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PHIVOLCS Website
LOCATION:
90 km NW of Manila, situated at the boundaries of ZAMBALES, PAMPANGA
and TARLAC in West Central Luzon (15.14°N - 120.35°'E)
PHYSICAL CHARACTERISTICS:
Height Before the 1991
Eruption: 1,745 m asl
Height After the 1991
Eruption: 1,445 m asl
Type of Volcano: Mainly lava domes and thick sequences of pyroclastic flows
Summit Caldera:
About 2 km dia. and 600 to 800 m deep; the crater lake was formed in
September 1991;
pH values of the lake water ranged from 6.0 to 1.9; pH became very
acidic
(1.9) during the
dome growth.
Composition of Lava:
Dacite with andesitic xenoliths. inclusions.
HISTORICAL ERUPTIONS:
No. of Recorded
Eruptions: 2 since 1380
Results of carbon dating indicate that the
latest eruption before
the June 1991 eruption
occurred 460 (+/- 30) years ago
First Sign of Unrest: Small
explosions on 02 April 1991 at about 4:00 PM formed NE
trending
steaming
vents at the NW upper slope. Several earthquakes with rumbling
sounds werre felt
at lower elevations of the volcano.
Dome Building:
a. June 7, 1991 - dome near the intersection of the
NW-SW trending fault on the
northern flank of the volcano, dimension: 100 m by 60 m and 30 m
high.
b. July to October 1992 - dimensions at its maximum growth: 350 m
N-S and
440 m E-W, 100 m above crater lake.
First Observed Major
Eruption: 12 June 1991 at 8:51 AM
Calderagenic Eruption:
14-16 June 1991, blew the top of Pinatubo and formed a summit
caldera.
This was characterized by violent explosions, continuous unloading
of earth materials,
subsidence and collapse.
Eruption Types:
Plinian - characterized by extremely violent and sustained ejection
of pyroclastics
(June 15, 1991 eruption) Dome formation (e.g. 1992 eruption)
Phenomena Associated
with Eruptions:
Airfall tephra (ash fall and pumice fall)
Pyroclastic flows
Dome building or dome growth
Associated Hazards:
Pyroclastic flows
Airfall Tephra
Earthquakes
Collapse or subsidence of volcanic edifice
Secondary explosions
Lahars and flooding/inundation
MONITORING TECHNIQUES:
Monitoring Methods:
A. Geophysical Method
Seismic monitoring - telemetered to Pinatubo Volcano Observatory in
Clark Airfield
and in PHIVOLCS, Quezon City
B. Geodetic Methods
Electronic Distance Measurement
C. Visual Observations
D. Geochemical methods
Gas chemistry - monitoring of sulfur dioxide emission using
Correlation Spectrometer
(COSPEC)
Crater lake chemistry - occasional sampling and analysis of water
from the crater lake
HAZARD ZONES:
10 km radius permanent danger zone (PDZ)
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