Blowout (geology)

Blowouts are sandy depressions in a sand dune ecosystem (psammosere) caused by the removal of sediments by wind.

Blowouts occur in partially vegetated dunefields or sandhills. A blowout forms when a patch of protective vegetation is lost, allowing strong winds to "blow out" sand and form a depression. Although they generally remain small, blowouts can expand to kilometers in size and up to around 70m in depth. [Pound, R. and Clements, F.E. 1900. The phytogeography of Nebraska. 2d ed. Lincoln, 442 pp.] [Jungerius, P.D. and van der Meulen, F. 1989. The development of dune blowouts, as measured with erosion pins and sequential air photos. Catena 16(4-5):369-376.]

Causes of vegetation loss include extended droughts, fire (natural and anthropogenic) or, in extreme cases, trampling by humans, cattle, horses, etc. [Wang Shuai, Hasi Eerdun, Zhuang Yanmei and Zhang Ping. 2008. A study of blowouts in the Hulun Buir Sandy Grassland, Northeast China. In: Correa, A.C., Agnello, M.F., Todd, R. and Peterson, R. (ed). Water in the Arid and Semiarid Lands. Proceedings of the 2006 International Conference, 15-17 November 2006, Lubbock, Texas, ICASALS Publication 2008-1, pp. 191-199.] Fire is the most common cause, however. In time, succession will begin again as suitable seeds are blown in and pioneers become re-established. [Barbour, E.H. 1895. Report of the geologist: Soils. In: Furnas, R.T. (ed), Annual Report, Nebraska State Board of Agriculture for the year 1894, pp. 61-92.]

Coastal sand dunes are found just inland from a beach, and are formed as the wind blows dry sand inland beyond the beach. It follows that this can only happen when there is an area of reasonably flat land inland from the beach. In time, this rather inhospitable surface will be colonised by pioneer species. These species (e.g. marram grass) will stabilise the dunes and prevent them moving any more. The process of plant succession will eventually see these dunes converted to woodland (depending on the climate) and a mature soil will have formed. [Hugenholtz, C.H. and Wolfe, S.A. 2006. Morphodynamics and climate controls of two aeolian blowouts on the northern Great Plains, Canada. Earth Surface Processes and Landforms 31(12):1540-1557.]

Blowouts provide an important habitat for flora and fauna. [Rydberg, P.A. 1895. Flora of the sand hills of Nebraska. Contributions from the United States National Herbarium 3:133-203.]

References

ee Also

*Sand Hills (Nebraska)
*Sandhill
*Dune
*Médanos
*Barchan

External links

* [http://www.lbk.ars.usda.gov/wewc/biblio/bar.htm The Bibliography of Aeolian Research (BAR)]