Where it is and what it carries
The Altiplano Plate covers about 832,000 square kilometers, or 0.16% of Earth’s surface, in the central Andes. It holds about a third of Bolivia, 22% of Peru and 8.5% of Chile. The cities of La Paz, Arequipa and Iquique sit on it, as do Lake Titicaca and the Salar de Uyuni, the world’s largest salt flat.
The plate is almost entirely continental crust. Its center is the Altiplano, a high plateau ringed by the Western Cordillera, a line of volcanoes, and the Eastern Cordillera, a belt of folded and faulted older rock.
Why geologists separate it
PB2002 treats the Altiplano as a separate plate because the central Andes do not move as one rigid piece with the rest of South America. The mountain belt is still being squeezed, and its crust continues to shorten and thicken slowly. This makes the Altiplano Plate more of a deforming block than a classic rigid plate. Its boundaries, especially on the east, are wide zones of faults, so their exact position is uncertain.
What happens at its edges
The western edge is the Peru-Chile Trench, where the Nazca Plate subducts beneath the Altiplano Plate at about 6.5 cm/yr along a 901 km stretch. This convergence drives the earthquakes and volcanoes of the region.
The plate’s other boundary, 2,957 km long, is with the South American Plate. It runs along the eastern foothills of the Andes and wraps around the plate’s northern and southern ends. In the east, the South American Plate is pushed under the mountains along the Subandean fold-and-thrust belt. The average relative speed along this boundary is about 1.3 cm/yr.
Earthquakes and volcanoes
The dataset lists 65 earthquakes of magnitude 6.5 or larger on the plate since 1900, three of magnitude 8 or more. The largest was the 2001 southern Peru earthquake (M8.4) near Atico. The 2014 Iquique earthquake (M8.2) in northern Chile filled part of a long-recognized seismic gap. A 1942 earthquake near Minas de Marcona, Peru, reached M8.1. Some quakes here are very deep: an M7.67 event in 1963 struck 550 km below southern Peru, inside the sinking Nazca slab.
The plate holds 20 volcanoes in the dataset, many of them above 5,000 m. Sabancaya and Ubinas in Peru have erupted in recent years. El Misti (5,793 m) towers over Arequipa, and Guallatiri in Chile reaches 6,071 m.