U3S3 Volcanoes

hot spot

An area where material from deep in the mantle rises and melts, forming magma.

magma

Molten rock found beneath Earth’s surface.

lava

Molten rock found on Earth’s surface.

magma chamber

A large pool of magma deep under Earth’s surface.

pipe

The channel in a volcano through which magma rises to reach Earth’s surface.

vent

The opening at the top of a volcano where molten material erupts.

plate

The Earth’s crust is broken into major pieces called plates that carry land and water and move slowly.

plate boundary

Where two plates meet; the three types are divergent, convergent, and transform.

divergent boundary

Where plates move away from each other, allowing magma to rise and create new crust.

convergent boundary

Where plates move toward each other; subduction can occur and cause volcanism.

transform boundary

Where plates slide past one another horizontally.

subduction

The process where a denser plate slides under a lighter plate, melting crust material and forming magma.

crater

The opening at the top of a volcano.

viscosity

The measure of a liquid’s resistance to flow.

volcano

A weak spot in Earth’s crust where molten material comes to the surface.

quiet eruption

An eruption where magma is low in silica and low in viscosity, gases bubble out gently and lava flows quietly.

explosive eruption

An eruption where magma is high in silica and high in viscosity; gases trap and erupt violently.

active

Erupting or showing signs of erupting again soon.

dormant

Hasn’t erupted for a long time but may erupt in the future.

extinct

Unlikely to erupt again.

shield volcano

A broad, gently sloping volcano formed by low-viscosity lava.

cinder cone volcano

A steep, cone-shaped volcano built from ash, cinders, and bombs.

composite volcano

A volcano with alternating layers of lava flows and ash.

lava plateau

A large flat area formed by extensive lava flows.

caldera

A large volcanic crater formed when a volcano collapses after an eruption.

volcanic neck

A pipe that fills with hardened magma after an eruption.

batholith

A large mass of cooled magma that solidified deep underground.

dome mountain

Raised crust formed by hardened magma that intrudes and uplifts surrounding rock.

dike

A vertical intrusion of magma that cuts through existing rock layers.

sill

A horizontal intrusion of magma that cuts between rock layers.

geysers

Geothermal features where heated water erupts periodically.

hot springs

Geothermal features where heated water rises to the surface.

mud pots

Pools of boiling, acidic mud in geothermal areas.

mid-ocean ridge

An underwater mountain range formed along divergent boundaries where crust is lifted by mantle upwelling.

island arc

A curved chain of volcanic islands formed at subduction zones under the sea.

rift valley

A valley formed when crust is pulled apart at divergent boundaries.

tiltmeter

A device that measures tiny tilts of the ground to detect volcanic surface changes.

GPS (global positioning system)

Technology used to detect ground movement around volcanoes.

seismometer

Instrument that detects vibrations below the surface related to volcanic activity.

gas monitoring

Measuring gases such as CO2 and SO2 around a volcano.

sound monitoring

Listening to underground sounds to monitor eruptions.