Volcanic Gases
Volcanic Gases
and  temperature of the magma and the gas content determines if an eruption will be effusive  or explosive.
 
On a global scale, volcanic gases produced our  atmosphere and our oceans. Without the atmosphere and oceans, life would not have evolved on Earth.   Gases emitted by volcanoes continue to influence the atmosphere but not to the  extent of man-made sources.
 
Gases also pose a hazard at many volcanoes.  At  other volcanoes, the gradual release of gas acts as an irritant and may  pose a long-term health hazard.
 
Right:  gas sampling at vents on the floor of Halemaumau  Crater, Kilauea  volcano, Hawaii.   Photo by Steve Mattox.
 
Average Compositions and Trace Gases
Most Common Gases
Water vapor (H2O), carbon dioxide (CO2), and sulfur dioxide (SO2)  are the most common volcanic gases.
Other Gases
In lesser amounts, volcanoes release carbon monoxide (CO), hydrogen  sulfide (H2S), carbonyl sulfide (COS), carbon disulfide (CS2), hydrogen chloride  (HCl), hydrogen (H2), methane (CH4), hydrogen flouride (HF), boron, hydrogen  bromine (HBr), mercury (Hg) vapor, organic compounds, even gold.  From Cadle  (1980).
Mercury is released by most volcanoes and has been measured at  Kilauea, Mauna Loa, Hekla, Erebus, at Mount St. Helens (Siegel and Siegel, 1987).   Kilauea produces about 270 tons of mercury each year and has been identified as  the source for mercury on Oahu, 320 km away.
Condensates, sublimates, and incrustations were studied at Merapi  volcano by Symonds and others (1987).  The following elements were found:
Se, Re, Bi, and Cd at concentrations 100,000 that in the
;
Au, Br, In, Pb, and W at concentrations 100,000 to 10,000 that  in the magma;
Mo, Cl, Cs, S, Sn, and Ag at concentrations 10,000 to 1,000  that in the magma;
As, Zn, F, and Rb at concentrations 1,000 to 100 that in the  magma;
Cu, K, Na, Sb, Ni, Ga, V, Fe, Mn, and Li at concentrations 100  to 1 that in the magma.
Gold has condensed from volcanic gases. Meeker and others (1991)  reported gold at  Mount Erebus, Antarctica. They found gold in the plume near the
, in the air up to 1000 km from the volcano and in near surface samples.
Most of these gases originate in the
mantle
and are transported to  the crust and surface by complex interactions with magma and rocks encountered  along the way.  In general, the gases are dissolved in the magma.  At shallow  depths, as pressure on the magma decreases, the gases leave the magma (exsolve).   The gases can interact with surrounding rocks or continue to the surface.
Inset Image:  Sulfur deposits near the summit of Griggs volcano, Alaska.
Photo  by Jay Robinson.
Gas Compositions and Tectonic Setting
Symonds, Rose, Bluth, and Gerlach (1994) published a  list of compositions of high-temperature volcanic-gas samples.  They also have a comprehensive  list of published sources for high-quality volcanic-gas data .
Convergent-plate volcanoes: Etna, Mount St. Helens, Merapi
Divergent-plate volcanoes: Erta Ale, Surtsey
Hot-spot volcano: Kilauea
Equilibrium compositions, temperatures, and log fO2  values of high-temperature and low-pressure (1 bar) volcanic gases.  Concentrations are in mole %;  log fO2 given in log bars.
 
There are three primary ways that gas geochemists collect data: 
Estimates from Rocks, Minerals, and Inclusions
Scientists can determine the amount and types of gas in a rock, in the minerals within a rock, or in the gas inclusions in minerals or glass  (Ihinger and others, 1994).  The methods fall into four classes: bulk extraction,  energetic particle bombardment, vibrational spectroscopic techniques, and phase  equilibrium studies.  These method are used in experimental studies and for rocks  from all tectonic settings, historic eruptions, and large pre-historic eruptions.   Some methods have been found to underestimate the observed amount of gas  released during some historic eruption.  Thus, the methods may give an estimate  of the minimum amount of gas released.  For example, Gerlach and McGee (1994)  used melt inclusion data to estimate 0.08 Mt of SO2 emitted by the Mount St.  Helens eruption.  TOMS, COSPEC and
leachate data provide an estimate of 2  Mt. Gerlach and McGee suggested a vapor phase carried most of the SO2.
 
 
Direct Sampling
The easiest, but often the most difficult, way  to collect a sample is by hand, placing a container directly in the gases.  This method was  perfected by the late Werner Giggenbach.  Difficulty arises because of the high  temperatures, dangers associated with being close to vents, and the possibility of contamination of the sample by  the atmosphere.  Left diagram: Evacuated-bottle sampling scheme.  Direct  samples are most commonly collected in solution-filled bottles (4N NaOH in a  titanium or
silica
tube) and then returned to the lab for analyses.   In the drawing  on the left, the enlargement shows an evacuated glass bottle.  The solution  contains NaOH and collected H20), H2S, SO2, HCl, HF, and CO2.  The headspace contains  collected H20, H2, CH4, O2, CO, N2, Ar, Ne.  Right diagram: Flow-through sampling  scheme. Figure from Sutton and others, 1992).
Right:   Volcanic gases from Kilauea collected using the flow-through  sampling scheme.   Photo by Steve Mattox.
Another way to measure gases released by a  volcano is to collect fresh ash samples (before it rains) and pour distilled water through the ash.   Then after the liquid passes through the ash it is collected.  This is the leachate.  The leachate is analyzed for Cl (chloride), F, SO4 and pH.  The ratio of Cl to S  increases prior to eruptions.
Leachates were measured prior to the 1980  eruption at Mount St. Helens (Nehring and Johnston, 1981).  Cl and  SO4 were measured in the field  and the S/Cl ratio was observed to increase gradually from March 28 to May 18.
The S/Cl ratio increased 30 times over its  initial value prior to an eruption of Asama volcano in Japan. At Fuego, in Guatemala, the S/Cl  ratio increased 5 times over its initial value and the size of the change was proportional to eruption size.
Continuous direct sampling is a relatively  new method to monitor gases. Results of measurements are telemetered to safe locations off the  volcano.  At Mount St. Helens, upward-moving fresh
Remote Sensing
The COSPEC (correlation spectrometer)
Volcanologist found an application for an instrument  used to measure  pollution.  A correlation spectrometer (COSPEC) is designed to measure   the amount of sulfur dioxide in a passing air mass (or volcanic plume).   The  spectrometer compares the amount of solar ultraviolet light  absorbed by sulfur  dioxide in the plume to an internal standard.  Numerous measurements are made to achieve  reliable results.
COSPEC used to measure SO2 released by Merapi Volcano.
 
Use of vehicle-mounted (left) and tripod-mounted (right)  ground-based COSPEC.
A. Side view.  B. Front view. C. Typical data.  From Sutton and others  (1992).
 
Balloons
Balloons are used to take samples in or to carry  instruments into aerosol layers.  For example, Sheridan and others (1992) collected samples of  atmospheric particles from the Pinatubo eruption by releasing balloons from Laramie,  Wyoming. Most of the fine particles were H2SO4 droplets.  Other larger particles  were supermicrometer sulfate particles and composite sulfate/crustal  particles. Deshler and others (1992) also used balloons to study the aerosols in  the Pinatubo layer.  Their study showed that 90% of the SO2 had been converted to  H2SO4 aerosol within one month of the eruption.  They also measured pressure,  temperature, ozone, and particle density.
LIDAR
LIDAR is a ground-based remote sensing method that is used to measure the distribution and amounts of  several gases in the atmosphere.  NOAA has a fine page that explains  LIDAR data.
TOMS
TOMS  image of the Mt. Pinatubo SO2 plume two days  after the June 15th  eruption The red dot marks the location of the volcano. The  concentration of  sulfur dioxide is expressed in units of  milli-atmosphere centimeters, which gives the  total column abundance in  the atmospheric column   Image created by Gregg  Bluth and Arlin  Krueger, NASA Goddard Space Flight Center.
 
 
The Total Ozone Mapping Spectrometer(TOMS) is  used for high resolution mapping and measurements of the ozone layer.  TOMS also detects volcanic eruptions and measures the amount of sulfur  dioxide released.  TOMS was used to measure the sulfur  dioxide clouds from three explosive eruptions of the
Peak vent of  Mount Spurr during the Summer of 1992.
AVHRR
 
The Advanced Very High Resolution Radiometer (AVHRR)  is used to track the aerosol layer produced by eruptions.  For example, during the Pinatubo  eruption, AVHRR showed that the layer circled the Earth in 21 days and that it had inhomogeneities that persisted for more than two months.  The layer  covered 42% of the Earth after only two months, over twice the area of El Chichon in  the same amount of time.  Data gathered allowed an estimate of the net global  cooling effect of 0.5 degree C for a period of 2-4 years after the eruption  (Stowe and others, 1992).  Maps show thickness of aerosol optical products prior to  and 20 days after the 1991 eruption of Pinatubo.  Photo credit: G.J., Orme,  Department of the Army.
Monitoring Volcanic Gases
(By S. Grocke, 2010)
Understanding volcanic gases is essential to understanding how and why volcanoes erupt. First, it is important to realize that gases can be both dissolved in a
. Gas emissions as well as the wind speed and wind direction are periodically sampled and get transmitted every 10 minutes to HVO. This allows HVO to monitor degassing at the active vent almost instantaneously.  
The Origin of the Atmosphere
The Origin of the Atmosphere
 
Two models are most favored for the origin of the  atmosphere: outgassing or accretion.  Outgassing is related to the differentiation of the Earth  and the release of gases by volcanoes.  Assuming that the gases we presently  observe were also released by early volcanoes the atmosphere would be made of water  vapor (H2O), carbon monoxide (CO), carbon dioxide (CO2), hydrochloric
(HCl), methane (CH4), ammonia (NH3), nitrogen (N2), & sulfur gases.
The  atmosphere was reducing (no free oxygen).
The present-day atmosphere is quite different:
78% nitrogen, 21% oxygen, 1% argon, 0.03% carbon dioxide plus small  amounts of water vapor
 
Early in Earth history, water vapor formed clouds,  rain, and ultimately all of the surface water (oceans, ground water, lakes, rivers, glaciers).  The  presence of the ancient oceans and lakes is recorded by different types of  sedimentary rocks.
Perhaps the best geologic evidence for the  composition of the early atmosphere is the presence and abundance of Banded Iron Formations.  These rocks  are made of layers of sulfide minerals (evidence for a reducing environment) and  chert or fine-grained quartz.  These rocks are not present in rocks younger than  1.8 - 2.5 billions of years ago, when oxygen starting becoming more abundant.
The amount of carbon dioxide was reduced by chemical  weathering of minerals at the surface:
CaSiO3 + CO2 <-> CaCO3 + SiO2.
The amount of oxygen increased due to early life  forms, like the algae in stromatolites.
The introduction of red beds, sedimentary rocks with  ferric oxide (hematite) cement, to the rock record indicates the  addition of free oxygen to the atmosphere.
Photo Inset:   Gas plume as
enters the Pacific Ocean at Kilauea volcano,  Hawaii.   Photo copyrighted  by Paul J. Buklarewicz.
 
Kasting, J.F., 1993: Earth's early atmosphere.  Science, v. 259, p. 920-926.
 
Man Versus the Volcano
 
Do humans add more gases to the atmosphere or do  volcanoes?  It's a simple question with a complicated answer.  Reaching a good estimate is important in  guiding global policy for standards to reduce emissions from man-made sources of  gases.
Carbon Dioxide
Present-day carbon dioxide (CO2) emissions from  subaerial and submarine volcanoes are uncertain at the present time.  Gerlach (1991) estimated a  total global release of  3-4 x 10E12 mol/yr from volcanoes.  While this is a  conservative estimate, man-made (anthropogenic) CO2 emissions overwhelm  this estimate by at least 150 times.
Sulfur Emissions
Andres and Kasgnoc (1997) estimated the time-averaged  inventory of subaerial volcanic sulfur emissions. There inventory was based upon the 25 year  history of making sulfur measurements, primarily sulfur dioxide (SO2), at  volcanoes. Actual measurements of subaerial volcanic sulfur dioxide emissions indicate a time-averaged flux of 13 Tg/yr sulfur dioxide from early 1970 to 1997.  [Note: a Tg is equal to 10E12 grams].  About 4 Tg come from explosive eruptions and 9  Tg is released by passivedegassing, in an average year.  When considering the  other sulfur species also present in volcanic emissions, a time-averaged  inventory of subaerial volcanic sulfur emissions is 10.4 Tg/yr sulfur.
Volcanoes and other natural processes release  approximately 24 Tg of sulfur to the atmosphere each year. Thus, volcanoes are responsible for 43% of the  total natural S flux each year. Man's activities add about 79 Tg sulfur to the atmosphere each year.   In an average year, volcanoes release only 13% of the sulfur added to  the atmosphere compared to anthropogenic sources. Andres and Kasgnoc (1997)   noted that the bulk of the anthropogenic flux is located in the northern  hemisphere while volcanic fluxes occur in much more focused belts around the world.
Gases from Kilauea provides a comparison of a man-made sulfur dioxide gas leaked at a refinery to  the gas released by a volcano.
Annual Average Global Emissions of HCl, HF, and  HBr, in Tg
Source
 
 
Data compiled by Cadle (1980).  Most of the gases  emitted by the ocean return to the oceans.
Heavy Metals
Volcanoes also release heavy metal elements as  particulate matter. Buat-Menard and Arnold (1978) looked at heavy metals released by Etna.   Compared to anthropogenic (man-made) sources, the amount of lead released by Etna  is insignificant, the amounts of cadmium, mercury, copper, and zinc are  comparable; and the amount of selenium is greater than other sources in the  Mediterranean atmospheric environment.
Sources of Information:
Andreae M.O., 1990, Ocean-atmosphere interaction in  the global biogeochemical sulfur cycle: Marine Chemistry, v. 30: 1-29.
Andres, R.J., and Kasgnoc, A.D.,  Global Emissions  Inventory Activity, 1997, Global Emissions Inventory Activity: Time-Averaged Inventory of Volcanic  Sulfur Emissions.
Barnes, Ivan, Irwin, W.P., and White, D.E., 1978,  Global distribution of carbon dioxide discrages, and major zones of seismicity: U.S. Geological Survey  Water Resources Investigation 78-79, Open-File Report, 12 p.
Bates, T.S., Lamb, B.K., Guenther, A., Dignon, J.,  Stoiber, R.E., 1992, Sulfur emissions to the atmosphere from natural sources. Journal of Atmospheric  Chemistry 14:315-337.
Buat-Menard, P., and Arnold, M., 1978, The heavy  metal chemistry of atmospheric particulate matter emitted by Mount Etna volcano: Geophysical Research  Letters, v. 5, p. 245.
Cadle, R.D., 1980, A comparison of volcanic with  other fluxes of atmospheric trace gas constituents: Reviews of Geophysics and Space Physics, v. 18,  p. 746-752.
Tamar Elias, written communication, , 28 May 1997.
Gerlach, T.M., 1991, Present-day CO2 emissions from   volcanoes:  Transactions of the American Geophysical Union  (EOS), v. 72, p. 249, and 254-255.
Gerlach, T.M., 1991, Etna's Greenhouse Pump: Nature,  351, p. 352-353.
Gerlach, T.M., 1990, Natural Sources of Greenhouse  gases: CO2 emissions from volcanoes. Geothermal Resources Council Transactions, vol. 14, part I,  pp. 639-641,
Deadly Gases
 
 
At certain concentrations some volcanic gases can be  fatal.  In historic time, deaths have been caused by sulfur dioxide, carbon dioxide, and carbonic
and hydrogen sulfide.  The following information is compiled from Volcanoes  of the World by Simkin and Siebert (1994), and the Bulletin of the  Global  Volcanism Program.
Right:  Photo of dead buffalo at Lake Nyos, Cameroon.   Jack Lockwood, U.S. Geological  Survey.
Vesuvius, Italy
at Vesuvius killed about 400 people.  Several people died from carbon dioxide.  In 1872, an unknown  number of fatalities were caused by carbon dioxide.  Seven people died of gas  inhalation in 1873.
Etna, Italy
The 1650 eruption of Etna caused about 40 deaths; some caused by opthalmias from sulfurous vapors and suffocation.  The  crew of a ship suffocated as it passed the volcano.
Oku Volcanic Field, Africa
In August, 1984, 37 people were killed when carbon  dioxide was released from Lake Monoun.
In August, 1986, 1,700 people were killed when a large amount of carbon  dioxide was released from Lake Nyos.  At least 300 people were hospitalized.
Karthala, Indian Ocean
with at least 16  historic eruptions.  In June of 1923, three boys were killed by asphyxiating gas.  Carbonic acid  and hydrogen sulfide were involved.  The volcano was not erupting.
Papandayan, Java, Indonesia
Papandayan is a stratovolcano with three historic  eruptions.  In December of 1924, a volcanological observer died, probably by suffocation due to  hydrogen sulfide.
Dieng Plateau, Java, Indonesia
The Dieng Plateau, a complex volcano, has had at  least 16 historic eruptions.  In February of 1979, at least 149 people died from poisonous gas(es) (either crbon dioxide or  carbon dioxide and hydrogen sulfide) as they fled eruptions at Sinila and  Sigludung Craters.
Hakone, Honshu, Japan
Hakone, a complex volcano, has not erupted in 1,000  years.  In May of 1933, one person was killed in association with fumarolic activity.
Aso, Japan
In December, 1997, two men died when sulfur dioxide  concentrations reached  ~5 to ~8 ppm.  Since 1980,  71 people have been hospitalized due to  inhalation of  volcanic gases at Aso.  Seven of these people died. Tseax River Cone, British Columbia, Canada
The Tseax River Cone, a
in 1907, Carran maar in 1955, and Mirador in 1979.  Two people were killed by  gases during the 1955 eruption.
Vestmannaeyjar (Heimaey), Iceland
During the 1973 eruption near Vestmannaeyjar a sleeping man was killed by carbon dioxide as it pooled in the
of his house.
La Palma, Canary Islands
La Palma is a stratovolcano with seven historic  eruptions.  Two eruptions caused fatalities.  In 1677, one man and many  animals were killed by gas.
Volcanic gases in Hawaii are not fatal but vog  (volcanic smog) may degrade lung function and compromise peoples  immune systems, especially in children, individuals with  chronic asthma or other respiratory impairments, or people with  circulatory problems.
Source of Information:
Simkin, T., and Siebert, L., 1994, Volcanoes of the  World: Geoscience Press, Tucson, Arizona, 349 p.
Case Studies
eruptions.  The Toba eruption may have caused about 3 to 4 degree C cooling at the surface but this impact is hard to detect  because of concurrent glacial conditions (Sigurdsson, 1990).
For More Information
Relevant peer reviewed journal references include:
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volcano
: Geophysical Research  Letters, v. 5, p. 245.
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Bluth, G.J.S., Doiron, S.D., Schnetzler, C.C., Krueger, A.J., and  Walter, L.S., 1992, Global tracking of the SO2 clouds from the June, 1991 Mount  Pinatubo eruptions, Geophys. Res. Lett., v. 19, p. 151-154.
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Fumarole
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