NOVA Online | Deadly Shadow of Vesuvius | Can We Predict ...

In a word, yes. But that assertion, like saying we can predict the weather,
bears significant caveats. Volcanologists can predict eruptions—if they have
a thorough understanding of a volcano's eruptive history, if they can install
the proper instrumentation on a volcano well in advance of an eruption, and if
they can continuously monitor and adequately interpret data coming from that
equipment. But even then, like their counterparts in meteorology,
volcanologists can only offer probabilities that an event will occur; they can
never be sure how severe a predicted eruption will be or, for that matter,
whether it will even break the surface.
Still, under ideal conditions, volcanologists have recently met with a great
deal of success in foretelling eruptions. While they were caught off guard by
the exact timing and magnitude of the 1980 Mt. St. Helens eruption, for
example, their timely warnings of an impending blow prompted the U.S. Forest
Service to evacuate people from dangerous areas near the volcano. Though 57
people died in the eruption, perhaps 20,000 lives were saved, says Dr. William
Rose, a volcanologist at Michigan Technological University. Similarly, a USGS
SWAT team that rushed to the Philippines' Mt. Pinatubo in the spring of
1991 successfully augured the June eruption, leading to evacuations that saved
thousands if not tens of thousands of lives and millions of dollars worth of
military equipment at the nearby Clark Air Force Base.
A Kilauea lava
fountain spews from Puu Oo vent on March 13, 1985.
Not surprisingly, volcanologists have had the most success at volcanoes that
host their own observatories. In 1912, Thomas A. Jaggar, head of the Geology
Department at the Massachusetts Institute of Technology, founded the first
volcano observatory in the United States on Kilauea. (There are now three
others—in Menlo Park, California; Anchorage, Alaska; and Vancouver,
Washington, near Mt. St. Helens.) Over the succeeding decades, researchers at
the Hawaiian Volcano Observatory developed many of the techniques used today
and can now predict Kilauea's eruptions to a tee.
They know when and how Kilauea will erupt because it does so frequently and
predictably, and because after decades of intensive study they know the volcano
inside and out. Learning as much as possible about a volcano's previous
behavior is the essential first step in anticipating future blows, just as
knowing a career criminal's record can help indicate what he might do next.
"There is no doubt that the eruptive history of a volcano is the main key for
long-term prediction," says Dr. Yuri Doubik, a Russian volcanologist who has
studied past eruptions on the Kamchatka Peninsula for 35 years. Such work
entails laboriously picking through the physical remains of previous eruptions.
And mapping such old lava flows, pyroclastic deposits, and other volcanic
debris distributed around a crater can reveal much about the timing, type,
direction, and magnitude of previous blows.
Close-up of a seismograph drum.
Satellite data can greatly aid such mapping, and volcanologists are looking
forward to using images generated by the Earth Observing System after it is
launched in 1999. The satellite's purpose is to study environmental ills such
as global warming and depletion of the ozone layer, but it will also gather
information of use to volcanologists, including gas concentrations in the
atmosphere over volcanoes and images clear enough to reveal the fallout from
former eruptions.
The Volcanologist's Toolkit
When a volcano's eruptive history is known, researchers can more confidently
turn to modern techniques to help them call the next eruption. The most
valuable among these, volcanologists agree, is monitoring a volcano's
seismicity—the frequency and distribution of underlying earthquakes. Use of
the seismologist's tool in volcanology has come a long way since Frank Perret,
one-time assistant to Thomas Edison, gleaned the frequency of the small shocks
that continually shake Vesuvius's flanks by biting down on the metal frame of
his bed, which was set in cement. Today sophisticated seismographs can register
the magnitude, escalation, and epicenters of earthquakes that occur as magma
moves beneath volcanoes. The more seismographs technicians deploy on a volcano,
the more complete the picture they get of the mountain's plumbing.
Tavurvur volcano erupts in the distance
as workers install a tiltmeter at Rabaul, Papua New Guinea, September
1994.
Seismic networks can transmit data by radio 24 hours a day to
computer-equipped monitoring stations well out of harm's reach. This enables
scientists to safely watch for changes in "nature's noise," as one
volcanologist labeled the geophysical status quo within a volcano.
Computer-based seismic data acquisition and analysis systems, which in essence
constitute portable observatories, enabled the USGS Volcano Disaster Assistance
Program's crisis-response team to successfully predict the 1991 eruption of Mt.
Pinatubo. Such "mobile observatories" themselves now constitute a major weapon
in the prediction arsenal.
While seismicity is the workhorse, monitoring ground deformation is another
up-and-coming technique that allows three-dimensional mapping of what's
occurring underground. Magma rising from the depths often pushes the skin of a
volcano up and out, like a balloon filling with air. Sensitive tiltmeters and
surveying instruments can measure and record the slightest changes, which help
volcanologists determine, for example, roughly how deep a magma source is, how
fast it is moving, and where on a volcano it might erupt. Such monitoring has
helped scientists anticipate eruptions at Hawaii's Kilauea and Mauna Loa
volcanoes, which deform in predictable ways and at predictable rates.
A USGS team prepares to fly a gas-measuring flight
at Montserrat, August 1995.
One drawback is that studying ground deformation has required scientists to
climb volcanoes to take measurements—a perilous undertaking. But USGS
volcanologists are now testing a prototype of a fully automated
ground-deformation system. Flown aboard satellites or aircraft, the so-called
"synthetic aperture radar" can automatically and continuously transmit
information on a volcano's ground movements to remote observatories. Though it
will not penetrate dense vegetation and is sensitive to moisture, the radar
provides a resolution of less than an inch under ideal conditions. "It's a
tremendous tool because it gives a complete map of ground movements, and we
don't have to go into the field to get it," says Dr. Dan Dzurisin, a geologist
with the USGS Volcano Hazards Program (VHP) who is helping to perfect the new
device. His colleague at the VHP, the volcanologist Dr. Robert Tilling, is
equally optimistic: "We're confident that by the turn of the century, we'll have
such a system and at low enough cost that it can be applied easily everywhere
in the world."
Measuring Vapors
Such is the long-term hope as well for techniques to monitor volcanic gases.
Magma deep underground lies under enormous pressure, which keeps vapors
dissolved. But as magma rises toward the surface, the pressure eases and gases
such as carbon dioxide and sulfur dioxide begin to bubble out of the liquid
rock and into the air. Theoretically, changes in concentrations of
CO2 and SO2 emitted by a volcano can be used to predict
eruptions, as can the escalating output of gases in general. The USGS team that
was sent to Pinatubo in the spring of 1991 successfully predicted the June
eruption in part after watching SO2 levels shoot up to unprecedented
levels of 16,500 tons per day.
Alaska's Spurr volcano blows its top
on August 19, 1992.
Monitoring of volcanic gases got its start in the 1950s when enterprising
Japanese researchers put beakers of potassium hydroxide, a strong, basic
solution, on Honshu's Asama volcano, which was beginning to show signs of
erupting. As the highly acidic gases released by the crater seeped through
holes in a crate covering the beakers, they increasingly altered the solution's
composition in the months before a large eruption. Today, volcanologists use
so-called "Japanese boxes" routinely, though again they must check the beakers
manually. To surmount this problem, Dr. Stanley Williams, an Arizona State
University volcanologist who was nearly killed during a small but deadly
eruption of Colombia's Galeras volcano in 1993, is designing an electronic
Japanese box that will automatically and continuously transmit data to a remote
observatory. About the size of a briefcase, the battery-powered unit has tiny
electrochemical sensors that create currents proportional to the amounts of
various volcanic gases in the air.
Concurrently, Williams and others are working on infrared telescopes to
monitor concentrations of gases escaping from volcanic vents. Williams's
version is modeled after the correlation spectrometer, a device originally
developed in the 1970s to monitor SO2 and other toxic gases from
factory smokestacks. His prototype unit measures the amount of infrared light
absorbed by CO2 molecules, from which an estimate of CO2
concentrations in the air can be made. Dr. Kenneth McGee, a volcanologist at
the Cascades Volcano Observatory in Vancouver, Washington, is perfecting an
infrared spectrometer that he says will detect still other volcanic gases that
absorb infrared light, including hydrochloric acid gas, carbon monoxide,
methane, and water vapor.
Mt. St. Helens erupting, May 18,
1980.
Calling the Next Big One
While volcanologists feel confident that these ever-improving technologies will
enable them to predict when an eruption is about to occur, they still cannot
reliably estimate an impending eruption's size or exact nature. How large will
the eruption be? Will it be explosive like Mt. St. Helens or effusive
like Kilauea? Indeed, will it even open a vent in the surface? To be able to
answer such questions, Tilling and USGS colleague Dr. Peter Lipman argued in a
1993 article in Nature for the need to develop "rugged, reliable
real-time systems" to measure changes not only in seismicity, ground
deformation, and gases, but also in gravitational and electromagnetic fields—in short, equipment to read the gamut of signals given out by a restless
volcano. "There's no magic bullet in predicting volcanic eruptions," says Dr.
Charles Connor, a volcanologist at the Southwest Research Institute in San
Antonia, Texas. "The key thing is to cross-correlate as many different
observations as possible."
Tilling says volcanologists also need to get a better handle on the basic
mechanisms behind precursory signals, such as the long-period earthquakes that
often precede eruptions. Dr. Bernard Chouet, a VHP volcano seismologist, says
these quakes provide a "direct window" into the magmatic fluid moving about
beneath a restless volcano. "These earthquakes are like stress gauges that
light up and reflect the pressurization going on below," he says. Careful
monitoring of such natural gauges can help forecast eruptive activity. The USGS
team that successfully predicted Pinatubo's burst did so in part by watching
the build-up of long-period quakes.
USGS Volcanologist Ken Yamashita surveys on the dome, Mt. St.
Helens, March 1986.
The urgent need to improve methods to call the next Big One holds especially
true for large caldera-forming eruptions. These true earth-shakers explode with
such Herculean force that they leave behind vast, basin-like depressions—calderas—that can stretch many miles across. The largest caldera-forming
eruptions, which fortunately have not occurred in human history, make the
explosive eruption of Mt. St. Helens in 1980 seem like a firecracker. In the
mid-1980s, three volcanic fields believed to hold the potential for one of
these monumental cataclysm—California's Long Valley, Papua New Guinea's
Rabaul, and Italy's Campi Flegrei—turned on almost simultaneously, throwing
the volcanological community into a bit of a frenzy. All three centers calmed
down without further ado, though Rabaul erupted a decade later (see
Planning for Disaster).
Tilling, for one, is confident that such an apocalyptic blast will not come
unheralded. "No volcano is going to suddenly produce one of these humongous
eruptions without giving a lot of signals," he says. "But what will those
signals be?"
Peter Tyson is Online Producer of NOVA. This piece was excerpted and updated
from a feature article by Mr. Tyson that originally appeared in Technology
Review (January 1996).