Large‐scale geomorphology: Classical concepts reconciled and integrated with contemporary ideas via a surface processes model

Abstract

Linear systems analysis is used to investigate the response of a surface processes model (SPM) to tectonic forcing. The SPM calculates subcontinental scale denudational landscape evolution on geological timescales (1 to hundreds of million years) as the result of simultaneous hillslope transport, modeled by diffusion, and fluvial transport, modeled by advection and reaction. The tectonically forced SPM accommodates the large‐scale behavior envisaged in classical and contemporary conceptual geomorphic models and provides a framework for their integration and unification. The following three model scales are considered: micro‐, meso‐, and macroscale. The concepts of dynamic equilibrium and grade are quantified at the microscale for segments of uniform gradient subject to tectonic uplift. At the larger meso‐ and macroscales (which represent individual interfluves and landscapes including a number of drainage basins, respectively) the system response to tectonic forcing is linear for uplift geometries that are symmetric with respect to baselevel and which impose a fully integrated drainage to baselevel. For these linear models the response time and the transfer function as a function of scale characterize the model behavior. Numerical experiments show that the styles of landscape evolution depend critically on the timescales of the tectonic processes in relation to the response time of the landscape. When tectonic timescales are much longer than the landscape response time, the resulting dynamic equilibrium landscapes correspond to those envisaged by Hack (1960). When tectonic timescales are of the same order as the landscape response time and when tectonic variations take the form of pulses (much shorter than the response time), evolving landscapes conform to the Penck type (1972) and to the Davis (1889, 1899) and King (1953, 1962) type frameworks, respectively. The behavior of the SPM highlights the importance of phase shifts or delays of the landform response and sediment yield in relation to the tectonic forcing. Finally, nonlinear behavior resulting from more general uplift geometries is discussed. A number of model experiments illustrate the importance of “fundamental form,” which is an expression of the conformity of antecedent topography with the current tectonic regime. Lack of conformity leads to models that exhibit internal thresholds and a complex response.

Drainage reorganization during mountain building in the river system of the Eastern Cordillera of the Colombian Andes

“…Koons, 1995; Kooi and Beaumont, 1996;Willett et al, 2001; Goren et al, 2014). However, 30 during mountain building, active folds and thrusts can deviate rivers from the regional slope 31 (e.g., Van der Beek et al, 2002).…”

Geomorphological evolution of western Sicily, Italy

“…The geomorphological setting of central-, and north-western Sicily is the result of the interaction between the tectonic uplift acting to elevate the relief and the following processes of river incision and denudation in general, which tend to lower it, removing great volumes of rock (e.g., Summerfield 1991; Kooi & Beaumont 1996;Burbank & Anderson 2012). These regions represent areas that became dry land long ago, and where erosion has already removed younger upper clastic deposits, destroyed ancient marine terraces, and progressively exhumed older underlying rock.…”

Comment on “The West Andean Thrust, the San Ramón Fault, and the seismic hazard for Santiago, Chile” by Rolando Armijo et al.

“…Contrary to this, the WAT, the active side of the orogen as interpreted by Armijo et al [2010], shows minor associated sedimentation, and counterintuitively their "back-thrust system" provides instead the major sediment source. This is against general theory and modeling of sediment flow across orogens as a response of surface processes to tectonic and climate forcing [Beaumont et al, 1992[Beaumont et al, , 2000Kooi and Beaumont, 1996;Stolar et al, 2006;Whipple and Meade, 2006]. These works demonstrate the importance of surface processes and sediment flux in relation to tectonic and climate forcing, implying a linear behavior and response to surface uplift and strong asymmetry of sediment delivery.…”