‘Bottom-up’ bedrock river response to rock uplift: Unravelling the controls of landscape responses to transience.
2010 (English)In: British Society for Geomorphology Programme & Abstracts. London, England, Aug 2010., 2010Conference paper (Other academic)
Bedrock rivers set the boundary conditions for landscape evolution. Most recent bedrock river research has been in steady-state settings in which rock uplift is matched by landscape lowering driven by bedrock river incision and slope lowering, but more attention is now being paid to bedrock rivers is transient settings (where transience in the fluvial system is triggered by changes in the rate of rock uplift and/or by climatic oscillations). Transient responses in bedrock rivers close to base-level are dominated by ‘bottom-up’ processes. Those processes remain less well understood than the ‘top-down’ processes that are thought to be characteristic of steady state landscapes and are driven by discharges of water and sediment. Key issues in understanding rates of landscape-wide response to transience are (i) rates of knickpoint retreat to transmit a base-level fall signal through the drainage net, and (ii) rates of hillslope response once that base-level fall has passed the foot of a hillslope. Terrestrial cosmogenic nuclide (TCN) data from a transient landscape in southern Spain point to the latter being the rate-limiting control (“fast rivers, slow hillslopes”). In terms of the former, morphometric and TCN data from coastal rivers in Scotland confirm knickpoint retreat in response to glacio-isostatic rebound, whereas TCN data from higher up these rivers, above the reach affected by glacio-isostatic base-level fall, point to more diffusive bedrock channel incision, without knickpoint retreat. Determining why diffusive incision is initiated at a particular locality in those settings is difficult but in at least one case the incision is probably ‘pinned’ on resistant lithologies. A wider and more taxing issue is the relationship between ‘bottom-up’ and ‘top-down’ incisional processes and whether the former must precede, and can evolve into, the latter.
Place, publisher, year, edition, pages
bedrock channel, knickpoint, sediment supply, Scotland, cosmogenic nuclides
Research subject Geography, Physical Geography
IdentifiersURN: urn:nbn:se:su:diva-54238OAI: oai:DiVA.org:su-54238DiVA: diva2:392410
British Society for Geomorphology