Types and characteristics of volcanoes

Volcano

A vent or fissure in Earth's surface where magma and gases explode

Extinct Volcano

Has never erupted in recorded history and probably never will again

Dormant Volcano

Are not currently erupting but based on past activity may erupt again

Active Volcano

Are currently erupting or show signs of erupting in the near future

Magma chamber

The body of molten rock that feeds a volcano

Vent

An opening at the surface of the Earth where volcanic material is released.

Crater

A funnel-shaped pit near the top of the central vent of a volcano.

Caldera

A large, semicircular depression, or pit, that forms when the magma chamber below partially collapses.

Shield Volcanoes

Built of layers of lava from repeated nonexplosive eruptions. The runny lava spreads out over a large area creating gently sloping sides.

Composite (Stratovolcano) Volcanoes

Very common. Form from explosive and nonexplosive eruptions creating layers of pyroclastic material and rock formed from lava.

Cinder cone Volcanoes

Made of pyroclastic material from moderate, short eruptions forming steep slopes.

Aa

This lava pours out quickly and forms a brittle, jagged crust that would be very painful to walk across barefooted!

Pahoehoe

This lava flows slowly, like wax dripping from a candle. Its glassy surface has rounded wrinkles.

Pillow Lava

This lava forms when lava erupts underwater. It hardens in rounded lumps that look like pillows.

Blocky Lava

This lava is cool and stiff and cannot move very far from an exploding vent.

Volcanic Bombs

Large blobs of magma that harden in the air.

Lapilli

Pebble-like bits of magma that harden before they hit the ground.

Volcanic Ash

This forms when gases in stiff magma expand rapidly and the walls of the gas bubbles explode into tiny, glasslike slivers.

Volcanic Blocks

These are pieces of solid rock that erupted from a volcano.

Measuring Small Quakes

Just before an eruption, magma moving upward causes surrounding rock to shift which produces earthquakes.

Volcanic Gases

Monitoring changes in the amount of gases that are released from a volcano can show signs that an eruption may soon occur.

Measuring Slope

As magma moves upward prior to an eruption, the surface of the volcano may swell or bulge.

Measuring Temperature

Infrared satellite imagery can measure an increase in the temperature of a volcano to predict an eruption.

International System of Units

The abbreviation comes from the original French name Susteme international d'unites.