MOUNT PINATUBO: PHILLIPINES
Mt. Pinatubo is located in island of Luzon in the bearings 15.13N and 120.35E. It is a strato-volcano
with an elevation of about 1600 metres. It last erupted on the 15th June 1991 realising sulphur
dioxide into the air. Mount Pinatubo is an active stratovolcano located on the island of Luzon, near
the tripoint of the Philippine provinces of Zambales, Tarlac, and Pampanga. It is located in the
Cabusilan Mountains separating the west coast of Luzon from the central plains. Before the volcanic
activities of 1991, its eruptive history was unknown to most people. It was heavily eroded,
inconspicuous and obscured from view.
It was covered with dense forest which supported a population of several thousand indigenous
people, the Aetas, who fled to the mountains during the Spanish conquest of the Philippines. Mount
Pinatubo, Philippines, Asia last eruption was June 12th-15th, 1991.
Mount Pinatubo is on the edge of the "Philippine Plate" and the "Eurasian Plate". The Volcano is an
'active stratovolcano' and the eruption was explosive; the second largest eruption of the 20th
century. There were Pyroclastic flow's after the eruption in 1991 and there was lava - The 1991
eruption blasted an estimated 800,000 tons of zinc, 600,000 tons of copper, 550,000 tons of
chromium, 300,000 tons of nickel, 100,000 tons of lead, 10,000 tons of arsenic, 1000 tons of
cadmium, and 800 tons of mercury to surface - The total volume of material erupted in the 1991
eruption may have been up to 25 cubic kilometers.
Mount Pinatubo is bordered by The Eurasian plate, The Pacific plate and The Philippines plate. These
plates are destructive as they move towards each other, hence cause earthquakes and volcanoes.
This is due to the fact that the oceanic plate is heavier than the continental plate, hence it subsides
under continental plate.
In plate tectonics, a convergent boundary, also known as a destructive plate boundary (because of
subduction), is an actively deforming region where two (or more) tectonic plates or fragments of
lithosphere move toward one another and collide. As a result of pressure, friction, and plate material
melting in the mantle, earthquakes and volcanoes are common near convergent boundaries. When
two plates move towards one another, they form either a subduction zone or a continental collision.
This depends on the nature of the plates involved. In a subduction zone, the subducting plate, which
is normally a plate with oceanic crust, moves beneath the other plate, which can be made of either
oceanic or continental crust. During collisions between two continental plates, large mountain
ranges, such as the Himalayas are formed.
Mount Pinatuba had been dormant for 500 years. The first sign that this situation might be changing
occured on July 16, 1990 when a magnitude 7.8 earthquake (roughly the size of the 1906 San
Francisco earthquake) struck about 60 miles (100 kms.) northeast of Mount Pinatubo on the island
of Luzon in the Philippines. This caused the shaking and squeezing of the Earth's crust beneath the
volcano. At Mount Pinatubo, scientists recorded a landslide, some local earthquakes, and a shortlived increase in steam emissions from a pre-existing geothermal area, but otherwise the volcano
seemed to be undisturbed. In March and April 1991, however, magma started rising towards the
surface from more than 20 miles (32 kms.) beneath Pinatubo. This triggered more small earthquakes
and caused powerful steam explosions that blasted three craters on the north side of the volcano.
Thousands of small earthquakes occurred beneath Pinatubo throughout April, May, and early June
1991, and many thousand tons of noxious sulphur dioxide gas were also emitted by the volcano.
On June 7th 1991, the first magma reached the surface of Mount Pinatubo but because it had lost
most of the gas contained in it on the way to the surface, the magma merely oozed out to form a
lava dome. However, on June 12th, large amounts of gas-charged magma reached the surface and
exploded in the volcano's first spectacular eruption. When even more highly gas charged magma
reached Pinatubo's surface on June 15th, the volcano exploded in a massive eruption that ejected
more than 5 cu. kms. of volcanic material. The ash cloud from this huge eruption rose 22 miles (35
kms.) into the air. A blanket of volcanic ash and larger pumice pebbles blanketed the countryside.
Fine ash fell as far away as the Indian Ocean, and satellites tracked the ash cloud several times
around the globe. Huge avalanches of red hot ash, gas, and pumice fragments called pyroclastic
flows roared down the sides of Mount Pinatubo, filling the deep valleys with fresh volcanic deposits
as much as 660 ft. (200 m.) thick. The eruption removed so much magma and rock from below the
volcano that the summit collapsed to form a large volcanic depression or caldera 1.6 miles (2.5 kms.)
across.
Scientists had been able to forecast Pinatubo's 1991 eruption and this resulted in the saving of many
lives and much property. Commercial aircraft were warned about the hazard of the ash cloud from
the June 15 eruption, and most avoided it. Although much equipment was successfully protected,
buildings on two U.S. military bases in the Philippines--Clark Air Base and Subic Bay Naval Station-were heavily damaged by ash. Nearly 20 million tons of sulphur dioxide were injected into the
stratosphere and the spread of this gas cloud around the world caused global temperatures to drop
temporarily (1991-1993) by about 0.5°C. About 20,000 Aeta highlanders, who had lived on the
slopes of the volcano, were completely displaced, and most still wait in resettlement camps for the
day when they can return home. About 200,000 other people who evacuated from the lowlands
surrounding Pinatubo before and during the eruptions have returned home but face continuing
threats from lahars (mudflows) that have already buried numerous towns, villages and fields.
•847 People Killed - 300 from collapsing roofs , 100 from the mud flows known as lahars, the rest
from disease in the evacuation centres including measles.
•650,000 workers lost jobs
•$700 Million Damages
•1.2million people lost homes
Electricity went off, water was contaminated, road links were destroyed, and telephone links were
cut
Social Effects
Economic Effects
Houses and bridges
58,000people had to be
destroyed and needed
evacuated from a 30km radius replacing and Manila airport
of the volcano
had to be closed
Environmental effects
Volcanic ash is blown in
directions over hundreds of
smothering fields and build
847 people lost their lives, Heavy rainfall from Typhoon
300 killed by collapsing roofs
Yunga causes buildings to
and 100 by lahars.
collapse.
Fast flowing volcanic mudf
(lahars) cause sever river
erosion, undercut bridges
Farmland destroyed by
falling ash and pumice,
1.2 million people lost their unusable for years, the 1991
homes around the volcano and harvest was destroyed and
had to migrate to shanty
650,000 people lost their Global cooling caused by ash
towns in Manila.
jobs
atmosphere of 0.5°C
Many still live near Pinatubo as a result of:
Volcanic ash makes very fertile soil for growing crops.
the soil there is good for farming