1. The Eruption of Mount Pinatubo June 15, 1991 Luzon, Philippines Jeng Funtanilla Nov. 16, 2005

2. Philippines LOCATION: Southeastern Asia, archipelago between the Philippine Sea and the South China Sea, east of Vietnam GEOGRAPHY: the Philippine archipelago is made up of 7,107 islands; favorably located in relation to many of Southeast Asia's main water bodies: the South China Sea, Philippine Sea, Sulu Sea, Celebes Sea, and Luzon Strait TERRAIN: mostly mountains with narrow to extensive coastal lowlands NATURAL HAZARDS: astride typhoon belt, usually affected by 15 and struck by five to six cyclonic storms per year; landslides; active volcanoes; destructive earthquakes; tsunamis http://www.cia.gov/cia/publications/factbook/geos/rp.html

3. Major Volcanoes in the Philippines http://vulcan.wr.usgs.gov/Volcanoes/Philippines/Maps/map_philippines_volcanoes.html

4. INTRODUCTION Before April 2, 1991, volcanologists knew Mount Pinatubo as an inconspicuous volcano, active within the past millennium, and the site of an aborted geothermal development. Before April 2, 1991, volcanologists knew Mount Pinatubo as an inconspicuous volcano, active within the past millennium, and the site of an aborted geothermal development. The Aetas, knew Mount Pinatubo as their home, their hunting ground, and their haven from an The mountain is the home of Apo Namalyari, the Great Protector and Provider. The Aetas, knew Mount Pinatubo as their home, their hunting ground, and their haven from an The mountain is the home of Apo Namalyari, the Great Protector and Provider. The people residing in the area, including those in nearby military bases (who received survival training from the Aetas) barely knew of Mount Pinatubo at all. The people residing in the area, including those in nearby military bases (who received survival training from the Aetas) barely knew of Mount Pinatubo at all. http://volcano.und.nodak.edu/vwdocs/volc_images/southeast_asia/philippines/pinatubo.html

5. MOUNT PINATUBO Stratovolcano: A volcano composed of both lava flows and pyroclastic material. Stratovolcano: A volcano composed of both lava flows and pyroclastic material. Location: 15.13N, 120.35E Location: 15.13N, 120.35E Elevation: Elevation: 5725 ft ( 1745 m) above sea level before the June 1991 eruption 5725 ft ( 1745 m) above sea level before the June 1991 eruption 5248 ft (1600 m) above sea level after the June 1991 eruption 5248 ft (1600 m) above sea level after the June 1991 eruption almost 500 ft (150 m) of the volcano was blasted away almost 500 ft (150 m) of the volcano was blasted away http://volcano.und.nodak.edu/vwdocs/volc_images/southeast_asia/philippines/pinatubo.html

6. GEOGRAPHIC FEATURES The location of Mount Pinatubo, within the Luzon volcanic arc

7. TECTONIC SETTING http://volcano.und.nodak.edu/vwdocs/volc_images/southeast_asia/philippines/tectonics.html The plate tectonics in the Philippines is complex and includes plate boundaries that are changing rapidly. Several micro- plates are getting squeezed between two convergent plate margins. Black triangles = active subduction zones with "teeth" on the over-riding plate, White triangles = inactive subduction zones with "teeth" on the over-riding plate, arrows = transform or major strike-slip faults, Red triangles = volcanoes active in the last 10,000 years.

8. TECTONIC SETTING In the west, more steeply east-dipping subduction of the Eurasian Plate (South China Sea basin and the transitional oceanic- continental crust of the Palawan block) along the 560 mile (900 km) length of the Manila and Sulu trenches produces a discontinuous line of active volcanoes from Taal in the south to Iraya in the north. Volcanism associated with this subduction zone began about 10 million years ago. http://volcano.und.nodak.edu/vwdocs/volc_images/southeast_asia/philippines/tectonics.html

9. TECTONIC SETTING In the east, shallow west-dipping subduction of the Philippine Plate at the Philippine Trench produces a line of volcanoes from Balut in the south to Mayon in the north. http://volcano.und.nodak.edu/vwdocs/volc_images/southeast_asia/philippines/tectonics.html

10. HISTORY Stacked pyroclastic-flow and lahar deposits outside Clark Air Base, testimony to a long history of explosive eruptions.

11. Largest eruption in the history of the modern Pinatubo occurred over 35,000 years ago. Largest eruption in the history of the modern Pinatubo occurred over 35,000 years ago. Distributed over 325 ft (100 m) of pyroclastic flow material on all sides of the volcano. Distributed over 325 ft (100 m) of pyroclastic flow material on all sides of the volcano. Marked the birth of the modern volcano. Marked the birth of the modern volcano. http://volcano.und.nodak.edu/vwdocs/volc_images/southeast_asia/philippines/pinatubo.htmlHISTORY Ancient Mount Pinatubo Ancestral Pinatubo was an andesite and dacite stratovolcano whose center was in roughly the same location as the modern Pinatubo. Today, ancestral Pinatubo is exposed in relict walls of an old 3.5x4.5-km caldera Modern Mount Pinatubo Radiocarbon ages suggest that eruptions from the modern Pinatubo have been clustered in at least six and possibly as many as a dozen eruptive periods.

12. Radiocarbon ages of modern Pinatubo deposits, arranged in chronologic order (not necessarily in stratigraphic order). ERUPTIVE HISTORY

13. CHRONOLOGICAL ACCOUNT CHRONOLOGICAL ACCOUNT DESTRUCTIVE AGENTS DESTRUCTIVE AGENTS ASHFALL ASHFALL PYROCLASTIC FLOW PYROCLASTIC FLOW LAHAR LAHAR 1991 VOLCANIC ACTIVITIES http://park.org/Philippines/pinatubo/page4.html

14. CHRONOLOGICAL ACCOUNT DAY 1: Sunday, June 9, 1991 DAY 1: Sunday, June 9, 1991 6:00 AM Eight hours of ash-laden steam clouds ejection ushered. Followed by pyroclastic flows which flowed down Pinatubo’s gullies into the Maraunot and Moraza rivers. The pyroclastic flows reached some 4-5 kilometers from the center of activity. 3:15 PM Philvolcs issued Alert Level 5 at around 3:15 in the afternoon as intermittent occurrences of small pyroclastic flows persisted the whole morning.

15. DAY 4: Wednesday, June 12, 1991 DAY 4: Wednesday, June 12, 1991 DAY 5: Thursday, June 13, 1991 DAY 5: Thursday, June 13, 1991 CHRONOLOGICAL ACCOUNT 8:15 AM DAY 6: Friday, June 14, 1991 DAY 6: Friday, June 14, 1991 DAY 7: Saturday, June 15, 1991 DAY 7: Saturday, June 15, 1991

16. Aircraft hangars at Clark Air Base that collapsed under the weight of rain-saturated ash. (Photograph by E.W. Wolfe, June 29, 1991.) BEFORE & AFTER

17. Three cornerstones Three cornerstones Interpretation of the origin of the unrest Interpretation of the origin of the unrest Simple five-level warning/alert Simple five-level warning/alert Hazard map based on the “worst-case” prehistoric eruption. Hazard map based on the “worst-case” prehistoric eruption. Warnings were coupled with intensive educational campaign to ensure they are not only received but UNDERSTOOD. Warnings were coupled with intensive educational campaign to ensure they are not only received but UNDERSTOOD.WARNINGS

18. WARNINGS Five Level Alerts Five Level Alerts Alert LevelCriteriaInterpretation No alertBackground; quietNo eruption in foreseeable future. 1Low-level seismic, fumarolic, or other unrest. Magmatic, tectonic, or hydrothermaldisturbance; no eruption imminent. 2 Moderate level of seismic or other unrest with positive evidence for involvement of magma. Probable magmatic intrusion; could eventually lead to an eruption. 3 Relatively high unrest including numerous b-type earthquakes, accelerating ground deformation, increased vigor of fumaroles, gas emissions. New or renewed eruption possible, probably within days to weeks. 4 Intense unrest, including harmonic tremor and (or) many "long-period" (low-frequency) earthquakes and (or) dome growth and (or) small explosions. Magma close to or at the Earth's surface. Large explosive eruption likely, possible within hours to days. 5 Hazardous explosive eruption in progress, with pyroclastic flows and (or) eruption column rising at least 6 km above sea level. Large explosive eruption in progress. Hazards in valleys and downwind.

19. CREDITS: Warnings issued by PVO (Pinatubo Volcano Observatory) before the eruption succeeded in saving many lives and property. Warnings issued by PVO (Pinatubo Volcano Observatory) before the eruption succeeded in saving many lives and property. Civil Defense and local officials Civil Defense and local officials Mount Pinatubo – followed a remarkable straight and rapid course toward eruption (gave fair warning, no false alarm) Mount Pinatubo – followed a remarkable straight and rapid course toward eruption (gave fair warning, no false alarm) PHILVOCS PHILVOCS USGS USGSWARNINGS

20. EVOLUTION OF SMALL CALDERA LAKE

21. BEFORE Pre-eruption Mount Pinatubo, April 16, 1991.

22. BEFORE

23. Summit caldera, as seen August 1, 1991, from the northeast. The caldera formed by collapse during the June 15, 1991, climactic eruption. A small explosion had just occurred, forming the expanding ash cloud. Throughout the latter half of June and much of July, ash emission kept the caldera obscured; as continuous ash emission changed to intermittent explosions, the caldera became visible.DURING

24. Summit caldera and lake, with partly submerged relics (rocky islets) of a dome that grew between July and October, 1992.AFTER

25. BEFORE & AFTER Mount Pinatubo, as seen from near the southwest end of the Clark Air Base runway

26. BEFORE & AFTER O’Donnell River

27. BEFORE & AFTER Sacobia Bamban River

28. BEFORE & AFTER A house by the Sacobia-Bamban River, Bamban, Tarlac, July 23, 1991. Nearly 9 m of sediment were deposited during a single lahar event on August 15, 1991

29. Mouth of the Bucao River, April 16, 1991. White-sand beaches of Zambales Province, consisting of pumice and coralline debris, attracted many tourists. The ocean was clear blue; little sediment was carried by the Bucao River. BEFORE & AFTER Muddy water at the mouth of the Bucao River, October 1, 1991. Muddy water at the mouth of the Bucao River, October 1, 1991. Massive amounts of sediment were carried from Mount Pinatubo into the Bucao River valley; an unknown but relatively small percentage of that sediment is carried into the South China Sea.

30. DURING & AFTER Sacobia Bamban River

31. Bridge to Poonbato, Botolan, Zambales, across the Bucao River, May 28, 1991. DURING & AFTER Poonbato bridge was buried (but not swept away) by lahars of 1991 and 1992. Deposits are approximately 25 m thick. Barangay Poonbato (immediately to the right of the field of view) was buried. Poonbato bridge was buried (but not swept away) by lahars of 1991 and 1992.

32. Thank You! http://pubs.usgs.gov/pinatubo/contents.html