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Chapter 57

Hazards of Volcanic

Glyn Williams-Jones Department of Sciences, Simon Fraser University, Burnaby, BC, Canada

Hazel Rymer Faculty of Science, The Open University, Walton Hall, Milton Keynes, UK

Chapter Outline 3.3. H2S 990 1. Introduction 985 3.4. HCl Hazards 990 2. Toxicity of Volcanic Species 985 3.5. HF Hazards 990 3. Hazards to Population and the Environment: 4. Gas Mitigation 991 Case Studies 987 5. Summary 991 3.1. CO2 Hazards 988 Further Reading 991 3.2. SO2 Hazards 989

GLOSSARY hazardous and responsible for deaths every year. They have an important effect on the regional and global environment A colloidal dispersion of liquid particles in a gas, e.g., SO2, and may contribute greenhouse gases to the . which will react with the OH in the atmosphere to form Indirectly, through the destruction of crops, tiny droplets of (H2SO4). hazard In a volcanic context, hazard refers to the phenomena pro- emissions have resulted in starvation and disease (40% of duced by a volcanic event and is directly related to Risk, where -related deaths between 1600 and 1982). Risk ¼ Hazard Vulnerability, with vulnerability referring to the The composition of volcanic gases depends on the type consequences for population and infrastructure. of volcano and its eruptive state. However, the most com- PEL The recommended permissible exposure limit to a given mon volcanic gases in order of abundance are (H2O, above which health risks may occur. The 30e90 mol%), dioxide (CO2,5e40 mol%), exposure limit is generally averaged over an 8-h day, 40-h week. It dioxide (SO2,5e50 mol %), (H2, <2 mol%), is measured in parts of compound (e.g., CO ) per million parts of 2 hydrogen sulfide (H2S, <2 mol%), and carbon monoxide air (ppm). (CO, <0.5 mol%). Some of these, when emitted from Gas solubility The maximum amount of a gas that can be dissolved active vents (Figure 57.1), react in the atmosphere or vol- in a given amount of water at 20 C; measured in g/L. canic plume to form , the most important being dgas The vapor density of a gas relative to air (density ¼ 1); measured in g/L. hydrochloric acid (HCl), hydrofluoric acid (HF), and sul- furic acid (H2SO4). 1. INTRODUCTION 2. TOXICITY OF VOLCANIC GAS SPECIES Gases are the invisible yet often continuous products of volcanic activity. Even volcanoes in a state of quiescence, It is difficult to determine accurately the contribution of not actually erupting or showing signs of unrest through gases to volcano-related deaths, since much of the data seismic activity, are able to degas continuously. Eruptions reflect deaths during eruptive periods, whereas the majority can produce lethal quantities of toxic gases, but long-term of gas-related deaths occurred during noneruptive periods. exposure to a lower dose also can pose a significant hazard. The long-term health effects of volcanic gases are poorly Although volcanic gases are only directly responsible for understood; they may be responsible for or accelerate 1e4% of volcano-related deaths, they are nevertheless epidemic diseases because of their irritant and depressing

The Encyclopedia of Volcanoes. http://dx.doi.org/10.1016/B978-0-12-385938-9.00057-2 985 Copyright Ó 2015 Elsevier Inc. All rights reserved. The Encyclopedia of Volcanoes, Second Edition, 2015, 985e992 986 PART | VII

TABLE 57.1 Toxicology of Volcanic Gases and Aerosolsdcont’d

Sulfur dioxide (SO2) Characteristics Colorless gas or liquid (<10 C) with characteristic pungent odor. Perceptible odor at 0.3e1.0 ppm and easily noticeable d ¼ at 3 ppm. gas 2.26 g/L. Gas sol- ubility ¼ 10 g/L. PEL ¼ 5 ppm in air; 13 mg/m3 of air. Effects of overexposure Short-term Inflammation and irritation of the eyes and respiratory tract resulting in burning of the eyes, coughing, and difficulty FIGURE 57.1 Degassing vent of Santiago crater at Masaya volcano, in breathing. Approximately 90% , 2006. of inhaled SO2 is absorbed in the upper respiratory tract, where it forms sulfurous acid which then oxidizes to effects, which reduce the resistance of ocular, respiratory, form sulfuric acid. Concentrations of e and digestive systems to microbial attack. From a health 6 12 ppm cause immediate irritation of nose and throat. Exposure to >20 ppm perspective, the most important volcanic gases and aerosols causes irritation of the eyes, while concen- are CO2,SO2, Rn, H2S, HCl, HF, and H2SO4 ( 57.1). trations of 10,000 ppm irritate moist Exposure to these has been the cause of the majority of skin within minutes. volcanic gas-related fatalities. Long-term Prolonged exposure to low concentrations may be dangerous for persons with preexisting cardiopulmonary diseases.

Hydrogen sulfide (H2S) TABLE 57.1 Toxicology of Volcanic Gases and Aerosols Characteristics Colorless, flammable gas with offensive odor (rotten eggs). Characteristic (CO2) odor perceptible at 0.77 ppm and easily d ¼ Characteristics Colorless odorless gas. Irritation of eyes, noticeable at 4.6 ppm. gas 1.19 g/L. nose, and throat only at high concentra- Gas solubility ¼ 2.9 g/L. PEL (averaged d ¼ 3 tions. Vapor density relative to air ( gas) over 10 min) 20 ppm in air; 28 mg/m ¼ 1.52 g/L. Gas solubility in water at of air. 20 C ¼ 0.14 g/L. Permissible exposure limit (PEL) averaged over 8 h ¼ 5000 ppm Effects of in air; 9000 mg/m3 of air. overexposure e Effects of Short-term Inhalation of 20 150 ppm may cause eye overexposure irritation, while slightly higher concentra- tions cause irritation of upper respiratory Short-term A simple asphyxiant, symptoms appear tract. In low concentrations, exposure only when such high concentrations are may result in headache, fatigue, dizziness, reached that there is insufficient excitement, staggering gait, diarrhea, fol- to support life. Inhalation may cause rapid lowed sometimes by bronchitis and bron- breathing and increase heart rate (at chopneumonia. In small amounts the gas >7.5%), headache, sweating, dizziness, acts as depressant and as stimulant in shortness of breath, muscular weakness, larger amounts. Very large amounts result mental , drowsiness, and ring- in paralysis of the respiratory center and ing in the ears. Concentrations at >11% death; exposure to 1000e2000 ppm may result in unconsciousness in 1 minute or cause coma after a single breath. less. Convulsions may occur at concentra- tions of >25%. Rapid recovery occurs on Long-term Prolonged exposure to concentrations as removal from exposure. low as 50 ppm may cause pharyngitis and bronchitis, while concentrations Long-term Prolonged exposure to concentrations of >250 ppm may result in pulmonary >10% may result in unconsciousness. edema.

The Encyclopedia of Volcanoes, Second Edition, 2015, 985e992 Chapter | 57 Hazards of Volcanic Gases 987

TABLE 57.1 Toxicology of Volcanic Gases and TABLE 57.1 Toxicology of Volcanic Gases and Aerosolsdcont’d Aerosolsdcont’d Radon (Rn) Effects of overexposure Characteristics Colorless, odorless, tasteless, radioactive gas, formed from the Short-term Extreme irritation and of the skin of uranium. and mucous membranes. Contact with the d ¼ ¼ gas 9.73 g/L. Gas solubility 51 g/L. eyes will cause deep-seated burns, and if PEL ¼ 200 the chemical is not removed immediately, Bq/m3. permanent visual impairment or blindness may result. Skin exposure produces severe Effects of burns, which are slow to heal. Subcutane- overexposure ous tissues may be affected becoming Short-term There is no information on the blanched and bloodless, which may result acute noncancerous effects of in gangrene. A severe irritant to the nose, radionuclides in humans; however, throat, and lungs, inhalation of the vapor animal studies have reported may cause ulcers of the upper respiratory e inflammation in the nasal passages tract; concentrations at 50 250 ppm are and kidney damage from acute dangerous even for brief exposures. inhalation exposure to uranium. Long-term Repeated or prolonged exposure to lower Long-term Chronic exposure by inhalation has concentrations may cause changes in the been linked to respiratory disorders, bones as well as chronic irritation of the such as lung disease and lung cancer, nose, throat, and lungs. in humans. Smokers exposed to radon Sulfuric acid (H2SO4) are at w10e20 times greater risk for lung cancer than nonsmokers. Characteristics Colorless to dark brown, oily, odorless liquid. Irritation of nose and eyes at low Hydrochloric acid (HCl) d ¼ concentrations. gas 3.4 g/L. Gas solubi- ¼ Characteristics Colorless gas or colorless fuming l lity miscible in all proportions. ¼ 3 iquid with an irritating pungent PEL 20 ppm in air, 1 mg/m of air. odor. Detectable odor by most people d ¼ Effects of between 1 and 5 ppm. gas 1.27 g/L. overexposure Gas solubility ¼ 62 g/L. PEL ¼ 5 ppm in air; 7 mg/m3 of air. Short-term Irritation of eyes, nose, and throat. Severe burns with rapid destruction of tissue and Effects of erosion of teeth may occur. Inhalation overexposure may also lead to difficulty in breathing Short-term Irritation of the mucous membranes and inflammation of upper respiratory of the eyes and respiratory tract tract. with burning, choking, and coughing. Long-term Repeated or prolonged exposure to the va- At concentrations >35 ppm, there is por may cause erosion of the teeth, chronic irritation of the throat after only irritation of the eyes, nose, throat, and short exposure. Severe breathing lungs. difficulties may occur along with skin inflammation or burns. Concentra- tions >100 ppm will result in pulmonary edema and often 3. HAZARDS TO POPULATION AND THE laryngeal spasm. ENVIRONMENT: CASE STUDIES Long-term Repeated or prolonged exposure may lead to erosion of the teeth and skin The relative degree of hazard from volcanic gases is rash. dependent upon the type of gas emitted. Some gases are Hydrofluoric acid (HF) poisonous, while others are dangerous only if present in such high concentrations that they block oxygen respira- Characteristics Clear, colorless, fuming corrosive tion. The dispersion of a given gas species is also directly liquid or gas with strong irritating odor. Irritation of nose and eyes at <5 ppm. related to the hazard. Emission of gases at high elevations d ¼ ¼ gas 0.7 g/L. Gas solubility miscible in (e.g., Mt Etna, ) will have less direct impact on pop- all proportions. PEL ¼ 3 ppm in air, 2 mg/ ulation than low-level gas plumes (e.g., Masaya, m3 of air. Nicaragua; Kilauea, USA). Relatively short-lived eruptions (Continued) may eject significant amounts of gases into the

The Encyclopedia of Volcanoes, Second Edition, 2015, 985e992 988 PART | VII Volcanic Hazards

with short-term global consequences (e.g., Mt Pinatubo, Monoun and flowed down several hundred Philippines). Persistently active volcanoes, however, degas meters, where it settled along the Panke depression. continuously and may present a long-term hazard The emission was heralded by an heard by the (e.g., , ). In some instances, even dormant people in Njindoun village (1 km north of the lake) and by volcanoes can pose a threat to human health and the local seismic shocks felt 6-km north in the village of Mban- environment (e.g., Long Valley, USA). kouop. At approximately 3 AM, the majority of the victims (39 in total) had left the village of Njindoun and were heading south toward the Foumbot market. The location of 3.1. CO2 Hazards the bodies indicated that the victims encountered and suc- The most lethal CO2-related events have been those in which cumbed to the dense gas cloud near the bridges over the CO2, which is colorless, odorless, and denser than air, flowed Panke River. When police arrived at the scene (w6:30 downhill as a density current, collecting in low-lying areas AM), a whitish smoky cloud still covered the area, drifting and asphyxiating all lives in its path. The first recorded with the wind off Lake Monoun. They were only able to incident of this occurred in the Dieng Volcanic Complex (or enter the area when the cloud had finally dissipated at Dieng ), : a complex of volcanic centers approximately 10:30 AM. It was then that they noted that forming a large depression, approximately 14-km long and the bodies of the victims were covered with reddish first- 6-km wide. On the morning of February 20, 1979, the in- degree burns and blisters and that mucous and blood had habitants of the village of Batur felt three seismic shocks at frothed from their noses and mouths. The surrounding 2:00 AM, 3:30 AM, and 4:00 AM and then observed a vegetation was bleached yellowish and withered, yet the at 5:15 AM, which ejected a dark gray cloud victims’ clothes were unaffected. The carcasses of from the Sinila crater (a small water-filled vent, 3 km domestic and wild animals were also found nearby. northeast of the village). This eruption, which formed a 90-m Between 9:00 PM and 10:00 PM (local time) on August wide and 100-m deep crater, was accompanied by the ejection 21, 1986, just 2 years after the Lake Monoun event, a cloud of blocks and , and gas, and a hot (or of concentrated CO2 was emitted from the lowest point of mudflow) that flowed 3.5 km downslope. At 6:45 AM, a the Nyos and spread into the surrounding second minor eruption occurred 300 m west of Sinila and valleys, affecting an area approximately 20-km long and resulted in the formation of a new crater, Sigludung. Many of 15-km wide. The gas emission appears to have been pre- the villagers from Koputjukan fled west toward Batur and ceded by the rise of a gas column at 4:00 PM and a weak were killed by a gravity current of gas (probably CO2 and explosion at 8:00 PM and then by two or three violent H2S), which was emitted from multiple small vents and fis- between 9:00 and 10:00 PM. No seismic events sures to the south and west of the two craters. Others, having were recorded. There was little or no damage to vegetation witnessed the deaths along the KoputjukaneBatur road, or housing, although taller vegetation was flattened in some retreated to a nearby elementary school, where they were also areas between the lake and Lower Nyos. As with the Lake killed. In total, the gas killed at least 149 people and injured Monoun event, the carcasses of many domestic and wild over 1000 people. animals were found in the affected area (Figure 57.2). The Some volcanic can also pose significant risk due to exact number of casualties is unknown, but according to the accumulation of CO2 and CH4 in thermally stratified government sources, at least 1700 people died, while , which when perturbed can lead to limnic eruptions or catastrophic gas discharge from the lakes. Lake Kivu (on the border between Rwanda and the Democratic Republic of Congo), Lake Monoun, and (Cameroon) are the best examples, with Monoun and Nyos being the only two with recorded events. The CO2 is believed to have originated from cold springs degassing below the lakes, which being thermally stratified, allowed for the gas accumulation. Although still somewhat controversial, it is generally believed that these two events may have been triggered by , which caused the deep gas-rich layer to rise to a point in the lakes where the hydrostatic pressure was insufficient to keep the CO2 in solution. Being denser than air, the CO2 gas that was released formed a large density current, which flowed over the crater rim and downslope. FIGURE 57.2 Cattle asphyxiated by the dense CO2 cloud emitted from On August 15, 1984, at approximately 11:30 PM local Lake Nyos, Cameroon, 1986. Photograph by M.L. Tuttle, U.S. Geological time, a cloud of concentrated CO2 burst from the crater in Survey.

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approximately 5000 people in the affected area escaped exposure or survived its effects. Another type of CO2-related hazard is that seen at Mammoth , , a large dacitic volcano located on the southwestern rim of the 760,000-year-old Long Valley . Beginning in 1990, extremely high levels of CO2 degassing (20e90% CO2) on the flanks of have resulted in tree-kill areas, which 2 cover >500,000 m . The CO2, which kills the trees during the winter by inhibition of root function and oxygen deprivation, originates from the degassing of intruded and gas release from magmatically heated carbonate metasedimentary rocks beneath the caldera. The CO flux 2 FIGURE 57.3 A continuous gas plume rises from the Pu’u ‘O’o vent on from Mammoth Mountain was estimated at 1200 metric Kilauea volcano, , USA. The prevailing winds from the northeast tons per day (t/d) in 1995 dropping down to w10 t/d in often lead to accumulation of or volcanic fog against the southwestern 2010, occurring principally in the tree-kill areas. This flank of and the Kona coast, 1983. Photograph by R.W. Decker, diffuse degassing may also be producing catastrophic U.S. Geological Survey. acidification of the soil and mobilization of toxic Al3þ into local aquatic ecosystems. Furthermore, although CO2 generally dissipates when it leaves the ground, its relatively has led to extensive fumigation and contamination of high density causes it to collect in hollows, wells, and >1200 km2 downwind of the volcano. Concrete and metal confined places, where it creates a serious asphyxia hazard. fences, telephone wires, and other metal equipment are also During the winter months, the relatively impermeable snow severely damaged in the affected areas (Figure 57.3). Since around Mammoth Mountain prevents CO2 from escaping, the nineteenth century, the significant economic impact dramatically increasing the hazard; a number of cases of from the degassing has led local coffee farmers to even asphyxia or near-asphyxia have been reported after skiers demand the capping or destruction (by aerial bombard- fell into snow-covered or took shelter in small ment) of the degassing vent; none of these attempts proved snow or snow-covered cabins. successful. Mixing of rain from Hurricane Mitch (late Global CO2 emission from subaerial volcanoes has been 1998) with the volcanic gas plume produced concentrated calculated, using CO2/SO2 ratios and SO2 flux estimates, to , which local farmers blamed for the damage to be approximately 0.15e0.26 billion metric tons (Gt) of young palm trees and even the complete destruction of a CO2 per year, with over half of that coming from passively soya field during a single afternoon. degassing volcanoes. Although only a fraction of that of On June 6, 1912, , a dacitic volcano located 3 anthropogenic emissions (36 Gt of CO2 in 2013), volcanoes on the Peninsula, explosively erupted w13 km of nevertheless contribute large amounts of CO2 to the magma and triggered the collapse of Mt Katmai volcano. atmosphere. In earlier geologic times, catastrophic volcanic The KatmaieNovarupta eruption released substantial event such as the eruption of the () may amounts of gas, which created acid rains that appear to have have added significant amounts of CO2 to the atmosphere greatly impacted the local environment. As with Masaya, and therefore may be partially responsible for increased acid rain was reported to have dissolved the metal work of global warming. buildings 400-km northeast at Seaward, while polished brass was tarnished 1100 km away at Cape Spencer. A month after the eruption, housewives in Vancouver, Canada 3.2. SO2 Hazards (2400 km south), reported that clothes left out to dry had When is released to the atmosphere, it oxi- “turned to shreds” upon being ironed. dizes with the OH radical in air to form sulfurous acid The conversion of volcanic sulfur dioxide into aerosol (SO3), which then reacts with water to produce sulfuric acid particles is often responsible for formation of an acid smog particles. At Masaya volcano, a basaltic complex of nested or “vog” (e.g., Kilauea, Hawaii; Figure 57.4). This acid vog and craters located in northwestern Nicaragua, the is slowly neutralized by in the atmosphere to long-term degassing activity from the currently active form a haze that may block solar ultraviolet rays from crater, Santiago (Figure 57.1), has had a significant impact reaching the lower atmosphere, which in turn may lead to a on the surrounding vegetation: high concentrations of SO2 cooling effect (e.g., Mt Pinatubo, Philippines). The volca- disturb stomatal respiration and cause necrosis. Sulfur di- nic haze may also act as cloud condensation nuclei and fluxes from the crater have been measured at as much perhaps even as sites for the catalytic destruction of as 2500 t/d. The presence of this gas, as well as HCl and HF, with obvious global implications.

The Encyclopedia of Volcanoes, Second Edition, 2015, 985e992 990 PART | VII Volcanic Hazards

fatalities, it is nevertheless an important component because of its effects on the environment. HCl is highly soluble in water and is therefore easily removed by rain from a volcanic plume, resulting in low-pH acid rains (e.g., Kilauea, USA; Masaya, Nicaragua). Significant amounts of HCl may also have been injected into the stratosphere during the cataclysmic eruption of El Chichon (Mexico) in 1982 with potentially serious environmental implications. In Hawaii, clouds of haze or “laze” are formed from the boiling and vaporization of when lava flows enter the sea. These large white laze plumes contain a mixture of HCl (up to 10e15 ppm) and seawater and produce acid rains (pH 1.5e2), which pose a hazard to the local population. FIGURE 57.4 A metal gate, 15 km downwind of Masaya volcano, Nicaragua, severely damaged by prolonged exposure to acid gases, 1999. 3.5. HF Hazards 3.3. H2S Hazards Hydrogen fluoride is highly soluble and with excessive Hydrogen sulfide is an extremely toxic gas, which has been intake leads to dental and skeletal degradation and is responsible for at least 46 fatalities (since the early twen- indirectly responsible for the most lethal gas-related vol- tieth century) at Rotorua () and a number of canic event. The fissure (), a NE-trending volcanoes in Japan, where it is believed to be the most 27-km-long row of cones and craters, was the source of common cause of volcanic gas accidents. This has led many the Grı´msvo¨tn caldera eruption, which lasted from June 8, volcano in Japan to install H S detectors and 1783 to May 26, 1785. The second largest historic basaltic 2 w automated warning systems in areas frequented by the fissure eruption since the AD 935 Eldgja´ eruption, it was preceded by tremors and starting on May 15. public. 3 One such incident occurred in 1971 on the flanks of The eruption involved at least 19 km of basaltic magma of which 15 km3 was erupted as lava and covering Kusatsu-Shirana volcano, Honshu, when six downhill 2 skiers died almost instantly after passing through a 565 km . Lava fountains are thought to have risen as high depression filled with H S. Being denser than air, the gas as 1400 m and were accompanied by convecting eruption 2 w may accumulate in snow-covered depressions or caves columns, which rose to a maximum altitude of 15 km, w which are breached from time to time, releasing lethal resulting in an atmospheric loading of 219 Mt of SO2, 7.0 concentrations to the surface. Another more recent accident Mt of HCl, and 15.0 Mt of HF over an 8-month period. A occurred on Adatara volcano, Honshu, a basaltic-to- low-altitude gas haze caused grasses contaminated by andesitic volcano, which forms part of the volcanic front fluorine to be stunted, leading to the loss of over 50% of of northeastern Japan. On September 15, 1997, 4 hikers, Iceland’s grazing livestock. This consequently lead to the from a party of 14, were killed after inhaling volcanic gases “Haze Famine,” which, in combination with various dis- on the floor of the Numano-taira crater. The group had eases and two severe winters, caused the death of 10,521 become disoriented because of fog and left the trail, which people, 22% of Iceland’s population. The injection of ash, had signs warning of volcanic gas hazards in the area. gases, and aerosols into the lower stratosphere also affected Three of the hikers fell into the crater, where they suc- parts of Western Europe, North , and Western Asia cumbed to noxious gases that had accumulated on the crater and resulted in cooling of the Northern Hemisphere by e floor due to calm wind conditions. The fourth hiker died, 1 2 C. after succumbing to the gases while attempting a rescue. Ambrym is a persistently and vigorously degassing > w Scientists from the Kusatsu-Shirane Volcano volcano ( 17,000 t/d SO2; 950 t/d HCl; 3400 reported that the fumarolic gas from the southwest rim of t/d HF) in Vanuatu, which is having a significant impact on the health of its 9000 residents. Since rainwater is used by the crater was composed of 0.5% SO2,33e37% CO2, and the majority of residents for cooking and drinking, fluoride 60e65% H2S. contamination is important with concentrations in rain- water tanks reaching 9.5 ppm F; the WHO-recommended F concentration in drinking water is 1 ppm. This has led up to 3.4. HCl Hazards 96% of the population suffering from moderate to extreme Although there are few cases of hydrochloric acid being dental fluorosis, and it is known that prolonged exposure to solely and directly responsible for volcano-related F concentrations of 4e6 ppm can lead to skeletal fluorosis.

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4. GAS HAZARD MITIGATION therefore critical, and some excellent resources are now available. The International Volcanic Health Hazard While it is impossible to stop volcanoes from degassing, Network (http://www.ivhhn.org) has prepared a compre- volcanic gases may be monitored and studied using a hensive set of guidelines and pamphlets for the public and variety of techniques ranging from direct sampling of fu- emergency managers. The International Association of maroles (e.g., Giggenbach bottles, MultiGAS) to remote and Chemistry of the Earth’s Interior (http:// sensing techniques (e.g., FLYSPEC, mini-DOAS, OMI). www.iavcei.org) also has safety recommendations for the Ideally, gas monitoring is carried out sufficiently frequently public online and has produced video on “Understanding by volcano observatories in order to characterize the Volcanic Hazards and Reducing Volcanic Hazards.” baseline or background activity for every volcano. Following the example of those working on industrial- related gas emissions, have begun to 5. SUMMARY develop and apply models of gas dispersion and deposition Volcanic gases, although a relatively minor hazard in downwind from the volcanic source (e.g., , Italy; comparison with other volcanic phenomena, can have Poa´s, Costa Rica). Based on this information, alert levels important short- and long-term impacts on people and the and hazard maps can then be developed and used for risk environment. Gases and resulting acid rains may some- management. However, it is often the case that areas at risk times be detected over 1000 km from the volcanic source lack the necessary funding and infrastructure to support but are generally directly responsible for relatively few such studies. deaths. Their effects on buildings are rarely totally In only a few instances, such as the artificial degassing destructive except in the case of long-term exposure being carried out at Lake Nyos, Cameroon, is it possible to (e.g., Masaya, Ambrym). Sulfur dioxide emissions from the reduce or eliminate the gas hazard physically. In most 1783 Laki fires were responsible in part for global tem- cases, monitoring of the volcano and limitation of access by perature decreases, while CO from subaerial volcanoes the public to affected areas are the only means of reducing 2 may contribute to global warming. Although some attempts the risk. On a short timescale, the impact of volcanic gases have been made to physically reduce gas hazards can be reduced by limiting exposure time, not overexerting (e.g., artificial degassing), gas monitoring and education of oneself, and resting frequently. Where possible, one should the public are the most effective means of reducing the remain to the windward side of the gas source and wear hazard from volcanic gases. full- or half-face gas masks (respirators) with appropriate absorbers/filters. Where gas masks are unavailable, a wet cloth held over the face can partially reduce the amount of water-soluble gases entering the lungs (Figure 57.5). FURTHER READING In some cases, evacuation is necessary, but for extended Allibone, R., Cronin, S.J., Charley, D.T., Neall, V.E., Stewart, R.B., long-term activity such as at Masaya or Ambrym, it is Oppenheimer, C., 2012. Dental fluorosis linked to degassing of clearly not feasible. Education of the population at risk is Ambrym Volcano, Vanuatu: a novel exposure pathway. Environ. Geochem. Health 34, 155e170. Baxter, P.J., 2005. Human impacts of volcanoes. In: Marti, J., Ernst, G.G.J. (Eds.), Volcanoes and the Environment. Cambridge University Press, New York, pp. 273e303. Blong, R.J., 1984. Volcanic Hazards. Academic Press, Orlando, Florida. Cantrell, L., Young, M., 2009. Fatal Fall into a volcanic . Wil- derness Environ. Med. 20, 77e79. Farrar, C.D., Sorey, M.L., Evans, W.C., Howle, J.F., Kerr, B.D., Kennedy, B.M., King, C.-Y., Southon, J.R., 1995. Forest-killing diffuse CO2 emission at Mammoth Mountain as a sign of magmatic unrest. 376, 675e678. Gerlach, T., 2011. Volcanic versus anthropogenic carbon dioxide. EOS Trans. Amer. Geophys. Union 92, 201e202. Hansell, A., Oppenheimer, C., 2004. Health hazards from volcanic gases: a systematic literature review. Arch. Environ. Health 59, 628e639. International Volcanic Health Hazard Network. Volcanic Gases and Aerosols Guidelines. http://www.ivhhn.org. FIGURE 57.5 A sulfur miner at Kawah Ijen volcano, Indonesia, carrying Le Guern, G., Tazieff, H., Faivre-Pierret, R., 1982. An example of health 70e80 kg of native sulfur. Without access to gas masks and filters, miners hazard: people killed by gas during a phreatic eruption, Dieng Plateau use a wet scarf in their mouth to limit gas entering their lungs, 2006. (Java, Indonesia), February 20th 1979. Bull. Volcanol. 45, 153e156.

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Le Guern, G., Tazieff, H., 1989. Lake Nyos. J. Volcanol. Geotherm. Res. Scarpa, R., Tilling, R.I. (Eds.), 1996. Monitoring and Mitigation of Vol- 39 special issue. cano Hazards. Springer-Verlag, Berlin. Schmid, M., Halbwachs, M., Wehrli, B., Wu¨est, A., 2005. Weak mixing in Thordarson, Th, Self, S., 1993. The Laki (Skafta´r Fires) and Grı´msvo¨tn Lake Kivu: new insights indicate increasing risk of uncontrolled gas eruptions in 1783e1785. Bull. Volcanol. 55, 233e263. eruption. Geochem. Geophys. Geosyst. 6, Q07009. Thordarson, Th, Self, S., O´ skarsson, N., Hulsebosch, T., 1996. Sulphur, Sigurdsson, H., Devine, J.D., Tchoua, F.M., Presser, T.S., Pringle, M.K.W., , and fluorine degassing and atmospheric loading by the Evans, W.C., 1987. Origin of the lethal gas burst from Lake Monoun. 1783e1784 AD Laki (Skafta´r Fires) eruption in Iceland. Bull. Vol- Cameroon. J. Volcanol. Geotherm. Res. 31, 1e16. canol. 58, 205e225.

The Encyclopedia of Volcanoes, Second Edition, 2015, 985e992