Marine terraces of San Juan de Marcona

Bay of San Juan de Marcona is renowned for its extraordinary twin sequences of well-preserved marine terraces that exhibit 20 staircased levels. These terraces are spectacular witnesses of the complex interaction between past sea-level variations and tectonic uplift of the coast. Each level corresponds to a paleo-sea-level position, now emerged and preserved in the landscape. San Juan de Marcona is located on the southern coast of Peru above the subducted segment of the Nazca Ridge. The area is characterized by significant coastal tectonic activity and major normal faults cutting across the coastal region. The two famous sectors where the terraces develop are Cerro El Huevo and Cerro Tres Hermanas, forming hills and peninsulas, but separated by ~8 kilometers and the bay.
In recent decades, scientific efforts have been made to determine the ages of these terraces, leading to more reliable results using cosmogenic nuclides such as 10Be. For example, the terrace now at an elevation of 220 meters formed 400 ka ago. The ages and present-day elevations of the marine terraces are indicative of variable and cumulative uplift through time during the interseismic period. Coastal tectonics in the Central Andes reflect the interaction of crustal tectonics of the upper plate with the seismic cycle of the subduction interface.