Background (Encyclopedia of Global Resources)
All volcanoes are related to the process of plate tectonics. Plate tectonics describes the continual movement of immense sections (plates) of the Earth’s crust relative to one another. Although this process is incredibly slow, geologic time is equally long. Both earthquakes and volcanoes most often occur along the boundaries of these plates. They result from the buildup of intense pressure as one plate collides with, or slides past, another. Here old crustal rock is melted as it plunges down into the upper mantle, or new rock forms as magma squeezes out from great fissures in the crust. In the process, old crustal rock is recycled to form new rock that is rich in mineral resources.
Major metallic mineral deposits from around the world are associated with plate boundaries past and present. The island of Cyprus is rich in copper that once formed on the seafloor of an ancient oceanic spreading center. The same process has been happening in the Red Sea, where copper-rich minerals are being extruded through volcanic activity.
The best evidence for submarine deposition of sulfide minerals by volcanic activity comes from structures called hydrothermal vents, also known as “black smokers.” In appearance, they resemble underwater geysers with cone-type vents emitting black smoke. They result from the seepage of seawater into the hot oceanic basalt crust. This heated seawater then interacts with the basalt by extracting iron,...
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Basaltic Volcanoes (Encyclopedia of Global Resources)
Basaltic volcanoes are usually low in silica (approximately 50 percent) and gas content. This type of volcano commonly produces fast-moving lava flows and is generally not explosive. The only mineral that is consistently associated with basaltic volcanoes is sulfur. It forms from sulfur-rich gases that escape from fissures in the cooling lava rock. As the hot gases escape, sulfur quickly crystallizes, with its distinctive yellow color present on the rock. Sulfur is mined at various volcanic locations. One is Mount Etna on the island of Sicily, where it is an important economic resource.
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Andesitic Volcanoes (Encyclopedia of Global Resources)
The second type of volcano results from andesitic magma. It is richer in silica (approximately 60 percent) and gas than basaltic volcanoes are. This results in a volcano that can be explosive and can produce a large quantity of lava, depending upon slight variations in its chemical composition. Volcanoes such as this can be extremely dangerous since no one is ever certain what will happen each time they erupt.
Mount St. Helens in the state of Washington and Mount Fuji in Japan are two examples of andesitic volcanoes, which can remain dormant for hundreds of years and then suddenly erupt. The 1980 eruption of Mount St. Helens devastated the area around it. In the aftermath, a rich volcanic ash covered the region. Despite the fact that considerable vegetation was destroyed by the eruption and associated flooding, vigorous plant life returned within a couple of years. This was possible because of the nutrient-rich ash that created a new soil.
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Rhyolitic Volcanoes (Encyclopedia of Global Resources)
A magma of rhyolitic composition produces the third volcanic type. Compared to the other two, rhyolitic magma is the richest in both its silica (approximately 70 percent) and its gas content. Both gases and fluids present are rich in dissolved metallic minerals. The magma, as it nears the Earth’s surface, first cracks crustal rock and then may erupt with a violent explosion.
Often, large hydrothermal mineral deposits are associated with rhyolitic volcanoes. These are deposits of various minerals such as malachite, chalcopyrite, and pyrite, where a metallic element like copper or iron is bonded with sulfur or bonded to a carbonate molecule. Such minerals tend to occur in veins where the mineral-rich fluids penetrate fissures in existing rock and then crystallize during cooling. Often gold and/or silver are deposited in this manner. Although such deposits are common, they do not usually occur in large quantities. Most often, huge amounts of rock must be mined in order to extract relatively small amounts of the valuable metals. The great Bingham copper mine in Utah is an excellent example of such a deposit.
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Diamond Pipes (Encyclopedia of Global Resources)
One important occurrence of a valuable mineral associated with volcanic activity is the diamond pipe. Diamond formation is typically associated with a high-pressure, high-temperature environment. Such conditions are present in the Earth’s upper mantle at depths of approximately 200 kilometers. Here diamonds slowly crystallize within magma. As a result of rapid upward movement, the diamonds are carried along with the magma column. Eventually, upon cooling, the magma will form a pipe structure. In shape it somewhat resembles a champagne glass.
Most volcanic pipes do not reach the surface and produce a volcano. The more probable situation is that they remain underground as a magma source for an erupting volcano. In those pipes which contain diamonds, the diamonds are disseminated throughout a rock called kimberlite. erosion may eventually destroy evidence of the volcano, exposing the diamond pipe. Erosion also acts as a natural means of extracting the diamonds and then depositing them as sediment in rivers or on beaches. The most important diamond pipes include those of South Africa, Siberia, and western Australia.
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Further Reading (Encyclopedia of Global Resources)
Coleman, Robert G. Geologic Evolution of the Red Sea. New York: Oxford University Press, 1993.
Decker, Robert, and Barbara Decker. Volcanoes. 4th ed. New York: W. H. Freeman, 2006.
Francis, Peter, and Clive Oppenheimer. Volcanoes. 2d ed. New York: Oxford University Press, 2004.
Martí, Joan, and Gerald Ernst, eds. Volcanoes and the Environment. New York: Cambridge University Press, 2005.
Parfitt, Elisabeth A., and Lionel Wilson. Fundamentals of Physical Volcanology. Malden, Mass.: Blackwell, 2008.
Schmincke, Hans-Ulrich. Volcanism. New York: Springer, 2004.
Stanton, R. L. Ore Elements in Arc Lavas. New York: Oxford University Press, 1994.
Tarbuck, Edward J., and Frederick K. Lutgens. Earth: An Introduction to Physical Geology. 9th ed. Illustrated by Dennis Tasa. Upper Saddle River, N.J.: Pearson Prentice Hall, 2008.
Wood, Charles A., and Jürgen Kienle, eds. Volcanoes of North America: United States and Canada. New York: Cambridge University Press, 1990.
Zeilinga de Boer, Jelle, and Donald Theodore Sanders. Volcanoes in Human History: The Far-Reaching Effects of Major Eruptions. Princeton, N.J.: Princeton University Press, 2005.
U.S. Geological Survey. Volcanoes, by I. Robert Tilling: On-Line Edition. http://pubs.usgs.gov/gip/volc
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Definition (Encyclopedia of Global Warming)
Volcanic activity has played a major geological and environmental role in the evolution of the Earth since the planet’s formation. As the proto-planetary Earth cooled and formed a solid crust, widespread volcanic activity dominated its surface. The Earth’s interior at this time retained a considerable amount of heat from accretion and the decay of short-lived radioactive isotopes. With interior temperatures well above the melting point of most Earth materials, high-density metals sank to the Earth’s center of gravity, while lower-density, silicate-rich materials were displaced toward the surface. It is believed that this process took place within the first 50 million years of Earth history, resulting in the present crust-mantle-core structure.
Little geological evidence remains of the period between the formation of a solid crust and the beginnings of plate tectonics. Scientists believe that during this 2-billion-year interval, massive volcanic structures gradually built up into continental masses. Plate tectonics, as it is known today, began about 2.5 billion years ago. It may have taken that long for the Earth’s upper mantle to become sufficiently hot and fluid to create convection cells that could fracture the crust and spread these huge sections apart from one another. It is along these plate boundaries where the majority of earthquakes and volcanic eruptions take place.
Volcanic eruptions have a significant...
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Significance for Climate Change (Encyclopedia of Global Warming)
Throughout Earth’s history, life has been closely associated with volcanic activity. One theory suggests that life on Earth may have had its origin in volcanic hot springs that were rich in organic compounds. Continuous volcanic eruptions also contributed to the water that would later become the oceans. With life flourishing in the oceans and later on land, volcanic activity became a major influencing factor on the continuing evolution and periodic mass extinctions of Earth’s biological inhabitants.
One reason for the occurrence of mass extinctions is a dramatic change in the Earth’s surface conditions. Most species live in what can be called a “habitable zone” based upon a suitable range in temperature, the availability of sufficient water, and the right amount of sunlight. When a particular species is exposed to conditions outside of this zone, it either adapts to the changing conditions or dies. As compared to life in the oceans, life on land seems to be more fragile and more susceptible to change. Recent theories for the cause of mass extinctions have concentrated on cosmic impacts or extensive volcanic activity. In each case, the apparent mechanism can be related to a blockage of sunlight by the huge amounts of dust and debris that an impact or volcano would eject into the upper atmosphere. The reduction of even a small amount of sunlight could disrupt the photosynthetic process and through it...
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Further Reading (Encyclopedia of Global Warming)
Blong, R. J. Volcanic Hazards: A Source Book on the Effects of Eruptions. Orlando, Fla.: Academic Press, 1984. An excellent reference book dealing with all aspects of volcanic eruptions. Most useful to earth science students at various levels.
Lang, Kenneth R. The Cambridge Guide to the Solar System. New York: Cambridge University Press, 2003. Chapter 4 is particularly relevant to the effects of volcanic activity on the Earth’s environment. Suitable for a general level science audience.
Marti, Joan, and Gerald J. Ernst, eds. Volcanoes and the Environment. New York: Cambridge University Press, 2005. A comprehensive work that examines all aspects of volcanic activity and its effects on the environment. Suitable for a wide range of readers.
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Volcanoes (Science Experiments)
How does a volcano blow its top?
Model of a Volcano: Will it blow its top?
Design Your Own Experiment
On August 24, in 79 A.D., the citizens of Pompeii, in what is now Italy, woke up to a warm, sunny day. Some probably went to sit outside their beautiful villas to sit and admire the fruit trees, ornamental wall paintings, and statues in their enclosed gardens. Many of the villas overlooked the sparkling Bay of Naples. Businesses were opening and some were already bustling with activity. But life in Pompeii ended abruptly that morning when nearby Mount Vesuvius erupted. Pompeii and the neighboring town of Herculaneum were destroyed. More than 2,000 people were suffocated by the gas and ash that spewed from Vesuvius and covered Pompeii or by the flow of molten rock that leveled Herculaneum. Pliny the Younger, a Roman historian, saw the terrible event from the nearby town of Miseneum and wrote the first written, eyewitness account of a volcano's eruption.
Today Vesuvius is still an active volcanoA conical mountain or dome of lava, ash, and cinders that forms around a vent leading to molten rock deep within Earth., a conical or domelike mountain of lava, ash, and cinders...
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