Pleistocene chronicles of large landslides activity on the western flank of the Central Andes revealed by cosmogenic nuclide dating

Abstract

The Western flank of the Central Andes presents a high concentration of giant paleo-landslides that are well preserved due to the long-term aridity of the region. However, the precise timing of most of these features remains unknown, hindering our understanding of their forcing factors and frequency. To address these questions, we focused on eight giant paleo-landslides located in the Locumba landslide Cluster, near and around the Aricota rockslide, to explore their possible temporal correlation. We employed cosmogenic nuclide exposure dating to constrain the timing of these failures, sampling a total of 52 boulders. In about half of the cases, the obtained exposure ages exhibited significant scattering, including very old apparent ages up to ∼1 Ma. For these, only probable time of landslide occurrence associated with large uncertainty could be proposed. We attribute this age scattering mainly to the inheritance problem, which is expected to be very strong in these arid regions where most slopes are slowly eroding, likely at steady-state equilibrium, resulting in very high cosmogenic nuclide concentrations at the surface and shallow depths (first 20 m). Nevertheless, we obtained reliable age constraints for five of the landslides, all of which occurred during the Late and Middle Pleistocene, with mean ages of approximately 16 ka, 18 ka, 115 ka, 190–220 ka and ca. 330 ka. When compared to previous dates in the region and other climatic proxies, the time ranges of 16–18 ka and 100–120 ka correspond to two well-defined humid periods, known as Heinrich Stadial 1a, the Ouki event (during MIS5), respectively. More generally, the activity of landslides along the Central Western Andes seems to increase during interglacial periods. These results suggest that past climate changes, particularly shifts from hyper-arid to prolonged wetter conditions, played a primary role in large landslide activity in the Central Andes.