Overview of South American Volcanoes: From Aconcagua to Cotopaxi

Eruption of Cotopaxi — *South America is home to many active and dormant volcanoes, mainly along the Andes mountain range. Image source: astronoo.com (new window)*

Historical Volcanic Eruptions in South America

Nevado del Ruiz, 1985

The eruption of Nevado del Ruiz in Colombia on November 13, 1985 is one of the deadliest natural disasters of the 20th century in South America. Although the eruption itself was not extremely violent, the melting of glaciers at the volcano's summit triggered massive lahars (volcanic mudflows) that buried the town of Armero, killing more than 23,000 people. This event marked a turning point in volcanic risk management in Colombia.

Chaitén, 2008

Chaitén volcano in Chile erupted unexpectedly on May 2, 2008, after more than 9,000 years of inactivity. The eruption produced an ash column reaching 20 km in altitude, causing major disruptions to air traffic and the evacuation of thousands of people. The nearby town of Chaitén was almost entirely destroyed by lahars and flooding. This eruption reminded the world that even volcanoes considered extinct can awaken.

Nevado del Huila, 2007-2008

Nevado del Huila, also in Colombia, erupted between 2007 and 2008, after more than 500 years of dormancy. Explosions and pyroclastic flows caused landslides and lahars, affecting local communities. This eruption highlighted the vulnerability of populations living near glacial volcanoes, where ice melt can exacerbate risks.

Cotopaxi, 1877

Cotopaxi, in Ecuador, is one of the most famous and dangerous volcanoes in South America. Its eruption in 1877 produced pyroclastic flows and lahars that devastated the surrounding valleys. Although less deadly than others, this eruption had a lasting impact on local infrastructure and agriculture. Today, Cotopaxi remains under close surveillance due to its destructive potential.

Llullaillaco, 1877

Llullaillaco, located on the border between Chile and Argentina, is famous for its altitude (6,739 meters), making it one of the highest volcanoes in the world. Its eruption in 1877 was mainly effusive, with lava flows visible from the surrounding valleys. This volcano is also known for hosting the mummies of Inca children, discovered near its summit, offering a unique insight into Inca rituals.

Villarrica, 1964 and 1971

Villarrica, in Chile, is one of the most active volcanoes in South America. Its eruptions in 1964 and 1971 produced spectacular lava flows and ash columns, causing mass evacuations. In 1971, an eruption caused several deaths and destroyed tourist infrastructure. Today, Villarrica is a popular tourist destination but also a closely monitored volcano.

Sangay, Continuous Activity Since 1934

Sangay, in Ecuador, is one of the most active volcanoes in the world, with almost continuous eruptive activity since 1934. Its eruptions, often explosive, produce ash columns, pyroclastic flows, and lahars. Although located in a sparsely populated area, Sangay has a significant impact on the local environment and climate.

Dynamics and Danger of South American Volcanoes

Volcanoes of the Andes Mountain Range

The Andes Mountain Range is a major subduction zone, where the Nazca oceanic plate dives beneath the South American plate. The volcanoes in this area, such as Cotopaxi, Aconcagua, or Villarrica, are often explosive gray volcanoes, with violent eruptions, pyroclastic flows, and ash plumes that can affect nearby cities.

Basaltic and Shield Volcanoes

Some volcanoes, like Llaima or the volcanic structures in Patagonia, produce effusive red volcanoes. The fluid basaltic lava forms extensive flows and creates spectacular landscapes, but they are generally less explosive.

Secondary Risks and Human Impacts

Eruptions can cause lahars, earthquakes, air traffic disruptions, and damage to crops and infrastructure. The eruption of Chaitén in 2008 illustrates the dramatic consequences of a gray volcano on local populations.

Table of Main South American Volcanoes

Main Active and Dormant Volcanoes of South America
Volcano	Color	Location	Altitude (m)	Type	Last Eruption	Comment	Status
Cotopaxi	Gray	Ecuador	5897	Stratovolcano	2023	Frequent eruptions, glaciers, and lahars.	Active
Villarrica	Gray	Chile	2847	Stratovolcano	2021	Permanent lava lake, recurrent activity.	Active
Sabancaya	Gray	Peru	5976	Stratovolcano	2024	Regular explosive eruptions, ash over surrounding valleys.	Active
Ubinas	Gray	Peru	5672	Stratovolcano	2023	Very active volcano, frequent ash emissions.	Active
Llaima	Red	Chile	3125	Shield volcano	2009	Effusive volcano, extensive basaltic flows.	Active
Chaitén	Gray	Chile	1122	Stratovolcano	2008	Major explosive eruption, destruction of nearby town.	Active
Lascar	Red	Bolivia	5300	Shield volcano	~1900	Effusive volcano, moderate activity.	Active
Aconcagua	Gray	Argentina	6960	Stratovolcano	Extinct	Highest peak in the Andes, no historical activity.	Dormant
Ojos del Salado	Gray	Chile / Argentina	6893	Stratovolcano	~1300	Highest active volcano in the world but currently dormant.	Dormant
Llullaillaco	Gray	Chile / Argentina	6739	Stratovolcano	~1877	Dormant, desert summit and extreme altitude.	Dormant
Licancabur	Red	Chile / Bolivia	5916	Shield volcano	~500	Dormant, salt crater lake at the summit.	Dormant
Lascar	Gray	Chile	5592	Stratovolcano	2023	Small but active, frequent ash emissions.	Active

Red and Gray Volcanoes: Two Eruptive Dynamics

Red volcanoes correspond to effusive volcanoes with fluid basaltic lava, such as Llaima or Licancabur. Their activity is spectacular but generally not very explosive, with extensive lava flows.

Gray volcanoes correspond to explosive volcanoes, rich in silica and gas, such as Cotopaxi, Villarrica, or Chaitén. Eruptions can be violent, with pyroclastic flows and ash plumes.

Comparison Between Red and Gray Volcanoes
Characteristic	Red Volcanoes	Gray Volcanoes
Magma Type	Basaltic, low in silica (<52% SiO₂)	Andesitic to rhyolitic, rich in silica (>55% SiO₂)
Viscosity	Low \(\eta \sim 10^{1-3}\, \text{Pa·s}\)	High \(\eta \sim 10^{5-9}\, \text{Pa·s}\)
Eruptive Style	Effusive: fluid lava flows	Explosive: ash plumes, pyroclastic flows
Visible Manifestations	Incandescent red lava, extensive lava fields	Gray ash, steep stratovolcanoes
Main Risks	Slow but destructive lava flows	Pyroclastic flows, sudden explosions, ashfall
South American Examples	Llaima (Chile), Licancabur (Chile/Bolivia)	Cotopaxi (Ecuador), Villarrica (Chile), Chaitén (Chile)