Dating topography of the sierra nevada
To explore this possibility, we quantified how bedrock strength, mineralogy and bulk chemistry vary among the granitic rock types exposed at our sites.Considered together, our data and analysis contribute to improved understanding of the dynamics of hybrid (bedrock/soil) landscapes by shedding light on feedbacks among erosion, rock strength, mineralogy and degree of chemical weathering in granitic terrain.
This raises the possibility that exposure of bedrock arises from contrasts in material properties rather than from random erosional exposure, as suggested by the hypothesis.
Yet few studies have been able to realistically predict the co-occurrence of bedrock and granular soil and its implications for mountain-scale topography -- despite marked advances in quantitative landscape evolution modeling over the last few decades.
Here we use terrain analysis, together with cosmogenic-nuclide measurements of erosion and weathering, to quantitatively explore Wahrhaftig's decades-old hypothesis for the development of “stepped topography” by differential weathering of bare and soil-mantled granite.
This suggests that the coupling between soil production and denudation in granitic landscapes harbors a crucial tipping point; if soils are stripped to bedrock, erosion slows and soil formation is restrained to the point that bare rock can persist and rise in relief relative to surrounding soil-mantled terrain.
Contrary to one of the main underpinnings of Wahrhaftig’s hypothesis, our observations suggest that the presence or absence of soil cannot be predicted from hillslope gradients alone.