KINDS OF VOLCANIC ERUPTIONS – CHAPTER 3.3 (pp. 94-98)
This section explains what happens when a volcano erupts and two types of volcanic eruptions. You will
also identify a volcano’s stage of activity.
Geologists classify volcanic eruptions as quiet or explosive
Quiet Eruptions: a volcano erupts quietly if its magma is low in silica.
How does the gases in magma bubble out? Gently or violently? ____________________
What is the type of island that is formed from quiet eruptions? ____________________
Explosive Eruptions: a volcano erupts explosively if its magma is high in silica.
Where does the magma build up in the volcano and “plugs it up” like a cork? ____________
What is trapped inside a volcano and cannot escape from the thick magma? ______________
Steam and gases push magma out of the volcano with incredible force. __________________
What mountain violently erupted in Washington State in 1980? _________________________
Pyroclastic flow: occurs when an explosive eruption hurls out a mixture of hot gases, cinders, cinders
and bombs.
Look at the Power of Volcanoes on pages 96-97
List the major volcanic eruptions, where they occurred and what kind of flow they were:
1883: ____________________________________________
1902: _____________________________________________
1912: _____________________________________________
1980: _____________________________________________
1991: _____________________________________________
2002: _____________________________________________
Monitoring Volcanoes: (p. 98) Geologists predict volcanic eruptions by using tiltmeters. The tiltmeters
measure gases escaping from the volcano and temperature increases in underground water. They also
monitor earthquakes that occur around the volcano.
1. Draw and Describe the surface of obsidian.
DESCRIBE Obsidian Rock:
DRAW Obsidian
The surface of obsidian is smooth and glossy
Obsidian formed when lava cooled very quickly
Magma Reaches Earth’s Surface (p. 91-93)
2. Where does lava come from?

Lava begins as magma, which forms in the asthenosphere.

The materials in the asthenosphere are under great pressure.

As magma rises, it flows upward into cracks in the rock above.

But, if an opening in weak rock allow the magma to reach the surface, a volcano forms.
3. Label the drawing with the following terms:

Magma chamber – magma collects in this pocket

Pipe – a long tube in the ground that connects the magma chamber to Earth’s surface

Vent –molten rock and gas leave the volcano through this opening

Crater – a bowl shaped area at the top of the volcano that may form around the vent
4. What is lava flow?

The area covered by lava as it pours out of a vent.