occurring in semiarid areas. Lunettes are fixed crescentic dunes on leeward margins of playas and river valleys.
Did You Know?
- The modern word 'dune' came into English from French around 1790, which came from Middle Dutch dūne.
- Dunes are generally defined as greater than 7 cm tall; ripples are less than 3 cm tall.
- The largest crescentic dunes on Earth, with mean crest-to-crest widths of more than three kilometres, are in China's Taklamakan Desert.
- Seif dunes in the Rub' al Khali (Empty Quarter) can reach heights of over 300 m and stretch for almost 200 km.
- Star dunes in the Badain Jaran Desert of China are up to 500 metres tall and may be the tallest dunes outside South America.
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