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Hydrology of Playas and the Genesis of Dust

The relations among playa type, playa hydrology, and surface sediment characteristics are important factors that control the type and amount of dust emitted from playas. The production of evaporite minerals during evaporative loss of near-surface ground water results in both the creation and maintenance of several centimeters or more of loose sediment at wet playas.

Schematic cross-sections illustrating elements of (a) wet and (b) dry playas, illustrated for a hydrologically closed basin. Modified from figure 2 in Rosen (1994, The importance of groundwater in playas: A review of playa classifications and the sedimentology and hydrology of playas, in Rosen, M.R. (ed.), Paleoclimate and basin evolution of playa systems: Geological Society of America Special Paper 289, p. 1-18.).

Observations at Franklin playa, Soda Lake, and West Cronese Lake playas in the Mojave Desert (California) indicate that these kinds of surface sediments are highly susceptible to dust emission and that deflation of the sediment by wind encourages rapid re-formation of evaporite minerals. The loss of water to vapor occurs in the capillary fringe zone between the water table and the playa surface. Accordingly, the surfaces of wet playas are dynamic-surface texture and mineral composition change rapidly in response to fluctuations in water-table depth and ground-water solute chemistry. In contrast, dry playas are characterized by ground water at depth or by shallow confining beds. Consequently, dry playas commonly have hard surfaces that produce little or no dust if undisturbed except for transient silt and clay deposited on surfaces by wind and water. Although not the dominant type of global dust, salt-rich dusts from wet playas may be important with respect to radiative properties of dust plumes and atmospheric chemistry.

Dust emission from Franklin Playa in wind strength of 9.8 m/s, March 14, 2005. Telephone wires in foreground. Inset photograph shows the same view during the day in lower wind. Photographs by remote digital camera triggered by wind. Camera system designed and built by Rian Bogle, based partly on a similar camera system built by Rich Tigges.

Dust clouds produced during a windstorm from the surface of Soda Lake when the dry lake surface consisted mostly of fluffy sediment composed of evaporite minerals, February 6, 2001. Photograph by Rob Fulton, Desert Studies Center, Zzyzx, CA.