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.