part of the Central Volcanic Zone of the Andes, and lie east of the Peru-Chile Trench. Notable among them are Ampato and Coropuna for exceeding a height of , Huaynaputina and El Misti for their large eruptions and Ubinas and Sabancaya for their recent activity. These volcanoes are found in places where strike-slip faults which delimit the volcanic arc and strike along its length intersect additional faults formed by extensional tectonics. Such faults, mainly normal faults, occur around Sabancaya as well and include the Huambo-Cabanaconde, the Huanca, the Ichupampa, the Pampa Sepina, Sepina, Solarpampa and Trigal faults; the volcanoes Ampato and Sabancaya are aligned on this fault, which may thus be responsible for their existence. These fault systems are still active and experience occasional earthquakes and deformation, and their activity appears to be in part triggered by underground magma movements at Sabancaya. Local Sabancaya is high and rises above the surrounding terrain. It forms a group of volcanoes with the northern Hualca Hualca and the southern Ampato in the Cordillera Occidental, which tower above the Colca Canyon in the north and the Siguas Valley in the southwest. Ampato and the more heavily eroded Hualca Hualca are the dominant volcanoes of this group, with Sabancaya forming a northeastward extension of the former away from Ampato's summit. There is evidence of age progression from the oldest, Hualca Hualca, over Ampato, to the youngest volcano, Sabancaya. Sabancaya consists of two separate centres that are formed by neighbouring domes, Sabancaya I North and Sabancaya II South. The summit crater of the volcano lies between these two domes, with traces of an additional crater just northeast. Despite the presence of an ice cap, lava flows are recognizable in the summit area. They have a total volume of . A set of over 42 Holocene lava flows emanate from the volcano, and cover a surface area of about , with individual lava flows extending up to east and west from between its two neighbours. The lava flows at larger distances are older than the ones close to the vent. These flows are blocky, have lobe structures and reach thicknesses of ; the total thickness of this pile of lava flows is about . Pyroclastic flow deposits are also found, but they might originate from Ampato rather than Sabancaya. Sabancaya, like its two neighbours, is covered by an ice cap which in 1988 extended to distances of