As the plate subducts, it releases water into the overlying mantle and causes it to melt, gives rise to the Southern Volcanic Zone of the Andes.

During the last six million years, the subduction process has been oblique and as a consequence, the Liquiñe-Ofqui Fault has developed within the volcanic arc and dominates the regional tectonics.

[11] Other volcanoes in the Southern Volcanic Zone have similar alignments, such as Nevados de Chillán and Puyehue-Cordón Caulle.

[11] Quetrupillán is a 2,360 metres (7,740 ft) high composite stratovolcano[11] and a shrinking glacier cover;[13] the existence of calderas is unconfirmed.

[14] The entire edifice has a north-south elongated shape[15] and covers a ground surface of 107 square kilometres (41 sq mi).

[4] The volcano contains a field of lava domes, maars and pyroclastic cones that occupy a surface of 400 square kilometres (150 sq mi).

[19] Huililco scoria cone has produced two lava flows and is considered to be also part of the Quetrupillán volcanic complex.

The first phase of activity involved the formation of calderas and stratovolcanoes; later during the ice ages lava flows and ignimbrites were emplaced.

Finally, the present stratovolcano was emplaced towards the end of glaciation; parasitic vents formed even later[11] and produced lava flows.

[8] In addition, three tephras in neighbouring lakes dated to 16,748–16,189, 15,597–12,582 and 12,708–12,567 years Before Present may originate from Quetrupillán but they have also been attributed to Sollipulli.

[1] Explosive activity has a recurrence interval of about 1,200 years, which given the age of the last event carries significant implications with regards to the volcanic hazard of Quetrupillán.