Skirrow, Grace
(2022)
The Long-term Dynamics of the Glacially-fed River Systems in Patagonia.
PhD thesis, University of Liverpool.
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Abstract
The acceleration of global glacier retreat in the 21st century will likely see glacially-fed rivers decouple from their glacial sources across all latitudes, incurring substantial changes to fluvial drivers and sensitivity to change. In Patagonia, water supply to the major eastward draining river systems is heavily reliant on drainage from the Andes Mountains which have undergone extensive changes in drainage dynamics during glacial periods caused by fluctuations in the extent of the Patagonian Ice Sheet. Key Climate systems (e.g. the southern westerlies) are important drivers of precipitation to Patagonia. They have responded to past shifts in temperature and are predicted to play a crucial role in future changes to weather patterns across Patagonia and the globe. Existing research on the glacial, lacustrine, vegetation and fire history has reconstructed the paleoenvironmental conditions in Patagonia, but the response of the major eastward draining rivers is largely unknown. This study combines geomorphological mapping, sedimentological and stratigraphic analysis, and luminescence dating techniques to investigate the preservation, timescales and drivers of past fluvial behaviour of the Río Chubut catchment (~42°S, ~70°W), Argentina. This thesis concludes that the Río Chubut catchment preserves a host of palaeofluvial features that formed on timescales as old as the last interglacial (MIS 5) and as recent as the last millennium (Late Holocene). The catchment preserves evidence of: (1) deep valley incision; (2) the aggradation and incision of glacially-derived sediments; (3) the shift from a braided to a meandering planform; and (4) the evolution of the contemporary meandering system. Under glacial conditions, the Río Chubut was braided and dominated by glaciofluvial outwash. Injections of sediment, from repeated glaciation of the headwaters, continued to be mobilised as a paraglacial braided river after decoupling from the ice sheet at the end of the last deglaciation. Whilst the sediment supplied by glaciation was vital to braiding in the Río Chubut, the water supply was not; this study shows that the last paraglacial braided planform was abandoned because of a reduction in precipitation via a weakening and southward shift in the southern westerlies, which caused a planform shift to the contemporary meandering regime. The contemporary regime has evolved to a mature meandering system, operating in a flood basin. Millennial-scale floodplain residence time preserves morphological evidence of substantial channel avulsions and meander migration. Still dependent on drainage from the Andes, the Río Chubut has persisted through the variable climatic conditions of the Holocene. This research suggests that modern paraglacial braided rivers may be vulnerable to future climate change as shown by the sensitivity of the Río Chubut to precipitation change in the Andes.
| Item Type: | Thesis (PhD) |
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| Divisions: | Faculty of Science and Engineering > School of Environmental Sciences |
| Depositing User: | Symplectic Admin |
| Date Deposited: | 16 Feb 2023 10:59 |
| Last Modified: | 16 Feb 2023 10:59 |
| DOI: | 10.17638/03168131 |
| Supervisors: |
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| URI: | https://livrepository.liverpool.ac.uk/id/eprint/3168131 |
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