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Draft volcano primer:
Mt. Pinatubo and Taal volcanoes,
the Philippines
Mt. PINATUBO ERUPTIONS
June 1991
Prior to eruption
Fumaroles on flanks, April 1991
June 12th, 1991 eruption
Giant pyroclastic flows, June 15th 1991
form off of collapsing eruption column
The view from space via the
Japanese GMS-5 geostationary satellite
Early effects on the ground
Sediment-laden rivers
destroy roads & bridges
Major landscape changes: Pyroclastic flows
in-filled pre-existing river valleys (the peaks
in two views below are the same feature)
AIR PHOTOS
(recent views)
Summit caldera of Mt. Pinatubo, Nov. 1999.
The low-point in the rim is a future hazard
as the lake will eventually over-top here.
Typical view of eastern flank, Nov. 1999
Erosion of ignimbrite fan on
NW. flank, November 1999
Erosion of river valley on the
northern flank, Nov. 1999
Sediment fills valley floor downslope
on lower E. flank November 1999
Detail of lahar-filled valley
E. flank, Nov. 1999
GROUND PHOTOS
Exploring eroded valley, SW flank
Nov. 1999
Crossing the sediment-laden streams is a
real challenge! So much sediment is in these
streams that they easily knock you over.
Valley erosion can be extreme in places: Up to 20 m down-cutting
during one typhoon! This mosaic shows the remains of the 1991
deposit (white unit) that has been cut by younger flash floods
Erosion of 1991 deposit
Vegetation is starting to grow back on western
fan. Summit of Mt. Pinatubo in background
“LAHARS” (MUDFLOWS)
AND
THE RESULTANT DAMAGE
Major changes in valley floor elevation after
single lahar has formed after typhoon.
The impact on villages within the path of a lahar can be extreme
While old houses are buried, new homes
are built on stilts to try to avoid the next lahar
An old church has been partially-buried so
that you now enter on the 2nd floor. Ronnie
Torres shows the church prior to the lahars.
Giant dikes made from old lahar and covered with
concrete now try to protect areas from new lahars
The contrast between areas protected by the
dikes and unprotected is striking -- and it’s
all an issue of insurance for redevelopment!
Some homes, once buried by lahar, and
now being exposed by recent erosion
REMOTE SENSING
DATA
Landsat 7
Path 116
Row 50
RADARSAT radar backscatter image
of Mt. Pinatubo, February 1998
SPOT image of Mt. Pinatubo December 1991
Comparison of
NW Summit
from SPOT data
obtained between
1991 and 1998
Red shows
vegetation,
the ash deposits
are light blue
Summit is at
lower right
Changes in Mt. Pinatubo lahar deposits.
Lower Pasig-Potrero River 1991 - 1996
TAAL VOLCANO
(just south of Manila)
RADARSAT
scansar beam 1
(50 m/pixel)
image of Taal
Volcano and
surrounding
area
View of Lake Taal and Volcano
Island from north rim, Nov. 1999
NW corner of Lake Taal
Over 4,000 people live without permission
on the shores of Volcano Island
In the event of an eruption of Taal,
all the population would have to
leave Volcano Island via small boats
View of the volcanic lake in middle
of Volcano Island (middle of Lake Taal)
In Fall 1999, this vent on
Volcano Island was actively geysering.
Close-up view
of recently active
vent on Volcano
Island, in the
middle of
Taal Volcano
Even around the rim of Lake Taal, people
and their fish farms are at risk from
tsunamis generated by eruptions.