Mount Pinatubo, located in the Philippines, erupted in 1991 after a period of increased seismic activity. The eruption ejected ash up to 34km into the atmosphere, covering over 125,000km2 in ash and destroying 800km2 of agricultural land. Over 800,000 livestock were killed and 1.2 million people lost their homes. Pyroclastic flows and lahars (volcanic mudflows) caused additional damage. International aid and relocation efforts helped respond to the eruption, but lahars continued to impact the area for years. The hazard is now managed through monitoring, hazard maps, and building designs to mitigate future lahar impacts.

1. slidesharCase Study: Mount Pinatubo - 1991
Where did it happen?Mount Pinatubo is a stratovolcano found in the north
east Philippines. It formed where the Eurasian plate is being subducted beneath
the Philippine plate. It last erupted in 1993.
What happened?
15th
March 1991 earthquakes felt by villagers on the north western side
of the volcano. Earthquakes of increasing intensity for the next 2
weeks.
2nd
April 1991 phreatic eruptions along a 1.5km fissure on the summit.
Small eruptions of volcanic ash over the next few weeks.
3rd
May first eruption of magma.
7th
June Large explosion generated an ash column 7km high.
12th
June more violent eruptions with small earthquakes producing ash columns 24km high.
15th
June ash was ejected 34km into the atmosphere. Pyroclastic flows travelled up to 16km
and the ash mixed with rain from typhoon Yunya creating lahars. The eruption lasted for 3
hours.
Primary effects Secondary effects
E
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v
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Ash cloud covered 125000km2
bringing darkness to central Luzon.
Volcanic ash smothered 80000
hectares of land.
150km2
of reforestation projects
destroyed.
Lahars caused severe erosion to
rivers.
Global cooling caused by the ash.
Temperatures dropped by 0.5°C.
Lahars continued to affect the area
for 6 years.
Acid rain due to the 22million tonnes
of SO2 erupted.
E
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800km2
agricultural land destroyed
and 800000livestock and poultry
killed costing 1.5 billion pesos.
Full economic recovery cost £10
billion.
S
o
c
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a
l
847 people killed by collapsing roofs
Ash and pumice destroyed 42000
homes
1.2 million people lost their homes
100 people killed by lahars
500 people died from diseases such
as measles in refugee camps
Many indigenous Aeta people had to
move into government organised
resettlement areas because their
homes were destroyed. This caused
the Aeta society to become
fragmented.

2. Immediate responses Long term responses
Manila airport closed
200000 people relocated
Red Cross, Action Aid and Oxfam
provided food and blankets in evacuation
camps
23 USGS personnel helped advise the
community and government officials for
8 weeks
President Ramos created the Mount
Pinatubo Commission to raise 10 billion
Filipino pesos in aid.
New houses have been built on stilts so
future lahars will not bury them.
Norway and UK government sent
millions in aid
Overseas Filipino Workers provided
clothing for victims
5 billion pesos spent on used to build
dykes for lahars (later washed away by
the lahars)
How was the hazard managed? The hazard was managed. There were lahar detecters in place and
hazard maps. The volcano was being monitored by scientists and evidence suggested that there was
going to be an eruption soon.