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Geological Terms Beginning With "V"



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Vadose Water

Vadose Water

Water that exists in the pore spaces of a rock or soil, between the ground surface and the water table.

Valence Electrons

Valence Electrons

Electrons in the outermost shell of an atom. The electrons that are typically involved in making chemical bonds.

Valley Glacier

Valley Glacier

A glacier that occurs in a mountainous region and occupies a valley. Also known as an Alpine Glacier.

Van der Waals Bond

Van der Waals Bond

A weak chemical bond in which atoms are held together by weak electrostatic attraction.

Variscite

Variscite

A mineral that is similar to turquoise in mode of formation and composition. It even looks like turquoise but in a blue-green to yellowish green color. Cut into cabochons, but its use is limited because it is soft (H: 4.5).

Varve

Varve

A thin layer of fine-grained sediment deposited in the still waters of a lake. Varves are frequently associated with glaciation and represent a yearly sedimentation cycle - a silty, light-colored layer deposited in summer and a darker, organic-rich clay layer deposited during winter.

Vein

Vein

A fracture that has been filled with mineral material.

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Ventifact

Ventifact

A rock that has been shaped or polished by the sandblasting effect of wind-blown sand.

Vertical Exaggeration

Vertical Exaggeration

In making sketches of landscapes and cross-sections, the vertical dimension is frequently exaggerated to show detail. Vertical exaggeration is a number that represents the magnitude of this exaggeration. It is a proportion between the vertical scale and the horizontal scale. For example, a cross section with a vertical exaggeration of 4 has a vertical scale that is four times the horizontal scale (in this example the vertical scale could be 1:25 while the horizontal scale is 1:100).

Vesicle

Vesicle

Spherical or elongated cavities in an igneous rock that are created when a melt crystallizes with bubbles of gas trapped inside.

Vesuvianite

Vesuvianite

Vesuvianite is a mineral formed by the contact metamorphism of limestone. It is often an attractive translucent green color that reminds people of jade. Rare transparent crystals are faceted. Named after Mt. Vesuvius.

Viscosity

Viscosity

The resistance of a fluid to flow. Fluids with a high viscosity resist flow. Fluids with a low viscosity flow freely.

Volcanic Arc

Volcanic Arc

A chain of volcanoes that forms on a continental plate when an oceanic plate collides with the continental plate and subducts beneath it. Also, a chain of volcanoes that forms on an oceanic plate in a similar collision with another oceanic plate. The image shows the Cascades Volcanic Arc of the northwestern United States.

Volcanic Ash

Volcanic Ash

Small particles, less than two millimeters, of igneous rock that form when a spray of liquid magma is blown from a volcanic vent by escaping gas. These cool quickly, usually into tiny glassy particles, similar to pumice, that are lifted out of the vent by escaping gas and carried away from the volcano by wind. These particles can be carried in the atmosphere for hundreds to thousands of miles and present a hazard to aircraft. The smallest and most mobile particles are known as "volcanic dust".

Volcanic Ash Fall

Volcanic Ash Fall

An accumulation of volcanic ash produced by an eruption. These can be very thick near the vent and decrease to a light dusting in a downwind direction. An ashfall presents a breathing hazard to people and animals. It can also cover crops and ruin harvest. When a significant accumulation occurs it can collapse buildings, fill storm drains and turn into a natural "concrete" if it becomes wet. It can be like a snowfall that does not melt and thus creates a disposal problem.

block

Volcanic Block

Also known as "volcanic block". A rock greater than 64 millimeters in diameter that was ejected from a volcano during an explosive eruption. They are typically pieces of the volcanic cone that were torn loose during the eruption rather than a mass of molten ejecta that solidified in flight. The block in the photo was found on Kilauea Volcano, Hawaii.

volcanic bomb

Volcanic Bomb

Fragments of lava that are ejected while molten or partially molten from a volcano, some developing aerodynamic shapes while flying through the air, and landing with a size over 64 millimeters in diameter. The image shows basaltic volcanic bombs erupted by Mauna Kea Volcano in Hawaii.

Volcanic Breccia

Volcanic Breccia

A rock made up of pyroclastic fragments that are at least 64 millimeters in diameter.

Volcanic Cone

Volcanic Cone

A cone-shaped hill or mountain composed of pyroclastic debris and/or lava that has accumulated around a volcanic vent during eruptions.

Volcanic Dome

Volcanic Dome

A round, steep-sided extrusion of very viscous lava that is squeezed from a volcanic vent without major eruption. The lava is too viscous to flow and is composed of rhyolite or dacite. The dome shown in the photo is the vent of the Novarupta eruption of 1912, the largest volcanic eruption of the 20th century. The small dome was overlooked when the source of the eruption was originally determined and the wrong volcano was blamed. Also called "lava domes".

Volcanic Neck

Volcanic Neck

A vertical intrusion with the geometry of a volcanic pipe. An erosional remant of a volcanic pipe.

Volcanic Pipe

Volcanic Pipe

A vertical or nearly vertical conduit that connects a magma reservoir to the surface. Magma and gas travel upwards through this conduit to produce a volcanic eruption. After the eruption the pipe can be filled with cooling magma which preserves its shape as an intrusive body or it can be filled with volcanic breccia and serve as a passageway for liquids, gases and their entrained solids.

Volcano

Volcano

A vent in Earth's surface through which molten rock and gases escape. The term also refers to deposits of ash and lava which accumulate around this vent.

V-shaped valley

V-shaped valley

A valley with a narrow bottom and a cross section shaped like the letter "V". Valleys of this shape are almost always cut by stream erosion.

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