South America is home to one of the most extensive and dynamic volcanic systems on the planet. The continent hosts a massive chain of peaks, many of which are active and represent a significant portion of the world’s highest volcanoes. This intense geological activity along the western margin is a direct consequence of interactions between the Earth’s tectonic plates.
The Reason: Plate Tectonics and Subduction
The presence of volcanoes along the western edge of the continent is controlled by a process called subduction, which occurs where two of the Earth’s lithospheric plates meet at a convergent boundary. In this region, the oceanic Nazca Plate is being forced downward beneath the continental South American Plate along the Peru-Chile Trench.
As the oceanic crust descends into the mantle, it carries trapped water and volatile compounds. At depth, heat and pressure cause these volatiles to be released from the subducting slab into the overlying mantle wedge.
The introduction of water significantly lowers the melting point of the mantle rock, a process known as flux melting. This generates magma, which is less dense than the surrounding solid rock and begins to rise through the continental crust. The magma collects in chambers and erupts on the surface, forming the characteristic volcanic chain.
Geographical Distribution and Volcanic Zones
The resulting chain of volcanoes is known as the Andean Volcanic Belt (AVB), which extends for approximately 7,000 kilometers along the western spine of the continent. The AVB is segmented into distinct zones, reflecting variations in the angle of the subducting plate. The belt is generally considered part of the larger Pacific Ring of Fire.
The Northern Volcanic Zone (NVZ) includes volcanoes in Colombia and Ecuador, where the subducting plate descends at a relatively steep angle, promoting magma generation. South of this, a significant break in volcanism occurs in Peru, a region where the subducting plate is nearly horizontal, creating a “flat-slab subduction” segment. This shallow angle prevents the oceanic plate from sinking deep enough to release the necessary volatiles for melting, thus inhibiting the formation of volcanoes.
The Central Volcanic Zone (CVZ) is one of the most volcanically dense arcs globally, spanning parts of Peru, Bolivia, Chile, and Argentina. This zone is characterized by a high concentration of massive volcanic edifices, many of which reach extreme elevations. A second major gap, the Pampean flat-slab segment, separates the CVZ from the Southern Volcanic Zone (SVZ), which extends through much of Chile and into Argentina. The SVZ is known for its high rate of activity and explosive eruptions, continuing south until the Austral Volcanic Zone begins near the southern tip of the continent.
Current Activity and Notable Peaks
The Andean Volcanic Belt hosts over 200 potentially active volcanoes, reflecting a dynamic geological environment with ongoing risks. Volcanoes are classified as active if they show signs of unrest, such as persistent gas emissions or seismic activity, even if they have not erupted recently. Many of the highest peaks in South America fall into this category.
Nevados Ojos del Salado, on the border of Chile and Argentina, holds the distinction of being the world’s highest active volcano, soaring to 6,893 meters. While no major historical eruptions have been confirmed, the peak displays continuous fumarolic activity, which is the emission of steam and volcanic gases, confirming its status as geologically active. This high-altitude location means that any eruption could pose unique hazards, though the surrounding area is sparsely populated.
Further north, the ice-clad stratovolcano Nevado del Ruiz in Colombia represents a different type of hazard due to its proximity to population centers and its icy summit. The 1985 eruption, though relatively small in magnitude, caused a devastating tragedy when its pyroclastic flows melted the summit’s ice cap. This rapid meltwater mixed with volcanic debris to create massive lahars, or volcanic mudflows, which traveled down river valleys and killed approximately 25,000 people. The risk of lahars remains a significant concern for the many high-altitude volcanoes in the region that are covered by ice or snow.