The The Eruption Eruption

ofof

Mount Mount PinatuboPinatubo

June 15, 1991June 15, 1991Luzon, PhilippinesLuzon, Philippines

Jeng FuntanillaNov. 16, 2005

PhilippinesPhilippines• 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

Major Volcanoes Major Volcanoes in the Philippinesin the Philippines

http://vulcan.wr.usgs.gov/Volcanoes/Philippines/Maps/map_philippines_volcanoes.html

INTRODUCTIONINTRODUCTION

Before April 2, 1991, volcanologists knew Mount Before April 2, 1991, volcanologists knew Mount Pinatubo as an inconspicuous volcano, active Pinatubo as an inconspicuous volcano, active within the past millennium, and the site of an within the past millennium, and the site of an aborted geothermal development. aborted geothermal development.

The The AetasAetas, knew Mount Pinatubo as their home, , knew Mount Pinatubo as their home, their hunting ground, and their haven from an their hunting ground, and their haven from an The mountain is the home of The mountain is the home of Apo Namalyari, Apo Namalyari, the Great Protector and Providerthe Great Protector and Provider. .

The people residing in the area, including those The people residing in the area, including those in nearby military bases (who received survival in nearby military bases (who received survival training from the Aetas) barely knew of Mount training from the Aetas) barely knew of Mount Pinatubo at all.Pinatubo at all.

http://volcano.und.nodak.edu/vwdocs/volc_images/southeast_asia/philippines/pinatubo.html

MOUNT PINATUBOMOUNT PINATUBO

Stratovolcano:Stratovolcano: A volcano composed of both A volcano composed of both lava flows and pyroclastic material. lava flows and pyroclastic material.

Location:Location: 15.13N, 120.35E 15.13N, 120.35E

Elevation:Elevation: 5725 ft ( 1745 m) above sea level before 5725 ft ( 1745 m) above sea level before

the June 1991 eruption the June 1991 eruption 5248 ft (1600 m) above sea level after the 5248 ft (1600 m) above sea level after the

June 1991 eruption June 1991 eruption almost 500 ft (150 m) of the volcano was almost 500 ft (150 m) of the volcano was

blasted away blasted away

http://volcano.und.nodak.edu/vwdocs/volc_images/southeast_asia/philippines/pinatubo.html

GEOGRAPHIC FEATURESGEOGRAPHIC FEATURES

The location of Mount Pinatubo, within the Luzon volcanic arc

TECTONIC TECTONIC SETTINGSETTING

http://volcano.und.nodak.edu/vwdocs/volc_images/southeast_asia/philippines/tectonics.html

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.

TECTONIC SETTINGTECTONIC SETTINGIn 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/southeast_asia/philippines/tectonics.html

TECTONIC SETTINGTECTONIC 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/southeast_asia/philippines/tectonics.html

HISTORYHISTORY

Stacked pyroclastic-flow and lahar deposits outside Clark Air Base, testimony to a long history of explosive eruptions.

Largest eruption in the history of the modern Pinatubo occurred Largest eruption in the history of the modern Pinatubo occurred over 35,000 years ago.over 35,000 years ago.

Distributed over 325 ft (100 m) of pyroclastic flow material on all Distributed over 325 ft (100 m) of pyroclastic flow material on all sides of the volcano. sides of the volcano.

Marked the birth of the modern volcano. Marked the birth of the modern volcano.

http://volcano.und.nodak.edu/vwdocs/volc_images/southeast_asia/philippines/pinatubo.html

HISTORYHISTORY

• 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.

Radiocarbon ages of modern Pinatubo deposits, arranged in chronologic order

(not necessarily in stratigraphic order).

ERUPTIVE HISTORYERUPTIVE HISTORY

CHRONOLOGICAL ACCOUNTCHRONOLOGICAL ACCOUNT

DESTRUCTIVE AGENTSDESTRUCTIVE AGENTS

ASHFALLASHFALL

PYROCLASTIC FLOW PYROCLASTIC FLOW

LAHAR LAHAR

1991 VOLCANIC 1991 VOLCANIC ACTIVITIESACTIVITIES

http://park.org/Philippines/pinatubo/page4.html

CHRONOLOGICAL CHRONOLOGICAL ACCOUNTACCOUNT

DAY 1: Sunday, June 9, 1991DAY 1: Sunday, June 9, 1991

6:00 AM

• Eight hours of ash-laden steam clouds ejection ushered.

• Followed by pyroclastic flows which flowed down Pinatubo’s gullies into the Maraunot and Moraza rivers. The pyroclastic flows reached some 4-5 kilometers from the center of activity.

3:15 PM

• Philvolcs issued Alert Level 5 at around 3:15 in the afternoon as intermittent occurrences of small pyroclastic flows persisted the whole morning.

DAY 4: Wednesday, June 12, 1991DAY 4: Wednesday, June 12, 1991 DAY 5: Thursday, June 13, 1991DAY 5: Thursday, June 13, 1991

CHRONOLOGICAL CHRONOLOGICAL ACCOUNTACCOUNT

8:15 AM

DAY 6: Friday, June 14, 1991DAY 6: Friday, June 14, 1991 DAY 7: Saturday, June 15, 1991DAY 7: Saturday, June 15, 1991

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

BEFORE & AFTERBEFORE & AFTER

Three cornerstonesThree cornerstones Interpretation of the origin of the unrestInterpretation of the origin of the unrest Simple five-level warning/alertSimple five-level warning/alert Hazard map based on the “worst-case” prehistoric Hazard map based on the “worst-case” prehistoric

eruption.eruption.

Warnings were coupled with intensive Warnings were coupled with intensive educational campaign to ensure they are educational campaign to ensure they are not only received but UNDERSTOOD.not only received but UNDERSTOOD.

WARNINGSWARNINGS

WARNINGSWARNINGS Five Level AlertsFive 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.

2Moderate 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.

CREDITS:CREDITS: Warnings issued by PVO (Pinatubo Warnings issued by PVO (Pinatubo

Volcano Observatory) before the eruption Volcano Observatory) before the eruption succeeded in saving many lives and succeeded in saving many lives and property.property.

Civil Defense and local officialsCivil Defense and local officials Mount Pinatubo – followed a remarkable Mount Pinatubo – followed a remarkable

straight and rapid course toward eruption straight and rapid course toward eruption (gave fair warning, no false alarm)(gave fair warning, no false alarm)

PHILVOCSPHILVOCS USGSUSGS

WARNINGSWARNINGS

EVOLUTION OF EVOLUTION OF SMALL SMALL

CALDERA LAKECALDERA LAKE

BEFORE BEFORE

Pre-eruption Mount Pinatubo, April 16, 1991.

BEFORE BEFORE

Pre-eruption Mount Pinatubo, April 16, 1991.

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.

DURINGDURING

Summit caldera and lake, with partly submerged relics (rocky islets) of a dome that grew between July and October, 1992.

AFTERAFTER

BEFORE & AFTERBEFORE & AFTER

Mount Pinatubo, as seen from near the southwest end of the Clark Air Base runway

BEFORE & AFTERBEFORE & AFTER

O’Donnell River

BEFORE & AFTERBEFORE & AFTER

Sacobia Bamban River

BEFORE & AFTERBEFORE & AFTER

A house by the Sacobia-Bamban River, Bamban, Tarlac, July 23, 1991.

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

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.

BEFORE & AFTERBEFORE & AFTER

Muddy water at the mouth of the Bucao River, October 1, 1991.

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.

DURING & AFTERDURING & AFTER

Sacobia Bamban River

Bridge to Poonbato, Botolan, Zambales, across the Bucao River, May 28, 1991.

DURING & AFTERDURING & 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. Poonbato bridge was buried (but not swept away) by lahars of 1991 and

1992.

Thank You!Thank You!

http://pubs.usgs.gov/pinatubo/contents.html