Erosion of a tectonically uplifting coastal landscape, NE Sicily, Italy R. Goswami ⁎, S.H. Brocklehurst, N.C. Mitchell Basin Studies and Petroleum Geoscience Research Group, School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester M13 9PL, United Kingdom abstract article info Article history: Received 20 September 2011 Received in revised form 9 May 2012 Accepted 12 May 2012 Available online 22 May 2012 Keywords: Channel concavity Uplift rate Channel steepness Channel width Bedrock erodibility Sicily We investigate the relative importance of tectonic uplift, climate, and bedrock resistance as controls upon channel morphology in the active orogen of NE Sicily. The study area displays spatial variations in uplift rate, precipitation, and bedrock resistance. The signiﬁcance of each of these gradients was tested using established morphometric relationships. Twenty catchments were investigated using the 28-m Aster digital elevation model (DEM) for longitudinal proﬁle analysis, Google Earth TM to determine channel widths, and Schmidt Hammer readings to quantify bedrock strength. Based on channel morphologies and hillslope gradi- ents, the basins exhibit three distinct reaches: upper, middle, and lower. The upper reaches of the bedrock channels display concave longitudinal proﬁles, positive correlation between uplift rate and steepness, and ex- ponents in the width–area relationship of 0.4–0.5, indicating that uplift is the major control on the morphol- ogy of this reach. The middle reaches, however, display sublinear longitudinal proﬁles, weak correlation between uplift rate and channel steepness, and no systematic width–area relationship. We interpret this to be caused by the presence of a shear zone, which, through fracturing, has tectonically increased the bedrock erodibility, irrespective of its lithology. In the lower reaches, the channels are alluvial. Neither channel con- cavity nor steepness seems to be affected by the spatial variation in precipitation in any of the reaches, indi- cating that climate does not noticeably affect channel morphology. These observations suggest a strong tectonic inﬂuence on channel evolution in this active mountainous region. Our study illustrates how reach- scale morphometric analysis can aid understanding of how ﬂuvial systems vary with potential controlling parameters. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Geomorphic studies on rivers incising bedrock in tectonically active landscapes have highlighted the importance of both climate and tectonics in landscape evolution (e.g., Molnar and England, 1990; Beaumont et al., 1992; Hancock et al., 1998; Whipple and Tucker, 1999; Burbank and Anderson, 2001; Burbank, 2002). Howev- er, a major challenge lies in isolating the effects of individual factors. Many studies have investigated the inﬂuence of tectonics on channel morphology in steady-state landscapes, where channels steepen their longitudinal proﬁles in association with faster uplift (e.g., Whipple and Tucker, 1999, 2002; Snyder et al., 2000, 2002, 2003a, 2003b; Kirby and Whipple, 2001; Kirby et al., 2003). However, the same association of steeper channels and faster rock uplift is also observed for landscapes that are not necessarily in steady state (Kirby and Ouimet, 2011). The channel steepness–uplift rate relationship gener- ally assumes an ideal bedrock channel, where channel width is a power-law function of discharge (Seidl and Dietrich, 1992; Snyder et al., 2000; Whipple et al., 2000a, 2000b; Kirby and Whipple, 2001; Wobus et al., 2006; DiBiase et al., 2010). Because the adjustment of a channel to changing external forces occurs not only along its longitudinal proﬁle but also across its width (e.g., Hancock and Anderson, 2002; Stark, 2006), several stud- ies have explicitly addressed changes to the width–area relationship (e.g., Leopold and Maddock, 1953; Montgomery and Gran, 2001; Snyder et al., 2003a, 2003b; Finnegan et al., 2005). Whittaker et al. (2007) demonstrated that the width–area scaling relationship breaks down in response to tectonic forcing; channels in the Apennines narrow during the transient response to an increase in uplift rate. Changes in channel width also reﬂect the local inﬂuence of bedrock lithology or erosivity along the channel length, i.e., weaker channels are wider, as shown by the mountainous channel systems in Washington and Oregon (Montgomery and Gran, 2001). Bedrock channels have also generally considered climate to be spatially uniform. Whipple et al. (1999) conducted an analytical study of the inﬂuence of climate on a landscape, and suggested that, in a steady-state, tectonically-active mountain range, climatically en- hanced erosion (e.g., from increased precipitation) reduces the relief along the channel. Zaprowski et al.'s (2005) study in the eastern High Plains region of the U.S. illustrated that higher mean annual rainfall and mean peak annual discharge increase overall bedrock channel concavity. However, both of these studies relate to uniform precipitation. Numerical studies of the effects of orographic precipita- tion have suggested that precipitation patterns can be a ﬁrst-order Geomorphology 171–172 (2012) 114–126 ⁎ Corresponding author. E-mail address: rajasmita@gmail.com (R. Goswami). 0169-555X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2012.05.011 Contents lists available at SciVerse ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph