EGU2020-10246, updated on 12 Jun 2020
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

The importance of lithology and throw rate on bedrock river behaviour and evolution in the Gediz (Alaşehir) Graben, Turkey.

Sarah Boulton1, Alexander Whittaker2, Emiko Kent1, M. Cihat Alcicek3, and Derek Fabel4
Sarah Boulton et al.
  • 1University of Plymouth, SoGEES, Plymouth, United Kingdom of Great Britain and Northern Ireland (
  • 2Department of Earth Science and Engineering, Royal School of Mines, Imperial College, London, UK
  • 3Department of Geological Engineering, Pamukkale University, Turkey.
  • 4Scottish Universities Environmental Research Centre, East Kilbride, U.K.

The Gediz (Alaşehir) Graben is located in the highly tectonically active and seismogenic region of Western Turkey, which has been experiencing high-angle normal faulting since ~ 2 Ma.  Rivers upstream of the normal fault-bounded graben each contain a lithologic knickpoint related to the change in bedrock geology (from soft sediments to hard metamorphic rocks) and a non-lithologic knickpoint, caused by an increase in fault slip rate at ~ 0.8 Ma.  Therefore, this system represents an ideal natural laboratory to investigate the relative roles of bedrock lithology / rock strength and rates of faulting on the behaviour and evolution of bedrock river systems. Our results show that metamorphic rocks in the catchments are 2-3 times harder than the sedimentary rocks. Stream power increases downstream reaching local maxima upstream of the fault within the metamorphic bedrock but declines rapidly once softer sedimentary rocks are encountered. We also demonstrate a positive correlation between throw rate and stream power in the metamorphic rocks characteristic of rivers obeying a detachment-limited model of erosion. In sedimentary rocks stream powers are invariant with throw rate but do scale with the river’s sediment transport capacity. We also present new Be10 denudation rates that show correlations with calculated stream power and fault throw rates. This study demonstrates that the strength of underlying bedrock is a major influence on river evolution and that the nature of the underlying lithology profoundly influences the way in which the river behaves.

How to cite: Boulton, S., Whittaker, A., Kent, E., Alcicek, M. C., and Fabel, D.: The importance of lithology and throw rate on bedrock river behaviour and evolution in the Gediz (Alaşehir) Graben, Turkey. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10246,, 2020

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  • CC1: Comment on EGU2020-10246, Jesse Zondervan, 04 May 2020

    Hi Sarah and Alex,

    To parametrise the erodibility (kb) from your field data, how do you characterize the uplift field (as you assume E=U)?

    Also, interesting finding on the relationship between transport capacity and throw rate. What does the c stand for in Qc for the MPM transport capacity?


    • AC1: Reply to CC1, Sarah Boulton, 05 May 2020

      Hi Jesse,


      Thanks for your questions. 1) Uplift.  We have previously calculated the motion on the graben boundary fault, so we have a value of throw. If we then assume that the graben is a horst with constant uplift we can take throw at the fault as the uplift. 

      2) Qis sediment transport capacity.

      Best wishes, Sarah