Dune

Erg Chebbi, Morocco

In physical geography, a dune is a hill of loose sand built by aeolian processes (wind) or the flow of water.[1] Dunes occur in different shapes and sizes, formed by interaction with the flow of air or water. Most kinds of dunes are longer on the stoss (upflow) side, where the sand is pushed up the dune, and have a shorter "slip face" in the lee side. The valley or trough between dunes is called a slack. A "dune field" or erg is an area covered by extensive dunes.

Dunes occur in some deserts and along some coasts. Some coastal areas have one or more sets of dunes running parallel to the shoreline directly inland from the beach. In most cases, the dunes are important in protecting the land against potential ravages by storm waves from the sea. Although the most widely distributed dunes are those associated with coastal regions, the largest complexes of dunes are found inland in dry regions and associated with ancient lake or sea beds. Dunes can form under the action of water flow (fluvial processes), and on sand or gravel beds of rivers, estuaries and the sea-bed.

The modern word "dune" came into English from French c. 1790,[2] which in turn came from Middle Dutch dūne.[1]

Formation

Sand hitting sand is more likely to stick; sand hitting a more coherent surface is more likely to bounce (saltation). This exacerbating feedback loop helps sand accumulate into dunes.

Dunes are made of sand; the sand may be quartz, calcium carbonate, snow, gypsum, or other materials. The upwind/upstream/upcurrent side of the dune is called the stoss side; the downflow side is called the lee side. Sand is pushed (creep) or bounces (saltation) up the stoss side, and slides down the lee side. A side of a dune that the sand has slid down is called a slip face.

The Bagnold formula gives the speed at which particles can be transported.

Other Languages
Afrikaans: Duin
العربية: كثيب
asturianu: Duna
azərbaycanca: Dyun
Bân-lâm-gú: Soa-lūn
беларуская: Дзюна
български: Дюна
Boarisch: Düne
brezhoneg: Tevenn
català: Duna
Cebuano: Dunes
čeština: Duna
dansk: Klit
Deutsch: Düne
eesti: Luide
Ελληνικά: Θίνα
español: Duna
Esperanto: Duno
euskara: Duna
français: Dune
Frysk: Dún
galego: Duna
한국어: 사구
Հայերեն: Դյուներ
hrvatski: Pješčana dina
Ido: Duno
íslenska: Sandalda
italiano: Duna
ქართული: დიუნა
Kiswahili: Tuta la mchanga
Kreyòl ayisyen: Din
Кыргызча: Дюна
Latina: Thinium
latviešu: Kāpa
lietuvių: Kopa
magyar: Dűne
македонски: Дина
Bahasa Melayu: Gumuk
Nederlands: Duin
日本語: 砂丘
Nordfriisk: Düner
norsk: Sanddyne
norsk nynorsk: Sanddyne
Nouormand: Mielle
occitan: Duna
oʻzbekcha/ўзбекча: Dyuna
Picard: Cro
Plattdüütsch: Düün
polski: Wydma
português: Duna
română: Dună
русский: Дюна
Scots: Dune
shqip: Duna
sicilianu: Muntarozzu
සිංහල: වැලි කඳු
Simple English: Dune
slovenčina: Piesočná duna
slovenščina: Sipina
српски / srpski: Дина (рељеф)
srpskohrvatski / српскохрватски: Dina
suomi: Dyyni
svenska: Sanddyn
Türkçe: Kumul
українська: Дюни
Tiếng Việt: Đụn cát
West-Vlams: Dune
粵語: 沙丘
Zeêuws: Kliengen
中文: 沙丘