Volcanism

Volcanism is the investigation of Earth’s volcanic activity in a number of environments. Volcanoes comprise not only the well-known cone-shaped mountains, but can also be found surrounded by dense vegetation, embedded in glaciers, and at the bottom of oceans. Some volcanic activity is sudden and violent, while other volcanic activity is more incremental and subtle.

Basic Principles

Volcanism is the eruption of materials from Earth’s inner layers. The planet features three general layers: the crust (the outermost layer, on which life exists), the mantle, and the core. High pressures and heat located in the core and mantle push molten rock (magma) outward into the cooler rock layers under the outer crust. Magma, according to the theory of plate tectonics (a model that argues that the various plates of the mantle, known collectively as the lithosphere, drift across a sea of superheated rock), is pushed through the boundaries of those plates and outward through openings in the crust. These openings are called volcanoes.

A volcano releases material in many ways. A key factor in the magnitude of a volcanic eruption is gas pressure. High degrees of gas pressure can eject magma, steam, ash, and other materials at an explosive rate, while low degrees of pressures can lead to a more subdued eruption or no eruption at all. Explosive eruptions, however, send magma, ash, rock, and smoke high into Earth’s atmosphere. Effusive eruptions, in contrast, are extremely slow and sometimes move no faster than human walking speed. In some cases, volcanism involves no eruption, as is the case when magma pushes slowly through the crust, cooling as it moves upward to form a volcano.

Background and History

Volcanoes have played a role throughout Earth’s history. Although they are noted for their destructiveness, volcanoes have also been instrumental in the creation of much of the planet’s landscape and composition. Mountains, oceans, and even the atmosphere were formed as volcanoes pushed gas and material through the crust. As a result, volcanoes are largely responsible for the conditions that support life on Earth.

While this creative element has piqued scientific interest, it may be said that most research on volcanism has been inspired by the destructive history of volcanoes. Some scientists believe that volcanoes may be responsible for ending the reign of the dinosaurs, linking their extinction to a series of tremendous volcanic explosions 65 million years ago. This show of volcanism would have sent enormous amounts of soot and ash into the atmosphere, choking the air and preventing plants from growing. In 1650 b.c.e., what is believed to be the largest volcanic eruption in the last 10,000 years took place under what is now the Greek island of Santorini. A tremendous eruption killed millions of people in the Mediterranean region. In 79 c.e., Mount Vesuvius erupted, sending a cloud of hot gas and ash into the sky that instantly killed everyone in the Italian cities of Pompeii and Herculaneum.

In the nineteenth century, the massive eruptions of two Indonesian volcanoes, Mount Tambora and another under the island of Krakatoa, affected weather around the world for years. In 1980, Washington State’s Mount St. Helens exploded, sending ash around the world within two weeks. In 2010, the Icelandic volcano Eyjafjallajökull sent an ash cloud into the sky that disrupted airline travel in Europe for weeks. In October and November of that same year, Mount Merapi erupted in Indonesia, prompting the evacuation of hundreds of thousands of people from the affected area. Despite the evacuations, more than 350 people died. These high-profile events are but a sample of the volcanism that has affected life on Earth.

Locations and Types of Volcanism

Volcanic eruptions are some of the most violent natural occurrences on Earth. They endanger lives, threaten property, and even cause major changes in the planet’s topography. Although scientists are unable to predict major eruptions, they have an extensive knowledge of how volcanism occurs and can interpret indicators of the likelihood of eruption.

Volcanoes are typically found along the edges of Earth’s tectonic plates. The majority of the world’s volcanoes (about 90 percent) are found along the Ring of Fire, a seismically and volcanically active region along the “edges” of the Pacific Ocean. Iceland, in the northern Atlantic region, also has a significant number of active volcanoes.

Volcanoes erupt in three general ways. The first of these eruptions centers on magma buoyancy. The mass of rock remains the same as it melts, even when its volume increases. When the rock melts, however, its density becomes lighter than that of the surrounding rock, causing the lighter magma to flow up through Earth’s surface. The rate of magma flow increases as the magma’s density decreases. The buoyancy element relies on the notion that magma is pure (that is, not polluted by compounds that can affect its structure).

In the second scenario, magma flow is aided by the presence of volatile substances (or volatiles). Some examples of volatiles are water, sulfur dioxide, and carbon dioxide. Volatiles also include certain forms of crystallized rock, which increase the density of the magma, causing greater pressure as it moves outward. When rock melts into magma, volatiles start to bubble, causing the magma to flow upward. As the magma approaches the surface, the bubbles intensify, releasing gas as the flow accelerates and causing a violent eruption. Scientists believe that the presence of these volatiles leads to explosive volcanism, whereas buoyancy alone leads to magma pooling and, possibly, cooling at the crust level unless the magma assumes an increased degree of buoyancy.

The third scenario involves the injection of new magma into a highly pressurized magma chamber (an underground reservoir of molten rock located beneath Earth’s crust). As magma flows outward toward the crust, it may pool in a magma chamber. As more magma is pushed into the chamber, however, pressure increases steadily. If a conduit presents itself under these conditions, magma will flow upward using the opening. However, if there is no conduit, the magma will continue to push until the crust fractures and allows the magma to escape. Volcanoes above magma chambers are known to erupt repeatedly over time as new magma is injected. This ongoing volcanism can lead to significant changes in a volcano’s structure.

Different Degrees of Intensity

Volcanic eruptions range from simple magma emissions to violent explosions, such as when Japan’s Mount Ontake erupted without warning in September 2014, killing dozens of people including mountain climbers who were surprised by the blast. Some eruptions, as was the case with Mount St. Helens and Mount Etna, take place within the conical shape of mountain volcanoes. Others, like the Kilauea volcano in Hawaii, simply burst from a fissure in the ground. The Eyjafjallajökull event in Iceland started out as an effusive eruption but later sent a large plume of steam and ash several kilometers into the sky.

The presence of volatiles within the magma is a major determinant in an eruption’s degree of intensity. Volatiles may also determine the shape of the eruption. For example, the Vesuvius eruption was considered a plinian eruption, forcing a column of ash and other material high into the sky. Plinian eruptions are some of the most dangerous types, capable of producing pyroclastic flows of fluidized and superheated gas that can slide down the side of a volcano at hurricane-like speeds.

Sometimes an eruption completely depletes the magma chamber beneath a volcano. The volcano then collapses into the empty chamber, creating a bowl-shaped indentation called a caldera. A volcano’s collapses into a caldera after an eruption does not meant that that volcano will become extinct or dormant. The Mount Aso volcano in Japan, for example, collapsed into a tremendous caldera more than 100,000 years ago, but its caldera remains the site of frequent volcanic activity.

Methods of Study

In the study of volcanism, the data that are collected at a given eruption site are both voluminous and complex. Adding to this challenge is the pursuit of general theories based on more than one eruption and, therefore, comparing the data sets from each event. It is here that mathematics proves an invaluable tool.

Scientists seeking to understand the eruption process at Mount Etna, for example, sifted through data from sixty-one earthquakes that took place before a 2001 eruption of the volcano. Researchers used a tensor (a mathematical concept that assigns nonlinear vectors to various geographic sites—in this case, points in and around the volcano at which the seismic activity was recorded) and compared the data input to other vector data. The tensor approach helped provide scientists with a more comprehensive profile of the processes and mechanisms that powered the volcano’s eruption.

To analyze the conditions of a volcano, scientists deploy a large array of sensor equipment at a given site. For example, seismographs are placed in key locations to detect any tremors and seismic waves radiating from deep beneath the site. Tiltmeters are used to measure any changes in the horizontal level of the ground. Furthermore, pressure sensors and water detectors are deployed at and near water sources; a change in pressure or the appearance of new streams can be a useful indicator of volcanic activity. Scientists also take gas samples using specialized bottles; as magma approaches the surface, the increased presence of sulfur dioxide and carbon dioxide (among other gases) emanating from that substance is a strong indicator of volcanic activity.

In addition to ground-based sensor equipment, aerial sensors are deployed near the volcanic site. Aircraft fly over the volcano using infrared scanners, thermal imaging cameras, and radar to detect any changes in the volcano’s environment. Satellite technology is utilized as well, focusing on heat sources, cloud plumes, and any other characteristics of the site. The use of such technology helps scientists maintain vigilance over an active volcanic site, generating scientific data and enabling greater awareness of the risks of potential eruption.

One of the most challenging aspects of studying volcanism is the impossibility of directly studying the mantle and the superheated rock beneath the lithosphere. In some cases, even sensors are rendered unusable because of the risk of eruption. Scientists are still able to study volcanism through chemical analysis.

Studying lava that flowed from a fissure, for example, can reveal the type of magma that was released and the gases that were contained in the magma (based on the types of crystals found in the composition). Scientists also can study the chemical properties of the ash and gas released after an eruption. These airborne elements, upon returning to Earth, can reveal a great deal about the volcanic activity.

An example of the value of chemical analysis may be found in a study of the Piton de la Fournaise volcano eruption. This volcano, located on an island near Mauritius in the Indian Ocean, experienced its largest eruption in April 2007. The remoteness of the island prevented scientists from installing sensor equipment before the eruption. However, volcanologists were able to study the chemical composition of steam, ash, and gas ejected above the volcano. Using the Ozone Monitoring Instrument’s special aerosol-sensing technologies (this device is onboard a National Aeronautics and Space Administration satellite), scientists gathered data about the volume and a mixture of sulfur dioxide that was part of the plume. The data collected during helped scientists gain vital information about the processes that created Piton de la Fournaise’s eruption.

Research

There are several U.S. government agencies that have departments dedicated to the study of volcanic activity. Within the Department of the Interior, for example, is the U.S. Geological Survey (USGS). The USGS operates the Volcano Hazards Program, which monitors volcanism within the United States. The USGS also focuses on active volcanoes whose activity has the potential to affect U.S. interests. In addition, the agency maintains several volcano observatories. Meanwhile, the National Oceanic and Atmospheric Administration (through the U.S. Department of Commerce) also works in volcanism, particularly concerning eruption plumes and how they affect air quality and transportation routes.

Universities and their faculties and research staff play a key role in studying volcanism. The University of Hawaii, for example, operates the Hawaii Center for Volcanology, an institution comprising leading researchers. The University of Utah, Oregon State University, and the University of California, Berkeley, all have leading volcano researchers on their faculties.

Because information can be shared so quickly online, the need for global volcano research networks remains high. The Smithsonian Institution, for example, operates a global network of volcano researchers, whose data and theories are shared within the group through the Smithsonian’s central repository. Meanwhile, the European Union formed the Network for Observation of Volcanic and Atmospheric Change, which allows experts from all over the world to collaborate on research on such topics as gas emission monitoring and volcanic risk assessment.

Implications and Future Prospects

There is no evidence to suggest that there is either less or more volcanic activity in the twenty-first century than in previous eras. However, human civilization has advanced significantly in terms of its transportation and telecommunications abilities. When a massive eruption occurs in these areas, the potential for regional and even global economic disruption goes hand in hand with risks to public safety. For example, the massive eruption of Eyjafjallajökull in Iceland caused a major disruption in world travel patterns. For several days, planes to and from Europe were either diverted or grounded, affecting travel around the world.

The development of computer modeling, cutting-edge chemical analysis, and photographic technologies (including satellite technologies) has helped volcanologists study these phenomena with greater clarity than ever before. One of the most important technological developments, the Internet, has brought the study of volcanic activity to a whole new level. Now, scientists from around the world can almost instantly share data from active volcanic sites and laboratory experiments. In addition to the ability to transfer large data sets and documents, scientists can share photographic images and videos. Furthermore, scientists can use the Internet to monitor active volcanic sites from around the world first-hand, simply by logging into an observatory’s network. Although the need for field research in the arena of volcanism is still high, a great deal of time can be saved through the application of modern technologies.

Principal Terms

caldera: a steep, bowl-shaped depression formed after an eruption, when a volcano collapses into a depleted magma chamber

lithosphere: a layer of large plates believed to be floating on molten rock beneath Earth’s outer crust

magma: molten rock pushed outward from Earth’s core

magma chamber: a reservoir of molten rock that builds under Earth’s crust

mantle: the superheated layer of molten rock located between Earth’s core and outer crust

plate tectonics: the theory that beneath the outer crust there is a series of plates in constant motion and through which magma flows

plinian eruption: a powerful eruption that forces a column of ash and other material high into the sky

pyroclastic flow: the fluidized and superheated mixture of gases and materials that slide down the side of a volcano at hurricane-like speeds

Ring of Fire: a seismically and volcanically active region along the perimeter of the Pacific Ocean

Bibliography

Castro, Jonathan M., and Donald B. Dingwell. “Rapid Ascent of Rhyolitic Magma at Chaiten Volcano, Chile.” Nature 461 (2009): 780–783. This article discusses the inclusion of the mineral rhyolite in magma at the Chaiten volcano, which erupted in 2008. The authors argue that the mineral’s presence in the magma played a significant role in the explosiveness of that eruption.

Gottsman, Joachim, and Joan Marti, eds. Analysis, Modeling and Response. Vol. 10 in Caldera Volcanism. Atlanta: Elsevier Science, 2008. The editors present a selection of articles on calderas, how they form, and ways to use caldera monitoring to forecast volcanic activity.

Lockwood, John P., and Richard W. Hazlett. Volcanoes: Global Perspectives. Hoboken, N.J.: Wiley-Blackwell, 2010. This book provides an overview of the various types of volcanic eruptions, based on observer accounts. The examples provided, from eruption sites around the world, range from effusive to explosive eruptions and include analyses of the processes that create such volcanism.

Paone, Angelo. “The Geochemical Evolution of the Mt. Somma-Vesuvius Volcano.” Mineralogy and Petrology 87, nos. 1/2 (2006): 53-80. This article discusses the presence of a number of minerals found in the rocks at Mount Somma-Vesuvius in Italy. The presence of these minerals may contribute to an eventual plinian eruption similar to the famous first-century eruption of the same volcano.

Schminke, Hans-Ulrich. Volcanism. New York: Springer, 2005. A comprehensive review of the forces that cause volcanic eruptions and other similar geologic activity. Presents a detailed analysis of how volcanoes form and the processes by which volcanic eruptions occur.

Taylor, Alan. “The Eruption of Japan’s Mount Ontake.” The Atlantic, 30 Sept. 2014, www.theatlantic.com/photo/2014/09/the-eruption-of-japans-mount-ontake/100823/. Accessed 5 Sept. 2017. Presents a photo essay showing the eruption of Mount Ontake.

Walter, Thomas R. “Structural Architecture of the 1980 Mount St. Helens Collapse: An Analysis of the Rosenquist Photo Sequence Using Digital Image Correlation.” Geology 39, no. 8 (2011): 767–770. The author reviews the eruption and subsequent collapse of Mount St. Helens, using photographic evidence and sensor data that were collected from each stage of the eruption and enhancing them using the latest in photographic analytical equipment.