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Cerro Azul ("blue hill" in Spanish) is an active stratovolcano located in central Chilemarker's Maule Region, immediately south of Descabezado Grandemarker volcano. Capped by a wide summit crater that is open to the north, the lower slopes host numerous scoria cones and flank vents.

In 1932, of dacitic tephra was erupted from Quizapu Crater on the northern flank of Cerro Azul. This was one of the largest volcanic eruptions of the 20th century. The volcano's latest eruption took place in 1967.

Geography and geology

Map of Chilean Volcanoes
Cerro Azul, located just south of Descabezado Grandemarker volcano, is part of the Andean Mountain Range's South Volcanic Zone which runs through central and western Chile. The volcano is part of the Descabezado Grande-Cerro Azul network, a volcanic field which hosts the two volcanoes. Both volcanoes are hosted on top of the extinct Casitas Shield. This volcano, which had twelve distinct eruptive periods, is layered with over 100 flows, many of which have been elementally analyzed. The outmost of these were dated at 340,000 years old. In particular, the tenth and eleventh eruptive periods from the shield were similar to early Azul activity.

Of the 200 volcanoes in the Andean Range, 36 historically eruptive ones are found in Chile.

As with the majority of the Andean volcanoes, Cerro Azul is a stratovolcano, meaning that it consists of layers, or strata of volcanic ash and lava flows. It also hosts many craters, with the majority of its eruptions in recorded history originating from Quizapu Crater. Two separate calderas are also within Quizapu: Cerro del Medio and Volcan Nuevo. Four other craters make up the volcano: Carasol, Crater los Quillayes, Crater la Resolana, and Crater sin Nombre. All are located relatively far up the summit, between 2000 and 3000 meters–excluding Quizapu, which is located 3,292 meters up the volcano.

Quizapu, which formed during the 1846 eruption, is the most prominent caldera. Forming during an effusive eruption involving hornblende-dacite flows accompanied by tephra, the crater was deepened by phreatic and strombolic eruptions between 1907 and 1932. Magma built up slowly in the crater, spawning an enormous Plinian eruption in 1932. This period ejected roughly as much lava as all of the volcano's other eruptions. No subsidence, however, suggests that no amount of material was ejected between 1846 and 1931 (9 kilometers, later revised to >9.5), though this has been proven wrong. Despite its size, the eruption had little effect on the already large caldera, due to the size of the past eruptions. Isopach mapping of the volcanic deposits, between , contradict 1930 estimates by about half.

Eruptive history

Cerro Azul has a history of explosive eruptions, dating at least to 1846. Its recorded eruptions have consisted of the creation of a vent followed by an explosive eruption, then phreatic eruptions. Pyroclastic flows and lava flows have also resulted from some of its eruptions. Its earliest recorded eruption occurred on November 26, 1846, later erupting on July 28, 1907, February 1912, September 18, 1914, and the volcano's last eruption on August 9, 1967. Eruptions for which officials are unsure of the dates include 1916, 1933, and April 15 ± 5 days 1949. Uncertain eruptions, those not recorded by officials, occurred in January 1903, and January 15 ± 45 days 1913.

1846

Cerro Azul's first recorded eruption in 1846 was an effusive one, forming what is now Quizapu crater. Hornblende-dacite lava erupted with small masses of tephra, which had been degassed shortly before the eruption.

1932

Cerro Azul's April 1932 eruption is now documented as one of the most enormous of the 20th century. The Global Volcanism Program reports that between 1916 and 1932, activity at the volcano's Quizapu crater widened a caldera to with a depth of . Releasing of lava, the volcano ejected primarily dacitic tephra, accompanied by rhyodacite, andesite, and minuscule amounts of andesitic and basaltic scoria. At least one eruptive period lasted for eighteen hours, creating an "exceptionally uniform" deposit. Eruption columns, extending into the air, were sighted. Phenocrysts compared similar to the effusive eruption in 1846. Soon after, both the Tinguiriricamarker and Descabezado Grandemarker volcanoes began erupting, sending clouds of ash into Argentina. The eruption had a VEI of at least 5.

See also



References

Bibliography

  • (in Spanish; also includes volcanoes of Argentina, Bolivia, and Peru)



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