1Université Grenoble Alpes, CNRS, ISTerre, CS-40700, 38058
2GET, Observatoire Midi Pyrénées, Université de Toulouse,
CNRS, IRD, 14 avenue E. Belin, 31400 Toulouse, France
3Department of Geology, FCFM, Universidad de Chile, Santiago, Chile
anow at: Department of Earth and Environmental Sciences, Tulane University,
New Orleans, LA 70118, USA
Received: 08 Aug 2016 – Discussion started: 17 Aug 2016
Abstract. Alluvial megafans are sensitive recorders of landscape evolution, controlled by both autogenic processes and allogenic forcing, and they are influenced by the coupled dynamics of the fan with its mountainous catchment. The Lannemezan megafan in the northern Pyrenean foreland was abandoned by its mountainous feeder stream during the Quaternary and subsequently incised, leaving a flight of alluvial terraces along the stream network. We use numerical models to explore the relative roles of autogenic processes and external forcing in the building, abandonment and incision of a foreland megafan, and we compare the results with the inferred evolution of the Lannemezan megafan. Autogenic processes are sufficient to explain the building of a megafan and the long-term entrenchment of its feeding river on time and space scales that match the Lannemezan setting. Climate, through temporal variations in precipitation rate, may have played a role in the episodic pattern of incision on a shorter timescale. In contrast, base-level changes, tectonic activity in the mountain range or tilting of the foreland through flexural isostatic rebound do not appear to have played a role in the abandonment of the megafan.
Revised: 09 Jan 2017 – Accepted: 30 Jan 2017 – Published: 21 Feb 2017
Mouchené, M., van der Beek, P., Carretier, S., and Mouthereau, F.: Autogenic versus allogenic controls on the evolution of a coupled fluvial megafan–mountainous catchment system: numerical modelling and comparison with the Lannemezan megafan system (northern Pyrenees, France), Earth Surf. Dynam., 5, 125-143, doi:10.5194/esurf-5-125-2017, 2017.