The El Laco volcanic complex is formed by about seven minor stratovolcanoes and lava domes. The complex started its activity in the Miocene-Pliocene, when porphyric andesites formed a stratovolcano. During the Pliocene, ash and pyroclastic eruptions formed a caldera with a diameter of , which also contains a central lava dome that formed 6.5 million years ago. Finally, probably during the Pleistocene, five iron-rich magmas were extruded, named Laco Sur, Laco Norte and Rodados Negros. Laquito and Cristales Grandes, two abyssal iron magma structures, date back to that era.:682-684 The volcanic complex is located an altitude of and covers a surface area of with a minimum volume of of volcanic rock.