Desert Pavement Formation

Desert Pavement

Desert Pavement

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 millennia. 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.

Published on March 11, 2009 at 1:25 PM  Leave a Comment  

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