Erg (ƙasa)

erg (har ma tekun yashi ko tekun dune, ko yashi idan ba shi da dunƙulewa) wani yanki ne mai faɗi, lebur na hamada wanda ke cike da yashi mai ɗauke da iska mai ɗanɗano ko ba shi da murfin ciyayi Kalmar ta samo asali ne daga kalmar larabci ʿirq (عرق), ma'ana "filin dune A taƙaice, an ayyana erg a matsayin yanki mai hamada wanda ya ƙunshi fiye da murabba'in kilomita 125 (48 sq mi) na yashi aeolian ko iska kuma inda yashi ke rufe sama da kashi 20% na saman. Ana kiran ƙananan yankuna da "filayen dune". Hamada mai zafi mafi girma a duniya, Sahara, ya kai murabba'in kilomita miliyan 9 (3.5×106 sq mi) kuma ya ƙunshi ergs da yawa, kamar Chech Erg da Issaouane Erg a Aljeriya. Kimanin kashi 85% na duk yashin wayar tafi da gidanka ana samun su a cikin ergs wanda ya fi murabba'in kilomita 32,000 (12,355 sq mi), mafi girma shine Rub' al Khali, Kwata maras amfani na yankin Larabawa. Ana kuma samun Ergs akan wasu jikunan sama, irin su Venus, Mars, da Saturn's moon Titan.

## Yanayin ƙasa

Tekun yashi da filayen dune yawanci suna faruwa a yankunan da ke ƙarƙashin iska na tushen ruwa mai yawa, yashi mai laushi, kamar busassun kogi da Deltas, Filayen ambaliyar ruwa, filayen wankewar glacial, tabkuna masu bushewa, da rairayin bakin teku. Ergs suna mai da hankali ne a cikin manyan bel biyu tsakanin 20 ° zuwa 40 ° N da 20 ° zuwa latitudes 40 ° S, wanda ya haɗa da yankunan da busassun iska, iska mai raguwa ta iskar kasuwanci ta haye. Ayyukan ergs suna iyakance ga yankunan da ke karɓar, a matsakaita, ba fiye da 150 mm na ruwan sama na shekara-shekara ba. Mafi girma suna a arewa da kudanci Afirka, tsakiya da yamma Asiya, da Tsakiyar Ostiraliya. &nbsp;

A Kudancin Amurka, tsaunukan Andes sun iyakance ergs, amma suna dauke da manyan dunes a bakin tekun Peru da arewa maso yammacin Argentina. Ana kuma samun su a sassa da yawa na gabar arewa maso gabashin Brazil. Abinda ke aiki kawai a Arewacin Amurka yana cikin Gran Desierto de Altar wanda ya kai daga Sonora Desert a arewa maso yammacin Mexico na Sonora zuwa Yuma Desert na Arizona da Algodons Dunes na kudu maso gabashin California. Wani erg wanda aka gyara ta hanyar ciyayi ya samar da Nebraska Sandhills.

## Bayyanawa

Kusan dukkanin manyan ergs suna cikin iska daga gadajen kogi a yankunan da suka bushe sosai don tallafawa murfin kayan lambu mai yawa kuma saboda haka suna ƙarƙashin lalacewar iska mai tsawo. Yashi daga waɗannan maɓuɓɓugar ruwa masu yawa yana ƙaura zuwa iska kuma yana gina cikin manyan dunes inda motsi ya tsaya ko raguwa ta hanyar shingen ƙasa ga iska ko ta hanyar haɗuwa da iska. 

Dukan ergs da filayen dune suna ƙaura zuwa iska har zuwa daruruwan kilomita daga tushen yashi. Irin wannan tarawa yana buƙatar dogon lokaci. Akalla ana buƙatar shekaru miliyan ɗaya don gina ergs tare da manyan dunes, kamar waɗanda ke kan Yankin Larabawa, a Arewacin Afirka, da kuma tsakiyar Asiya. Tekun yashi waɗanda suka tara a cikin raguwar tsarin tsari da taswirar ƙasa, kamar Murzuk Sand Sea na Libya, na iya kaiwa babban kauri (fiye da 1000 m ) amma wasu, kamar ergs na dunes na layi a cikin Simpson Desert da Great Sandy Desert na Ostiraliya, bazai fi kauri fiye da dunes da aka ɗora a kan fili. A cikin teku na yashi a cikin wani yanki, dunes suna da nau'i ɗaya. Misali, akwai ergs ko filayen dunes na layi, na dunes na crescentic, na duns na taurari, da na dunes masu juyawa, kuma waɗannan jerin dunes suna da daidaitattun daidaito da girma.&nbsp;

Ta hanyar halitta, ergs suna da ƙwazo sosai. Ƙananan dunes suna samuwa kuma suna ƙaura tare da gefen manyan dunes da tsaunuka. ruwan sama na lokaci-lokaci yana cika wuraren da dunes suka kafa; yayin da ruwa ke narkewa, ana barin gishiri a baya.

dunes guda ɗaya a cikin ergs yawanci suna da faɗi, tsayi, ko duka biyun girma sama da mita 500 (1,600 ft).[1] Dukansu girman murfin yashinsu da sarƙaƙƙiya da girman dunes ɗinsu sun bambanta ergs da filayen dune. Zurfin yashi a cikin ergs ya bambanta a ko'ina cikin duniya, kama daga zurfin santimita kaɗan kawai a cikin Selima Sand Sheet na Kudancin Masar, zuwa kusan mita 1 (3.3 ft) a cikin Hamadar Simpson, da mita 21-43 (69-141 ft) a cikin Sahara. Wannan ya yi zurfi sosai fiye da ergs a zamanin kafin tarihi. Shaida a cikin bayanan ƙasa sun nuna cewa wasu ergs Mesozoic da Paleozoic sun kai zurfin mita ɗari da yawa.

## Ergs na waje

Ergs fasalin yanayi ƙasa ne wanda za'a iya samunsa a kan taurari inda yanayi mai iya haifar da mummunar lalacewar iska ke aiki a saman na tsawon lokaci, samar da yashi kuma yana ba da damar tarawa. A yau akalla abubuwa uku a cikin Tsarin hasken rana, ban da Duniya, an san su da siffofi a farfajiyarsu: Venus, Mars da Titan.

### Venus
At least two ergs have been recognized by the Magellan probe on Venus: the Aglaonice dune field, which covers approximately , and the Meshkenet dune field (~). These seem to be mostly transverse dune fields (with dune crests perpendicular to prevailing winds).

### Mars
Mars yana nuna manyan ergs, musamman kusa da polar caps, inda dunes zasu iya kaiwa girman gaske. Ergs a kan Mars na iya nuna siffofi da alamu masu ban mamaki, saboda hulɗa mai rikitarwa tare da ƙasa da kuma hanyar iska.

### Titan
Hotunan Radar da jirgin saman *Cassini* ya  yayin da Titan ya tashi a watan Oktoba na shekara ta 2 suna nuna dunes na yashi a ma'aunin Titan kamar waɗanda ke cikin hamada na Duniya. An lura da erg guda ɗaya ya wuce kilomita 930 (1,500) tsawo. Dunes sune mafi girman yanayin ƙasa a kan Titan. Kimanin kashi 15-20% na farfajiyar an rufe ta da ergs tare da kimanin jimlar yanki na kilomita miliyan 12-18 wanda ya sa ya zama mafi girman filin dune a cikin tsarin hasken rana da aka gano har zuwa yau.

An yi imanin cewa yashi ya samo asali ne daga iska da aka samar sakamakon karfin ruwa daga Saturn a kan yanayin Titan. Hotunan shaida ne cewa an gina waɗannan dunes daga iskõki da ke hurawa a wata hanya kafin su sauya zuwa wata sannan su koma zuwa hanya ta farko da sauransu, suna haifar da dunes na yashi su gina a cikin layi mai tsawo. Wadannan iskõki masu tasowa tare da iskar yamma zuwa gabas ta Titan suna haifar da dunes da suka daidaita daga yamma zuwa gaba kusan ko'ina sai dai kusa da duwatsu, wanda ke canza hanyar iska.

Yashi a kan Titan na iya zama lokacin da ruwa methane ya yi ruwan sama kuma ya rushe dutsen kankara, mai yiwuwa a cikin hanyar ambaliyar ruwa. A madadin haka, yashi na iya fitowa daga kwayoyin halitta da aka samar ta hanyar halayen photochemical a cikin yanayin Titan.

## Manazarta