The modelling of windblown mineral dust emissions remains a challenge. This is in part due to the coarse spatial and temporal resolution of the data on which these models are based, but also because the processes and mechanisms of aeolian dust emission are not well understood. Satellite imagery has been used extensively in the study of dust from the late 1990s with important contributions being made in terms of sources, transport pathways and deposition areas. Using MODIS imagery, the Namib Desert has been identified as one of the largest sources of dust in southern Africa. The recent opening of the Landsat archive presents the opportunity to investigate these events at a higher spatial resolution (up to 15 X 15 m) than previously possible. Despite the low temporal resolution, we used Landsat imagery to identify 40 major dust episodes over the last 25 years that originated primarily from the ephemeral river valleys and pan complexes, providing new insight into the spatial and temporal evolution of the dust sources from the Namib Desert. Examination of the imagery enabled the identification of local-scale landform source points to direct ground based testing of the surfaces responsible for dust emission. Emissivity tests were undertaken using a PI-SWERL portable wind tunnel in three of the major dust producing river systems along the Namib coast, namely the Kuiseb, Omaruru and Huab Rivers. Preliminary observations suggest that human impact on the hydrological systems in two of the river basins, to cater for the increasing demand of water, have dramatically altered the emission of dust. The source areas of greatest dust emission are found to be located on recently deposited fluvial surfaces which are not active in the contemporary environment.

This paper serves as a brief review and overview of the surface geology and geomorphology around Gobabeb in the Central Namib Desert. It introduces the major lithologies associated with the Damara Orogen of Precambrian and Cambrian age, followed by Tertiary sandstones and conglomerates and Quaternary Kuiseb valley conglomerates, silts and gravels. To celebrate the 50th anniversary of the Gobabeb research station and the recent designation of the Namib Sand Sea as a world heritage site, we are presenting a map to inform and guide future research and educational activities around Gobabeb. The contrast between an ancient gravel plain to the north, a dynamic aeolian sand sea to the south and ephemeral river environments in between become apparent. These natural laboratories have attracted investigations of contemporary sand dune movement, hyper saline waters, evaporites and duricrusts and ephemeral flooding and recharge processes as well as environmental change and human impacts.

In an effort to construct roads more quickly, high-plasticity index soils stabilized with lime are now routinely compacted the day after mixing. With this practice has come an increasing number of heaves due to soluble sulfates reacting with the lime to form ettringite. Soils with sulfate concentrations below 7,000 to 8,000 parts per million (ppm) can generally be treated with lime. This research was performed to identify stabilizers that can be used with sulfate concentrations above 10,000 ppm. The effectiveness of the stabilizers was determined by the measurement of three-dimensional (3-D) swell reduction and unconfined compressive strength. The researchers evaluated 12 stabilizers, including enzymes, polymers, acids, emulsions, fly ash, and ground granulated blastfurnace slag (GGBFS). Three stabilizers significantly reduced volumetric swell. A polymer and an acid reduced swell by about 8%. GGBFS plus lime reduced swell by 10%. GGBFS plus lime was the only stabilizer that reduced swell, increased strength, and was cost-effective enough for the Texas Department of Transportation to consider as an alternative to lime in high-sulfate soils.

Modeled estimates of eolian dust emission can vary by an order of magnitude due to the spatiotemporal heterogeneity of emissions. To better constrain location and magnitude of emissions, a surface erodibility factor is typically employed in models. Several landscape‐scale schemes representing surface dust emission potential for use in models have recently been proposed, but validation of such schemes has only been attempted indirectly with medium‐resolution remote sensing of mineral aerosol loadings and high‐resolution land surface mapping. In this study, we used dust emission source points identified in Namibia with Landsat imagery together with field‐based dust emission measurements using a Portable In‐situ Wind Erosion Laboratory wind tunnel to assess the performance of schemes aiming to represent erodibility in global dust cycle modeling. From analyses of the surface and samples taken at the time of wind tunnel testing, a Boosted Regression Tree analysis identified the significant factors controlling erodibility based on Portable In‐situ Wind Erosion Laboratory dust flux measurements and various surface characteristics, such as soil moisture, particle size, crusting degree, and mineralogy. Despite recent attention to improving the characterization of surface dust emission potential, our assessment indicates a high level of variability in the measured fluxes within similar geomorphologic classes. This variability poses challenges to dust modeling attempts based on geomorphology and/or spectral‐defined classes. Our approach using high‐resolution identification of dust sources to guide ground‐based testing of emissivity offers a valuable means to help constrain and validate dust emission schemes. Detailed determination of the relative strength of factors controlling emission can provide further improvement to regional and global dust cycle modeling.

No abstract