Nevado Sajama is part of the Central Volcanic Zone of the Andes, where volcanism is triggered by the subduction of the Nazca Plate beneath the South America Plate.
Changes in the subduction regime took place during the Oligocene and directed an increase of volcanic activity in the region.
Volcanoes in the region have ages ranging from Pleistocene to Miocene and grew on top of earlier ignimbrites; the whole volcanic activity was controlled by faults.

The mountain is a stratovolcano located atop several lava domes.
The stratovolcano consists of lava flows and pyroclastic material which radiate away from the centre of the volcano.
Some parasitic vents occur southeast of Sajama and their location appears to be controlled by radial dikes; the whole complex is a compound volcano.
Two later volcanic units are known as the Colquen Wilqui lavas and the Jacha Khala tuff.
The Sajama volcano rises within a caldera that has been buried by later volcanic activity so that it is only recognizable on its eastern-northeastern side.
A circular structure around Sajama may be the origin of the 2.7 million years old Lauca-Perez Ignimbrite.

Argon-argon dating has yielded ages of 679,000 years ago from Sajama and of 80,900 to 25,000 years ago for the Kkota Kkotani lavas, which are unrelated to the main Sajama volcano.
The date of the last eruption is not known, it may have occurred in the Pleistocene or Holocene.
Hot springs occur on the Junthuma River and reflect the presence of geothermal heat with temperatures of about 250–230 °C (482–446 °F) on the western foot of Sajama, and volcanic rocks of Sajama bear traces of fumarolic activity.

Three major geologic lineaments occur in the region, the north-northwesterly trending Sajama lineament, a west-southwesterly one aligned with high topographical features and a west-northwesterly one.
The west-southwesterly one played an important role in the development of Sajama volcano.
Nevado Sajama is part of the Central Volcanic Zone of the Andes, where volcanism is triggered by the subduction of the Nazca Plate beneath the South America Plate. Changes in the subduction regime took place during the Oligocene and directed an increase of volcanic activity in the region. Volcanoes in the region have ages ranging from Pleistocene to Miocene and grew on top of earlier ignimbrites; the whole volcanic activity was controlled by faults.
The mountain is a stratovolcano located atop several lava domes. The stratovolcano consists of lava flows and pyroclastic material which radiate away from the centre of the volcano. Some parasitic vents occur southeast of Sajama and their location appears to be controlled by radial dikes; the whole complex is a compound volcano. Two later volcanic units are known as the Colquen Wilqui lavas and the Jacha Khala tuff. The Sajama volcano rises within a caldera that has been buried by later volcanic activity so that it is only recognizable on its eastern-northeastern side. A circular structure around Sajama may be the origin of the 2.7 million years old Lauca-Perez Ignimbrite.
Argon-argon dating has yielded ages of 679,000 years ago from Sajama and of 80,900 to 25,000 years ago for the Kkota Kkotani lavas, which are unrelated to the main Sajama volcano. The date of the last eruption is not known, it may have occurred in the Pleistocene or Holocene. Hot springs occur on the Junthuma River and reflect the presence of geothermal heat with temperatures of about 250–230 °C (482–446 °F) on the western foot of Sajama, and volcanic rocks of Sajama bear traces of fumarolic activity.
Three major geologic lineaments occur in the region, the north-northwesterly trending Sajama lineament, a west-southwesterly one aligned with high topographical features and a west-northwesterly one. The west-southwesterly one played an important role in the development of Sajama volcano.
Nevado Sajama