Browsing by Author "Harries, Rebekah M."

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    Climate aridity delays morphological response of Andean river valleys to tectonic uplift
    (2023) Harries, Rebekah M.; Aron, Felipe; Kirstein, Linda A.
    In the south Central Andes, a complex relationship between climate, tectonics, erosion and topography is well documented. Building on recent advances in the mechanical modelling of subduction zones, we isolate the contribution of fault motion to topography and observe how rock uplift has been recorded in river valley morphology. Rivers on the wetter, western Chilean-side of the Andean cordillera have steep and narrow valleys, in stark contrast to those draining east across the arid Argentinian cordillera, whose valleys are variably wider and less steep. The Chilean rivers have responded to fault slip along the western mountain front by incising vertically and propagating a steepening zone upstream. In Argentina, there is little evidence of channel steepening despite predictions for higher vertical rock uplift rates. We hypothesise that the aridity of the Argentinian region has limited the transport capacity of the rivers to export their sediment fill and as a result, vertical incision has been inhibited and lateral incision and valley widening favoured. The long-term climate gradient appears to have been important in modulating the morphological response of these rivers to fault slip. These factors precondition future landscape sensitivity to both tectonic and climatic change.
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    Impact of climate on landscape form, sediment transfer and the sedimentary record
    (2021) Harries, Rebekah M.; Gailleton, Boris; Kirstein, Linda A.; Attal, Mikael; Whittaker, Alexander C.; Mudd, Simon M.
    The relationship between climate, landscape connectivity and sediment export from mountain ranges is key to understanding the propagation of erosion signals downstream into sedimentary basins. We explore the role of connectivity in modulating the composition of sediment exported from the Frontal Cordillera of the south-central Argentine Andes by comparing three adjacent and apparently similar semi-glaciated catchment-fan systems within the context of an along-strike precipitation gradient. We first identify that the bedrock exposed in the upper, previously glaciated reaches of the cordillera is under-represented in the lithological composition of gravels on each of three alluvial fans. There is little evidence for abrasion or preferential weathering of sediment sourced from the upper cordillera, suggesting that the observed bias can only be explained by sediment storage in these glacially widened and flattened valleys of the upper cordillera (as revealed by channel steepness mapping). A detailed analysis of the morphology of sedimentary deposits within the catchments reveals catchment-wide trends in either main valley incision or aggradation, linked to differences in hillslope-channel connectivity and precipitation. We observe that drier catchments have poor hillslope-channel connectivity and that gravels exported from dry catchments have a lithological composition depleted in clasts sourced from the upper cordillera. Conversely, the catchment with the highest maximum precipitation rate exhibits a high degree of connectivity between its sediment sources and the main river network, leading to the export of a greater proportion of upper cordillera gravel as well as a greater volume of sand.