Contents

• Bibliography
• Introduction
• Where and What is Mt. Pinatubo?
• What caused the eruption of Mt. Pinatubo in 1991?
• What happened before and after the eruption of Mt. Pinatubo in 1991?
• What were the effects of the Mt. Pinatubo eruption?
• Conclusion

Bibliography

With special thanks to the sources stated below that made this website possible. The sources where reliable and helped me add further information than what is provided from the vast, highly unreliable internet.

BOOKS

• Volcano; written by Susanna Van Rose
• Volcano-Focus On Disasters; written by Fred Martin
• Natural Disasters; written by Andrew Langley

WEBSITES

• www.wikipedia.com
• www.google.com
• www.learner.org/exhibits/volcanoes
• www.calstata.edu

OTHER

• In the path of a killer volcano; Channel 4

Introduction

Mount Pinatubo is an active volcano on the Philippine island of Luzon. Until relatively recently it was classified as a dormant volcano as it had not erupted for five hundred years. It was partially eroded and covered with lush forest. However in June 1991 it erupted violently with huge effects on the Aeta (the people who inhabit the island of Luzon, who fled to the mountains when the Spanish invaded in 1565) and the whole world. The successful predictions of the eruptions avoided a huge death toll as tens of thousands of people were evacuated with swift accuracy. Unfortunately thousands of homes were destroyed by pyroclastic flows, ash deposits, and later lahars caused by rainwater remobilising earlier volcanic deposits.

Mt. Pinatubo erupting on 15th June 1991.

Where and what is Mt. Pinatubo?

Mt. Pinatubo is a part of a chain of composite volcanoes along the Luzon arc on the west coast of the Pilipino island of Luzon. It is one of the many volcanoes that make up the Ring of Fire (a belt of volcanoes that encircle the Pacific Ocean). It is 4,875ft or 1,486m. The volcano is situated only 55miles (90km) northwest of Manila, the Capital of Luzon.
"The arc of volcanoes is caused by the subduction of the Manila trench to the west." (Mt. Pinatubo Eruption 2001).

Until relatively recently it was believed to be a dormant volcano and had not erupted for 600 years. There had been no reason to question this statement until villagers noticed the first signs of volcanic activity, steam started exploding from the side of the mountain.

click on the images to enlarge

What caused the eruption of Mt. Pinatubo in 1991?

The relatively small Phillipine tectonic plate slowly moving west sliding underneath the larger Indo-Australian plate caused the Mount Pinatubo eruption of 1991. The plate rocks then melted to form magma and made its way to the surface through Mount Pinatubo and the other volcanoes in the famous ring of fire. This is bad news for the people of the Philippines who live on the island of Luzon as due to the nature of the cause of this huge devastating eruption, it looks likely that it will erupt again in the near future. However with careful monitoring, if the volcanic activity of Mt. Pinatubo does begin to rise more than normal no one will be killed or at least the death toll may be kept to the minimum by evacuation etc.

What happened before and after the eruption of Mt. Pinatubo in 1991?

On 2nd April the first signs of volcanic activity were seen from the volcano. There was a series if explosions that rocked the volcano and its near occupants. One Aeta said after once such eruption:
“There was a rumbling and I ran from the volcano I thought I was going to die!”

It was the first explosion recorded from Mt. Pinatubo. U.S. volcanologists began investigating the rumblings and steam eruptions 3weeks after that account. A volcanologist who wanted to remain anonymous said:
“It could be letting off steam and not going to erupt, or it could be under tectonic stress or it could be about to erupt due to a surge of magma.”

After some investigation the volcanic team agreed and declared a Level 2 and immediate evacuation began.

On 3rd June 20,000 Philippines were evacuated. Some of the people and equipment from the Clarke Airbase were flown off the island. What followed this evacuation was lots of pressure on the volcanologist team on whether they had got the decision right, if they had made the wrong call then thousands of dollars would be lost and people would have had to leave their homes disrupting their daily activities. In a documentary about the events leading up to the eruption Rick Hoblet spoke about how there had been no irregular activity from the volcano since the Level 2 had been declared.

They were discussing what to do and maybe to lower the level, as it seemed to be not as active as they thought. However once he left the meeting and looked at the seismometer the activity was huge. The activity kept rising on two of their investigative stations, UBO and PIE and it was decided that a Level 4 should be declared. This means an eruption could be probable within 24hrs therefore everyone within a 12mile radius of the volcano had to be evacuated. 120,000 people left their homes for temporary evacuation centres. General Williams Studer decided the airbase would not leave until the geologists said there was only six hours until an eruption.
On 8th June they looked at Pinatubo again. They observed a dome. One geologist, called Dave who saw it described it as follows:
“This dome is… like a slug of magma, cold, relatively cold magma, squirting out on the ground. This is a sign of a very explosive magma. The ash samples showed it was the same stuff, which had erupted out before, previously. At that time we became very concerned.”

June 10th General Studer had everyone evacuated leaving only 15,000 security officials behind. He said when questioned as to why:
“My objective has to be to get everyone to safety.”
Every hour that passed from the evacuation heightened tension on the PVO (Philippines Volcanology Organisation). They were risking a lot predicting a volcanic eruption and having so many people evacuated.

48hrs after Clarke Airbase was evacuated, Mt. Pinatubo erupted on 12th June the PVO team were ecstatic and awed by the eruption. They had got it right!
Dave said later:
“Fundamentally we knew it would explode but you start asking the ‘what ifs’. What if it takes a long time to do so.”
The city became covered in ash. Evacuations continued day and night. 48hrs after the explosions communities as far as 50miles away were showered in ash and sand. To make matters even worse a major typhoon hit the island 6hrs later.

On 15th June there were a series of minor eruptions that triggered the major huge explosion, sending ash 100ft in the air. It also exploded 20million tons of sulphur dioxide into the atmosphere. The 6am explosion was the 5th of the morning and started lightning. All personnel then abandoned the airbase. The volcanogists however stayed behind. There was no light as ash had blocked it out and it began raining rocks, pebbles, pumice, and mud.

The typhoon unfortunately spread fear and damage far into the evacuation zone. Towns 20miles away from Mt. Pinatubo were covered in ash and roofs collapsed due to the weight of rain soaked ash. Farms 50miles away from the origin of the explosion were damaged and covered in ash. 10,000 people suffered, 250,000 were displaced but less than 500 died. Weeks after 15th June it was still spewing out ash.

Mt. Pinatubo erupting on 15th June 1991.

Thanks to the prediction and investigation of the PVO many thousands of deaths were avoided.
It is now recognised as the biggest eruption of the last 80years. 5-8Km³ of ash was deposited. The eruption was 10times more powerful than St. Helens.

The eruption was later described by the Philippine Institute of Volcanology and Seismology as a Plinian eruption. A plinian eruption is an eruption of great violence recognized by large amounts of explosive ejections of pumice and pyroclastic flows. The copious extrusion of gas-rich silicious magma is commonly followed by the collapse of the top of the volcanic cone forming a caldera.

What were the effects of the Mt. Pinatubo eruption of 1991?

There were many short-term and long-term effects of the Mt. Pinatubo eruption on the 15th June 1991. Many of them may not have been as bad had a typhoon not have hit the island of Luzon.

SHORT-TERM EFFECTS

The most immediate effect of the eruption was the 10km stream of mud and lava that flowed down the slopes of the volcano at 80kmph killing anything in its path. It wrecked homes and crops in its way with ease. It would have killed much more maybe even thousands of people had the geologists not been so accurate with their predictions and evacuated thousands of people out of the danger zone.

Ash was thrown an enormous 35km or 22miles into the sky. This huge amount of ash blocked out the sun’s light. One of geologists investigating the volcanic activities leading up to the violent eruption on 15th June said:
“It was as if day had turned to night!”
Copious ash, pumice, and rocks rained on the surrounding cities injuring people and making breathing difficult for many people and giving them pneumonia. The Clarke Airbase (US air base) was destroyed by the weight of ash and was never rebuilt due to the effect it would have had on the financial state of the USA and because it was then seen as not necessary.
The Subic Bay naval base was covered in ash and pumice badly damaging it. One US Subic Bay naval base officer was heard to say,
“Our base is grey, the same colour as our ships.”
In panic some people died in car accidents trying to flee from the volcano.

The photo above shows the air bunkers at Clarke Airbase th their roofs collapsed due to the wieight of ash.

LONG-TERM EFFECTS

There were many long-term effects of the eruption, including the 250,000 people displaced after wet ash made their homes collapse or lahars swept away their home or acted as a concrete filling in the buildings. Millions of dollars were spent rebuilding the lost buildings. The Naval Base unlike the Clarke Airbase was considered too valuable to be left destroyed.

½ of livestock died in the months following the eruption and crops were highly less than the year previous due to flooding and ash deposits.

Disease became rife due to the homelessness killing many.

The massive amounts of sulphur that exploded high into the atmosphere were blown by winds around the whole globe. This gas filtered some of the Sun’s light and thus reduced the temperature of the world by 1ºC for five years. This may be good for the Earth for five years but after that geologists have said it will increase the average temperature all over the world due to global warming.

The image above shows a satellite image of the sulphur dioxide which was released from Mt. Pinatubo and then blown aroung the whole world by winds.

Some rivers were blocked with ash and pumice posits which meant any remaining rivers burst their banks whenever there was rain. This flooding is supposed to continue for decades.
Monsoon rains that fell after the eruption caused avalanches of volcanic debris killing many and destroying more houses. The typhoon destroyed even more buildings as it made the ash wet increasing its weight. It also caused many mudslides and lahars. As well as that it blew ash far into the evacuation zones and to Manila (capital of Luzon) making people with asthma have serious breathing difficulties.

Mt. Pinatubo still erupts today regularly however just with not as much force as on 15th June 1991.

To view the colclusion, click older posts below.