Browsing by Author "Hancock, GR"

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    Eroding Australia: slowly.
    (Elsevier, 2008-07) Heimsath, AM; Chappell, J; Hancock, GR; Fink, D; Fifield, LK
    We use in situ produced 10Be and 26Al to quantify erosion rates across a wide variety of field settings in Australia. Here we present the full suite of data from our diverse studies to provide an overview of how Austalia is eroding, as well as showing how robust this methodology is. Field sites range from several soil-mantled landscapes spanning the passive margin escarpment of southeastern Australia, to rocky, bedrock dominated landscapes in the Flinders Ranges and the Central Australia Outback. Also, in the far north, we examine an undisturbed catchment in the rugged topography of Arnhem Land: Tin Camp Creek. We sample detrital sands draining the landscape in a nested fashion at each of our field sites: from small to large catchments. We also sample across the slopes to quantify point-specific rates of soil production and bedrock erosion. Soil production rates and mechanisms across the escarpment have been presented in previous publications and will be used here to compare with a new, ‘humped’ soil prodction function from the Arnhem Land field site. In the rocky landscapes of the Flinders Ranges and MacDonnell Ranges, we sample the blocky slopes as well as catchment sands to constrain a block failure model for slope retreat. Point specific rates are also compared with detrital rates for Kings Canyon and the Todd River drainage to examine the potential for long-term landscape equilibrium. To conclude we show the first, unequivocal example of a regolith mantled landscape eroding in dynamic equilibrium from the western MacDonnell Range. Rates span an order of magnitude, from about 4 to 40 m/Ma across the escarpment in southeastern Australia. The ‘humped’ soil production function peaks at just over 20 m/Ma under about 30 cm of soil and decreases to less than 5 m/Ma under 70 cm of soil. Rates in the Outback are extremely slow, from less than 1 in places to the distance evidence for equilbrium in the Western MacDonnells, at about 7 m/Ma. These results raise many provocative questions and suggest new directions for quantifying how landscapes evolve. Copyright © 2008 Published by Elsevier Ltd.
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    The 'Humped' soil production function: eroding Arnhem Land, Australia.
    (Wiley-Blackwell, 2009-09-30) Heimsath, AM; Fink, D; Hancock, GR
    We report erosion rates and processes, determined from in situ-produced beryllium-10 (Be-10) and aluminum-26 (Al-26), across a soil-mantled landscape of Arnhem Land, northern Australia. Soil production rates peak under a soil thickness of about 35 cm and we observe no soil thicknesses between exposed bedrock and this thickness. These results thus quantify a well-defined 'humped' soil-production function, in contrast to functions reported for other landscapes. We compare this function to a previously reported exponential decline of soil production rates with increasing soil thickness across the passive margin exposed in the Bega Valley, south-eastern Australia, and found remarkable similarities in rates. The critical difference in this work was that the Arnhem Land landscapes were either bedrock or mantled with soils greater than about 35 cm deep, with peak soil production rates of about 20 m/Ma under 35-40 cm of soil, thus supporting previous theory and modeling results for a humped soil production function. We also show how coupling point-specific with catchment-averaged erosion rate measurements lead to a better understanding of landscape denudation. Specifically, we report a nested sampling scheme where we quantify average erosion rates from the first-order, upland catchments to the main, sixth-order channel of Tin Camp Creek. The low (similar to 5 m/Ma) rates from the main channel sediments reflect contributions from the slowly eroding stony highlands, while the channels draining our study area reflect local soil production rates (similar to 10 m/Ma off the rocky ridge; similar to 20 m/Ma from the soil mantled regions). Quantifying such rates and processes help determine spatial variations of soil thickness as well as helping to predict the sustainability of the Earth's soil resource under different erosional regimes. © 2009, Wiley-Blackwell. The definitive version is available at www3.interscience.wiley.com