Vadose Water:
Water that exists in the pore spaces of a rock or soil, between the ground surface and the water table.
Valence Electrons:
Electrons in the outermost shell of an atom. The electrons that are typically involved in making chemical bonds.
Valley Glacier:
A glacier that occurs in a mountainous region and occupies a valley. Also known as an Alpine Glacier.
Van der Waals Bond:
A weak chemical bond in which atoms are held together by weak electrostatic attraction.
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:
A fracture that has been filled with mineral material.
Ventifact:
A rock that has been shaped or polished by the sandblasting effect of wind-blown sand.
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:
Spherical or elongated cavities in an igneous rock that are created when a melt crystallizes with bubbles of gas trapped inside.
Viscosity:
The resistance of a fluid to flow. Fluids with a high viscosity resist flow. Fluids with a low viscosity flow freely.
Volcanic Ash:
Sand-sized particles of igneous rock that form when a spray of liquid magma is blown from a volcanic vent by escaping gas.
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.
Volcanic Bomb:
A projectile of hot magma or rock that is blown from the vent during a volcanic eruption. These solidify in flight and frequently form an elongated rock of streamlined shape.
Volcanic Breccia:
A rock made up of pyroclastic fragments that are at least 64 millimeters in diameter.
Volcanic Cone:
A cone-shaped hill or mountain composed of pyroclastic debris and/or lava which builds up around a volcanic vent during eruptions.
Volcanic Dome:
A steep-sided extrusion of very viscous lava that is squeezed from a volcanic vent without major eruption. These are frequently rhyolitic in composition and produce a rounded mound above the vent.
Volcanic Neck:
A vertical intrusion with the geometry of a volcanic pipe. An erosional remant of a volcanic pipe.
Volcanic Pipe:
A vertical or nearly vertical tunnel which connects a magma reservoir to the surface. Magma and gas travel up this tube to produce the eruption. After the eruption the tube can be filled with a cooling magma which preserves its shape as an intrusive body.
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:
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.