It is a large ice-capped, basaltic andesite volcano which is elongated in the northeast-southwest direction, due to its construction along an 11 km (7 mi) long fissure.

Numerous cinder cones and lava flows have erupted from vents along this linear fissure.

Together with Hekla in Iceland, Callaqui is one of the few volcanoes with a morphology between a crater row and stratovolcano (built from mixed lava and tephra eruptions).

[1] The volcano is the centerpiece of Ralco National Reserve.

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