Guallatiri

Geography

Guallatiri is located in the Putre commune, Parinacota province of Arica y Parinacota, Chile. Parinacota, Quisiquisini, Guallatiri and Poquentica form the eastern limit of the Lauca basin.

The towns of Putre, Socoroma and Zapahuira are closest to the volcano. The volcano is located in the Lauca National Park, along with the two higher Pomerape and Parinacota volcanoes. Sometimes Guallatiri is considered to be part of the Nevados de Quimsachata volcanic chain, a 50 kilometres (31 mi) long chain of volcanoes.

Other volcanoes with historical phreatic-phreatomagmatic activity in northern Chile include Irruputuncu, Isluga, Lascar and San Pedro. Further, fumarolic activity has been reported at Alitar, Lastarria, Olca, Ollague, Putana and Tacora.

Geology

Guallatiri is a complex volcano. Dacitic lava domes are also present. The summit is formed by a pyroclastic cone. Alternative interpretations see it as a lava dome or a hydrothermally altered, scree-covered lava plug. The vent lies south of the summit. The summit crater is breached westwards and northwards. The volcano is principally constructed from lava flows. Lava flows radiate from the summit and lava domes dot its flanks. Some lava flows are up to 7 kilometres (4.3 mi) long and 100 metres (330 ft) high. Thick lava flows are particularly noticeable on the western and northern slope of the volcano. Guallatiri is 1,700-metre-high (5,600 ft) above the basement rocks and has a total volume of 40 cubic kilometres (9.6 cu mi). "Breadcrust" lava bombs are found on the northern flanks, probably carried there by glaciers. Other eruption products include ash flows and tephra layers. The former are particularly developed on the south-southwest flank and the tephras particularly on the southern-eastern flanks.

Guallatiri is underpinned by the rocks of the Lauca Formation, which has an age of 10–0.5 million years. An older basement domain known as the Lupica formation is exposed north, west and south of the volcano and contains sediments and volcanic rocks. It is of Oligocene-Miocene age. Like other volcanoes in the area, it formed on top of the Chilean Altiplano.

Guallatiri may have formed during the Pliocene. During the Pleistocene volcanic activity recommenced. Two stages of volcanic activity in the Pleistocene-Holocene have been identified. Volcanic activity in the Quimsachata volcanic chain migrated south from the now deeply eroded Acotango and Humarata volcano to the more recent Capurata and Guallatiri volcanoes. There is evidence indicating that lava flows forming the Stage I of activity were erupted during the middle Pleistocene and the lava domes forming Stage II were erupted in the Pleistocene-Holocene. The lava bombs on the northern flank suggest that small volume activity occurred in recent times.

Glaciation and hydrology

Guallatiri has glaciers, including one on the summit. It is the most southern volcano in the Central Andes with an ice cap, with a surface area of 6,000 square metres (65,000 sq ft). South of Guallatiri tropical summer precipitation is insufficient to support glaciation; only south of 27° does winter precipitation become sufficient to support glaciers again. Fumaroles have melted holes in the glaciers. Thin moraines are preserved on the flanks at altitudes of 4,260 metres (13,980 ft).

These glaciers drain towards the Chungara river. A number of streams and dry valleys originate on Guallatiri. Parts of the western and southern flank drain into the Rio Lauca.

Petrology

Guallatiri has erupted andesite, dacite and rhyolite, with dacite dominating. Pyroxene andesites are found up to 4,800 metres (15,700 ft) of altitude. Analysis of lava at Domo Tinto lava dome has indicated phenocrysts include amphibole, biotite, pyroxene and some apatite. Mafic inclusions have also been found in Domo Tinto rocks. The Domo Tinto eruption may have been triggered by the injection of basaltic andesite into two magma chambers containing crystalline andesite. Native deposits of sulfur are also found.

Domo Tinto rocks have been analyzed for isotope and chemical composition studies. They are potassium-rich calc-alkaline rocks as is typical for Andean volcanism in this area. On the basis of petrology magma temperatures of the Tinto rocks have been estimated at 790 °C (1,450 °F) for the andesitic component and 890–930 °C (1,630–1,710 °F) for the basaltic andesite component. SiO₂ contents range from 58 to 75%, with dacites having a content of 63–70%.

Eruptive activity

Solfataric activity is ongoing. In 1985 and 1987 yellow (sulfur containing) steam clouds were reported, with altitudes of 500 metres (1,600 ft) above the summit. The fumaroles are located in the crater, the southern flank and the southern flank where they reach over 300 metres (980 ft) down. The fumaroles are reported to make "jet"-like noises. ASTER imaging has indicated temperature anomalies of up to 8 degrees Kelvin. Mud pots have also been observed.

Likewise, the volcano features ongoing seismic activity, including about two earthquakes per day and three seismic swarms in 2011–2012. Another earthquake swarm is associated with the 2001 Peru earthquake. No deformation of the edifice has been observed, however.

A lava dome on the southern flank (Domo Tinto) was K-Ar dated at 5,000 ± 3000 BP. Its eruption was probably a relatively tranquil effusive eruption. Ash eruptions are reported in the first half of the 19th century. 1913 and 1959 glow was observed in the summit crater, and a phreatic eruption was reported in 1960. Activity is also reported for 1779, 1802, 1826–1831, 1850, 1859, 1864, 1864, 1870, 1902, 1904, 1908, 1912 and 1959. Guallatiri is one of northern Chile's most active volcanoes. In 2015 volcano alert levels on Guallatiri was temporarily raised due to deformation of the edifice and changes in the seismic activity.

Threats and preparedness

The Chilean National Geology and Mining Service does keep a record of regular reports of the activity status of Guallatiri. A hazard map exists of Guallatiri with three areas of different risk. The red zone occupies the areas interested by late activity of the volcano and river valleys, in total most of the upper parts of the volcano. The orange and yellow zones are areas threatened in the case of medium-large and large scale eruptive activity, respectively.

Flank eruptions, lahars and pyroclastic flows are hazards associated with Guallatiri. The town of Guallatiri on its southern flank is especially threatened. Explosive activity with eruption columns of 20 kilometres (12 mi) height may result in ashfall in Arica and Putre depending on the season. There are small villages in western Bolivia that may be impacted by Guallatiri tephra.

Religious and archeological importance

Unlike on several other Andean summits, no Inka archeological sites are visible on Guallatiri, perhaps discouraged by the persistent volcanic activity.

It is said that townfolk of Guallatire worshipped the mountain from nearby mountain Capurata. Even today churches in Ancuta and Guallatire point towards the volcano.