EGU2020-19935
https://doi.org/10.5194/egusphere-egu2020-19935
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Geomorphic feedbacks on the moraine record

Leif Anderson1 and Dirk Scherler1,2
Leif Anderson and Dirk Scherler
  • 1GFZ, German Research Centre For Geosciences, Section 3.3, Potsdam, Germany (leif@gfz-potsdam.de)
  • 2Institute of Geological Sciences, Freie Universität, Berlin, Germany

Glacial moraines represent one of the most spatially diverse climate archives on earth. Moraine dating and numerical modeling are used to effectively reconstruct past climate from mountain ranges at the global scale. But because moraines are often located downvalley from steep mountain headwalls, it is possible that debris-covered glaciers emplaced many moraines preserved in the landscape today.

Before we can understand the effect of debris cover on the moraine recored we need to understand how debris modulates glacier response to climate change. To help address this need, we developed a numerical model that links feedbacks between mountain glaciers, climate change, hillslope erosion, and landscape evolution. Our model uses parameters meant to represent glaciers in the Khumbu region of Nepal, though the model physics are relevant for mountain glaciers elsewhere.

We compare simulated debris-covered and debris-free glaciers and their length evolution. We explore the effect of climate-dependent hillslope erosion. We also allow temperature change to control frost cracking and permafrost in the headwall above simulated glaciers. Including these effects holds special implications for glacial evolution during deglaciation and the long-term evolution of mountain landscapes.

Because debris cover suppresses melt, debris-covered glaciers can advance independent of climate change. When debris cover is present during cold periods, moraine emplacement can lag debris-free glacier moraine emplacement by hundreds of years. We develop a suite of tools to help determine whether individual moraines were formed by debris-covered glaciers. Our analyses also point to how we might interpret moraine ages and estimate past climate states from debris-perturbed settings.

How to cite: Anderson, L. and Scherler, D.: Geomorphic feedbacks on the moraine record, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19935, https://doi.org/10.5194/egusphere-egu2020-19935, 2020

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Presentation version 1 – uploaded on 05 May 2020
  • CC1: Comment on EGU2020-19935, Michael Dietze, 05 May 2020

    Hi Leif, very cool question(s) asked. How does the glacier model implement the effect of debris cover, just by thermal effects (shielding vs. albedo)? 

    Where do you see opportunities to test the hypotheses (or potential model scenarios) raised with real world landforms?

    • AC1: Reply to CC1, Leif Anderson, 06 May 2020

      Hi Michael, Thank you for your comment! The effect of debris on surface melt is represented by a scaling approach that follows a hyperbolic relationship b’ = b_environment (debris*/(debris* + debris thickness)). b_environment is the melt rate independent of debris, debris* is a critical debris thickness that controls how rapidly melt does to zero as debris thickness increases. So we neglect the melt amplifying effect of debris less than ~ 5 cm. It follows Anderson and Anderson, 2016 (). I have played with the melt amplifying effect of debris this model but I wonder what the area-averaged (~100m x 100m) melt rates are where debris is thin. Some newer work considers this question and I think it is an important topic in debris-covered glacier research.

      There are a number of opportunities to test the model with real world landforms. Looking at the timing of moraine formation where there are also known, independent climate histories would be interesting and possibly fruitful for teasing out these geomorphic effects.