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Transcript of Mount Pinatubo
Mount Pinatubo- Eruption 1991
Mount Pinatubo is located in the Philippines, Asia. The Philippines lie on a destructive plate margin where the Philippines plate is subducted by the Eurasian Plate. Through the process of subduction, the oceanic plate is converted into magma which eventually rises to the surface and forms a volcano.
Mount Pinatubo had been dormant for 500 years and had not erupted since 1380, people living in the area no longer considered the volcano to be a hazard. Ash and lava from previous eruptions had weathered and formed fertile soil, ideal for rice growing.
The first signs that the volcano was no longer dormant occurred on July 16, 1990 when a magnitude 7.8 earthquake struck 60 miles northeast of Mount Pinatubo on the Island of Luzon in the Philippines.
The earthquake caused shaking and squeezing of the Earth's crust beneath the volcano. Scientists recorded landslides, local earthquakes and an increase in steam emissions at Mount Pinatubo.
In March and April 1991, magma started rising towards the surface from more than 20 miles beneath Pinatubo. This caused thousands of small earthquakes beneath Pinatubo for about three months. The volcano released thousands of tons of noxious sulfur dioxide gas and dusted local villages with ash.
On June 7,1991 the formation of a lava dome occurred - magma reached the surface but because it had lost most of the gas, the magma only oozed out.
Due to its location on the Pacific Ring of Fire and close to the equator makes the Philippines prone to earthquakes and typhoons, It has a population of more than 98 million people and at the time of the 1991 eruption approximately 30,000 people lived on the flanks of Mount Pinatubo. Many people believed Mount Pinatubo did not pose a risk.
The first evacuation of 5,000 people was ordered in late April.
The first eruption
On June 12th, more gas charged magma reached the surface and erupted. The danger radius was extended to 30 kilometers resulting in the evacuation of 58,000 people.
The volcano ejected four vertical eruptions and thirteen smaller eruptions that caused pyroclastic flows. The flows filled the deep valleys with volcanic deposits, about 200m thick.
A blanket of volcanic ash and pumice pebbles covered the whole island of Luzon. Fine ash fell as far away as the Indian Ocean and satellites tracked the ash cloud around the globe.
On June 15, the major eruption of Mount Pinatubo began at 1:42pm. The eruption lasted for nine hours and cause many earthquakes due to the collapse of the summit of Mt. Pinatubo and the formation of a caldera about 1.6 miles across. The ash cloud from this eruption rose 22 miles into the air, the mix of ash and water vapor caused a heavy downfall of tephra.
Due to the volcano showing signs of erupting in early June 1991, it gave advanced warning to allow time for the evacuation of thousands of people. As well as the evacuation of 15,000 personnel from the American air base.
The ash destroyed all crops on adjacent farm land.
Buildings collapsed, including 200,000 homes, a local hospital and many factories.
Power supplies were down for three weeks.
Relief operations were slowed due to the destruction of roads and bridges.
Long Term Effects
The thick layers of ash, ruined the harvest of 1991 and 1992, over one million farm animals died through starvation. Thousands of farmers were forced to take refuge in large cities but with the vast majority taking refuge in shanty type houses.
Malaria, chicken pocks and diarrhoea were rapidly spread due to poor living conditions in the shanty housing, doctors had to treat hundreds of people for respiratory and stomach illnesses. The eruption and its after effects were blamed for about 700 deaths, however only 6 deaths were as a result of the original eruption.
Mount Pinatubo is a strato volcano. It is built up of layers of lava, tephra, pumice and volcanic ash. Strato volcanoes are associated with andesitic lava which means the lava is fairly viscous with temperatures of 750- 950°C. Mount Pinatubo is a VEI 6, classified as Plinian and described as a colossal eruption.
After the eruption and throughout 1993, typhoons occurred producing heavy rainfall and causing flooding and lahars- suffocation by lahars accounted for 70 deaths. The eruption is believed to be responsible for the 1993 floods along the Mississippi river as well as the drought in the Sahel region of Africa. The US experienced its third coldest and wettest summer in 77 years during 1992.
The United States Geological Service helped predict the eruption because of this 75,000 people were evacuated. Refugee camps for evacuees were set up as well as long and short term aid provided by The Red Cross.