Unit 6: Volcanoes

volcano

 A weak spot in the crust where magma has come to the surface. 

magma

 The molten mixture of rock-forming substances, gases, and water from the mantle.

lava

 Liquid magma that reaches the surface.  

ring of fire

A major belt of volcanoes that rims the Pacific Ocean.  

island arc

 A string of volcanoes that form as the result 

of subduction of one oceanic plate beneath a second oceanic plate.

hot spot

An area where magma from deep within the mantle melts through the crust above it.

magma chamber

The pocket beneath a volcano where magma collects

pipe

A long tube through which magma moves from the magma chamber to Earth's surface.

vent

The opening through which molten rock and gas leave a volcano.

lava flow

The area covered by lava as it pours out of a

crater

A bowl-shaped area that forms around a volcano's central opening.

silica

 A material found in magma that is formed from the elements oxygen and silicon; it is the primary substance of Earth's crust and mantle.

pyroclastic flow

The flow of ash, cinders, bombs, and gases down the side of a volcano during an explosive eruption.

dormant

Not currently active but able to become active in the future (as with a volcano).

extinct

 Term used to describe a volcano that is no longer active and unlikely to erupt again. 

calders

The large hole at the top of a volcano formed when the roof of a volcano's magma chamber collapses.

cinder cone

a steep, cone-shaped hill or small mountain made

of volcanic ash, cinders, and bombs piled up around a volcano’s

opening.

composite volcano

 A tall, cone-shaped mountain in which layers of lava alternate with layers of ash and other volcanic materials. 

shield volcano

A wide, gently sloping mountain made of layers of lava and formed by quiet eruptions.

volcanic neck

 A deposit of hardened magma in a volcano's pipe.

dike

A slab of volcanic rock formed when magma forces itself across rock layers. 

sill

 A slab of volcanic rock formed when magma squeezes between layers of rock. 

batholith

A mass of rock formed when a large body of  magma cools inside the crust.