great escarpment
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2021 ◽  
Author(s):  
Yanyan Wang ◽  
Sean Willett ◽  
Datian Wu ◽  
Negar Haghipour ◽  
Marcus Christl

Author(s):  
J. Knight ◽  
S.W. Grab

Abstract Mountains are areas of high potential sediment yield due to their steep slopes and generally cool, wet climates. Mountain sediments are moved by gravity-driven and often cryogenically-influenced processes, and captured within valleys or footslopes in the form of screes, alluvial/colluvial fans and terraces, or on hillslopes in the form of solifluction sheets, debris lobes/ridges and openwork block deposits. This study critically examines the geomorphic, sedimentary, stratigraphic and dating evidence from cryogenically-influenced late Quaternary slope deposits found along the highest sectors of the Great Escarpment in the Eastern Cape Province (South Africa) and Maloti–Drakensberg range (Lesotho, and KwaZulu-Natal Province, South Africa). This evidence is set in the context of mountain weathering and erosion/transportation processes during the late Quaternary, and the dynamics of such sedimentary systems. Despite many general reports and observations, there is little detailed and quantitative evidence for late Quaternary slope processes, products and stratigraphy in southern Africa. This study integrates the existing morphological, sedimentary and dating evidence to examine mountain slope evolution in southern Africa based on the conceptual framework of sediment cascades. Application of this framework can help explain the spatial and temporal differences in sediment supply and dynamics observed in different sectors of the Great Escarpment during the late Quaternary.


Bothalia ◽  
2021 ◽  
Vol 51 (2) ◽  
Author(s):  
Ben Strohbach

Background: The Great Escarpment of southern Africa takes the form of an extended mountainous highland in central-western Namibia, commonly referred to as the ‘Khomas Hochland’. It is regarded as an area of high botanical diversity. Yet only few localised studies on the vegetation composition are available. The Khomas Hochland is formed on the southern part of the Damara Orogen and dominated by metamorphosed sediments. Climatically it forms a transition between the hot desert of the Namib and the slightly cooler hot steppe in the inland.Objectives: To classify and provide syntaxonomical descriptions of the vegetation of the Khomas Hochland.Methods: A dataset comprising 1151 relevés and 914 species was compiled from various surveys, mostly collected under, and to the standards of, the umbrella project ‘Vegetation Survey of Namibia’. For first classifications, the data set was reduced to a synusial set consisting of trees, shrubs, dwarf shrubs and grasses only.Results: The classification resulted in four major landscape units, being the Pre-Namib and Escarpment zone, the Khomas Hochland proper, riverine habitats as well as surrounding lowlands. The classification was further refined using Cocktail procedures to produce 30 associations, one with four sub-associations. These are described in this paper.Conclusion: A classification of synoptic data grouped the associations into five orders and one undefined cluster of associations on specialised desert habitats. Four of these orders correspond to the habitat types identified in the first classification. The fifth order, the Senegalio hereroensis–Tarchonanthoetalia camphorathi, represents high mountains of the central Khomas Hochland, which link biogeographically to the grassland biome in South Africa.


2021 ◽  
Author(s):  
Yanyan Wang ◽  
Sean Willett ◽  
Datian Wu ◽  
Negar Haghipour ◽  
Marcus Christl

2021 ◽  
pp. 120368
Author(s):  
Tebogo V. Makhubela ◽  
Jan D. Kramers ◽  
Sibusiso M. Konyana ◽  
Herman S. van Niekerk ◽  
Stephan R. Winkler

ZooKeys ◽  
2020 ◽  
Vol 936 ◽  
pp. 1-24
Author(s):  
Chantal L. Taylor ◽  
Nigel P. Barker ◽  
Helen M. Barber-James ◽  
Martin H. Villet ◽  
Lyndall L. Pereira-da-Conceicoa

This study investigates genetic diversity in three species of Ephemeroptera, one eurytopic and therefore widespread (Afroptilum sudafricanum) and two stenotopic and thus endemic (Demoreptus natalensis and Demoreptus capensis) species, all of which co-occur in the southern Great Escarpment, South Africa. Mitochondrial DNA was analysed to compare the genetic diversity between the habitat generalist and the two habitat specialists. Afroptilum sudafricanum showed no indication of population genetic structure due to geographic location, while both Demoreptus species revealed clear genetic differentiation between geographic localities and catchments, evident from phylogenetic analyses and high FST values from AMOVA. In addition, the phylogenetic analyses indicate some deeper haplotype divergences within A. sudafricanum and Demoreptus that merit taxonomic attention. These results give important insight into evolutionary processes occurring through habitat specialisation and population isolation. Further research and sampling across a wider geographic setting that includes both major mountain blocks of the Escarpment and lowland non-Escarpment sites will allow for refined understanding of biodiversity and associated habitat preferences, and illuminate comparative inferences into gene flow and cryptic speciation.


2020 ◽  
Author(s):  
Jamie Glass ◽  
Alexandru Codilean ◽  
Reka Fülöp ◽  
Klaus Wilcken ◽  
Tim Cohen ◽  
...  

<p>The eastern seaboard of Australia is characterized by a passive margin and a continental divide that separates the inland-draining rivers from those that drain to the Coral and Tasman seas. Seaward of this divide lies the Great Escarpment (GE) of Australia that separates a moderate relief coastal plain from a low relief, high elevation plateau. Quantifying the spatial variation of erosion rates from temperate New England (NE), NSW and tropical Bellenden Ker (BK), Queensland, two regions with distinctly different climates and escarpment embayment, could help constrain erosional controls that contribute to escarpment form. In this study, we compared forty detrital 10Be samples collected from sediments in the main trunk and tributaries of five major rivers: the Macleay, Bellinger, and Clarence in NE and the Russel-Mulgrave and North Johnstone in BK. We then traced the escarpment position in ARCGIS and calculated a sinuosity ratio to better compare the degree of embayment in each region. Across both datasets we found that for NE, which has deep gorges cutting into the plateau, the degree of embayment was twice that of BK, where the escarpment position is significantly less embayed and erosion rates significantly more variable (ratio of .18 vs .38). Erosion rates in low slope areas, such as on the plateau, were universally low with no other significant controlling factors. There was no correlation between erosion rates and catchment area, and that our data echo previous studies that find that once mean rainfall passes an approximate threshold (around 2000mm/yr) basin characteristics that are known to control erosion rates, such as slope and lithology, are subdued.</p><p> In temperate NE, where rainfall ranges from approximately 800-1200mm/yr, there was a moderate linear correlation with mean catchment rainfall and erosion rates (R<sup>2</sup> .50), which is likely due to a strong orographic effect due to the escarpment. Erosion rates from tributaries below the plateau were highly variable and ranged from 5m/Ma up to 60m/Ma and correlated strongly with mean catchment slope (R<sup>2</sup> .86). In addition, there were moderate inverse linear correlations between erosion rate and the catchment total percent granite and sedimentary rock (R<sup>2</sup> .53 and .63 respectively) and a moderate correlation between erosion rate and catchment total percent metamorphic rock (R<sup>2</sup> .57). Similar to previous studies, these data suggest that in temperate climates with moderate amounts of annual rainfall, individual basin characteristics play a significant role in controlling basin wide erosion rates.</p><p>In contrast, data from tropical BK, where mean rainfall amounts are in excess of 2000mm/yr, erosion rates from tributaries below the plateau were significantly less variable than NE. Rates had a mean of 37m/Ma ± 9 (standard deviation 5m/Ma, N=10) and were not significantly correlated with mean catchment slope nor catchment lithology. The mean erosion rate of BK is similar to that of other studies in the region, though with slightly less variability, and possibly reinforces the hypothesis from other researchers that in tropical climates with significant mean rainfall, soil depth effectively armors hillslopes and prevents bedrock erosion from occurring.</p>


2020 ◽  
Author(s):  
Jeni McDermott ◽  
Tim Redfield

<p>The sharp, asymmetric ‘Great Escarpment’ of southwestern Norway mimics landforms commonly associated with fault-controlled ‘footwall uplift’ mountain ranges, bringing into question whether climate-driven erosion and consequent mass redistribution can generate kilometer scale topographic relief, or if tectonic forces are required instead.  Here we report on patterns of relief and fluvial incision in a region characterized by glacial sculpting, rapid isostatic uplift, and a well-established brittle template of normal faults.</p><p>The Surna valley (Surnadalen) of mid-southern Norway is a SW-NE striking wide, alluvial, U-shaped valley whose SW margin defines part of the Great Escarpment. Surnadalen displays clear morphometric asymmetry: its inland (SE) side is defined by high elevation (>1000 m) and well-developed drainage networks that display clear evidence of alpine glacial carving, while its seaward side is lower (~500 m) and has neither developed drainage networks nor evidence for valley glaciers. Inland drainages display a distinct set of aligned knickzones that maintain characteristics inconsistent with transient fluvial response to deglaciation. Incision occurs across fluvial process zones with no correlation to drainage area, suggesting regional forcing rather than catchment-scale drivers. Both lithology and structure are nearly identical across greater Surnadalen, and no change in rock type or erodibility correlate with the incision zones. Incision is axially asymmetric: All knickzones occur at the base of the ‘Great Escarpment,’ and the Tjellefonna Fault Zone (TFZ), a strand of a regionally important fault complex, projects into Surnadalen’s axis and aligns directly with the knickzone trace. The depth of incision decays from SW to NE in the direction of propagation of the TFZ tip at a mathematically predictable rate. We interpret the knickzone alignment to reflect active normal fault control over incision localization and depth. The depth and morphology of incision suggests Surnadal’s incision survived multiple glacial cycles. This interpretation implies that Norway’s ancestral structural template continues to impose a fundamental control over the creation and maintenance of the Great Escarpment. Although fault reactivation is not the result of regional tectonic extension, but rather is likely the product of erosion-induced shifting of loads, the pre-existing margin architecture appears to dominate the isostatic response to erosion.</p>


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