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Transcript
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.