Draft volcano primer: Mt. Pinatubo and Taal volcanoes, the Philippines

Draft volcano primer:Mt. Pinatubo and Taal volcanoes,

the Philippines

Mt. PINATUBO ERUPTIONSJune 1991

Prior to eruption

Fumaroles on flanks, April 1991

June 12th, 1991 eruption

Giant pyroclastic flows, June 15th 1991form off of collapsing eruption column

The view from space via theJapanese 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 onNW. flank, November 1999

Erosion of river valley on thenorthern flank, Nov. 1999

Sediment fills valley floor downslope on lower E. flank November 1999

Detail of lahar-filled valleyE. flank, Nov. 1999

GROUND PHOTOS

Exploring eroded valley, SW flankNov. 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 westernfan. Summit of Mt. Pinatubo in background

“LAHARS” (MUDFLOWS) AND

THE RESULTANT DAMAGE

Major changes in valley floor elevation aftersingle lahar has formed after typhoon.

The impact on villages within the path of a lahar can be extreme

While old houses are buried, new homesare built on stilts to try to avoid the next lahar

An old church has been partially-buried sothat you now enter on the 2nd floor. RonnieTorres shows the church prior to the lahars.

Giant dikes made from old lahar and covered withconcrete now try to protect areas from new lahars

The contrast between areas protected by thedikes and unprotected is striking -- and it’s

all an issue of insurance for redevelopment!

Some homes, once buried by lahar, andnow being exposed by recent erosion

REMOTE SENSINGDATA

Landsat 7Path 116Row 50

RADARSAT radar backscatter imageof Mt. Pinatubo, February 1998

SPOT image of Mt. Pinatubo December 1991

Comparison of NW Summitfrom SPOT dataobtained between1991 and 1998

Red showsvegetation,the ash depositsare light blue

Summit is atlower right

Changes in Mt. Pinatubo lahar deposits.

Lower Pasig-Potrero River 1991 - 1996

TAAL VOLCANO(just south of Manila)

RADARSATscansar beam 1(50 m/pixel)image of TaalVolcano andsurroundingarea

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 viewof recently activevent on VolcanoIsland, in themiddle of Taal Volcano

Even around the rim of Lake Taal, people

and their fish farms are at risk from tsunamis generated by eruptions.