Glossary Starting with the letter: V


The property of a substance which determines the amount of its internal resistance to flow. The opposite of fluidity.

Visible light

The portion of the electromagnetic spectrum with wavelengths shorter than infrared radiation but longer than ultraviolet radiation. Visible light includes wavelengths that include all the colors we see: violet, blue, green, yellow, orange, and red light from the Sun.


Elements and compounds that evaporate readily under normal surface conditions.


Any of the processes by which magma and its associated gases rise to the crust from the Earth’s interior and are discharged onto the surface and into the atmosphere.


A vent or fissure in the Earth’s surface through which molten lava, ash, and gases are ejected. It is also the name for the structure, usually conical, formed by the materials ejected from the vent or fissure.


The study of the causes and phenomena associated with volcanoes and volcanism.