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Mt. Pinatubo Eruption
Mt. Pinatubo: An Observer's Log

MANILA, PHILIPPINES. March 16, 1990. A magnitude 7.8 earthquake strikes the island of Luzon. Its epicenter is 100 km (60 mi) northeast of Mount Pinatubo. This quake rivals the ferocity of the 1906 San Francisco earthquake in intensity and originates from violent movements of the Earth's crust below our island. On Mount Pinatubo there is a landslide, a few minor tremors, and, for a short time, steam emissions from old vents; but to most of us the mountain seems unchanged. "It has not erupted for 500 years. Why should it erupt now?" we ask, hopefully.

April 30, 1991
Molten rock is rising! Volcanologists announce that molten rock, more than 30 km (20 mi) underground, is rising to the surface of Mount Pinatubo. This is the cause behind the small earthquakes and powerful steam explosions we are feeling. Three new craters have been blasted onto the north flank of the volcano. Scientists are quite concerned. So are we.

May 31
Since April, thousands of small quakes have been reported coming from beneath Pinatubo, and tens of thousands of tons of harmful sulfur dioxide gas have been emitted. Drugstore owners are reporting an increase in the sale of nasal masks by those who seek safety and can afford them.

June 5
For some time now, scientists, from both the Philippine Institute of Volcanology and Seismology and the U.S. Geological Survey, have been warning of a possible, major eruption of Mount Pinatubo. The evacuation of communities and villages believed to be in harm's way is being carried out, in spite of protests by a handful of local farmers whose homes have been in their family's possession for many years.

June 11
Molten rock appears! The molten rock, called magma, has reached the surface of Mount Pinatubo. Fortunately, we've been told that most of the gas was lost as this batch of magma ascended, and it has merely oozed out to form a lava dome. Scientists liken the process to a bottle of carbonated soda gone flat, which, in this instance, is very good news. Meanwhile (as if we don't have enough to worry about!), meteorologists are asking islanders to watch out for a typhoon that they are tracking, that is moving towards the Philippines.

June 13
Yesterday, on our Independence Day, residents of the capital in Manila, at Subic Bay Naval Station, and Clark Air Force Base, and at assorted villages and communities in central Luzon, got an unexpected (and unwanted, I might add) fireworks display. Millions of cubic yards of magma, this time charged with gases, reached the surface of Mount Pinatubo and exploded, producing a major eruption on the part of the now-awake-and-kicking volcano. It was truly spectacular, but everyone hopes that this has appeased Vulcan, the Roman god of fire, and that Pinatubo will now go back to sleep. We are all singing our favorite lullabies!

MANILA, PHILIPPINES. June 17, 1991. What everyone dreaded has happened. Two days ago, June 15, Mount Pinatubo literally blew its stack! Additional supplies of highly-gas-charged magma reached the volcano's surface and burst into a series of cataclysmic eruptions. Many compared these eruptions to an atomic bomb explosion, and they feared the end of the world was at hand. Scientists estimate that one cubic mile of materials shot out of the volcano, a cloud of ash rose 35 km (22 mi) into the air, and rock debris has been falling up to 30 km (22 mi) from the peak! At the same time, typhoon-strength winds blew the ash in all directions. Ash and volcanic pumice, the size of teeny pebbles, created an eerie blanket all over the countryside, giving us an idea of what it must be like to live where it snows. Unfortunately, when the ash mixed with the typhoon's rain, it became so heavy that thousands of roofs collapsed.

Huge avalanches of the ash, pumice, and gas also shot down the mountain's slopes in, what the scientists call pyroclastic flows. They filled up deep valleys with deposits that one volcanologist estimated to be 200 m (600km) deep! The eruptions removed so much magma and rock from below the volcano that some 150 meters (500 feet) of the peak collapsed into the vent! It is now a large, shallow, bowl-shaped caldera that is more than a mile-and-a-half wide!

Thanks to early warnings and evacuation efforts on the part of scientists and government officials, at least 5,000 lives have been spared in this disaster. Still, between 500 and 850 people died, and some 100,000 people have been left homeless. As it is, experts are saying that this is the century's largest volcanic eruption to affect a densely populated region anywhere in the world. A dubious honor, I'd say.

Review Questions

1) An earthquakes strikes the Phillipines, describe the conditions surround Mt. Pinatubo that might follow.

2) How does a volcanic eruption impact each of the four spheres?

3) What efforts were made by scientists to save lives prior to/during the Mt. Pinatubo eruption?


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