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Aeolian dust emission in the Namib Desert: measurements of small-scale erodibility controls

Johanna von Holdt 1, Frank Eckardt1, Giles Wiggs2, Martin Hipondoka3
1University of Cape Town, jrvonholdt@gmail.com; frank.eckardt@uct.ac.za, Cape Town, South Africa, 2University of Oxford, giles.wiggs@bnc.ox.ac.uk, Oxford, UK, 3University of Namibia, mhipondoka@unam.na, Windhoek, Namibia

Aeolian dust emission in the Namib Desert: measurements of small-scale erodibility controls


Johanna von Holdt1
Frank Eckardt1
Giles Wiggs2
Martin Hipondoka3


The modelling of mineral dust emissions remains a challenge given the coarse spatial and temporal resolution of the data on which these models are based. The Namib Desert has been identified as one of the largest sources of dust in the southern hemisphere, with emissions from the ephemeral river valleys caused by the erosive Bergwind playing a pivotal role during morning hours. The opening of the Landsat archive, and its AM overpass, presents the opportunity to investigate these events at a higher spatial resolution (up to 15 X 15 m) than previously possible. Landsat identified 38 major dust episodes over the last 25 years that originated primarily from the ephemeral valleys. Examination of the imagery enabled the identification of small-scale geomorphological controls acting on the dust emission process.
Landsat allowed us to focus on emission sites in three major river catchments (Kuiseb, Omaruru and Huab Rivers), which encompass a range of source geomorphologies, including channels, river and delta terraces, stone pavements, dunes and salt flats. Emissivity tests were undertaken using a Pi-Swerl portable wind tunnel both on erodible and control surfaces in order to determine the micro-scale surface characteristics that control erodibility. The characteristics assessed included particle size, elemental composition, mineralogy, moisture content, shear strength and compressive strength. Combining the high spatial resolution remote sensing data with Pi-Swerl measurements and surface erodibility variables, provided the opportunity to explore interrelationships between variables controlling emissivity.
Our findings suggest that surface disruption by humans plays a major role in the dust emission dynamics of the region. Some field areas have been heavily impacted by human activity especially with regard to their hydrological regime, and our data confirm the significant influence this has on dust emission potential. We also find that disruption of the stable gravel plain stone pavements as a result of development and tourism has a demonstrative impact on dust emissions and this presents a significant challenge for future land management of the region.