Sand dune
Also called: Dune · Topic: Landforms and their Evolution: Rivers, Groundwater, Glaciers, Waves and Wind · NCERT: Class 7, Ch 1 "Geographical Diversity of India"; Class 9, Ch 2 "Shaping of the Earth's Surface"; Class 11, Ch 6 "Landforms and their Evolution"
Meaning
A sand dune is a mound or ridge of sand piled up by the wind. It needs three things: plenty of sand, a steady wind, and an obstacle that slows the wind so the sand drops. Dunes form in hot, dry deserts and on sandy coasts. Most dunes keep shifting as the wind moves the sand, but some become fixed near settlements. Their shapes (barchan, seif, parabolic, longitudinal, transverse, star) depend on how much sand there is and how the wind blows.
Example
The Sam sand dunes near Jaisalmer in the Thar desert, Rajasthan, are well-known shifting dunes. Shelterbelts (rows of trees) are planted in Rajasthan to fix dunes and stop them moving.
Don't confuse with
- Loess: thick layers of fine, wind-blown silt (finer than sand) that cover land evenly, as on the Loess Plateau of China. It does not pile into dunes.