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V-shaped valley
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A valley whose walls have a more-or-less uniform slope from top to bottom, usually formed by stream erosion. While the valley takes on a V-shape the river itself flows in a U-shaped bed similar to that created by a glacier.
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vadose zone
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The region in the ground between the surface and the water table in which pores are not filled with water. Also called the unsaturated zone.
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valence electron
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" An electron of the outermost shell of an atom; one of those most active in bonding. "
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valley glacier
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A glacier that is smaller than a continental glacier or an icecap, and which flows mainly along well-defined valleys, many with tributaries.
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van der Waals bond
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A bond much weaker than the ionic or covalent, which bonds atom by small electrostatic attraction.
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varve
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"A layer of sediment deposited in lakes during one year. Each layer consists of two parts, grading upward from coarse to fine and light to dark, which are deposited at different seasons and which differ in color and texture; thus the layers can be counted and measured. In a complete series the number of layers gives the date on which the ground was vacated by retreating ice."
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vector
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A mathematical element that has a direction and magnitude, but no fixed position. Examples are force and gravity.
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vein
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Tabular rock or mineral filling of a generally small crack or joint such as a quartz vein. A product of chemical precipitation from a watery solution, in contrast to a dike crystallized from magma, although gradations exist.
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veneer
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A thin, widespread layer of sediment covering an older surface.
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vent
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The opening at the earth's surface through which volcanic materials reach the surface.
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ventifact
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A rock that exhibits the effects of sand-blasting or snowblasting on its surfaces, which become fiat with sharp edges in between.
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vertical exaggeration
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The ratio of the horizontal scale (for example, 100,000
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vesicle
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A small cavity (bubble) in an igneous rock that was formerly occupied by a bubble of escaping gas.
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vesicular basalt
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Holes and other openings in basaltic flow which are the result of trapped gas bubbles. Vesicles are often filled at a later date with a wide variety of materials, including quartz, agate, zeolite, and many other mineral.
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viscosity
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A measure of resistance to flow in a liquid (molasses in January has high viscosity while molasses in August has lower viscosity).
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vitreous
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Similar to broken glass.
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vitrophyre
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A volcanic rock with larger crystal (phenocrysts) embedded in a glassy groundmass.
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volatile
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Elements that are soluble in magma at elevated pressure and temperature that exsolve as gas from magmas during ascent and eruption at the earth's surface. They include sulfur, water, carbon dioxide, chlorine and fluorine.
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volcanic aerosol
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Very small (microns to fraction of micron in diameter) particles or droplets, composed mainly of sulfuric acid and water, produced by the gas-to-particle conversion of sulfur dioxide gas to sulfuric acid in the volcanic eruption plume.
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volcanic arc
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Arcuate chain of volcanoes formed above a subducting plate. The arc forms where the downgoing descending plate becomes hot enough to release water and gases that rise into the overlying mantle and cause it to melt. Arc rocks are mostly volcanic rock from the volcanoes and sedimentary rocks made up of eroded debris from the volcanoes. Melted rock in the deeper plumbing of the arc which may crystallizes at depth to become an arc root pluton.
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volcanic ash
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A volcanic sediment of rock fragments, usually glass, less than 4 millimeters in diameter that is formed when escaping gases force out a fine spray of magma.
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volcanic ash fall
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A deposit of volcanic ash resting where it was dropped by eruption and winds.
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volcanic ash flow
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A mixture of volcanic ash and gases that moves downhill as a density current in the atmosphere.
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volcanic block
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A pyroclastic rock fragment ranging from about fist- to car-sized.
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volcanic bomb
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A pyroclastic rock fragment that shows the effects of cooling in flight in its streamlined or bread-crust surface.
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volcanic breccia
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A pyroclastic rock in which all fragments are more than 2 millimeters in diameter.
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volcanic cone
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The deposit of lava and pyroclastic materials that has settled close to the volcano's central vent.
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volcanic dome
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"A rounded accumulation around a volcanic vent of congealed lava too viscous to flow away quickly; hence usually rhyolite lava. Volcanic dust"
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volcanic dome
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A steep-sided mass of viscous (doughy) lava extruded from a volcanic vent often circular in plane view and spiny, rounded, or flat on top. Its surface is often rough and blocky as a result of fragmentation of the cooler, outer crust during growth of the dome. In structural geology, a round or elliptical upwarp of strata resembling a short anticline.
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volcanic ejecta blanket
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A collective term for all the pyroclastic rocks deposited around a volcano, especially by a volcanic explosion.
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volcanic emanations
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Gases, especially steam, emitted from a vent or released from lava.
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volcanic front (arc)
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Elongate zone of maximum volcanic activity that defines the main volcanic (or magmatic) arc.
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volcanic neck
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Solidified lava that fills the conduit of a volcano. Volcanic necks (also called plug) are usually more resistant to erosion than the material making up the surrounding cone and may remain standing as a solitary pinnacle when the rest of the original structure has eroded away.
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volcanic pipe
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"The vertical chamber along which magma and gas ascend to the surface; also, a formation of igneous rock that cooled in a pipe and remains after the erosion of the volcano. "
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volcanic rock
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Igneous rock that cools and solidifies at or very near the Earth’s surface. Volcanoes produce volcanic rock.
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volcano
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Any opening through the crust that has allowed magma to reach the surface, including the deposits immediately surrounding this vent.
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