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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/esurf-2020-29
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/esurf-2020-29
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  02 Jun 2020

02 Jun 2020

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A revised version of this preprint is currently under review for the journal ESurf.

Box canyon erosion along the Canterbury coast (New Zealand): A rapid and episodic process controlled by rainfall intensity and substrate variability

Aaron Micallef1,2, Remus Marchis3, Nader Saadatkhah1, Roger Clavera-Gispert1, Potpreecha Pondthai4, Mark E. Everett4, Anca Avram5,6, Alida Timar-Gabor5,6, Denis Cohen2, Rachel Preca Trapani2, and Bradley A. Weymer1 Aaron Micallef et al.
  • 1Helmholtz Centre for Ocean Research, GEOMAR, Kiel, Germany
  • 2Marine Geology & Seafloor Surveying, Department of Geosciences, University of Malta, Malta
  • 3Department of Geological Sciences, University of Canterbury, Christchurch, New Zealand
  • 4Department of Geology and Geophysics, Texas A&M University, Texas, USA
  • 5Faculty of Environmental Science and Engineering, Babes-Bolyai University, Cluj-Napoca, Romania
  • 6Interdisciplinary Research Institute on Bio-Nano-Sciences, Babeş-Bolyai University, Cluj-Napoca, Romania

Abstract. Box canyon formation has been associated to groundwater seepage in unconsolidated sand to gravel sized sediments. Our understanding of box canyon evolution mostly relies on experiments and numerical simulations, and these rarely take into consideration contrasts in lithology and permeability. In addition, process-based observations and detailed instrumental analyses are rare. As a result, we have a poor understanding of the temporal scale of box canyon formation and the influence of geological heterogeneity on their formation. We address these issues along the Canterbury coast of the South Island (New Zealand) by integrating field observations, optically stimulated luminescence dating, multi-temporal Unmanned Aerial Vehicle and satellite data, time-domain electromagnetic data, and slope stability and landscape evolution modelling. We show that box canyon formation is a key process shaping the sandy gravel cliffs of the Canterbury coastline. It is an episodic process associated to groundwater flow that occurs once every 227 days on average, when rainfall intensities exceed 40 mm per day. The majority of the box canyons in a study area SE of Ashburton has undergone erosion, predominantly by elongation, during the last 11 years, with the most recent episode occurring 3 years ago. The two largest box canyons have not been eroded in the last 2 ka, however. Canyons can form at rates of up to 30 m per day via two processes: the formation of alcoves and tunnels by groundwater seepage, followed by retrogressive slope failure due to undermining and a decrease in shear strength driven by excess pore pressure development. The location of box canyons is determined by the occurrence of hydraulically-conductive zones, such as relict braided river channels and possibly tunnels, and of sand lenses exposed across sandy gravel cliff. We also show that box canyon formation is best represented by a linear diffusive model and geometrical scaling.

Aaron Micallef et al.

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Aaron Micallef et al.

Aaron Micallef et al.

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Short summary
Box canyons are wide valleys that are associated with seepage of groundwater. Here we study box canyons along the Canterbury coast of New Zealand using field observations, sample analyses, drones, satellites, geophysical instruments and modelling. We show that these box canyons form when rainfall intensity is higher than 40 mm per day. The canyons form by landslides where buried channels or sand lenses are located. This information allows us to predict where box canyons may form in the future.
Box canyons are wide valleys that are associated with seepage of groundwater. Here we study box...
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