Active tectonics in the Sierra Nevada (Betic Cordillera, SE Spain): Insights from geomorphic indexes and drainage pattern analysis José Vicente Pérez-Peña a, ⁎, Antonio Azor a , José Miguel Azañón a,b , Edward A. Keller c a Departamento de Geodinámica, Universidad de Granada, Campus de Fuentenueva s/n, 18071 Granada, Spain b Instituto Andaluz de Ciencias de la Tierra – Consejo Superior de Investigaciones Científicas (UGR-CSIC), Spain c Department of Geological Sciences, University of California at Santa Barbara, CA 93106, USA abstract article info Article history: Received 25 September 2009 Received in revised form 20 February 2010 Accepted 27 February 2010 Available online 8 March 2010 Keywords: Tectonic geomorphology Mountain fronts Drainage pattern Geomorphic indexes Active folding and faulting DEM The Sierra Nevada of the central Betic Cordillera is a 3000 m-high mountain range surrounded by Neogene– Quaternary sedimentary basins, having been uplifted since Late Miocene times. The southern and western mountain fronts of the Sierra Nevada are fault-bounded, while the northern one is an unconformity between the Neogene–Quaternary sediments of the Guadix–Baza basin and the metamorphic rocks of the Nevado– Filabride complex. We have carried out a geomorphic study by examining drainage patterns and characteristics of mountain fronts in order to reveal areal variations and styles of rock uplift. Mountain front sinuosity (S mf ), area–altitude relations (hypsometric curves), and valley floor entrenchment differ significantly between the northern, western, and southern mountain fronts. The lack of important faults along the northern Sierra Nevada mountain front, together with the elevated topographic position of the Guadix–Baza basin (average altitude is around 1100 m), points to similar uplift of both geomorphic units (sierra and basin) in a single large-scale crustal block. The asymmetry factors show systematic asymmetries at both sides of the Lanjarón River, probably due to the presence of an active NNE–SSW oriented antiform in the western Sierra Nevada. Finally, river profiles indicate maximal river entrenchment in the western part of the Sierra Nevada, probably related to the uplift of the footwall of the Padul–Nigüelas fault-system. Therefore, our geomorphic analysis suggests that the western part of the Sierra Nevada is tectonically active by means of a combination of normal faults along the mountain front and NNE–SSW oriented active folds, which, in turn, likely have a gravitational origin related to the exhumation of the footwall of the normal fault-system. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Active tectonics is one of the fastest growing disciplines in Earth Sciences due to the recent development of new geochronological and geodetic tools which facilitate the acquisition of accurate rates (uplift rates, incision rates, erosion rates, slip rates on faults, etc.) at variable (10 3 –10 6 years) time-scales (e.g., Schumm et al., 2000; Burbank and Anderson, 2001; Keller and Pinter, 2002; Bull, 2007, 2009a,b). Furthermore, this discipline is becoming important because the results of regional studies on active tectonics are important for evaluating natural hazards, as well as for land use planning and management in populated areas (e.g., Cloetingh and Cornu, 2005). Apart from its social and economic interest, studies of active tectonics follow a multi-disciplinary approach, integrating data from structural geology, geomorphology, stratigraphy, geochronology, seismology, and geodesy. In mountain ranges, recent and active tectonics can be viewed as the main factor contributing to rock uplift, their present-day topography being the result of the competition between tectonic and erosional processes (e.g., England and Molnar, 1990; Bishop, 2007). In the same way, topography, drainage pattern analysis, and geomorphic features can be used to evaluate recent and present-day tectonic activity (e.g., Keller et al., 2000; Azor et al., 2002; Molin et al., 2004; Bull, 2007; Pérez-Peña et al., 2009a). The drainage pattern in tectonically active regions is very sensitive to active processes such as folding and faulting. These processes can be responsible for accelerated river incision, asymmetries of the catchments, and river diversions, among other effects (e.g., Cox, 1994; Jackson et al., 1998; Clark et al., 2004; Salvany, 2004; Schoenbohm et al., 2004). River incision in such regions is related to tectonic uplift, although other processes such as stream piracy, base-level lowering, and climatic episodes are also responsible for differential and accelerated river incision (e.g., Hancock and Anderson, 2002; Starkel, 2003; Azañón et al., 2005). Numerical dating of geomorphic surfaces and/or recent deposits is always necessary in order to obtain rates for the tectonic (folding, faulting, etc.) and geomorphic (river incision, Geomorphology 119 (2010) 74–87 ⁎ Corresponding author. E-mail address: vperez@ugr.es (J.V. Pérez-Peña). 0169-555X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2010.02.020 Contents lists available at ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph