Lava

lava (lä`və), molten rock that erupts on the earth's surface, either on land or under the ocean, by a volcano or through a fissure. It solidifies into igneous rock that is also called lava. Before reaching the earth's surface, the mixture of solid and liquid rock, and gases, is known as magma. Lavas are composed chiefly of silica and the oxides of aluminum, iron, magnesium, calcium, sodium, and potassium. Silica, with soda and potash, predominates in the light-colored, acid felsites; iron oxides, lime, and magnesia, in the dark-colored, basic basalts. Rock froth forms on the upper part of a lava flow if bubbles solidify before the gas can escape. Light-colored, glassy froth is pumice; dark, cindery or slaggy froth, of a coarser texture than pumice, forms what is known as scoriae. Lava flows which solidify as a mass of blocks and fragments with a rough surface are called block lava, or aa; those which solidify with a smooth, ropy, billowy surface are known as corded lava, or pahoehoe. Lava can sometimes cover wide regions through great fissures in the earth's surface, as in the ancient Columbia River plateau of the NW United States, where it is spread over 30,000 sq mi (77,700 sq km) and is up to 5,000 ft (1,524 m) deep. Other such regions are found in the Deccan plateau of India, in E Brazil, and in Iceland. Submarine lavas develop through volcanic activity along the mid-oceanic ridges and plate boundaries, where the mid-oceanic ridges produce more lava than any continental eruptions. Such underwater eruptions also harbor rich fauna unique to the vent area, such as red tube worms and giant clams, whose food supply is based on the hydrogen sulfide abundant in the vent waters. Unique features include black smokers, or hot springs of mineral-rich water that belch out from the ocean ridge where it is most active. In many instances the reasons for the heat and liquidity of magma, its exact source, and the causes of its rise in the earth are not clearly known, though the volcanic activity is often related to seafloor spreading. Other volcanic areas also lie along colliding plate boundaries and around rising magma hot spots. See plate tectonics.

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lava

Molten rock originating as magma in the Earth's mantle that pours out onto the Earth's surface through volcanic vents (see volcano) at temperatures of about 1,300–2,200 °F (700–1,200 °C). Mafic lavas, such as basalt, form flows known by the Hawaiian names pahoehoe and aa. Pahoehoe is smooth and gently undulating; the lava moves through natural pipes known as lava tubes. Aa is very rough, covered with a layer of loose, irregular fragments called clinker, and flows in open channels. Lava that starts out as pahoehoe may turn into aa as it cools. Lavas of intermediate composition form a block lava flow, which also has a top consisting largely of loose rubble, but the fragments are fairly regular in shape, mostly polygons with relatively smooth sides. See also bomb; nuée ardente.

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lava

1. magma emanating from volcanoes and other vents

2. any extrusive igneous rock formed by the cooling and solidification of molten lava

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lava [′lä·və]

(geology)

Molten extrusive material that reaches the earth's surface through volcanic vents and fissures.

The rock mass formed by consolidation of molten rock issuing from volcanic vents and fissures, consisting chiefly of magnesium silicate; used for insulators.

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LAVA - A language for VLSI that deals with "sticks", i.e. wires represented as lines with thickness. ["A Target Language for Silicon Compilers", R.J. Matthews et al, IEEE COMPCON, 1982, pp. 349-353].

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Lava 

(Polish Łyna), a river in Kaliningrad Oblast, RSFSR, and in Poland; a left tributary of the Pregolia River. The Lava measures 289 km long and drains an area of 7,130 sq km. It originates from the Masurian Lakes in Poland and is fed by snow, rain, and groundwaters. The mean flow rate at the mouth is 40.4 cu m/sec. The Lava freezes during the winter for a period of two to three months. It is navigable in its lower course and is linked with Lake Mamry by the Masurian Canal. The city of Pravdinsk is located on the river.

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Lava 

liquid-molten, primarily silicate material that issues out onto the earth’s surface during volcanic eruptions. It differs from magma by the absence of gases, which escape into the air during the eruption.

Different effusive rocks form from the lava depending on its composition during solidification. Acidic, silica-rich rhyolitic lavas are viscous and usually relatively cool; as a rule, they form domes and, more rarely, spread in the form of lava flows; eruptions are accompanied by a large quantity of ejecta which, together with sedimentary material, is deposited in the form of various tuffs. Medium-composition (andesite) and basic (basaltic) lavas are more mobile and, near the vent, where their temperature is sufficiently high (up to 1000^o-1200°C), may flow as fast as 30 km/hr. In cooling gradually the lava becomes viscous and the rate of flow decreases to a few meters an hour. Lava sometimes issues from the central crater, but more often it issues from the lateral lava fissures (bocca) and flows along depressed parts of the relief in the form of lava flows. When there are large eruptions, lava fills up all depressions and spreads over the surface, forming lava sheets; in such cases “mountain plains,” or lava plateaus, often occur.

V. P. PETROV

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Lava 

a battle formation and tactical procedure used by the cossack hosts and, with the institution of the 1912 Cavalry Regulations, in all the Russian cavalry.

The troop lava consisted of a forward part (one to four platoons) and a support (at least one platoon) or a guide (one squad). The forward part operated in different orders (primarily a single rank). Among its missions, the lava formation was used for scouting the terrain and enemy forces, disorganizing closed enemy battle formations before a mass cavalry attack, covering a maneuver by friendly troops, and pursuing the enemy.