Science Center Objects

Dust emission from Playas (Dry Lakes)

Dust emission from Franklin Lake playa

Accelerated deflation on Mesquite Lake playa, Mojave Desert

Wind-tunnel studies of playa surfaces

LiDAR studies of wind erosion at Mesquite lake playa (California-Nevada)

Dust Emission from Playas (Dry Lakes)

Reynolds, R.L., Yount, J.C., Reheis, M.C., Goldstein, H., Chavez, Jr., P., Fulton, R., Whitney J., Fuller, C., Forester, R.M., 2007, Dust Emission from wet and dry playas in the Mojave Desert: Earth Surface Processes and Landforms, v. 32, 1811-1827. DOI: 10.1002/esp.1515.

The interactions between playa type, playa hydrology, and playa-surface sediments are important factors that control the type and amount of dust emitted from playas as a result of wind erosion. 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 on and near the surfaces of wet playas. Observations that characterize the texture, mineralogic composition, and hardness of playa surfaces at Franklin Lake, Soda Lake, and West Cronese Lake playas in the Mojave Desert (California), along with imaging of dust emission using automated digital photography, indicate that these kinds of surface sediments are highly susceptible to dust emission. The surfaces of wet playas are dynamic-surface texture and sediment availability to wind erosion change rapidly, primarily in response to fluctuations in water-table depth, rainfall, and rates of evaporation. In contrast, dry playas are characterized by ground water at depth. 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, atmospheric chemistry, windborne nutrients, and human health. Examples of regionally important dust sources from dry lake beds that behave as wet playas include parts of the Aral Sea (Kasachstan and Usbekistan), Owens Lake (California, USA), and probably the Hamoun wetlands (now mostly dry) of Afghanistan and Pakistan.

 

Dust Emission at Franklin Lake Playa

Reynolds, R.L., Bogle, R., Vogel, J., Goldstein, H., and Yount, J.C., 2009, Dust emission at Franklin Lake playa, Mojave Desert (USA): Response to meteorological and hydrologic changes 2005-2008, in Oren, A., Naftz, D.L., and Wurtsbaugh, W.A. (eds.). Saline lakes around the world: unique systems with unique values. Natural Resources and Environmental Issues 15:105-116 (ISSN 1069-5370).

Playa type, size, and setting; playa hydrology; and surface-sediment characteristics are important controls on the type and amount of atmospheric dust emitted from playas. Soft, evaporite-rich sediment develops on the surfaces of some Mojave Desert (USA) playas (wet playas), where the water table is shallow (< 4 m). These areas are sources of atmospheric dust because of continuous or episodic replenishment of wind-erodible salts and disruption of the ground surface during salt formation by evaporation of ground water. Dust emission at Franklin Lake playa was detected between March 2005 and April 2008. The dust record, based on day-time remote digital camera images captured during high wind, and compared with a nearby precipitation record, shows that aridity suppresses dust emission. High frequency of dust generation appears to be associated with relatively wet periods, identified as either heavy precipitation events or sustained regional precipitation over a few months. Several factors may act separately or in combination to account for this relation. Dust emission may respond rapidly to heavy precipitation when the dissolution of hard, wind-resistant evaporite-mineral crusts is followed by the development of soft surfaces with thin, newly formed crusts that are vulnerable to wind erosion and (or) the production of loose aggregates of evaporite minerals that are quickly removed by even moderate winds. Dust loading may also increase when relatively high regional precipitation leads to decreasing depth to the water table, thereby increasing rates of vapor discharge, development of evaporite minerals, and temporary softening of playa surfaces. The seasonality of wind strength was not a major factor in dust-storm frequency at the playa. The lack of major dust emissions related to flood-derived sediment at Franklin Lake playa contrasts with some dry-lake systems elsewhere that may produce large amounts of dust from flood sediments. Flood sediments do not commonly accumulate on the surface of Franklin Lake playa because through-going drainage prevents frequent inundation and deposition of widespread flood sediment.

Additional information: Goldstein, H.L., Breit, G.N., Yount, J.C., Reynolds, R.L., Reheis, M.C., Skipp, G.L., Fisher, E.M., and Lamothe, P.J., 2011, Physical, chemical, and mineralogical data from surficial deposits, groundwater levels, and water composition in the area of Franklin Lake playa and Ash Meadows, California and Nevada: U.S. Geological Survey Data Series 607, 153 p.

 

Accelerated deflation on Mesquite Lake playa, Mojave Desert

Mesquite Lake Playa is a significant sediment source for high levels of dust in Las Vegas, Nevada. Located just south of the California-Nevada border, Mesquite Lake Playa is a gypsiferous playa characterized by scattered yardangs and sand sheets, and is partly ringed by high mesquite-stabilized dunes. A rapidly expanding deflation basin has been found on the southeastern part of the playa. The deflation basin is visible on a 2002 Landsat image, but it is not present on 1989 or earlier aerial photographs. By 2006, the basin was four times larger than in 2002 and nearly 60,000 m3 of sediment, calculated by a GIS analysis, had been excavated by the wind. The deflation basin has exposed late Pleistocene paludal sediment with good preservation of delicate surface features (e.g. mud cracks and tracks) that are quickly eroded after exposure to the wind. Wind measurements recorded over one year on the playa reveal that sand-moving winds (>5.42 m/s) occur only about 6 percent of the time with the greatest concentration of windstorms taking place during April and May. Approximately a third of the eroded sediment was likely added to the dust flux exiting this basin. The recent rapid expansion of the 1-2-m deep basin is attributed to lowering of the water table and exposure of dry, unconsolidated, gypsum-rich sediment. Loss of soil moisture reduces cohesion of the playa sediment, rendering it more susceptible to wind erosion. Wind-tunnel tests indicate that wind will transport eight times as much of the newly exposed, gypsum-rich sediment compared with the cohesive sediment of the undisturbed playa surface. Measured water levels on three old wells marginal to the playa show that the 2009 water table is 3-4 m lower than during the 1960s. The current water table is at 4 to 5 m beneath the playa, which may be lower than at any time since the Pleistocene. The recent water-level decline may be the result of ground-water extraction and a regional drought that began in the late 1990s. Continued expansion of the deflation basin due to sustained low ground-water levels may significantly augment the dust flux into the Las Vegas Valley.

We are employing LiDAR to measure the effects of wind erosion at Mesquite lake playa in the Mojave Desert.

Additional information: Whitney, J.W., Breit, G.N., Buckingham, S., Reynolds, R.L., Bogle, R.C., Luo, Lifeng, Goldstein, H.L., Vogel, J.M., 2015, Aeolian responses to climate variability during the past century on Mesquite Lake Playa, Mojave Desert: Geomorphology, v. 230, p. 13-25. [doi:10.1016/j.geomorph.2014.10.024].

 

Wind-tunnel studies of playa surfaces

Wind-tunnel experiments were conducted at Franklin Lake playa (wet playa) and Mesquite Lake playa (dry playa) using the portable in-situ wind erosion laboratory (PI-SWERL) developed by collaborators at the Desert Research Institute (Etyemezian and others, 2007). Experiments were conducted during three different seasons: fall 2007, spring 2008, and winter 2009. The wind-tunnel experiments provide a way to characterize the dust-emission potential of the playa surfaces through determinations of the threshold friction velocity (u*).

This parameter is critical to understanding wind-erosion dynamics, especially at settings like Mesquite Lake playa, where deflation from wind erosion is extreme. In addition to characterization of dust-emission potential, the PI-SWERL permits collection of the dust generated during the experiments that can then be used for chemical and physical property characterizations and comparisons. The physical and chemical property comparisons between the dust generated from the PI-SWERL and the associated surface crust, together with historical meteorological data, enables understanding of the controls on dust emission and dust composition.

 

LIDAR studies of wind erosion at Mesquite lake playa (California-Nevada)

LiDAR (Light Detection and Ranging) methods are becoming an increasingly important tool in Earth sciences. In this method, laser pulses are used to determine distances to objects. As one application, repeated measurements of the same object over time can be analyzed to calculate changes in the dimensions of objects. We are employing LiDAR to measure the effects of wind erosion at Mesquite lake playa in the Mojave Desert. We are finding that wind-erosion features, such as yardangs, and wind-deflated surfaces are undergoing rapid erosion over periods of a few months. For more on yardangs, please see:

Additional information:  

Whitney, J.W., Breit, G.N., Buckingham, S., Reynolds, R.L., Bogle, R.C., Luo, Lifeng, Goldstein, H.L., Vogel, J.M., 2015, Aeolian responses to climate variability during the past century on Mesquite Lake Playa, Mojave Desert: Geomorphology, v. 230, p. 13-25. [doi:10.1016/j.geomorph.2014.10.024].

The Encyclopedia of Geomorphology, edited by Andrew Goudie, Routledge, in Volume 2, pp. 1120-1121.