Irazú Volcano
Encyclopedia
The Irazú Volcano is an active volcano
in Costa Rica
, situated in the Cordillera Central
close to the city of Cartago
.
The name could come from either the combination of "ara" (point) and "tzu" (thunder) or a corruption of Iztarú, which was the name of an indigenous village on the flanks of the volcano. In Costa Rica it is known by the name of "El Coloso" (The Colossus) due to the catastrophes that it has provoked in the past.
The volcano's summit has several craters, one of which contains Diego de la Haya, a green crater lake
of variable depth. It is the highest active volcano in Costa Rica. It is easily visited from San José
, with a road leading right up to the summit craters and a weekly bus service to the top. It is thus a popular tourist
spot. The volcano summit also spots a few television transmitters for television stations in San José.
From the top it is possible to see both the Atlantic and Pacific Oceans on a clear day. However, such clear days are very rare indeed, and it is typical for the volcano's summit to be covered in cloud for much of the time.
volcanic shield. It is the highest active volcano in Costa Rica, and has an area of 500 sqkm. It has an irregular subconic shape, and its temperature oscillates between 3 and 17 °C (37.4 and 62.6 F). It is a stratovolcano
with a summit elevation of 3432 metres (11,259.8 ft). Its five craters are easily differentiated. The most important ones, because of their activity, are The Main Crater, which is almost circular has very inclined walls and it measures 1050 metres (3,444.9 ft) in diameter and 300 metres (984.3 ft) depth; The Diego de la Haya crater is 600 metres (1,968.5 ft) in diameter and 100 metres (328.1 ft) deep. Other craters are Playa Hermosa, La Laguna, and El Piroclastico.
Irazú is the southernmost of the ten Quaternary
volcanoes which form a northwest-trending line through central and northern Costa Rica. Radioactive dating has shown an age of at least 854,000 years with eruption peaks at 570,000 years and the most recent active phase from 136,000 years to present. The most recent activity includes lava flows along with strombolian and phreatomagmatic explosions. Lava types include basalt
and andesite
erupted during different events suggesting the volcano is fed by two distinct magma chamber
s.
started a state visit
to Costa Rica and showered the capital San José
and much of the central highlands of Costa Rica with ash
.
Its historical eruptions generally have VEIs
of 1 to 3. All historical eruptions have been explosive, and there have been many phreatic eruption
s, and some have produced pyroclastic flow
s. The latest eruption lasted only 1 day, and occurred on December 8 1994. It occurred at a flank vent and was a phreatic eruption, which produced lahar
s.
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
in Costa Rica
Costa Rica
Costa Rica , officially the Republic of Costa Rica is a multilingual, multiethnic and multicultural country in Central America, bordered by Nicaragua to the north, Panama to the southeast, the Pacific Ocean to the west and the Caribbean Sea to the east....
, situated in the Cordillera Central
Cordillera Central, Costa Rica
The Cordillera Central is a volcanic mountain range in central Costa Rica which continues the Continental Divide east of Cordillera de Tilarán. It extends 80 km from Tapezco Pass to the Turrialba Volcano and ending on the Pacuare River...
close to the city of Cartago
Cartago, Costa Rica
- See also :* Cartago Agrarian Union Party* Provincial Integration Party Three* Cartago in Spanish...
.
The name could come from either the combination of "ara" (point) and "tzu" (thunder) or a corruption of Iztarú, which was the name of an indigenous village on the flanks of the volcano. In Costa Rica it is known by the name of "El Coloso" (The Colossus) due to the catastrophes that it has provoked in the past.
The volcano's summit has several craters, one of which contains Diego de la Haya, a green crater lake
Crater lake
A crater lake is a lake that forms in a volcanic crater or caldera, such as a maar; less commonly and with lower association to the term a lake may form in an impact crater caused by a meteorite. Sometimes lakes which form inside calderas are called caldera lakes, but often this distinction is not...
of variable depth. It is the highest active volcano in Costa Rica. It is easily visited from San José
San José, Costa Rica
San José is the capital and largest city of Costa Rica. Located in the Central Valley, San José is the seat of national government, the focal point of political and economic activity, and the major transportation hub of this Central American nation.Founded in 1738 by order of Cabildo de León, San...
, with a road leading right up to the summit craters and a weekly bus service to the top. It is thus a popular tourist
Tourism
Tourism is travel for recreational, leisure or business purposes. The World Tourism Organization defines tourists as people "traveling to and staying in places outside their usual environment for not more than one consecutive year for leisure, business and other purposes".Tourism has become a...
spot. The volcano summit also spots a few television transmitters for television stations in San José.
From the top it is possible to see both the Atlantic and Pacific Oceans on a clear day. However, such clear days are very rare indeed, and it is typical for the volcano's summit to be covered in cloud for much of the time.
Geology
The Irazú volcano is a complexComplex volcano
A complex volcano, also called a compound volcano, is a volcano with more than one feature. They form because changes of their eruptive characteristics or the location of multiple vents in an area...
volcanic shield. It is the highest active volcano in Costa Rica, and has an area of 500 sqkm. It has an irregular subconic shape, and its temperature oscillates between 3 and 17 °C (37.4 and 62.6 F). It is a stratovolcano
Stratovolcano
A stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions...
with a summit elevation of 3432 metres (11,259.8 ft). Its five craters are easily differentiated. The most important ones, because of their activity, are The Main Crater, which is almost circular has very inclined walls and it measures 1050 metres (3,444.9 ft) in diameter and 300 metres (984.3 ft) depth; The Diego de la Haya crater is 600 metres (1,968.5 ft) in diameter and 100 metres (328.1 ft) deep. Other craters are Playa Hermosa, La Laguna, and El Piroclastico.
Irazú is the southernmost of the ten Quaternary
Quaternary
The Quaternary Period is the most recent of the three periods of the Cenozoic Era in the geologic time scale of the ICS. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present...
volcanoes which form a northwest-trending line through central and northern Costa Rica. Radioactive dating has shown an age of at least 854,000 years with eruption peaks at 570,000 years and the most recent active phase from 136,000 years to present. The most recent activity includes lava flows along with strombolian and phreatomagmatic explosions. Lava types include basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
and andesite
Andesite
Andesite is an extrusive igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture. In a general sense, it is the intermediate type between basalt and dacite. The mineral assemblage is typically dominated by plagioclase plus pyroxene and/or hornblende. Magnetite,...
erupted during different events suggesting the volcano is fed by two distinct magma chamber
Magma chamber
A magma chamber is a large underground pool of molten rock found beneath the surface of the Earth. The molten rock in such a chamber is under great pressure, and given enough time, that pressure can gradually fracture the rock around it creating outlets for the magma...
s.
Eruptive history
Irazú has erupted frequently in historical times — at least 23 times since its first historically recorded eruption in 1723. Its most famous recent eruption began in 1963 and continued until 1965. It began on the day US President John F. KennedyJohn F. Kennedy
John Fitzgerald "Jack" Kennedy , often referred to by his initials JFK, was the 35th President of the United States, serving from 1961 until his assassination in 1963....
started a state visit
State visit
A state visit is a formal visit by a foreign head of state to another nation, at the invitation of that nation's head of state. State visits are the highest form of diplomatic contact between two nations, and are marked by ceremonial pomp and diplomatic protocol. In parliamentary democracies, heads...
to Costa Rica and showered the capital San José
San José, Costa Rica
San José is the capital and largest city of Costa Rica. Located in the Central Valley, San José is the seat of national government, the focal point of political and economic activity, and the major transportation hub of this Central American nation.Founded in 1738 by order of Cabildo de León, San...
and much of the central highlands of Costa Rica with ash
Volcanic ash
Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions, less than in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact...
.
Its historical eruptions generally have VEIs
Volcanic Explosivity Index
The Volcanic Explosivity Index was devised by Chris Newhall of the U.S. Geological Survey and Stephen Self at the University of Hawaii in 1982 to provide a relative measure of the explosiveness of volcanic eruptions....
of 1 to 3. All historical eruptions have been explosive, and there have been many phreatic eruption
Phreatic eruption
A phreatic eruption, also called a phreatic explosion or ultravulcanian eruption, occurs when rising magma makes contact with ground or surface water. The extreme temperature of the magma causes near-instantaneous evaporation to steam, resulting in an explosion of steam, water, ash, rock, and...
s, and some have produced pyroclastic flow
Pyroclastic flow
A pyroclastic flow is a fast-moving current of superheated gas and rock , which reaches speeds moving away from a volcano of up to 700 km/h . The flows normally hug the ground and travel downhill, or spread laterally under gravity...
s. The latest eruption lasted only 1 day, and occurred on December 8 1994. It occurred at a flank vent and was a phreatic eruption, which produced lahar
Lahar
A lahar is a type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris, and water. The material flows down from a volcano, typically along a river valley. The term is a shortened version of "berlahar" which originated in the Javanese language of...
s.