A timeline of Mt. Pinatubo's 'big bangs' in 1991

By: Tricia Aquino, InterAksyon.com
June 9, 2016 3:06 PM

From Zambales, a view of Mount Pinatubo's mushroom cloud. Photo by Albert Garcia.

InterAksyon.com
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MANILA - Filipinos 25 years old and younger are all too familiar with disasters caused by tropical storms. But a quarter of a century ago, a calamity of a different kind brought horrors to the nation, and caused climates to cool all over the world. It changed parts of central Luzon's topography, buried entire villages, but thousands of lives were saved, thanks to timely alerts from government scientists led by Phivolcs. Mount Pinatubo erupted for several days in June 1991, blackening the morning skies in Zambales, Pampanga, and Tarlac.

Here is a timeline of events from an unforgettable catastrophe. Most of the photos were provided by photojournalists who chronicled and survived the eruption:

July 16, 1990, 4:26 p.m.

A 7.8-magnitude earthquake strikes Central and Northern Luzon, originating from the Digdig, Nueva Ecija part of the Philippine Fault. At 6:10 p.m., an aftershock strikes ten kilometers away from Pinatubo.

by Google Map

August 4, 1990

Sr. Emma Fondevilla, a nun working with Aetas living near Pinatubo, tells the Philippine Institute for Volcanology and Seismology (Phivolcs) about a landslide and black and grey smoke coming from a fissure on the northwest slope of Pinatubo.

August 5, 1990

Phivolcs director Dr. Raymundo Punongbayan sends a team to inspect the mountain from a helicopter. Their videotape reveals heavy, continuous steaming from Pinatubo.

Raymundo Santiago Punongbayan, a geologist, was Phivolcs director during the Pinatubo eruption. His correct predictions led to timely evacuations near and around the volcano, and saved tens of thousands of lives. Photo from the blog of his son, Stauro Punongbayan, https://thegloriousfaithfuljourney.wordpress.com/.

April 2, 1991

Phivolcs installs earthquake monitoring devices on Pinatubo, and sees that it releases more steam. Punongbayan orders surveillance.

April 10, 1991

Sulfurous fumes from the volcano kill one and send others to the hospital.

April 26, 1991

Phivolcs teams up with the United States Geological Survey (USGS), led by Dr. Chris Newhall, Punongbayan's friend. They set up the Pinatubo Volcano Observatory in Clark Air Base, Pampanga; and seven seismometers (record vibrations) and two tilt meters (measure ground swelling to see whether the volcano is bulging and ready to explode) around Pinatubo.

Later on, they conclude that Pinatubo is preparing to erupt in a "Plinian" manner -- messy, explosive, and with many pyroclastic flows. Newhall defines the latter as "hot fragments that roll down the volcano's flanks in enormous clouds... so dense they wipe out everything in their path."

May 13, 1991

Phivolcs issues a five-level Volcano Warning System, as well as a Pyroclastic-Flow Hazard Map to show where the expected path of the pyroclastic flows would be.

May 27, 1991

Phivolcs issues posters and brochures to the public about what to do during an eruption. Scientists also go to schools to educate them. Copies are made of a Betamax tape showing "shocking" video by volcanologist Maurice Kraff of lahar, pyroclastic flows, and volcanic landslides from eruptions around the world.

June 7, 1991

The Poonbato Phivolcs monitoring station in Botolan, Zambales reports volcanic quakes, indicating that "hot rocks (are) being pushed upward, and that the volcanic materials (are) almost reaching the surface," signaling a "major eruption."

June 9, 1991, 2:55 p.m.

Pinatubo erupts, "spewing lava fragments, boiling mud, hot rocks, and gases which streamed down the slopes of the volcano and immediately filled the air with voluminous dark grayish ash clouds." The eruption is punctuated by "two thunderous explosions."

The USGS-Phivolcs team raises the alert level to 5, "Eruption in progress." Aetas are evacuated from the volcano's surroundings.

Aetas being evacuated. Photo by Nick Sagmit

June 10, 1991

Clark officials go on FEN-TV to announce that an evacuation will begin at 6 a.m. By 12 p.m., Clark is empty for "the first time in its 90-year history."

In the "American exodus," 15,000 Air Force evacuees from Clark leave for the Subic Bay Naval Station and the Cubi Point Naval Air Station. "In anticipation of heavy ash fall, all Clark aircraft (are) flown to Cubi Point."

As thousands of Americans sleep on cardboard beds that night, Filipino residents around Clark are puzzled about the Americans' departure.

June 11, 1991

A lava dome appears near Pinatubo's summit, meaning "magma (is) pushing up the surface of the earth with lots of harmonic tremors and that the volcano (is) already preparing for the 'big bang,'" Punongbayan explains.

June 12, 1991, 5:15 a.m.

The first big bang occurs for 15 minutes, "sending voluminous ash clouds four kilometers above the vent before drifting toward the northwestern slopes."

At 8:15 a.m., the most powerful big blast occurs, "accompanied by rumbling sounds as the volcano (throws) a grayish-colored ash column more than 20 kilometers upward before it (drifts) southward toward San Marcelino in Zambales."

At 11:49 a.m., the third big blast occurs, with another ash column "hurled five kilometers upward together with hot pyroclastic materials."

Pinatubo produces "a billowing gigantic column of ash and steam that (shoots) up to the blue sky at an astonishing speed of 1,300 feet per second," then spreads out to form a mushroom cloud, like a nuclear explosion. Pyroclastic flows speed toward the Maraunot River. Huge pumice stones and ash are hurled toward the South China Sea.

"Day (turns) into night as heavy ash clouds and sand (block) the sunlight and (hover) over many towns." Zambales towns experience total darkness.

Ash engulfs Olongapo City. Photo by Albert Garcia.

"The sight (is) scary enough to cause pandemonium. Church bells (peal), passenger jeepneys (speed) away without stopping for passengers, and women (run) in the streets weeping and calling their children's names."

President Cory Aquino oversees relief operations and orders P73 million for this purpose.

At 10:52 p.m., the volcano erupts again.

June 13, 1991

At 8:41 a.m., another ash cloud shoots up from Pinatubo. In Manila, the Airline Operators Council orders planes to stay clear of the volcano by at least 50 nautical miles.

Residents flee Zambales. Photo by Albert Garcia.

June 14, 1991

Typhoon Diding heads to Pinatubo. At 1:09 p.m., another eruption occurs, the first of 13 "explosive eruptions over the next 24 hours."

Mixed with ash, the rain becomes milky in color.

Ash falls from the sky in Zambales. Photo by Albert Garcia.

June 15, 1991

65,000 people, mostly Aetas, are in evacuation camps outside Clark. At 5:55 a.m., the volcano explodes in "the Big One." Its Plinian eruption begins.

"Clouds of steam, gas, and rock particles (burst) horizontally from the vent and (merge) with the main cloud from the crater to form one sprawling giant column." Diding carries the ash to Pampanga, the South China Sea, and Subic. The seismometers are gone, and wet ash fall causes Phivolcs' equipment to malfunction.

Pinatubo erupts continuously, raining "tons and tons of ash and rock fragments all over Pampanga, Zambales, Bataan, and Tarlac."

"From afar it (looks) like a dark curtain being pulled down from the sky to the ground, completely blocking out the sun and plunging the provinces in a total blackout."

"At 1:42 p.m., Pinatubo (gives) one colossal blast, which (reaches) a mind-blowing height of 35 kilometers -- higher than jet airplanes could fly, higher even than the ozone layer in the upper stratosphere."

By 2 p.m., Diding approaches Pinatubo, "scattering ash and pumice like a huge industrial fan hitting a tall wedding cake and splattering it across the room."

By 3 p.m., pumice sand and pebbles pelt down continuously, as well as the wet ash.

"Soon an eerie silence (takes) over -- the result of sand saturating the earth, or the ash fall being so thick even soundwaves (cannot) penetrate it."

At 3:39 p.m., earthquakes begin, continuing until late in the evening. Communications systems are disrupted even in Metro Manila. Over 200,000 people evacuate to safer locations, but are "slowed down by the typhoon's gale-force winds and blinding rain of mud, sand, and gravel. Roads (are) either blocked by fallen trees or narrowed by the steady stream of refugees on both sides, going in opposite directions."

Zambales residents begin the slow journey to safety. Photo by Albert Garcia.

Roofs cave in. 30 evacuees are killed when the roof of a bus terminal in Angeles City falls on them, and five more die in a barangay chapel in Dau for the same reason. 166 buildings in Subic are damaged.

"The sounds were overwhelming with the clatter of the pumice hitting the metal roof and cars and thunder going on above us. One of the most frightening things was this low roar in the background that... probably was a lahar going down a nearby river valley," USGS volcanologist Jim Mori says.

Lahars, boulders, and logs flow into river channels. Bridges fall.

By 10:30 p.m., the eruption finally ends. Pinatubo's peak is reduced from 5,725 feet to 4,872 feet, leaving a 2.5-kilometer caldera in its wake -- "a huge gaping hole where the mountain used to be."

Pinatubo has "released hundreds of times more energy than the largest thermonuclear weapon ever tested, which was equivalent to the energy of 58 megatons (million tons) of TNT, over a million times more the energy than the atomic bomb that leveled Hiroshima."

June 16, 1991

17,300 "dependents of U.S. Air Force and U.S. Navy servicemen" begin sailing on 21 warships from Subic to Cebu, where they transfer to flights to Guam, and then to mainland United States.