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Active Tectonics: Studies in Geophysics 15 Volcanoes: Tectonic Setting and Impact on Society DONALD W.PETERSON U.S. Geological Survey, Vancouver ABSTRACT Volcanic eruptions frequently interfere with human affairs; impacts range from minor nuisances to major disasters. Some 50 to 65 different volcanoes typically are active in any given year, and among these a small number may cause significant damage and human casualties. Eruptions of catastrophic proportions occur but a few times in a century. Volcanoes are a dramatic manifestation of tectonic processes, and the distribution of most of them is closely related to tectonic belts. Consequently only about 10 percent of the world’s population lives in localities that may, at one time or another, be affected by volcanic activity. Near long-dormant volcanoes, public attitudes toward hazards commonly reflect unconcern. In contrast, the onset of activity may spawn unreasoning fear. Geological studies of volcanic systems and monitoring of active volcanoes have revealed important insights into volcanic processes. Volcanologists can inform people about volcanoes and help to improve responses to volcanic crises. But in so doing, volcanologists stray into unfamiliar territory, dealing frequently with public officials, land managers, and members of the news media. Misunderstandings may arise among these groups because of differences in background, objectives, and perceptions, and at times even well-based scientific opinions may encounter skepticism. It is vital, however, for volcanologists to communicate effectively with civic leaders and journalists, for it is only through constructive and harmonious interactions that optimum public response to volcanic hazards can be developed. INTRODUCTION Volcanic eruptions are among the most spectacular and awesome of all natural phenomena. From earliest human history they have both fascinated and terrorized mankind. Volcanoes have created some of the Earth’s most beautiful scenery but also caused some of its greatest catastrophes. The geologic record reveals countless prehistoric eruptions that were orders of magnitude more voluminous and violent than any that have occurred in the brief span of human history; when such huge events occur again they will cause unprecedented disasters. The problems posed by known volcanism during recorded history and contemporary times, as well as those posed by the unknown but inevitable volcanism of the future, are compelling reasons to improve our understanding of volcanic phenomena. Even though little hope exists for controlling other than the most benign volcanic manifestations, some forms of volcanic energy can be harnessed for man’s benefit; an example is the
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Active Tectonics: Studies in Geophysics utilization of geothermal energy as a source of heat and electrical power. Compared with many other fields of science, volcanology is in its infancy; yet substantial progress is being made both in understanding volcanic processes and in developing methods of forecasting eruptions. This paper (1) reviews the relations that volcanoes bear to the tectonic belts of the Earth, (2) summarizes the major kinds of volcanic activity, (3) reviews principal methods that scientists have used to study and forecast volcanic activity, and (4) discusses the ways that people react to volcanic activity. VOLCANISM IN THE CONTEXT OF TECTONICS The distribution of volcanoes throughout the world broadly parallels the major tectonic belts, although they do not precisely coincide (Figure 15.1). Epicenters of major earthquakes are much more widely scattered than are volcanoes, and large segments of active tectonic belts have no volcanoes at all. Nevertheless, all but a few of the world’s active volcanoes lie close enough to the major zones of active earth movement to have long provoked speculation and discussion on the nature of and connection between earthquakes and volcanoes. The current theory of plate tectonics provides a unifying framework explaining the association. Most volcanoes lie on or near two of the three principal types of boundaries between the moving crustal plates: (1) spreading boundaries, where plates move away from each other, and (2) compressive boundaries, where plates move toward each other and one overrides the other. The third type of boundary, transform, along which the plates slide laterally, is rarely associated with volcanism. But some volcanoes lie far from plate margins, and most of these are explained as a result of the plate moving across a stationary, magma-generating spot beneath the crust. Other intraplate volcanoes require a more elaborate explanation. FIGURE 15.1 Map of the volcanoes of the world, showing the relation between volcanoes and tectonic belts. Solid circles are volcanoes with eruptions since 1880; open circles are volcanoes with dated eruptions prior to 1880; triangles are volcanoes with undated but geologically recent eruptions; small crosses are volcanoes with uncertain or solfataric activity. Light double lines are spreading boundaries; thin cross-hatched lines are compressive boundaries (adapted from Simkin and Siebert, 1984). Most spreading boundaries are sites of frequent volcanism, but most submarine eruptions go undetected (see text), hence few specific submarine volcanoes appear on this map.
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Active Tectonics: Studies in Geophysics The basic concepts of plate tectonics have been formulated during the past two decades through multidisciplinary efforts; useful summaries of the developments are found in Oxburgh (1971), Vine (1971), Wyllie (1971), and LePichon et al. (1973). An easily read summary of how volcanoes fit into plate-tectonics theory is provided by Decker and Decker (1981). The following discussion summarizes the concept and its relations to volcanism. Most spreading boundaries lie on the floors of oceans (Figure 15.1), where they form a broad, linear ridge typically surmounted by a narrow trough or graben along the crest. As the opposing plates separate from each other, magma rises from depth along the tensional cracks to erupt as fluid basaltic lava on the ocean floor, thus forming new crust along the spreading boundary. Although no deep ocean-floor eruptions have been detected or observed in progress, bathymetric mapping of the seafloor, studies of the basalt recovered by deep-sea dredging, and photography and other observations from deep-diving submersible vehicles provide evidence demonstrating the close relations between volcanism and the spreading process. Computations based on rates of seafloor spreading and the relative ages of mid-ocean ridge basalts show that the worldwide total volume rates of eruption from submarine volcanism are several times the totals from subaerial volcanism (Nakamura, 1974). However, this most common form of the Earth’s volcanism has essentially no direct impact in the form of hazards on human society because of its depth and remote location beneath the ocean. Future technology may change this if attempts are made to recover mineral deposits believed to be associated with submarine volcanoes. However, in a few places, spreading-type volcanism does impinge on people: it has produced islands such as Iceland astride the mid-Atlantic ridge, and a spreading rift crosses part of East Africa. Most compressive or convergent plate boundaries form a subduction zone along which one plate descends beneath the other. A linear submarine trench commonly marks the boundary between two such plates. Within, adjacent to, or above the downward-moving slab, partial melting occurs. The resulting magma migrates upward through the crust to emerge eventually at the surface, causing volcanic eruptions from a linear belt of volcanoes that typically lies inland from but parallel to the compressive boundary. The long-recognized circum-Pacific “ring of fire” is the result of subduction. More than 80 percent of the world’s recorded historic volcanism has occurred along the Pacific margin and offshoots such as the Indonesian and Marianas arcs. The third type of plate boundary, transform faults, does not seem to cause volcanism, but some transform faults may incidentally offset a spreading or compressive boundary along which volcanoes are located. Although most active volcanism is associated with plate boundaries, some important volcanic centers lie within the interior of plates, in some cases thousands of kilometers from a boundary. An explanation of some intraplate centers of volcanism is the concept of a melting or hot spot—an inferred stationary source in the upper mantle producing magma that rises through the overlying moving plate to form volcanoes at the surface (Wilson, 1963, Morgan, 1971, 1972a,b). The melting-spot hypothesis has been further supplemented by the concept of “gravitational anchors,” a model that explains both the processes at melting spots and many of the geophysical and geochemical data observed at intraplate volcanoes (Shaw and Jackson, 1973). The most fully documented example of such a system is that of the volcanic islands and seamounts of the Hawaiian-Emporer chain (Dalrymple et al. 1973). Several other volcanic centers in the mid-Pacific Ocean may be associated with melting spots. Other intraplate volcanic centers lie in the western United States, central and eastern Asia, west Africa, and west-central Europe. Most of these show no apparent evidence for being related to a melting spot, and how they fit the plate-tectonic theory requires special explanation. The structures and volcanic evolution of the western United States have been related to complex interactions among plates and subplates along the Pacific-North American margin throughout the past 30 m.y. (Christiansen and Lipman, 1972). The prehistoric but potentially active volcanic centers throughout this region are associated with an extremely complicated and continually changing state of stress, and pulses of motion along structural lineaments have been proposed as triggering the formation of magma (Smith and Luedke, 1984). These ideas demonstrate the important role of volcanism in the past and ongoing development of the concepts of plate tectonics. CHARACTERISTICS OF VOLCANOES AND ERUPTIONS The term “volcano” is defined in two ways; both definitions are valid and are in common use. A volcano is (1) the opening or vent through which volcanic material (molten, solid, or gaseous) is emitted to the surface, and (2) the edifice—hill or mountain—built by the emitted material. The first definition applies chiefly to new volcanoes that have not yet emitted enough material to build an edifice and to those whose products have been dispersed by post-eruption processes. The second defini-
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Active Tectonics: Studies in Geophysics tion is perhaps the more familiar. The size, shape, and structure of volcanoes vary widely with the physical and chemical characteristics and amount of the emitted material, and they are classified according to these various factors. Examples of large volcanic edifices include composite cones and shield volcanoes. Composite cones are typically steep-sided structures, some of great beauty like Mayon in the Philippines and Fuji in Japan. Most large volcanoes associated with compressive plate boundaries are composite cones. They are built of lava flows alternating with layers of pyroclastic fall, pyroclastic flow, and other fragmental material. Shield volcanoes, in contrast, are broad, gently sloping structures, built of many overlapping tongues of lava that had great fluidity; Mauna Loa and Kilauea in Hawaii are examples. Descriptions of these and other volcanic landforms are in such textbooks on volcanoes as those by Macdonald (1972), Bullard (1976), Williams and McBirney (1979), and Decker and Decker (1981). Material erupted by volcanoes is of widely diverse type and character. Eruptions cover the spectrum of size, violence, and rates of ejection and travel of the material. Hazards vary accordingly. Volcanic products assume a variety of forms, including lava flow, pyroclastic fall, pyroclastic flow, lahar, volcanic gas, and debris avalanche and a wide assortment of intermixtures and intergradations. Lava flows originate by quiet welling from a vent or by more vigorous lava fountains, and they vary from fluid and mobile to viscous and slow. Fluid flows may travel long distances, they may be either sheetlike or lobate depending on topography, and they are thin relative to their length and breadth. On steep slopes, speeds may reach several tens of kilometers per hour. Viscous flows travel slowly and only short distances, and they are thick relative to fluid flows of comparable lateral dimensions. Speeds are typically a few meters to a few hundred meters per hour. Lava flows commonly destroy property, arable land, buildings, and other structures, but relatively few have taken human lives. A rare exception was the 1977 eruption of the African volcano Nyiragongo, from which a highly fluid, fast-moving lava flow overwhelmed several villages and killed about 300 people. Pyroclastic falls result from violent ejection of fragmented or pulverized rock that travels through the air and falls to the ground. “Tephra” is a widely used term for this material. Mechanisms that cause fragmentation include explosive eruptions and vigorous streaming of gas from a vent. Fallout may be directly from eruption columns or from clouds produced by convective columns and transported by the wind. Convective clouds may rise above pyroclastic flows (see below) and be transported and deposited as pyroclastic falls. Pyroclastic falls probably constitute the most common of all volcanic hazards. A small to moderate amount of tephra, with thicknesses of up to a few centimeters, is a nuisance and causes damage and inconvenience by clogging machinery and covering buildings, roads, and vegetation. It causes breathing difficulties for humans and animals, and it can abrade tooth enamel. Voluminous tephra falls may be highly destructive; eruptions during historical and recent times have produced deposits many meters thick that collapsed structures and buried towns and farms. Fine material may be carried tens to hundreds of kilometers; some large prehistoric eruptions have deposits that can be recognized thousands of kilometers from their source. Pyroclastic flows, also known in various forms as ash flows, pumice flows, glowing avalanches, and nuées ardentes, are gravity-controlled ground-hugging masses of rapidly moving hot particulate matter. Their high mobility is the result of fluidization of the mass of particles, thought to be caused by both dissolved gases escaping from the hot particles during travel and the rapid expansion of suddenly heated air engulfed by the advancing mass. The size and shape of source vents, volume-rate of ejection, temperature of material, and mechanism of transport all vary widely, and each is a factor in determining the characteristics of the resulting deposit. Pyroclastic-flow deposits may range from narrow and lobate to broad and sheetlike, and thicknesses may vary from a fraction of a meter to hundreds of meters. Particularly high-temperature and/or voluminous pyroclastic flows may result in the flattening and welding of particles within parts of the deposit to form welded tuffs. The rapid ejection of large volumes of material from a magma reservoir may cause the overlying surface area to collapse, producing a caldera. Calderas are circular to elongate depressions that are from one to several tens of kilometers across with walls that may be hundreds of meters high. Crater Lake, Oregon, is an example of this process. Relatively few caldera-forming eruptions have occurred during historical time, but they include some of the more notable eruptions such as Tambora (in 1815); Krakatau (in 1883), and Katmai (in 1912). These voluminous eruptions represent perhaps the most severe of all known volcanic hazards, and localities throughout the circum-Pacific belt and elsewhere have the potential for producing such eruptions. Their frequency of occurrence, fortunately, is very low by human time standards. Several times during the past million years, however, calderas have formed during truly immense eruptions of pyroclastic flows with volumes one or two orders of magnitude larger than those of historic erup-
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Active Tectonics: Studies in Geophysics tions. For example, calderas at Yellowstone National Park, Long Valley (California), Lake Taupo (New Zealand), and Lake Toba (Sumatra) all developed during pyroclastic-flow eruptions with volumes of tens to hundreds of cubic kilometers. General summaries of pyroclastic-flow deposits are provided by Smith (1960a,b) and Ross and Smith (1961); summaries of the concepts of relations between pyroclastic-flow deposits and calderas include those of Williams (1941), Smith (1960a, 1979), Smith and Bailey (1966, 1968), and Fisher and Schminke (1984). Pyroclastic surge is a type of flow of particulate matter characterized by a relatively low ratio of solids to gas. Consequently surges are less dense, and they tend to be of relatively low temperature; their deposits are commonly sorted and stratified and display assorted bedforms, such as crossbedding. In contrast, typical pyroclastic flows have a high ratio of particulate matter to gas and have relatively high temperatures; deposits are typically nonsorted and nonstratified. Surges tend to be pulsating, whereas other pyroclastic flows are more continuous. Like pyroclastic flows, surges may travel at high speed, commonly in the range of 50 m per second but sometimes exceeding 100 m per second. Large historical surges have traveled as much as 30 km from the source. Surges may occur either separately or together with pyroclastic flows, and sometimes surges precede or follow pyroclastic flows, forming intergradational deposits. For these reasons, pyroclastic surge is here considered as a variant form of pyroclastic flow, even though some authors regard it as a distinct process. Several different types of surge have been described, and the development of the concept and additional references are found in Moore (1967), Sparks (1976), Wohletz and Sheridan (1979), and Fisher and Schminke (1984). Both flows and surges are highly destructive of property, crops, and natural resources; they have taken many human lives. The eruption of Pelée in 1902, for example, which included both flow and surge phenomena, claimed 28,000 lives. Lahars are dense slurries of water-saturated volcanic debris that travel downslope, occasionally at velocities as high as 40 m/sec. They are sometimes called volcanic mudflows; but because they consist of material of all sizes, including blocks as much as several meters in diameter, the Indonesian term lahar is preferred. They may be generated during eruptions when fragmented volcanic material becomes intermixed with water, such as from a crater lake or any other body of water or from eruption-induced melting of snow and ice or from eruption-induced rainfall. They may also be generated during quiet periods between eruptions when heavy rain or breaching of ponds or lakes mobilizes unconsolidated tephra. Historically, lahars have been one of the most destructive of all volcanic agents, with a high toll of both lives and property. Some historical deposits are tens of cubic kilometers, and some prehistoric deposits are hundreds of cubic kilometers in volume, and large lahars can travel over 100 km from their source. Kelut Volcano, Indonesia, is a notorious example where dozens of historical eruptions have been accompanied by lahars; in 1919 more than 100 villages were destroyed and over 5000 people were killed. Ruiz volcano (Colombia) had a moderate eruption in November 1985; melted snow and ice generated lahars that destroyed cities and towns greater than 50 km from the volcano, and more than 20,000 people were buried. During volcanic eruptions gases are not only a major product of emission, but they are considered to be the chief agent that propels the eruption. The most abundant volcanic gases include H2O, CO2, CO, SO2, SO3, H2S, HCl, and HF, and minor amounts of many other gases have been identified. Gas emissions often continue between eruptions, and some vents issue volcanic gas continually for years and decades. Several of the gases are poisonous, and some are corrosive; and in developed areas near gas vents humans, animals, plants, and property may be adversely affected. Certain forest trees and agricultural crops may become stunted or fail to survive gas emissions, such as during the 1783 eruption of Laki, Iceland, when fluorine-poisoned crops resulted in a famine that led to 10,000 deaths. At some volcanoes heavy gases have accumulated in basins or flowed down valleys, displacing oxygen and killing humans and animals. At Dieng, Indonesia, such gas emitted during a small eruption in 1979 killed 150 people. Another important volcanic process, which became much more widely recognized as a result of the 1980 eruption of Mount St. Helens, is the debris avalanche. At Mount St. Helens, an earthquake triggered the unstable, oversteepened north flank of the volcano into motion, and a catastrophic large landslide ensued that deposited some 2.8 km3 of debris in the nearby river courses and lake basin (Voight et al. 1981). Although large landslide deposits had previously been identified at a number of volcanoes, many additional deposits of similar origin have subsequently been recognized throughout the world. The experience at Mount St. Helens demonstrates that not only is the avalanche itself destructive, but the abrupt removal of material can depressurize an underlying phreatomagmatic system, which may then explode with cataclysmic violence (Lipman and Mullineaux, 1981). At Mount St. Helens, the debris avalanche launched a whole array of additional volcanic processes, including pyroclastic surges, flows and falls, and lahars.
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Active Tectonics: Studies in Geophysics IMPACT OF VOLCANOES ON PEOPLE Distribution of Volcanoes in Relation to Human Population Concentration of volcanoes along relatively narrow belts means not only that a relatively small proportion of the land area of the world is close to volcanoes but also that a relatively small proportion of the human population has direct exposure to volcanic activity. Table 15.1 shows an approximation of the percentage of the world’s population under risk from volcanic activity, either continuously, often, or only occasionally. It is assumed that people living within, say, about 300 km of an active volcano would be the most aware of and concerned about volcanoes. The table shows a total world population of 3709 million persons, of whom approximately 357 million live near volcanoes. As a result, somewhat less than 10 percent of the world’s population is likely to experience risk from volcanic activity, and many of these for only relatively brief periods. Hence efforts to generate support for research and surveillance of volcanoes frequently encounter only apathy and disinterest because the great majority of people have not directly experienced the problems. Only after major volcanic disasters does general interest become widespread, such as that generated by the 1980 eruption of Mount St. Helens. A high proportion of those countries having large segments of the population living in hazardous areas are developing countries, such as Indonesia, the Philippines, and countries in Central and South America (Table 15.1). These countries have but limited resources for dealing with the problems posed by volcanoes. Some developed countries with volcanic problems, such as New Zealand and Iceland, have but small populations. In western Europe, only Italy has historically active volcanoes located in areas that affect major population centers. The United Kingdom and France have overseas possessions with volcanoes (Caribbean and Indian Ocean regions), but these island colonies have small populations and lie far from the centers of government and industry. Similarly, the volcanoes of Spain and Portugal lie in the Canary and Azore Islands, well removed from national centers. Geologically young volcanic districts in France and West Germany have had no activity during human recorded history. Most of the volcanoes of the Soviet Union lie in a remote region of eastern Siberia thousands of kilometers from the center of government. The historically active volcanoes of the United States lie only in Hawaii and Alaska and in the Cascade Range of California, Oregon, and Washington. They directly affect less than 5 percent of the people of the United States. Other volcanic centers throughout the western United States have the potential for extremely destructive eruptions (Smith and Luedke, 1984), but because they have had no historical activity, public perception of their hazard is low. Among the largest powers, only Japan has active volcanoes in areas where they have direct and frequent influence on a high proportion of the population near the centers of national life. This selective distribution of volcanoes relative to centers of major influence in world affairs appears to be a cause of the rather low level of concern and understanding of volcanic hazards among the people of the world. Effects of Volcanoes on People and Their Activities In spite of the widespread lack of concern, nearly 10 percent of the world’s people do live and work near active volcanoes. Among the discussions of volcanic hazards and their implications to society are those by Macdonald (1972, 1975), Murton and Shimaburuko (1974), Warrick (1975, 1979), Marts (1978), Hodge et al. (1979), Sheets and Grayson (1979), Williams and McBirney (1979), Blong (1984), Crandell et al. (1984), and Tomblin and Fournier d’Albe (in press). Each provides insight into the hazards and risks posed by volcanoes. Most conclude that except during and shortly after crises, most people in risk-prone regions have little concern even about their own neighborhood, although they may be aware that elsewhere major eruptions cause serious consequences. The adverse effects of volcanoes are partly offset by often-overlooked beneficial effects. Volcanoes are builders of land. Many oceanic islands throughout the world owe their very existence to volcanic activity, and in these and other coastal areas volcanoes occasionally add new land. Even greater benefits are the water and air of the planet. Ancient volcanoes transferred volatile components from the molten depths to the surface to form the primitive oceans and atmosphere, and these were gradually modified to form the environment in which living things could develop. Hence volcanoes are one of the agents to which life itself owes its existence. Fertile soils develop from volcanic rock, and products from eruptions naturally renew them from time to time. In Indonesia the heaviest population is concentrated in the parts of Java and Bali that experience frequent damage or destruction by volcanic ejecta, for these are also the areas that sustain the richest agriculture. Where the climate is compatible, virtually every volcanic region on Earth is noted for its agricultural productivity. Volcanoes also produce outstanding scenery, and many volcanic areas support thriving tourist industries. The common proximity of volcanic belts to coastlines
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Active Tectonics: Studies in Geophysics TABLE 15.1 Tabulation of Estimated Population Dwelling Near Volcanoes in Each Continent or World Region Compared with Total Population for Each Region Continent or Region Country or Section Within Continent or Region That Has Volcanoesb Name Total Populationa (in millions) Name Total Population Population Near Volcanoesc Subtotals Africa 354 Ethiopia 26 2 Other E. Africa 74 4 Central Africa 37 1 West Africa 104 2 9 Asia (except USSR) 2,104 Indonesia 125 105 Philippines 39 32 Japan and Ryukyus 106 95 232 North America (including Hawaii) 229 Alaska 0.3 0.2 Washington 2.9 2.9 Oregon 1.8 1.8 California 18.8 6 Hawaii 0.7 0.7 11 Middle America 96 Mexico 53 40 Central America 17 13 Caribbean Islands 26 4 57 South America 195 Colombia 22 7 Ecuador 6 6 Peru 14 5 Chile 10 3 21 Europe (except USSR) 466 Iceland, Jan Mayan 0.3 0.3 Italy 54 22 Greece 9 0.4 Canary Is., Azores 1.3 1 USSR 245 Kamchatka 0.4 0.2 24 Oceania 20 New Zealand 3 1.5 Papua New Guinea 3 0.5 Island groups (i.e., Mariannas, Solomons, New Hebrides, Samoa) 1 1 3 Total World Population 3,709 Total Population Near Volcanoes 357 aPopulation figures are for early 1970s and have been adapted from Ehrlich and Ehrlich (1972). Some sectional figures have been derived from various geographic atlases. bPrecise data not available in convenient references; figures are estimates based on broad distribution of populations both within and outside volcanic belts. cThe countries and sections listed are derived from those having appreciable historic activity as shown in Simkin et al. (1981). means that some volcanoes lie near heavily used transportation and shipping routes. Geographic location and the benefits of volcanoes thus combine to attract human populations and activities to certain eruption-prone regions. Agriculture, tourism, shipping, and accompanying commercial and industrial activities may grow and flourish, especially near volcanoes with long eruption-recurrence intervals. At some places the activity is frequent and people learn to coexist with the volcanoes, carrying out mitigating measures as necessary. When the activity is mild, eruptions are an inconvenience, but more vigorous activity may cause minor to major destruction. Repeated destruction in some areas has led to adoption of land-use zoning, where frequently damaged areas are left undeveloped or minimally developed. Relatively successful adaptations are found in Japan, Philippines, Indonesia, and Iceland, but even in these countries some authorities are concerned over excessive development in places susceptible to damage by volcanoes. Volcano observatories have been established at a several frequently active volcanoes throughout the world, where systematic sur-
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Active Tectonics: Studies in Geophysics veillance and monitoring are carried out to provide advance warnings of impending activity. At many volcanoes, however, intervals between eruptions may be so long that the hazards are overlooked or forgotten. Commercial, industrial, agricultural, and residential development may proceed without regard to the potential threat of the volcano. When indications of potential activity commence, it may be difficult to evaluate their significance. Many such signs either subside with no activity or lead only to mild activity. However, sometimes precursory signs are followed by major disastrous eruptions that destroy both lives and property. Several well-known, large eruptions that followed quiet intervals of decades to centuries are Vesuvius (Italy, AD 79); Krakatau (Indonesia, 1883); Pelée (Martinique, 1902); Lamington (Papua New Guinea, 1951); Agung (Indonesia, 1963); Mount St. Helens (United States, 1980); and El Chichon (Mexico, 1982). Each of these eruptions cost human lives. Minor symptoms precede almost all large eruptions, but at infrequently active volcanoes they may be either ignored or misinterpreted. Even at Mount St. Helens, where the early minor symptoms were extensively studied, it was not possible to forecast the time or character of the cataclysmic event. However, precursors have been successfully interpreted to predict more than a dozen subsequent eruptions (Swanson et al., 1983). Cataclysmic events, although uncommon, have a far greater influence on human perceptions than do the many lesser eruptions that occur each year throughout the world. Major eruptions arouse the awareness of people everywhere to this natural process and its capacity for destruction. Such eruptions demonstrate the need for improved understanding of the processes that cause volcanic activity. The interest generated by new major eruptions generally leads to temporary modest increases in support of research on volcanic processes and improvement of surveillance techniques. VOLCANO MONITORING From a world total of about 540 volcanoes with identified historical activity (Simkin et al., 1981), about 50 to 65 different volcanoes erupt every year. Many eruptions occur in remote regions where their impact on human affairs is minimal, and many of those reported are small and cause but minor damage. Even so, on the average about a dozen volcanoes per year cause appreciable damage and sometimes human casualties, and from one to a few times per decade volcanic eruptions cause major damage and disruption with many casualties. In spite of the subordinate ranking of volcanic hazards in public consciousness, most countries with active volcanoes have been able to organize some effort to observe and study them. The United Nations and several of the more developed countries with foreign aid programs have given occasional assistance to countries whose own resources are small, and efforts are being made to improve and continue these programs. However, in every country decisions must be made on how to allocate the limited available resources in the most effective way. For example, it must be decided whether to achieve broad but dilute coverage for an entire region or instead to concentrate on one or a few frequently active volcanoes. The ideal goal would be to monitor them all, but this is rarely possible. Decisions on priority are reached by fitting the available surveillance program to known patterns of volcanic behavior. Even with abundant resources, it is difficult to achieve fully satisfactory warning capabilities. While great strides have been made in monitoring procedures and general volcanic processes are becoming better understood, each volcano has a wide range of individual behavior, and few volcanoes exhibit the same precursors or eruptive style. Virtually every eruption at every volcano adds new information to the scope of possibilities. Within this framework of limitations and difficulties, a wide array of tools and techniques has proven important for study, monitoring, and forecasting. Some techniques have universal applicability, whereas others prove useful only at some volcanoes or for certain eruptive episodes. Hence monitoring techniques applied at any volcano are best established by trial and error, gradually discovering the most effective techniques and adapting them to local behavior patterns. As more data are collected, perhaps more universal behavior patterns will be recognized. Monitoring Techniques The most basic of all techniques, and one frequently overlooked or ignored in these times of high technology, is that of careful, systematic, visual observation. Descriptions by trained and practiced observers for background and quiet conditions, for precursory periods, for eruptive activity, and for changes caused by eruptions constitute the most essential surveillance technique of all. Such observations are the starting point from which all other techniques begin. It is desirable for the observations to be supplemented by topographic maps at several scales, aerial photographs with stereographic coverage, and systematic documentary photographs—all made at appropriate time intervals. But even when these valuable supplements are not available, the records of keen and diligent observers are vital. An extensive literature describes the multitude of in-
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Active Tectonics: Studies in Geophysics strumental techniques utilized in volcano monitoring. Useful summaries and applications of common techniques are provided by Stacey (1969), UNESCO (1971), Civetta et al. (1974), Lipman and Mullineaux (1981), Martin and Davis (1982), and Tazieff and Sabroux (1983). Citations to individual papers within these collections will not be given in this abbreviated summary. Seismic monitoring is the single most essential instrumental technique used in volcano surveillance. As magma rises toward the surface before eruption, stresses forming in the adjacent rocks are relieved by fracturing and slippage, which seismographs detect as earthquakes. Most of these are of very small magnitude (less than Richter magnitude 1), although these microearthquakes may be interspersed with some quakes of larger magnitude (1 to 5). Another type of signal commonly recorded is a fairly continuous, low-frequency rhythmic vibration that is termed volcanic tremor (more commonly but slightly erroneously called harmonic tremor). It is generally thought to be associated with the movement of fluid through passageways in rock, though the mechanism that generates volcanic tremor is not fully understood. At most volcanoes the numbers of earthquakes per unit time and the rate of seismic energy release show systematic increases prior to eruptions. Such increases, particularly when accompanied by or interspersed with volcanic tremor, are one of the most important techniques in forecasting volcanic eruptions (Figure 15.2). They are used with most confidence where repeated similar patterns have been observed prior to earlier eruptions. Each volcano seems to have an individual set of characteristic signals, so although the general principles are common to all, the details recorded at one volcano do not necessarily apply at any other. Not every increase in seismic activity at a volcano precedes an eruption, which sometimes greatly complicates the forecasting process and emphasizes the importance of utilizing multiple techniques for surveillance. However, rarely if ever does an eruption begin without being preceded by an increase in seismicity; hence any volcano with even primitive seismic instrumentation will likely give some warning before eruption. Nearly as important as seismic monitoring are various techniques of measuring ground deformation. As magma rises, it displaces rock, and these displacements are transmitted through intervening rock and expressed at the surface. Displacement of the surface may also be caused by pressure exerted by gases exsolving from the magma. These displacements cause points on the surface of the ground to move in relation to one another, both vertically and horizontally, and the amounts and rates of movement can be detected by a variety of tech FIGURE 15.2 Plot showing data as detected by three different monitoring methods spanning a 2-month period at Mount St. Helens. The period includes an episode of lava extrusion during September 1984. Increases in seismicity, rate of ground displacement, and rate of gas emission were associated with this extrusion. The extrusion of lava began about September 10 and continued for a few days. Signals commonly increase at accelerating rates during days prior to the onset, and decrease when extrusion begins. A, Seismicity as shown by daily earthquake count at a seismograph located in the crater. Counts began to increase in late August and progressively increased for several days; signals saturated the record from about September 8 to 11. Seismicity returned to background about September 14. B, Maximum daily rate of displacement of selected target on lava dome. Prior to September 1, the background rate was from about 2 to 5 cm/day; from September 2 to 8 the rate increased from 10 cm/day to about 3.5 m/day. The displacement rate exceeded 50 m/day just prior to onset of extrusion and declined rapidly after extrusion began. C, SO2 gas emission rate as measured by aircraft-mounted COSPEC. Data are not continuous because flights are made at irregular intervals. This extrusion was preceded and accompanied by a pronounced increase in emission rate, but some events show little or no change. niques. The simplest of these is a measuring tape; if cracks or faults develop, distances between fixed points on opposite sides of the break can be measured periodically, and rates, and sometimes directions, can be determined and plotted. Across distances from tens of meters to tens of kilometers, horizontal displacement between fixed points can be monitored by electronic distance meters; modern precise instruments utilize a laser beam. Vertical changes can be determined by repeated leveling along survey lines. Changes in slope of the ground are determined by tilt measurements by precise surveying techniques, water-tube devices, or electronic tiltmeters. High-precision photogrammetry is now capable of detecting ground displacements to within fractions of a
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Active Tectonics: Studies in Geophysics meter, so it holds promise of being a useful supplement in detecting deformation, particularly in places where access is difficult. Repeated measurements by any of these techniques may give an indication of when swelling of the volcano is occurring, but ideally a combination of all of them is employed, preferably with multiple stations and lines to attain a broad coverage. Constant rates of displacement indicate steady inflation or deflation of the volcano. Days to weeks before an eruption, rates of displacement may increase or total displacement may reach some critical level. Such changes, especially when correlated with seismic observations, are important in predicting eruptions (Figure 15.2). When observations are made over a wide enough area, displacement vectors can estimate the location of the center of swelling, and further analysis may give indications of the depth, size, and behavior of the magma body. Ground deformation studies are, therefore, important both to forecasting and to improving understanding of volcanic processes. The chemical and mineralogical composition of the erupted products is important in assessing the character of an eruption and the general state of the volcano, and systematic collection and analysis of lava and tephra samples are critical activities. Any change in composition during an eruption provides clues to magmatic processes and may hint of potential changes in eruptive behavior. Changes in the gravitational-field strength are caused by a change in elevation or a change in the density of nearby rocks or both. At a volcano the altitude of points on the surface may change in response to intrusion or withdrawal of magma, and the nearby mass distribution may also change in response to the same processes. Eruptions add new rock to the surface, and other volcanic processes may cause collapse or other redistribution of material, which affects the local gravity field. Changes in the level of groundwater associated with eruptions, rainfall, or accumulated snow and ice can cause changes in the gravitational-field strength. Because of these complexities, it is unlikely that gravity measurements can be used as a forecasting tool. But when coupled with other techniques, especially ground-deformation measurements, they can be useful in constraining and better defining models for movement of magma and other volcanic processes. Gases are significant components of magma, and their chemistry, rate of emission, and relative proportions provide clues to magmatic behavior and to volcanic processes in general. The manner and rate at which gases are liberated from the magma are primary factors determining the type and style of any eruption. Moreover, during the times between eruptions, gases being exhaled from vents and fumaroles provide the only component of magma that can be readily sampled. Hence gases have long been recognized as an important subject for study, both for potential value in eruption forecasting as well as in improving the understanding of volcano behavior. Modern collecting and analytical techniques can yield reliable results for gas composition, and changes in ratios among different gases can help scientists to infer the eruptive potential of a volcano. Changes in the absolute emission rates of volcanic gas empirically would seem to reflect the likelihood of eruption because, as magma rises, confining pressure decreases and cracks develop in adjacent rocks, which should tend to increase gas flux. Use of the correlation spectrometer (COSPEC) at Mount St. Helens and other volcanoes has helped to confirm this concept. The COSPEC, an instrument originally designed to monitor air pollution, can be utilized to measure the flux rate of SO2 gas, and results have demonstrated broad, and sometimes specific, fluctuations that correlate with volcanic behavior (Figure 15.2). Electronic probes to detect hydrogen emissions and transmit data via telemetry have been deployed at a few volcanoes. Changes in the strength of the magnetic field at a volcano can be caused either by the underground movement of magma or by changes in the stress patterns in the adjacent rocks. Regardless of the cause, a change in field strength should be a useful supporting technique to forecast eruptions. Studies have been carried out at a number of volcanoes, generally by deploying an array of magnetometers at sites on the volcano with one instrument established at a site remote from the volcano; the readings are systematically telemetered to a recording station. In addition to the absolute magnetic field measurements, the field-strength differences between the distant and near sites are recorded so as to neutralize nonvolcanic fluctuations such as magnetic storms and diurnal variations. Promising results have been obtained at several volcanoes, showing some changes in field strength associated with volcanic events, but assorted difficulties with instruments, telemetry, and volcano-induced damage have not yet allowed the technique to achieve its full potential. Several kinds of study have been performed at volcanoes using a variety of electrical and electromagnetic techniques. Electrical resistivity of magma and molten lava is low, whereas that of dry solidified lava is high; resistivity is further modified by the variable conductivity of permeating groundwater. The contrasts are adaptable to a wide variety of studies and experiments with different kinds of instruments and equipment. Self-potential, very-low-frequency electromagnetic, resistivity, and induced polarization are a few of the tech-
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Active Tectonics: Studies in Geophysics niques that have been used for experiments and studies at volcanoes. Measurement of temperature changes at the surface seems to be an obvious method of detecting change within a volcano, but it must be applied with caution. Under certain conditions at some volcanoes, increases in temperature occur at hot springs, fumaroles, and crater lakes, and systematic temperature surveillance is a useful monitoring tool. But surface temperatures can be affected by many nonvolcanic factors—rainfall, snow, changing groundwater levels, vegetation, weather conditions such as clouds and wind, and diurnal changes—so measurements must be carefully interpreted. A number of methods may be used to determine temperature; the simplest being direct measurements using thermometer, thermistor, or thermocouple, depending on the temperature range. Care must be taken on successive readings to occupy the same location under as consistent environmental conditions as possible. Thermal infrared techniques have been used at some volcanoes; measurements can be made remotely, either from ground stations or by aerial survey. These methods are useful in detecting broad changes in thermal patterns, but unless expensive calibrated equipment is used they do not yield quantitative results. Readings depend heavily on atmospheric conditions; clouds, rain, dust, and volcanic fume will affect results. In spite of these difficulties, efforts are under way at some volcanoes to establish consistent calibrated thermal surveys. Fluctuating temperatures at some crater lakes have preceded some eruptions; such changes can supplement symptoms revealed by other techniques to help forecast activity. PUBLIC RESPONSE TO VOLCANIC ERUPTION Most people, in areas impacted by a volcanic eruption, are not especially interested in the research that keeps volcanologists occupied. During an emergency, they are concerned chiefly with the practical matters that affect them directly. Their questions are: Will the volcano erupt again? Will the lava (or volcanic ash) come in our direction? How often will it happen? How long will the eruption last? When can we go home? When can we resume our regular work? People generally expect scientists to answer these questions, yet they rarely can be answered with confidence. When confronted with the stark conditions of displacement, discomfort, and perhaps survival, people may be surprised that the volcanologists are concerned with such seemingly esoteric matters as rock chemistry, tiny motions of survey markers, and wiggly lines on paper charts. While some people are interested and understanding, others will regard such activities as irrelevant, inane, or futile, and scientists may be viewed with indifference, skepticism, or hostility. It is difficult for some people to comprehend that answers to the scientific questions are ultimately the chief hope for answering their own questions. For a more beneficial outlook, people need information and education, both about volcanoes and about methods used in their study. Hence in regions likely to experience volcanic eruptions, it is important for regular programs of education to be carried out before times of crisis. It is in the interest of scientists themselves to provide impetus, encouragement, and even to sponsor such education. In making long-range plans for appropriate use and development of land, zones may be established as defined by relative degrees of volcanic hazard (Crandell et al., 1984). Various ways can be utilized to inform people about volcanoes, such as special meetings; talks to schools, civic groups, and clubs; and through booklets and pamphlets, displays at museums and visitor centers, newspaper articles, television and radio programs, and open houses at volcano observatories or other research facilities. The specific means can be adapted to local conditions. In the broad scheme of interactions between a volcano and the people, three other groups besides the scientists play key roles: public officials, land and property managers, and representatives of the news media. When a nearby volcano is quiet, all groups have the opportunity to participate in the important functions of education about volcanoes and preparation for crises, both for their own enlightment and for the benefit of the people they serve. When the volcano becomes active, all become responsible for critical functions. In many branches of science, scientists have but minimal or casual dealings with public officials, land managers, and news media, but when working with an active volcano, scientists must deal regularly with them all. Each group will find it advantageous to attain a good understanding of the role of the other and to gain appreciation and respect for the requirements, capabilities, and limitations of one another. While each group performs a different role, all have the common goal of promoting the welfare of the community. Interactions Between Volcanologists, Public Officials, and Property and Land Managers Wide variations exist from one country to another in the type of government and land ownership. Regardless of the prevailing system, however, those vested with appropriate responsibility each have an essential role to play when confronting problems posed by volcanoes. In areas of high volcanic risk, public officials and property
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Active Tectonics: Studies in Geophysics and land managers will be wise to gain at least minimal knowledge about the nature, characteristics, and range of behavior of the volcanoes in and near their jurisdiction. Ideally volcanologists will assist them, and members of each group will establish acquaintance and a good working relationship during times when the volcano is quiet. All can foster education, both for children in schools and for adults in meetings and forums by public and private groups. Officials can formulate contingency plans that prescribe courses of action for all departments in the event of a volcanic emergency. Property and land managers can anticipate questions regarding operations and access on their property and develop contingency policies in conjunction with public officials. Drills may be held by all groups for practice and to test and improve the plans. At some volcanoes, the hazards affect two or more local jurisdictions, in which case the adjoining governments should cooperate in developing the plans and in practicing the procedures. Volcanologists may serve as advisors in such exercises. In most societies, elected or appointed officials hold authority for making the decisions on common action in response to a volcanic crisis (Warrick, 1979; Blong, 1984; Tomblin and Fournier d’Albe, in press). Depending on the situation and conditions, the officials may be at the local, regional, or national level. They must decide if and when people are to be evacuated; designate the boundaries of the evacuated area; determine routes and transportation methods; arrange for food, shelter, sanitation, medical care, and other needs of the evacuees; and pay the costs. An evacuation is an economic loss in terms of the cost of evacuation, care of those evacuated, and interrupted productivity; it is a social disruption because of the displacement of people from their homes and occupations. Officials face grave decisions when confronted with a volcanic crisis: to fail to evacuate during early activity when a destructive eruption follows may result in lives lost; yet to evacuate when no eruption follows results in social and economic loss. Either circumstance is inevitably followed by a hail of criticism (Hodge et al., 1979; Blong, 1984; Fiske, 1984; Tomblin and Fournier d’Albe, in press). Officials themselves are rarely able to judge independently whether the condition of a volcano warrants evacuation; they must depend on the advice of scientists. At frequently active volcanoes, especially those where an observatory keeps the volcano under regular surveillance, the advice of the scientists is usually reliable. At these volcanoes, procedures for a warning and subsequent decisions and actions are generally well established; familiarity and frequent practice aid officials in making sound decisions. Several correct decisions on warning and evacuation will build up public confidence and likely some tolerance for an occasional incorrect decision. Officials tend to lean toward the side of caution when issues of public safety are involved. The expenses incurred in unnecessary evacuations may help to convince officials that costs of volcano research are sound investments. But all should realize that even well-monitored volcanoes produce surprises. In contrast, at volcanoes that are little studied, infrequently active, or believed to be extinct, the onset of unrest may create confusion and uncertainty. Public officials are likely to be unsure over the proper steps to protect the people and to uphold the public interest. They desperately need sound scientific advice, yet volcanologists brought in to evaluate such situations must often make conclusions based on inadequate data gathered quickly. Any resulting advice to officials may be heavily qualified with uncertainties. Unless mutual understanding has been established earlier, such advice may be perceived as inadequate or incompetent. During such situations, controversy may develop between scientists and public officials. Sometimes the officials want the scientists to make and be responsible for the decisions on evacuation and degree of allowable public access; more commonly the officials prefer not to relinquish this authority. Such decisions involve economic and social consequences about which scientists generally have little expertise, and the officials must weigh carefully the degree of hazard against the consequences of various choices. The volcanologists have the responsibility to state the degree of risk in language that is as clear and unambiguous as possible, recognizing that few officials are familiar with technical terminology or with scientific methods of judging uncertainties based on scant evidence. However, if evidence is compelling that hazards are severe or unequivocal, volcanologists must make this clear by making appropriate recommendations. Yet all parties should understand that, unless authority is otherwise vested, the ultimate decisions about public safety are in the hands of the public officials. Interactions Between Volcanologists and the News Media Newspapers, magazines, television, and radio constitute the principal means by which people learn about potential or actual eruptive activity at any particular volcano. The degree and type of news coverage is determined by the size and character of the volcano or eruption, its accessibility, and the size and distribution of the local population. Journalists are generally more interested in the impact of an event on people than in the scientific aspects. Major eruptions in isolated regions of-
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Active Tectonics: Studies in Geophysics ten receive little or no notice by the press, whereas even minor events in populated areas receive much attention. It is important that public officials, property and land managers, and scientists have effective means for communicating with the press, because the public welfare requires that prompt, reliable, accurate information be conveyed to the news media. Both public officials and large land managers deal with the press regularly, so channels and procedures are normally already in place. Volcanologists, however, may be unfamiliar with media procedures, so it is important that they prepare themselves. If a group of scientists is studying an erupting volcano or one showing signs of erupting, it is well to designate a single member of the group to communicate with the news media; if the team is small the person may be the leader. Having a single representative ensures continuity and consistency and permits mutual confidence and rapport to develop while minimizing the chances for misunderstandings. Ideally this scientist-for-information is fully informed on the status of the volcano and on the activities, findings, and opinions of every team member and reports to the press regularly after consultation with the other scientists. Reports should be as complete and factual as possible, emphasizing what has happened and is happening. The scientist must be prepared on how to respond to questions regarding the timing, nature, and magnitude of future events. These are important questions, and seeking their answers is one of the principal reasons for the scientists’ activities; yet most of the time these questions do not have clearly defined answers. The scientist must still respond in a factual, helpful manner, stating the range of possibilities and the degrees of uncertainty in terms of ongoing processes that are understood. Many reporters will be dealing with an unfamiliar subject, and information should be presented, insofar as possible, in straightforward, everyday language. The scientist should be patient with reporters as they learn and be genuinely concerned in helping them to produce complete and accurate stories. Honesty and sincerity inspire confidence from media members, which in turn enhances the quality of the news stories. Departures from this ideal sometimes occur. Controversies between scientists may arise, sometimes when two or more groups come from different institutions or different countries. It is best to try to resolve such controversies privately. But if the news media learn of them, the controversies can still be handled constructively by showing that volcanology is a young, inexact science and that progress is made by testing opposing hypothesis. Sometimes, however, such public disagreements become antagonistic; the disagreement may rival the story of the eruption, relations between scientists and media deteriorate, the public becomes confused or angry, and scientists lose credibility. Such a controversy occurred at La Soufrière Volcano on Guadeloupe in 1976 (Fiske, 1984). While constructive and mutually supportive relations between scientists and the news media are the ideal goal, it is sometimes not achieved. Most scientists who have experienced more than a few interviews can cite examples of misquotations, quotations out of context, or news stories that are flatly inaccurate. On the other hand, reporters have equally valid complaints about scientists who talk in obtuse language, refuse to see them, or are perceived to be arrogant. Differences in perceptions and goals between scientists and journalists are probably the cause of most of this antagonism and controversy. In an effort to help members of each group better understand the other, Table 15.2 outlines some of the complaints scientists and journalists have expressed about each other. These problems stem partly from the basically different personalities attracted by the contrasting professions. Their respective job requirements are different. Scientists must be accurate, analytical, and deliberate, and they must consider many lines of evidence before reaching conclusions. Statements of their conclusions are commonly hedged with qualifiers. In contrast, journalists must be quick and decisive, and while they strive for accuracy it must be achieved within a framework of perpetual deadlines. Further, they must quickly identify the key factors, emphasize them, and reduce a body of information to its simplest terms. Table 15.2 is arranged to illustrate opposite but corresponding complaints, which demonstrate how mutual misunderstandings develop from particular situations. Obviously not every aspect of these problems can be covered in an abbreviated and generalized table, but even so it implies ways to improve understanding between scientists and journalists. When scientists understand the reporters’ needs to get quickly to the main point, they can dispense with lengthy preambles and excessive qualifiers. Scientists can minimize jargon and be sure that those technical terms that are necessary are clearly defined. It is useful for them to remember that they are not delivering a paper at a scientific meeting but instead are conveying information, through the reporter, to people from all walks of life. Reporters in turn have the responsibility to strive for accuracy in expressing the information. Nothing is more frustrating to the scientist than to find himself misquoted or to have his statements used in a wrong context. He is put in the position of seeming to provide incorrect, perhaps damaging, information to the public. Reporters should not be reluctant to check back to
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Active Tectonics: Studies in Geophysics TABLE 15.2 Some Common Sources of Friction Between Scientists and Journalists Complaints by Scientists About Reporters Complaints by Reporters About Scientists We get misquoted in news stories Scientists talk in jargon that no one else can understand Reporters are too pushy and aggressive Scientists are aloof, hard to reach, uncooperative Reporters are not satisfied with what we tell them; they are always looking for hidden angles; they are too suspicious Scientists do not tell the whole story, they hold back and conceal information Many reporters are poorly prepared; they know nothing about the subject or even about what has already happened here Scientists expect us to be experts in their subject, they are impatient in giving us the background we need Reporters interrupt our work schedules; they do not seem to see how they themselves are hindering us in trying to find answers to their (and everyone’s) questions Scientists do not understand the time deadlines under which we are required to operate Reporters do not really listen to the whole story we try to tell them; their coverage is shallow; they omit the all-important qualifiers to our statements; they think all answers should be black and white but ignore all the intermediate shades of gray Scientists are too long-winded; they talk all around the subject and never get to the point. They do not understand that we need to use straightforward simple statements; we have to convert their complicated discourses to words that people can read Reporters seek out differences of opinion between scientists and overemphasize them; they try to make a story by fabricating discord When we try to verify our story with a second opinion, we cannot get any consistency between different scientists. How do we know who to believe? NOTE: This table shows examples of attitudes and actions that lead to antagonism between scientists and journalists. Their listing here is not intended as criticism of either group nor to fuel controversy. Instead they are intended to help each group recognize how its own attitudes and actions impinge on the other, thereby aiding members of each group to seek ways to improve the perceptions of the other. Happily, the complaints are not universal, and many members of both groups understand and accommodate the others’ viewpoints and requirements. verify the accuracy of their stories; scientists should welcome such opportunities. Many of the hard-to-reach scientists about whom the reporters complain are those who have been embarrassed by past misquotations. These potential problems demonstrate the value of having a specified scientist to provide information; this person can become practiced in responding to reporters’ needs, seek ways to improve each presentation and avoid past mistakes, and build up friendly rapport. Likewise it is helpful if the same reporters stay on the story long enough to gain knowledge and build consistency; when new reporters are assigned, they can avoid many problems if they acquire appropriate background before starting their interviews. It is important that each group understand the work requirements and time schedules of the other. Newspapers and television have deadlines at different times, and neither necessarily fits the normal working schedule of a field volcanologist. When the scientific staff is small, stopping work to grant interviews interferes with the acquisition and interpretation of data. However, when both groups better understand the others’ legitimate requirements and limitations, it is almost always possible for them to accomodate each other. When such cooperation is achieved, the public reaps the benefits. Summary of the Volcanologist’s Role in Enhancing Public Understanding People properly informed about the character and behavior patterns of volcanoes are best prepared to deal with volcano emergencies when they arise. Only near volcanoes that either erupt frequently or have just recently erupted, however, are members of the general public likely to have much awareness of volcano hazards (Murton and Shimaburuko, 1974). In areas distant from volcanoes, or in areas near long-dormant volcanoes, people are unlikely to be aware of problems posed by volcanoes. Even at times of volcanic crisis elsewhere, the general reaction is commonly, “aren’t we lucky those things don’t happen here.” Among all groups of people, volcanologists and other earth scientists are the most likely to be aware of the troublesome potential of nearby volcanoes. Many recognize the responsibility to raise the general awareness of the hazards, yet their efforts are often misunderstood or misconstrued. For example, when the now-renowned report by Crandell and Mullineaux (1978) on volcanic hazards at Mount St. Helens first appeared, it received considerable local criticism for being scarey and potentially adverse to the economy. Then, in spite of the les-
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Active Tectonics: Studies in Geophysics sons learned at Mount St. Helens in 1980, a storm of criticism arose when a notice of potential hazard was issued in 1982 at Mammoth Lakes, California, in response to repeated earthquake swarms (the hazards are summarized in Miller et al., 1982). The warnings were perceived by some of the local population and the press as self-serving to the scientists as well as highly damaging to property values and local business. Even in Hawaii, where, if anywhere, people should be aware of problems posed by volcanoes, a report describing volcanic hazards of the Island of Hawaii (Mullineaux and Peterson, 1974) was severely criticized by some community leaders for depressing the local economy and hampering development in volcano-prone areas. Similar reactions have occurred during recent seismicity and deformation at both Rabaul, Papua New Guinea, and Pozzuoli, Italy. Such reactions demonstrate traits typical of human nature and emphasize the attitudes of indifference or hostility induced when receiving information about potentially unpleasant matters. They also underscore the challenge that faces scientists as they attempt to inform the public about volcano hazards. The importance of the message is great enough that the scientists must not only be willing to face the adverse reactions but also to persist in finding truly effective ways of conveying information that is important to societal needs. Competent scientific information does little good if it is ignored, scorned, or disbelieved. It is important for scientists to be tactful, patient, and perservering as they deal with the news media and public officials on matters concerning volcano hazards. They must find ways to employ the same qualities of innovation and resourcefulness that they normally display in scientific research if their hazard messages to the public are to be heard and heeded. ACKNOWLEDGMENTS This paper reflects the experience, ideas, and opinions developed during service at both the Hawaiian Volcano Observatory and the Cascades Volcano Observatory (CVO). I am grateful to my colleagues at each facility for support, discussions, and constructive debate on both the scientific and societal issues associated with hazardous volcanoes. I am also grateful to the public officials, land managers, and representatives of the press in both regions, with whom we explored together to find positive ways to solve the problems that we faced. The paper was reviewed by D.R.Mullineaux, R.W.Decker, and several colleagues at CVO, and it has been greatly improved by their suggestions. REFERENCES Blong, R.J. (1984). Volcanic Hazards, Academic Press, Sydney, Australia, 424 pp. Bullard, F.M. (1976). Volcanoes of the Earth, Univ. of Texas Press, Austin, Texas, 579 pp. (2nd ed. published 1984, 629 pp.). Christiansen, R.L., and P.W.Lipman (1972). 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Representative terms from entire chapter: