The story of a summit nucleus: hillslope boulders and their effect on erosional patterns and landscape morphology in the Chilean Coastal Cordillera

Lodes, Emma; Scherler, Dirk; Dongen, Renee van; Wittmann, Hella

doi:10.5194/esurf-11-305-2023

Cited by 3 publications

(1 citation statement)

References 64 publications

(130 reference statements)

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“…It has been shown that outcropping bedrock can erode at a smaller rate than surrounding loose material in a catchment (e.g Bierman and Caffee, 2001;Heimsath et al, 2006;Lodes et al, 2023). We may wonder if this difference can affect the estimation of the mean scarp erosion rate from the 10 Be concentration in colluvium.…”

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confidence: 99%

Evidence of slow millennial cliff retreat rates using cosmogenic nuclides in coastal colluvium

Bossis,

Regard,

Carretier

et al. 2024

Preprint

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Abstract. The erosion of rocky coasts contributes to global cycles of elements over geological times and also constitutes a major hazard that may potentially increase in the future. Yet, it remains a challenge to quantify rocky coast retreat rates over millennia; a time span that encompasses the stochasticity of the processes involved. Specifically, there are no available methods that can be used to quantify slow coastal erosion (< 1 cm yr-1) averaged over millennia. Here, we use the 10Be concentration in colluvium, corresponding to the by-product of aerial rocky coast erosion, to quantify the local coastal retreat rate averaged over millennia. We test this approach along the Mediterranean coast of the Eastern Pyrenees (n=8) and the desert coast in Southern Peru (n=3). We observe a consistent relationship between the inferred erosion rates, the geomorphic and climatic contexts. The retreat rates are similar, 0.3–0.5 mm yr-1 for five samples taken on the Mediterranean coast, whereas one sample located on a cape and two samples from a vegetated colluvium have a lower rate of ~0.1 mm yr-1. The coastal retreat rate of the drier Peruvian coast is slower at 0.05 mm yr-1. Although the integration periods of these erosion rates may encompass pre-Holocene times, during which the sea-level and thus the retreat rate were much lower, we conclude here that the associated bias on the inferred retreat rate is less than 80 %. We anticipate that this new method of quantifying slow rocky coastal erosion will fill a major gap in the coastal erosion database and improve our understanding of both coastal erosion factors and hazards.

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mentioning

confidence: 99%

Evidence of slow millennial cliff retreat rates using cosmogenic nuclides in coastal colluvium

Bossis,

Regard,

Carretier

et al. 2024

Preprint

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Grain Size in Landscapes

Sklar

2024

Annual Review of Earth and Planetary Sciences

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Earth's terrestrial topography evolves in response to the interaction of tectonics, climate, and lithology. Recent discoveries suggest that the grain size of sediments produced on hillslopes and transported through river networks is key to understanding these interactions. Hillslope grain size varies systematically with erosion rate and residence time, the degree of chemical and physical weathering, and the fracture density and susceptibility to weathering of rock. Variations in initial grain size strongly influence the spatial evolution of grain size distributions as particles mix and wear during downstream transport through channel networks. In rivers, the size and flux of the coarse fraction of the sediment load control the rate of incision into bedrock and thus govern channel slope and ultimately the relief of actively eroding landscapes. These relationships suggest that a primary way that tectonics, climate, and lithology influence landscape evolution is through their controls on sediment grain size. ▪ Recent research reveals the central role of sediment grain size in controlling bedrock river morphodynamics, linking grain size to channel slope and topographic relief. ▪ Tectonics, climate, and lithology govern the size of sediments produced on hillslopes; hence, grain size mediates their influence on landscape evolution. ▪ Feedbacks linking sediment grain size, topography, weathering, erosion, and sediment transport provide new opportunities for advances in Earth surface science.

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3D shear wave velocity imaging of the subsurface structure of granite rocks in the arid climate of Pan de Azúcar, Chile, revealed by Bayesian inversion of HVSR curves

Trichandi,

Bauer,

Ryberg

et al. 2024

Earth Surf. Dynam.

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Abstract. Seismic methods are emerging as efficient tools for imaging the subsurface to investigate the weathering zone. The structure of the weathering zone can be identified by differing shear wave velocities as various weathering processes will alter the properties of rocks. Currently, 3D subsurface modelling of the weathering zone is gaining increasing importance as results allow the identification of the weathering imprint in the subsurface not only from top to bottom but also in three dimensions. We investigated the 3D weathering structure of monzogranite bedrock near the Pan de Azúcar National Park (Atacama Desert, northern Chile), where the weathering is weak due to the arid climate conditions. We set up an array measurement that records seismic ambient noise, which we used to extract the horizontal-to-vertical spectral ratio (HVSR) curves. The curves were then used to invert for 1D shear wave velocity (Vs) models, which we then used to compile a pseudo-3D model of the subsurface structure in our study area. To invert the 1D Vs model, we applied a transdimensional hierarchical Bayesian inversion scheme, allowing us to invert the HVSR curve with minimal prior information. The resulting 3D model allowed us to image the granite gradient from the surface down to ca. 50 m depth and confirmed the presence of dikes of mafic composition intruding the granite. We identified three main zones of fractured granite, altered granite, and the granite bedrock in addition to the mafic dikes with relatively higher Vs. The fractured granite layer was identified with Vs of 1.4 km s−1 at 30–40 m depth, while the granite bedrock was delineated with Vs of 2.5 km s−1 and a depth range between 10 and 50 m depth. We compared the resulting subsurface structure to other sites in the Chilean coastal cordillera located in various climatic conditions and found that the weathering depth and structure at a given location depend on a complex interaction between surface processes such as precipitation rate, tectonic uplift and fracturing, and erosion. Moreover, these local geological features such as the intrusion of mafic dikes can create significant spatial variations to the weathering structure and therefore emphasize the importance of 3D imaging of the weathering structure. The imaged structure of the subsurface in Pan de Azúcar provides the unique opportunity to image the heterogeneities of a rock preconditioned for weathering but one that has never experienced extensive weathering given the absence of precipitation.

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The story of a summit nucleus: hillslope boulders and their effect on erosional patterns and landscape morphology in the Chilean Coastal Cordillera

Cited by 3 publications

References 64 publications

Evidence of slow millennial cliff retreat rates using cosmogenic nuclides in coastal colluvium

Evidence of slow millennial cliff retreat rates using cosmogenic nuclides in coastal colluvium

Grain Size in Landscapes

3D shear wave velocity imaging of the subsurface structure of granite rocks in the arid climate of Pan de Azúcar, Chile, revealed by Bayesian inversion of HVSR curves

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