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Analysis of Dust Trap Sediments Collected on the Southern High Plains
Preliminary data derived from six dust traps installed on the Southern High Plains show that dust deposition varies locally and seasonally in response to natural and man-induced factors. Monthly rates of dustfall at individual stations ranged from 0.658 g/m^2 at Muleshoe to 13.4-41 g/m^2 at Palo Duro Canyon. Dust deposition contributes significantly to the renewal of the High Plains surface.
The Southern High Plains has been identified as the dustiest region in the contiguous USA (Orgill and Sehmel, 1976). Sources of dust are numerous and include desiccated playa bottoms, sand dunes, floodplain deposits, plowed fields, overgrazed rangeland, and unpaved roads. Ambient dust deposition is a continuous process augmented by rapid influx of material during duststorms and precipitation events. This study focuses on the amount and characteristics of present-day ambient dustfall. This information is necessary to assess the influence of future eolian deposition and its effect on landscape evolution over the expected lifespan of a high-level nuclear waste repository.
Six dust collectors, consisting of quart-sized, glass canning jars with screened openings, and glycerol as the trapping medium, were installed at pre-established weather-monitoring stations. The traps were designed to collect material deposited by gravitational settling and were mounted at heights of 135 to 147 cm above ground level. The collection sites were chosen to represent natural conditions as accurately as possible. Dust collection was initiated in February 1983 and is expected to continue for 3 to 5 years. Samples are collected monthly (± 3 days) and analyzed for dust quantity, mineralogic composition, and grain-size distribution. Dustfall values are reported as D, g/m^2/month (American Society for Testing and Materials, 1979).
Preliminary results show that the quantity of dust varies greatly between stations. As regional weather patterns are fairly homogeneous over this physiographic province, local differences in soils, land-use practices, vegetation density, topography, and subsequent wind flow account for the variations.Bureau of Economic Geolog
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Modern Eolian Processes on the Southern High Plains
Eolian processes have substantially modified the landscape on the Southern High Plains within historic times. The maximum inferred rate of deflation was 18.9 mm/year at a site in Bailey County, Texas, a region of loose, sandy soils and frequent, seasonal dust storms. At least locally, agricultural practices have accelerated natural rates of erosion and deposition by winds. An extensive cover of windblown sand and silt mantles the gently sloping surface of the Southern High Plains. Eolian deflation and deposition are among the dominant geomorphic processes affecting this region throughout most of the Holocene and Pleistocene time. Historically, human activities have heightened the importance of wind action by disrupting the natural vegetative cover, thereby exposing the unconsolidated sediments.
Agriculture, particularly dry-land cultivation, has been the principal form of land use in the area since the early 1900s or before (Webb, 1931). The effects of tilling practices on deflation are shown in Figure 1. The cultivated field on the right (east) is approximately 0.8 m lower than the range site on the left (west). This long, narrow field was cleared and probably brought into cultivation in the 1920s (C. D. Tunnell, personal communication, 1983). Its furrows run from north to south, along the field's long axis. The orientation of these furrows tends to maximize local deflation, as the furrows are parallel to the dominant winds. During the winter and early spring, some of the strongest winds are from the north, whereas the prevailing wind direction is southerly at other times of the year (Bomar, 1983). Other factors that enhance the erosional impact of the wind include antecedent dry conditions and frost heaving. Both are seasonal effects that increase the soil's susceptibility to removal during the frequent spring dust storms. After becoming entrained, soil aggregates from this field and others like it are transported from their source and redeposited as a broad sheet of eolian sediment.Bureau of Economic Geolog