REDUCING THE RISK FROM VOLCANO HAZARDS

Benefits of Volcano Monitoring Far Outweigh

Costs —The Case of Mount Pinatubo

T

Villagers fleeing the vicinity of Mount Pinatubo, Philippines, during heavy ash fall from the volcano’s

cataclysmic June 15, 1991, eruption. Scientists from the Philippine Institute of Volcanology and Seismology

and the U.S. Geological Survey forecast this eruption, enabling people living near the volcano to evacuate to

safety. The timely forecasts of these scientists saved at least 5,000 lives and prevented property losses of at

least $250 million. (Photo by Philippe Bourseiller/Jacques Durieux.)

Scientists from the U.S.

Geological Survey and the

Philippine Institute of

Volcanology and

Seismology making

emergency repairs to

monitoring instruments on

Mount Pinatubo,

Philippines, with U.S. Air

Force helicopter support,

the day before the

volcano’s cataclysmic June

15, 1991, eruption. (Photo

by MSgt. Val Gempis, U.S.

Air Force.)

U.S. Department of the Interior

U.S. Geological Survey

On the morning of June 15, 1991, Mount

Pinatubo on the island of Luzon in the Philippines exploded in the largest volcanic eruption

on Earth in more than three-quarters of a century. The most powerful phase of this cataclysmic eruption lasted more than 10 hours, creating an enormous cloud of volcanic ash that rose

as high as 22 miles into the air and grew to more

than 300 miles across, turning day into night

over central Luzon. Falling ash blanketed an

area of thousands of square miles, and avalanches of hot ash (pyroclastic flows) roared

down the slopes of the volcano and filled deep

valleys with deposits of ash as much as 600

feet thick.

Before the cataclysmic eruption, about

1,000,000 people lived in the region around

Mount Pinatubo, including about 20,000 American military personnel and their dependents at

the two largest U.S. military bases in the Philippines—Clark Air Base and Subic Bay Naval

Station. The slopes of the volcano and the adjacent hills and valleys were home to thousands

of villagers. Despite the great number of people

at risk, there were few casualties in the June 15

eruption. This was not due to good luck but

rather was the result of intensive monitoring of

Mount Pinatubo by scientists with the Philippine Institute of Volcanology and Seismology

(PHIVOLCS) and the U.S. Geological Survey

(USGS).

The first recognized signs that Pinatubo

was reawakening after a 500-year slumber were

a series of small steam-blast explosions in early

April 1991. Scientists from PHIVOLCS immediately began on-site monitoring and soon declared a 10-kilometer- (6-mile-) radius danger

zone around the volcano. They were joined in

a few weeks by USGS scientists from the Volcano Disaster Assistance Program, a cooperative effort with the Office of Foreign Disaster

Assistance of the U.S. Agency for International

Development.

The USGS scientists brought with them

specially designed, portable instruments,

which the joint Philippine-American team

used to quickly set up monitoring networks

on and around Mount Pinatubo. The team

also conducted intensive studies of the

volcano’s past eruptive history. When the data

from these efforts indicated that a huge eruption of the volcano was imminent, the joint

team issued urgent warnings. These timely

forecasts enabled civil and military authorities to arrange the evacuation of people and

aircraft and other equipment to safe areas

before Mount Pinatubo exploded on June 15.

Lives and Property Saved

The USGS and PHIVOLCS estimate

that their forecasts saved at least 5,000 lives

and perhaps as many as 20,000. The people

living in the lowlands around Mount Pinatubo

were alerted to the impending eruption by the

forecasts, and many fled to towns at safer dishe climactic June 1991

eruption of Mount

Pinatubo, Philippines, was the

largest volcanic eruption in this

century to affect a heavily

populated area. Because it was

forecast by scientists from the

Philippine Institute of Volcanology and Seismology and the

U.S. Geological Survey, civil

and military leaders were able

to order massive evacuations

and take measures to protect

property before the eruption.

Thousands of lives were saved

and hundreds of millions of

dollars in property losses

averted. The savings in property alone were many times the

total costs of the forecasting

and evacuations.
For more information contact:

U.S. Geological Survey

Cascades Volcano Observatory

5400 MacArthur Blvd., Vancouver, WA 98661

Tel: (360) 696-7693, Fax: (360) 696-7866

http://volcanoes.usgs.gov/

See also Mobile Response Team Saves Lives in Volcano

Crises (USGS Fact Sheet 064-97)

U.S. Geological Survey Fact Sheet 115-97

1997

COOPERATING ORGANIZATIONS

Armed Forces of the Philippines

National Disaster Coordinating Council, Philippines

Philippine Institute of Volcanology and Seismology

U.S. Agency for International Development

United States Air Force

United States Navy

Chris Newhall, James W. Hendley II,

and Peter H. Stauffer

Graphic design by

 Susan Mayfield and Sara Boore

On June 15, 1991, Mount

Pinatubo in the

Philippines erupted

cataclysmically, raining

volcanic ash over an

area of thousands of

square miles and

sending high-speed

avalanches of hot ash

(pyroclastic flows) roaring

down the flanks of the

volcano. Falling ash

caused thousands of

roofs to collapse, clogged

stream channels, made

roads impassable, and created massive cleanup problems (photos). Before the

eruption more than 1,000,000 people lived within 30 miles of the volcano,

including about 20,000 American military personnel and their dependents.

Because forecasts of this powerful eruption by a joint team of U.S. Geological

Survey and Philippine scientists allowed timely evacuations, fewer than 300

people were killed. (U.S. bases have reverted to Philippine control since 1991.)

U.S. DEPARTMENT OF THE INTERIOR • U.S. GEOLOGICAL SURVEY

tances from the volcano or took shelter in

buildings with strong roofs. Additionally, more

than 15,000 American servicemen and their dependents were evacuated from Clark Air Base

prior to the June 15 eruption. In the eruption,

thousands of weaker roofs, including some on

Clark, collapsed under the weight of ash made

wet by heavy rains, yet only about 250 lowland

residents were killed. Of the 20,000 indigenous

Aeta highlanders who lived on the slopes of

Mount Pinatubo, all but about 20 were safely

evacuated before the eruption completely devastated their villages. Some might have left on

their own—troubled by the steam blasts and

earthquakes that preceded the eruption—but

most would have remained had it not been for

the forecasts and government-led evacuations.

In addition to the many lives saved, property worth hundreds of millions of dollars was

protected from damage or destruction in the

eruption. When aircraft and other equipment at

the U.S. bases were flown to safe areas or covered, losses of at least $200 to 275 million were

averted. Philippine and other commercial airlines prevented at least another $50 to 100

million in damage to aircraft by taking similar actions. By heeding warnings of hazardous volcanic ash clouds from Pinatubo, commercial and military pilots avoided severe

damage to their aircraft and potentially saved

hundreds of lives. Other commercial savings

are harder to quantify but were probably less

than $100 million, and there is no way to estimate the sentimental or monetary value of

the personal property saved by families.

Cost of Forecasting and Evacuations

PHIVOLCS and USGS scientists spent

less than $1.5 million responding to Mount

Pinatubo's reawakening and forecasting its June

15, 1991, eruption, including salaries, helicopter and other logistical support, and the replacement of equipment destroyed by the eruption.

Their forecasts were made possible by previous work in the area by PHIVOLCS and by the

USGS’ mobile monitoring capability, also available to respond to volcano crises in the United

States. The costs of these earlier efforts can be

roughly estimated at $15 million (10 percent

of the combined 1980–90 volcano hazards budgets of PHIVOLCS and the USGS). Additionally, the Philippine and U.S. Governments and

nongovernmental organizations together spent

about $40 million to evacuate, house, and feed

local residents and American military personnel and their dependents.

Were These Efforts a Good Investment?

The monitoring of Mount Pinatubo in

1991 and the successful forecasting of its cataclysmic June 15 eruption prevented property

losses of at least $250 million (this figure is

intentionally conservative and should be considered a minimum value). No monetary value

has been placed on the more than 5,000 lives saved,

although other cost-benefit analyses have used

values from $100,000 to $1 million per life.

Even when the costs of developing the

portable monitoring capability and of the earlier studies of Mount Pinatubo are included, the

total costs of safeguarding lives and property

yyyy

San Fernando

Cabanatuan

Manila

0 10 MILES

0 10 KILOMETERS

Angeles

City

Tarlac

Olongapo

CLARK

AIR BASE

 (U.S.)

MOUNT

PINATUBO

MOUNT

 NATIB

MARIVELES

MOUNTAIN

BASA

AIR BASE

SUBIC BAY

NAVAL STATION (U.S.)

CUBI POINT

NAVAL AIR STATION (U.S.)

MANILA BAY

SUBIC BAY

S O U T H

C H I N A S E A

Pasig- Potrero River O'Donnell River

Marella River

Bamban River

SacobiaPampanga River

Pampanga River

PHILIPPINES

Extent of

ash cloud

from the

June 15,

1991

eruption

MOUNT PINATUBO

Manila

Pyroclastic flows

from the volcano’s June 15, 1991, eruption were

only about $56 million. The savings in property alone amounted to at least five times this

total investment!

Although savings may not always be as

dramatic as those realized at Pinatubo, many

lives can be saved and major property losses

avoided in other volcano crises through similar

relatively modest investments in volcano monitoring and eruption forecasting. The experience

gained by scientists during Pinatubo’s 1991

eruption crisis is being used by the USGS Volcano Hazards Program in the United States and

by PHIVOLCS in the Philippines to better protect people’s lives and property from the future

volcanic eruptions that will inevitably occur.