Volcanoes : Mt. Pinatubo

Question 1

Stratovolcano definition

Answer 1

A conical volcano built with many layers of ash and lava.

Question 2

Destructive ( convergent ) subduction boundary :

Answer 2

A plate boundary between an oceanic plate and a continental plate. The oceanic plate subducts under due to its higher density, and the plate melts into the magma. This results in magma being forced up to the surface through cracks and therefore forming volcanoes.

Question 3

VEI ( Volcanic Explosive Index ) definition

Answer 3

It measures how much volcanic material is ejected, the height of the material thrown into the atmosphere, and how long the eruptions last.

Question 4

Basic Information :

Answer 4

• Mt. Pinatubo is a volcano on an island found in the Philippines. It is formed at a destructive subduction boundary between the Eurasian and the Philippine plate.
• It erupted in 1991 with a VEI of 6. This made it the 2nd biggest eruption in the 20th century.
• It was by far the largest eruption to affect a densely populated area.

Question 5

Causes :

Answer 5

• Destructive subduction boundary. The Philippine plate subducting and sinking underneath the Eurasian plate, due to the convection currents in the mantle
• On July 16, 1990, a big earthquake ( magnitude of 7.8 ) struck roughly 100km northeast of Mr. Pinatubo. This caused a landslide, some local earthquakes, among other things. This also caused the tectonic plates underneath Mt. Pinatubo to shift, thereby leading to an eruption.

Question 6

Immediate consequences :

Answer 6

• Predictions at the start of the eruption led to the evacuation of 58,000 people from the surrounding areas - saving many lives.
• The arrival of typhoon Yunya at the same time added large amounts of rainwater which brought a lethal mix of ash and rain to towns and cities surrounding the volcano.
• It ejected roughly 10, 000, 000, o00 tonnes of magma
  20, 000, 000 tonnes of sulphur dioxide. The pyroclastic flow mixed with rain water ( typhoon Yunya ) causing lahars. This covered large areas of land and destroyed infrastructure. Surrounding areas were severely damaged by pyroclastic surges.
• 847 people died. 300 people died from the collapsing roofs. 100 people died from the lahars.

Question 7

Social consequences : Ash

Answer 7

• Ash falls settled on infrastructure and houses resulting in their collapse
• 1.2 million people became homeless. Those homeless had to move into shanty towns in Manila
• The damage to infrastructure cost the government millions in repair costs.
• People living in isolated areas were trapped, as roads were destroyed and no help could get to them.

Question 8

Social consequences : Hospitals

Answer 8

• Hospitals became overcrowded
• Overworked doctors, that could lead to inefficiency
• Medicine/other supplies being used up quickly, and more supplies could not get to them because roads were destroyed.
• Many people injured in the eruption couldn’t get sufficient aid

Question 9

Social consequences : Mudflows

Answer 9

• Mudflows led to severe erosion of soil and river banks.
• Increases risks of flooding, another natural disaster
• Water contamination, sewage systems

Question 10

Economic consequences : Farmland

Answer 10

• Farmland was destroyed
• Became unsuitable for growing crops for several years after.
• Affects food supply and government needs to import it + lowers economy
• People working in agriculture + food industry don’t have jobs

Question 11

Economic consequences : Businesses

Answer 11

• Businesses were destroyed
• 650,000 people lost their jobs as farmland and businesses were destroyed
• Impacts economy and lowers GDP
• Government has to provide infrastructure to support businesses and this also costs money
• Manila airport was closed. This was because flights were grounded because of ash clouds.
• Leads to a loss of income for flight companies.

Question 12

Environmental consequences :

Answer 12

• Lahars changed river systems for years after the eruption. This led to the damage of plant and animal life in rivers, and affected quality of water supplies.
• Global temperatures dropped - global cooling. Global temperatures dropped by about 0.5C during the years 1991 - 1993. In the months after the eruption, the ash and gases formed a global layer of sulphuric acid haze, covering the sun.
• The sulphuric acid haze further mixed with water vapour in the atmosphere to cause acid rain. The acid rain further damages marine life