Chacana is a massive, eroded caldera complex of Pliocene-Holocene age that forms one of the largest rhyolitic centers of the northern Andes. The caldera is 32 km long in the N-S direction and 18-24 km wide E-W. It was constructed during three cycles of andesitic-to-rhyolitic volcanism, with major eruptions about 240,000, 180,00, and 160,000 years ago. Dacitic lava flows were erupted from caldera-floor fissures between about 30,000 and 21,000 years ago. Numerous lava domes were constructed within the caldera, which has been the source of frequent explosive eruptions throughout the Holocene as well as historical lava flows during the 18th century. The massive Antisana stratovolcano was constructed immediately to the SE.