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The Mount Pinatubo Eruption in the Philippines
The Volcanic
Mount Pinatubo Eruption of 1991 that Cooled the Planet
In June 1991, the second-largest volcanic
eruption of the twentieth century took place on the island of
Luzon in the Philippines,
a mere 90 kilometers (55 miles) northwest of the capital city Manila.
Up to 800 people were killed and 100,000 became homeless
following the Mount Pinatubo eruption, which climaxed with nine hours of
the eruption on June 15, 1991.
On June 15, millions of tons of sulfur dioxide were discharged
into the atmosphere, resulting in a decrease in the temperature worldwide over
the next few years.
The Luzon Arc
Mount Pinatubo is part of a chain of composite volcanoes along
the Luzon arc on the west coast of the island (area map).
The arc of volcanoes is due to the subduction of the Manila
trench to the west. The volcano experienced major eruptions approximately 500,
3000, and 5500 years ago.
The events of the 1991 Mount Pinatubo eruption began in July
1990, when a magnitude 7.8 earthquake occurred 100 kilometers (62 miles)
northeast of the Pinatubo region, determined to be a result of the reawakening
of Mount Pinatubo.
Before the Eruption
In mid-March 1991, villagers around Mount Pinatubo began feeling
earthquakes and volcanologists began to study the mountain.
(Approximately 30,000 people lived on the flanks of the volcano
prior to the disaster.)
On April 2, small explosions from vents dusted local villages
with ash. The first evacuations of 5,000 people were ordered later that month.
Earthquakes and explosions continued.
On June 5, a Level 3 alert was issued for two weeks due to the
possibility of a major eruption.
The extrusion of a lava dome on June 7 led to the issuance of a
Level 5 alert on June 9, indicating an eruption in progress.
An evacuation area 20 kilometers (12.4 miles) away from the
volcano was established and 25,000 people were evacuated.
The following day (June 10), Clark Air Base, a U.S. military
installation near the volcano, was evacuated.
The 18,000 personnel and their families were transported to
Subic Bay Naval Station and most were returned to the United States.
On June 12, the danger radius was extended to 30 kilometers
(18.6 miles) from the volcano resulting in the total evacuation of 58,000 people.
The Eruption
On June 15, the eruption of Mount Pinatubo began at 1:42 p.m.
local time.
The eruption lasted for nine hours and caused numerous large
earthquakes due to the collapse of the summit of Mount Pinatubo and the
creation of a caldera.
The caldera reduced the peak from 1745 meters (5725 feet) to
1485 meters (4872 feet) high is 2.5 kilometers (1.5 miles) in diameter.
Unfortunately, at the time of the eruption Tropical Storm Yunya
was passing 75 km (47 miles) to the northeast of Mount Pinatubo, causing a
large amount of rainfall in the region.
The ash that was ejected from the volcano mixed with the water vapor in
the air to cause a rainfall of tephra that fell across almost the entire island
of Luzon.
The greatest thickness of ash deposited 33 centimeters (13
inches) approximately 10.5 km (6.5 mi) southwest of the volcano. There was 10
cm of ash covering an area of 2000 square kilometers (772 square miles).
Most of the 200 to 800 people (accounts vary) who died during
the eruption died due to the weight of the ash collapsing roofs and killing the
occupants.
Had Tropical Storm Yunya not been nearby, the death toll from
the volcano would have been much lower.
In addition to the ash, Mount Pinatubo ejected between 15 and 30
million tons of sulfur dioxide gas.
Sulfur dioxide in the atmosphere mixes with water and oxygen in
the atmosphere to become sulfuric acid, which in turn triggers ozone depletion.
Over 90% of the material released from the volcano was ejected
during the nine-hour eruption of June 15.
The eruption plume of Mount Pinatubo's various gasses and ash
reached high into the atmosphere within two hours of the eruption, attaining an
altitude of 34 km (21 miles) high and over 400 km (250 miles) wide.
This eruption was the largest disturbance of the stratosphere
since the eruption of Krakatau in 1883 (but ten times larger than Mount St. Helens in
1980).
The aerosol cloud spread around the earth in two weeks and
covered the planet within a year.
During 1992 and 1993, the Ozone hole over Antarctica reached an
unprecedented size.
The cloud over the earth reduced global temperatures.
In 1992 and 1993, the average temperature in the Northern
Hemisphere was reduced 0.5 to 0.6°C and the entire planet was cooled 0.4 to
0.5°C.
The maximum reduction in global temperature occurred in August
1992 with a reduction of 0.73°C.
The eruption is believed to have influenced such events as 1993
floods along the Mississippi River and the drought in the Sahel region of
Africa.
The United States experienced its third coldest and third
wettest summer in 77 years during 1992.
The Aftermath
Overall, the cooling effects of the Mount Pinatubo eruption were
greater than those of the El NiƱo that was taking place at the time or of the greenhouse
gas warming of the planet.
Remarkable sunrises and sunsets were visible around the globe in
the years following the Mount Pinatubo eruption.
The human impacts of the disaster are staggering. In addition to
the up to 800 people who lost their lives, there was almost one-half of a
billion dollars in property and economic damage.
The economy of central Luzon was horribly disrupted.
In 1991, the volcano destroyed 4,979 homes and damaged another
70,257.
The following year 3,281 homes were destroyed and 3,137 were damaged.
Damage following the Mount Pinatubo eruption was usually caused
by lahars - rain-induced torrents of volcanic debris that killed people and
animals and buried homes in the months after the eruption.
Additionally, another Mount Pinatubo eruption in August 1992
killed 72 people.
The United States military never returned to Clark Air Base,
turning over the damaged base to the Philippine government on November 26,
1991.
Today, the region continues to rebuild and recover from the
disaster.
Matt
Rosenberg
Geography
Expert
Education
M.A.,
Geography, California State University - Northridge
B.A.,
Geography, University of California - Davis
Introduction
Award-winning
professional geographer
Author
of two books on geography
Experience
Matt
Rosenberg is a former writer for ThoughtCo. He covered geography for ThoughtCo
and About.com for over 20 years. He was an adjunct professor of geography at
California State University, Sacramento, a city planning and GIS intern
for local government, and is a former newspaper columnist.
Rosenberg
has been featured on PBS and NPR, and he has conducted many interviews about
geographical topics for television, radio, and newspapers. He was director of
emergency services for the American Red Cross and served on more than two dozen
major disaster relief operations around the United States. He has traveled
widely across North America and has visited or studied in Europe, Asia, Africa,
and the Middle East. He is a member of the Association of American
Geographers and the National Council for Geographic Education.
Education
Matt
Rosenberg holds a bachelor's degree in geography from the University
of California, Davis and a master's degree in geography from California State
University, Northridge.
Publications
and Awards
"The Handy Geography Answer Book" (Barnes & Noble,
2004)
"The Geography Bee Complete Preparation Handbook"
(Three Rivers Press, 2002)
Excellence
in Media Award, National Council for Geographic Education, October 2006
ThoughtCo
and Dotdash
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