Mount Pinatubo

Location: Luzon Philippines
Latitude: 15.13 North
Longitude: 120.35 East
Height: 1,745 meters before the June 15, 1991 eruption
and 1,485 meters (highest point caldera rim) after eruption
Volcano Type: Stratovolcano
1991 Eruption timeline

The Eruption and Atmospheric Effects of the 1991 Mt. Pinatubo Event.

Volcanic Gasses

Explosive volcanic eruptions, Such as with the 1991 Mt. Pinatubo eruption, expel large amounts of water, greenhouse gasses, and other gasses into the atmosphere. This includes but is not limited to:
Water vapor, carbon dioxide, sulfur dioxide, hydrogen chloride, hydrogen fluoride, and ash. (McGee 2001 et al) These ash and gasses can be expelled into the stratosphere to 32.1 Km where sulfur dioxide converts into sulfuric acid that condenses into sulfate aerosols.

The result is an added reflectance of sunlight back into space. In turn this cools the Earths surface and lower atmosphere. The sulfates then absorb the heat-radiated form the Earth and warm the stratosphere. The stratosphere had a resulting in warming of between 2.5 and 3 deg. C. (NASA web page) This may seem contradictory but involves two separate atmospheric levels and the earth's surface.

These sulfate aerosols will also accelerate chemical reactions that destroy the ozone. Ozone destruction allows dangerous levels of ultraviolet radiation to reach the earths surface and can increase the risk of skin cancers. Mid latitude ozone levels reached their lowest recorded concentrations during 1992-93. The ozone hole over Antarctica became the largest ever recorded and in 1991 the ozone levels in the troposphere decreased in time with the Pinatubo aerosol arrival. Mt. Pinatubo 2001)

Carbon dioxide is the main greenhouse gas that allows a warming of the Earth. Volcanic gasses that are added to the atmosphere by volcanic eruptions increases this greenhouse gas and thereby the greenhouse effect. Initially the gaseous products cool the Earth for a period of 1 to 3 years. After the cooling effect is removed the increased carbon dioxide remains to potentially increase global warming.

Large amounts of volcanic ash that is thrown into the atmosphere blocks sunlight. This also causes a world wide cooling trend. Ash spreads out over large areas and can circulate in the atmosphere to cover the entire globe. The ash settles out relatively quickly, in days to months, and has only a short term cooling effect.

The 1991 Mt. Pinatubo Eruption

"Mt. Pinatubo is part of a chain of composite volcanoes along the Luzon arc on the west coast of the island (Luzon). The arc of volcanoes is caused by the subduction of the Manila trench to the west." (Mt. Pinatubo Eruption 2001)

In June of 1991 Mt. Pinatubo erupted and released volcanic products that made a large impact on the stratosphere. (NASA web page) On June 15, 1991 the climatic eruption occurred with a duration of 9 hours, this eruptive event disgorged a cubic mile of volcanic debris and vented 18.14 million metric tons of sulfur dioxide into the atmosphere and after reaching the stratosphere encircled the Earth in 3 weeks. This was the largest sulfur dioxide cloud ever detected to date by satellite (McGee 2001), and was 3 times more sulfur dioxide than was released by the El Chichon eruption . (Average comp. Pinatubo web page)

The Pinatubo eruption was a Plinian style eruption that produced 5 to 10 cubic Km of dacitic pumice and ignimbrite. It was called the second largest eruption of this century and formed a 2.5 Km diameter caldera. The eruption columns that were produced reached an altitude of over 35 Km in height.

The dense aerosol cloud created caused decreases in the amount of solar radiation that reached the Earths surface. This caused a climatic forcing that cooled the northern hemisphere by 0.6 deg C. This climate forcing was more profound than from the opposite anthropogenic greenhouse gases and the Simultaneous El Nino event during 1991 to 1993. The sulfate aerosols formed in the stratosphere increased reflection of solar radiation and within 3 years caused a 1.3 deg. C. overall cooling of the earth.

The concentration of sulfur dioxide aerosols in Antarctica was elevated from 1991 to 1994. This was shown by snow samples collected in 1996 during a stable non-volcanic background. (Dai 1999) This can be used to show aerosol mass loadings in the Antarctic ice core records.

Regional effects

Pinat10.jpg

The formation of the 2.5 Km caldera reduced the elevation of Mt. Pinatubo from 1745 meters to 1485 meters. This was a reduction of 260 meters. Due to the proximity of tropical storm Yunya ash from the eruption mixed with atmospheric moisture and fell as tephra covering nearly the complete island of Luzon. The greatest thickness of ash and tephra was at a distance of 10.5 Km from the volcano and was to a depth of 33 cm. Further from the center an area of 2000 square kilometers received 10 cm of debris. Ash caused collapse of roofs killed between 200 and 800 persons in the Philippines. (Mt. Pinatubo Eruption)

Worldwide effects

Fig.1

The eruption expelled large amounts of ash, aerosols and gases that influenced the world climate for several years. This caused an enlarging of the Antarctic ozone hole to an unprecedented size. Global temperatures were reduced at a maximum of 0.73 deg. C. It is believed that the 1993 Mississippi River Valley flood was influenced by the eruption and that the drought in the Sahel was caused by the eruption (Mt. Pinatubo Eruption) causing the third coolest summer and the third wettest summer during 1991.

Conclusions

Volcanic eruptions can have dramatic major short-term effects on the Earth. Such as short term atmospheric and earth surface cooling and/or an increasing effect of global warming.

Localized effects from the eruption products can cause much disruption to the environment and cause large-scale hazards for the population.

McGee, Kenneth A. USGS. 2001. World Wide Web homepage URL: http://pubs.usgs.gov/openfile/of97-262/0f97-262.html

Web page. 2001. Volcanic Gases: Average Composition and Minor or Trace gases. World Wide Web homepage URL: http://volcano.und.nodak.edu/vwdocs/Gases/impacts.html

NASA web page. 2001. World Wide Web homepage URL: http://eosweb/arc/nasa.gov/EDDOCS/Aerosols/Data.html

Web page. 2001. Volcanic Gases: Average Composition and Minor or Trace gases. World Wide Web homepage URL: http://volcano.und.nodak.edu/vwdocs/Gases/pinatubo.html

Mt. Pinatubo web page. 2001. Mount Pinatubo. World Wide Web homepage URL: http://earth.agu.org/revgeophys/selfool/node3.html

Dai, J, Thompson, E. 1999. web page. The pinatubo eruption in South Pole Snow and its potential value to Ice Core Paleovolcanic Records. World Wide Web homepage URL: http://www-bprc.mps.ohio-state.edu/icecore/abstracts/PES-99.html

Web page. Mount Pinatubo Eruption. World Wide Web homepage URL: http://www.geography.tqn.com/science/geography/library/weekly/ea030901a.htm

Web page. CVO Menu. Stratovolcanoes and Composite Volcanoes. World Wide Web homepage URL: http://vulcan.wr.usgs.gov/Glossary/StratoVolcano/framework.html

Image. pinta10.jpg.http://www.park.org:8888/Philippines/pinatubo/page5.html

Fig1. (Fig5).http://pubs.usgs.gov/pinatubo/self/fig5.jpg