Bedrock structural control on catchment-scale connectivity and alluvial fan processes, High Atlas Mountains, Morocco

Mather, Anne E.; Stokes, Martin

doi:10.1144/sp440.15

Cited by 22 publications

(21 citation statements)

References 62 publications

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“…Studies of active fans at tributary junctions have typically considered systems where the mainstem is relatively narrow and confined in the valley, and thereby limits fan growth ((e.g. Al-Farraj andHarvey, 2005, 2010;Gómez-Villar et al, 2006;Mather and Stokes, 2018;Stokes and Mather, 2015;Wang et al, 2008). In contrast, the Tapuaeroa River is braided and wide (at the junctions in this dataset, the active braid-plain is 190-590 m wide).…”

Section: Introductionmentioning

confidence: 76%

“…Al-Farraj andHarvey, 2005, 2010;Gómez-Villar et al, 2006;Mather and Stokes, 2018;Stokes and Mather, 2015;Wang et al, 2008). Al-Farraj andHarvey, 2005, 2010;Gómez-Villar et al, 2006;Mather and Stokes, 2018;Stokes and Mather, 2015;Wang et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

“…Such studies provide a detailed understanding of how different forces shape tributary-junction fans in the field. Recently, Mather and Stokes (2018) used high-resolution satellite imagery to examine active processes on four fans over 10 years. To our knowledge, however, there are no long-term field datasets that record fan responses to large-scale changes in environmental conditions.…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, studies of tributary fans have often considered systems where the mainstem bed-level is stable or incising (e.g. Mather and Stokes, 2018;Wang et al, 2008). In contrast, the Tapuaeroa River aggraded substantially during the study period.…”

Section: Introductionmentioning

confidence: 99%

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Tributary‐junction fans as buffers in the sediment cascade: a multi‐decadal study

Leenman

Tunnicliffe

2020

Earth Surf Processes Landf

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Alluvial fans at tributary junctions modulate sediment flux through river networks, by buffering the mainstem channel from disturbance in the tributaries. Buffering occurs through the storage (and release) of sediment in fans. Here, we use an extensive historic dataset to characterise the ways in which fan buffering can change as sediment supply varies. In New Zealand's East Coast region, sediment supply and fluvial transport are prolific by global standards. We reconstruct how tributary‐junction fans in this region have responded to sediment generated by deforestation and extreme storms. The dynamics of five fans along the Tapuaeroa River are examined for the period 1939–2015. In response to major sediment loading, fans aggraded by up to 12 m and prograded by up to 170 m. Net sediment accumulation ranged from near zero to 1.5×106 m3. Fan size, gradient, sediment storage and buffering were influenced by both upstream and downstream controls. Key upstream (tributary) influences were sediment supply and stream power; downstream (mainstem) influences included distal confinement and, importantly, the nature of fan interaction with the mainstem, which aggraded by up to 6 m. The fans' ability to buffer the Tapuaeroa River from change in the tributaries was largely governed by this downstream interaction: as the mainstem aggraded, it increasingly curtailed fan progradation, thus limiting buffering. Previous studies of tributary‐junction fans have related fan morphometry to basin characteristics. However, we find that fan slope and area can vary considerably at decadal, annual or even monthly timescales. Consequently, we suggest that such studies could benefit by examining regional histories of disturbance. © 2019 John Wiley & Sons, Ltd.

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Section: Introductionmentioning

confidence: 76%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Tributary‐junction fans as buffers in the sediment cascade: a multi‐decadal study

Leenman

Tunnicliffe

2020

Earth Surf Processes Landf

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“…1b). Next the drainage advective slopes (Mather and Stokes, 2018). The High Atlas is set in a semi-arid climate, which 154 means that the effect of weathering on rock erodibility is expected to be low.…”

Section: Study Area 111mentioning

confidence: 99%

Rock strength and structural controls on fluvial erodibility: Implications for drainage divide mobility in a collisional mountain belt

Zondervan

Stokes

Boulton

et al. 2020

Earth and Planetary Science Letters

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Highlights 9• We estimate rock strength, erodibility and drainage divide mobility in the High Atlas 10Mountains 11• The weakest rock-type in the High Atlas is up to two orders of magnitude more erodible than 12 the strongest 13• In gently deformed horizontal strata of the sedimentary cover the drainage divide is mobile 14• Faulted and folded metamorphic sedimentary bedrock coincide with a stable drainage divide 15• Exhumation of crystalline basement forces the drainage divide into the centre of exposed 16 basement 17 Abstract 18 Numerical model simulations and experiments have suggested that when migration of the main 19 drainage divide occurs in a mountain belt, it can lead to the rearrangement of river catchments, 20 rejuvenation of topography, and changes in erosion rates and sediment flux. We assess the 21 progressive mobility of the drainage divide in three lithologically and structurally distinct groups of 22 bedrock in the High Atlas (NW Africa). The geological age of bedrock and its associated tectonic 23 architecture in the mountain belt increases from east to west in the study area, allowing us to 24 track both variations in rock strength and structural configuration which influence drainage 25 mobility during erosion through an exhuming mountain belt. Collection of field derived 26 measurements of rock strength using a Schmidt hammer and computer based extraction of river 27 channel steepness permit estimations of contrasts in fluvial erodibilities of rock types. The 28 resulting difference in fluvial erodibility between the weakest and the strongest lithological unit is 29 up to two orders of magnitude. Published evidence of geomorphic mobility of the drainage divide 30 indicates that such a range in erodibilities in horizontal stratigraphy of the sedimentary cover may 31 lead to changes in erosion rates as rivers erode through strata, leading to drainage divide 32 migration. In contrast, we show that the faulted and folded metamorphic sedimentary rocks in the 33 centre of the mountain belt coincide with a stable drainage divide. Finally, where the strong 34 igneous rocks of the crystalline basement are exposed after erosion of the covering meta-35 sediments, there is a decrease in fluvial erodibility of up to a factor of three, where the drainage 36 divide is mobile towards the centre of the exposed crystalline basement. The mobility of the 37 drainage divide in response to erosion through rock-types and their structural configuration in a 38 mountain belt has implications for the perception of autogenic dynamism of drainage networks 39 and fluvial erosion in mountain belts, and the interpretation of the geomorphology and 40 downstream stratigraphy. 41 42

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Lithological controls on the timing of strath terrace staircase formation in a collisional mountain belt

Zondervan,

Stokes,

Boulton

et al. 2024

Earth Surf Processes Landf

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In mountain belts, strath terrace staircases serve as markers for deriving river incision rates and erosional patterns. Distinguishing between terrace patterns influenced by external perturbations like changes in climate and tectonics and those driven by internal dynamics including feedbacks between topography, erosion and sediment transport remains challenging. We demonstrate that in a collisional mountain belt, lithology can act as a first‐order control on the spatial and temporal scales of strath terrace formation. Here, we investigate the role of lithology in modulating internal dynamics and the formation of strath terraces in the Mgoun River catchment of the High Atlas in Morocco, a region characterised by constant low‐rate rock uplift, a cyclical cool‐warm/arid‐humid Quaternary climate history and contrasting bedrock lithologies. By collecting (1) modern river and terrace clast data, (2) bedrock strath and strath‐top sediment elevations of four terrace levels, (3) terrace sedimentology and (4) integration with published terrace chronology, we found a dominance of local sediment input from hillslopes, mostly from recycled bedrock conglomerates. Additionally, we found valley width, controlled by the stratigraphic and structural configuration of lithological erodibility, significantly impacts sediment connectivity. The isolation between valleys with varying widths results in varied timescales of river channel response to hillslope coupling, with hillslope‐derived stochastic sediment gravity flows preserved in fluvial terraces in some river reaches and not in others. Furthermore, asynchronous terrace formation and abandonment ages result from the low longitudinal river connectivity between multiple valleys formed in erodible rock separated by gorges in high‐strength rock. These gorges limit knickpoint migration rates, inhibiting the ability of terraces formed in one valley to spread through the catchment. These findings can inform future research distinguishing between autogenic and external signals in erosional landscapes and help carefully derive river incision rates and climate insights from terraces.

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Bedrock structural control on catchment-scale connectivity and alluvial fan processes, High Atlas Mountains, Morocco

Cited by 22 publications

References 62 publications

Tributary‐junction fans as buffers in the sediment cascade: a multi‐decadal study

Tributary‐junction fans as buffers in the sediment cascade: a multi‐decadal study

Rock strength and structural controls on fluvial erodibility: Implications for drainage divide mobility in a collisional mountain belt

Lithological controls on the timing of strath terrace staircase formation in a collisional mountain belt

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