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Biota, fractures, thresholds: Emergent self-organization in landscape evolution?

EarthShape
(EarthShape)
Figure 1. Field area locations and features. A) Map of precipitation and vegetation gradient in Chile showing Mean Annual Precipitation (MAP), with field areas marked by red stars. Photographs of a typical landscape in B) Santa Gracia, C) La Campana, and D) Nahuelbuta. E, F and G) Simplified geologic maps with major geologic units and faults.
Figure 1. Field area locations and features. A) Map of precipitation and vegetation gradient in Chile showing Mean Annual Precipitation (MAP), with field areas marked by red stars. Photographs of a typical landscape in B) Santa Gracia, C) La Campana, and D) Nahuelbuta. E, F and G) Simplified geologic maps with major geologic units and faults. (Figure: E. Lodes)
Figure 2. Schematic illustration of how fractures set grain size, showing fractured bedrock and blocks exhumed at the surface, with their size dictated by the spacing of fractures at depth. Meant to represent hillslopes in the Nahuelbuta Range. Adapted after Sklar et al. (2017).
Figure 2. Schematic illustration of how fractures set grain size, showing fractured bedrock and blocks exhumed at the surface, with their size dictated by the spacing of fractures at depth. Meant to represent hillslopes in the Nahuelbuta Range. Adapted after Sklar et al. (2017). (Figure: E. Lodes)

EarthShape BIOFRESH is a DFG-funded project in the second phase of the Earthshape SPP, in which we investigate how biota, climate, bedrock fracture density, and lithology affect hillslope denudation rates. Our overarching hypothesis is that biota and climate operate in conjunction with hillslope strength (fracture density and lithology) to modulate hillslope denudation and fluvial incision through the transport and load of hillslope sediment in the Chilean Coastal Cordillera (Fig. 1).

With tectonic uplift and slope held constant, variations in bedrock fracture density and lithology influence grain size and the susceptibility of bedrock to weathering. Vegetation cover and precipitation directly influence weathering rates, and dictate how easily grains are transported downslope and downstream. Thus, fracturing, lithology, biota and climate operate in conjunction to sculpt hillslopes and carve out streams within landscapes.

In BIOFRESH, we utilize the natural laboratory of the Chilean Coastal Cordillera, which hosts a dramatic climate and vegetation gradient from the humid, forested south to the hyper-arid, barren north. We measure fracture density, grain size, and the erosion rates of bedrock, corestones and soils in three different climate and vegetation zones (humid, mediterranean, and semi-arid), to understand the interplay between fracturing, grain size, biota and climate in hillslope denudation (Fig. 2).

To obtain erosion rates, we measure cosmogenic Beryllium-10 in the HELGES labs in section 3.3. In addition, we are looking at how the compositions of two granitic plutons in the semi-arid field site in Chile affect denudation rates, weathering, biota, and drainage density.

Project partner

  • Luca Mao, University of Lincoln, School of Geography, United Kingdom

Time frame

  • 2019 - 2023

Funding

  • DFG-SPP 1803: “EarthShape - Earth Surface Shaping by Biota”. DFG-grant SCHE 1676/4-2 to D. Scherler.

Publications

  • Lodes, E., Scherler, D.,  van Dongen, R., Wittmann, H. (2023): The story of a summit nucleus: hillslope boulders and their effect on erosional patterns and landscape morphology in the Chilean Coastal Cordillera, Earth Surface Dynamics, 11, 305-324, doi:10.5194/esurf-11-305-2023.
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