Glassy dynamics of landscape evolution

Geology, 2001

Landscape evolution models are widely used to explore links between tectonics, climate, and hillslope morphology, yet mechanisms of hillslope erosion remain poorly understood. Here we use a laboratory hillslope of granular material to experimentally test how creep and landsliding contribute to hillslope erosion. In our experimental hillslope, disturbance-driven sediment transport rates increase nonlinearly with slope due to dilation-driven granular creep, and become increasingly episodic at steep slope angles as creep gives way to periodic landsliding. We use spectral analysis to quantify the variability of sediment flux and estimate the slopedependent transition from creep to landsliding. The power spectrum of sediment flux steepens with hillslope gradient, exhibiting fractal 1/f scaling just below the creep-landsliding transition. By evolving the experimental hillslope under fixed base-level boundary conditions, we demonstrate how disturbance-driven transport generates hillslope convexity. The transient evolution is consistent with numerical predictions derived from a recently proposed nonlinear transport model, as initially steep hillslopes are lowered rapidly by landsliding before slopes decay slowly by creep-dominated transport.

Physical Review E, 1998

We propose and study numerically a stochastic cellular automaton model for the dynamics of granular materials with temporal disorder representing random variation of the diffusion probability 1 − µ(t) around threshold value 1 − µ0 during the course of an avalanche. Combined with the slope threshold dynamics, the temporal disorder yields a series of secondary instabilities, resembling those in realistic granular slides. When the parameter µ0 is lower than the critical value µ ⋆ 0 ≈ 0.4, the dynamics is dominated by occasional huge sandslides. For the range of values µ ⋆ 0 ≤ µ0 < 1 the critical steady states occur, which are characterized by multifractal scaling properties of the slide distributions and continuously varying critical exponents τX(µ0). The mass distribution exponent for µ0 ≈ 0.45 is in agreement with the reported value that characterizes Himalayan sandslides. At µ0 = µ ⋆ 0 the exponents governing distributions of large relaxation events reach numerical values which are close to those of parity-conserving universality class, whereas for small avalanches they are close to the mean-field exponents.

Water Resources Research, 1999

Steep, soil-mantled hillslopes evolve through the downslope movement of soil, driven largely by slope-dependent transport processes. Most landscape evolution models represent hillslope transport by linear diffusion, in which rates of sediment transport are proportional to slope, such that equilibrium hillslopes should have constant curvature between divides and channels. On many soil-mantled hillslopes, however, curvature appears to vary systematically, such that

Géotechnique, 2018

Fluidised landslides are one of the most dangerous types of mass movements as they can run over long distances at high velocity. A flow-like landslide can occur in both artificially designed and natural slopes, resulting in extensive property damage and significant loss of life. Although various studies have examined the initiation mechanism of this type of landslide, the understanding of the phenomenon of instability which can occur in loose granular slopes deserves further attention. Specific influential factors, such as the changes in the soil microstructure due to water infiltration and seepage forces, still need to be further examined. In this study, the initiation of a fluidised landslide is investigated through flume tests. The tested material was collected from a coseismic landslide deposit in the 2008 Wenchuan earthquake area. These loose, granular deposits can fail due to intense rainfall and exhibit flow-like movement, potentially evolving into destructive debris flows. T...

Rock Mechanics and Rock Engineering, 2008

Experience shows that slope movements occurring in similar geomorphogical contexts may display very different styles and magnitude. This has important practical implications, since the risk associated with a landslide depends just on its magnitude. The paper discusses the mechanics of slope failure in coarse-grained and in fine-grained soils with particular reference to flow-like landslides, showing that even small details can affect their movement pattern.

Landslides

Rock avalanches are among the most hazardous processes on hillslopes because of high velocity, great dimensions, and long run-out distance. For this reason, understanding the dynamics and factors of rock avalanches and their role in hillslope evolution is crucial. Studies evidenced that occurrence and evolution of these phenomena are influenced by lithological, structural, and climatic factors. Statistical analysis on natural cases demonstrated correlations between slope geometry and rock avalanche volume. Most of the studies referred to experimental tests which represent powerful tools to understand these landslides. Many models focused on the mechanism leading to high velocity and long run-out, but few studies discuss the role of rock avalanches in the evolution of a bedrock hillslope. The influence of slope geometry and physical properties of the substratum on the dynamics of rock avalanches is poorly constrained. We present results from analog models of a hillslope evolving by base level lowering. We tested several slope widths and two analog materials. The experimental apparatus allowed for checking the mass of mobilized material at each step and for taking a 3D scan of the whole surface. Our results, coupled with a statistical analysis, indicated that hillslope evolution is influenced by the material internal friction and by the friction with box walls (i.e., valley walls) when the slope is narrow. Widening the slope, the influence of lateral friction disappears, confirming observations in other models and nature. These results represent a new contribution to understand the dynamics of rock avalanches on bedrock hillslopes.

A geomorphic transport law is a mathematical statement derived from a physical principle or mechanism, which expresses the mass flux or erosion caused by one or more processes in a manner that: 1) can be parameterized from field measurements, 2) can be tested in physical models, and 3) can be applied over geomorphically significant spatial and temporal scales. Such laws are a compromise between physics-based theory that requires extensive information about materials and their interactions, which may be hard to quantify across real landscapes, and rules-based approaches, which cannot be tested directly but only can be used in models to see if the model outcomes match some expected or observed state. We propose that landscape evolution modeling can be broadly categorized into detailed, apparent, statistical and essential realism models and it is the latter, concerned with explaining mechanistically the essential morphodynamic features of a landscape, in which geomorphic transport laws are most effectively applied. A limited number of studies have provided verification and parameterization of geomorphic transport laws for: linear slope-dependent transport, non-linear transport due to dilational disturbance of soil, soil production from bedrock, and river incision into bedrock. Field parameterized geomorphic transport laws, however, are lacking for many processes including landslides, debris flows, surface wash, and glacial scour. We propose the use of high-resolution topography, as initial conditions, in landscape evolution models and explore the applicability of locally parameterized geomorphic transport laws in explaining hillslope morphology in the Oregon Coast Range. This modeling reveals unexpected morphodynamics, suggesting that the use of real landscapes with geomorphic transport laws may provide new insights about the linkages between process and form.

Journal of Geophysical Research: Earth Surface, 2014

High mobility of natural avalanches ? substratum erosion plays a key role in flow dynamics !

Earth and Planetary Science Letters, 2009

Geology, 2001

Landscape evolution is modeled widely using a simple creep law for complex processes of sediment transport. Here, field data show how a new transport model, combined with an exponential soil production law, better captures spatial variations of soil thickness on hillslopes. We combine parameterizations of simple and depth-dependent creep with overland flow to predict soil thickness and suggest how soil distribution evolves in response to climatic and tectonic forcing. We present an empirical expression for the response time of the system to external forcing that shows strong dependence on relief and is independent of soil production rate. We suggest that this parameterization may be used to quantify upland carbon storage and removal and predict impacts of deforestation or rapid climatic changes.