Geological and Geomorphological Controls on the Physical Landscape of the Free State

Holmes, Peter J.; Barker, Charles

doi:10.1080/03736245.2006.9713841

Cited by 14 publications

(6 citation statements)

References 17 publications

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“…Characteristic of the area are its upland, duplex soils (Hensley et al ., 2006) that frequently display red, sandy, apedal A horizons. These soils overlie fine‐grained shales of the Beaufort Group (Karoo Supergroup) and appear to be in‐part aeolian‐derived as they do not necessarily reflect the textural properties of the geological substrate (Holmes and Barker, 2006). In late winter and spring the region is characterized by strong winds associated with steep pressure gradients which, in turn, are associated with the west to east passage of frontal systems across the Western, Eastern and Northern Cape Provinces (Kruger, 2002).…”

Section: Study Areamentioning

confidence: 99%

Dynamic controls on wind erosion and dust generation on west‐central Free State agricultural land, South Africa

Wiggs

Holmes

2010

Earth Surf Processes Landf

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The west-central part of South Africa's Free State Province falls within the transition zone between South Africa's sub-humid, temperate grasslands to the east, and the semi-arid Karoo and arid Kalahari to the south and west, respectively. The area is characterized by low rainfall (typically 500 mm or less) with high variability, but environmental conditions allow widespread dryland commercial agriculture (maize, sunflowers and stock farming). However, human activity promotes wind erosion and the area is susceptible to dust emissions. This study is the first to quantify the degree of wind erosion on the agricultural soils in the region under prevailing winter to spring climatic conditions and land management practices. Using arrays of cup anemometers, dust deposition traps and saltation impact sensors (Safires), measurements were made of the key erosivity and erodibility drivers that control the degree of wind erosion. Results demonstrate that significant quantities of dust are mobilized, particularly during the months of September and October. Thresholds of wind erosion are shown to respond particularly closely to changes in surface and aerodynamic roughness (z0) with the amount of collected dust correlating well with measures of wind erosivity that weight the impact of higher wind speeds. Given the importance of surface roughness in controlling erosion thresholds, results show that the opportunity exists for well designed farming practices to control wind erosion. However, it is likely that climatically driven environmental change will impact on some of the identified controls on erosion (wind power, moisture availability) with the result that the wind erosion hazard is likely to increase within this marginal environment.

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Section: Study Areamentioning

confidence: 99%

Dynamic controls on wind erosion and dust generation on west‐central Free State agricultural land, South Africa

Wiggs

Holmes

2010

Earth Surf Processes Landf

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“…The result is an amphitheatre in which Soutpan and its adjacent pans are situated (Figure 1). The local geology comprises Ecca Formation shale, which has been shown to be conducive to pan formation in the western Free State (Holmes and Barker 2006). Local drainage is endorheic, and has almost certainly contributed to solution processes within the amphitheatre and the development of Soutpan.…”

Section: Gross Morphology and Structural Controlsmentioning

confidence: 99%

“…Florisbad is situated at the eastern extremity of the western Free State Panfield (Holmes and Barker 2006) at the apex between adjacent lunette dunes located on the lee side of Soutpan ( Figure 2). Through extensive mapping, Loock and Grobler (1998) demonstrated the existence of a large palaeodrainage system north, north-east and west of Florisbad, …”

Section: Regional Settingmentioning

confidence: 99%

Depositional environments of the Florisbad Spring site and surrounds: a revised synthesis

Rabumbulu

Holmes

2012

South African Geographical Journal

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The Florisbad Spring site displays lithological and stratigraphical complexity within a unique geomorphological setting. Various hypotheses have been proposed to explain this complex depositional environment, and the origins of the spring site and mound are an ongoing topic of debate. To provide a context within which better to understand the depositional environment of Florisbad, the site and its surroundings were investigated. To this end, aerial photographs and Google Earth imagery, combined with field mapping and an analysis of sediments from and around the spring mound, were used to assist in a broad palaeoenvironmental reconstruction. Particular attention was paid to the depositional environment on and around the spring mound. The results did not reveal obvious differences with respect to the sedimentology of lunette dunes in the vicinity, and the spring mound itself. However, there were minor, but potentially significant differences in structure and chemical composition. Evidence suggests that the sediments are primarily of aeolian origin, while geochemical differences suggest that the south-western lunette could predate the spring mound. Optically stimulated luminescence ages confirm reworking of sediment for one of the lunettes. The morphology of the lunettes suggests that this technique would not necessarily yield primary ages for lunette formation due to sediment reworking. The meso-scale geomorphology suggests a shallow depression in which structural control and both fluvial and aeolian processes have worked together to create a unique landscape that promoted the formation and preservation of dune deposits and the unique archaeological site that is Florisbad.

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“…The western part of the study area is dominated by pans (Holmes and Barker 2006;Figure 3), and surface drainage in this area is poorly developed. Even during exceptionally high rainfall events (as in 1988), no apparent signs of overflow between pans and the main streams occurred (CSIR 1988).…”

Section: Study Areamentioning

confidence: 99%

Utilising published data for DTM construction and drainage basin delineation in the Modder River catchment, Free State, South Africa

Barker

2011

South African Geographical Journal

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The proliferation of hardware and software to facilitate the use of computers in geomorphological research since 1990s has not only placed a premium on the collection of relevant data but also on the reliability of models prepared from such data. Data availability is often a serious drawback in the successful modelling of landscapes and geomorphological processes and often researchers have to make do with published data. Data from such secondary sources are frequently created for other purposes and are not always suitable for digital geomorphological modelling. This paper reports on a suggested methodology to incorporate as many terrain features as possible into a digital terrain model for a particular central South African landscape. It is shown that by carefully manipulating available data, an accurate presentation of the landscape can be created.

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Geological and Geomorphological Controls on the Physical Landscape of the Free State

Cited by 14 publications

References 17 publications

Dynamic controls on wind erosion and dust generation on west‐central Free State agricultural land, South Africa

Dynamic controls on wind erosion and dust generation on west‐central Free State agricultural land, South Africa

Depositional environments of the Florisbad Spring site and surrounds: a revised synthesis

Utilising published data for DTM construction and drainage basin delineation in the Modder River catchment, Free State, South Africa

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