Preprints
https://doi.org/10.5194/esurf-2021-4
https://doi.org/10.5194/esurf-2021-4

  10 Feb 2021

10 Feb 2021

Review status: this preprint is currently under review for the journal ESurf.

Stochastic alluvial fan and terrace formation triggered by a high-magnitude Holocene landslide in the Klados Gorge, Crete

Elena T. Bruni1, Richard F. Ott1, Vincenzo Picotti1, Negar Haghipour1,2, Karl W. Wegmann3,4, and Sean F. Gallen5 Elena T. Bruni et al.
  • 1Department of Earth Sciences, ETH Zürich, Switzerland
  • 2Laboratory of Ion Beam Physics, ETH Zürich, 8092 Zurich, Switzerland
  • 3Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, NC, USA
  • 4Centre for Geospatial Analytics, North Carolina State University, Raleigh, NC, USA
  • 5Department of Geosciences, Colorado State University, Colorado, USA

Abstract. Alluvial fan and terrace formation is traditionally interpreted as related to Quaternary climate oscillations under the backdrop of slow and steady tectonic activity. However, several recent studies challenge this conventional wisdom, showing that such landforms can evolve rapidly as a geomorphic system responds to catastrophic and stochastic events, like large magnitude mass-wasting. Here, we contribute to this topic through a detailed field and geochronological investigation of alluvial sequences in the Klados catchment in southwestern Crete, Greece. The Klados River catchment is characterised by well-preserved, alluvial terraces and a set of fans at the river mouth, which do not seem to fit the sediment capacity of a small catchment with a drainage area of ~ 11.5 km2. Previous studies interpreted the formation of the deposits and their development to be of Pleistocene age and controlled by climate variations and the region's long-term tectonic activity. We find that the > 20 m thick intermediate fan buries a paleoshoreline uplifted in AD 365 placing the depositional age of this unit firmly into the Late Holocene. This is supported by seven new radiocarbon dates that infer mid to late Holocene ages for the entire fan and terrace sequence. As sediment source, we identify a landslide scar at the head of the catchment. We document landslide deposits 100 m above the modern stream and utilise landslide runout modelling to reconstruct landslide volumes and validate our hypothesis. We find that a landslide volume of 0.0908 km2 matches the observed distribution of landslide deposits and the landslide scar dimensions. We hypothesise that subsequent aggradation and incision cycles of the alluvial deposits are not linked to long-term tectonic uplift and climate variations but rather stochastic events such as mobilisation of sediment in large earthquakes, storm events, or blockage in the valley's narrow reaches. The Klados case study represents a model-environment for how stochastically-driven events can mimic climate-induced sedimentary archives, and how catchments can become ultrasensitive to external perturbations after catastrophic events.

Elena T. Bruni et al.

Status: open (until 02 Apr 2021)

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Elena T. Bruni et al.

Elena T. Bruni et al.

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Short summary
The Klados River catchment contains seemingly overlarge, well-preserved, alluvial terraces and fans. Unlike previous studies, we argue that the deposits formed in the Holocene based on their relative position to a paleoshoreline uplifted in AD365 and seven radiocarbon dates. Besides, we find that constant sediment supply from high-lying landslide deposits disconnected the valley from regional tectonics and climate controls, which resulted in fan and terrace formation guided by stochastic events.