Chapter 18 Volcanoes Section Two Volcanic Activity

Vocabulary  Magma Chamber:  The pocket beneath a volcano where magma collects.  Pipe:  A long tube through which magma moves from the magma chamber to Earth’s surface.  Vent:  The opening through which molten rock and gas leave a volcano.

Vocabulary  Lava Flow:  The area covered by lava as it pours out of a volcano’s vent.  Crater:  A bowl-shaped area that forms around a volcano’s central opening.  Silica:  A material that is formed from the elements oxygen and silicon; silica is found in magma.

How Magma Reaches Earth’s Surface  True or False: Magma forms in the lithosphere.  False  What happens during a volcanic eruption?  During a volcanic eruption gasses that have been dissolved in the magma rush out, carrying the magma with them.

Inside a Volcano  Circle the letter of each feature that all volcanoes share.  A. pocket of magma beneath the surface.  B. crack to the surface.  C. side vents.  D. crater.

Inside a Volcano  What is a lava flow?  A lava flow is the area covered by lava as it pours out of a vent.  Where does a crater form?  A crater forms at the top of a volcano around the central vent.  True or False: The pipe of a volcano is a horizontal crack in the crust.  False

Characteristics of Magma  What factors determine the force of a volcanic eruption.  Factors that determine the force of a volcanic eruption include the amount of gas dissolved in the magma, how thick or thin the magma is, its temperature, and its silica content.

Types of Volcanic Eruptions  Hot, fast-moving lava is called ________.  Cool, slow-moving lava is called _____.  What is a pyroclastic flow?  A pyroclastic flow is an explosive eruption of ash, cinders, bombs, and gases. pahoehoe aa