Volcano
A volcano is a hole in Earth's surface through which magma (called lava when it reaches Earth's surface), hot gases, ash, and rock fragments escape from deep inside the planet. The word volcano also is used to describe the cone of erupted material (lava and ash) that builds up around the opening.
Volcanic activity is the main process by which material from Earth's interior reaches its surface. Volcanoes played a large part in the formation of Earth's atmosphere, oceans, and continents. When Earth was new, the superheated gases within it (including carbon dioxide) streamed out through countless volcanoes to form the original atmosphere and oceans.
Volcanoes are found both on land and under the oceans (where they are called seamounts). Geologists label volcanoes by their periods of activity. If a volcano is erupting, it is called active. If a volcano is not presently erupting but might at some future date, it is called dormant. If a volcano has stopped erupting forever, it is called extinct. Generally, volcanoes are labeled extinct when no eruption has been noted in recorded history.
Chemosynthesis: Process by which the energy from certain chemical reactions, rather than light (as in photosynthesis), is used by some organisms to manufacture food.
Hot spot: An upwelling of heat from beneath Earth's crust.
Ignimbrite: Rock formation that results from a large pyroclastic flow.
Lava: Magma at Earth's surface.
Magma: Molten rock deep within Earth that consists of liquids, gases, and particles of rocks and crystals.
Photosynthesis: Process by which light energy is captured from the Sun by pigment molecules in plants and algae and converted to food.
Pyroclastic flow: A dense wave of superheated air and rock that moves as a fluid from an erupting volcano, sometimes crossing thousands of square miles of landscape.
Seafloor spreading: Spreading of the seafloor outward at ridges where two oceanic plates are diverging.
Seamount: Large, submarine volcano.
Tuff: Fused hard rock formed from a large pyroclastic flow.