@article{BrookeWhittakerArmitageetal.2018,
  author    = {Brooke, Sam A. S. and Whittaker, Alexander C. and Armitage, John J. and Watkins, Stephen E. and D'Arcy, Mitchell},
  title     = {Quantifying sediment transport dynamics on alluvial fans from spatial and temporal changes in Grain Size, Death Valley, California},
  series = {Journal of geophysical research : Earth surface},
  volume    = {123},
  journal   = {Journal of geophysical research : Earth surface},
  number    = {8},
  publisher = {American Geophysical Union},
  address   = {Washington},
  issn      = {2169-9003},
  doi       = {10.1029/2018JF004622},
  pages     = {2039 -- 2067},
  year      = {2018},
  abstract  = {How information about sediment transport processes is transmitted to the sedimentary record remains a complex problem for the interpretation of fluvial stratigraphy. Alluvial fan deposits represent the condensed archive of sediment transport, which is at least partly controlled by tectonics and climate. For three coupled catchment-fan systems in northern Death Valley, California, we measure grain size across 12 well-preserved Holocene and late-Pleistocene surfaces, mapped in detail from field observations and remote sensing. Our results show that fan surfaces correlated to the late Pleistocene are, on average, 30-50\% coarser than active or Holocene fan surfaces. We adopt a self-similar form of grain size distribution based on the observed stability of the ratio between mean grain size and standard deviation downstream. Using statistical analysis, we show that fan surface grain size distributions are self-similar. We derive a relative mobility function using our self-similar grain size distributions, which describes the relative probability of a given grain size being transported. We show that the largest mobile grain sizes are between 20 and 35mm, a value that varies over time and is clearly lower in the Holocene than in the Pleistocene; a change we suggest is due to a drier climate in the Holocene. These results support recent findings that alluvial fan sedimentology can record past environmental change and that these landscapes are potentially sensitive to climatic change over a glacial-interglacial cycle. We demonstrate that the self-similarity methodology offers a means to explore changes in relative mobility of grain sizes from preserved fluvial deposits. Plain Language Summary A key challenge in Earth Science is understanding how landscapes respond to climate. It may be possible to observe measurable differences in certain landscapes settings such as alluvial fans in desert regions. Alluvial fans are believed to be effective recorders of climate, representing a cumulative store of material transported downstream by rainfall-sensitive river systems. In northern Death Valley, California, we measure at high resolution grain size on three alluvial fans with surfaces that date from the Holocene and the arid climate of today to the 20-40\% wetter late-Pleistocene epoch. We find that older late-Pleistocene surfaces are coarser on average than surfaces deposited during the modern and Holocene dry period, suggesting a changing sediment transport regime potentially in response to precipitation. We also show that measured grain size distributions within and between surfaces can be successfully normalized based on the decay in mean grain size and variance downstream, exhibiting a self-similar pattern. Finally, we employ a grain size relative mobility model using our field data to establish which grain sizes are likely to be in transport or locked in the substrate. This model predicts that during the wetter late-Pleistocene mobile grain sizes are up to 40\% larger than during the Holocene.},
  language  = {en}
}
@article{RodaBoludaMcDonaldWhittakeretal.2018,
  author    = {Roda-Boluda, Duna C. and McDonald, Jordan and Whittaker, Alexander C. and D'Arcy, Mitchell},
  title     = {Lithological controls on hillslope sediment supply},
  series = {Earth surface processes and landforms : the journal of the British Geomorphological Research Group},
  volume    = {43},
  journal   = {Earth surface processes and landforms : the journal of the British Geomorphological Research Group},
  number    = {5},
  publisher = {Wiley},
  address   = {Hoboken},
  issn      = {0197-9337},
  doi       = {10.1002/esp.4281},
  pages     = {956 -- 977},
  year      = {2018},
  abstract  = {The volumes, rates and grain size distributions of sediment supplied from hillslopes represent the initial input of sediment delivered from upland areas and propagated through sediment routing systems. Moreover, hillslope sediment supply has a significant impact on landscape response time to tectonic and climatic perturbations. However, there are very few detailed field studies characterizing hillslope sediment supply as a function of lithology and delivery process. Here, we present new empirical data from tectonically-active areas in southern Italy that quantifies how lithology and rock strength control the landslide fluxes and grain size distributions supplied from hillslopes. Landslides are the major source of hillslope sediment supply in this area, and our inventory of similar to 2800 landslides reveals that landslide sediment flux is dominated by small, shallow landslides. We find that lithology and rock strength modulate the abundance of steep slopes and landslides, and the distribution of landslide sizes. Outcrop-scale rock strength also controls the grain sizes supplied by bedrock weathering, and influences the degree of coarsening of landslide supply with respect to weathering supply. Finally, we show that hillslope sediment supply largely determines the grain sizes of fluvial export, from catchments and that catchments with greater long-term landslide rates deliver coarser material. Therefore, our results demonstrate a dual control of lithology on hillslope sediment supply, by modulating both the sediment fluxes from landslides and the grain sizes supplied by hillslopes to the fluvial system.},
  language  = {en}
}