Multi-Scale Analyses of Landscape: New Tools for Studying the Effect of
Erosion and Deposition on Landscape Morphology and Complexity
Abstract
Understanding the complex interplay between erosional and depositional
processes, and their relative roles in shaping landscape morphology is a
question at the heart of geomorphology. A unified framework for
examining this question can be developed by simultaneously considering
terrain elevation statistics over multiple scales. We show how a
long-standing tool for landscape analysis, the elevation-area or
hypsometry, can be complemented by an analysis of the elevation scalings
to produce a more sensitive tool for studying the interplay between
processes, and their impact on morphology. We then use this method, as
well as well-known geomorphic techniques (slope-area scaling relations,
the number of basins and basin size as a function of channel order) to
demonstrate how the complexity of an experimental landscape evolves
through time. Our primary result is that the complexity increases once a
flux equilibrium is established as a consequence of the role of
diffusive processes acting at intermediate elevations. We gauge
landscape complexity by comparing results between the experimental
landscape surfaces and those produced from a new algorithm that fixes in
place the elevation scaling statistics, but randomizes the elevations
with respect to these scalings. We constrain the degree of randomization
systematically and use the amount of constraint as a measure of
complexity. The starting point for the method is illustrated in the
figure, which shows the original landscape (top-left) and three
synthetic variants generated with no constraints to the randomization.
The value quoted in these panels is the root-mean-squared difference in
the elevation values for the synthetic cases relative to the original
terrain. This value is greatest where the original ridge becomes a
valley. All these landscapes contain the same elevation values (i.e. the
same probability distribution functions), and the same elevation
scalings at a point. The differences emerge because the elevations
themselves are distributed randomly across the surface.