The Eruption of Mount Pinatubo

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The Eruption ofMount Pinatubo

• June 15, 1991
• Luzon, Philippines

Jeng Funtanilla Nov. 16, 2005
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Philippines

• LOCATION Southeastern Asia, archipelago between
  the Philippine Sea and the South China Sea, east
  of Vietnam
• GEOGRAPHY the Philippine archipelago is made up
  of 7,107 islands favorably located in relation
  to many of Southeast Asia's main water bodies
  the South China Sea, Philippine Sea, Sulu Sea,
  Celebes Sea, and Luzon Strait
• TERRAIN mostly mountains with narrow to
  extensive coastal lowlands
• NATURAL HAZARDS astride typhoon belt, usually
  affected by 15 and struck by five to six cyclonic
  storms per year landslides active volcanoes
  destructive earthquakes tsunamis

http//www.cia.gov/cia/publications/factbook/geos/
rp.html
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Major Volcanoes in the Philippines
http//vulcan.wr.usgs.gov/Volcanoes/Philippines/Ma
ps/map_philippines_volcanoes.html
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INTRODUCTION

• Before April 2, 1991, volcanologists knew Mount
  Pinatubo as an inconspicuous volcano, active
  within the past millennium, and the site of an
  aborted geothermal development.
• The Aetas, knew Mount Pinatubo as their home,
  their hunting ground, and their haven from an The
  mountain is the home of Apo Namalyari, the Great
  Protector and Provider.
• The people residing in the area, including those
  in nearby military bases (who received survival
  training from the Aetas) barely knew of Mount
  Pinatubo at all.

http//volcano.und.nodak.edu/vwdocs/volc_images/so
utheast_asia/philippines/pinatubo.html
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MOUNT PINATUBO

• Stratovolcano A volcano composed of both lava
  flows and pyroclastic material.
• Location 15.13N, 120.35E
• Elevation
• 5725 ft ( 1745 m) above sea level before the June
  1991 eruption
• 5248 ft (1600 m) above sea level after the June
  1991 eruption
• almost 500 ft (150 m) of the volcano was blasted
  away

http//volcano.und.nodak.edu/vwdocs/volc_images/so
utheast_asia/philippines/pinatubo.html
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GEOGRAPHIC FEATURES
The location of Mount Pinatubo, within the Luzon
volcanic arc
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TECTONIC SETTING

• The plate tectonics in the Philippines is complex
  and includes plate boundaries that are changing
  rapidly. Several micro-plates are getting
  squeezed between two convergent plate margins.
• Black triangles active subduction zones with
  "teeth" on the over-riding plate,
• White triangles inactive subduction zones with
  "teeth" on the over-riding plate, arrows
  transform or major strike-slip faults,
• Red triangles volcanoes active in the last
  10,000 years.

http//volcano.und.nodak.edu/vwdocs/volc_images/so
utheast_asia/philippines/tectonics.html
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TECTONIC SETTING
In the west, more steeply east-dipping subduction
of the Eurasian Plate (South China Sea basin and
the transitional oceanic-continental crust of the
Palawan block) along the 560 mile (900 km) length
of the Manila and Sulu trenches produces a
discontinuous line of active volcanoes from Taal
in the south to Iraya in the north. Volcanism
associated with this subduction zone began about
10 million years ago.
http//volcano.und.nodak.edu/vwdocs/volc_images/so
utheast_asia/philippines/tectonics.html
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TECTONIC SETTING
In the east, shallow west-dipping subduction of
the Philippine Plate at the Philippine Trench
produces a line of volcanoes from Balut in the
south to Mayon in the north.
http//volcano.und.nodak.edu/vwdocs/volc_images/so
utheast_asia/philippines/tectonics.html
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HISTORY
Stacked pyroclastic-flow and lahar deposits
outside Clark Air Base, testimony to a long
history of explosive eruptions.
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HISTORY

• Largest eruption in the history of the modern
  Pinatubo occurred over 35,000 years ago.
• Distributed over 325 ft (100 m) of pyroclastic
  flow material on all sides of the volcano.
• Marked the birth of the modern volcano.

• Ancient Mount Pinatubo
• Ancestral Pinatubo was an andesite and dacite
  stratovolcano whose center was in roughly the
  same location as the modern Pinatubo.
• Today, ancestral Pinatubo is exposed in relict
  walls of an old 3.5x4.5-km caldera
• Modern Mount Pinatubo
• Radiocarbon ages suggest that eruptions from the
  modern Pinatubo have been clustered in at least
  six and possibly as many as a dozen eruptive
  periods.

http//volcano.und.nodak.edu/vwdocs/volc_images/so
utheast_asia/philippines/pinatubo.html
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ERUPTIVE HISTORY
Radiocarbon ages of modern Pinatubo deposits,
arranged in chronologic order (not necessarily
in stratigraphic order).
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1991 VOLCANIC ACTIVITIES

• CHRONOLOGICAL ACCOUNT
• DESTRUCTIVE AGENTS
• ASHFALL
• PYROCLASTIC FLOW
• LAHAR

http//park.org/Philippines/pinatubo/page4.html
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CHRONOLOGICAL ACCOUNT

• DAY 1 Sunday, June 9, 1991

• 600 AM
• Eight hours of ash-laden steam clouds ejection
  ushered.
• Followed by pyroclastic flows which flowed down
  Pinatubos gullies into the Maraunot and Moraza
  rivers. The pyroclastic flows reached some 4-5
  kilometers from the center of activity.
• 315 PM
• Philvolcs issued Alert Level 5 at around 315 in
  the afternoon as intermittent occurrences of
  small pyroclastic flows persisted the whole
  morning.

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CHRONOLOGICAL ACCOUNT

• DAY 4 Wednesday, June 12, 1991

• DAY 5 Thursday, June 13, 1991

• DAY 6 Friday, June 14, 1991

• DAY 7 Saturday, June 15, 1991

815 AM
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BEFORE AFTER
Aircraft hangars at Clark Air Base that collapsed
under the weight of rain-saturated ash.
(Photograph by E.W. Wolfe, June 29, 1991.)
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WARNINGS

• Three cornerstones
• Interpretation of the origin of the unrest
• Simple five-level warning/alert
• Hazard map based on the worst-case prehistoric
  eruption.
• Warnings were coupled with intensive educational
  campaign to ensure they are not only received but
  UNDERSTOOD.

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WARNINGS

• Five Level Alerts

Alert Level Criteria Interpretation
No alert Background quiet No eruption in foreseeable future.
1 Low-level seismic, fumarolic, or other unrest. Magmatic, tectonic, or hydrothermaldisturbance no eruption imminent.
2 Moderate level of seismic or other unrest with positive evidence for involvement of magma. Probable magmatic intrusion could eventually lead to an eruption.
3 Relatively high unrest including numerous b-type earthquakes, accelerating ground deformation, increased vigor of fumaroles, gas emissions. New or renewed eruption possible, probably within days to weeks.
4 Intense unrest, including harmonic tremor and (or) many "long-period" (low-frequency) earthquakes and (or) dome growth and (or) small explosions. Magma close to or at the Earth's surface. Large explosive eruption likely, possible within hours to days.
5 Hazardous explosive eruption in progress, with pyroclastic flows and (or) eruption column rising at least 6 km above sea level. Large explosive eruption in progress. Hazards in valleys and downwind.
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WARNINGS

• CREDITS
• Warnings issued by PVO (Pinatubo Volcano
  Observatory) before the eruption succeeded in
  saving many lives and property.
• Civil Defense and local officials
• Mount Pinatubo followed a remarkable straight
  and rapid course toward eruption (gave fair
  warning, no false alarm)
• PHILVOCS
• USGS

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EVOLUTION OF SMALL CALDERA LAKE
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BEFORE
Pre-eruption Mount Pinatubo, April 16, 1991.
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BEFORE
Pre-eruption Mount Pinatubo, April 16, 1991.
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DURING
Summit caldera, as seen August 1, 1991, from the
northeast. The caldera formed by collapse during
the June 15, 1991, climactic eruption. A small
explosion had just occurred, forming the
expanding ash cloud. Throughout the latter half
of June and much of July, ash emission kept the
caldera obscured as continuous ash emission
changed to intermittent explosions, the caldera
became visible.
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AFTER
Summit caldera and lake, with partly submerged
relics (rocky islets) of a dome that grew between
July and October, 1992.
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BEFORE AFTER
Mount Pinatubo, as seen from near the southwest
end of the Clark Air Base runway
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BEFORE AFTER
ODonnell River
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BEFORE AFTER
Sacobia Bamban River
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BEFORE AFTER
A house by the Sacobia-Bamban River, Bamban,
Tarlac, July 23, 1991. Nearly 9 m of sediment
were deposited during a single lahar event on
August 15, 1991
A house by the Sacobia-Bamban River, Bamban,
Tarlac, July 23, 1991.
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BEFORE AFTER
Muddy water at the mouth of the Bucao River,
October 1, 1991. Massive amounts of sediment were
carried from Mount Pinatubo into the Bucao River
valley an unknown but relatively small
percentage of that sediment is carried into the
South China Sea.
Mouth of the Bucao River, April 16, 1991.
White-sand beaches of Zambales Province,
consisting of pumice and coralline debris,
attracted many tourists. The ocean was clear
blue little sediment was carried by the Bucao
River.
Muddy water at the mouth of the Bucao River,
October 1, 1991.
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DURING AFTER
Sacobia Bamban River
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DURING AFTER
Poonbato bridge was buried (but not swept away)
by lahars of 1991 and 1992. Deposits are
approximately 25 m thick. Barangay Poonbato
(immediately to the right of the field of view)
was buried.
Bridge to Poonbato, Botolan, Zambales, across the
Bucao River, May 28, 1991.
Poonbato bridge was buried (but not swept away)
by lahars of 1991 and 1992.
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Thank You!
http//pubs.usgs.gov/pinatubo/contents.html