Erosion Assessment at Earthen Archeological Sites by Morphometric Analysis of Digital Surface Models: The Case of Huaca Fortaleza (Pampa Grande, Peru, 600–750 AD)

Earthen archeological sites may be damaged by rain-induced erosion processes. Huaca Fortaleza (HF; 600–750 AD) is an originally four-level truncated pyramid in the semi-arid Lambayeque region of northern Peru, an area affected by seasonal intense rain due to El Niño Southern Oscillation (ENSO). We use data from a UAV-based photogrammetric survey and generate a Digital Surface Model from which we extract selected geomorphometric parameters and apply a hillslope diffusion model. The obtained data show that HF steep flanks exhibit a marked erosion expressed by a drainage network of parallel rills and gullies with architectural structures controlling pathways for concentrated flow. The southwestern flank is affected by gravity instability. Localized pits at the top of HF cause infiltration of rainwater. The erosion by ENSO rainfall is responsible for extensive architectural loss, with the HF lower platforms now entirely obliterated. We calculate vertical erosion rates of 0.28–0.38 m/century, a range of values comparable with that estimated for river incision. Erosion due to diffusion processes is estimated in the order of ~0.015 m/century. Our approach represents a transferable methodology applicable to other earthen archeological sites affected by erosion worldwide.