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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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