Understanding Volcanoes and Volcanic Hazards
Summary and Keywords
Between 50 and 70 volcanoes erupt each year—just a fraction of the 1,000 identified volcanoes that may erupt in the near future. When compared with the catastrophic loss of lives and property resulting from typhoons, earthquakes, and floods, losses from the more infrequent but equally devastating volcanic eruptions are often overlooked. Volcanic events are usually dramatic, but their various effects may occur almost imperceptibly or with horrendous speed and destruction. The intermittent nature of this activity makes it difficult to maintain public awareness of the risks. Assessing volcanic hazards and their risks remains a major challenge for volcanologists.
Several generations ago, only a small, international fraternity of volcanologists was involved in the complex and sometimes dangerous business of studying volcanoes. To understand eruptions required extensive fieldwork and analysis of the eruption products—a painstaking process. Consequently, most of the world’s volcanoes had not been studied, and many were not yet even recognized. Volcano research was meagerly supported by some universities and a handful of government-sponsored geological surveys. Despite the threats posed by volcanoes, few volcanological observatories had been established to monitor their activity.
Volcanology is now a global venture. Gone are the days when volcanologists were educated or employed chiefly by the industrial nations. Today, volcanologists and geological surveys are located in many nations with active volcanoes. Volcanological meetings, once limited to geologists, geophysicists, and a smattering of meteorologists and disaster planners, have greatly expanded. Initially, it was a hard sell to convince volcanologists that professionals from the “soft sciences” could contribute to the broad discipline of volcanology. However, it has become clear that involving decision makers such as urban planners, politicians, and public health professionals with volcanologists is a must when exploring and developing practical, effective volcanic-risk mitigation.
Beginning in 1995, the “Cities on Volcanoes” meetings were organized to introduce an integrated approach that would eventually help mitigate the risks of volcanic eruptions. The first conference, held in Rome and Naples, Italy, encompassed a broad spectrum of topics from the fields of volcanology, geographic information systems, public health, remote sensing, risk analysis, civil engineering, sociology and psychology, civil defense, city management, city planning, education, the media, the insurance industry, and infrastructure management. The stated mission of that meeting was to “better evaluate volcanic crisis preparedness and emergency management in cities and densely populated areas.” Since that meeting nearly twenty years ago, Cities on Volcanoes meetings have taken place in New Zealand, Hawaii, Ecuador, Japan, Spain, and Mexico; the 2014 venue was Yogyakarta, Indonesia. The significant and rewarding result of these efforts is a growing connection between basic science and the practical applications needed to better understand the myriad risks as well as the possible hazard mitigation strategies associated with volcanic eruptions.
While we pursue this integrated approach, we see advances in the technologies needed to evaluate and monitor volcanoes. It is impossible to visit all the world’s restless volcanoes, let alone establish effective monitoring stations for most of them. However, we can now scrutinize their thermal signatures and local ground deformation with instruments on earth-observing satellites. When precursory activity is detected by remote sensors in an area where a population is at risk, teams can be deployed for ground-based monitoring of that activity. In addition, by evaluating a volcano’s past eruption history, scientists can forecast both future activity and the possible risks to inhabitants. Using physics-based modeling, there is a better understanding of the types and severity of potential eruption phenomena such as pyroclastic flows, ash eruptions, gaseous discharge, and lava flows. Field observations of changes indicating an imminent eruption are now monitored with geophysical and geochemical instrumentation that is smaller, tougher, and more affordable.
Volcanology has evolved into a broader, integrated scientific discipline, but there is much still to be accomplished. The new generation of volcanologists, who have the advantage of knowing the theoretical underpinnings of volcanic activity, can now turn to the allied endeavor of reducing risk—their aspiration for the 21st century.
It has been 132 years since the eruption of Krakatau, Indonesia, with its caldera collapse, pyroclastic density currents, catastrophic tsunamis, and global atmospheric effects. The Krakatau eruption killed 36,417 residents along the coastlines of southern Sumatra and eastern Java. Since that eruption, the study of volcanic processes and their hazards has grown exponentially. In the 21st century, with myriad earth-observing satellites, rapidly evolving geophysical technology, instant communication, coordinated teams, and over a century of volcano studies, we are in a far better position for forecasting eruptions and mitigating volcanic risk.
Volcanoes are exciting for people of all ages and cultures—stimulating awe and respect. However, the many eruption phenomena and their effects are often misunderstood by the public and even by well-educated media personalities. For example, a TV newsperson standing near an eruption talks about the effects of the lava flows, but volcanologists watching the show grit their teeth and mutter “those are not lava flows!” Scientific terminology frequently baffles the general public, who complain that it is too complicated or not well defined. Volcanologists are guilty as charged when they toss about obscure terms that only their colleagues can understand (and sometimes even they don’t fully comprehend). Words describing volcanic activity and effects also have evolved through time; for example, “air fall” has become “ash fall”—a far more logical term because air doesn’t leave much of a deposit.
Before entering this account of volcanoes, the types of activity, and specific hazards associated with them, here is a visual summary of the basic kinds of activity that have and still do occur at the earth’s many active volcanoes (see Figure 1).
Where Are the World’s Volcanoes?
Most are located along the earth’s plate boundaries; these are easily defined features such as the “Pacific Ring of Fire.” However, there is also a lot of volcanic activity in areas within the continental crust itself. Crustal areas may be thinned by extension and then penetrated by “hot spots,” which are the loci for volcanic activity far from any plate margin. Our knowledge of volcanic activity within the ocean basins is increasing slowly because of the limited number of research vessels engaged in studying an area that comprises two thirds of the earth’s surface. But the Smithsonian Institution’s Global Volcanism Program (GVP) estimates that, on land surfaces alone, approximately 1,000 volcanoes above or near sea level are likely to erupt in the future. Throughout historical time, 550 volcanoes are known to have erupted. Some 50 to 70 volcanoes erupt each year. If you are yearning to visit to an eruption, the GVP website describes eruptions in progress (see Figure 2).
Volcanology Studies Before the Mid-20th Century
The catastrophic eruptions of Krakatau in Indonesia (1883) and Mont Pelée in the French Antilles (1902) are the volcanic events from past centuries that are best known to the public. Even the 1912 eruption of Novarupta on the Alaskan Peninsula, the largest of the 20th century, however significant for the people of Alaska, was not headline news for the United States, much less the world as a whole, during the buildup toward World War I. In fact, until the latter part of the 20th century, volcanic eruptions did not necessarily make the international news. Although there was a significant decline in reports of global volcanic activity in the years just before and during World War II, the activity itself did not decline; other global events simply took precedence. (Simkin et al., 1981).
Before the second half of the 20th century, volcano observatories were relatively few and far between. The famous volcanologist Thomas A. Jaggar established the Hawaiian Volcano Observatory in 1912, used it as his base until 1940, and made systematic observations of Kilauea and Mauna Loa. He also led expeditions to young volcanoes in Asia, Alaska, and the Americas. His most interesting popular book was Volcanoes Declare War: Logistics and Strategy of Pacific Volcano Science (1945). Japan, with its astounding 116 active or potentially active volcanoes, already had several volcano observatories. Italy’s Vesuvian Observatory functioned throughout WWII, and France built an observatory to monitor Mont Pelée, on the island of Martinique. With so many active volcanoes located near its populated areas, the Dutch-led Indonesian government established a volcano survey in 1920.
Early research on volcanic activity and hazards was led by a small international group that could accurately term themselves volcanologists. A few were famous and wrote influential books (for example, T. Anderson, Volcanic Studies in Many Lands, 1903, and J. P. Iddings, The Problem of Volcanism, 1914), but many were caught up in their interests in specific phenomena or perhaps wrote only basic reports for the files. Methodical geologic mapping by most industrial nations was geared toward economic geology, engineering geology, and mitigation of natural hazards. Geologists fortunate enough to be working in a volcanic field made progress toward building a classification scheme for volcanoes and their activity. However, only a few were assigned to systematically monitor eruptions—for example, William Foshag from the U.S. National Museum, and Carl Fries Jr. and Ray Wilcox of the U.S. Geological Survey (USGS) were sent to observe the eruption of Parícutin, Mexico, from 1943 to 1952.
One of the more influential but controversial scientists of his time, the Belgian volcanologist Haroun Tazieff began his career in 1945, studying volcanic eruptions along the East African Rift in the Belgian Congo. His popular adventure book Craters of Fire (New York: Harper, 1952) influenced many youngsters (and some adults) to pursue a dramatic, but perhaps not pragmatic, approach to volcanic studies. Tazieff, a good volcanologist, but a daredevil, took many unnecessary risks “in the name of science;” his accounts, though entertaining, may not be the most objective of the earlier studies available.
Volcanological Research Increased After the Mid-20th Century
Volcanology began to change as a profession in the mid-20th century. Improved economies, especially in developing countries with volcanic hazards; the growth of research universities; and exponentially evolving technologies encouraged more research directed at volcanic processes. With greater global communication, there was also an increasing awareness of the risks posed by volcanic eruptions. Understanding those risks required definition, comprehension, and prediction of volcanic activity—the complex science of volcanology.
The 1960s were a busy time for the earth sciences. Major discoveries included plate tectonics and mass extinctions—vitally important processes that help shape the earth’s surface. Powerful earthquakes caused severe damage and loss of life in Chile, and shallow submarine eruptions occurred off the coast of Iceland and in Lake Taal, Philippines. The same decade saw major breakthroughs in our understanding of explosive eruption phenomena and hazards. The formation of a new island off Iceland’s south coast triggered research on interactions of magma and water that are now classified under the general term “hydrovolcanism.”
Early in the morning of November 14, 1963, the crew of the fishing boat Isleifur II was alerted to eruption precursors by a strong sulfur odor and smoke rising from the sea. It was the beginning of a submarine eruption that eventually formed the island of Surtsey and established a new direction in volcanological research. One of the first on the scene was the distinguished Icelandic volcanologist Sigurdur Thorarinsson, who continued to monitor that eruption until its conclusion in June 1965. Explosive columns of steam and volcanic ash were generated about every 30 seconds as seawater flowed into the crater and mixed with the rising magma. When the ash-laden plumes collapsed, they flowed radially from the vent as density currents from the crater across the new island and then across the sea floor. These density currents were later dubbed “base surges,” a term that had previously been coined to describe clouds of water or dust moving radially from nuclear blasts. At Surtsey, a tuff cone was constructed by these density currents and ash fallout. After Surtsey’s cone rose above sea level, water could no longer flow into the crater and the activity changed from violent blasts to lava fountaining (see Figure 3).
An eruption of basaltic magma on land produces fire fountains and lava flows. If the same type of eruption encounters water (shallow surface waters or aquifers), the energy release increases exponentially. An apt analogy for magma/water interaction is the devastation caused in a foundry accident, when a small amount of water remaining in a mold mixes explosively with molten metal during the pour. Substantial hydrovolcanic eruptions construct tuff rings and tuff cones (also known as maar volcanoes), which are broad, shallow-rimmed features common wherever magma encounters water; for example, in shallow intermittent lakes of America’s Great Basin or along Honolulu’s shoreline (Diamond Head and Koko Head).
Observation of these phenomena at Surtsey led George Walker to coin the term Surtseyan. At about the same time, similar deposits on the Italian island of Vulcano were being called Vulcanian. As more tuff rings and cones similar to Surtsey were studied throughout the decade, nearly everyone used their own name for the phenomenon. Years later, a consensus evolved to use the term hydrovolcanic, which refers to rising magma mixing with any water, be it seawater, groundwater, or water in shallow lakes.
Surtsey was a new island. The eruption could provide unalloyed fascination for geologists because it posed no risks to humans or animals there. The story was very different in the Philippines in 1965, when Volcano Island in Taal Caldera erupted. There, frequent density currents swept the slopes of the volcano over 2 days. The ash in the density currents was fine-grained and stickily moist. Objects ranging from trees to cattle were sandblasted and coated with ash; buildings were leveled, and there were 190 deaths (Moore, Nakamura, & Alcaraz, 1966). Additional casualties were prevented by the authorities’ swift evacuation of the island’s inhabitants. Such events have demonstrated that in populated areas, hydrovolcanic activity and its density currents provide uniquely hazardous results.
Calderas and Pyroclastic Density Currents
The earth’s largest volcanoes can also be some of the most difficult to recognize. Visual evidence of their broad, low-rimmed craters may be masked by more recent geological deposits. The eruptions that formed these features are explosive, of short duration, and capable of producing tens to thousands of cubic kilometers of volcanic ash and pumice. In these volcanoes, when the breached magma chamber supplying the ash and pumice drains quickly, the surface collapses, leaving a crater hundreds to thousands of meters deep. The collapse is fast, and much of the erupted material falls back into the growing crater, called a caldera. Such eruptions only occur about every 100,000 years on the earth, but both individually and collectively they have had considerable impact in shaping the earth’s surface.
Such calderas are currently being called super-volcanoes, by the media and are pitched to television and movie audiences to generate drama and concern; at times, no distinction is made between these and other types of less catastrophic volcanic features. Unfortunately, some television and movie material is pure hype, not adequately or accurately supported by reputable scientific fact. Yes, these caldera-forming eruptions are large and dangerous, but infrequent. However, if such an eruption occurred today, with volcanic ash covering thousands to millions of square kilometers, it certainly would have a significant, widespread effect on many life forms.
One of the youngest and largest caldera complexes in the United States covers most of Yellowstone National Park. The three caldera-forming eruptions there occurred 2 million, 1.3 million, and 600,000 years ago and, collectively, dumped volcanic ash over most of the central and western United States (see Figure 4). Magmas beneath the national park continue to be observed remotely with geophysical studies. These magma bodies supply the heat for many thermal features, such as the Old Faithful geyser; their greatest contemporary hazard is to tourists who cross the fences and risk being badly burned. Movement of the magma also causes the ground surface to rise and fall on a regular basis.
Worldwide, the largest known young caldera is Toba, Indonesia, with a crater 85 by 35 km. The eruption there, 74,000 years ago, emitted about 2,800 cubic kilometers of ash and pumice. The widespread ash deposits from the Toba eruption have been mapped as far away as central India. Jaxybulatov et al. (2014), using seismic imaging, have identified multiple partly molten sills below a depth of 7 km. How long will it be before the magma from these sills evolves into a shallow magma body is a question that needs to be resolved before volcanologists can forecast the next super-volcano eruption at Toba.
In Europe, some of the best-known calderas are in Italy and Greece. The city of Naples has developed both within and adjacent to two overlapping calderas formed during eruptions 37,000 and 12,000 years ago. Since that time, 38 smaller volcanoes have erupted within the area known as the Phlegrean Fields, the most recent being Monte Nuovo in 1548. These calderas contain large thermal anomalies; the ground surface continues to rise and fall, and thus the threat of eruptions within Naples and adjacent towns remains very real. The youngest caldera at Thira (also known as the island of Santorini), Greece, was formed by an eruption during the Bronze Age (about 1630 bce). During that event, pumice fallout buried towns, which were subsequently devastated by pyroclastic density currents. Tsunamis generated by the eruption swept across much of the eastern Mediterranean and are the basis for many flooding legends. The threat of eruptions remains fresh for Thira—the last eruption occurred within the bay in 1950 ce.
Large calderas are always surrounded by volcanic ash deposited mostly as pyroclastic density currents (PDCs). These deposits were left by pyroclastic flows and pyroclastic surges: pyroclastic flows have high particle concentrations and pyroclastic surges are fast-moving flows with low particle concentrations and no respect for topography. Widespread PDCs have had volumes ranging from millions of cubic meters to several thousand cubic kilometers. They are composed of volcanic ash, pumice, and a scattering of lithic clasts (rock fragments from vent walls). These deposits were emplaced with temperatures of up to 600 °C.
A number of seminal works published since the mid-20th century have described PDCs in detail. After studying abundant PDC deposits of all ages spread across the western United States, Clarence S. Ross and Robert L. Smith of the USGS assembled a comprehensive review of the topic. Ash-Flow Tuffs: Their Origin, Geological Relations, and Identification (Ross & Smith, 1961) was the standard for many years until the publication of Fisher and Schmincke’s Pyroclastic Rocks (Fisher & Schmincke, 1984). Smith, along with Roy Bailey (also of the USGS), examined the Bandelier Tuff of New Mexico, which comprises substantial plateaus of volcanic ash deposited during the two massive eruptions that formed the Toledo Caldera (1.6 Ma) and the Valles Caldera (1.2 Ma).
Until imagery from earth-orbiting satellites was able to complement volcanological field observations, many of the earth’s calderas had not even been recognized because of their immense size. Nor was it possible to understand the magnitude of devastation caused by these eruptions. The Earth Resources Technology Satellite (ERTS) provided imagery of the earth’s surface, beginning in 1972. Although primitive by today’s standards, the imagery at that time was instrumental in identifying caldera systems.
At the General Assembly of the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI), held in Santiago, Chile, in 1974, many speakers described widespread volcanic ash deposits across the Andean Altiplano of Chile, Argentina, and Bolivia. These deposits have volumes ranging from tens to hundreds of cubic kilometers. When asked about the sources of these widespread deposits, most speakers didn’t know. In the next year, a swath of Skylab color photography across the Altiplano was released by NASA (National Aeronautics and Space Administration), and ten large caldera complexes were recognized on just the first day of analysis. Using both satellite imagery and field work, Peter Francis, a British volcanologist working on the Altiplano area, began publishing papers on calderas and particularly on Cerro Galán in Argentina (Francis, Hammill, Kretzchmar, & Thorpe, 1978), a two-million-year-old caldera formed during the eruption of about 1,000 km3 of pumice and ash. Francis also noted that all calderas are not circular and that their shapes could have been controlled by their pre-caldera structural framework.
After the eruption of large volumes of ash and pumice accompanied by caldera collapse, eruption activity may continue intermittently over tens of thousands of years. Silicic magmas, partly depleted in volatiles, can ooze up around caldera margins or along structures that have developed within a caldera. The post-caldera activity documented by Bailey, Dalrymple, and Lanphere (1976) within the Long Valley caldera, California, showed post-caldera eruptions and a slow resurgence of magma that deformed the caldera floor. The authors assumed that the resurgence took tens of thousands of years. However, later research on modern caldera resurgence that is forming the island of Iwo Jima (rising out of a submarine caldera) concluded that the rate of active rise there is tens of centimeters a year (Kaizuka, Newhall, Oyagi, & Yagi, 1989); interestingly, derelict landing craft from the 1945 WWII battle for Iwo Jima are now 10 meters above sea level.
Shigeo Aramaki of the University of Tokyo led research on PDCs in Japan, which included a study of the Aira caldera that erupted 30,000 years ago, covering much of southern Kyushu and leaving what is now a volcanic ash plateau and valley fills. Today, the water-filled Aira caldera is lined with fishing villages; now, few residents of these villages are aware of their home’s violent past.
Out of sight but still significant, submarine calderas match many of their landlocked cousins in scale and consequence. The ability to use submersibles has allowed Fiske, Naka, Iizasa, Yuasa, and Klaus (2001) to map and study submarine caldera complexes south of Japan. Likewise, Carey and Sigurdsson (2007) were able to map the Kolombo caldera, located immediately northeast of the Greek island of Thira (Santorini), where the 1650 eruption caused culture-destroying damage and casualties.
For the 100-year anniversary of the famous eruption of Krakatau, Tom Simkin and Dick Fiske, of the Smithsonian Institution’s Museum of Natural History, compiled a monograph that includes major studies published at that time by Dutch geologists and the Royal Society of London (Simkin & Fiske, 1983). Celebration of the 1883 eruption included a weeklong meeting about calderas, held in San Francisco during the American Geophysical Union’s annual conference. It was a remarkable week, with an international group reporting mostly new information about calderas, their various deposits, and potential risks associated with such volcanoes. Peter Lipman, the lead organizer, also published a landmark paper based upon his work with his USGS colleagues on the mid-tertiary calderas of the volcanic field of San Juan Mountains, Colorado. These older calderas, which have been uplifted and eroded, provide an accessible window through which to view the link between calderas and their underlying plutonic bodies. Observations of the exposed roots of ancient calderas are important for understanding the behavior of magmas underlying young, potentially active calderas.
With the establishment of the Hawaiian Volcano Observatory (HVO) in 1912, personnel of the U. S. Geological Observatory were ready for the eruption of Kilauea Volcano from 1959 to 1960 (Eaton & Murata, 1960). Using rudimentary seismic monitoring and level-line surveys, they were able to anticipate the fissure that opened on the edge of Kilauea Iki crater. Lava fountains there were some of the highest ever observed and continued until the old pit crater was partly filled with a lava lake. Several months later, a fissure eruption began along Kilauea’s East Rift, 47 km from the summit. Just another month after that, lava flows from the fissure had covered 10 km2, burying the village of Kapoho. Today (2015) lava flows from Kilauea’s east rift are now creeping into the Hawaiian Village of Pahoa (see Figure 5). The flows do move slowly, so there is no great risk of fatalities, but homes are at risk, roads are being cut off, and livelihoods have been lost. The HVO, having grown into a premier facility for eruption studies, continues to monitor Kilauea and develop technologies that provide early warnings of activity.
Scoria (Cinder) Cones
The 1970s brought a better understanding of some of the most common volcanic landforms on earth—scoria cones (cinder cones) on dry land and tuff rings and tuff cones near or in shallow water and over aquifers.
Tom McGetchin and his students at Massachusetts Institute of Technology employed new techniques in the study of Strombolian eruptions (lava fountaining). Using high-speed cameras and acoustic gear to examine the lava fountains on Mount Etna and Stromboli in Italy, they were able to measure the ballistic trajectories of bombs (molten blobs) and blocks (angular bits of rock torn from vent walls). From these data, they determined that a scoria cone’s growth begins with deposition of the ejecta until the cone reaches a stage where deposits surrounding the vent exceed the angle of repose. After that, cone growth continues with alternating deposition and avalanching (Chouet, Hamisevicz, & McGetchin, 1974; McGetchin, Settle, & Chouet, 1974).
When compared with infrequent but catastrophic caldera-forming eruptions, Strombolian-type eruptions appear to be insignificant. So why worry about the volcanic hazards of such events? Some answers lie in the nature of the volcanic products, and some lie in the proximity of many volcanoes to large population centers. Ash fallout and gases from Strombolian eruptions are downwind health hazards. Lava flows associated with lava fountaining have affected villages throughout the world and, in the case of one large city—Catania in Sicily—the flows from Mount Etna in 1669 reached the city’s margins. The city of Auckland, New Zealand, has grown within the boundaries of a volcanic field composed of young scoria cones (see Figure 6). In fact, the City of Auckland and the New Zealand Government take seriously the risks of eruptions that actually could occur within the city limits.
In 1973, on the island of Heimaey, Iceland, a Strombolian eruption began only 1 km from the town center. Many houses were buried by volcanic ash. A thick lava flow threatened to block the harbor, which was crucial for this isolated fishing village. Residents and officials used large pumps to spray seawater onto the flow front, lowering its temperature and increasing the lava’s viscosity. This simple but effective effort halted the flow and saved the harbor. After the eruption, the town was cleared of ash and rebuilt—with practical improvements. Not ones to pass up an opportunity in this frigid climate, the Icelanders excavated into 5 m of ash overlying the 100-m-thick lava flow to install heat exchangers that now provide the town’s heat.
Volcanic Ash Beds, Eruption Histories, and Eruption Forecasting
Sigurdur Thorarinsson of Iceland, Ray Wilcox of the United States, and John Westgate of Canada were pioneers of “tephrochronology,” the study of volcanic ash layers, beginning in the 1960s. The composition of ash beds and the means of dating them are important for understanding eruption frequencies and to identify the sources for those ashes. Data for widespread ash beds from caldera-forming eruptions are also vital to stratigraphers, who need time markers within rock sequences. Some of the best ash marker beds in the United States and Canada originated from eruptions of the Yellowstone calderas, the Valles Caldera in New Mexico, and Long Valley Caldera in California. A much younger ash bed was spread across the Pacific Northwest during the eruption of Crater Lake, Oregon, 7,000 years ago. In 1975, D. R. Crandell and colleagues were studying ash beds from Mount St. Helens, Washington, to determine past eruption frequencies and magnitudes. Based on their tephrochronological studies, they proposed in Science magazine that an eruption of Mount St. Helens was overdue (Crandell, Mullineaux, & Rubin, 1975) and that it could erupt before the end of the decade—which it did, catastrophically, in 1980.
Widespread ash falls from large volcanic eruptions also have played an important role in helping scientists understand human origins. Nearly all of the significant Pliocene-Pleistocene paleoanthropological sites in the East African Rift (Ethiopia and Kenya) are associated with volcanic ash deposits, which have been used to age-date the sedimentary sequences (see Figure 7). Although these caldera-forming eruptions were obviously catastrophic for life forms in the rift over the last 5 million years, ash falls and ash-laden sediments from flooding streams have preserved not only the hominins themselves but also the plant and animal fossils anthropologists need in order to understand the environmental settings.
Tragic Eruptions in Recent Decades
Wider, more accessible coverage by television news organizations has exposed viewers to the drama of volcanic eruptions. Newspaper reports of eruptions have always been informative, but in the latter half of the 20th century, the media realized there is nothing like the immediacy and visual impact of fire and brimstone on the screen to raise public interest and ratings.
On March 20, 1980, Mount St. Helens, in the state of Washington, was shaken by a magnitude-4.0 earthquake. Several days later, a crater was blown through the summit glaciers by successive steam blasts. A massive bulge began to rise slowly on the northern flank of the volcano. On the morning of May 18, the northern flank of the volcano collapsed and formed an enormous avalanche deposit. The release of pressure also allowed a directed volcanic blast to the north. The eruption’s avalanche and pyroclastic flows devastated forests, meadows, and streams; it took 67 human lives as well as those of countless other creatures. Eruptions at St. Helens continued intermittently until 2008.
Insights gained from the St. Helens eruption helped shape the future of volcanological studies. The distinctive avalanche deposits caused by sector collapse have now been identified at volcanoes throughout the world. Recognition of the connection between sector collapse, pyroclastic density currents, ash fallout, and volcanic mudflows (lahars) has allowed volcanologists to view the complexity of eruption events and examine how each component creates its own unique hazard. The Mt. St. Helens event also brought international attention to the value of volcano observatories; the Cascades Volcano Observatory in Vancouver, Washington, was established during that eruption and today continues to monitor all Cascade volcanoes. The observatory is also responsible for public outreach and professional training. In broader service, their rapid response team is on call for assistance at any eruption in the World.
In 1985, neither observation nor geologic training was able to help the people living along river valleys below the Nevado del Ruiz volcano in Colombia. The relatively small eruption was responsible for melting ice and snow at the volcano summit, which then generated volcanic mudflows. The potential hazard had already been recognized and mapped. Some level of public education for those at risk had been established by the Colombian authorities. However, somewhere along the line, there was confusion in communications about the eruption. The result was the loss of 23,000 lives in the mudflows from Ruiz. If the hazard information resources had functioned well, if instructions had been given clearly, if the population had understood the warning, they would have realized that all they needed to do for survival was walk relatively short distances to high ground.
In 1986, a silent-volcanic-hazard story from Cameroon in West Africa also made it into the world news. When an overturn of CO2 breached the surface of the Nyos Crater Lake, clouds of CO2 swept down the valleys below the volcano. All living things, from insects to humans, were asphyxiated. The CO2 flowed as 50-m-thick, ground-hugging gas clouds; below the transparent current’s surface was death, yet above that level life went on as normal. Such CO2 hazards are an underrated risk for populations in many parts of the world; for example, issuing from volcanic features around Naples and Rome, Italy, and on the island of Java, Indonesia. Recent observations of the body casts at Pompeii—remains of residents once believed to have been buried alive by ash fallout—now offer an alternate interpretation: people fleeing from the eruption of Vesuvius in 79 ce initially may have been asphyxiated by CO2 and then buried by pyroclastic density currents and ash fallout.
Almost two millennia later, volcanic ash clouds threaten lives and livelihoods in yet another way. Many of the world’s airline routes are downwind from active or potentially active volcanoes. One of the busiest routes is from Europe and North America to Asia; the typical flight path crosses Alaska and then angles southeast near the volcanoes of the Alaskan Peninsula, Aleutian Islands, Kamchatka, Kurile Islands, and Japan—a strip sometimes referred to as the “Pacific Rim of Fire.” When a plane encounters a plume of volcanic ash, the fine particles can melt, then clog and shut down the engines. The first notable incident of this type occurred in 1982, when British Airways flight 9, from Kuala Lumpur to Perth, flew over Galunggung Volcano in Java and directly into its eruption plume. The plane lost all four engines and the windows were sandblasted to opacity. Thanks to exceptionally competent pilots, several of the 747’s engines were restarted, and an emergency landing was accomplished in Djakarta.
Learning from this 1982 incident, the International Civil Aviation Organization convened a volcanic ash warnings committee that, over the next several decades, constantly pushed for better communications between volcanologists and the airlines industry and for development of new satellite observational techniques to monitor eruption plumes. The best example of the benefits of this international collaboration occurred in 2010, when flights to western Europe were shut down for a week (see Figure 8) because of dense ash plumes from the eruption of the Icelandic volcano Eyjafjallajökull.
Recognizing and Mitigating the Hazards Posed by Volcanoes
Those working on plumes from the Eyjafjallajökull eruption had already enhanced their expertise beyond earlier studies of volcanic ash clouds. Bill Rose and colleagues from the National Center of Atmospheric Research had used the Center’s observation plane to sample eruption plumes in Central America during the late 1970s (Rose et, al., 1980).
Comprehensive observations of eruption plumes, using ground and satellite-based technologies, were developed following studies of the relatively small 1982 eruption of El Chichón Volcano in southern Mexico. Villages near this remote volcano were certainly devastated, but most of the attention was focused on sulfuric acid aerosols that accompanied the global circulation of El Chichón’s ash plume (Krueger, 1983). There were months with brilliant red sunsets and atmospheric effects similar to those described after the 1883 eruption of Krakatau, when volcanic aerosols stayed in the stratosphere. The spectacular sunsets, visible in the northern hemisphere, were caused by diffraction and reflection of incident sunlight by the sulfuric acid aerosols.
During the 1980 eruption of Mount St. Helens, plumes were tracked across North America and sampled by U.S. Air Force and NASA high-altitude aircraft (U-2s and WB57Fs). The integration of aerial sampling, satellite tracking, and ground-based Doppler radar observations have led to significant advances in understanding the content of eruption plumes and their widespread effects—which became such important data for airline safety during the Icelandic event of 2010. The growing collaboration, between volcanologists, the aviation industry, and agencies responsible for flight control, has undoubtedly averted disasters and continues to actively promote appropriate safety policies.
In other work around the world, a better understanding of the behavior of volcanic ash plumes answers some questions about some vastly different types of catastrophic events and emphasizes the value of cross-discipline scientific collaborations, as noted in the following examples.
The Australian volcanologist Russel Blong was working in Papua, New Guinea, when he pieced together two sets of observations that led to identification of a significant prehistoric eruption. Going from valley to valley and culture to culture, Blong found that many of the ethnic groups had in common oral traditions that described a “time of darkness.” He also noticed that a specific volcanic ash layer was found in those areas. In his book The Time of Darkness (1982), Blong determined that the “time of darkness” occurred during a major eruption of Long Island Volcano, which was upwind from the affected regions.
Dick Fisher studied the deposits left by the 1902 eruption of Mt. Pelée, Martinique, which destroyed the city of St. Pierre and caused 29,000 deaths. In addition to identifying the unique deposits left by the dense pyroclastic flows and the less dense surges, he determined that a “ground effect” had actually turned some flows back up the stream valleys toward the peak. Nearly a century later, an eerily similar effect was actually observed when dust clouds (density currents) billowed through the streets of Manhattan during the collapse of the World Trade Center towers. One scene showed people running from a dust cloud, then encountering a similar cloud that had flowed down a parallel street and turned across and back because of the ground effect.
A Few of the Notable Eruptions of the 1990s
Since 1990, Kīlauea’s Pu‘u ‘Ō‘ō–Kupaianaha East Rift Zone eruption has been a classroom for volcanologists. The eruption has outlasted six directors of the Hawaiian Volcanological Observatory, tested the stamina and resources of countless staff members, and seen the dawn of many modern geological, geophysical, and geochemical techniques we use to unravel the complexities of basaltic eruptions. This eruption has also been a major attraction for millions of visitors to the Big Island, allowing them to witness a volcanic event in real time. In 2015, a lava flow from Kilauea’s east rift is edging into the Pahoa Village—moving slowly but inexorably, rolling over orchards, streets, and homes.
The Eastern Caribbean island of Montserrat has had a long history of colonial activity, from sugar plantations to offshore banking, and by the early 1990s, the beautiful “Emerald Isle of the West” was attracting more and more tourists. However, in July 1995, the Soufriere Hills volcano began to erupt. The main city of Plymouth was at risk of being overwhelmed by pyroclastic density currents and volcanic mudflows. Evacuations were declared, then canceled; but in early December 1995, the area was again threatened by vigorous eruptive activity. When the activity tapered off once more, some people returned home. This back-and-forth migration finally ended in June 1997, when Soufriere’s rising dome collapsed and pyroclastic density currents swept the volcano’s slopes. Now both Plymouth and the Bramble airport have been abandoned permanently. Because silicic lava domes elsewhere in the world have been known to grow for periods ranging from six months to over 90 years, the controversial question for scientists, residents, and government officials at Soufriere is “How long will this eruption continue?” The answer is “We don’t know.” We still do not have the means to predict periods of dome growth.
Another significant dome-growth eruption occurred at Japan’s Unzen Volcano from 1991 to 1995 (see Figure 9). As the dome grew, lava spines were forced outward, breaking off and tumbling downslope. The lava spines then disintegrated, sending hot pyroclastic density currents (block and ash flows) downslope into Unzen’s drainages. During the five years of activity, 9,400 of these density currents were generated. Farms were overwhelmed and houses destroyed. One fast-moving pyroclastic flow, on June 3, 1991, killed 43 people (mostly media representatives), including volcanologists Maurice and Katia Krafft and Harry Glicken.
In a sad irony, the Kraffts have left an invaluable legacy to the profession: they had just completed an International Association of Volcanology film on volcanic hazards. Just that year an early edition of the film had been used to persuade 50,000 residents to evacuate the region around Mount Pinatubo, Philippines. The Kraffts’ dramatic movies showing the destructive power of volcanic eruptions, coupled with the visible precursory activity of Pinatubo, were enough to persuade even reluctant individuals to leave their homes for evacuation centers.
When Mount Pinatubo’s precursory activity began on March 15, 1991, steam blasts and earthquakes alerted the Philippines Institute of Volcanology and Seismology, which immediately established preliminary geophysical networks. As older domes and pyroclastic flow deposits were quickly mapped, scientists determined that the last major eruption of Pinatubo occurred only about 500 years earlier—just long enough to be forgotten in the region’s oral histories.
On June 7, a dome began to grow near Pinatubo’s summit. There were sporadic explosive eruptions, and 58,000 people were evacuated. On June 15, a climactic eruption column rose to an altitude of 34 km, and pyroclastic density currents swept down slopes into the surrounding valleys. The valleys were filled with 50- to 200-m-thick hot ash deposits. At the same time, Typhoon Yunya passed over the volcano, producing heavy rainfall and secondary explosions when water seeped into the hot ash. The results were volcanic mudflows (lahars) that swept down the watersheds, eastward across the central valley and to the western coast. All major bridges were destroyed. At least 329,000 families lost their homes, and many lost their livelihoods.
Most of Pinatubo’s violent activity tapered off in 1994, but volcanic mudflows, triggered by monsoon rains, continue to flood portions of the plains below Pinatubo. Life there has been forever changed. The agricultural economy is recovering slowly, because the land was covered by thick ash deposits. Some villages and towns have been rebuilt and are protected by dikes. The United States’ Clark Air Force Base now has been developed as an international industrial park; the Subic Bay Naval Base has been turned into a free-port zone for shipping, and its forested coastal portions have become an eco-tourism center.
Since the Pinatubo eruption, volcanological research has grown globally, focusing on eruption phenomena, post-eruption processes, and the sociological and economic effects for people at risk. A substantial monograph on the eruption (Fire and Mud: Eruptions and Lahars of Mount Pinatubo, Philippines, 1996, edited by Chris Newhall of the USGS and the late Raymundo Punongbayan of the Philippine Institute of Volcanology and Seismology) provides a comprehensive view of the effects of an eruption on a population and a variety of recovery efforts.
Policies for the protection of aircraft during volcanic eruptions have also continued to evolve. Although some commercial aircraft were slightly damaged in the Pinatubo eruption plume, there were no accidents. Coincident with the Pinatubo eruption was the first International Symposium of Volcanic Ash and Aviation Safety (1991), held in Seattle, Washington. It brought together volcanologists, flight controllers, pilots, and aircraft builders to understand the ash hazard and how to best protect flights.
Mass Extinctions—Were They Caused by Meteor Impacts or Volcanoes?
Mass extinctions of life on earth have occurred throughout geologic time. The one best known to the public is the Cretaceous-Tertiary (K-T) boundary extinction 65 million years ago. The consensus for the cause of the K-T extinction is that a large meteor impacted the area of the Yucatan Peninsula, Mexico (Chicxulub), leaving an enormous crater, causing global tsunamis, and generating an enormous debris cloud.
Although many massive extinctions may have been caused by meteor impacts, an alternative and less-discussed cause was the eruption of thousands of cubic kilometers of basaltic lava and extensive plumes of sulfur dioxide. Some clearly identified lava plateaus left by such eruptions include the Columbia River Basalts in the United States, the Deccan Basalts of India, and widespread basalt provinces in Brazil and Siberia; these features all have generated many unanswered questions. How were the thousands of cubic kilometers of lava and large volumes of volcanic gases generated, and how did the lavas flow great distances, leaving flow units that can be correlated over hundreds of kilometers? Volcanological studies of “large igneous processes” continue to produce answers but generate still more questions. One of the most interesting recent findings was by Self, Thordarson, and Keszthelyi (1997), who envisioned high flux rates, with lavas flowing through lava tubes (which preserved their heat) and, via distributaries, covering large areas.
Teamwork Is Vital to Volcanic Hazard Mitigation
The small phreatic eruptions of Soufrière de Guadeloupe, French Antilles (1976–1977) had a disproportionately large impact on the development of volcanology. Soufrière is a dacitic dome complex that looms above the city of Basse Terre and surrounding villages. A volcano observatory had been established there in 1948, complete with observers and a small seismic network. From November 1975 through March 1976, the staff noticed that there was a significant increase in seismicity, and in March the first seismic swarm could be felt at the surface. From April to June, the level of seismicity remained high, and on July 8 the summit dome was broken by a 300-m-long fissure. A powerful phreatic explosion followed, and other explosions continued sporadically through March 1, 1977 (see Figure 10).
Needless to say, Basse-Terre and the surrounding villages were evacuated, and the volcanologists moved in, establishing a new observatory in a coastline colonial-period fortress (within the danger zone!). The seismic network was too small to correctly locate earthquake foci, but the tilt network, although primitive and inadequate, was able to detect inflation prior to and deflation following the steam blasts. Detailed analysis of the ejecta revealed that the “juvenile” (ash from magma) components were actually hydrothermally altered rock from the geothermal system under the summit.
An unfortunate error by the French government resulted in their sending two rival research groups to respond to the volcanic crisis. One group said that an eruption was imminent, and the other said that there would not be an eruption. The continuing evacuation of 75,000 residents depended upon a coherent scientific analysis and information dissemination, which was not possible because of the professional disagreement and lack of cooperation. No lives were lost, but the residents lost faith in both their government and the scientists. The crisis in Guadeloupe drew worldwide attention and involved volcanologists from many countries, including the United States. The problem at Soufrière de Guadeloupe now serves as an example of how important it is for scientists to work together during crises.
In 1999, the IAVCEI Subcommittee for Crisis Protocols published recommended guidelines for professional conduct during eruption crises. The basis for the guidelines was that a volcanologist’s highest duty is to public safety and welfare. This encompasses efficient teamwork between volcanologists and public officials and a balance of proven volcanologic methods. Disagreements between volcanologists must be worked out in private and the risk mitigation strategy presented to the public with one voice.
Communications Between Scientists and the Public
In 1975, the Smithsonian Institution initiated SEAN, the Scientific Events Alert Network, whose printed notices reported many natural events, including volcanic eruptions, to an international mailing list. In a pre-internet era, SEAN was the first global system to provide continual, current, technical information about natural hazards. Its work was eventually subsumed by a variety of e-list and web-based systems with contributors from around the world.
The importance of the Smithsonian Institution’s volcanological research was underscored with the publication of Volcanoes of the World (Simkin et al., 1981), which has become the standard volcano reference on every volcanologist’s bookshelf. Volcanoes and its subsequently updated editions summarize the history of every documented and many prehistoric eruptions. In the mid 1980s, the same geosciences team established the Global Volcanism Program—a printed monthly bulletin that has morphed into the online newsletter and database that we use today.
Eruption Prediction and Public Safety—Example from Mt. Ontake, Japan
Mount Ontake, a 3,076-m-high (10,062 ft) sacred mountain, located in central Honshu about 200 km west of Tokyo, is a volcano popular with hikers and pilgrims, and hundreds of visitors were near the summit on a beautiful fall Saturday. Although Ontake was thought to be dormant, there had been intermittent phreatic (steam) eruptions there since 1979, and on September 27, 2014, phreatic eruptions caught hundreds of hikers unaware. The muddy, turbulent clouds of fine-grained material billowed downhill, turning day into night and making breathing very difficult. More dangerous were the large rocks blown out during the eruption that carpeted the crater rim and upper slopes. Fifty-five people were killed and nine were never found. What could have been done to protect hikers on these volcanoes? At least there should have been warning signs about this type of intermittent—yet difficult to predict—activity, and trails to the summit should have been closed until public safety could be ensured.
“Safety Recommendations for Volcanologists and the Public” (Aramaki, Barberi, Casadevall, & McNutt, 1994) was published by IAVCEI and serves as a straightforward safety manual for field volcanologists and public safety officials. The safety protocols aren’t meant to be requirements, but they provide reasonable guidelines for those visiting or working at an active volcano. Most geologists are careful in the field, but we have lost valued colleagues who did not have or did not observe a field safety plan.
Volcanic Risks and Integrated Urban Science
During the 1995 General Assembly of the International Union of Geodesy and Geophysics in Boulder, Colorado, a small group of geologists sat around discussing the future of geology and, in particular, volcanology. The group determined that a new focus was necessary: the geology of cities, encompassing everything from their geologic underpinnings to the risks of natural hazards. Effective efforts would require broadening the field’s horizons to include the health sciences, infrastructure engineering, city planners, and others with specialized knowledge.
From their beginnings in Rome and Naples in 1998, the Cities on Volcanoes (COV) meetings have continued to be successful, with COV2 in Auckland, New Zealand in 2001, COV3 in Hilo, Hawai’i, COV4 in Quito, Ecuador, COV5 in Shimbara, Japan in 2007, COV6 on the Spanish island of Tenerife in 2010, COV7 in Colima, Mexico in 2012, and COV8 in Jogyakarta, Indonesia in 2014. The technical content of the last (Jogyakarta) meeting was well-balanced: 41% traditional volcano science and monitoring, 29% volcanic processes and hazards assessment, and 30% studies of sociology, archeology, health issues, education, and infrastructure protection. The 2016 COV meeting will be held in Puerto Varas, Chile, a city affected by the eruption of nearby Calbuco Volcano in early 2015.
When 1990 marked the beginning of United Nations International Decade for Natural Disaster Reduction, the International Association of Volcanologists asked each of its member nations to select a “Decade Volcano” for interdisciplinary study. That approach not only benefited research on the specific features, but also has moved studies in volcanic hazards beyond the traditional geology and geophysics into more integrated studies.
In the 21st Century—Better Global Communication About Natural Catastrophes
Earthquakes and tsunamis dominated the news of natural disasters in the first decade of the 21st century. The 2004 tsunami that swept the Indian Ocean took 250,000 lives; 69,000 people died during the 2008 Wenchuan, China, earthquake.
Global warming and climate change became household words for both believers and deniers. Interestingly, volcanology played a role here as well: some individuals blamed volcanic activity for increased CO2 in the atmosphere; however, Terry Gerlach of the USGS actively refuted that theory by determining that the volcanic output was but a fraction of anthropogenically generated CO2 (Gerlach, 2011).
In perhaps the most completely covered volcanic event of the decade, explosive eruptive activity began at Eyjafjallajökull, Iceland, on April 14, 2010, when buoyant, steam-rich ash columns rose to elevations of about 9 km. By explosive eruption standards, this was not so very high, but the jet stream crossing Iceland was stable and drove the plume steadily to the southeast, across northern Europe. Over the next six days, the plume caused the shutdown of air travel in 32 European countries. Five million passengers on 95,000 flights were stranded around the world; sporting and cultural events were cancelled; and the delayed delivery of everything—from African fresh flowers to auto and electronics parts from Asia—affected global commerce. The International Air Transport Association estimated industry losses at about $200 million per day. Scientists and government entities used an impressive array of techniques, from ground-based radar to the Meteosat orbiting observatory, to monitor the eruption plume (Bonadonna et al., 2011).
Satellite images of widespread ash deposits from earlier volcanic eruptions have been employed in more recent studies within the last few decades to study their regional socio-economic effects. On May 2, 2008, Chaitén volcano in southern Chile produced eruption columns that quickly moved into the stratosphere (Lara, 2009). Satellite color imagery revealed substantial volcanic clouds that were changing direction as they moved east, leaving ash fallout across large areas of southern Argentina. These were the best-documented volcanic clouds until the 2010 Icelandic eruption (Carn et al., 2009; Folch, Jorba, & Viramonte, 2008). In the same region, the 1991 eruption of Mount Hudson had affected vast areas of Patagonia, severely damaging livestock operations (see Figure 11). Data from that eruption were later used by the team from the Canterbury University of New Zealand to study ash fall’s effects on the infrastructure and farming operations across Patagonia (Wilson, Cole, Stewart, Cronin, & Johnston, 2009).
Day-to-day reporting of volcanic eruptions is now available and, indeed, expected, via the Volcano ListServ and the Global Volcanism Program. The World Organization of Volcano Observatories now has 77 member observatories—an astonishing growth from its inception 50 years ago.
Established in 2003, the International Volcano Health Hazard Network has initiated publications and a website in multiple languages to mitigate health effects caused by exposure to volcanic gases and ash. Peter Baxter (Cambridge University) and Claire Horwell (Durham University) were instrumental in establishing this branch of volcanology. Just a decade ago, the idea that members of the geologic profession were performing post-mortems and evaluating inhalation risks for event sites would have been unheard of.
And Now What?
In this century, ground deformation preceding an eruption can be monitored with a variety of earth-observing satellites. This technology permits observations at many of the world’s volcanoes, regardless of their location. The ability to note accelerated deformation allows volcanologists to move in and establish geophysical networks for forecasting eruption activity. Increasingly, the future of effective disaster-mitigation efforts depends on an easily understood warning system that is based on the culture of nearby residents at risk and on trusting, supportive relationships between volcanologists, officials, and the public. Widely disseminated education and readily understood hazard maps are essential.
Of course, being able to forecast the frequency and nature of a volcanic eruption is crucial to reducing risks from the hazards. The needed science and technology is rapidly evolving—new ideas and techniques for observation are the subjects of many tens of sessions at the more traditional scientific meetings of the American Geophysical Union, the European Geoscience Union, and the International Union of Geodesy and Geophysics. Each year and each meeting brings more than a few scientific advances in volcanology. One of the greatest problems for the future is finding an efficient, effective way of handling the massive data sets that are being produced. After many years of establishing links between the world’s more than 100 volcano observatories and research institutes, Chris Newhall and his colleagues have established WOVOdat (a collective record of volcano monitoring worldwide, sponsored by the World Organization of Volcano Observatories). The purpose of this database extends far beyond research and into crisis response. As it grows, WOVOdat will become an indispensable utility for the scientists and emergency managers who work toward mitigating the risks of a volcanic eruption.
One encouraging example of collaborative research efforts is the announcement of the first of a series of scientific and educational workshops, which will be held in 2016 at Santiaguito Volcano, Guatemala. Using the latest techniques for volcano studies, principal scientists will establish tools for synchronous observations for a two-week period. During that time, students will help with observations and data analysis. After the workshop, results, tools, and integrated results will be delivered to all participants. Published results will be available in 2017.
In modern times since the eruption of Krakatau, Indonesia, 132 years ago, volcanic activities reported throughout the world have caused significant loss of life, economic consequences, and other disturbing global effects. Today, myriad earth-observing satellites, rapidly evolving geophysical technology, instant methods of communication, coordinated and diverse scientific teams, and data from a century of volcano studies, are improving our ability to both forecast volcanic eruptions and minimize volcanic risk.
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