1. Volcanic Eruptions ch. 6 section 2

2. Inside a Volcano
Beneath a volcano, magma collects in a pocket called a magma chamber. The magma moves upward through a pipe, which is a long tube in the ground that connects the magma chamber to the Earth’s surface. Molten rock and gas leave the volcano through an opening called a vent.

5. A volcanic eruption
Dissolved gases are trapped in magma and are under great pressure. As magma reaches the surface, the dissolved gases begin to expand and exert an enormous force. When a volcano erupts, the force of the expanding gases pushes magma from the magma chamber through the pipe until it flows or explodes from the vent.

7. What do you think?
What might happen if more magma is injected into the chamber from below?

8. Kinds of volcanic eruptions
Geologists classify volcanic eruptions as quiet or explosive. The properties of magma determine how the volcano erupts. The type of eruption depends on the magma’s silica content. Silica is the material found in magma that is formed from the elements oxygen and silicon

9. Quiet eruptions
A volcano erupts quietly if its magma is low in silica. Low silica magma is thin, runny and flows easily. The gases in the magma bubble out gently.

10. Quiet eruptions
Quiet eruptions can produce two types of lava. Pahoehoe is fast moving, hot lava that is thin and runny. It looks like wrinkles when it hardens. Aa is cooler and slower moving. It is also thicker and has a rough surface when it hardens.

12. Explosive eruptions
A volcano erupts explosively if its magma is high in silica. High silica magma is thick and sticky. The gases cannot escape the thick magma so they build up pressure until they explode!

13. Explosive eruptions
An explosive volcano breaks lava into pieces that cool and harden in all different sizes. A pyroclastic flow is a type of explosive eruption that hurls out a mixture of hot gases, ash and cinders.

14. What do you think
Identify if each of the following is an example of a high silica or low silica lava.
A lava river flowing away from a volcano
A plug of lava covering a volcano’s vent
Small pieces of lava being blasted high into the air.

15. Volcano hazards.
Both types of eruptions can cause damage far from the volcano’s location. During a quiet eruption lava flows from vents setting fire to, and then burying everything in its path..

16. Volcano hazards
During an explosive eruption, a volcano can release deadly gases, as well as ash and cinders

17. Life cycle of a volcano
The activity of a volcano may last from less than a decade to more than 10 million years. Geologists use the terms active, dormant and extinct to describe a volcano’s stage of activity.

18. Life cycle of a volcano
An active, or live volcano, is one that is erupting or showing signs to erupt in the future. A dormant, or sleeping volcano is expected to awaken and become active in the future. An extinct, or dead volcano is unlikely to erupt again.

20. Hot Springs and Geysers
Hot Springs and geysers are found in areas of present or past volcanic activity. A hot spring forms when water deep underground is heated by magma or hot rock. The hot water rises to the surface and collects in a pool.

21. Hot springs and geysers
Sometimes, the rising water and
steam become trapped in a narrow
crack. The pressure builds until it
sprays above the surface as a geyser.
A geyser is a fountain of steam and
water that erupts from the ground.

22. Monitoring volcanoes
Geologists use tiltmeters and other instruments to detect changes in or around a volcano. The changes may give warning a short time before an eruption. Scientists cannot predict the type of eruption or how powerful it may be.