Volcanic gases include a variety of substances given off by active (or, at times, by dormant) volcanoes. Plate tectonics and hotspots Divergent plate boundaries At the These include gases trapped in cavities (vesicles) in volcanic rocks, dissolved or dissociated gases in magma and lava, or gases emanating directly from lava or indirectly through ground water heated by volcanic action. Volcanic rock is an Igneous rock of volcanic origin Texture Volcanic rocks are usually fine-grained or Aphanitic to glassy in This page is about the physical properties of gas as a state of matter Magma (Plurals magmas and magmata) is molten rock that sometimes forms beneath the surface of the Earth (or any other Terrestrial planet Lava is molten rock expelled by a Volcano during an eruption When first expelled from a volcanic vent it is a Liquid at Temperatures Hydrothermal circulation in its most general sense is the circulation of hot water 'hydros' in the Greek meaning water and 'thermos' meaning heat
The sources of volcanic gases on Earth include:
Substances that may become gaseous or give off gases when heated are termed volatile substances.
Gases are released from magma through volatile constituents reaching such high concentrations in the base magma that they evaporate. Magma (Plurals magmas and magmata) is molten rock that sometimes forms beneath the surface of the Earth (or any other Terrestrial planet (Technically, this would be described as the exsolution and accumulation of the gases upon reaching excess supersaturation of these constituents in the host solution (magmatic melt), and their subsequent loss from the host by diffusion and phase separation into bubbles). Diffusion is the net movement of particles (typically molecules from an area of high concentration to an area of low concentration by uncoordinated random movement In the Physical sciences a phase is a Set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties Molten rock (either magma or lava) near the atmosphere releases high-temperature volcanic gas (>400 °C). Magma (Plurals magmas and magmata) is molten rock that sometimes forms beneath the surface of the Earth (or any other Terrestrial planet Lava is molten rock expelled by a Volcano during an eruption When first expelled from a volcanic vent it is a Liquid at Temperatures Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five In explosive volcanic eruptions, 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.
If the magmatic gas traveling upward encounters meteoric water in an aquifer, steam is produced. An aquifer is an underground layer of Water -bearing Permeable rock or unconsolidated materials ( Gravel, Sand, Silt, or Clay Latent magmatic heat can also cause meteoric waters to ascent 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, causing volume changes and phase transitions, reactions and thus an increase in ionic strength of the upward percolating fluid. Country rock is a geological term meaning the rock native to an area The ionic strength, I, of a solution is a function of the Concentration of all Ions present in a Solution. This process also decreases the fluid's pH. pH is the measure of the acidity or alkalinity of a Solution. Cooling can cause phase separation and mineral deposition, accompanied by a shift toward more reducing conditions. In the Physical sciences a phase is a Set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition a highly ordered atomic structure and specific At the surface expression of such hydrothermal systems, low-temperature volcanic gases (<400 °C) are either emanating as steam-gas mixtures or in dissolved form in hot springs. Hydrothermal circulation in its most general sense is the circulation of hot water 'hydros' in the Greek meaning water and 'thermos' meaning heat A hot spring is a spring that is produced by the emergence of geothermally heated Groundwater from the earth's crust. At the ocean floor, such hot supersaturated hydrothermal fluids form gigantic chimney structures called black smokers, at the point of emission into the cold seawater. A black smoker or sea vent is a type of Hydrothermal vent found on the Ocean floor. Seawater is Water from a Sea or Ocean. On average seawater in the world's oceans has a Salinity of about 3
The gas release can occur by advection through fractures, or via diffuse degassing through large areas of permeable ground as Diffuse Degassing Structures (DDS). At sites of advective gas loss, precipitation of sulfur and rare salts forms sulfur deposits and small sulfur chimneys, called fumaroles. Very low-temperature <100 °C) fumarolic structures are also known as solfataras. Sites of cold degassing of predominantly carbon dioxide are called mofettes. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single Mofetta (Italian from Latin mephitis a pestilential exhalation is a name applied to a Volcanic discharge consisting chiefly of Carbon dioxide, often associated Hot springs on volcanoes often show a measurable amount of magmatic gas in dissolved form. A hot spring is a spring that is produced by the emergence of geothermally heated Groundwater from the earth's crust.
The principal components of volcanic gases are water vapor (H2O), carbon dioxide (CO2), sulfur either as sulfur dioxide (SO2) (high-temperature volcanic gases) or hydrogen sulfide (H2S) (low-temperature volcanic gases), nitrogen, argon, helium, neon, methane, carbon monoxide and hydrogen. General properties of water vapor Evaporation/sublimation Whenever a water molecule leaves a surface it is said to have evaporated Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single Sulfur or sulphur (ˈsʌlfɚ see spelling below) is the Chemical element that has the Atomic number 16 Hydrogen sulfide (or hydrogen sulphide) is the Chemical compound with the formula H 2 S. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 This article pertains to the chemical element For other uses see Argon (disambiguation. Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical Neon (ˈniːɒn is the Chemical element that has the symbol Ne and Atomic number 10 Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. Carbon monoxide, with the chemical formula CO is a colorless odorless tasteless yet highly toxic Gas. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Other compounds detected in volcanic gases are oxygen (meteoric), hydrogen chloride, hydrogen fluoride, hydrogen bromide, nitrogen oxide (NOx), sulfur hexafluoride, carbonyl sulfide, and organic compounds. A chemical compound is a substance consisting of two or more different elements chemically bonded together in a fixed proportion by Mass. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Structure HF forms orthorhombic crystals consisting of zig-zag chains of HF molecules Hydrogen bromide is the diatomic molecule H[[Bromine Br]] Under standard conditions HBr is a gas but it can be liquified The term nitrogen oxide typically refers to any Binary compound of Oxygen and Nitrogen, or to a mixture of such compounds Nitric Sulfur hexafluoride is an Inorganic compound with the formula. Carbonyl sulfide is the Chemical compound with the formula OCS An organic compound is any member of a large class of Chemical compounds whose Molecules contain Carbon. Exotic trace compounds include methyl mercury, halocarbons (including CFCs), and halogen oxide radicals. Methylmercury (sometimes methyl mercury) is an Organometallic Cation with the formula + Halocarbon compounds are Chemicals in which one or more Carbon Atoms are linked by Covalent bonds with one or more Halogen Atoms Abundance Owing to their high Reactivity, the halogens are found in the environment only in compounds or as Ions Halide ions and oxoanions An oxide is a Chemical compound containing at least one Oxygen atom as well as at least one other element In Chemistry, radicals (often referred to as free radicals) are atoms molecules or ions with Unpaired electrons on an otherwise Open shell
The abundance of gases varies considerably from volcano to volcano. However, water vapor is consistently the most common volcanic gas, normally comprising more than 60% of total emissions. Carbon dioxide typically accounts for 10 to 40% of emissons. 
Volcanoes located at convergent plate boundaries emit more water vapor and chlorine than volcanoes at hot spots or divergent plate boundaries. In Plate tectonics, a convergent boundary – also known as a convergent plate boundary or a destructive plate boundary – is an actively deforming region Chlorine (ˈklɔriːn from the Greek word 'χλωρóς' ( khlôros, meaning 'pale green' is the Chemical element with Atomic number 17 and HotSpot is the primary Java Virtual Machine for desktops and servers produced by Sun Microsystems. In Plate tectonics, a divergent boundary or divergent plate boundary (also known as a constructive boundary or an extensional boundary) is a This is caused by the addition of seawater into magmas formed at subduction zones. In Geology, a subduction zone is an area on Earth where two tectonic plates meet and move towards one another with one sliding underneath the other Convergent plate boundary volcanoes also have higher H2O/H2, H2O/CO2, CO2/He and N2/He ratios than hot spot or divergent plate boundary volcanoes. HotSpot is the primary Java Virtual Machine for desktops and servers produced by Sun Microsystems. 
Volcanic gases can be sensed (measured in-situ) or sampled for further analysis. Volcanic gas sensing can be:
Volcanic gas sampling is often done by a method involving an evacuated flask with caustic solution, first used by Robert W. Bunsen (1811-1899) and later refined by the German chemist Werner F. Robert Wilhelm Eberhard Bunsen (31 March 1811 &ndash 16 August 1899 was a German Chemist. Giggenbach (1937-1997), dubbed Giggenbach-bottle. Other methods include collection in evacuated empty containers, in flow-through glass tubes, in gas wash bottles (cryogenic scrubbers), on impregnated filter packs and on solid adsorbent tubes.
Analytical techniques for gas samples comprise gas chromatography with thermal conductivity detection (TCD), flame ionization detection (FID) and mass spectrometry (GC-MS) for gases, and various wet chemical techniques for dissolved species (e. Chromatography (from Greek χρώμα chroma, color and γραφειν"graphein" to write is the collective term for a family of Laboratory In Physics, thermal conductivity, k is the property of a material that indicates its ability to conduct Heat. A flame ionization detector (FID is a type of Gas detector used in Gas chromatography The first flame ionization detector was developed in 1957 by scientists Mass spectrometry is an analytical technique that identifies the chemical composition of a compound or sample based on the Mass-to-charge ratio of charged particles g. , acidimetric titration for dissolved CO2, and ion chromatography for sulfate, chloride, fluoride). Titration is a common laboratory method of Quantitative chemical analysis that is used to determine the unknown Concentration of a known Reactant Ion-exchange chromatography (or ion chromatography) is a process that allows the separation of Ions and Polar molecules based on the charge properties of The chloride Ion is formed when the element Chlorine picks up one Electron to form an Anion (negatively-charged ion Cl&minus Fluoride is the reduced form of Fluorine. Both organic and Inorganic compounds containing the element fluorine are considered fluorides The trace metal, trace organic and isotopic composition is usually determined by different mass spectrometric methods. Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides
Certain constituents of volcanic gases may show very early signs of changing conditions at depth, making them a powerful tool to predict imminent unrest. Used in conjunction with monitoring data on seismicity and deformation, correlative monitoring gains great efficiency. Harmonic tremor describes a continuous rhythmic Earthquake in the Earth's upper Lithosphere that can be detected by a Seismograph and often precedes or In Materials science, deformation is a change in the shape or size of an object due to an applied force. Volcanic gas monitoring is a standard tool of any volcano observatory. A volcano observatory is an institution that conducts research and monitoring of a Volcano. Unfortunately, the most precise compositional data still require dangerous field sampling campaigns. However, remote sensing techniques have advanced tremendously through the 1990s. Remote sensing is the small or large-scale acquisition of information of an object or phenomenon by the use of either recording or real-time sensing device(s that is not in physical
Volcanic gases were directly responsible for approximately 3% of all volcano-related deaths of humans between 1900 and 1986.  Some volcanic gases kill by acidic corrosion; others kill by asphyxiation. Corrosion means the breaking down of essential properties in a material due to Chemical reactions with its surroundings The greenhouse gas, carbon dioxide, is emitted from volcanoes, although volcanic emissions account for less than 1% of the annual global total. Greenhouse gases are gaseous constituents of the atmosphere bothnatural and anthropogenic that absorb and emit radiation at specific wavelengths within the spectrum of thermal infrared  Some volcanic gases including sulfur dioxide, hydrogen chloride, hydrogen sulfide and hydrogen fluoride react with other atmospheric particles to form aerosols. Technically an aerosol is a suspension of fine solid particles or liquid droplets in a gas