UNED | COMUNICACION About erosion process

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al CAMPUS


	Madrid, 31 de agosto de 2015


	Do we need big flood to cut spectacular river gorges? The work recently published by Loreto Anton and co-authors in Nature Communications show evidence of extremely rapid gorge formation in granite. Authors report the strong influence of the bedrock fracture pattern in the erosion rates; however the amount of erosion shows no relationship with flood size.


	The research from the UNED, in collaboration with Plymouth University and Universidad Complutense de Madrid reports an example of fluvial erosion occurred in the 1930s in a dam spillway (Ricobayo, Spain). Historic documents, photographs and surveys preserved at the Iberdrola Historical Archive allowed the reconstruction of the whole erosion process. Data reveal extremely high (>100 m/year) erosion rates, the highest reported so far on earth, associated to small-moderate floods (~100-1500m3/s). Results come to nuance the established models of erosion and gorge formation which are used to analyze the landscape evolution. The example demonstrates that moderate water discharges are capable of radical erosion suggesting that adjustments to changes such as drainage diversion and capture, or glacier outburst, may be initially much more rapid than has hereto been assumed. Structural preconditioning of the bedrock through jointing and faulting was the primary control on landscape change, conditioning gorge morphology and the rate at which erosion progress.


	The research, led by Loreto Anton, Assistant Professor at the Faculty of Sciences, UNED, was partially funded by the TopoIberia Project (Consolider Ingenio 2006 Programme). The work achieves the reconstruction of the scour site topography prior to the gorge formation and during the erosion events, and analyses the erosion mechanisms involved in the canyon cutting. A ~270 m long, ~100 m deep and ~100 to 160 m wide amphitheater headed canyon was carved over 6 years. Amphitheater headed canyons are a common geomorphological feature on Earth, also described in Mars, and currently focus of numerous scientific research. Spectacular examples of fluvial erosion could be shown at the Vitoria or the Niagara Falls (in Zimbabwe and Canada, respectively) and more locally at the Arribes del Duero area (Spain), where the studied case occurred. However, this is the first example of eye witness account and quantitative survey of amphitheatre headed gorge formation in granite.


	L. Anton with co-authors and other colleagues in the study area.


	Canyon carved at the dam spillway. 1934 (left); 1935 (right).Credit: Iberdrola.


	Exceptional natural analogue and unique example The erosion that took place at the Ricobayo spillway is an exceptional natural analogue where elements involved in the canyon formation - original topography, discharges (weather), rock type (strength, weathering) and structural pattern (tectonic) - are well constrained.


	DEM of the canyon formed in the dam spillway between 1934 and 1940. Credit: L. Anton


	In addition to the above findings, the study reveals that the response of bedrock rivers to external environmental perturbations can be extremely rapid in the initial stages, and episodic rather than quasi continuous. These observations raise important questions about the use of average incision rates to infer rates of external driving mechanisms (tectonic and climate). From the Geological point of view, the Ricobayo dam spillway is a unique eye witness example of dramatic erosion, which allows an accurate reconstruction of a new river gorge formation and development. This natural experiment provides interesting findings and a large collection of data useful to constrain models of landscape development, as well as for modern engineering strategies (e.g. design of hydraulic structures or dams and reservoirs safety).


	Reference:: L. Anton, A.E. Mather, M. Stokes, A. & G. Martin Munoz-De Vicente (2015). Exceptional river gorge formation from unexceptional floods. Nat. Commun. 6:7963 doi: 10.1038/ncomms8963.


	Spanish version

	Loreto Anton at Research Gate


	Itziar Romera Edición web: Elena Lobato Comunicación UNED