Nebkha or nabkha with prosopis glandulosa

A nabkha, nebkha or nebka is a type of sand dune. Other terms used include coppice dune and dune hummock or hummocky dune, but these more accurately refer to similar, but different, sand dune types.Langford, R. P. (2000)
Nabkha (coppice dune) fields of south-central New Mexico, USA.
''Journal of Arid Environments'' 46(1) 25-41. Authors have also used the terms phytogenic hillock,El-Sheikh, M. A., et al. (2010)
Vegetation ecology of phytogenic hillocks (nabkhas) in coastal habitats of Jal Az-Zor National Park, Kuwait: Role of patches and edaphic factors.
''Flora'' 205(12) 832-40. bush-mound, shrub-coppice dune, knob dune, dune tumulus, rebdou, nebbe, and takouit.Khalaf, F. I., et al. (1995)
Sedimentological and morphological characteristics of some nabkha deposits in the northern coastal plain of Kuwait, Arabia.
''Journal of Arid Environments'' 29(3) 267-92. In simplest terms, a nabkha is a sand dune that forms around vegetation. It is an aeolian landform, a structure built and shaped by the action of

wind Wind is the natural movement of atmosphere of Earth, air or other gases relative to a planetary surface, planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heatin ...

. Nabkhas are common and occur in many regions. Well known nabkha fields occur in the Lut Desert of

Iran Iran, officially the Islamic Republic of Iran (IRI) and also known as Persia, is a country in West Asia. It borders Iraq to the west, Turkey, Azerbaijan, and Armenia to the northwest, the Caspian Sea to the north, Turkmenistan to the nort ...

, Arabian Desert of

Kuwait Kuwait, officially the State of Kuwait, is a country in West Asia and the geopolitical region known as the Middle East. It is situated in the northern edge of the Arabian Peninsula at the head of the Persian Gulf, bordering Iraq to Iraq–Kuwait ...

, the Hotan River Basin in

Xinjiang Xinjiang,; , SASM/GNC romanization, SASM/GNC: Chinese postal romanization, previously romanized as Sinkiang, officially the Xinjiang Uygur Autonomous Region (XUAR), is an Autonomous regions of China, autonomous region of the China, People' ...

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

,Wu, S., et al. (2008)
The morphological characteristics and growth mode of nabkha in the basin of Hotan River, Xinjiang.
''Geographical Research'' 27(2) 314-22. and

New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...

in the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

and adjacent Chihuahua in

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

Structure

Many species of sand-dwelling plants form nabkhas. In the Chihuahuan Desert they include soaptree (''Yucca elata''), creosote (''Larrea tridentata''), and

atriplex ''Atriplex'' () is a plant genus of about 250 species, known by the common names of saltbush and orache (; also spelled orach). It belongs to the subfamily Chenopodioideae of the family Amaranthaceae ''s.l.''. The genus is quite variable and ...

(''Atriplex'' spp.). In China nabkhas form quite often around ''

Caragana microphylla ''Caragana'' is a genus of about 80–100 species of flowering plants in the family Fabaceae, native to Asia and eastern Europe. They are shrubs or small trees growing tall. They have even-pinnate leaves with small leaflets, and solitary or cl ...

'', as well as '' Cleistogenes squarrosa'', '' Leymus chinensis'', '' Caragana stenophylla'', '' Stipa grandis'', and '' S. glareosa'',Wang, X., et al. (2006)
Nebkha development and its significance to wind erosion and land degradation in semi-arid northern China.
''Journal of Arid Environments'' 65 129-41. plus tamarisks, reeds, and alhagi.Li, Z., et al. (2010
Bio-geomorphologic features and growth process of ''Tamarix'' nabkhas in Hotan River Basin, Xinjiang.
''Journal of Geographical Sciences'' 20(2) 205-18. In Jal Az-Zor National Park in Kuwait, they occur around '' Nitraria retusa'', '' Zygophyllum qatarense'', '' Haloxylon salicornicum'', and ''

Panicum turgidum ''Panicum turgidum'' is an old world clumping desert bunchgrass of the genus '' Panicum''. It is a plant of arid regions across Africa and Asia, and has been introduced to other parts of the world. Description ''Panicum turgidum'' is a perenni ...

''.

Halophyte A halophyte is a salt-tolerant plant that grows in soil or waters of high salinity, coming into contact with saline water through its roots or by salt spray, such as in saline semi-deserts, mangrove swamps, marshes and sloughs, and seashores. ...

s such as '' Tamarix aucheriana'', '' Halocnemum strobilaceum'' and '' Salicornia europaea'' have nabkhas in saline soils, while '' Cyperus conglomeratus'', '' Rhanterium epapposum'', '' Astragalus spinosus'', '' Lycium shawii'', and '' Citrulus colocynthis'' are seen in non-saline zones.Al-Dousari, A. M., et al. (2008)
Characteristics of nabkhas in relation to dominant perennial plant species in Kuwait.
''Kuwait Journal of Science'' 35(1). On the

Sinai Peninsula The Sinai Peninsula, or simply Sinai ( ; ; ; ), is a peninsula in Egypt, and the only part of the country located in Asia. It is between the Mediterranean Sea to the north and the Red Sea to the south, and is a land bridge between Asia and Afri ...

Egypt Egypt ( , ), officially the Arab Republic of Egypt, is a country spanning the Northeast Africa, northeast corner of Africa and Western Asia, southwest corner of Asia via the Sinai Peninsula. It is bordered by the Mediterranean Sea to northe ...

they are recorded on '' Artemisia monosperma'', '' Moltkiopsis ciliata'', '' Calligonum polygonoides'', '' Stipagrostis scoparia'', and '' Retama raetam''.El‐Bana, M. I., et al. (2007)
Role of host identity in effects of phytogenic mounds on plant assemblages and species richness on coastal arid dunes.
''Journal of Vegetation Science'' 18(5) 635-44. In central Asia and surrounding areas they occur on '' Calotropis'', '' Ziziphus'', '' Salvadora'', and '' Heliotropium'' species.Cooke, R. U., et al. ''Desert Geomorphology''. Taylor & Francis. 1993. pg. 357. A nabkha is variable in size and shape. The typical example is a steep mound with a flat top. The larger nabkhas of the Chihuahuan Desert reach about 4.3 meters tall by 40 meters wide. The largest known were 10 meters tallMilich, L
Dunes.
Arid Lands Resource Sciences. The University of Arizona. Tucson. 1998. and a kilometer long; these large dunes have been called mega-nabkhas. Mega-nabkhas in various places have also been called precipitation ridges, bordering dune ridges, and in Dutch, ''randwallen''. Sometimes only the tips of the branches of the plant within protrude from the sand, and sometimes the plant is completely engulfed.Saqqa, W. and M. Atallah. (2004)
Characterization of the aeolian terrain facies in Wadi Araba Desert, southwestern Jordan.
''Geomorphology'' 62(1) 63-87. Nabkhas may join together and form broad, hilly dune fields, or more often, chains and scattered dune patches. The sand composition is also variable.

Silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension (chemistry), suspension with water. Silt usually ...

and

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...

pellets can be part of the dune. Nabkhas in the Namib Desert are rich in

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

. On the Kuwaiti coastline nabkhas form around ''Nitraria retusa'' growing on sabkhas, a form of salt pan. These dunes are composed of

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

, gypsum, and

feldspar Feldspar ( ; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagiocl ...

sands mixed with bits of

volcanic rock Volcanic rocks (often shortened to volcanics in scientific contexts) are rocks formed from lava erupted from a volcano. Like all rock types, the concept of volcanic rock is artificial, and in nature volcanic rocks grade into hypabyssal and me ...

and

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

grains. Fragments of

mollusc Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

shell and oolites can be found. Traces of

garnet Garnets () are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. Garnet minerals, while sharing similar physical and crystallographic properties, exhibit a wide range of chemical compositions, de ...

, zircon, topaz, and

tourmaline Tourmaline ( ) is a crystalline silicate mineral, silicate mineral group in which boron is chemical compound, compounded with chemical element, elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. This gemstone comes in a ...

occur. Dolomite is common. Coastal nabkhas can be eroded by saltwater, and even washed away completely, leaving the plant behind. The type of plant influences the shape of the nabkha; for example, treasure flower (''Gazania rigens'') forms tall, conical or elongated dunes, while beach daisy (''Arctotheca populifolia'') forms shorter, semi-circular dunes.Hesp, P. and A. McLachlan. (2000)
Morphology, dynamics, ecology and fauna of ''Arctotheca populifolia'' and ''Gazania rigens'' nabkha dunes.
''Journal of Arid Environments'' 44(2) 155-72. ''Retama raetam'' is a

salinity Salinity () is the saltiness or amount of salt (chemistry), salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensio ...

-tolerant woody

shrub A shrub or bush is a small to medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from trees by their multiple ...

that can extend roots up to 20 meters deep in the soil, persisting through harsh conditions and eventually building nabkhas up to 8 meters wide. A plant generally cannot hold enough sand to start a nabkha until it is at least 10 centimeters tall.Mares, M. A. ''Encyclopedia of Deserts''. University of Oklahoma Press. 1999. pg. 189.Ahmed, M. M., et al. (2009)
Chemical and morphological characteristics of phytogenic mounds (nabkhas) in Kuwait.
''Arab Gulf Journal of Scientific Research'' 27(3) 114-26. Some sources describe nabkhas as ephemeral features of the landscape, but other research shows that they may last longer than previously thought. Some last over 100 years. Still, a nabkha on an annual plant generally only lasts one season. A nabkha can also be self-limiting if the sand accumulation lifts the plant far enough out of the

water table The water table is the upper surface of the phreatic zone or zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with groundwater, which may be fresh, saline, or brackish, depending on the loc ...

that it dies.

Ecology

Nabkhas are common features in landscapes that are undergoing

desertification Desertification is a type of gradual land degradation of Soil fertility, fertile land into arid desert due to a combination of natural processes and human activities. The immediate cause of desertification is the loss of most vegetation. This i ...

. In North America, a characteristic sign of desertification is the spread of mesquites (''Prosopis'' spp.) into the habitat. Mesquites rapidly accumulate windblown sand, forming nabkhas. In northern China, nabkhas were present on

grassland A grassland is an area where the vegetation is dominance (ecology), dominated by grasses (Poaceae). However, sedge (Cyperaceae) and rush (Juncaceae) can also be found along with variable proportions of legumes such as clover, and other Herbaceo ...

s before they were converted to agriculture, but this conversion accelerated their development and they are a common feature of abandoned farm fields in the region. They are indicators of soil

erosion Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...

there. Nabkhas develop their own

ecosystem An ecosystem (or ecological system) is a system formed by Organism, organisms in interaction with their Biophysical environment, environment. The Biotic material, biotic and abiotic components are linked together through nutrient cycles and en ...

s. They are home to a variety of animals, including many invertebrates such as

nematode The nematodes ( or ; ; ), roundworms or eelworms constitute the phylum Nematoda. Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitic. Parasitic worms (h ...

s and the sand flea '' Talochestria capensis''. The dune tends to have more organic material than the surrounding sand, as windblown plant matter accumulates in it and the roots of the plant penetrate it. In degraded and oil- polluted desert areas in Kuwait, plants with nabkhas act as ecosystem engineers, hosting a sheltered site with layers of relatively rich soil in which other plants can grow. Nabkhas on

nitrogen-fixing Nitrogen fixation is a chemical process by which molecular dinitrogen () is converted into ammonia (). It occurs both biologically and abiological nitrogen fixation, abiologically in chemical industry, chemical industries. Biological nitrogen ...

plants like

legume Legumes are plants in the pea family Fabaceae (or Leguminosae), or the fruit or seeds of such plants. When used as a dry grain for human consumption, the seeds are also called pulses. Legumes are grown agriculturally, primarily for human consum ...

s can have elevated nitrogen levels and other nutrients that other plants can use. The dunes can become islands of plant diversity in otherwise poor habitat.

Etymology

''Nabkha'' is an

Arabic Arabic (, , or , ) is a Central Semitic languages, Central Semitic language of the Afroasiatic languages, Afroasiatic language family spoken primarily in the Arab world. The International Organization for Standardization (ISO) assigns lang ...

word that has been in use for at least 14 centuries. It translates roughly to "small, sandy hillock".

References

{{reflist Dunes Arabic words and phrases