Quaternary coastal evolution of the southern edge of the atacama desert: Modeling uplift and wave erosion of pan de azúcar marine terraces (26°S, 70.6°W)

Abstract

The Pan de Azúcar National Park (∼26°S, 70.6°W), located on the southern edge of the Atacama Desert, exhibits for almost 30 km an alongshore morphological segmentation. In this work, we characterized the two contrasting morphological arrangements observed in this area: (1) a wide marine terrace landward backed by a tall coastal cliff, and (2) a sequence of poorly preserved, relatively narrow marine terraces landward backed by a short coastal cliff. Three domains that feature these arrangements are identified. The Central Domain represents the first arrangement, and the Northern and Southern domains represent the second. To understand their formation, we used a simple numerical model that allowed us to better understand the long-term evolution of coastal landscapes in rocky areas. The model gives us first-order insights into the driving processes of the development of coastal morphologies: tectonic history, eustatic sea-level change, and marine erosion. Model results reveal that an initial event of slow subsidence (0.04 mm/yr) between 1 Myr and 400 kyr is likely a necessary condition to develop all contrasting domains. Also, variable uplift rates (0.25–0.35 mm/yr) during the last 400 years have allowed the emersion of dated terraces. With this tectonic history, model results suggest values of marine erosion higher than 1 m²/yr to develop a morphological arrangement such as the Central Domain. Conversely, much lower erosion rates, for instance, 0.25–0.5 m²/yr or less, are necessary to replicate the morphology observed in the Northern and Southern domains. Hence, improving numerical models is a key task in unraveling the modes and temporal and spatial variability of driving and modulating processes.