3) Volcanic Gases

Each episode of high fountaining from Pu'u 'O'o released a tremendous plume
of volcanic gas into the atmosphere.

Volcanic gases are emitted during all types of eruptions. Gases also can be released during
repose periods by inactive vents and fumaroles, vents that may never have produced any lava.
The gas plume rising from an active vent on Kilauea consists of about 80% water vapor with lesser amounts of sulfur dioxide, carbon dioxide, and hydrogen. Small quantities (typically less
than 1% by volume) of carbon monoxide, hydrogen sulfide, and hydrogen fluoride are also present. ***extreme***ly small amounts of mercury and other metals have been detected in gases emitted from vents along the east rift zone of Kilauea, but none have been found in
concentrations large enough to create a direct health hazard.

Any hazard posed by volcanic gases is greatest immediately downwind from active vents; the concentration of the gases quickly diminishes as the gases mix with air and are carried by winds away from the source. Brief exposure to gases near vents generally does not harm healthy
people, but it can endanger those with heart and respiratory ailments, such as chronic asthma.

A common gas produced during Hawai'ian eruptions that is potentially harmful to human health
is sulfur dioxide. Even small concentrations of sulfur dioxide can combine with water to form sulfuric acid, which can attack skin, cloth, metal, and other materials. When a volcanic plume mixes with atmospheric moisture, acid rain results. Acid rain can significantly retard the growth
of cultivated or natural plant life downwind of a vent that degasses over a long period of time.

The sulfur dioxide emitted from Kilauea's summit during typical non-eruptive periods affects a relatively small area downwind of the summit. Similarly, the gases produced during short-lived eruptions affect only a limited area, although their odor may be detected many miles from the
vent. The continuous emission of volcanic fumes during Kilauea's Pu'u 'O'o-Kupaianaha eruption, however, resulted in persistent volcanic haze and acid rain conditions in the South Kona
district on the leeward side of the island.

This digital shaded-relief map shows the usual wind conditions on the island of Hawai`i.
Moderate to strong trade winds carry gases and vog from Kilauea Volcano around the
southern tip of the island where the gas tends to accumulate on the leeward or "kona" coast. During these usual conditions, volcanic fog ('vog') often becomes trapped by
daytime (onshore) and night-time (offshore) breezes (double-headed arrows). During the day, onshore sea breezes carry vog up the slopes of Hualalai and Mauna Loa volcanoes, and into the topographic saddle between Mauna Loa and Mauna Kea. When the
landmass cools in the evening, cooler, denser air and vog flow back down to the coast. However, when the trade winds are light or absent or when winds blow from the south, much of the vog stays on the eastern side ofthe island where it sometimes moves into
the city of Hilo.


This illustrates the SO2 emission rates from Kilauea, 1992 - 1998.

In late 1987, studies conducted on private water-catchment systems in the South Kona area revealed higher than average acidity in several water samples. Drinking the acidic water does not pose a health hazard, but such water can leach lead from the lead roof flashings, lead-headed nails, and solder connections found in many plumbing systems, resulting in unsafe levels of lead in the drinking water. Extensive testing in 1988 determined that many water-catchment systems on the island, particularly those in the districts adjacent to or downwind of the active vent, contained elevated levels of lead.

Volcanic fumes can also damage agricultural crops. During the 1969 - 74 eruption of Kilauea's Mauna Ulu vent, the South Kona district experienced prolonged periods of eruption-related
smog. A study conducted in 1972 by the University of Hawaii's Agricultural Experiment Station
at Hilo concluded that the acid rain resulting from the fume was responsible for severe damage to tomato crops. The Pu'u 'O'o-Kupaianaha eruption of Kilauea caused similar problems for vegetable and flower growers in both the Kona and Puna districts, who reported light-to-moderate crop damage during periods when winds blew the gases over their fields.

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