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May 29, 1996
A weekly feature provided by scientists at the Hawaiian Volcano
Observatory.
Vog: A Volcanic Hazard
Sometimes great things happen when you get the right people
together! Recently, the U.S. Geological Survey's Volcano Hazards
Program sponsored a workshop on gas geochemistry, which includes the
study of the type and amount of gas coming out of volcanoes. We went
around the room from group to group, sharing our latest gas experiences
from our favorite volcanoes. One goal of this activity was to see
whether we could improve our hazard assessments and our understanding
of how volcanoes work. Those of us from the Hawaiian Volcano
Observatory seized the opportunity to talk about one of our favorite
topics: vog.
Now, it's easy to start a conversation with a group of volcanic gas
chemists about the hazards associated with gases like sulfur dioxide -
the biting, choking odor you smell when you visit Halema'uma'u crater
or when you've just lit a kitchen match; hydrogen sulfide - the gas
with the rotten egg smell; or carbon dioxide - the gas dissolved in
soda, beer, and some volcanic lakes. The hazards of these gases are
well known; but in fact, gases have not caused many deaths (with a few
notable exceptions) in historic time, compared to hot ash flows,
explosive volcanic eruptions, and mud and lava flows. So gases and vog
aren't serious hazards, right? Not so fast!
There are at least two problems in dismissing vog itself as a
not-so-serious hazard. The first problem is that vog (volcanic smog)
is a mixture that includes gases but is predominately aerosols
(tiny particles and droplets) formed when volcanic gas reacts with
moisture, oxygen, and sunlight. It is this unique mixture of gas and
aerosols that makes vog both difficult to study and potentially more
harmful than either gases or particles alone. What we have learned
from limited studies about the aerosols that comprise vog is that most
of the aerosols are acidic and are of a size that is readily retained
by the lung. Also, studies done in urban areas having similar
pollutants show that these types of aerosols degrade lung function and
can compromise our immune system. These effects are especially
pronounced for children, individuals who have chronic asthma or other
respiratory impairments, or those with circulatory problems. Remember,
though, that these are studies of mainland urban areas that have
similar pollutants, not studies of vog itself.
The second problem with thinking of vog as a not-so-serious volcanic
hazard may lie with the way we volcano folks think about volcanic
hazards and their associated risks. A volcanic hazard is defined as a
destructive event that can occur in a given area or location, such as a
lava flow or a volcanic earthquake, along with the probability of the
event's occurrence. It is important to understand the hazard, but, in a
practical sense, we can't do anything to reduce the hazard itself;
eruptions are beyond our control. Risk, which is quite different from
hazard, is mathematically defined as the hazard, multiplied by the
vulnerability (the proportion of some resource, like people or land
likely to be affected if the event occurs) multiplied, in turn, by the
value (lives or property threatened). In shorthand: risk = hazard x
vulnerability x value.
As a hypothetical example of risk, we might have a 25 percent chance
(risk) in the next 70 years of a lava flow (hazard) occurring at a
given location in the summit area of the National Park that would cover
0.5 percent of the road (vulnerability) that stretches 20 total miles
around the summit (value). Two important things about this example are:
(1) the effect of the hazard event is immediate and spectacular: when a
lava flow meets a road, the lava flow wins every time! (2) the lava
flow hazard and the road's vulnerability and total value are well
understood.
When we try to use our equation to examine vog as a volcanic hazard
and to determine its associated risks, several issues arise. The main
issue is that the specific hazards associated with vog have not yet
been clearly defined. Studies incorporating information from a diverse
group of health professionals and physical scientists would help
provide a broader base for assessing hazards from vog. Physical
scientists, including air quality specialists, can provide data that
characterize chemical and physical aspects of vog. Toxicologists and
industrial hygienists can examine groups of individuals in order to
understand the acute effects of vog pollutants on respiratory function,
while epidemiologists can use their skills to conduct studies on larger
populations, perhaps using medical records from the time before the
eruption started to the present.
It seems that in examining volcanic hazards, there is a tendency to
focus on those hazards that are acute (relatively brief and severe),
like lava flows or volcanic earthquakes. We need to broaden our
definition of volcanic hazards to include sustained, low-level volcanic
events, like volcanic air pollution. A sustained event, such as vog,
could possibly produce more subtle but chronic (long-term) hazardous
effects, such as degraded lung function, or higher incidences of
asthma. This won't be known with certainty until the integrated health
and physical science studies, like those we suggested earlier, are
completed.
Even though potentially hazardous effects of vog may be less
dramatic than those of lava flows or earthquakes, there are many, many
people who would be vulnerable to such a hazard. With about 1,000 tons
of sulfur dioxide being released by the volcano each day, some large
area on the island always gets vog. If trade winds blow, vog can be
found in areas from Kilauea to Ka`u to North and South Kona. If trade
winds are absent, areas in east Hawai'i from Volcano to lower Puna to
Honoka'a can be affected. Remember, risk = hazard x vulnerability x
value, so a large, vulnerable population would be at higher risk in
either wind regime.
Of course, the effects of volcanic hazards are not restricted to
people. Ideally, the risk equation should be considered for
agricultural crops, domestic animals and even metal objects exposed to
the air. People living or working near the summit of Kilauea know how
fast automobiles rust in this area of the island.
In order to address the immediate concern of reducing the risk to
people from vog, the Hawaii State Department of Health (DOH) has
recently taken on the formidable challenge of developing an index which
would identify the levels of vog for areas of the island. If we can
categorize vog levels, we will be able to reduce our risks by
controlling our exposure even before we fully understand what the
precise hazards associated with vog. If the DOH is successful, the
index value could be combined with the results of the proposed health
and physical science study on vog hazards to help us to evaluate and
reduce our risk in a more measured way.
The success of this overall venture, to better understand the
health-effects from vog and reduce our risks, relies on good
communication and cooperation among people in the health and physical
science communities, Civil Defense and the public. The U.S. Geological
Survey's Hawaiian Volcano Observatory will continue to support this
goal by providing physical science data and interpretation to
characterize Kilauea emission sources and air quality, as well as to
actively conduct cooperative scientific studies with health
professionals and other physical scientists and to remain responsive to
the public. Great things really can happen if we get the right
people together!
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