Geoscience Reference
In-Depth Information
Development and elaboration of transport laws offer the potential to connect
studies of active processes with their signatures in landscapes and the related
sedimentary and climatic record. In addition, recent studies have highlighted the
importance of regional context in sorting out controls on landscape development and
evolution as competing theories are seen to have more or less explanatory power in
different physiographic, tectonic, and climatic settings. For example, numerous
studies have documented evidence for the operation of a so-called “glacial buzzsaw”
through which efficient glacial erosion above the glacial equilibrium line altitude
(ELA) limits the height of mountains (Brozović et al., 1997; Mitchell and
Montgomery, 2006; Enghold et al., 2009). In contrast, glaciers in the southern Andes
have the opposite effect and instead shield alpine topography from erosion and
thereby enhance elevation (Thomson et al., 2010). Likewise, a recent study that
reviewed global erosion rates found that, contrary to the often invoked conventional
wisdom that glaciers are the most efficient erosional agents, erosion by rivers can
keep up with glacial erosion in tectonically active mountain belts (see Figure 2.15). In
some regions the landscape-scale pace of erosion is correlated with hillslope
steepness (or local relief; Ahnert, 1970), whereas in others it is correlated with
changes in river profile steepness (Wobus et al., 2003). Like these examples, many of
the key controls on landscape evolution appear to have context-dependent aspects that
present challenges—and opportunities—for developing integrated global
understanding of the controls on landscape dynamics. Greater understanding is
needed not only to identify fundamental controls on, and theory for, landscape
evolution but also to understand how different circumstances and settings influence
the driving forces or dominant factor(s) and how systems interact in different regional
contexts. Only then can the range and limits to the applicability of theories and the
strength and consequences of interactions among processes be known.
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