Galeras (Urcunina among the 16th-century

indigenous people There is no generally accepted definition of Indigenous peoples, although in the 21st century the focus has been on self-identification, cultural difference from other groups in a state, a special relationship with their traditional territ ...

) is an

Andean The Andes ( ), Andes Mountains or Andean Mountain Range (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long and wide (widest between 18°S ...

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

in the

Colombia Colombia, officially the Republic of Colombia, is a country primarily located in South America with Insular region of Colombia, insular regions in North America. The Colombian mainland is bordered by the Caribbean Sea to the north, Venezuel ...

n department of Nariño, near the departmental capital

Pasto Pasto, officially San Juan de Pasto (; "Saint John of Pasto"), is the capital of the department of Nariño, in southern Colombia. Pasto was founded in 1537 and named after indigenous people of the area. In the 2018 census, the municipality ...

. Its summit rises above

sea level Mean sea level (MSL, often shortened to sea level) is an mean, average surface level of one or more among Earth's coastal Body of water, bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical ...

. It has erupted frequently since the

Spanish conquest The Spanish Empire, sometimes referred to as the Hispanic Monarchy or the Catholic Monarchy, was a colonial empire that existed between 1492 and 1976. In conjunction with the Portuguese Empire, it ushered in the European Age of Discovery. It ...

, with its first historical

eruption A volcanic eruption occurs when material is expelled from a volcanic vent or fissure. Several types of volcanic eruptions have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior has ...

being recorded on December 7, 1580. A 1993 eruption killed nine people, including six scientists who had descended into the volcano's crater to sample gases and take gravity measurements in an attempt to be able to predict future eruptions. It is currently the most active volcano in Colombia.

Geological history

Galeras has been an active volcano for at least a million years, with

andesite 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 predomina ...

as the dominant product. Two major

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcanic eruption. An eruption that ejects large volumes of magma over a short period of time can cause significant detriment to the str ...

-forming eruptions have occurred, the first about 560,000 years ago in an eruption which expelled about of material. The second some time between 40,000 and 150,000 years ago, in a smaller but still sizable eruption of of material. Subsequently, part of the caldera wall has collapsed, possibly due to instabilities caused by hydrothermal activity, and later eruptions have built up a smaller cone inside the now

horseshoe-shaped Many shapes have metaphorical names, i.e., their names are metaphors: these shapes are named after a most common object that has it. For example, "U-shape" is a shape that resembles the letter U, a bell-shaped curve has the shape of the vertical ...

caldera. In light of its violent eruptive history and proximity to the 450,000 people of Pasto, Galeras was designated a

Decade Volcano The Decade Volcanoes are 16 volcanoes identified by the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) as being worthy of particular study in light of their history of large, destructive eruptions and pr ...

in 1991, identifying it as a target for detailed study as part of the

United Nations The United Nations (UN) is the Earth, global intergovernmental organization established by the signing of the Charter of the United Nations, UN Charter on 26 June 1945 with the stated purpose of maintaining international peace and internationa ...

' International Decade for Natural Disaster Reduction.

Eruptive history

Galeras is considered the most active volcano in Colombia, followed by

Nevado del Ruiz Nevado del Ruiz (), also known as La Mesa de Herveo () is a volcano on the border of the departments of Caldas and Tolima in Colombia, being the highest point of both. It is located about west of the capital city Bogotá. It is a stratovolca ...

. Its earliest activity during the

Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...

has been dated at 7050 BC ± 1000 years through

radiocarbon dating Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for Chronological dating, determining the age of an object containing organic material by using the properties of carbon-14, radiocarbon, a radioactive Isotop ...

. Other eruptions similar to this event include those in 3150 BC ± 200 years, 2580 BC ± 500 years, 1160 BC ± 300 years, 490 BC ± 100 years, and in 890 AD ± 200 years. Typically these eruptions consist of a central vent explosion, conducive to an explosive eruption causing

pyroclastic flow A pyroclastic flow (also known as a pyroclastic density current or a pyroclastic cloud) is a fast-moving current of hot gas and volcanic matter (collectively known as tephra) that flows along the ground away from a volcano at average speeds of b ...

s and/or

lahar A lahar (, from ) is a violent type of mudflow or debris flow composed of a slurry of Pyroclastic rock, pyroclastic material, rocky debris and water. The material flows down from a volcano, typically along a valley, river valley. Lahars are o ...

s. Eruptions in more recent times, which have been recorded consist of those in 1535, December 1580, July 1616, 1641, 1670, 1754, November 1796, June 1823, October 1828, 1834, October 1865, July 1889, 1891, December 1923, October 1924, October 1932, February 1936, July 1947, January 1950, 1974, February 1989, January 1990, January 1993, March 2000, June 2002, July 2004, November 2005, October 2007, January 2008, February 2009, March 2009, January 2010, and August 2010. Reported incidents with no official proof occurred in 1836, 1930, 1933, and 1973.

1993 eruption

Galeras became active again in 1988 after 10 years of dormancy. A Decade Volcano conference in the city of

, in 1993, ended in disaster when several of the scientists present mounted an impromptu expedition on 14 January to the crater of Galeras. An eruption occurred unexpectedly while they were at the summit, resulting in the deaths of six scientists and three tourists.Baxter & Gresham, 1993 Elements in the media made the event controversial by suggesting the expedition leader, geologist Stanley Williams, who survived along with four others, had ignored safety procedures. A prediction had been made three days before the eruption based on B-Type activity seen on a seismograph. Seismic B-types had been used successfully to predict eruptions on other volcanoes. However, the prediction was based simply on the one seismographic printout viewed in the light of previous history of Galeras, without any additional scientific measurements showing any serious activity within the volcano.

21st-century activity

Activity at a low level has continued at Galeras, with small explosions occasionally dusting nearby villages and towns with

ash Ash is the solid remnants of fires. Specifically, ''ash'' refers to all non-aqueous, non- gaseous residues that remain after something burns. In analytical chemistry, to analyse the mineral and metal content of chemical samples, ash is the ...

. The volcano has continued to be well-studied, and predictions of eruptions at the volcano have improved. One phenomenon, which seems to be a reliable precursor to eruptive activity, is a low-frequency seismic event known as a

tornillo event {{Short description, Seismic event associated with volcanoes A tornillo event is a low-frequency seismic event associated with volcanoes. The term, which means "screw" in Spanish, was coined in the mid-1990s at the Observatorio Vulcanológico y Sism ...

. These have occurred before about four-fifths of the explosions at Galeras, and the number of tornillo events recorded before an eruption is also

correlated In statistics, correlation or dependence is any statistical relationship, whether causal or not, between two random variables or bivariate data. Although in the broadest sense, "correlation" may indicate any type of association, in statistic ...

with the size of the ensuing eruption. More than 100 minor tremors were felt during a major eruption in April 2002, although no damage or injury was reported. An eruption in November 2005 forced an evacuation of the dangerous area surrounding the volcano, and about 9,400 people from nearby villages (most of them farmers) were ordered to leave. The city of

, about from the volcano, was blanketed by a layer of ash after the volcanic explosion, forcing the residents to don goggles and face masks. Numerous minor tremors and ash emissions since March 2006 culminated on 12 July 2006 in three explosive eruptions, producing an ash and gas column reaching an altitude of . Rock falls and

s were reported from towns as distant as Consacá, west of the main crater. The Colombian government has repeatedly ordered evacuations to temporary shelters, of more than 8500 people residing in the highest risk areas surrounding the volcano, with hopes of eventual assistance toward permanent relocation. On January 17, 2008, the volcano erupted around 20:06 (local) (01:06

UTC Coordinated Universal Time (UTC) is the primary time standard globally used to regulate clocks and time. It establishes a reference for the current time, forming the basis for civil time and time zones. UTC facilitates international communica ...

). There were no immediate reports of injuries or serious property damage. Later the experts confirmed partial damage in the national and local

TV tower Radio masts and towers are typically tall structures designed to support antenna (radio), antennas for telecommunications and broadcasting, including television. There are two main types: guyed and self-supporting structures. They are among the ...

s. Then, on February 14, 2009, the volcano erupted around 19:10 (local) (00:10 UTC). Some 8,000 residents were evacuated, and there were no immediate reports of injuries or serious property damage. As in 2005, the city of

was blanketed by a layer of

after the volcanic explosion (due to the direction of the wind). The local authorities ordered two

water treatment Water treatment is any process that improves the quality of water to make it appropriate for a specific end-use. The end use may be drinking, industrial water supply, irrigation, river flow maintenance, water recreation or many other uses, ...

plants near Galeras to shut down. On March 13, 2009, Galeras erupted twice at around 15:55 and 17:00 (local time). Ash fell on Pasto and some other towns near the volcano, where an evacuation was ordered but reportedly ignored. No injuries or damage were reported.

2010 eruption

The volcano erupted on January 3, 2010, forcing the evacuation of 8,000 people. This was the 10th such eruption of the volcano in the preceding 12 months, and the first of 2010. Colombian authorities also stated that it could remain volatile in the weeks to come. Galeras erupted again on August 25, 2010 with an ash plume visible in the air. The eruption, which was described as non-explosive, caused authorities to raise an alert for neighbouring towns. This volcano is monitored by the

Deep Earth Carbon Degassing Project The Deep Earth Carbon Degassing (DECADE) project is an initiative to unite scientists around the world to make tangible advances towards quantifying the amount of carbon outgassed from the Earth's deep interior (core, mantle, crust) into the surfac ...

Gallery

File:VolcanGaleras.jpg, Galeras Volcano shrouded in cloud and rare snow, overlooking the city of Pasto

References

Bibliography

External links

GOES imagery of the 03 January 2010 eruption (CIMSS Satellite Blog)

Galeras volcano website

Watch Galeras in realtime

BBC on the November 2005 eruption

Colombia: Galeras volcano situation map
{{Authority control Mountains of Colombia Stratovolcanoes of Colombia Active volcanoes Andean Volcanic Belt Complex volcanoes Decade Volcanoes Holocene stratovolcanoes Quaternary South America Subduction volcanoes Calderas of South America 20th-century volcanic events Geography of Nariño Department Pasto, Colombia Four-thousanders of the Andes Pleistocene stratovolcanoes