Desert pavement

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A desert pavement is a desert surface that is covered with closely packed, interlocking angular or rounded rock fragments of pebble and cobble size. Several theories have been proposed for their formation. The more common theory is that they form by the gradual removal of the sand, dust and other fine grained material by the wind and intermittent rain leaving only the larger fragments behind. This does not continue indefinitely however, because once the pavement has been formed it can act as a barrier to further erosion. Secondly it has been proposed that desert pavement forms from the shrink/swell properties of the clay underneath the pavement; when precipitation is absorbed by clay it causes it to expand and later when it dries it cracks along planes of weakness. This geomorphic action is believed to have the ability to transport small pebbles to the surface over time; it stays this way due to the lack of abundant precipitation that would otherwise destroy the pavement development through transport of the clasts or excessive vegetative growth. Finally a new theory suggests that they form as a consequence of the entrapment of fine grained material which infiltrates below the rocky surface. This surface continues to be pushed up above the fine grained material by microbial activity which makes small bubbles that help raise the more coarse grained materials to their surface layer, this cycle of events can continue to make a thick layer of windblown dust below the pavement over the millenia.

Desert pavement in the Cima Volcanic Field of the Mojave Desert (30 November 2000)

Frequently the stones are polished by the abrasion of wind-borne dust and may even be reduced to a streamlined shape with the narrow point on the windward side, becoming ventifacts. Desert pavement surfaces are often coated with desert varnish which is a dark brown, sometimes shiny coating that contains clay minerals; a famous example can be found on Newspaper Rock in Canyonlands, Utah. Desert pavement in Australia is called The Gibber.

[edit] References

Al-Qudah, K.A. 2003. The influence of long-term landscape stability on flood hydrology and geomorphic evolution of valley floor in the northeastern Badin of Jordan. Doctoral thesis, University of Nevada, Reno, 208 pp. (Note: desert pavements)

Anderson, K.C. 1999. Processes of vesicular horizon development and desert pavement formation on basalt flows of the Cima Volcanic Field and alluvial fans of the Avawatz Mountains Piedmont, Mojave Desert, California. Doctoral thesis, University of California, Riverside, 191 pp.

Bach, Andy. (Lecturer) 2008. (Class Notes). The Soil Environment. Western Washington University.

Grotzinger, et. al. 2007. Understanding Earth, fifth edition. Freeman and Company. NY, NY. 458-460

Haff, P.K. and Werner, B.T. 1996. Dynamical processes on desert pavements and the healing of surficial disturbance. Quaternary Research 45(1):38-46.

McFadden, L.D., Wells, S.G. and Jercinovich, M.J. 1987. Influences of eolian and pedogenic processes on the origin and evolution of desert pavements. Geology 15(6):504-508.

Meadows, D.G., Young, M.H. and McDonald, E.V. 2006. Estimating the fine soil fraction of desert pavements using ground penetrating radar. Vadose Zone Journal 5(2):720-730.

Qu Jianjun, Huang Ning, Dong Guangrong and Zhang Weimin. 2001. The role and significance of the Gobi desert pavement in controlling sand movement on the cliff top near the Dunhuang Magao Grottoes. Journal of Arid Environments 48(3):357-371.