Shaping the Huara Intrusive Complex in the Hyperarid Atacama Desert-Erosional Near-Stasis Contrasting High Topographic Gradients

The Atacama Desert is one of the driest and oldest deserts on Earth, with extremely low precipitation rates (< 2 mm/yr). Mostly abiotic hyperarid environmental conditions prevail, and surface processes act at extremely low rates over the long-term. To gain knowledge about the rate of surface processes and age of landscapes in desert environments, terrestrial cosmogenic nuclide derived erosion rate estimates can be used. Within the Huara Intrusive Complex, situated in the hyperarid core of the Atacama Desert, basin-averaged bedrock erosion rates from channel sediments are extremely low, that is, less than 1 m/Myr. Such low rates indicate that fluvial processes operate very slowly or are almost absent. Bedrock erosion rates of channel knickpoints, however, reveal one to two orders of magnitude higher erosion rates (2-12 m/Myr). Erosion rates are remarkably low when compared to the steep surrounding topography. Tectonic uplift creates higher gravitational potentials for surface processes, controlling the overall erosion rate capacity. However, erosion itself is taking place by local precipitation capable of exceeding thresholds for surface activity. In the Atacama Desert, this happens only due to rare severe precipitation events, explaining the extremely low erosion rates. The efficiency of these events is modulated by local intrinsic processes and conditions, such as high infiltration capacities of Atacama soils and/or large channel boulder accumulations. Due to the virtual absence of these precipitation events capable of erosion, the landscape appears to be in hibernation. Plain Language Summary The Atacama Desert is one of the driest and oldest deserts on Earth, with extremely low precipitation rates (< 2 mm/yr). Surface processes operate at very low rates and on small spatial scales. To understand the rates of surface activity, cosmogenic nuclides are a widely used tool to constrain the exposure duration of sediments on the Earth's surface. Within the Huara Intrusive Complex, situated in the hyperarid core of the Atacama, basin-averaged erosion rates from channel sediments are extremely low. Such low rates indicate that the transport of sediment is very slow or almost absent, revealing a landscape in hibernation. Bedrock erosion rates in channels, however, are one to two orders higher. The studied catchments have been subject to Quaternary tectonic activity, which can explain higher bedrock erosion rates. Rare precipitation events, typical for desert environments, have to be strong enough to provoke erosion. Processes associated with extreme long-term aridity modulate the erosive impact of precipitation events; for example, CaSO4-rich soils soak up water preventing surface runoff or channel boulder accumulations buffer surface flow reducing the capacity to erode.

Automated summary

The Atacama Desert is a very dry and old desert with extremely low precipitation rates. Surface processes operate at very slow rates over long periods of time. Terrestrial cosmogenic nuclide derived erosion rate estimates can be used to understand the rate of surface processes and age of landscapes in desert environments. In the hyperarid core of the Atacama Desert, basin-averaged bedrock erosion rates from channel sediments are extremely low, indicating slow or almost absent fluvial processes. However, erosion rates of channel knickpoints reveal higher rates. These low erosion rates are explained by the rare severe precipitation events that cause erosion in the desert, modulated by local intrinsic processes and conditions.