Transcript Mt. Pinatubo - GEOCITIES.ws

The
Eruption
of
Mount
Pinatubo
June 15, 1991
Luzon, Philippines
Jeng Funtanilla
Nov. 16, 2005
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
Major Volcanoes in the
Philippines
http://vulcan.wr.usgs.gov/Volcanoes/Philippines/Maps/map_philippines_volcanoes.html
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/southeast_asia/philippines/pinatubo.html
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/southeast_asia/philippines/pinatubo.html
GEOGRAPHIC FEATURES
The location of Mount Pinatubo, within the Luzon volcanic arc
TECTONIC
SETTING




The plate tectonics in the Philippines is
complex and includes plate boundaries
that are changing rapidly. Several microplates 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/southeast_asia/philippines/tectonics.html
TECTONIC SETTING
In the west, more steeply
east-dipping subduction of
the Eurasian Plate (South
China Sea basin and the
transitional oceaniccontinental 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 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
HISTORY
Stacked pyroclastic-flow and lahar deposits outside Clark Air Base, testimony to a long history of
explosive eruptions.
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/southeast_asia/philippines/pinatubo.html
ERUPTIVE HISTORY
Radiocarbon ages of modern Pinatubo deposits, arranged in chronologic order
(not necessarily in stratigraphic order).
1991 VOLCANIC ACTIVITIES

CHRONOLOGICAL ACCOUNT

DESTRUCTIVE AGENTS

ASHFALL

PYROCLASTIC FLOW

LAHAR
http://park.org/Philippines/pinatubo/page4.html
CHRONOLOGICAL ACCOUNT

DAY 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.
CHRONOLOGICAL ACCOUNT

DAY 7:
4: Saturday,
5:
6:
Wednesday,
Thursday,
Friday,
June
June
June
June
14,15,
13,
1991
12,
1991
1991
1991
8:15 AM
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.)
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.
WARNINGS

Five Level Alerts
Alert Level
No alert
Criteria
Interpretation
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.
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

EVOLUTION OF
SMALL
CALDERA LAKE
BEFORE
Pre-eruption Mount Pinatubo, April 16, 1991.
BEFORE
Pre-eruption Mount Pinatubo, April 16, 1991.
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.
AFTER
Summit caldera and lake, with partly submerged relics (rocky islets) of a dome that grew between
July and October, 1992.
BEFORE & AFTER
Mount Pinatubo, as seen from near the southwest end of the Clark Air Base runway
BEFORE & AFTER
O’Donnell River
BEFORE & AFTER
Sacobia Bamban River
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.
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,
many of
tourists.
The ocean
clear 1,
blue;
little sediment was
Muddy
waterattracted
at the mouth
the Bucao
River, was
October
1991.
carried by the Bucao River.
DURING & AFTER
Sacobia Bamban River
DURING & AFTER
Poonbato bridge was buried (but not swept away) by lahars of 1991 and 1992.
Deposits are approximately 25 m thick. Barangay Poonbato
Bridge
Poonbato
to Poonbato,
bridge wasBotolan,
buried
Zambales,
not
across
away)
the
Bucao
lahars
River,
ofburied.
1991
Mayand
28, 1992.
1991.
(immediately
to the(but
right
ofswept
the
field
of by
view)
was
Thank You!
http://pubs.usgs.gov/pinatubo/contents.html