Inside Earth: Chapter 3- Volcanoes
Section 1: Volcanoes and Plate Tectonics
What is a volcano?
 ___________________________- weak spot in the crust where molten material, or magma, comes to the surface
 _________________________ - molten mixture of rock, gasses, and water from the mantle
 _____________________- magma that reaches the surface
Location of volcanoes
 There are about ________________ active volcanoes on land. Many more lie below the sea.
 ________________________________________- a major volcanic belt formed by many volcanoes at the rim of the
Pacific Ocean
 Most volcanoes occur along ________________________________ plate boundaries, such as the
___________________________________ or in __________________________________ zones around the edges of oceans
Volcanoes at Diverging Plate Boundaries
 Volcanoes form along the _______________ _________________ ___________________, which marks a diverging plate
boundary. Most of this is located underwater, except for places such as _______________________________ and the
Azores Islands in the Atlantic Ocean.
Volcanoes at Converging Boundaries
 Many volcanoes form near the plate boundaries where the oceanic crust returns to the crust
(_________________________________)
 Subduction causes ocean crust to sink into the mantle forming a ___________________.
 The crust melts and forms _____________________________, which then rises back towards the surface.
 Many volcanoes occur on __________________________, near boundaries where two plates collide. The resulting
volcanoes create a string of islands called an _____________________________ _____________________.
Hot Spot Volcanoes
 Some volcanoes result from _______________ ____________________ in Earth’s mantle. A hot spot is a weak spot
where magma from deep in the mantle melts through the crust like a blow torch.
 Hot spots often lie in the middle of continental or oceanic plates far away from plate boundaries.
 Can gradually form a series of volcanic islands, for example ________________________________________, which
formed one by one over millions of years as the ____________________ plate drifted over a hot spot.
 They can also form under the continents. An example of this is ______________________________________________ in
Wyoming, which marks a major hot spot under the __________________________________________ plate.
Section 2: Volcanic Activity
How magma reaches Earth’s surface
 Liquid magma is ________________ _________________ than the surrounding solid material, so it flows upward into
any cracks in the rock above
 During a volcanic eruption, the _______________ dissolved in magma rush out, carrying the magma with them
Inside a volcano (see page 95)
Characteristics of magma
 The force of volcanic eruption depends partly on the amount of ________________ dissolved in magma
 Other important factors that affect an eruption: How _________________ or ____________ the magma is, the
__________________________ and its _______________________ content.
 More silica= _______________viscosity (thicker)
 Less silica=____________ viscosity (thinner)
Types of volcanic eruptions
 The silica content of magma helps to determine whether the volcanic eruption is quiet or explosive
o High viscosity (thick) causes an _____________________________ eruption
o Low viscosity (thin) causes a _____________________________ eruption
 A volcano erupts quietly if its lava flows easily
o Two types of lava produced by quiet eruptions
 ____________________________-fast moving, hot lava (Low viscosity)
 _______________-slow moving, cooler lava (High viscosity)
 Magma rises through the lithosphere because it is less dense and it is rising through the solid rock. As the
magma materials rise, the rock cracks and magma goes through.
 Both quiet and explosive eruptions can cause damage far from the crater’s rim.
3 Stages of a Volcano
o _________________________________- it will erupt or is erupting
o _________________________________- there is a possibility that it will erupt (may not be for a long time)
o _________________________________- it will not erupt
Other types of volcanic activity
 ____________________: forms when groundwater heated by nearby magma, rises to the surface and collects in a
natural pool
o Pressure can build and cause a _________________- a fountain of water and steam that erupts from the
ground
 ____________________________: a clean, reliable energy source caused when water is heated by magma