Sphere Report on Mt. Pinatubo
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Mt. Pinatubo is a volcano that erupted in 1991 in the Philippines. This eruption was a
shock to the world because this particular volcano had been inactive for a long period of time.
Not only did it erupt, which was unexpected, but it was a large explosion and left a huge
devastating impact. This volcano eruption caused one of the largest terrestrial eruptions of the
twentieth century (Wikipedia). The sphere that consists of the land on Earth is called the
lithosphere. This sphere was directly affected my Mt. Pinatubo. The disturbance had many
impacts on the land in that area and the surrounding area as well. It can take many years for
the land to fully recover after a volcano eruption.
Volcanic eruptions like the June 15th, 1991 eruption of Mt. Pinatubo can enhance global
warming by adding carbon dioxide into the atmosphere although a far greater amount of
carbon dioxide is released into the atmosphere by human activities. The small amount of global
warming caused by greenhouse gases
sent out during a volcanic eruption is
often offset by the haze effect. Haze is
particles of dust, volcanic ash or salt that
is roughly 0.1 microns large that are
suspended in the atmosphere (see Figure
1). The haze effect happens when
particles like ash and dust are suspended
in the atmosphere and block out the sun
light trying to reach Earth. Because there
is less solar radiation reaching Earth’s
surface, the global temperature drops.
The effect often gives way to amazingly
red sunsets that are due to particles in
the stratosphere and upper troposphere
scattering the color red in the light
spectrum.
The June 11th, 1991 eruption
caused many disastrous effects to
aircrafts and their flight paths. The
Figure 1: Aerosol optical depth in the stratosphere before the
volcano injected tremendously large
Pinatubo eruption to two years after the eruption. Red
amounts of ash upwards of 10,000 feet
represents high values, while blue represents normal low values.
into the atmosphere. The June 15th
eruption produced the largest ash cloud;
it was carried by the upper levels winds to the west and circled the globe in twenty two days.
According to the United States Geologic Service, “the June 15 cloud spread laterally to cover a
broad equatorial band from about 10 degrees south to 20 degrees north latitude and
contaminated some of the world's busiest air traffic corridors.” Between June 12th and 18th,
there were sixteen in-flight encounters with ash that spewed from the volcano. There were
reportedly more than two dozen airplanes on the ground in surrounding areas that were also
physical damaged by the volcanic ash.
References:
Casadevalla, T.J., Delos Reyes, P.J., & Schneider, D. J. The 1991 Pinatubo Eruptions and Their
Effects on Aircraft Operations. Retrieved from: http://pubs.usgs.gov/pinatubo/casa/index.html
http://vulcan.wr.usgs.gov/Volcanoes/Philippines/Pinatubo/Publications/FireMud/CasadevallOther
s/framework.html
http://en.wikipedia.org/wiki/Mount_Pinatubo
http://gsc.nrcan.gc.ca/volcanoes/intro_e.php
http://volcano.oregonstate.edu/vwdocs/frequent_questions/group4_new.html
http://www.geology.sdsu.edu/how_volcanoes_work/climate_effects.html
http://www.britannica.com/EBchecked/topic/257938/haze
http://www.geology.sdsu.edu/how_volcanoes_work/climate_effects.html
http://www.uen.org/utahlink/tours/tourElement.cgi?element_id=32963&tour_id=17182&catego
ry_id=27175
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Global temperature can drop by several degrees Fahrenheit when sulfur dioxide emitted from
the eruption combines with water vapor in the stratosphere. According to Rosenberg, Mt.
Pinatubo ejected somewhere between 25 and 30 million tons of sulfur dioxide into the
atmosphere and stratosphere more specifically. In the stratosphere they form minute sulfuric
acid droplets that can lower temperatures in the troposphere because the actually can absorb
the radiation coming from the sun and scatter it back into space. According to NASA, the 1991
eruption of the Mount Pinatubo contributed to a strengthening of a climate pattern called the
Arctic Oscillation (see Figure 2);
this is a natural pattern of
circulation of air where the
atmospheric pressure at the
middle and polar latitudes
change. It thus brings lower
than normal pressure to areas
of the world with roughly a
forty-five degree north latitude
and a higher than normal
pressure at the Polar Regions.
For two years following the
Figure 2: Arctic Oscillation (NASA, 2003)
volcanic eruption of Mt. Pinatubo in 1991, the entire planet cooled 0.4 to 0.8C. The largest
cooling in North America came in the summer of 1992. The ice on the Hudson Bay melted a
month later than normal, thus allowing time for the polar bears to feed and nurse their cubs.
These polar bears were called the “Pinatubo Bears” and were a lot heavier and healthier than
the polar bears born in years before and after.
References:
Biello, D. (January 2008). Scientific Nature: Researchers Use Volcanic Eruption as Climate Lab.
Scientific America. Retrieved from: http://www.scientificamerican.com/article.cfm?id=scientificnature-researc
Holasek, R.E., King, A.J., Self, S., Torres, R.C., & Zhao, J. The Atmospheric Impact of the 1991
Mount Pinatubo Eruption. Retrieved from: http://pubs.usgs.gov/pinatubo/self/index.html
Myers. (1997). What are Volcano Hazards?: USGS Fact Sheet 002-97. Retrieved from:
http://vulcan.wr.usgs.gov/Glossary/VolcWeather/description_volcanoes_and_weather.html
Robock, A. Introduction: Mount Pinatubo as a Test of Climate Feedback Mechanisms. Retrieved
from: http://climate.envsci.rutgers.edu/pdf/VEAChapter1_Robocknew.pdf
Rosenberg, M. (August 2007). Mount Pinatubo Eruption: The Volcanic Mount Pinatubo Eruption
of 1991 that Cooled the Planet. Retrieved from:
http://geography.about.com/od/globalproblemsandissues/a/pinatubo.htm
Wolfe, J. (September 2000). Volcanoes and Climate Change. Earth Observatory. Retrieved
from: http://earthobservatory.nasa.gov/Features/Volcano/
(April 2009). Greenhouse Gases Continue to Climb Despite Economic Slump, Carbon Dioxide,
Methane Increased in 2008. Retrieved from:
http://www.noaanews.noaa.gov/stories2009/20090421_carbon.html
http://www.physicalgeography.net/fundamentals/7y.html
http://www.ngdc.noaa.gov/hazard/stratoguide/img/aerosol.gif
http://www.innovations-report.de/html/berichte/geowissenschaften/bericht-17078.html
http://www.agu.org/pubs/crossref/2006/2005JD006286.shtml
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The 1991 eruption of Mt. Pinatubo received a Volcanic Explosivity Index (VEI) score of 6 on a
scale of 8. This VEI score is described qualitatively as “colossal” (Smithsonian, 2009). The
water content of a volcano’s magma plays a major role in determining the explosivity of an
eruption. Within Earth’s interior, the presence of water decreases the melting point of rock. As
rock melts and absorbs the water vapor, magma is formed.
Magma contains dissolved gasses that can either be released into the atmosphere during
eruptions or released while the magma is still
underground or rising to the surface. Deep
within Earth’s surface, volcanic gasses are
dissolved in molten rock. The melted rock,
containing dissolved water vapor, is more
buoyant than the surrounding solid rock and
begins to rise to the surface. As the magma
rises, pressure is reduced and the water vapor
comes out of solution and forms bubbles. In
volcanoes with highly viscous magma, like Mt.
Pinatubo, the bubbles cannot easily escape.
Instead, the water vapor bubbles expand until
they escape explosively in a violent up thrust
(Water Encyclopedia).
Throughout a volcanoes life, gasses may be
released into the atmosphere from the soil,
hydrothermal systems, and volcanic vents and
from fumaroles. Fumaroles are vents where
volcanic gas can escape and they can be
located in tine cracks, long fissures and even on
the surface of lava flows. According to Myers,
ninety prevent of all gas emitted by volcanoes is
water vapor which comes from heated ground
water from either rain fall or streams. Volcanic
gasses can rise many miles into earth’s
atmosphere and be blown all the way around
the world. Besides for water vapor, volcanic gas
contains other natural elements like hydrogen,
sulfur, fluorine, chlorine, hydrogen and
compounds like carbon dioxide, sulfur dioxide
and carbon monoxide. In high concentrations
fluorine or F, can soak into ash particles that
later fall onto the lithosphere. These particles
can soak into the Earth’s water s supplies and
not only harm the vegetation but also the
Figure 3: Distribution of aerosols following the Mt.
Pinatubo eruption
Figure 4: Distribution of Mount Pinatubo’s sulfur
dioxide and dust aerosol plume (red and yellow
areas) between June 14 and July 26, 1991.
organisms that feed upon it. To humans it can cause skin irritation, conjunctivitis, degeneration
of the bone and the rotting of teeth. Excess fluorine results in a significant cause of death and
injury in livestock during ash eruptions. Sulfur dioxide or SO2 can also cause harm to vegetation
because it corrodes the lithosphere by combining with water in the atmosphere, thus forming
acid rain. The eruption of Mt. Pinatubo in 1991 released 3-5 km 3 of dacite magma and expelled
roughly 17 million tons of sulfur dioxide into the stratosphere. Carbon dioxide or CO2 is also a
volcanic gas, it is heavier than air and when it accumulates in low areas in high concentrations
it can be deadly to most organisms. It is extremely imperative to avoid small depressions and
low areas because they can trap carbon dioxide. The boundary between the lethal carbon
dioxide and healthy air is very rigid, sadly even a single step either way may be the difference
between living and dying. Even though volcanic gas is comprised of a lot of carbon dioxide (it
gives off about 110 million tons per year) it is not abundant enough to play any part in the
greenhouse effect that humans are contributing to (roughly about 10 billion tons per years).
References:
Doukas, M.P., Gerlach, T.M., Kessler, R. & McGee, K.A. (May 2009). Impacts of Volcanic Gases
on Climate, the Environment, and People. U.S. Geological Survey Open-File Report 97-262.
Retrieved from: http://pubs.usgs.gov/of/1997/of97-262/of97-262.html
Myer. ( 1997). What are Volcano Hazards?: USGS Fact Sheet 002-97. Retrieved from:
http://vulcan.wr.usgs.gov/Glossary/VolcWeather/description_volcanoes_and_weather.html
Smithsonian National Museum of Natural History. Global Volcanism Program. Retrieved from
http://www.volcano.si.edu/
Water Encyclopedia. Volcanoes and Water. Retrieved from
http://www.waterencyclopedia.com/Tw-Z/Volcanoes-and-Water.html
http://volcano-pictures.info/glossary/fumarole.html
http://volcanoes.usgs.gov/hazards/gas/index.php
http://volcanology.geol.ucsb.edu/gas.htm
http://www.sciencemaster.com/jump/earth/gases.php
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Volcanic smog or vog, forms when sulfur dioxide found in magma reacts with atmospheric
moisture. You cans see it in the air as haze around a volcano and is caused by combination of
wind, weather and volcanic activity. Vog can cause severe respiratory problems, headaches,
sore throats and watery eyes. When this sulfur dioxide in the atmosphere encounters water
droplets, vog (volcanic smog) and acid rain are formed. Acid rain can stunt vegetation and alter
pH in rivers and lakes, altering water quality for aquatic organisms. Acid rain also corrodes
metals. Leaching of heavy metals from acid rain corrosion can lead to contaminated water
supplies.
References:
Heliker. (1997). Living on Active Volcanoes -- The Island of Hawai'i: USGS Fact Sheet 074-97.
Retrieved from:
http://vulcan.wr.usgs.gov/Glossary/VolcWeather/description_volcanoes_and_weather.html
USGS Volcano Ovservatory. Mount Pinatubo, Philippines. Retrieved from
http://vulcan.wr.usgs.gov/Volcanoes/Philippines/Pinatubo/framework.html
http://hawaii.gov/gov/vog
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The impact of the eruption of Mt. Pinatubo was
magnified by its timing within the monsoon season
and the coincidental arrival of Typhoon Yunya on
the same day as the eruption (see Figure 1). USGS
estimates that rainfall intensity was at least
75mm/day, but was most likely significantly
greater. Though this amount of rainfall was not
out of the ordinary for the wet season, its
concurrence with the release of 125,00 square
kilometers of ash had disastrous consequences.
The ash that ejected from the volcano mixed with
the water vapor from the air resulted in a rainfall of
tephra that fell across almost the entire island of
Luzon like snow. The greatest thickness of ash
deposited 33cm approximately 10.5 km southwest
of the volcano. The 200 to 800 people who died
during the eruption died due to the weight of the
ash collapsing roofs and killing the occupants.
According to reports, if Tropical Storm Yunya was
not nearby, the death toll from the volcano would
have not been so high.
References:
Figure 5 Path and timing of Typhoon Yunya
Spense et al. (1999) Building Damage Caused by the Mount Pinatubo Eruption of June 15,
1991. USGS. Retrieved from http://pubs.usgs.gov/pinatubo/spence/index.html
http://geography.about.com/od/globalproblemsandissues/a/pinatubo.htm
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The arrangement of the lithosphere’s
continental plates underneath Mt. Pinatubo
is an integral reason why the volcano
erupted. Mt. Pinatubo is one of many
volcanoes that are located on top of the
Philippine Mobile Belt. These volcanoes are
called subduction volcanoes because they
were created by the Philippine Mobile Belt
moving above the Eurasion Plant and the
Manila Trench to the west. As the
Eurasian plate becomes subducted
beneath the Philippine Mobile Belt, it seeps
Figure 6
into the earth’s mantle, which causes the
mantle to melt and produces the volcanic arc as lighter rock rises. Additionally, as the plates
converge and mantle rock begins to melt and break, earthquakes occur.
The earthquakes caused by the lithosphere’s movement results in volcanic eruptions.
Earthquake cause the melted magna beneath the volcano to be released and rise. As the
magna rises all the way up the volcano to beneath the summit, it becomes blocked by rocks,
and pressure builds. Eventually the pressure will become so strong that the slightest
earthquake can trigger the volcano to erupt in order to release the built-up energy. Scientists
believe that the Mt. Pinatubo’s eruption may have first been initiated by the colossal 1990 Luzon
earthquake, which was the largest earthquake in recorded history in 1990 with a magnitude of
7.8 occurred and located only 80 miles north of Pinatubo. However, this reasoning is not
supported by hard evidence and is only a scientific speculation. About a year later, in 1991, a
series of earthquakes that increased in strength over time, provided more convincing proof that
volcanic activity would be likely. A month after the initial series of earthquakes, small eruptions
of volcanoes occurred for the next few months while small earthquakes were simultaneously
reported. These dusted ash over the surrounding towns and the nearly 30,000 villagers who
lived near the volcano. Then when the extrusion of a lava dome formed on June 7th, the
issuance of a level 5 alert indicated an eruption was in progress. An evacuation area 20km away
from the volcano was established and 25, 000 people were evacuated. On June 12th, the
danger radius was extended to 30km from the volcano, resulting in the total evacuation of 58,
000 people. Then eventually after many minor eruptions, in June 1991, the pressure was so
titanic Mt. Pinatubo erupted and became the second largest terrestrial eruption of the last 100
years. The crust’s rupture allowed hot ash, gas, and roughly 10 billion metric tones (10 cubic
kilometers) of magma to be release from the lithosphere, creating effects felt worldwide.
Deposits from the eruption of Mt. Pinatubo radically altered watershed hydrology.
Pyroclastic material settled into the natural drainage network with developed in the centuries
since Pinatubo’s last eruption. This lead to increased over-land flow of rain water as rainfall had
no channels to occupy. As water swept
through the watershed, it eroded the
accumulated volcanic deposits forming
lahars (volcanic mud-flows). As water and
lahars swept down the watershed, some
homes were inundated by the flowing
sediment (see Figure 7), while others were
undercut as bank erosion striped flow
channels to the bedrock (see Figure 8).
Lahars resulted in 100, 000 of people
becoming homeless. Furthermore, there
was also one half of a billion dollars in
property and economical damage. The
Figure 7
economy of central Luzon was terribly
disrupted. Due to the volcano’s eruption
and lava flow, 4, 979 homes were destroyed and another 70, 257 homes were damaged. The
following year 3, 281 homes were destroyed while 3, 137 homes were damaged. The lahars
continued to kill people and animals and buried homes even in the months after the eruption.
Furthermore, in August 1992, Mt. Pinatubo erupted again killing 72 people. The region
continues to rebuild and recover from the disaster.
Despite being evacuated from the area and having their homes destroyed, the citizens
were then able to use some of the deposited materials from the eruption to construct buildings
and roads. The material is also used as abrasive and cleaning agents, and even as raw material
materials for many chemical and industrial uses. Furthermore metallic minerals such as copper,
gold, silver, lead, and zinc are found deep within the roots of extinct volcanoes that are located
above subduction zones and these minerals are used by people to make steel, glass, concrete,
and explosives etc.
References:
Major, J.J., Janda, R.J., Daag, A.S. (1999). Watershed disturbance and lahars on the east side
of Mount Pinatubo during the mid-June 1991 Eruptions. USGS. Retrieved from
http://pubs.usgs.gov/pinatubo/major/index.html
Rangin and Pubellier (1990) in Tectonics of
Circum-Pacific Continental Margins ISBN 906764-132-4 p140 ff The Philippine Mobile Belt
has also been called the Philippine Microplate[3]
and the Taiwan-Luzon-Mindoro Belt.[4]- ^ Nicolas
Pinet and Jean Francois Stephan (1989) in
Tectonics of Circum-Pacific Continental Margins
ISBN 90-6764-132-4 p165
Inter-Agency Committee for Documenting and
Establishing Database on the July 1990
Earthquake. Philippine Institute of Volcanology
and Seismology. 2001.
Figure 8
The Cataclysmic 1991 Eruption of Mount
Pinatubo, Philippines.Retrieved from: http://pubs.usgs.gov/fs/1997/fs113-97/
http://geography.about.com/od/globalproblemsandissues/a/pinatubo.htm
http://distance.una.edu/ess/_event_f02/00000093.htm
http://wiki.answers.com/Q/What_are_minerals_used_for
http://geography.about.com/od/globalproblemsandissues/a/pinatubo.htm
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The eruption of Mt Pinatubo created a 2.5km wide collapse
caldera. The caldera filled with hot highly acidic water, forming a
crater lake (Lake Pinatubo). When first formed, the lake water
had a pH of 2 and a temperature of about 105oF. Over time,
rainfall diluted the lake, cooling the water to 78oFwith a pH of
5.5. Rainfall increased lake depth by about 1m per month, until
fears of flooding lead the government to drain a quarter of the
lake level in 2001 (see Figure 9).
Figure 9
References:
BBC News. (2001). Filipinos return as volcano lake drains. Retrieved from
http://news.bbc.co.uk/2/hi/asia-pacific/1530182.stm
USGS Volcano Ovservatory. Mount Pinatubo, Philippines. Retrieved from
http://vulcan.wr.usgs.gov/Volcanoes/Philippines/Pinatubo/framework.html
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The Mt. Pinatubo eruption caused pyroclastic flow, which altered the terrestrial structure of the
lithosphere surrounding Mt. Pinatubo. Pyroclastic flow is a current of hot gas and rock, which is
also called tephra that gushes from the volcanically erupted summit and thereafter streams for
long distances. The flow can be extremely hot, reaching temperatures around 1830 degrees
Fahrenheit! Mt. Pinatubo’s eruption caused nearly a volume of 25 cubic kilometers pyroclastic
flow material to be released and as a result the pyroclastic deposits were found to be nearly
100 meters deep on the mountain side. Therefore, the breadth and structure of the
mountainside dramatically changed as small rocks deposits, tephra, were left behind as well as
the fusion of these hot rocks creating large mountainside boulders. So a once richly forested
mountainside, was replaced with small and boulder-sized rocks. Furthermore, when the volcano
erupted, some of the pyroclastic flow quickly solidified around the summit, which created a
structure called a lava dome. A lava dome is a mound that circles the entire summit, forming a
dome, and that is composed of stick lava that eventually cools and solidifies. Mt. Pinatubo’s
dome had a maximum diameter of approximately 200 meter and a height of 40 meters. Thus
the geological formation of the Mount Pinatubo changed.
The rock deposits that were pushed by the pycroclastic flow into surrounding
ecosystems, severely influenced the hydrosphere around the volcano. Surrounding the
mountain was an intricate weaving of river systems; these rivers were filled with pyroclastic
deposits as the deposits travel from the mountainside into the lower-level valleys and eventually
into the rivers. The deposits filled the rivers with sediments, which eventually blocked and
altered the flow of the rivers. Many scientific studies suggest that it will take many years for
these river ecosystems to recover, but there is not any precise numbers as to how long.
References:
http://pubs.usgs.gov/fs/1997/fs113-97/fs113-97.pdf
http://pubs.usgs.gov/gip/msh//pyroclastic.html
http://pubs.usgs.gov/fs/1997/fs113-97/