Long‐term landscape evolution: linking tectonics and surface processes

Abstract

Research in landscape evolution over millions to tens of millions of years slowed considerably in the mid-20th century, when Davisian and other approaches to geomorphology were replaced by functional, morphometric and ultimately process-based approaches. Hack's scheme of dynamic equilibrium in landscape evolution was perhaps the major theoretical contribution to long-term landscape evolution between the 1950s and about 1990, but it essentially 'looked back' to Davis for its springboard to a viewpoint contrary to that of Davis, as did less widely known schemes, such as Crickmay's hypothesis of unequal activity. Since about 1990, the field of long-term landscape evolution has blossomed again, stimulated by the plate tectonics revolution and its re-forging of the link between tectonics and topography, and by the development of numerical models that explore the links between tectonic processes and surface processes. This numerical modelling of landscape evolution has been built around formulation of bedrock river processes and slope processes, and has mostly focused on high-elevation passive continental margins and convergent zones; these models now routinely include flexural and denudational isostasy.Major breakthroughs in analytical and geochronological techniques have been of profound relevance to all of the above. Low-temperature thermochronology, and in particular apatite fission track analysis and (U-Th)/He analysis in apatite, have enabled rates of rock uplift and denudational exhumation from relatively shallow crustal depths (up to about 4 km) to be determined directly from, in effect, rock hand specimens. In a few situations, (U-Th)/He analysis has been used to determine the antiquity of major, long-wavelength topography. Cosmogenic isotope analysis has enabled the determination of the 'ages' of bedrock and sedimentary surfaces, and/or the rates of denudation of these surfaces. These latter advances represent in some ways a 'holy grail' in geomorphology in that they enable determination of 'dates and rates' of geomorphological processes directly from rock surfaces. The increasing availability of analytical techniques such as cosmogenic isotope analysis should mean that much larger data sets become possible and lead to more sophisticated analyses, such as probability density functions (PDFs) of cosmogenic ages and even of cosmogenic isotope concentrations (CICs). PDFs of isotope concentrations must be a function of catchment area geomorphology (including tectonics) and it is at least theoretically possible to infer aspects of source area geomorphology and geomorphological processes from PDFs of CICs in sediments ('detrital CICs'). Thus it may be possible to use PDFs of detrital CICs in basin sediments as a tool to infer aspects of the sediments' source area geomorphology and tectonics, complementing the standard sedimentological textural and compositional approaches to such issues.One of the most stimulating of recent conceptual advances has followed the considerations of the relationships between te...

Natural experiments in landscape evolution

“…Kirkby, 1971, 1995. Recent reviews of mathematical landscape evolution models (LEMs) can be found in Coulthard (2001), Willgoose (2005), Codilean et al (2006), Bishop (2007), and Tucker and Hancock (submitted for publication).…”

Using topographic map interpretation methods to determine Tookany (Tacony) Creek erosion history upstream from Philadelphia, Pennsylvania, USA

“…While Thornbury (1969, p 29) argues, "Little of the earth's topography is older than Tertiary and most of it is no older than the Pleistocene" Bishop (2007) claims the Thornbury conclusion is based on "measured erosion rates that were almost certainly too high because of anthropogenic disturbance" and even "when more 'reasonable' long-term erosion rates were used… the Davisian erosion cycle required between 10 and 25 Myr to run its full course." Newer research approaches to studying landform evolution that replaced the Davis developed erosion cycle models do not challenge the Davis concept that landscapes evolve slowly over long periods of time.…”

Analysis of longitudinal profiles along the eastern margin of the Qinghai-Tibetan Plateau

“…As one of the primary mechanisms by which landscapes manifest and express changes in external boundary conditions, longitudinal profiles allow us to determine if channel incision exceeds, equals or is less than the influx of material into the drainage basin (Bishop 2007). Traditionally, this has been achieved by classifying longitudinal profiles as either upwardly concave or convex (Tippet and Hovius 2000).…”