3.2 Volcanoes form as molten rock erupts

Caldera

A huge crater formed by the collapse of a volcano when magma rapidly erupts from underneath it.

Shield Volcano

A broad, flat dome. Low levels of silica in the magma. The largest volcano on Earth is an example.

silica

A compound of silica and oxygen.

pyroclastic flow

A dense cloud of super hot gases and rock fragments that races downhill.

Volcanoes are common...

Along tectonic plate boundaries where oceanic plates sink beneath other plates.

volcano

An opening in Earth's crust through which molten rock, rock fragments and hot gases erupt.

Igneous rocks

Are formed when magma cools in a magma chamber.

violently or gently

Two ways which volcanoes may erupt

Composite Volcano

Cone shaped volcanoes. Built by layers of lava and rock fragments. High levels of silica in the magma.

Crater Lake

Example of a caldera

1500

Fahrenheit (temperature)--is the number that shows how hot pyroclastic flow can get.

Earthquake activity and changes in the tilt of the ground

Indications that magma is moving underneath a volcano.

Low silica magma

Magma flows easily, so gas bubbles move up through it and escape fairly gently.

500

Number of years that it is estimated that Mount Pinatubo had not erupted.

Volcanic eruption

Occurs when a magma chamber is not large enough to hold additional magma that pushes in.

Many lives are saved through advanced warning.

Reason to study volcanoes even though we can not stop them from erupting.

High silica magma

Resistant to flowing, so expanding gases are trapped in it. Pressure builds up until the gases blast out in a violent, dangerous explosion.

Cinder Cone

Steep cone shaped hills. Gas rich magma. Many of them form on the sides of other types of volcanoes.

Ages and types of Volcanic rock

Tells scientist how much time has passed between eruptions and how violent the eruptions have been. It may even give clues to future eruptions.

Ring of Fire

The majority of active volcanoes on Earth (about 80%) take place here.

lava

This is magma that has reached Earth's surface.

Examples of Rock Fragments

Volcanic ash, cinders, bombs, and blocks.

Main Gases in Magma

Water vapor and carbon dioxide

Magma chambers

When magma stops rising it can collect here.

100

miles per hour (speed)--of the pyroclastic flow during a volcanic eruption.