Evaluating a new landform evolution model: A case study using a proposed mine rehabilitation landform

Landform evolution models are powerful tools for determining long-term erosional stability and denudation rates spanning geological timescales. SIBERIA, CAESAR and CHILD are examples of these model. The newly developed State Space Soil Production and Assessment Model (SSSPAM) coupled soilscape-landform evolution model has the ability to assess overall erosion rates of catchment scale landforms either using short-term precipitation events, variable precipitation or time-averaged precipitation (annual average). In addition, SSSPAM has the capability of developing the subsurface soil profile through weathering and armouring. In SSSPAM, physical processes of pedogenesis such as erosion and armouring, diffusion, sediment deposition and weathering are modelled using a state space matrix approach. In this article we simulate the short-term evolution (100 years) of a proposed post-mining landform using both SIBERIA and SSSPAM and compare the erosion and sediment output results. For the short-term simulations SSSPAM's armouring capability was disabled. The models were then used to simulate the evolution of the catchment for 10,000 years. Results demonstrate that the short-term SSSPAM simulation results compare well with the results from the established landform evolution model SIBERIA. The long-term armouring disabled SSSPAM simulations produces simulated erosion rates comparable with SIBERIA simulations both of which are similar to upper limit of field measured denudation rates. The SSSPAM simulation using armouring demonstrated that armouring reduced the erosion rate of the catchment by a factor of 4 which is comparable with the lower limit of field measured denudation rates. This observation emphasizes the importance of armouring in long-term evolution of landforms. Soil profile cross-sections developed from the same results show that SSSPAM can also reproduce subsurface soil evolution and stratification and spatial variability of soil profile characteristics typically observed in the field.     

Predicting gully erosion using landform evolution models: Insights from mining landforms

Incision as a result of fluvial erosion is an important process to model when simulating landform evolution. For gullies, it is apparent that coupled with the processes that cause incision there must be a range of processes that stop incision. Once started, rills and gullies will grow infinitely without a reduction in support area and/or being arrested by deposition and armouring. Some of these processes have been well studied under the heading of inter-rill erosion. Other limiting processes are related to the shape of the landform and how downstream deposition areas are linked geomorphically to the upstream gullies. Armouring is also an important process that reduces gully incision and extension, where the gully erodes to bedrock and the resistant base limits further development. Post-mining landscapes are new surfaces with new materials and provide the opportunity to examine gully initiation, extension and stabilization. The work presented here has largely been driven by the mining industry, where there has been a need to assess erosion over hazardous wastes like mine tailings and low-level nuclear waste. We demonstrate the usefulness of computer-based landscape evolution models and the more recent soilscape models (that include both surface and subsurface processes) to understand both fluvial and diffusive processes as well as armouring in a digital elevation model framework (as well as landscape evolution). Landscape evolution models provide insights into complex non-linear systems such as gullies. A key need is that of field data to parameterize and validate the models. It is argued that current models have more capability than field data available for parameterization and importantly the validation of model outputs.     

The Australia telescope 20 GHz survey: hardware, observing strategy, and scanning survey catalog

The Australia Telescope 20 GHz (AT20G) survey is a large area (2?? sr), sensitive (40 mJy), high frequency (20 GHz) survey of the southern sky. The survey was conducted in two parts: an initial fast scanning survey, and a series of more accurate follow-up observations. The follow-up survey catalog has been presented by Murphy et al. (MNRAS 402:2403, 2010). In this paper we discuss the hardware setup and scanning survey strategy as well as the production of the scanning survey catalog.     

Secondary Fe and Al in Antarctic paleosols: Correlation to Mars with prospect for the presence of life

Middle-Miocene age paleosols in the Antarctic Dry Valleys were studied for their compositional variation and concentrations of secondary oxides/coatings in <2 mm matrix material in tills. The paleosols date to between 10-18 Ma by ¹⁰Be, forming prior to and just following the transition from warm-based to cold-based ice, when the climate is thought to have entered a prolonged cold/dry period in which soil moisture would have been frozen most of the year. The progression of release of secondary oxides of Fe and Al shows variable percentages of individual oxihydrites relative to chemical element totals, and thus, to consume total Fe and Al would require tens of millions of additional years. The slow progression of Fe_d/Fe_t, used as a measure of relative age in other warmer alpine and Arctic climates, is shown here to amount to <15 percent of the total Fe available for weathering. Ferrihydrite variability in paleosols, often used to indicate the presence of fluctuating/perched ground water tables, suggests that liquid water may have accumulated in mid-profile in some instances, perhaps during periods when the climate was somewhat warmer for several weeks during the summer. Variable Fe and Al ratios and arithmetic functions argue for extremely slow but sustainable release of oxides in a cold, polar desert climate, in which temperatures prohibit the formation of clay minerals. The secondary mineral species present likely amount to residue from past climates that were more conducive to clay mineral genesis and aerosolic input over time. The presence of microbial life in Antarctic paleosols, with minor amounts of Fe available for physiological processes to function, argues for the potential existence of microorganisms in ice-enriched paleosols of Mars, particularly given its watery and dynamic geologic past and relatively high concentration of total Fe in subaerial paleosols. The distribution of Fe over a large part of the northern plains of Mars as determined by the GRS instrument is invoked as a comparison with the Antarctic.     

Implications of variability on many time scales for scientific advice on sustainable management of living marine resources

The conceptual basis for understanding and management of living marine resources is built on three basic ecological principles developed in the first half of the past century: the law of the minimum, competitive exclusion, and succession. This paper highlights aspects of these principles that make them insufficient as a sound foundation for understanding and managing marine ecosystems, points out dangers of continuing to use approaches built on them, and presents alternatives which might be more appropriate and of lower risk.To do this, the paper considers variability of marine ecosystems on annual, medium and long-term time scales, highlighting that these scales correspond to less than, approximately equal to, and much greater than, the generation times of dominant predators in the systems. It also considers how each interval of variability may affect directly ecosystems which are controlled from the bottom up, top down, and middle outward, and how position and duration of forcing affect five types of responses: growth, maturation, recruitment, predation, and competition. Generally these five processes have manifestations at the scale of individuals, populations, and ecosystems, attention is drawn to which manifestations are the most significant for each duration and position of forcing.Effects of some combinations of duration of forcing and position of forcing can be explained reasonably well by conventional ecological theory. For other combinations, particularly forcing at time scales of predator generations on top-down or middle-out ecosystems, theory based on contest competition and equilibria are likely to be misleading. In these systems the major dynamics are transients, when many ecosystems are far from their carrying capacities, so scramble competition dominates, and the carrying capacity is not helpful in explaining the system dynamics. This review clarifies the sorts of questions that we should be asking, in order to begin to understand the transient behaviour of these non-equilibrium ecosystems. The answers to the new classes of questions may lead to great improvements in how ecosystems are managed, as well as how their variation is explained.     

The Influence of Strong-Motion Duration on the Seismic Response of Masonry Structures

The influence of strong-motion duration on the response of saturated soils is clearly recognised and accounted for in the assessment of liquefaction potential. The degree to which duration of shaking influences damage to structures, however, remains a topic of debate, with resolution of the issue complicated by the variety of definitions of duration and the variety of structural behaviours, as well as the difficulty of decoupling the specific effect of duration from other features of the ground motion. A suite of seven structural models with strength and stiffness degrading characteristics, designed to reflect the seismic behaviour of masonry structures commonly encountered in many parts of Europe, are analysed using a suite of almost 500 strong-motion accelerograms. Correlations are explored between the damage, measured in terms of the strength degradation, and a range of strong-motion parameters, demonstrating that Arias intensity and spectral acceleration at the fundamental initial period of the structure are both reasonably good damage indicators for such structures. A significantly improved correlation is obtained by using the elastic spectral accelerations averaged over a period range from the initial period of the structure to a value approximately three times greater, reflecting the stiffness degradation as the shaking progresses. The scatter in the correlation is shown to be partially explained by differences in duration. This revised version was published online in July 2006 with corrections to the Cover Date.     

The use of a landscape simulator in the validation of the SIBERIA landscape evolution model: transient landforms

SIBERIA is a physically based model for the geomorphic evolution of landforms. It is essential that the SIBERIA model be tested or validated against controlled landform development. Previous studies have demonstrated that SIBERIA is able to simulate declining equilibrium landforms and in this paper we examine SIBERIA's ability to simulate landforms as they evolve to their declining equilibrium form. These landscapes are termed transient landforms. Landscapes generated by SIBERIA were compared to those produced by a physical model (experimental model landforms) at stages of evolution. Comparison of the experimental landscapes with the simulated landscapes using total mass, hypsometric curve, width function, cumulative area distribution and area–slope demonstrate that SIBERIA can simulate the experimental model landscape during development (i.e. transient landscapes). Copyright © 2002 John Wiley & Sons, Ltd.