Where it is and what it carries
The South American Plate covers about 41.8 million square kilometers, or 8.2% of Earth’s surface. It holds all of Brazil, Paraguay, Uruguay, Guyana and Suriname, nearly all of Argentina, and most of Chile, Venezuela and Peru. Its eastern half is the floor of the South Atlantic Ocean.
The interior is old and stable. The Guiana and Brazilian shields are blocks of ancient continental rock, and the Amazon Basin lies between them. All the mountain building happens on the western edge, in the Andes. PB2002 splits parts of the northern and central Andes into two small plates, the North Andes Plate and the Altiplano Plate. The southern Andes, including Aconcagua (6,961 m), the highest peak in the Americas, stay on the South American Plate.
What happens at its edges
The longest boundary, 14,972 km, is the Mid-Atlantic Ridge, where the plate spreads away from the African Plate at about 3.2 cm/yr. New seafloor forms here, so the South Atlantic keeps widening.
The western edge is a subduction zone. Along the Peru-Chile Trench, the Nazca Plate sinks beneath South America at about 7.8 cm/yr. This convergence crumples and thickens the crust to build the Andes. South of the Chile Triple Junction, the Antarctic Plate subducts more slowly; the average relative speed along that whole boundary is about 1.8 cm/yr.
In the far south, the plate meets the Scotia Plate along transform faults through Tierra del Fuego at about 0.5 cm/yr. In the South Atlantic, South American seafloor dives beneath the Sandwich Plate at the South Sandwich Trench at about 7.4 cm/yr. In the north, the boundary with the Caribbean Plate combines transform faults in Venezuela with subduction beneath the Lesser Antilles, at about 1.9 cm/yr. The boundaries with the Altiplano and North Andes plates move slowly, at about 1.3 cm/yr and 0.9 cm/yr.
Earthquakes
The dataset lists 362 earthquakes of magnitude 6.5 or larger on the plate since 1900, 17 of them magnitude 8 or more. The 1960 Valdivia earthquake in southern Chile (M9.5) is the largest earthquake ever recorded. Chile also had the 2010 Maule earthquake (M8.8), the 1922 Vallenar earthquake (M8.5) and the 2015 Illapel earthquake (M8.3). Peru’s largest on this plate was an M8.2 near Huacho in 1940.
Not every big quake here is shallow. The 1994 Bolivia earthquake (M8.2) struck 631 km below the surface, inside the sinking Nazca slab. It is one of the largest deep earthquakes ever recorded.
Volcanoes
The plate holds 108 volcanoes in the dataset, nearly all in the Andes. Active ones include Villarrica, Lascar, Calbuco and Puyehue-Cordon Caulle in Chile, and Sangay and Reventador in Ecuador. They form where water from the subducting Nazca Plate triggers melting in the mantle. A long gap in volcanoes through central Peru lines up with a stretch where the Nazca slab sinks at a shallow angle.