Fast long-term denudation rate of steep alpine headwalls inferred from cosmogenic 36Cl depth profiles

David Mair,Romain Delunel,Serdar Yesilyurt,Dmitry Tikhomirov,Fritz Schlunegger,Naki Akçar,Christof Vockenhuber,Alessandro Lechmann

doi:10.1038/s41598-019-46969-0

David Mair, Romain Delunel + Show 6 more

Open Access

https://doi.org/10.1038/s41598-019-46969-0

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Abstract

Quantifications of in-situ denudation rates on vertical headwalls, averaged over millennia, have been thwarted because of inaccessibility. Here, we benefit from a tunnel crossing a large and vertical headwall in the European Alps (Eiger), where we measured concentrations of in-situ cosmogenic 36Cl along five depth profiles linking the tunnel with the headwall surface. Isotopic concentrations of 36Cl are low in surface samples, but high at depth relative to expectance for their position. The results of Monte-Carlo modelling attribute this pattern to inherited nuclides, young minimum exposure ages and to fast average denudation rates during the last exposure. These rates are consistently high across the Eiger and range from 45 ± 9 cm kyr−1 to 356 ± 137 cm kyr−1 (1σ) for the last centuries to millennia. These high rates together with the large inheritance point to a mechanism where denudation has been accomplished by frequent, cm-scale rock fall paired with chemical dissolution of limestone.

Highlights

Denudation in its broader sense is a complex process, which is initiated and controlled by a variety of mechanisms and conditions such as chemical and physical erosion[1], glacial sculpting[2,3], tectonics[4], and climate[5]
All 34 samples collected along five depth profiles have 36Cl concentrations that generally decrease with depth (Table 2)
We proceed to discussing the implications arising from the concentration patterns in the depth profiles and from the Monte Carlo (MC) modelling thereof, before we outline the results in a broader context regarding the rates and the mechanisms of headwall denudation

Summary

Introduction

Denudation in its broader sense is a complex process, which is initiated and controlled by a variety of mechanisms and conditions such as chemical and physical erosion[1], glacial sculpting[2,3], tectonics[4], and climate[5]. Our understanding of the spatial scale, rate and timing of denudation, is coined by a very large set of scale-specific data, quantified with a small number of methods For mountain belts such as the European Alps, quantitative data on surface denudation is often inferred from concentrations of in-situ cosmogenic nuclides[6,7,8,9], records of low temperature thermochronology[10,11] and river sediment loads[12]. This permits us, for the first time, to determine a rate at which denudation has operated on a vertical headwall over millennia

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Conclusion