The volcano is set along the Zunil fault zone and has a central caldera surrounded by several dacitic and rhyolitic lava domes and formed in a back-arc volcanic setting, with activity commencing 84,000BP. Almolonga stratovolcano is the oldest edifice and underwent collapse prior to the caldera forming eruption of Lake Atitlan, the major chronological marker of volcanism in the region. The collapse of the stratovolcano left a caldera with a diameter of 3,3 km and a depth of 350m that was subsequently occupied by lava domes on its northern edge and covered by tephra layers from numerous volcanoes, both in the Almolonga field and others. Cerro Quemado is the largest (about 2 km3) and youngest lava dome complex formed by eight vents with viscous lava flows and plugs during four distinct volcanic phases - the first two involving effusion of lava and formation of new domes. Cerro Quemado underwent a flank collapse 1,150BP, generating a landslide that went 6 km SSW in the Llano de Pinal valley and occupied an area of 13 km2, generating a lateral blast that affected the neighbouring Volcán Siete Orejas volcano as well. A lava dome emerged inside the collapse scar subsequently. 1818 an eruption formed a block lava flow over half a year that travelled 2.5 km eastward. Lahars and further explosive activity are potential hazards from this volcano.
