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Cerro Galan Volcano - John Seach
Argentina
25.98 S, 66.93 W
summit elevation 6100 m
Caldera
Cerro Galan Caldera is located in an arid region of Catamarca province, NW Argentina. The caldera is elliptical in shape, 40 x 24 km in diameter. The floor of the caldera is at an altitude of 4500 m. Cerro Galan is one of the world's largest calderas, and was only identified from satellite photos in 1975. It is the largest post-Miocene caldera in the Andes.
The caldera contains well defined ring fractures.
The formation of the caldera was associated with the eruption of 1000 cubic kilometers of ignimbrites. The ignimbrites are fine grained, and lack lithic clasts and pumice. Dacitic to rhyodacitic ignimbrites form a dissected plateau up to 400 m thick on the flanks surrounding the caldera.
Post-Caldera Eruptions
Post caldera eruptions occurred along the northern
extension of the eastern boundary fault and the western caldera margin. A large resurgent dome
occupies the centre of the caldera. Some youthful basaltic cinder
cones and lavas lie on the youngest ignimbrite. Post caldera lavas are located along a regional fault rather than the ring
fracture.
Caldera forming eruption (2.1 Ma)
The cerro Galan ignimbrite and caldera forming eruption occurred 2.1 million years ago. The eruption came after a 2 million year dormancy. A single major eruption emitted 1000 cubic km of rhyodacitic magma. The ignimbrite is pumice-poor, crystal-rich containing
few lithic clasts.
Toconquis ignimbrites (4-7 Ma)
The volume
of Toconquis ignimbrite exceeds 500 cubic km. The total thickness of the ignimbrites is
about 250 m at a distance of 22 km from the caldera rim. The Toconquis ignimbrites is the first defined activity at
Cerro Galan volcano.
Cerro Galan Volcano Eruptions
2.1 Ma (caldera forming event)
4-7 Ma (Toconquis ignimbrites)