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Works Cited
Pendick, Daniel. "Under The Volcano." Earth 3.3 (1994): 34. MAS Ultra - School
Edition. Web. 5 Dec. 2012.
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UNDER THE VOLCANO
As the global population grows, more and more people are crowding near the world's
volcanoes, raising the risk of disaster from eruptions.
But for a last-minute change in plans, Harry Glicken would have perished on May 17,
1980, when the explosive collapse of Mount St. Helens volcano obliterated the
observation post he had manned until the day before. A decade later, however, his luck
ran out. Glicken lost his life at an eruption of Mount Unzen, a volcano on Japan's Kyushu
Island.
On June 3, 1991, Glicken went into an evacuated area on Unzen's eastern flank with
French volcanologists Maurice and Katia Krafft to shoot close-up footage of the eruption
for an educational film on volcanic hazards. Late that afternoon, the volcano unleashed a
mammoth torrent of ash, rocky debris and 500-degree gases that raced down the
Mizunashi River to KitaKamikoba, a residential district of nearby Shimabara City nestled
at the foot of Unzen's summit cone. This pyroclastic flow blew through the evacuated
zone like a hurricane, killing the three volcanologists and 40 Japanese citizens.
Since that day, nine more volcanologists have died at volcanoes in Ecuador, Indonesia
and Colombia. By far the worst incident occurred at Colombia's Galeras Volcano in
January 1993, when an unexpected shower of debris killed six scientists and three
tourists.
University of Arizona volcanologist Stanley Williams saw friends and colleagues die that
day and barely survived himself. The scientists had climbed to the restless volcano's
13,680-foot summit crater (4,170m) to collect seeping volcanic gases. They hoped that an
analysis of the gases' chemical makeup might show whether the volcano's magma-filled
plumbing system was changing in a way that could signal an eruption. At 1:30 that
afternoon, fog rolled in and the scientists prepared to leave.
There was barely a warning of what was to come. Moments before the blast, Williams
says, rocks began to tumble from the crater wall. "I yelled, 'Something's gone wrong.
We've got to get the hell out of here.' But before anyone could react it just exploded."
He watched as his friend Igor Menyailov and several others were shredded in the initial
blast. Flying debris felled Williams several times as he tried to flee the crater rim. He
finally found refuge behind a boulder, where he lay for hours with a fractured skull, thirddegree burns and a shattered leg.
Williams says he will return to violent volcanoes, as Glicken had returned after his close
brush with death. In large part, he and other volcanologists are motivated by the potential
value of their work to people who live under the world's restless volcanoes. "To pursue
this work," he says "you have to get hooked on the idea that you can actually make a
difference in how bad disasters will be."
Globally, the threat of volcanic disaster has grown in proportion to the population of the
developing world, where man of the world's most dangerous active volcanoes are located.
The number of people at risk from eruptions may reach 500 million by the turn of the
century, according to U.S. Geological Survey volcanologists Robert Tilling and Peter
Lipman.
Typical volcanic hazards include earthquakes, explosive emissions of ash and debris,
rivers of mud called lahars, rampaging lava and pyroclastic flows ground-hugging
mixtures of hot gas, ash and rocky debris that can race downhill at more than 100 miles
per hour. To reduce the human toll, volcanologists rush to volcanoes showing signs of
life, set up monitoring devices and attempt to warn local residents of impending doom.
But an eruption is also an opportunity to study an ultraviolent process that has shaped the
contours of the planet and cooked up most of its foundational rock. In this sense,
volcanology is geology in the present tense - the study of a world in the making.
Mount Unzen has created such an opportunity. For three years, Japanese scientists have
monitored the volcano with seismometers, heat-sensitive cameras, microphones,
advanced imaging radar systems and video cameras. Unzen's frequent, highly destructive
pyroclastic flows have received the most attention. Efforts to harvest new information
from them range from the ordinary to the ingenious. For example, one group of
volcanologists has used microphones to record the low-frequency growl of moving
pyroclastic flows, whose acoustic signature comes in part from colliding particles of
debris. By comparing these sounds to the laboratory-generated clacking of different-sized
steel balls, the scientists have extracted information about the size and distribution of
particles in the flows.
Studies like these may lead to better ways of anticipating the risks presented by Mount
Unzen and volcanoes like it. "The motivation behind studying the dynamics of these
things is prediction - to be able to get people out of the way," says USGS volcanologist
Rick Hoblitt, who studied pyroclastic flows at Mount St. Helens.
At Unzen, pyroclastic flows are born at the edges of the volcano's 300-foot-high (90 m)
summit lava dome, a plug of congealed magma that began forming near the 4,485foot
summit (1,359m) in May of 1991. Riddled with cracks and gasfilled pores, this clot of
silica-rich lava hangs precariously over the Mizunashi and Oshigadani river valleys on
Unzen's eastern flank.
Periodically, huge masses of lava 200 to 300 feet high crumble from the dome and
disintegrate on Unzen's steep summit slope. Hot gases formerly trapped in the lava
escape, helping to convert these avalanches into slippery, highly mobile pyroclastic flows
and more dilute "ash hurricanes," or pyroclastic surges. These flows and surges follow
Unzen's river valleys toward outlying areas of Shimabara City, a community of 45,000
whose center lies just a few miles from Unzen's summit.
Unzen's unique combination of cliffhanging topography and steady magma supply has
spawned more than 7,000 pyroclastic flows since 1991, creating the best natural
laboratory in the world to study this phenomenon. "At Unzen you have a very rare chance
to witness live pyroclastic flows," says Sigeo Aramaki, a Japanese volcanologist at
Hokkaido University. "You can go - well, it depends on how brave you are - as close as
one kilometer."
Studying this phenomenon is important because it is one of the most deadly of volcanic
events. Worldwide, pyroclastic flows and surges have been responsible for the majority
of deaths and injuries from eruptions in the 20th century. The death toll includes nearly
all 29,000 residents of St. Pierre, a city that was obliterated by a pyroclastic flow and
surge during the 1902 eruption of Martinique's Mont Pelee - the most deadly volcanic
eruption in the last 100 years.
Although Mount Unzen is today an excellent place to study pyroclastic flows, it has been
known for relatively gentle lava flows. During its last eruption, in 1792, a vent opened up
on the volcano's northeast flank and disgorged about 20 million cubic yards (15 million
cubic m) of runny lava. According to Kazuya Ohta, director of the Shimabara Earthquake
and Volcano Observatory, 18th-century tourists would climb Unzen's wooded slope to
drink sake and watch the lava spew.
When disaster struck in the past, it came not from Unzen but from nearby Mount
Mayuyama. A month after the Unzen lava flow of 1792, powerful earthquakes loosened
the eastern slope of Mayuyama, a now-extinct volcanic cone just east of Fugendake, the
currently active cone that makes up part of Mount Unzen. Mayuyama's flank collapsed,
unleashing a massive landslide that rode over Shimabara City and into the Ariake Sea.
Some 15,000 people died from the landslide and the tsunami it caused. This was the
worst volcanic disaster in Japan's history.
Until recently, however, the people of the Shimabara Peninsula have mostly lived in
harmony with their volcanoes. After the Shimabara catastrophe, Mount Unzen again
became the centerpiece of local tourism. Tourists traveled to Unzen-Amakusa National
Park, 50 minutes by bus from Nagasaki, to watch the azaleas bloom on the volcano's
fertile slopes or to visit the area's hot spring resorts.
But all that changed in November 1989, when something big and dangerous awoke
beneath the Shimabara Peninsula. Scientists from the Shimabara Earthquake and Volcano
Observatory detected earthquake swarms 12 miles (19 km) beneath Chijiwa Bay, a
semicircular body of water west of Unzen that some scientists believe marks the crater
formed in a huge prehistoric eruption. These earthquakes - a sign that magma was on the
move - began to migrate east towards Unzen. In the spring of 1991, the volcano swelled
with magma. Finally, on May 24, it began to grow a lava dome and cast off pyroclastic
flows.
Evacuations were ordered for areas at risk, including Kita-Kamikoba, a village on the
Mizunashi River. But on June 3, despite official warnings, some journalists and residents
staved to watch the pyroclastic flows rip down the Mizunashi River. Police and fire
fighters were also on hand, as were Glicken and the Kraffts. The scene was set for Japan's
worst volcanic accident in 60 vears.
At 4:09 p.m., Unzen's lava aome collapsed, leaving behind a horseshoe-shaped
depression 450 feet (140 m) icross. A flood of debris traveled a surprising 2.5 miles (4
km) down the Mizunashi River valley, smashing houses, snapping trees and tossing cars
around like toys. Those in the path of the flow didn't stand a chance.
For all the destruction flows and surges have caused, volcanologists still don't fully
understand their inner workings. "Our understanding of what's going on inside these
things is pretty primitive," admits Hoblitt.
One reason is that a pyroclastic flow's inner machinery is so hard to see. Outwardly, it
looks like a rolling mass of billowing gray ash tumbling down the side of a volcano at
race-car speed. But hidden inside the curtains of ash lies a complex, multilayered creature
that behaves more like a dense, hot fluid than a simple, gravity-driven rockfall. A generic
pyroclastic flow has three basic components. The basal flow carries the largest, heaviest
chunks of debris. Often, but not always, a more dilute, fluidlike surge develops over the
basal flow. Finally, a buovant, bil]owing column of the finest ash rises from the flow,
towering hundreds of feet into the air.
These parts don't necessarily stay together, and that's what makes pyroclastic flows so
lethal and unpredictable. "There's an interplay between the pyroctastic flow and the path
it follows," Hoblitt says. When it reaches a steep slope or rides off a cliff, the flow
accelerates and ingests more air, which causes it to inflate. "Conditions being right, the
surge can separate from the main flow."
These conditions apparently existed the day of the Kita-Kamikoba disaster, according to
a study by the Geological Survey of Japan. Takahiro Yamamoto, Shinji Takarada and
Shigeru Suto carefully mapped the debris and devastation along the Mizunashi River and
concluded that individual pyroclastic surges peeled off the basal flow four times. The
final surge the lethal blow to residents of Kita-Kamikoba as well as Glicken and the two
French volcanologists came when the towering ash column over the main flow collapsed,
generating an ash hurricane that charged ahead a half-mile at a speed of nearly 200 miles
per hour.
To USGS volcanologist James Riehle, the widespread destruction wrought by the June 3
flow highlighted the limitations of relying on a volcano's past behavior to predict future
hazards. "The volcanologists who went up to Unzen made the reasonable assumption that
the pyroclastic flows would pretty much continue to go where they'd gone before," he
savs. "Then a rogue flow came down and killed them."
Traditionally, Riehle explains, volcanologists have relied on the geological record of past
eruptions to predict the likely size and range of pyroclastic flows that could occur during
future eruptions. In addition, the location of river valleys and other key topographical
features suggests directions that flows might take. Volcanologists use this information to
create "hazard maps," which indicate the areas most likely to be attacked.
However, these maps can't tell you why one flow behaves differently than another in the
same area, Riehle savs. "To get at why some flows go farther than others - why we get
these rogue flows - requires that you think about the factors that govern the movement of
the flows themselves."
Jonathan Fink and Susan Kieffer, volcanologists at Arizona State University, have
created a theoretical model that could help Thousands of tons of ash, debris and hot gas
race down Unzen's slope (above) at hurricane speed in a 1992 pyroclastic flow - one of
7,000 such flows since 1991. Racing flows like this are powerful enough to level trees
and toss vehicles around like toys. researchers do just that. Like other pyroclastic flow
models, this one is composed of equations that approximate the basic motions and
properties of pyroclastic flows.
Fink and Kieffer developed their model to explore the process that sets pyroclastic flows
in motion at crumbling lava domes. Their work suggests that the explosive release of gas
- mostly water vapor - that accompanies a dome collapse can boost the initial energy of
the debris significantly, creating unusually destructive and far-ranging flows like the one
that flattened Kita-Kamikoba. If Fink and Kiefer are right, the appearance of especially
water-rich magma could presage trouble.
At present, however, pyroclastic flow models are better at explaining past events than
predicting the future. To improve prediction, says Riehle, "first we have to create a
theoretical model that reproduces what you see in nature."
Partly because of the deaths at Kita-Kamikoba, U.S. and Japanese researchers have
decided to give top priority to developing models that add that needed realism to
simulations of dome collapses and pyroclastic flows, savs Chris Newhall of the USGS,
who helped organize a March 1993 meeting of volcanologists from both countries. If
researchers can develop more realistic models, they might be able to predict how far a
volcano's pyroclastic flows are likely to run based on changes in the rate of dome growth,
lava chemistry or gas content in the dome lava. Newhall cautions, however, thit the
inherent complexity of volcanoes may limit the predictive power of pyroclastic flow
models.
For example, the size of the lava chunks that peel off Unzen's dome helps determine the
ultimate size of the pyroclastic flows. And anything from the number of internal cracks in
the dome to the strength of local seismic tremors can affect what comes off the dome or
whether it will collapse cornpletely. "It's very difficult to know up front what the
conditions are at a dome, whether at Unzen or any other volcano," Newhall savs. "So
really the models will define a spectrum of possible outcomes."
On the low end of the spectrum, the shedding of cold, lifeless dome material might let
loose something like an ordinary avalanche, which may not go very far down the
mountain. Or, on the high end, a hot, voung dome packed with dissolved water and other
volatile materials could collapse explosively, sending out far-reaching flows and surges.
Given the uncertainties of predicting what a volcano might throw at people living nearby,
the only way to insure safety is to assume that the worst will happen and evacuate
everybody at risk when a volcano stirs, Newhall savs. This option probably saved
thousands of lives during the 1991 eruption of Mount Pinatubo in the Philippines. Tens of
thousands were evacuated from nearby settlements on the advice of Newhall and other
volcanologists, who provided accurate warnings of eruptions based on seismic
monitoring.
Unfortunately, large-scale evacuation is not practical in Japan. In this crowded land of
perpetual volcanism, people can't possibly leave every time a volcano raises hell. So the
Japanese will likely stay strongly interested in developing models for predicting the
hazard from pyroclastic flows.
"Our reaction when we have a restless volcano is to get people out of the way and
discourage development in areas vulnerable to volcanic hazards," says Hoblitt. "In Japan,
where land is dear, they don't have that option."
MAPS: Mount Unzen sits on the Shimabara Peninsula about 50 minutes by bus from the
city of Nagasaki. Some geologists believe Chijiwa Bay is the remians of crater formed in
a prehistoric eruption.
PHOTO: Smoke wreathes the summit of Martinique's Mt. Pelee (above), one of the
world's most dangerous volcanos. An eruption in 1902 caused a monstrous pyroclastic
flow that obliterate the city of St. Pierre at its foot, killing all 29,000 residents. All that
remains of an insane asylum in the path of this flow is a solid cast iron chair (above,
right) in which unruly inmates were strapped. The chair's eerie lean testifies to the
cataclysmic force of the eruption.
PHOTO: Japan's Shimabara City and Fukae Town lie beneath the smoking summit of
Mount Unzen. On June 3, 1991, torrents of hot rock, ash and gas raced down the
mountain killing 43 poeple. But this event was minor compared to Unzen's 1792
eruption, which triggered the worst disaster in Japan's history. Two earthquakes that
followed a relatively gentle lava flow caused the eastern flank of nearby Mount
Mayuyama to collapse. The resulting landslide rode through Shimabara City and killed
15,000 people. Mayuyama (the mountain below and to the right of Unzen) was left with a
huge amphitheater in its side.
PHOTO: Washington's Mount St. Helens (foreground) exploded on May 10, 1980,
devastating an area of 220 square miles, killing 57 people and causing more than $1
billion in damage. It is still considered to be one of the most hazardous volcanoes in the
world. All told, 13 major volcanic centers are located in the northwestern United States,
including Mount Rainier (horizon, upperleft) and Mount Adams (upper right).
PHOTO: At night, eruptions from Mount Unzen cast an alarming glow above an
evacuated subdivision in Shimabara City. (The star trails were recorded by a long
exposure.)
PHOTOS: Thousands of tons of ash, debris and hot gas race down Unzen's slope (above)
at hurricane speed in a 1992 pyroclastic flow - one of 7,000 such flows since 1991.
Racing flows like this are powerful enough to level trees and toss vehicles around like
toys.
~~~~~~~~
By Daniel Pendick
Daniel Pendick is a former writer for Science News. He now writes freelance about earth
science and other topics from Madison, Wisconsin.
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