Draft volcano primer Mt Pinatubo and Taal volcanoes

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

Mt. PINATUBO ERUPTIONS June 1991

Prior to eruption

Fumaroles on flanks, April 1991

June 12 th, 1991 eruption

Giant pyroclastic flows, June 15 th 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 2 nd 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.