3) Volcanic Gases
episode of high fountaining from Pu'u 'O'o released a tremendous
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
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.
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
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
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