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| Titel |
Rock particle fragmentation, as an alternative to fluvial transport, explains size sorting on arid hillslopes |
| VerfasserIn |
Zhengyao Nie, Gavan McGrath, Christoph Hinz |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250050318
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| Zusammenfassung |
| To date fluvial transport processes have been suggested as the underlying mechanisms
explaining the sorting of rock particles on arid hillslopes, whereby mean particle
sizes typically decrease in the downslope direction. Here we show that a dynamic
fragmentation model of particles can also reproduce similar emergent patterns. We
measured rock particle size distributions using photographic techniques on three mesa
hillslopes slopes in the Great Sandy Desert, Australia. On each hill four transects were
constructed in the direction of steepest descent and on each transect four photographs
covering one square meter at a minimum resolution of 0.28 mm2/pixel, were taken at
each three meter interval to a maximum transect length of 60 meters. From the
resulting photographs the projected Feret’s diameter was determined following
digitisation of individual rock particles. Rock particles were typically distributed
lognormally at each location, with distributions narrowing and shifting to smaller sizes
downslope. Both parameters of the lognormal distribution were found to decrease linearly
with distance down the transects. As particle sizes were often much larger than
those which could be expected to be transported downslope by fluvial processes
on these short hills we assessed whether a dynamic fragmentation model could
reproduce the observed patterns instead. The particle size distribution measured
at the top of the slope was used as the initial condition. We further assumed that
distance along a transect could be replaced by time in the fragmentation model.
The model, with just two parameters, reproduced the observed trends in particle
size distributions and did so better than the linear regressions. We found that in
order for the fragmentation model to reproduce the observed behaviour a particular
form of fragmentation was required where larger particles were less resistant to
weathering fragmentation than smaller particles. Our results have implications for
understanding the evolution of rock armoured slopes in natural and engineered contexts,
sensitive to the dynamics of surface rocks affecting runoff, erosion and infiltration. |
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