Volcanic Gases: Effects and Composition PDF

Ninety-nine percent of the gas molecules emitted during a volcanic eruption are water vapor (H ~2~ O), carbon dioxide (CO ~2~ ), and sulfur dioxide (SO ~2~ ) . The remaining one percent is comprised of small amounts of hydrogen sulfide, carbon monoxide, hydrogen chloride, hydrogen fluoride, and othe...

Ninety-nine percent of the gas molecules emitted during a volcanic eruption are water vapor (H ~2~ O), carbon dioxide (CO ~2~ ), and sulfur dioxide (SO ~2~ ) . The remaining one percent is comprised of small amounts of hydrogen sulfide, carbon monoxide, hydrogen chloride, hydrogen fluoride, and other minor gas species. How do volcanic gases affect people? Inhaling volcanic gases and ash can be harmful to your health. Breathing in volcanic gases at high concentrations can cause mild symptoms, such as irritation of the eyes, and more severe symptoms, such as difficulty breathing or even death  Volcanic gases were directly responsible for approximately 3% of all volcano-related deaths of humans between 1900 and 1986.[^\[4\]^](https://en.wikipedia.org/wiki/Volcanic_gas#cite_note-Encyclovolc-4) Some volcanic gases kill by acidic [corrosion](https://en.wikipedia.org/wiki/Corrosion); others kill by [asphyxiation](https://en.wikipedia.org/wiki/Asphyxiation). Some volcanic gases including sulfur dioxide, hydrogen chloride, hydrogen sulfide and hydrogen fluoride react with other atmospheric particles to form [aerosols](https://en.wikipedia.org/wiki/Aerosol).[^\[4\]^](https://en.wikipedia.org/wiki/Volcanic_gas#cite_note-Encyclovolc-4) **Volcanic gases** are gases given off by active (or, at times, by dormant) [volcanoes](https://en.wikipedia.org/wiki/Volcano). These include gases trapped in cavities ([vesicles](https://en.wikipedia.org/wiki/Vesicular_texture)) in [volcanic rocks](https://en.wikipedia.org/wiki/Volcanic_rock), dissolved or dissociated [gases](https://en.wikipedia.org/wiki/Gas) in [magma](https://en.wikipedia.org/wiki/Magma) and [lava](https://en.wikipedia.org/wiki/Lava), or gases emanating from lava, from volcanic craters or vents. Volcanic gases can also be emitted through [groundwater heated by volcanic action](https://en.wikipedia.org/wiki/Hydrothermal). The sources of volcanic gases on Earth include: - primordial and recycled constituents from the [Earth\'s mantle](https://en.wikipedia.org/wiki/Earth%27s_mantle), - assimilated constituents from the [Earth\'s crust](https://en.wikipedia.org/wiki/Earth%27s_crust), - [groundwater](https://en.wikipedia.org/wiki/Groundwater) and the [Earth\'s atmosphere](https://en.wikipedia.org/wiki/Atmosphere_of_Earth). Substances that may become gaseous or give off gases when heated are termed volatile substances. **Composition** \[(https://en.wikipedia.org/w/index.php?title=Volcanic_gas&action=edit&section=1)\] Sketch showing typical [carbon dioxide emission](https://en.wikipedia.org/wiki/Greenhouse_gas_emissions) patterns from volcanic and magmatic systemsAverage carbon dioxide (CO~2~) emissions of subaerial volcanoes globally from the time period of 2005 to 2017Degassing at the summit [crater](https://en.wikipedia.org/wiki/Volcanic_crater) of [Villarrica, Chile](https://en.wikipedia.org/wiki/Villarrica,_Chile) The principal components of volcanic gases are [water vapor](https://en.wikipedia.org/wiki/Water_vapor) (H~2~O), [carbon dioxide](https://en.wikipedia.org/wiki/Carbon_dioxide) (CO~2~), [sulfur](https://en.wikipedia.org/wiki/Sulfur) either as [sulfur dioxide](https://en.wikipedia.org/wiki/Sulfur_dioxide) (SO~2~) (high-temperature volcanic gases) or [hydrogen sulfide](https://en.wikipedia.org/wiki/Hydrogen_sulfide) (H~2~S) (low-temperature volcanic gases), [nitrogen](https://en.wikipedia.org/wiki/Nitrogen), [argon](https://en.wikipedia.org/wiki/Argon), [helium](https://en.wikipedia.org/wiki/Helium), [neon](https://en.wikipedia.org/wiki/Neon), [methane](https://en.wikipedia.org/wiki/Methane), [carbon monoxide](https://en.wikipedia.org/wiki/Carbon_monoxide) and [hydrogen](https://en.wikipedia.org/wiki/Hydrogen). Other [compounds](https://en.wikipedia.org/wiki/Compound_(chemistry)) detected in volcanic gases are [oxygen](https://en.wikipedia.org/wiki/Oxygen) (meteoric)^\[[*clarification\ needed*](https://en.wikipedia.org/wiki/Wikipedia:Please_clarify)\]^, [hydrogen chloride](https://en.wikipedia.org/wiki/Hydrogen_chloride), [hydrogen fluoride](https://en.wikipedia.org/wiki/Hydrogen_fluoride), [hydrogen bromide](https://en.wikipedia.org/wiki/Hydrogen_bromide), [sulfur hexafluoride](https://en.wikipedia.org/wiki/Sulfur_hexafluoride), [carbonyl sulfide](https://en.wikipedia.org/wiki/Carbonyl_sulfide), and [organic compounds](https://en.wikipedia.org/wiki/Organic_compounds). Exotic trace compounds include [mercury](https://en.wikipedia.org/wiki/Mercury_compounds),[^\[1\]^](https://en.wikipedia.org/wiki/Volcanic_gas#cite_note-1) [halocarbons](https://en.wikipedia.org/wiki/Halocarbons) (including [CFCs](https://en.wikipedia.org/wiki/Chlorofluorocarbon)),[^\[2\]^](https://en.wikipedia.org/wiki/Volcanic_gas#cite_note-2) and [halogen](https://en.wikipedia.org/wiki/Halogen) [oxide](https://en.wikipedia.org/wiki/Oxide) [radicals](https://en.wikipedia.org/wiki/Radical_(chemistry)).[^\[3\]^](https://en.wikipedia.org/wiki/Volcanic_gas#cite_note-3) The abundance of gases varies considerably from volcano to volcano, with volcanic activity and with tectonic setting. Water vapour is consistently the most abundant volcanic gas, normally comprising more than 60% of total emissions. Carbon dioxide typically accounts for 10 to 40% of emissions.[^\[4\]^](https://en.wikipedia.org/wiki/Volcanic_gas#cite_note-Encyclovolc-4) Volcanoes located at [convergent plate](https://en.wikipedia.org/wiki/Convergent_plate) boundaries emit more water vapor and [chlorine](https://en.wikipedia.org/wiki/Chlorine) than volcanoes at [hot spots](https://en.wikipedia.org/wiki/Hotspot_(geology)) or [divergent plate](https://en.wikipedia.org/wiki/Divergent_plate) boundaries. This is caused by the addition of seawater into magmas formed at [subduction zones](https://en.wikipedia.org/wiki/Subduction_zone). Convergent plate boundary volcanoes also have higher H~2~O/H~2~, H~2~O/CO~2~, CO~2~/He and N~2~/He ratios than [hot spot](https://en.wikipedia.org/wiki/Hotspot_(geology)) or divergent plate boundary volcanoes.[^\[4\]^](https://en.wikipedia.org/wiki/Volcanic_gas#cite_note-Encyclovolc-4) **Magmatic gases and high-temperature volcanic gases** \[(https://en.wikipedia.org/w/index.php?title=Volcanic_gas&action=edit&section=2)\] Magma contains dissolved [volatile components](https://en.wikipedia.org/wiki/Volatile_(astrogeology)#Igneous_petrology), as described above. The solubilities of the different volatile constituents are dependent on pressure, temperature and the composition of the [magma](https://en.wikipedia.org/wiki/Magma). As magma ascends towards the surface, the ambient pressure decreases, which decreases the solubility of the dissolved volatiles. Once the solubility decreases below the volatile concentration, the volatiles will tend to come out of solution within the magma (exsolve) and form a separate gas phase (the magma is [super-saturated](https://en.wikipedia.org/wiki/Supersaturation) in volatiles). The gas will initially be distributed throughout the magma as small bubbles, that cannot rise quickly through the magma. As the magma ascends the bubbles grow through a combination of expansion through decompression and growth as the solubility of volatiles in the magma decreases further causing more gas to exsolve. Depending on the viscosity of the magma, the bubbles may start to rise through the magma and coalesce, or they remain relatively fixed in place until they begin to connect and form a continuously connected network. In the former case, the bubbles may rise through the magma and accumulate at a vertical surface, e.g. the \'roof\' of a magma chamber. In volcanoes with an open path to the surface, e.g. [Stromboli](https://en.wikipedia.org/wiki/Stromboli) in [Italy](https://en.wikipedia.org/wiki/Italy), the bubbles may reach the surface and as they pop small explosions occur. In the latter case, the gas can flow rapidly through the continuous permeable network towards the surface. This mechanism has been used to explain activity at Santiaguito, [Santa Maria volcano](https://en.wikipedia.org/wiki/Santa_Mar%C3%ADa_(volcano)), [Guatemala](https://en.wikipedia.org/wiki/Guatemala)[^\[5\]^](https://en.wikipedia.org/wiki/Volcanic_gas#cite_note-5) and [Soufrière Hills](https://en.wikipedia.org/wiki/Soufri%C3%A8re_Hills) Volcano, [Montserrat](https://en.wikipedia.org/wiki/Montserrat).[^\[6\]^](https://en.wikipedia.org/wiki/Volcanic_gas#cite_note-6) If the gas cannot escape fast enough from the magma, it will fragment the magma into small particles of ash. The fluidised ash has a much lower resistance to motion than the viscous magma, so accelerates, causing further expansion of the gases and acceleration of the mixture. This sequence of events drives explosive volcanism. Whether gas can escape gently (passive eruptions) or not (explosive eruptions) is determined by the total volatile contents of the initial magma and the [viscosity](https://en.wikipedia.org/wiki/Viscosity) of the magma, which is controlled by its composition. The term \'closed system\' degassing refers to the case where gas and its parent magma ascend together and in [equilibrium](https://en.wikipedia.org/wiki/Chemical_equilibrium) with each other. The composition of the emitted gas is in equilibrium with the composition of the magma at the pressure, temperature where the gas leaves the system. In \'open system\' degassing, the gas leaves its parent magma and rises up through the overlying magma without remaining in equilibrium with that magma. The gas released at the surface has a composition that is a mass-flow average of the magma exsolved at various depths and is not representative of the magma conditions at any one depth. Molten rock (either magma or lava) near the atmosphere releases high-temperature volcanic gas (\>400 °C). In explosive [volcanic eruptions](https://en.wikipedia.org/wiki/Volcanic_eruption), the sudden release of gases from magma may cause rapid movements of the molten rock. When the magma encounters water, seawater, lake water or groundwater, it can be rapidly fragmented. The rapid expansion of gases is the driving mechanism of most explosive volcanic eruptions. However, a significant portion of volcanic gas release occurs during quasi-continuous quiescent phases of active volcanism. **Low-temperature volcanic gases and hydrothermal systems** \[(https://en.wikipedia.org/w/index.php?title=Volcanic_gas&action=edit&section=3)\] As magmatic gas travelling upward encounters [meteoric water](https://en.wikipedia.org/wiki/Meteoric_water) in an [aquifer](https://en.wikipedia.org/wiki/Aquifer), steam is produced. Latent magmatic heat can also cause meteoric waters to ascend as a vapour phase. Extended fluid-rock interaction of this hot mixture can leach constituents out of the cooling magmatic rock and also the [country rock](https://en.wikipedia.org/wiki/Country_rock_(geology)), causing volume changes and phase transitions, reactions and thus an increase in [ionic strength](https://en.wikipedia.org/wiki/Ionic_strength) of the upward percolating fluid. This process also decreases the fluid\'s [pH](https://en.wikipedia.org/wiki/PH). Cooling can cause [phase separation](https://en.wikipedia.org/wiki/Phase_separation) and [mineral](https://en.wikipedia.org/wiki/Mineral) deposition, accompanied by a shift toward more reducing conditions. At the surface expression of such [hydrothermal](https://en.wikipedia.org/wiki/Hydrothermal) systems, low-temperature volcanic gases (\