Vents in the surface of the Earth through which magma and associated gases erupt; also, the forms or structures, usually conical, that are produced by the erupted material. [Glossary of Geology, 4th ed.]
Landmasses that project conspicuously above their surroundings. [USGS Circ 1048]
Tracts of land smaller than a continent, surrounded by the water of an ocean, sea, lake or stream. [Glossary of Geology, 4th ed.]
Episodes during which gases, ash, and lava (molten rock) escape from vents in the earth's crust, accompanied by minor tremors.