Hiekka-aavikko

Hiekkadyyni eräällä Saharan erg-alueella eli hiekkameressä Marokossa.

Hiekka-aavikko (arab. عرق‎, erg) eli hiekkameri, dyynimeri tai hiekkaerämaa on aavikko, jossa on vaihtelevan korkuisia tuulen kasaamia hiekkakumpuja, dyynejä. Hiekka on pääosin irtonaista ja siinä liikkuminen on hyvin vaikeaa.[1] Hiekka-aavikolla saattaa kasvaa joitakin ruohomättäitä ja pensaita dyynien harjalla.

Hiekka-aavikoilla esiintyy hiekkamyrskyjä. Monesti hiekka-aavikot ovat kuumuutensa ja kuivuutensa takia elämälle hyvin vihamielisiä ympäristöjä. Dyynit muistuttavat monesti vuorta tai suurta aaltoa, ja yleensä vaeltavat aikojen saatossa tuulen mukana. Dyynejä on eri kokoisia ja ne muodostavat enemmän tai vähemmän säännöllisen kuvion. Aavikoiden sisäosissa dyynit asettuvat yleensä vallitsevan tuulen suuntaisiksi, mutta aavikoiden reunoille syntyy kuunsirpin muotoisia barkaaneja, jotka asettuvat vallitsevaan tuuleen nähden poikittain. Rannikolla kasvillisuus voi aiheuttaa joko rantaviivan suuntaisia tai vallitsevaan tuuleen nähden poikittaisia dyynejä.[2]

Yleensä hiekka-aavikot ovat erittäin kuivia ja niissä ei ole pysyvää asutusta. Jos alueella on keitaita, aavikon poikki voi kulkea vakiintuneita matkareittejä.[3]

Saharasta 20 % on hiekka-aavikkoa ja 70 % sora-aavikkoa.[4]

Taklamakanin autiomaa, jossa kasvaa hiekan seassa ruohomättäitä harvakseltaan.

Maailman laajin hiekka-aavikko on Arabian aavikoihin kuuluva Rub al-Khali, 595 700 km2.[3] Pohjois-Afrikan Saharassa on monia suuria ergejä, muun muassa Itäinen iso erg, Läntinen iso erg, Majabat al-Koubra, Erg Chebbi, Erg Iguidi ja Erg Chech, jotka kattavat yhteensä noin 15–25 % Saharasta[5].

Saharan ergit

Bilma erg Nigerissä.

Suurimmat Saharan dyynikentät eli ergit:

Algeria
Tšad
Egypti
Libya
Mali
Mauritania
Marokko
Niger
Sudan

Lähteet

  1. ↑ Erg or Sand sea Encyclopedia Britannica
  2. ↑ Asko Lehtinen: Lapin dyynit (pdf) (s. 2–3) LuK-tutkielma. 1961. Geologian tutkimuskeskus, Arkisto. Viitattu 17.3.2013.
  3. ↑ a b Causes of Aridity, and Geography of the World’s Deserts University of Nevada, Las Vegas. Viitattu 17.3.2013. (englanniksi)
  4. ↑ Sahara Africa: Physical Geography. National Geographic. Viitattu 17.3.2013. (englanniksi)
  5. ↑ Spectrum, artikkeli Sahara ja Otavan suuri ensyklopedia, artikkeli Sahara

Kirjallisuutta

  • Swift, Jeremy: Sahara. Sarja: Maailman villi luonto/Time-Life-kirjat -sarja. WSOY 1982. ISBN 951-0-10936-3.

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