Olca is a

stratovolcano A stratovolcano, also known as a composite volcano, is a conical volcano built up by many layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and peri ...

on the border of

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the eas ...

and

Bolivia , image_flag = Bandera de Bolivia (Estado).svg , flag_alt = Horizontal tricolor (red, yellow, and green from top to bottom) with the coat of arms of Bolivia in the center , flag_alt2 = 7 × 7 square p ...

. It lies in the middle of a 15 km long ridge composed of several stratovolcanos. Cerro Minchincha lies to the west and Paruma to the east. It is also close to the pre-

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togeth ...

Cerro Paruma. It is

andesitic Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomin ...

and

dacitic Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyol ...

in composition, with lava flows extending several kilometres north of the peak. The only activity from the ridge during historical times was a flank eruption from 1865 to 1867. The exact source of this eruption is unclear.

Gas emissions and composition

The gasses emission is comprised by a single warm

spring Spring(s) may refer to: Common uses * Spring (season), a season of the year * Spring (device), a mechanical device that stores energy * Spring (hydrology), a natural source of water * Spring (mathematics), a geometric surface in the shape of a h ...

at the base and a persistent

fumarole A fumarole (or fumerole) is a vent in the surface of the Earth or other rocky planet from which hot volcanic gases and vapors are emitted, without any accompanying liquids or solids. Fumaroles are characteristic of the late stages of volcani ...

field over at the crater's dome for at least 60 years. The

fumarolic A fumarole (or fumerole) is a vent in the surface of the Earth or other rocky planet from which hot volcanic gases and vapors are emitted, without any accompanying liquids or solids. Fumaroles are characteristic of the late stages of volc ...

field is about 0.1 km² and the emissions measured in situ at the crater show a highly mixed magmatic system between high temperature temperature gasses and hydrothermal fluids. The gas composition indicates low concentration of H₂, CO and acidic gasses, and high concentration of H₂S and hydrocarbons. The carbon/sulfur ratios are high and the isotopic values suggest the mixture between magmatic, hydrothermal, and atmospheric fluids. Other techniques used to measure the amount of SO₂ includes remote sensing techniques called

Differential Optical Absorption Spectroscopy In atmospheric chemistry, differential optical absorption spectroscopy (DOAS) is used to measure concentrations of trace gases. When combined with basic optical spectrometers such as prisms or diffraction gratings and automated, ground-based observa ...

(DOAS) giving maximum concentration of 35 ppm.m of SO₂; and the most recent taken with a UV camera suggesting an average of 18.4 t d⁻¹.

Eruptive history and latest activity

Different information exists regarding the activity and activity migration of Olca. There is a study dating two flows, which suggest a formation during the

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

, while others suggest to be much older with the appearance of the edifices volcanic activity migrated east over time. There is also evidence that glaciers were on the volcano in the late Pleistocene. The Unconfirmed historical eruptions are suspected to have occurred in 1865–1867. The last activity has been reported of low-intensity seismicity accompanied with fumarolic activity in November 1989 and March 1990 intense degassing. In 2010, there a campaign conducted seismic activity showing 3 potencial swarms without a clear interpretation. Olca

Gas emissions and composition

Eruptive history and latest activity

See also