Transcript Mount Pinatubo, Philippines, Asia June 12th

Mount Pinatubo, Philippines, Asia
June 12th-15th, 1991
WHAT WERE THE CAUSES, IMPACTS,
RESPONSES AND MANAGEMENT
TECHNIQUES?
Mount Pinatubo is
a Strato (or
composite cone)
volcano, located in
north-west
Philippines, Asia. It
is north-west of the
capital, Manila.
A series of events
led to the several
volcanic eruptions
between June 7th
and June 15th, 1991.
So what were these
events?
What, where and when?
What caused the eruptions?
 Mount Pinatubo was dormant for 500 years.
 On July 16, 1990 a magnitude 7.8 earthquake (roughly the size of the 1906




San Francisco earthquake) struck about 60 miles (100 kms.) northeast of
Mount Pinatubo on the island of Luzon in the Philippines.
This caused the shaking and squeezing of the Earth's crust beneath the
volcano.
“At Mount Pinatubo, scientists recorded a landslide, some local
earthquakes, and a short-lived increase in steam emissions from a preexisting geothermal area, but otherwise the volcano seemed to be
undisturbed.” (http://www.georesources.co.uk/pinatubo.htm)
In March and April 1991, magma started rising towards the surface from
more than 20 miles (32 kms.) beneath Pinatubo, triggering more small
earthquakes and causing powerful steam explosions that blasted three
craters on the north side of the volcano.
Thousands of small earthquakes occurred beneath Pinatubo throughout
April, May, and early June 1991, and many thousand tons of noxious
sulphur dioxide gas were also emitted by the volcano.
The eruptions
 On June 7th 1991, the first magma reached the surface of
Mount Pinatubo but because it had lost most of the gas
contained in it on the way to the surface, the magma merely
oozed out to form a lava dome.
 However, on June 12th, large amounts of gas-charged magma
reached the surface and exploded in the volcano's first
eruption.
 When even more highly gas charged magma reached
Pinatubo's surface on June 15th, the volcano exploded in a
massive eruption that ejected more than 5 cu. Kms of volcanic
material
 The June 15th eruption is recognised as the largest volcanic
eruption in 80 years, the second-largest volcanic eruption of
this century. It is by far the largest eruption to affect a densely
populated area.
What were the primary impacts?
 The ash cloud from this huge eruption rose 22 miles (35
kms.) into the air.
 At lower altitudes, the ash was blown in all directions by the
intense cyclonic winds of a coincidentally occurring
typhoon, and winds at higher altitudes blew the ash southwestward.
 Fine ash fell as far away as the Indian Ocean, and satellites
tracked the ash cloud several times around the globe.
 Huge Pyroclastic flows (avalanches of red hot ash, gas, and
pumice fragments) roared down the sides of Mount
Pinatubo, filling the deep valleys with fresh volcanic
deposits as much as 660 ft (200 m) thick.
What were the secondary impacts?
 Social:
 300 people killed.
 About 75,000 people were evacuated.
 About 20,000 indigenous Aeta highlanders, who had lived on
the slopes of the volcano, were completely displaced, and as
late as 2005 most still waited in resettlement camps for the
day when they could return home.
 The eruptions have dramatically changed the face of central
Luzon, home to about 3 million people.
What were the secondary impacts?
 Economic:




Although much equipment was successfully protected, buildings on
two U.S. military bases in the Philippines--Clark Air Base and Subic
Bay Naval Station--were heavily damaged by ash.
A number of jets flying far to the west of the Philippines encountered
ash and sustained about $100 million in damage.
Ash fall also inundated the two largest U.S. military bases in the
Philippines. On Clark Air Force Base, which was home to more than
15,000 American servicemen and dependents, many buildings
collapsed under the weight of rain-saturated ash. Facilities at the
U.S. Naval Station at Subic Bay, 25 miles from Pinatubo, were also
severely damaged.
The drifting ash cloud from the June 15, 1991, eruption of Mount
Pinatubo damaged more than 20 passenger jetliners (including those
of American air carriers), most of which were flying more than 600
miles from the volcano.
What were the secondary impacts?
 Environmental:
 A blanket of volcanic ash and larger pumice lapilli (frothy
pebbles) blanketed the countryside.
 The eruption removed so much magma and rock from below
the volcano that the summit collapsed to form a large volcanic
caldera (depression) 1.6 miles (2.5 kms.) across.
 Nearly 20 million tons of sulphur dioxide were injected into
the stratosphere and the spread of this gas cloud around the
world caused global temperatures to drop temporarily (19911993) by about 0.5°C.
 “Much weaker but still spectacular eruptions of ash occurred
occasionally through early September 1991. From July to
October 1992, a lava dome was built in the new caldera as fresh
magma rose from deep beneath Pinatubo.”
(http://pubs.usgs.gov/fs/1997/fs113-97/)
That are continuous hazards?
 Even after more than 5 years, hazardous effects from the
June 15,1991 eruption continued.
 The thick pyroclastic-flow deposits from the eruption
insulated themselves and have kept much of their heat.
 These deposits still had temperatures as high as 900°F
(500°C) in 1996 and may retain heat for decades.
 When water from streams or underground seepage comes
in contact with these hot deposits, they explode,
spreading fine ash downwind.
 Since the eruption, ash deposits have also been
remobilized by monsoon and typhoon rains to form giant
mudflows of volcanic materials (lahars).
What were the responses from volcanologists and
seismologists?
 Fortunately, scientists from the Philippine Institute
of Volcanology and Seismology and the U.S.
Geological Survey had forecast Pinatubo's 1991
climactic eruption, resulting in an alert for
evacuation.
 This saved at least 75,000 lives and at least $250
million in property through evacuation up to a
radius of 30km.
 Commercial aircraft were warned about the hazard
of the ash cloud from the June 15 eruption, and most
avoided it. This saved hundreds of millions of dollars
in military aircraft and hardware.
Immediate/ short-term responses
 200,000 people relocated to safer areas
 Manila airport closed.
 Temporary shelters set up by the government for
those who had been displaced.
 Evacuation camps built for refugees.
 Red Cross, Action Aid and Oxfam provided food and
blankets in evacuation camps.
 23 USGS (U.S. Geological Survey) helped advise the
community and government officials for 8 weeks.
Long-term responses and hazard management
 President Ramos created the Mount Pinatubo




commission to raise 10 billion Philippine Peso.
Long and short term aid organized especially from
the Red Cross and the United States, with Norway
and UK sending millions in aid.
Overseas Philippino workers provided clothes for
victims.
New houses have been built on stilts so that any
future lahars will not burry them.
Volcano continued to be monitored and new
technology was used such as lahar detectors
Was the management successful?
 Due to the careful monitoring of the volcano once strange activity
began to occur, the eruptions were predicted, saving thousands of
lives.
 However, some people argue that the relatively low-impact eruption
was due to the timing of the events that occurred:

http://www.livescience.com/14603-pinatubo-eruption-20-anniversary.html
(the aftermath)
 Additionally:
 About 20,000 Aeta highlanders, who had lived on the slopes of the
volcano, were completely displaced, and as late as 2005 most still
waited in resettlement camps for the day when they could return
home.
 About 200,000 other people who evacuated from the lowlands
surrounding Pinatubo before and during the eruptions have
returned home but face continuing threats from lahars (mudflows)
that have already buried numerous towns, villages and fields.