volcanic glass Any glassy rock formed from lava or magma that has a chemical composition close to that of granite. Such molten material may reach very low temperatures without crystallizing, but its viscosity may become very high. Because high viscosity inhibits crystallization, the combination of sudden cooling and loss of volatiles, as when lava extrudes from a volcanic vent, tends to chill the material to a glass rather than crystallize it.
volcanism Vval-ko-.ni-zomX or vulcanism Any of various processes and phenomena associated with the surface discharge of molten rock or hot water and steam, including volcanoes, geysers, and fumaroles. Most active volcanoes occur where two plates converge and one overrides the other (see plate tectonics). Volcanism can also occur along the axis of an oceanic ridge, where the plates move apart and magma wells up from the mantle. A few volcanoes occur within plates, far from margins. Some of these are thought to occur as a plate moves over a “hot spot” from which magma can penetrate to the surface; others appear to result from an extremely slow form of plate spreading.
volcano Vent in the crust of the Earth from which molten rock, hot rock fragments, ash, gas, and steam issue. Most volcanoes are found on the boundaries of the enormous plates that make up the Earth’s surface. Some of the most violent eruptions take place along convergent boundaries where one plate margin is forced beneath another. The most famous such bound¬ ary is the circum-Pacific belt bordering the Pacific Ocean; the island arcs and mountain ranges of this “Ring of Fire” have seen gigantic explosions, among them the eruptions of Mount Pinatubo in the Philippines in 1991,
Mount Saint Helens in the U.S. state of Washington in 1980, and Krakatoa (Krakatau) in Indonesia in 1883. Volcanic activity is also common at diver¬ gent boundaries, where two plates slowly pull apart and allow molten rock to escape to the surface; the most prominent example is the Mid-Atlantic Ridge, site of volcanic islands such as Iceland, the Azores, Ascension, Saint Helena, and Tristan da Cunha. Yet another type of volcanic activity is found on the island of Hawaii, located on a “hot spot” near the middle of the Pacific Plate where plumes of partially melted rock rise from below the Earth’s crust; there the volcanoes Kilauea and Mauna Loa frequently eject streams and fountains of lava. Some of the best-known volcanism takes place around the Mediterranean Sea, where the eruptions of Mount Etna, Vesuvius, the islands of Stromboli and Vulcano, and other volcanoes have been observed for millennia. Some volcanoes have cultural or religious sig¬ nificance for the peoples around them; these include Misti Volcano in Peru, Mount Fuji in Japan, and Ol Doinyo Lengai in Tanzania.
A volcano forms when magma beneath the Earth's crust forces its way to the sur¬ face. Alternating layers of solidified lava and pyroclastic materials (ash and cin¬ ders) build up the typical cone shape of a stratovolcano as they are ejected through the central vent during eruptions.
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Volcano Islands Japanese Kazan-retto or lo-rettd Group of three small volcanic islands, western Pacific Ocean. Administratively part of Japan, they lie south of the Bonin Islands. After they were visited by Japanese fishermen and sulfur miners in 1887, the three islands of Kita 16, 16 (Iwo Jima; the largest), and Minami 16 were claimed by Japan in 1891. 16 was the scene of heavy fighting during World War II. After the war Japan retained residual sovereignty over the islands, but the U.S. administered them from 1951 until they were returned to Japan in 1968.
volcanology or vulcanology Scientific discipline concerned with all aspects of volcanic phenomena. Volcanology deals with the formation, distribution, and classification of volcanoes, as well as their structure and the kinds of materials ejected during an eruption (e.g., lava, dust, ash, and gas). It also involves research on the relationships between volcanic erup¬ tions and other large-scale geologic processes, such as mountain building and earthquakes. One of its chief aims is to determine the nature and causes of volcanic eruptions in order to predict them. Another practical concern is obtaining data that may aid in locating commercially valuable deposits of ores, particularly those of certain metallic sulfides.
Volcker, Paul A(dolph) (b. Sept. 5, 1927, Cape May, N.J., U.S.) U.S. economist. He worked as an economist for the Chase Manhattan Bank (1957-61; 1965-68). As an undersecretary at the U.S. Treasury Depart¬ ment (1969-74), Volcker was the chief architect of the U.S.’s abandon-
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ment of the gold-exchange standard and the devaluations of the U.S. dollar (1971, 1973). After serving as president of the Federal Reserve Bank (1975-79), he was appointed head of the Federal Reserve System in 1979 by Pres. Jimmy Carter and served until 1987. To end a period of very high inflation, he slowed the growth of the money supply and allowed interest rates to rise, causing a recession (1982-83) but dramatically reducing inflation.
vole Any burrowing rodent (family Cricetidae) with a blunt snout, small ears, and short limbs. Most species are herbivorous and are found throughout North America and Eur¬ asia. The approximately 45 species of the genus Microtus, also called meadow mice, are 4-10 in. (10-26 cm) long, including the tail. Their long, shaggy fur is grayish brown.
About 10 species of pine voles inhabit swamps, fields, and hard¬ wood forests. Red-backed voles inhabit forests in cold regions. Water voles are found only in Eurasia and usually live near a stream, ditch, or lake.
Volga River River, western Russia. Europe’s longest river and the prin¬ cipal waterway of western Russia, it rises in the Valdai Hills northwest of Moscow and flows 2,193 mi (3,530 km) southeastward to empty into the Caspian Sea. It is used for power production, irrigation, flood control, and transportation. The river has played an important part in the life of the Russian people, and in Russian folklore it is characteristically named “Mother Volga.”
Volga-Baltic Waterway Series of rivers and canals, western Russia. The navigable system links the Volga River with the Baltic Sea and includes the Neva River, a canal along the southern shore of Lake Ladoga, and the Sheksna River past Cherepovets through the Rybinsk Reservoir. Its total length is some 685 mi (1,100 km). The system was completed in 1964, replacing the antiquated Mariinsk Canal system using the same route that had been constructed originally in the 18th century and later several times enlarged and improved. The system includes seven automatic locks.
Volga Tatar language See Tatar language
Volgograd formerly (until 1925) Tsaritsyn (1925-61) Stalingrad
City (pop., 2001 est.: 982,900), southwestern Russia. Located on the Volga River, it was founded as the fortress of Tsaritsyn in 1589. During the Russian Civil War (1918-20), Joseph Stalin organized the city’s defense against the White Russian armies, and it was later renamed in his honour. During World War II it was reduced to rubble in the Battle of Stalingrad; it was rebuilt in the postwar era. Its manufactures include steel and alu¬ minum, engineering products, timber goods, building materials, and food¬ stuffs. A major railroad junction and river port, it is the eastern terminus of the Volga-Don Ship Canal.
Volhynia \val-'hi-ne-o\ Historical region, northwestern Ukraine. Located around the headstreams of the Pripyat and Bug rivers, it originally was a Russian principality (10th-14th century), west of Kiev. In the 14th century it became part of the Grand Duchy of Lithuania but was ruled largely by its own aristocracy. It passed to Poland in 1569. In 1793 it was transferred to Russia under the second partition of Poland. The Treaty of Riga (1921) divided it between Poland and the U.S.S.R. The U.S.S.R. took the Polish section in 1939 and made it part of the Ukrainian S.S.R. after World War II.