Wednesday, March 16, 2011

Mount Pinatubo Eruption

In June 1991, the second largest volcanic eruption of the twentieth century* took place on the island of Luzon in the Philippines, a mere 90 kilometers (55 miles) northwest of the capital city Manila. Up to 800 people were killed and 100,000 became homeless following the Mount Pinatubo eruption, which climaxed with nine hours of eruption on June 15, 1991. On June 15, millions of tons of sulfur dioxide were discharged into the atmosphere, resulting in a decrease in the temperature worldwide over the next few years.

Mount Pinatubo is part of a chain of composite volcanoes along the Luzon arc on the west coast of the island (area map). The arc of volcanoes is due to the subduction of the Manila trench to the west. The volcano experienced major eruptions approximately 500, 3000, and 5500 years ago.

The events of the 1991 Mount Pinatubo eruption began in July 1990, when a magnitude 7.8 earthquake occurred 100 kilometers (62 miles) northeast of the Pinatubo region, determined to be a result of the reawakening of Mount Pinatubo.

In mid-March 1991, villagers around Mount Pinatubo began feeling earthquakes and vulcanologists began to study the mountain. (Approximately 30,000 people lived on the flanks of the volcano prior to the disaster.) On April 2, small explosions from vents dusted local villages with ash. The first evacuations of 5,000 people were ordered later that month.

Earthquakes and explosions continued. On June 5, a Level 3 alert was issued for two weeks due to the possibility of a major eruption. The extrusion of a lava dome on June 7 led to the issuance of a Level 5 alert on June 9, indicating an eruption in progress. An evacuation area 20 kilometers (12.4 miles) away from the volcano was established and 25,000 people were evacuated.

The following day (June 10), Clark Air Base, a U.S. military installation near the volcano, was evacuated. The 18,000 personnel and their families were transported to Subic Bay Naval Station and most were returned to the United States. On June 12, the danger radius was extended to 30 kilometers (18.6 miles) from the volcano resulting in the total evacuation of 58,000 people.

On June 15, the eruption of Mount Pinatubo began at 1:42 p.m. local time. The eruption lasted for nine hours and caused numerous large earthquakes due to the collapse of the summit of Mount Pinatubo and the creation of a caldera. The caldera reduced the peak from 1745 meters (5725 feet) to 1485 meters (4872 feet) high is 2.5 kilometers (1.5 miles) in diameter.

Unfortunately, at the time of the eruption Tropical Storm Yunya was passing 75 km (47 miles) to the northeast of Mount Pinatubo, causing a large amount of rainfall in the region. The ash that was ejected from the volcano mixed with the water vapor in the air to cause a rainfall of tephra that fell across almost the entire island of Luzon. The greatest thickness of ash deposited 33 centimeters (13 inches) approximately 10.5 km (6.5 mi) southwest of the volcano. There was 10 cm of ash covering an area of 2000 square kilometers (772 square miles). Most of the 200 to 800 people (accounts vary) who died during the eruption died due to the weight of the ash collapsing roofs and killing to occupants. Had Tropical Storm Yunya not been nearby, the death toll from the volcano would have been much lower.

In addition to the ash, Mount Pinatubo ejected between 15 and 30 million tons of sulfur dioxide gas. Sulfur dioxide in the atmosphere mixes with water and oxygen in the atmosphere to become sulfuric acid, which in turn triggers ozone depletion. Over 90% of the material released from the volcano was ejected during the nine hour eruption of June 15.

The eruption plume of Mount Pinatubo's various gases and ash reached high into the atmosphere within two hours of the eruption, attaining an altitude of 34 km (21 miles) high and over 400 km (250 miles) wide. This eruption was the largest disturbance of the stratosphere since the eruption of Krakatau in 1883 (but ten times larger than Mount St. Helens in 1980). The aerosol cloud spread around the earth in two weeks and covered the planet within a year. During 1992 and 1993, the Ozone hole over Antarctica reached an unprecedented size.

The cloud over the earth reduced global temperatures. In 1992 and 1993, the average temperature in the Northern Hemisphere was reduced 0.5 to 0.6°C and the entire planet was cooled 0.4 to 0.5°C. The maximum reduction in global temperature occurred in August 1992 with a reduction of 0.73°C. The eruption is believed to have influenced such events as 1993 floods along the Mississippi river and the drought in the Sahel region of Africa. The United States experienced its third coldest and third wettest summer in 77 years during 1992.

Overall, the cooling effects of the Mount Pinatubo eruption were greater than those of the El NiƱo that was taking place at the time or of the greenhouse gas warming of the planet. Remarkable sunrises and sunsets were visible around the globe in the years following the Mount Pinatubo eruption.

The human impacts of the disaster are staggering. In addition to the up to 800 people who lost their lives, there was almost one half of a billion dollars in property and economic damage. The economy of central Luzon was horribly disrupted. In 1991, the volcano destroyed 4,979 homes and damaged another 70,257. The following year 3,281 homes were destroyed and 3,137 were damaged. Damage following the Mount Pinatubo eruption was usually caused by lahars - rain-induced torrents of volcanic debris that killed people and animals and buried homes in the months after the eruption. Additionally, another Mount Pinatubo eruption in August 1992 killed 72 people.

The United States military never returned to Clark Air Base, turning over the damaged base to the Philippine government on November 26, 1991. Today, the region continues to rebuild and recover from the disaster.

Article: Volcanoes. (volcanologists are scientists who study how forces and materials inside the earth cause volcanoes to erupt)

Article: Volcanoes. (volcanologists are scientists who study how forces and materials inside the earth cause volcanoes to erupt)

You are walking along a mountain path. Suddenly the ground rumblets. Stream and hot ash rise from the mountain top. Red hot lava pours out. It's a volcano! Is this a scene from a dinosaur movie? No, it is just another work day for a volcanologist, or volcano scientist.

Earth's Layers

All the rumbling and shaking you feel are part of an eruption. What causes them? Until 30 years ago, no one really knew. Since then scientist have discovered that the Earth's surface, or crust, is broken into huge plates of solid rock. The plates move like giant icebergs over a layer of hot, gooey rock called the mantle. In some places, the plates pull away from each other. In others, the plates crash together. This movement makes cracks in the crust that let melter rock called magma rise up from the center of the Earth's super-hot core.

Inside a Volcano

Scientist have a name for each part of a volcano. The pool of melted rock below the ground is called the magma chamber. The magma rises up through vents to the surface. Once it is above ground, magma is called lava. Then it flows over the sides, or flanks, of a volcano. If an explosion blows the top off the mountain, the hole that is left is called a crater.

Volcano Power

Volcanoes can be very destructive. Besides lava, volcanoes can throw out rocks and boulders, ash, poisonous fumes, and smoke. Heat from a volcano can melt ice and snow and cause huge mud slides and floods. The force from an eruption can knock down everything for many miles.

Volcanoes also help the Earth. Soil that forms from volcanic ash is very good for growing things. Volcanoes can build new land, like the Hawaiian Islands. They also bring precious minerals to the surface where they can be more easily mined. In places like Iceland, they even provide a source of heat and power for homes.

Volcano Know-How

Volcanologists continue to study volcanoes to learn more about predicting eruptions. This knowledge can save lives and protect property. The more we know about volcanoes, the better we can understand the powerful forces that shape our Earth.

Dear Subscriber,

The power and intensity of volcanoes hold a fascination for all ages. From its fiery eruptions to its molten lava flow, studying volcanoes helps us in our quest to understand what is happening inside of our Earth. This Volcanoes issue will help your students discover and learn more about this ancient and ever-present force of nature.

Sincerely, Claude, Mayberry, Publisher


Volcanic eruptions have been a source of wonderment and awe since the dawn of the human race. Civilizations all around the world have told volcano myths to explain the unimaginable power of these destructive mountains. The ancient Romans told of Vulcan, god of fire and metals, who housed his blacksmith shops beneath certain mountains. Smoke and fire flew from Vulcan's chimneys whenever he worked. The Hawaiians believed the hot-tempered goddess Pele was responsible for the formation of their islands. When Pele had frequent arguments with her sister, her foot stamping would cause earthquakes. She'd then use her magic digging stick to gouge out the volcanic craters from which the lava flowed.

Plate Tectonics

In fact, it has only been within the last 30 years that scientists have developed the theory of moving continents called plate tectonics. We now understand …

Volcanoes video

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