Ticsani is a volcano in Peru northeast of Moquegua and consists of two volcanoes ("Old Ticsani" and "Modern Ticsani") that form a complex. "Old Ticsani" is a compound volcano that underwent a large collapse in the past and shed 15–30 cubic kilometres (3.6–7.2 cu mi) of mass down the Rio Tambo valley. Today an arcuate ridge remains of this edifice. "Modern Ticsani" is a complex of three lava domes which were emplaced during the Holocene. Two large eruptions took place during the Holocene, producing the so-called "Grey Ticsani" and "Brown Ticsani" deposits; the last eruption occurred after the 1600 eruption of neighbouring Huaynaputina. The volcano is seismically active and features active hot springs and fumaroles; since 2015 the volcano is monitored by the Peruvian government.
Geography and geomorphology Ticsani is in the Ichuna District of Peru, 59 kilometres (37 mi) northwest of Moquegua. The Putina River passes northwest and the Carumas River southwest of the volcano. The area is remote, which has hampered exploration efforts. There are paved roads in the area, which can be accessed mainly through the Ilo-Desaguadero highway that passes within 12 kilometres (7.5 mi) from the Ticsani domes. Volcanism in South America occurs along its western coast and in several volcanic belts, including the Central Volcanic Zone that Ticsani is part of. In southern Peru the Central Volcanic Zone includes the volcanoes Solimana, Coropuna, Ampato, Sabancaya, Chachani, El Misti, Ubinas, Huaynaputina, Ticsani, Tutupaca, Calientes, Yucamane, Purupuruni and Casiri. The volcanoes of Peru were active in the Plio-Quaternary and produced mainly calc-alkaline magmas such as andesite although more silicic rocks also occur. Ticsani features three lava domes, which were generated by latest Pleistocene and Holocene activity; two of which are located within or at the margins of craters. The southeasternmost dome is 1.6 kilometres (0.99 mi) wide and 250 metres (820 ft) high, the middle dome with a width of 2 kilometres (1.2 mi) and a height of no less than 0.25 kilometres (0.16 mi) is the largest of Ticsani. The northwestern dome has dimensions of 1.95 by 1.5 kilometres (1.21 mi × 0.93 mi). Pyroclastic flow deposits, generated during the collapse and growth of the lava domes, fill shallow valleys on the eastern flank. An earlier compound volcano is today preserved as a 3 kilometres (1.9 mi) long arcuate ridge, which is northeast of the northernmost dome and opens to the west. This earlier volcano ("old Ticsani") crops out over an area of 65 square kilometres (25 sq mi) and consists of ignimbrites, lava flows, volcaniclastic deposits and debris from a large sector collapse; a cryptodome is exposed within the arcuate ridge. The complex reaches an elevation of 5,408 metres (17,743 ft). The position of the lava domes and the structure of the compound volcano were influenced by local fault systems.
Geology Off the southwestern coast of South America, the Nazca Plate subducts beneath the South America Plate in the Peru-Chile Trench, at a rate of 10.3 centimetres per year (4.1 in/year). This subduction process is responsible for the growth of the Andes and for volcanism in the region; the oblique character of subduction has further led to the onset of strike-slip faulting. Ticsani is grouped together with the neighbouring volcanoes Huaynaputina and Ubinas, given their tectonic context, which is unusual for Peruvian volcanoes and shared geochemical traits. Huaynaputina had a large eruption in 1600 and Ubinas is presently the most active volcano in southern Peru. These volcanoes appear to share a magma chamber at a depth of 20–30 kilometres (12–19 mi). The basement on which these volcanoes rose includes a Paleoproterozoic pluton. It is covered by the Mesozoic Yura Group and Matalaque Formation (sedimentary and volcanic rocks, respectively) which are exposed at the Rio Tambo. Volcanic activity continued during the Miocene, Pliocene and Pleistocene, forming ignimbrites and the Barroso Group.
Composition The complex has erupted andesite during the compound volcano stage and dacite during the lava dome stage; both define a potassium-rich calc-alkaline suite. Phenocrysts found in the later eruption products include amphibole, biotite, feldspar, plagioclase, pyroxene and quartz.
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