Long-term development of fluvial systems: separating the effects of climate and tectonic change

Introduction

Fluvial down cutting, river valley development and knick point recession have been reported to be driven by mainly tectonic uplift and regional tilt of tectonic blocks, by successive pulses of regional uplift and fault displacement, by climatically induced base-level lowering, and in many cases by a combination of both. Separating both factors is indeed a formidable task as processes operate at different speeds on different temporal and spatial scales and feedback mechanisms cause non-linear, time-delayed behaviour. Long-term upland erosion and downstream deposition for instance, may cause crustal rebound, which in turn may force a river to attain a new state of equilibrium. At the same time, climate/vegetation-induced changes in discharge and sediment run-off interfere by changing the pattern of erosion and deposition within the system. This PhD research therefore focuses on separating the effects of tectonics and climate on landscape development and specifically on fluvial landscapes. The tectonics vs climate problem is one of the oldest and still most controversial problems in geomorphological research. With the arrival of new research techniques (DEM information, dating techniques and numerical modelling), we can finally address this matter in an efficient way.

Approach

To untangle the attributions of all these driving forces, a multi-disciplinary approach is used. Fluvial terrace genesis and tectonics are studied using DEM-information, aerial photographs and field studies; the influence of climate is assessed by studying marine pollen cores and creating a long-term vegetation map; Age assessment is done by a combination of various dating techniques such as 21Ne and 10Be cosmogenic nucleid dating and OSL quartz and feldspar dating. Finally, a combation of erosion and fluvial process models (LAPSUS and Fluver) with tectonic models will be used to reconstruct fluvial landscape evolution over the past 0.5 million years. 

Team

We are cooperating with various universities to ensure our unique interdisciplinary approach. The Vrije Universiteit Amsterdam is working on the tectonic component, Delft University on the OSL-dating, the University of A Coruña in Spain works on OSL and 21Ne-dating techniques; CEREGE in France on 10Be-dating,  and the University of Bordeaux on the marine pollen record and vegetation maps.

The project is also imbedded the European “TOPO-Europe” project and is specifically part of the “PyrTec” project.

Study area

Subject of our research is the Northwestern Iberian Miño-Sil river system. Its headwaters are found in the Cordillera Cantabrica after which the Sil passes by the intramontane Bierzo basin. Then it enters Galicia through a series of narrow gorges after which the Miño considerably broadens up before entering the Atlantic Ocean. The lower part of the Miño (Baixo Miño) forms the natural border between Galicia and Portugal. The region is very mountanous with peaks up to 2000 m and consists for the greater part of granite and metamorphic sedimentary rock. Main landuse forms are eucalypt forests and viniculture.

Fieldwork concentrates on the Baixo Miño, both on the Portugese and Spanish side. Here a very extensive fluvial terrace staircase is found. The second fieldwork area is found in the Bierzo basin, which acts as a temporary sediment trap for the sediments derived from the Cordillera Cantabrica. In this way a “source to sink” approach is established.