Rivers are a major component of sediment routing systems that control the transfer of terrigenous sediments from source to sink. Although it is widely accepted that rivers are perturbed by millennial-scale climatic variability, the extent to which these signals are buffered or transferred down river systems to be recorded in sediments at or beyond the river mouth remains debated. Here, we employ a physically based numerical model to address this outstanding issue. Our model shows that river transport strongly amplifies high-frequency sediment flux variations arising from changing water discharge, due to positive feedback between discharge and the channel gradient. This behavior is distinctly different from short-period sediment flux signals (with constant water discharge) where the output sediment flux is strongly dampened within the river, due to negative feedback between the channel gradient and sediment concentration. We conclude that marine sedimentary basins may record sediment flux cycles resulting from discharge (and ultimately climate) variability, whereas they may be relatively insensitive to pure sediment flux perturbations (such as for example those induced by tectonics)

Super-eruptions are extremely rare events. Indeed, the global frequency of explosive volcanic eruptions is inversely propor- tional to the volume of magma released in a single event1,2. The rate of magma supply, mechanical properties of the crust and magma, and tectonic regime are known to play a role in controlling eruption frequency and magnitude3–7, but their relative contributions have not been quantified. Here we use a thermomechanical numerical model of magma injection into Earth’s crust and Monte Carlo simulations to explore the fac- tors controlling the recurrence rates of eruptions of different magnitudes. We find that the rate of magma supply to the upper crust controls the volume of a single eruption. The time interval between magma injections into the subvolcanic reser- voir, at a constant magma-supply rate, determines the duration of the magmatic activity that precedes eruptions. Our simu- lations reproduce the observed relationship between eruption volume and magma chamber residence times and replicate the observed correlation between erupted volumes and caldera dimensions8,9. We also find that magma buoyancy is key to triggering super-eruptions, whereas pressurization associated with magma injection is responsible for relatively small and frequent eruptions. Our findings help improve our ability to decipher the long-term activity patterns of volcanic systems

This paper presents a mathematical model coupling water flow and sediment transport dynamics that enables calculating the changing surface morphology through time and space. The model is based on the shallow water equations for flow, conservation of sediment concentration, and empirical functions for bed friction, substrate erosion and deposition. The sediment transport model is a non-capacity formulation whereby erosion and deposition are treated independently and influence the sediment flux by exchanging mass across the bottom boundary of the flow. The resulting hyperbolic system is solved using a finite volume, Godunov-type method with a first-order approximate Riemann solver. The model can be applied both to short time scales, where the flow, sediment transport and morphological evolution are strongly coupled and the rate of bed evolution is comparable to the rate of flow evolution, or to relatively long time scales, where the time scale of bed evolution associated with erosion and/or deposition is slow relative to the response of the flow to the changing surface and, therefore, the classical quasi-steady approximation can be invoked. The model is verified by comparing computed results with documented solutions. The developed model can be used to investigate a variety of problems involving coupled flow and sediment transport including channel initiation and drainage basin evolution associated with overland flow and morphological changes induced by extreme events such as tsunami. r

[1] Sediment fans are a potentially useful and underexploited recorder of Earth's climatic and tectonic history, but historical observations have led to conflicting views on the importance of tectonic, climatic, and lithologic variables in controlling fan morphology and deposition. A one-dimensional model of a sediment fan and its associated catchment is used to explore the sensitivity of such simple sediment routing systems to perturbations in fault slip and precipitation rates. A transport-limited catchment is coupled to a fan whose surface slope is set by the balance between catchment sediment efflux and the available tectonically generated basin accommodation. Rock uplift rate is spatially variable across the model space. Increasing the fault slip rate, or decreasing the precipitation rate, leads to an increase in fan slope, temporary back-stepping of the fan toe, and a pronounced angular unconformity. Conversely, a decrease in slip rate, or an increase in precipitation rate, results in a decrease in fan slope, and progradation and eventual stabilization of the fan toe. Once perturbed, the system evolves toward a new equilibrium state with time constants of $0.5 to 2 Myr; these response times are insensitive to slip rate but are strongly dependent on precipitation rate. Variations in fan slope are well described by a dimensionless parameter that expresses equilibrium slope as a function of slip rate, precipitation rate, system size, and catchment lithology. This parameter holds promise as a predictive tool in inverting the morphology of natural fans for environmental variables.Citation: Densmore, A. L., P. A. Allen, and G. Simpson (2007), Development and response of a coupled catchment fan system under changing tectonic and climatic forcing,

[1] This paper quantifies how the ratio of sediment transport on hillslopes to sediment transport in channels influences surface and channel network morphologies and the dynamics of topographic evolution. This problem is investigated by development and investigation of a simple deterministic model incorporating mass balance of sediment and runoff coupled with a law combining dispersive and concentrative sediment transport processes. Our analysis includes the identification of a new nondimensional parameter D e that is a function of rainfall, system size, rock type, and hydraulic regime and that is a measure of the relative importance of fluvial and hillslope sediment transport. We show that D e has an important influence on the surface morphology (e.g., total exposed surface area and interface width which reflects surface roughness and relief), channel network form (e.g., channel sinuosity), channel spacing, and timescale of surface evolution. Surface and channel network morphologies are also strongly influenced by the overall surface slope relative to the magnitude of initial topographic roughness. Topographic evolution occurs in distinct phases of relief growth and decay, the transition between which is controlled by a saturation phenomenon related to the growth of spatial correlations. The scaling behavior of simulated topography with respect to both time and space is obtained and is shown to be independent of D e . Roughness exponents are found to be independent of D e but dependent on the magnitude of initial roughness. Interface width is shown to grow and decay as a logarithm of time.INDEX TERMS: 1625 Global Change: Geomorphology and weathering (1824, 1886); 1815 Hydrology: Erosion and sedimentation; 1860 Hydrology: Runoff and streamflow; 3210 Mathematical Geophysics: Modeling; KEYWORDS: erosion, landscape, topography, drainage network, diffusion, FEM modeling Citation: Simpson, G., and F. Schlunegger, Topographic evolution and morphology of surfaces evolving in response to coupled fluvial and hillslope sediment transport,