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Submitted to: Geomorphology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/14/2006 Publication Date: 3/15/2007 Citation: Stout, J.E. 2007. Simultaneous observations of the critical threshold of two surfaces. Geomorphology. 85(2):3-16. Interpretive Summary: Under naturally turbulent wind conditions, gusts may intermittently exceed a critical threshold wind speed, producing bursts of sediment entrainment and transport leading to dust emissions, topsoil loss, and a host of other environmental problems. Recently, a new technique was developed that provides a practical method for establishing the critical threshold of an erodible surface under natural wind conditions. Threshold is calculated from measurements of wind erosion activity and the mean and standard deviation of wind speed. Here we report results from field experiments in which two sampling systems were deployed to measure the threshold of two surfaces simultaneously. One surface was a simple sand surface that lacked vegetation and the other surface was that of a dry lakebed, both located in the Southern High Plains of West Texas. Results reveal that threshold could be established with enough precision to identify clear differences between the two surfaces. Results also reveal that a sand surface tends to maintain a somewhat consistent threshold while the threshold of a lakebed can vary more dramatically due to changing surface conditions. Technical Abstract: Threshold is an important parameter in wind erosion research and in the field of aeolian research in general. A new technique was recently developed that provides a means of determining threshold with a sampling system that continuously collects wind data along with critical information regarding saltation activity. By employing two identical sampling systems, it was possible to monitor the threshold of a highly mobile sand surface while simultaneously monitoring the threshold of a less mobile playa surface. Results indicate that threshold could be measured at both locations with enough precision to establish clear differences between the surfaces. The sandy surface at the Morgenstern Dunes site was considerably more active than the Yellow Lake playa site over the 113-day sampling period because of its consistently lower threshold. The Morgenstern site tended to maintain a fairly constant threshold of around 5.4 to 5.5 m/s whereas the threshold of the Yellow Lake playa surface varied from a low of 6.4 m/s to values greater than 13.3 m/s. Limitations of this method lie in the fact that threshold can be determined only when winds are blowing sufficiently strong to cause sediment transport. |
