Weathering Systems

Viles, Heather

doi:10.1002/9780470710777.ch6

Cited by 9 publications

(3 citation statements)

References 59 publications

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“…Dryland environments, which constitute about 47% of the global land area [1], are extreme in their nature, typified by non-equilibrium conditions in climate, vegetation and geomorphology [2,3]. The strong interannual variability in precipitation characteristic of drylands [4,5] often results in ephemeral vegetative cover [6] or distinctive spatial patterning [7].…”

Section: Introduction: the Drylands Contextmentioning

confidence: 99%

Vegetation in Drylands: Effects on Wind Flow and Aeolian Sediment Transport

Mayaud

Webb

2017

Land

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Drylands are characterised by patchy vegetation, erodible surfaces and erosive aeolian processes. Empirical and modelling studies have shown that vegetation elements provide drag on the overlying airflow, thus affecting wind velocity profiles and altering erosive dynamics on desert surfaces. However, these dynamics are significantly complicated by a variety of factors, including turbulence, and vegetation porosity and pliability effects. This has resulted in some uncertainty about the effect of vegetation on sediment transport in drylands. Here, we review recent progress in our understanding of the effects of dryland vegetation on wind flow and aeolian sediment transport processes. In particular, wind transport models have played a key role in simplifying aeolian processes in partly vegetated landscapes, but a number of key uncertainties and challenges remain. We identify potential future avenues for research that would help to elucidate the roles of vegetation distribution, geometry and scale in shaping the entrainment, transport and redistribution of wind-blown material at multiple scales. Gaps in our collective knowledge must be addressed through a combination of rigorous field, wind tunnel and modelling experiments.

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Section: Introduction: the Drylands Contextmentioning

confidence: 99%

Vegetation in Drylands: Effects on Wind Flow and Aeolian Sediment Transport

Mayaud

Webb

2017

Land

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“…Chemical weathering rates in dryland Namibia are slow (Garzanti et al, 2021; Viles, 2011), and so changes in sediment composition are more likely to have resulted from physical processes. Increased collisions and more efficient abrasion from geomorphic processes would have resulted in more effective partitioning of sand particles (Cleary & Conolly, 1972; Fontana et al, 2003; Harrell & Blatt, 1978).…”

Section: Discussionmentioning

confidence: 99%

Holocene fluvial depositional regimes of the Huab River, Skeleton Coast, Namibia

Walsh

Caracciolo

Ravidà

et al. 2022

Earth Surf Processes Landf

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Dryland fluvial systems respond to hydroclimate changes on Quaternary timescales, yet deciphering the palaeoenvironmental histories they preserve is often complex.Whilst hydrological signals are preserved in sediment stores as variations in sediment amount, character, and composition, studies in dryland settings such as Namibia that link sedimentological and compositional changes to palaeoflow are limited. Focusing on the Huab River, Skeleton Coast, this paper presents the first integrated study of textural, compositional, and stratigraphic features from a Namibian fluvial archive.Petrographic and heavy mineral assemblages from Raman laser spectroscopy are combined with lithostratigraphic and particle size analysis. Together with a chronology established through 42 optically stimulated luminescence ages, we reconstruct provenance, changes in river style, and fluvial response to climate.The Huab lithostratigraphic record details periods of flashy ephemeral flow interbedded with flow within well-defined channels. Compositional assemblages indicate that humid conditions during the early to mid-Holocene resulted in activation of sediment stores across the catchment. Episodic discharge within an ephemeral river from 12 to 9 ka was followed by a more sustained river flow in a channelized system from 7 to 5 ka. During the late Holocene, better hydraulic sorting, increased mechanical breakdown of polycrystalline grains, and flash flood lithofacies suggest that flow occurred within a more arid climate. This fine-scaled analysis of an ephemeral fluvial system indicates the utility of assessing compositional changes to distinguish between depositional regimes. This is an important approach for reconstructing fluvial response to climate and for obtaining palaeoenvironmental records from complex sedimentary archives in dryland river settings.

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“…Namely, flakey rock crusts and thin layers (<4 cm) of sandy calcareous material weakly adhere to the canyon wall at and below the spring sites, consistent with an exfoliation mechanism driven by calcite precipitation from the exfiltrating groundwater (Laity and Malin, 1985). Salt weathering occurs as salts exert pressure on pore walls in the near surface, possibly due to repeated crystallization and dissolution, thermal expansion and in some cases mineral hydration (Viles, 2011). Other mechanisms may also be responsible for seepage erosion, such as freeze–thaw frost wedging and icicle formation, as well as the seepage pressure exerted by the emerging water itself (Laity and Malin, 1985; Howard and McLane, 1988; Dunne, 1990).…”

Section: Study Areasmentioning

confidence: 99%

Amphitheatre‐headed canyons of Southern Utah: Stratigraphic control of canyon morphology

Ryan

Whipple

2020

Earth Surf Processes Landf

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Amphitheatre-headed canyons are common on Earth and Mars and researchers have long sought to draw inferences about canyon-forming processes from the morphology of canyon heads and associated knickpoints, often suggesting that amphitheatre heads indicate erosion by groundwater seepage erosion. However, the conditions and processes that lead to amphitheatre-headed canyon formation have been debated for many years. We consider two hypotheses that attribute the amphitheatre-headed canyon formation to fluvial erosion of strong-over-weak stratigraphy or, alternatively, groundwater spring discharge and seepage erosion. A spatial analysis of canyon-form distribution with respect to local stratigraphy along the Escalante River and on Tarantula Mesa, Utah indicates that canyon form is most closely related to variations in local sedimentary rock strata, rather than inferred groundwater spring intensity. Lateral facies variations that affect the continuity of strong layers can induce or disrupt the formation of amphitheatres. Furthermore, we find that amphitheatre retreat rate is dictated by the interaction of fluvial processes downstream of the amphitheatre headwalls and stratigraphy, rather than waterfall and groundwater processes that likely importantly influence headwall form. We conclude that fluvial erosion of strong-over-weak stratigraphic layering alone is sufficient to form amphitheatres at knickpoints and canyon heads. Thus, we reaffirm that formation process should not be inferred from canyon-head morphology, particularly where a strong-over-weak layering is known or plausible.

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Weathering Systems

Cited by 9 publications

References 59 publications

Vegetation in Drylands: Effects on Wind Flow and Aeolian Sediment Transport

Vegetation in Drylands: Effects on Wind Flow and Aeolian Sediment Transport

Holocene fluvial depositional regimes of the Huab River, Skeleton Coast, Namibia

Amphitheatre‐headed canyons of Southern Utah: Stratigraphic control of canyon morphology

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