Volcanic and Geothermal Processes: Health Effects

Volcanic and Geothermal Processes: Health Effects

Volcanic and Geothermal Processes: Health Effects A Cook and P Weinstein, School of Population Health, University of Western Australia, Crawley, WA, A...

195KB Sizes 0 Downloads 32 Views

Volcanic and Geothermal Processes: Health Effects A Cook and P Weinstein, School of Population Health, University of Western Australia, Crawley, WA, Australia & 2011 Elsevier B.V. All rights reserved.

Abbreviations ARDS

COPD PTSD TSP

acute respiratory distress syndrome/adult respiratory distress syndrome chronic obstructive pulmonary disease Posttraumatic stress disorder total suspended particles

Introduction Volcanic and geothermal activities are among the most dramatic of all natural phenomena, and they can affect human health through a range of direct and indirect pathways. The death toll over the past 500 years has been estimated to be more than 250 000, with major eruptions at Tambora in 1815, Krakatoa in 1883, and Pele´e in 1902. The majority of casualties in the past few centuries are result of pyroclastic flows, lahars, and suffocation or building collapse from ash or debris; tsunamis, which may spread for hundreds of miles from the active site; and indirect consequences of eruptions, such as famine or infectious disease outbreaks. The devastating power of volcanoes is evident even in the modern day, as illustrated by the activity of the Nevado Del Ruiz volcano in Colombia. In 1985, heat from the eruption melted a portion of the overlying icecap: the resulting lahars (mudslides) buried the city of Armero and surrounding areas, killing over 23 000 people. Although morbidity following eruptions is often comparable to those seen in other natural disasters – such as earthquakes – a number of diseases are more specific to the characteristics of volcanic and geothermal processes. The nature of the eruption (or other volcanic event) influences the duration of emissions, the chemical composition of the toxic compounds expelled, and the range of dispersal. Eruptions may be broadly grouped as explosive (releasing large quantities of gas, hot ash, and dust, such as Mt. St. Helens), effusive (associated with large lava flows but less dramatic outpourings of gas and dust, such as the basaltic volcanoes of Hawaii), or mixed (a combination of the two patterns). Volcanic products vary in terms of particle size, concentration, pH, and water solubility. All these factors can influence the bioavailability of toxins, and thereby processes that result in adverse health effects. Apart from the obvious thermal

664

and physical injuries resulting from an eruption, volcanic materials may also contain toxic elements and compounds that disrupt biological systems. These compounds may be released in the form of gases, or carried with volcanic matter falling from eruptive columns or ash plumes. Some toxic compounds, such as radon, may persist in volcanic products (and continue to cause injury) long after the eruptive event ceases. The duration of exposure plays one of the most crucial roles in determining health outcomes. For example, some insults may be short-lived and reversible, as with conjunctival irritation due to ash particles, or may be chronic, as with inhalation of silica particles resulting in the lifelong respiratory problems of silicosis. These health effects are summarized in Table 1. Although not as dramatic as full-scale eruptions, other types of geothermal activity also generate a variety of toxic gases. These include hot springs, geysers, and other vents that emit steam and volcanic gases (fumaroles/ solfataras). Because such activity may often continue unabated over prolonged periods, and because the benefits of hot springs may encourage the presence of humans, there is a risk of thermal injury and toxic exposure. For example, numerous fumaroles are present in some areas (such as Yellowstone Park) and may emit high levels of various gases, including CO2, SO2, HCl, and H2S. Volcanic and geothermal product elements may also have beneficial effects. Historically, thermal pools have been linked to healing properties, and are still used in many nations for arthritic and skin disorders. Geothermal resources are used for energy including electricity generation, as well as direct heating of industries, domestic facilities, and swimming pools. Many high temperature fields actively deposit precious metals such as gold and silver.

Near-Vent Eruptive Processes Explosion Initial explosive events herald the start of many eruptions and can generate a number of immediate hazards. The behavior of eruptions relate to the rate at which gases are released from magma or surrounding material. Where magmatic or other gases cannot freely escape and become concentrated, dramatic explosions are more likely. Some eruptions are ‘phreatic,’ in which preexisting water (from groundwater sources, overlying seawater, or crater

Volcanic and Geothermal Processes: Health Effects Table 1

665

Summary of major health impacts due to volcanic/geothermal events

Eruptive event

Exposure pathway

Direct health impact

Explosion

Blast, rock fragments, shock waves Lightning Forest and bush fires, combustion of buildings and vehicles Lava flow Forest/bush fires Pyroclastic flows, ash flows and falls Dispersion of fine ash/dust less than 10 mm in diameter

Trauma, skin burns, lacerations Electrocution Burns, smoke inhalation

Lava Pyroclastic flows and other thermal emissions Ashfall

Dispersion of siliceous dust

Gas emissions H2O, SO2, CO, CO2, H2S, HF

Radon emissions Drainage of crater lakes, Lahars

Contamination of water supplies with fluoride, possibly also heavy metals Contamination of food/ destruction of crops and livestock Pooling in low-lying areas Dispersion of irritant gases

Acid rain Dispersion of radon gas Mudflows, floods

Engulfing and burns Burns Skin and lung burns, Asphyxiation Exacerbation of preexisting respiratory disease (such as asthma/COPD), foreign bodies in eyes/conjunctivitis, corneal abrasions Acute silicosis

Gastrointestinal upset and electrolyte disturbance/ toxicity Gastrointestinal upset and electrolyte disturbance/ toxicity Asphyxiation/suffocation Exacerbation of preexisting respiratory disease (such as asthma/COPD), mucosal/ conjunctival irritation, skin irritation

Engulfing, drowning

Indirect/delayed health impacts

Chronic silicosis due to high and prolonged exposure of free silica content

Malnutrition from food scarcity; toxicity, e.g., from fluoride or metal contamination Toxicity, e.g., from fluoride or metal contamination

Lung cancer Toxicity, e.g., from fluoride or metal contamination

Note: COPD, Chronic obstructive pulmonary disease. Source: Adapted from Baxter (1983, 1990). Baxter P (1983) Health hazards of volcanic eruptions. Journal of Royal College of Physicians of London 17(3): 180–182; Baxter P (1990) Medical effects of volcanic eruptions. Bulletin of Volcanology 52: 532–544.

lakes) is vaporized, and the resulting pressurized steam acts to eject overlying rocks and soil. These ‘steam boiler’ events are often followed or accompanied by ‘magmatic’ eruptions, in which upwelling molten rock is released. The emission of large fragments of debris, such as ‘blocks’ and ‘bombs,’ may cause severe physical injury, such as lacerations and fractures. Heavy fallouts (especially of pumice) can lead to burial and asphyxiation, either directly or, for example, through roof collapse. Lava Flows One of the more visually dramatic outcomes of volcanism is the ejection of fluid or semifluid material, lava (Figure 1). Temperatures usually range between 900 1C and 1200 1C. In some locations (e.g., Hawaii), eruptions may be associated with fountaining of molten material, in which globules of plastic lava are sprayed over a kilometer high. These may feed into lava lakes and lava flows,

which take a course that is away from the volcano. The direct threats to health posed by lava flows are primarily thermal injuries. Often casualties occur because of unexpected rapid flows, escape routes being cut off, or steam explosions created when the lava strikes a water source. In some circumstances, the potential human exposure may be significant: although the area around an erupting crater is generally evacuated, emergency crews often work in proximity to lava flows. In 1973 on Heimaey, Iceland, crews spent many days on or near lava flows, applying cold waters in a successful attempt to solidify and direct flows away from the main town. Lava flows may result in considerably less illness less than exposing humans directly to toxic chemicals. The basaltic lava flows in Hawaii are often associated with the release of sulfur dioxide and aerosolized droplets of sulfuric acid. As will be discussed, HCl (hydrochloric acid) and, to a lesser degree, HF (hydrofluoric acid), may also be formed, particularly when molten lava strikes the

666

Volcanic and Geothermal Processes: Health Effects

deep penetration into the subcutaneous tissues, to the extreme of complete incineration. Victims are commonly described as appearing dried and ‘mummified,’ rather than charred (the outcome usually observed with fire injuries). Respiratory effects occur as a result of intense heat, oxygen deficiency, ash inhalation, and toxicity of the gases in the flow. Asphyxia from plugs of ash in the upper airways was described as the cause of death in those caught in the flow of the Mt. St. Helens eruption. Survivors of the devastating flows from Lamington, Papua New Guinea, in 1953, suffered from symptoms suggestive of pharyngeal burns, including throat pain, shortness of breath, and inability to swallow. Health effects subsequent to the acute injury include pneumonia, tracheobronchitis, and adult respiratory distress syndrome (ARDS) resulting from irritation and secondary infection of injured respiratory tissues. Owing to the capacity to disperse toxic compounds flows, surges, and debris avalanches also affect human health. During the Mt. Pinatubo eruption in 1991, pyroclastic flows contributed to the volcanic material, which covered a wide area and filled the surrounding valleys. Subsequent erosion, often triggered from monsoon rains, then acted to mobilize the volcanic chemicals for many subsequent years.

Figure 1 Selinus.

Eruption at Krafla, Iceland. Image courtesy of Olle

ocean, thus creating acid rain from the steam plume. Lava may also act to taint subterranean wells by the process of leaching. Pyroclastic Flows Pyroclastic flows are intensely hot flows of gas and dispersed fragments of debris, which may travel at speeds above 350 km h 1. They arise from collapses of the eruption column or lava domes. The exact composition and temperature varies greatly, but may reach 1000 1C. The gas content will usually include H2O (which may be superheated), CO2, SO2, and H2S. With their considerable kinetic energy, these deadly ‘volcanic hurricanes’ simultaneously sear and blast objects in their path. The mortality rate of those caught in such flows is usually extremely high: common causes of death include asphyxiation (often due to burial), trauma, and severe burns (especially for the respiratory system). During the 1902 eruption of Mt. Pele´e on the island of Martinique, a pyroclastic flow rapidly enveloped the city of St. Pierre, resulting in approximately 30 000 casualties in a few minutes. Pyroclastic flows result in varying degrees of thermal injury to the skin ranging from superficial erythema,

Tephra Dispersal The dispersal of tephra, or the fragmentary material ejected by a volcano, is a major cause of morbidity following eruptions. Tephra thrown into the atmosphere may cause disease through the fallout of particles from eruption columns or plumes on human populations, or through the movement of individuals into eruptive clouds (e.g., when aircraft inadvertently fly into ash clouds). Smaller particles of pumice, scoria, and ash may be distributed over a wide area around the eruption site, and in some cases plumes may affect settlements situated hundreds of kilometers away. For example, the 1992 eruption of Cerro Negro, Nicaragua, distributed 1.7 million tons of ash over a 200 km2 area and forced the evacuation of 28 000 people. Volcanoes may undergo dome formation from slow ongoing exudation of material (e.g., the Soufrie`re Hills from 1995 on the Caribbean island of Montserrat), which results in repeated ash generation (as well as pyroclastic flows) as the domes repeatedly build up and then collapse. Volcanic ash (solid ejecta o2 mm in diameter) has the potential to physically irritate or injure mucous membranes, eyes, and skin. The eyes are particularly vulnerable to fine tephra particles, and common ocular injuries include abrasions of the cornea and conjunctivitis due to accumulation of ash in the conjunctival sac. Superficial tissues such as the skin, lips, mouth, and other mucous

Volcanic and Geothermal Processes: Health Effects

membranes may also be exposed. Nasal and throat irritation are commonly reported by those exposed to ashfall. Skin irritation (‘ash rash’), such as in the axillary area, may follow deposition of volcanic ash particles on the skin. The ‘respirable’ portion of tephra refers to particles less than 10 mm in diameter, which can penetrate into the airways. Particles with diameters less than 2.5 mm may penetrate farthest into the lungs – the terminal bronchial and alveoli – and thus are not removed by mucociliary clearance. The proportion of respirable ash varies greatly across eruptions. Higher levels of total suspended particles (TSP) caused by ashfall may precipitate some preexisting respiratory complaints, including asthma and bronchitis. The probable mechanism, by which ash produces such respiratory symptoms, is by provoking hypersecretion of mucus and bronchoconstriction (narrowing of the air passages): both are usually reversible, however, and typically diminish once exposure ceases. For example, an eruptive episode at Popocatepetl, Mexico, in December 1994, lasted for more than 4 months and deposited ash over an area of 4000 km2. Transient increases in respiratory symptoms in affected farming communities were reported. Similar increases in respiratory symptoms were reported in those exposed to ash from the Mt. Tungurahua and Guagua Pichincha eruptions in Ecuador in 1999. Dispersal of tephra may also result in adverse health effects for a longer duration, and from this perspective one of the most troublesome compounds produced by volcanic activity is silica. Inhalation of fine particles of crystalline silica, including quartz, is a wellestablished cause of both acute and chronic inflammatory reactions in lung tissue, raising the long-term risk of silicosis in affected communities. Certain forms of silica, such as cristobalite and tridymite, occur in lava and may be formed when amorphous silica or quartz is heated to high temperatures. The risk of silicosis has been recognized for the residents of the Caribbean island of Montserrat. This island has been subject to many years of sustained volcanic fallout from the mid1990s, and a large proportion of the land area is coated with varying levels of ash. The silica content of the ash is approximately 10–24% by weight of the sub-10 mm fraction, and the exposure is prolonged. In the areas most frequently affected by ashfalls, a risk assessment conducted in 2003 for the UK Department for International Development suggested that the risk of developing early radiological changes of silicosis was highest among gardeners and other outdoor workers, with increased risks of up to 10% if their cumulative exposure over 20 years was at the extreme end of the likely range. The prevalence of wheeze among Montserratian children is greater in those heavily or moderately exposed to volcanic ash compared with the group exposed to low

667

levels. It has been hypothesized that populations living in proximity to Mt. Pinatubo are also vulnerable to silicosis following exposure to high rates of respirable silica.

Volcanic Gas Emissions Steam, from both magmatic and superficial sources (such as overlying lakes or groundwater), is the most common volcanic gas. Other, often very toxic, gases are also emitted during eruptive events, and there are numerous accounts of volcanic gases causing death (Figure 2). Some urban centers, such as Rotorua in New Zealand, are built around geothermal fields, thereby raising the risk of toxic gases (including CO2, H2S, and radon) to enter buildings directly from the ground. In terms of adverse affects on human health, volcanic gases may be classified as follows: gases that act as inert asphyxiants; those with irritant effects on the respiratory system; and those that combine both the properties and act as noxious asphyxiants. Of the ‘inert’ asphyxiants, carbon dioxide (CO2) is among the most notorious gases because it is heavier than air, and may pool at ground level where it replaces the available oxygen. Concentrations of CO2 are particularly high near emission vents, and the degassing of volcanic soil may result in the collection of carbon dioxide in cellars, huts, and low-lying areas. In Java’s Dieng Volcanic Complex, it is believed that emissions of CO2 from a fissure in 1979 resulted in 149 deaths. Low concentrations (e.g., less than 5%) produce accelerated breathing, and often feelings of discomfort, by direct activation of the respiratory centers in the brain. Headache and vertigo are early symptoms. If sufficient concentrations are reached (e.g., concentrations of 7–10% for a few minutes),

Figure 2 Sampling gas levels near a volcanic vent, White Island, New Zealand. Image courtesy of Michael Durand.

668

Volcanic and Geothermal Processes: Health Effects

fainting occurs. Elevated levels of CO2 in the bloodstream (hypercapnia) eventually result in circulatory failure and asphyxia. Volcanic gases that have primarily irritative (i.e., directly injurious) effects include the hydrogen halides (hydrofluoric acid and hydrochloric acid) and the oxides of sulfur and nitrogen. Sulfur dioxide (SO2) is a wellestablished cause of acute and chronic disease as a result of volcanic activity. Both the gas and the sulfuric acid aerosols, which are formed, are highly irritant, particularly to the eyes, nasal passages, throat, and respiratory tract. For example, degassing of the Masaya volcano in Nicaragua throughout the 1990s produced continuous emissions of SO2 at rates increasing from 600 metric ton per day (7.0 kg s 1) in 1995 to 1800 metric ton per day (21.0 kg s 1) in 1999; high levels of atmospheric hydrofluoric acid have also been detected around this site. The effects of long-term emissions have been examined at Kilauea, Hawaii, which has been erupting for 15 years with outputs of approximately 1500 tons of sulfur dioxide per day. Episodes of increased SO2 in the ambient air have exceeded health standards 80 times in the past 15 years and are correlated to ongoing eye irritations, throat pain, and respiratory problems, including asthma exacerbations. Mists containing HCl and HF are also generated when molten material strikes the ocean, which are then carried to adjacent villages in and around the Hawaii Volcanoes National Park. The HCl-/ HF-acidic aerosol may exacerbate preexisting lung disease, even at great distances from volcanic vents. In addition to the direct action of such gases, droplets of rainfall or mud may pass through toxic gas clouds or ash plumes, thereby creating acid rain. The health effects of this process were experienced by the people on Kodiak Island, who suffered from both ashfalls and sulfuric acid rains following the Katmai eruption on the Alaskan mainland in 1912. A number of islanders, 160 km downwind from the active vent, suffered from ‘stinging burns’ when this rain came in contact with their lips or skin. The pungent gas hydrogen sulfide (H2S) acts as a noxious asphyxiant. Its metabolic effect is to inhibit cytochrome oxidase, one of the enzymatic drivers of cellular metabolism. Early signs of poisoning include headaches, ocular and respiratory irritation, and loss of smell (anosmia). Apart from these effects, inhalation of the gas also directly damages the respiratory tract, and precipitates pulmonary edema in the lungs. At 1000 ppm, fainting occurs. Ultimately, H2S causes cessation of breathing by direct action on the respiratory centers of the brain. In 1997, four hikers died on the crater floor of the Adatara volcano in Japan. The most likely cause of these casualties was identified as H2S emitted from nearby fumaroles, which got concentrated at ground level on a wind-free day.

Other volcanic/geothermal gases can affect human health but are usually present in much lower concentrations, including CO (carbon monoxide), nitrogen dioxide, methane, and ammonia. Ash may have high uranium content and carry adherent particles of radon, an alpha-radioactive gas linked to the development of lung cancer. Metals in the gaseous phase are directly emitted from volcanic vents and could potentially act as respiratory irritants. For example, mercury vapor is released in some eruptions, usually in proximity to the eruption site. Mercury vapor is also produced from some geothermal springs, such as at Ngawha in New Zealand’s North Island, where mercury deposits exist in sufficient quantities to have once supported a small mining industry.

Risks from Other Volcanic Processes Crater Lakes A number of active volcanoes contain crater lakes, some of which act to condense volcanic gases and hydrothermal fluids, thereby yielding extremely acidic, sulfur-saturated contents. These lakes can also be a source of fluoride and other elements, including Cu, Pb, Zn, Ni, As, Sb, Hg, Mg, and Cd. These contaminants may be released into waterways or soils through a gradual seepage or overflow, or more dramatically through the action of lahars (volcanic mudflows), which are discussed later. Outflows from volcanic lakes can also result in destruction of food sources or heavy metal contamination, as illustrated by the highly acidic Kawah Ijen crater lake in East Java, which carries a very high load of SO4, NH4, F, Fe, Cu, Pb, Zn, Al, and other potentially toxic elements to irrigated croplands downstream. Some lakes, such as the Poas volcano, Costa Rica, sit atop a degassing system. At this site, steady emissions of sulfur dioxide pass through a shallow lake, which is often hot and intensely acidic (pHo1). These emissions, together with particles of rock dissolved in the acid lake water, are periodically dispersed out of the crater and have been linked to respiratory problems in communities downwind. Crater lake emissions were responsible for two disasters in the Cameroon: at Lake Monoun, in 1984, and Lake Nyos, in 1986. Large volumes of CO2 were emitted from these crater lakes, carried downward by gravity, engulfing whole villages in their path. A widely accepted hypothesis suggests that soda springs deep in these crater lakes act to release CO2, which causes supersaturation of cooler water at the base of the lake. Any disturbance (most likely a landslide entering the lake) abruptly forced large volumes of CO2 out of solution. As a result of the abrupt generation and movement of the gas cloud, 37 people were asphyxiated near Lake Monoun; the death toll reached 1700 at Lake Nyos. The survivors from the Lake Nyos disaster reported to have been in a deep state

Volcanic and Geothermal Processes: Health Effects

of unconsciousness for up to 36 h. No long-term respiratory effects occurred in the survivors, although some sustained burns by falling into cooking fires during the period of CO2-induced coma. Landslides and Lahars Volcanic debris following eruptions, including the rubble from lava flows and unconsolidated ash, is often unstable and prone to collapse. Seismic events or heavy rainfall may accelerate the landslides of such material. A fastmoving, and potentially lethal, consequence of volcanic eruptions is the lahar. These torrential flows of mud, water, and debris wash down the sides of the volcano and are often associated with crater lakes, melting snow or ice, or heavy rainfall events, with or without a concurrent eruptive event. Lahars from some volcanic lakes may be hot and often acidic. For communities situated in the path of lahars, the opportunities for timely warnings may be limited – sometimes with lethal consequences. In a lahar generated from the 1919 eruption of Kalut in Indonesia, 5000 people died. Those caught in the flow suffered from drowning, suffocation while entrapped, or severe trauma from penetrating wounds and fractures. In New Zealand, a lahar from Mt. Ruapehu in 1953 washed out a rail bridge shortly before the arrival of the main train servicing the North Island. The front carriages plunged over the edge of the washed out bridge with a catastrophic result: 151 killed out of the 285 people on board. Tsunami Among the most destructive impacts of volcanic eruptions are tsunami. Tsunami may also be triggered by (usually undersea) earthquakes – such as the 1960 Great Chilean Earthquake and the 2004 Indian Ocean tsunami – and landslides. Among the most famous of historical tsunami linked specifically to volcanic events are the Minoan (or Thera) eruption in the Santorini archipelago of the Aegean, which occurred 3600 years ago and triggered a massive tsunami that hit Crete, 100 km to the south. This event is believed to have contributed to the destruction of the thriving Bronze Age civilization of the Minoans. More recently, tsunamis from the Krakatau (Krakatoa) eruption of 1883 contributed to the destruction of 165 villages and a significant fraction of the official death toll of more than 35 000 (the unofficial death toll suggests that up to 120 000 were killed). Among the affected towns was Merak, a seaport in western Java, destroyed by a tsunami more than 40 m high.

Indirect Effects of Volcanic Emissions Natural disasters, regardless of their cause, must be evaluated in terms of a number of common threats to

669

human health. Disasters lead to a marked reduction in the ability of individuals to sustain their normal living conditions, thus risking their life, health, or livelihoods. Urgent humanitarian relief may be required if massive relocation is necessary, as occurred during the Pinatubo eruption of 1991 where 100 000 were left homeless and hundreds of thousands more displaced. This event was further complicated by an epidemic of measles in the resettlement camps, which affected 18 000 individuals. The risk of communicable disease is usually proportional to the population density and displacement. Disasters put pressure on water and food supplies, and increase the risk of contamination by disrupting preexisting sanitation services such as piped water and sewage. Anxiety and depression are common immediately after disasters; and posttraumatic stress disorder (PTSD) can affect people for months or years after such an event. In some regions, economic costs of disasters can be marked and thereby threaten livelihoods. A number of factors, such as (i) poverty and its consequences (e.g., malnutrition, homelessness, and isolation) and (ii) urbanization, increase the vulnerability of communities to disasters, including volcanic eruptions. It has been noted that urban areas ‘concentrate’ risk because of dense concentrations of people, services, and infrastructure that are easily disrupted (including pipelines and roads). As noted, volcanic activity may create health effects indirectly through their damaging effects on food and water sources. Food security may be compromised through burning, defoliation or burial of crops, and reduced photosynthesis from ash clouds. This geophysical activity may continue for many years, sometimes requiring complete relocation away from nonviable land. The impact on Icelandic society following the eruption of Laki in 1783 is a classic example. During this eruption, more than 140 cones were formed along a 27 km fissure; it is estimated that 150 megatons of sulfur dioxide and 8 megatons of fluoride compounds were discharged. This vast quantity of gas, and the aerosolized acid it formed, had destructive consequences for vast tracts of surrounding pasturelands. With extensive crop damage, livestock starved from loss of feed. The deposition of high concentrations of fluorine on pastures and waterways also proved directly fatal for numerous animals. The event tipped the balance in the already marginal farming environment of Iceland. The ensuing period of crop damage resulted in massive livestock losses: half of all the island’s cattle and horses, and four-fifths of the sheep, perished. Thousands of Icelanders died or migrated as a consequence of famine (called the ‘haze-famine’ from the persistent presence of sulfur compounds in the atmosphere). Volcanic emissions may also be deposited onto bodies of water, including irrigation or filtration plants, thus rendering the water highly turbid and unusable. Tephra may also carry a variety of adsorbed chemicals. Plumes of

670

Volcanic and Geothermal Processes: Health Effects

ash and dust, which may cover hundreds of kilometers, effectively disperse such ‘stowaway’ toxic compounds. After the ash settles to the ground, these toxins may be dissolved – often by rainwater – and thus leach into the environment. The dominant chemicals that may adsorb to tephra, and thus act as leachates, include chlorine (Cl), sulfur (S) compounds, sodium (Na), calcium (Ca), potassium (K), magnesium (Mg), and fluorine (F). Water runoff from volcanic or low-level geothermal also contains heavy metals, including arsenic, which can be deposited in soil or water (including seepage into subterranean wells). Some of these elements and compounds have safety levels established in drinking water and could potentially cause harm if ingested in quantities exceeding these concentrations. Even light tephra falls may have significant effects on water pH. During the 1953 eruption of Mt. Spurr (Alaska), a 3–6 mm tephra fall on Anchorage caused the pH of the town water supply to fall to 4.5, returning to 7.9 after a few hours. Such excursions in pH and turbidity can alter the chlorine demand significantly at treatment plants, adding a significant, albeit indirect, microbial water hazard to that already presented by toxins. Through the creation of acid rain, ‘mud rain,’ and volcanic smog, volcanic processes may cause the corrosion of metal surfaces, such as sheetmetal roofs and water tanks. This indirect process may allow newly liberated metal ions to enter food and water supplies. This mode of action is well illustrated by the reaction between volcanic acid rain and zinc in galvanized roofs, which have tainted water supplies as a result. Fluoride, a relatively common volcanic product, may produce toxicity if ingested in high concentrations. Much of the evidence related to emission of ash rich in soluble fluorine originates from assessing its effects on other mammals, such as livestock. Following the 1947 eruption of the Icelandic volcano Hekla, a mere 1 mm deposition of fluoride-rich ash was sufficient to kill thousands of sheep; similar outcomes have been observed in Chile in the 1988 Lonquimay eruption. Geochemical studies of meltwater around ash particles from Hekla show fluoride levels up to 2000 ppm. Although rapidly diluted to approximately 200 ppm in stagnant water, and 20 ppm in flowing surface water, these fluoride concentrations could readily produce symptomatic fluorosis if ingested by humans. A recent study of communities living adjacent to the volcanic vents in Vanuatu highlighted the risk of fluoride-rich ash being collected on leaves of crops and in water supplies, including freshwater lakes and rainwater tanks.

Monitoring and Management of Volcanic Events From the perspective of health protection, the purposes of volcanic monitoring are threefold: (i) to provide an

early warning system of potential health hazards and thereby allow a preparation period for resident populations, health services, transport services, electricity utilities, etc., which will respond to the disaster; (ii) to minimize illness due to contaminated water supplies, tainted or fouled foodstuffs, and air pollutants for at-risk populations; and (iii) to provide accurate records of adverse health events for use in public health surveillance. Volcanic monitoring starts in the pre-eruptive phase, which extends from the elevation of alert levels above the baseline state to the actual start of the eruption. This period involves preparation of at-risk populations for the impending volcanic event. Assessments of seismicity, ground deformation, gas emissions, geophysical variables, and hydrology are conducted to help predict the temporal and spatial pattern of an eruption, together with the scale and path of any pyroclastic flows, lahars, or lava flows. Disaster scenarios will usually include the need for evacuation, and identification of secure locations and safe travel routes for displaced populations. An important strategy during the preeruptive phase is the dissemination of information regarding potential health effects and strategies for minimizing exposure. The eruptive phase is the period surrounding the eruptive event (or degassing episode), including event imminence, the primary volcanic event, and periods of ongoing volcanic activity. Early warning systems should be established for affected communities to ensure that the public and organizations designed to preserve the societal infrastructure are prepared for the consequences of the eruption. Given the range of health consequences due to exposure to volcanic ash and dust, monitoring tephra dispersal is an important component of eruption-phase management. Gas production at the vent should be monitored to alert downwind communities of the potential hazards on a daily basis. Prior warnings of emission coupled with regular announcements on air quality allow susceptible individuals to minimize their exposure or to seek medical advice where appropriate. Water quality may also be rapidly degraded by increased turbidity and fluctuations in pH levels and should be closely monitored. Other health hazards of ash, which must be anticipated, include the mechanical effects (particularly of wet ash), causing roofs to collapse resulting in trauma, and traffic accidents due to poor visibility and ash coating on roads. As the post-eruptive phase commences, and recovery becomes possible, monitoring should continue for as long as toxic compounds are present in the environment. The conclusion of the ‘disaster phase’ does not indicate the cessation of monitoring requirements, and collection of geological and health-related data should be ongoing.

Volcanic and Geothermal Processes: Health Effects See also: Impact of Natural Dusts on Human Health, Landslides: Human Health Effects, Volcanogenic Contaminants: Chronic Exposure.

Further Reading Baxter PJ (1983) Health hazards of volcanic eruptions. Journal of Royal College of Physicians of London 17(3): 180--182. Baxter PJ (1990) Medical effects of volcanic eruptions. Bulletin of Volcanology 52: 532--544. Blong RJ (1984) Volcanic Hazards: A Sourcebook on the Effects of Eruptions. Sydney: Academic Press. Ciottone GR (2006) Disaster Medicine, 3rd edn., vol. xxxi, 952 pp. Philadelphia: Elsevier/Mosby. Cook A and Weinstein P (2005) Volcanic emissions and health risks of metal contaminants in New Zealand. In: Moore T, Black A, Centeno J, Harding J, and Trumm D (eds.) Metal Contaminants in New Zealand, Christchurch: University of Canterbury Press, (Ch 23) pp. 465–473. Dent AW, Barret P, and de saint Ours PJA (1995) The 1994 eruption of the Rabaul volcano, Papua New Guinea: Injuries sustained and medical response. Medical Journal of Australia 163: 635--639. Durand M and Scott BJ (2005) Geothermal ground gas emissions and indoor air pollution in Rotorua, New Zealand. Science of the Total Environment (345): 69--80. Forbes L, Jarvis D, Potts J, and Baxter PJ (2003) Volcanic ash and respiratory symptoms in children on the island of Montserrat, British West Indies. Occupational and Environmental Medicine 60(3): 207--211.

671

Hansell AL, Horwell CJ, and Oppenheimer C (2006) The health hazards of volcanoes and geothermal areas. Occupational and Environmental Medicine 63: 149--156. Hansell A and Oppenheimer C (2004) Health hazards from volcanic gases: A systematic literature review. Archives of Environmental Health 59(12): 628--639. Horwell CJ and Baxter PJ (2006) The respiratory health hazards of volcanic ash: A review for volcanic risk mitigation. Bulletin of Volcanology 69: 1--24. Kullmann CJ, Jones WG, Cornwell RJ, and Parker JE (1994) Characterization of air contaminants formed by the interaction of lava and sea water. Environmental Health Perspectives 102(5): 478--482. Michaud JP, Krupitsky D, Grove JS, and Anderson BS (2005) Volcano related atmospheric toxicants in Hilo and Hawaii Volcanoes National Park: Implications for human health. Neurotoxicology 26(4): 555--563. Newhall CG and Fruchter JS (1986) Volcanic activity: A review for health professionals. American Journal of Public Health 76(supplement): 10--24. Noji EK (2005) Public health in the aftermath of disasters. British Medical Journal 330(7504): 1379--1381. Simkin T, Siebert L, and Blong R (2001) Volcano fatalities – Lessons from the historical record. Science 291: 255. Weinstein P and Cook A (2005) Volcanic emissions and health. In: Selinus O (ed.) Essentials of Medical Geology, pp. 203--226. Amsterdam: Academic Press. Weinstein P and Patel A (1997) The Mount Ruapehu eruption, 1996: A review of potential health effects. Australian and New Zealand Journal of Public Health 21(7): 773--778.