Volcanic eruptions released dissolved gases from magma into the atmosphere. The gases that are released from magma remains in ground and then it rising towards the surface of the earth. In these sort of cases, the gases may escape directly into the environment from volcanic vents, soil, hydrothermal systems and fumaroles. A number of different gases including CO2,CO and water vapour are injected during volcanic activity.90% of emitted gases are water and carbon dioxide(Natural hazards ,Edward A Keller, Robert H Blodgett).These emitted gases cause lot of problems like health problems to the human beings and the plants in the earth and sometimes it leads to the death of human beings. In this paper we are going to discuss volcanic gases and their effects on the atmosphere .
Volcanic gases are dissolved in molten rock at very high pressures deeply under the earth's surface. These gases held in the molten rock begin to form tiny bubbles when the magma rises to the earth's surface ,where the pressure is lower. Because of the increased volume of the gas bubbles, magma become less dense than surrounding rock, this helps the magma to continue its movement to the surface of the earth . Closer to the surface of the earth ,these gas bubbles increase in size and number so that the volume of the gas may exceed over the melt volume in magma and this causes to the formation of magma foam." These rapidly expanding gas bubbles of the foam can lead to highly explosive volcanic eruptions which causes the melt to fragmented into pieces of volcanic rock, called as" tephra". Volcanic gases increase tremendously in volume when magma rises to the Earth's surface and erupts. The most abundant gas injected into the environment from volcanic eruption is in the order of water vapour, followed by carbon dioxide(CO2)and sulphur dioxide(SO2)".Volcanoes also release some other gases in smaller amounts including hydrogen (H2),Hydrogensulfide (H2S),hydrogen (H2),carbonmonoxide (CO),Helium (He),hydrogen chloride (HCL) and hydrogenfluoride (HF) (Ref: Volcanic Gases and Their Effects, Volcano Hazards Program, NRC)
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TABLE 1: Examples of volcanic gas compositions ,in volume percent concentrations(Symonds et.al.,1994)
We have to discuss about each volcanic gases in detail for understanding the effects of volcanic gases in the atmosphere.
1 Sulphur dioxide(SO2)
"The effects of S02 on the environment vary widely depends on (1)the amount of gas a volcano injects into the atmosphere (2) whether the gas is injected into the troposphere or stratosphere". Sulphur dioxide (SO2) gas is a colorless one with a pungent odor that affects the tissues ,skin and mucous membranes of the eyes, throat and nose. Sulfur dioxide mainly affects respiratory system and bronchi.SO2 injects into atmosphere and it causes volcanic air pollution .Sulphur dioxide also causes to form volcanic smog by reacts it chemically with oxygen, sunlight ,water and dust particles .The SO2 gas also playing an important role in the destruction of the ozone layer of the earth.
Hydrogen sulfide is a colorless gas with an offensive order. At some points it irritates the eyes and the upper respiratory system. It also causes some diseases like headache, excitement, diarrhea and bronchitis.
Volcanoes release almost 130 million tonnes of CO2 into the environment every year. This colorless gas does not leads to a hazard to the life of human beings because it dilutes very easily to low concentrations .If we breath air which contains more than 30% of carbon dioxide can cause unconsciousness and automatically it leads to death. The presence of 6-10% of CO2 in air causes some problems for breathing ,sweating and dizziness.
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The volcanoes emitted chlorine gas in the form of hydrogen chloride. This gas causes some irritations on the mucous membranes of the eyes. If the hydrogen chloride concentration is higher it causes some kind of irritation for the throat. Hydrogen chloride is the another main reason for the occurrence of acid rain in the earth.
Hydrogen fluoride is actually yellow gas containing fine ash particles, and pollutes lakes and streams. If we expose to this gas even for a short time it causes conjunctivitis, bone degeneration and skin irritation. It also causes death of animals by strongly affecting their bones.
EFFECTS OF VOLCANIC GASES ON VEGETATION
The volcanic gases play an important role in maintaining the atmospheric physics and chemistry with implications in terms of evolution of life. The development of continental basalt provinces and igneous provinces coincides with extinction events and it causes the emission of large volume of gases namely carbon dioxide ,sulphur dioxide and hydrogen sulfide into the environment. The volcanic gases are important factors that restricting the development of vegetation and during the period of global scale volcanism it could have been responsible for the death of vegetation . Hydrogen sulfide is sometimes considered to be phytotoxin, being harmful to the development and growth of plants especially when the gas quantities are much higher than the plant necessity. Moreover the plants are absorbed atmospheric pollutants produced by volcanic gases such as hydrogen sulfide and sulfur dioxide and volcanic activity via the stomata as well as the cuticle. The plants which are exposed to highly poisonous volcanic gases may show symptoms of damage including defoliation and death. However the plant damage is mainly related to identity of the gases ,gas concentration, plant resilience and gas persistence in the atmosphere.
THE EFFECTS OF VOLCANIC GASES ON CLIMATE
The volcanic plumes deposits toxic gases and fine ash particles in to the atmosphere and it leads to notable temperature change in the atmosphere. The effect on climatic change by the volcanic eruptions depends mainly on its ability to emit gases into the stratosphere and on the date of eruption. The volcanic eruptions however are associated with widely spread strong lava flows which lose heat in large amounts and generate convection in the atmosphere. This type of convection known as penetrative convection acts to erode the lower atmosphere and generates thick heated atmospheric layer in a short period of time. This layer provides buoyancy forces which always ensures that volcanic gases get moved to the stratosphere. In the atmosphere ,buoyant plumes are often made by man from nuclear explosions and oil fires or from products of industries. They are also formed by natural phenomena such as volcanic eruptions and forest fires. These volcanic plumes consist of vertical upwellings carrying number of solid and gaseous components such as ash particles and volcanic gases. The explosive volcanic eruptions impact very severely on the environment such as ash deposits and acid rains and the powerful deposit induces global climate change. For example ,the eruption of Mount Pinatubo released almost twenty five megatons of aerosols in the atmosphere. This causes to a slight increase in the average temperature in summer of about 10C and to a slight decrease in average winter temperature of almost 0.50C.The Laki eruption in 1783 which emitted large amount of sulfur dioxide almost ten times than the Pinatubo eruption in 1991,led to the high summer temperatures in Europe and it also causes very cold winter and air pollution over Northern hemisphere.
Figure 1: Emission of SO2 gas from Mount Pinatubo on June 15,1991(ref:Volcanic Gases and Climate Change Overview,Volcano Hazards Program,NRC)
While sulfur dioxide emitted in volcanic eruptions has occasionally caused detectable cooling of lower atmosphere, but the carbon dioxide emitted by volcanic activities has never produced any detectable cooling of atmosphere that is because CO2 is a green house gas and makes the atmosphere heat up generally.
EXAMPLES FOR VOLCANIC GAS EMISSION AND ITS BAD EFFECTS ON THE ATMOSPHERE
In the past there are lot of volcanic gas emissions into the atmosphere are happened from different volcanoes quite regularly. We can go through one of the volcanic gas emissions happened at Cameroon highlands of Africa. In August 1986,Nyos lake released misty cloud of dense gas mainly carbon dioxide. The CO2 gas emitted from these volcanoes into the valleys and the farm fields and displaced the air. Then the gas cloud became invisible as it loses its water droplets and then it spreads silently through the five villages. The gas cloud travelled almost 23 km from the Nyos lake suffocating more than 1742 people and countless other animals. Lake Nyos is now continuously accumulating CO2 in the lake and there is a chance for another carbon dioxide release at any time. Scientists now studying the hazards now people are returning to farm the land very close to the lake. An alarm system has installed by the scientists at the lake for detecting the level of carbon dioxide in the lake. This alarm will make a sound if the C02 level in the lake increases beyond a certain level. They have also set up a pipe from the bottom of the lake to the degassing station on the surface of the lake ,it helps to escape carbon dioxide gas into the atmosphere. The hazard is now reduced slowly because the degassing station now releasing more gas to the atmosphere than it releasing normally. The fluorine which contained in the cloud contaminated pastures and caused the death of cattles within two days. In some cases the volcanic chemicals contaminated the soil and plants absorbed these chemicals and eaten by people and it causes death of the people.
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EFFECTS OF VOLCANIC GASES ON STRATOSPHERIC CHEMISTRY
In this topic we are going to discuss about the importance of volcanic gas emissions on the atmospheric chemistry focusing mainly on the troposphere and stratosphere. The strong explosive volcanic eruptions which penetrating through the stratosphere impact directly on the stratospheric chemistry and also on the climate. These explosive volcanic eruptions occur every 5.5 years and emits large amounts of volcanic gases like sulphur and other gas SO2 oxidised to form sulphate in the stratosphere. The volcanic gas sulphur reacts with other non-volcanic compounds like carbonyl sulphide to form the jungle layer. This global aerosol layer causes cooling of the lower atmosphere by reflecting sunlight and it also causes local heating because of absorption of sunlight. These aerosol particles provide the surface for the chemical reactions which cause stratospheric ozone depletion.
EFFECT OF VOLCANIC GASES ON TROPOSPHERIC CHEMISTRY
Volcanoes emit large amount of sulphur compounds into the atmosphere and these sulphur compounds lead to the acid deposition on the atmosphere and the radioactive effects of sulphate aerosol. These sulphate aerosols cause the cooling of the earth's surface by scattering sunlight into the space.
VOLCANIC HAZARD REDUCTION TECHNIQUES
We should have to recognise the changes in chemical composition ,that is the primary objective of monitoring volcanic gas emissions.
Monitoring Volcanic Gas Emissions
The changes in relative amounts of sulfur dioxide and carbon dioxide and changes in gas emission rates are correlated with subsurface volcanic processes. These changes are helpful to indicate the movement of magma towards the surface.
Electro chemical sensing of volcanic eruptions
This is another form of detecting volcanic gas emissions from the volcanoes. Electrochemical sensors are installed into a circuit to trigger an alarm ,is used as a warning system if a gas leak detected from the volcanoes. A wide range of low cost electro chemical sensors are commercially developed in the industries to detect the presence of gases like H2S,S02 and CO. These electro chemical sensors have integrated into lot of highly portable devices for monitoring of environmental polluted regions mainly volcanic plumes.
"National volcano Early Warning System"
This is an another type of volcanoes waning system. This is a proposed national scale plan for making sure that volcanoes are monitored and detected properly without any threats to the atmosphere. This plan was formed by volcano hazards programme conducted by U.S geological survey. Currently most of the volcanoes contain insufficient systems for monitoring gas emissions like continuous gps system and seismometers and other volcanoes have outdated equipments. This system ensures that most of the hazardous volcanoes are properly monitored ,making it possible for scientists to improve the accuracy of hazard detection and timeliness and it also help people to take proper action to eliminate risk. This plan got good results as it helped for identifying 57 active volcanoes under monitored for the threats posed ,and then scientists target these volcanoes for improved monitoring networks.
Fourier Transform Infra-red Spectroscopy
This is another important widely used technique for measuring different volcanic gases mainly HCL,SO2,HF,H2O,CH4,CO2 and CO etc. This technology was applied for the first time in volcanology in 1990s when a first compact FTIR spectrometer was introduced. This is mainly used for measuring gas ratios and to calculate fluxes of the volcanic gases by using S02 fluxes. Sulfur dioxide fluxes can be measured directly by using FTIR. There are two types of FTIR measurements namely passive and active measurements.
From this paper we can understand that volcanic emissions are very dangerous hazards to the human beings ,animals and plants in the atmosphere. So the environmental scientists should do a proper study about these volcanic hazards and its effects and they should have to find out advanced technologies for detecting the volcanic emissions .In addition to the above mentioned technologies, in the near future unmanned aerial vehicles should be a key platform for investigating volcanic gases at very affordable costs compared to manned aircraft and it also reduces the risk for the persons who involved in this investigation. Atmospheric scientists should use improved numerical models to know information about volcanic gas emissions.