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A metallic element (V) that occurs naturally in fossil fuel deposits as well as in a variety of different minerals. Vanadium is mainly used to produce specialty steel alloys.

vascular plant

Member of a large informal group of plants characterized by lignified tissues for conducting water, minerals, and photosynthetic products through the plant. Vascular plants have stiffer tissues that help support them, transport nutrients and water, and allow vascular plants to grow taller and farther from water.Vascular plants include club mosses, ferns, seed plants, conifers, and flowering plants.See also mineral, plant fossils.


A soil order ; these are clayey soils with a high moisture capacity. During dry periods, these soils shrink and develop wide cracks; during wet periods, they swell with moisture.


Porous or pitted with vesicles (cavities). Some extrusive igneous rocks have a vesicular texture.

volcanic ash

Fine, unconsolidated pyroclastic grains under 2 millimeters (0.08 inches) in diameter. Consolidated ash becomes tuff.

volcanic islands

A string of islands created when molten rock rises upward through oceanic crust. Volcanic islands are common in several contexts, including at subduction zones between colliding oceanic plates, above oceanic hot spots, and along mid-ocean ridges.
At subduction zones, the friction between the plates generates enough heat and pressure to melt some of the crust. In the case of hot spots, islands form as magma from the mantle breaks through the sea floor.

volcanic, volcanism

The eruption of molten rock onto the surface of the crust. Most volcanic eruptions occur along tectonic plate boundaries, but may also occur at hot spots. Rocks that form from molten rock on the surface are also called volcanic.
Prior to eruption, magma ascends from the mantle to a relatively shallow (1 - 10 kilometers / 0.5 - 6 miles) magma chamber. Upward movement reduces the pressure on the magma until it is low enough to permit dissolved gas to exsolve (come out of solution and form bubbles). All eruptions are driven by the exsolution of dissolved gas. As the gas forms bubbles, it expands in volume and forces the magma out of the vent/chamber system onto the surface. The combination of magma viscosity and gas content can produce a range of eruptive styles, from gentle, effusive eruptions to violent explosions.