Final answer:
The tectonic plates that meet below the Atacama are the Nazca Plate and the South American Plate. The Nazca Plate is being subducted, or forced beneath, the South American Plate, leading to volcanic activity. This process of melting and resurfacing is part of the cycle of plate tectonics.
Step-by-step explanation:
The tectonic plates that meet below the Atacama Desert in South America are the Nazca Plate and the South American Plate. The Atacama Desert is located on the western edge of the South American Plate. In this region, an event referred to as subduction is occurring. Subduction is when one tectonic plate is being forced under another. Here, the oceanic Nazca Plate is being subducted, or forced beneath, the continental South American Plate.
This process of subduction often creates deep oceanic trenches, high pressure and temperature zones, and results in volcanic activity. As the Nazca Plate is pushed deeper into the mantle, it melts, adding to the mantle's convection flow. This process of melting and resurfacing through volcanic eruptions is what we call the cycle of plate tectonics.
Learn more about Tectonic Plates